WEBVTT

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So thanks, everybody.
My name is David Teira.

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I'm one of the co-editors
of the VSPS Open

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Series and my role
here is to kill just two or

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three minutes until
Helen Vivi, our editorial

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chair and also the chair
of the session, decides

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to start the session.
So if anybody wants

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to say hello, Al,
welcome. Al Wilson, our

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third speaker, was
updating his computer in

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this precise minute. So I'm
very glad to see you there.

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So we are all
here, Helen.

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So okay, should we
decide everyone's here now?

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Okay. Well, so
thank you so much for

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coming, everyone. It's amazing
to see so many people here.

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That's
really nice.

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My name is Helen Vivi.
I'm the editorial chair of the

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VSPS Open Series, to
which Jeremy's splendid

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book is the
latest contribution.

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And I'm also a past president
of the British Society for

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the Philosophy of
Science. Before we get on

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to the business that
you're all here for,

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which is to talk about
Jeremy's book, I just

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wanted to say a little
bit about the VSPS

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Open Series, partly
just to tout for business

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in front of a whole bunch
of philosophers of science.

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We are always
looking for high

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quality manuscripts in
the philosophy of science.

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So if anybody has a
manuscript in mind, you

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know, think about
us. So for those of you

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who don't know about
it, the point of this

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sub series is to
publish landmark cutting

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edge books that
represent the full breadth

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and diversity of the
philosophy of science.

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Importantly, sorry, there's a
very noisy plane going overhead.

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Importantly,
the books are

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all fully open access.
They're fully downloadable

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as PDFs in their published
form at no cost to the reader.

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But even more importantly, what's
distinctive about the VSPS Open Series

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is that they're published at no cost
to the author or their institution.

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I think this is known as diamond
open access, or it was at some point.

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As many of you
know, that contrasts

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dramatically with what
is the current standard

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model where the cost
of publication often

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runs to several thousand
pounds. So in practice,

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that puts open access
monograph publishing

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just out of the financial
reach of most researchers

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who don't have a big
externally funded research

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project to charge that
cost to. So I'm really

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delighted that the VSPS
has been endorsing

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and supporting this
project. And I want to

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use this opportunity
as well to say a massive

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thank you to the
University of Calgary Press,

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who are the publishers
of the existing books

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in the series, including
this one, although

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that's going to switch to
UCL Press in due course.

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The series just
couldn't exist without

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the support and the
generosity of University

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of Calgary Press. And
those of you who've

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looked at Jeremy's
book, or indeed some of

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the earlier books will
know that they've done

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a really nice job, like the
books just look really nice.

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So big thank you
to Brian Scrivener

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and everyone at the
University of Calgary Press.

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Also, thanks to
David Terra and Brian

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Roberts, who's here, I
think. I think I just saw him.

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Yes. Thank
you to Brian.

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So David and Brian got the
whole project off the ground.

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And also thank you
to Phyllis Ilari, who has

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taken over from
Brian as co-editor.

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I don't know if Phyllis
is here. I can't see her.

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Just quickly to fill you
in on the other books

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in the series, we've
already published the

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Material Mind by Max
Kistler, and not one

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but two volumes by John
Norton, Material Theory

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of Induction and the
Large-Scale Structure

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of Inductive Inference.
Those two volumes

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have just won this
year's Lakatos Prize.

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So no pressure, Jeremy.
The next volume is coming

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out in November, I think.
That's Adrian Currie's

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The Science of Lost
Worlds. After that, we

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have a further two on
the slate. Dirk Milstein

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and Skipper's Survival of
the Luckiest Perspectives

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on the History and
Philosophy of Drift in

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Evolutionary Biology,
and Harold Kincade's

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Advancing Social and
Behavioural Science,

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How the Philosophy
of Science Can Help.

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But as I say, that's
not the end of it.

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We still have the possibility
to publish more books.

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So anyone
interested, let us know.

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But let's get on to the
main business now, which is

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Jeremy's new book, The Multiverse,
A Philosophical Introduction.

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I'm not going
to say anything

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about it because
Jeremy is going to do that.

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And then we have
in this order, I believe,

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Richard Davids and Al
Wilson, who are going

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to say some more
about it. And then after

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that, we should probably
have half an hour

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or so, I think, for Q&A.
So over to you, Jeremy.

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Ah, thank you
so much, Helen.

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And I will speak for, I hope,
no more than five minutes.

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But I would must, of
course, start by saying

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what a great piece
of luck and delight and

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privilege it's been
to be in this series,

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which is such a splendid
brainchild of, well,

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David and Brian are
the ones I know, but of

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the BSPS as a whole.
And I really am very

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grateful to the Society,
but also very grateful

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to the University of
Calgary, with whom the

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whole process was
as efficient and expert

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and pleasant and sheer,
lovely as it could have been.

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So they're
just terrific.

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And I really commend to
fellow philosopher, aspiring

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book authors to
go for this series.

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So I feel very grateful.
Now, that said, I understand

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that I can share screens.
I'm going to do that.

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And I'm even going to
do it in a full screen way.

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Yeah, right. So I,
well, there's the book.

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And as you see,
the cover's nice.

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And that was one part
of the pleasure, actually,

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was I was only asked
what are my favourite

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colours and
unfavourite colours.

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And do I like bubbles? To
which the answer was no,

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there are too many
bubbles in the multiverse

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graphic culture. And so
we got the veil instead.

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And the book's about
three topics, really.

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There are three
multiverses to consider.

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First of all, there's the
philosopher's multiverse.

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Then there's the
Everettian quantum theory.

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And then there's the
cosmological multiverse.

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And I decided in writing
it to stress a philosophy

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theme as a kind of
philosophical girder for

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each of those three
central chapters.

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And they were obviously
what is a possibility?

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And for the Everett, I
chose what is probability

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or objective probability.
And for the cosmological

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multiverse, there was
the question of how

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could you confirm it?
Since on the face of

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it, it's a more empirical
hypothesis than

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the first two seem to
be. And I stress as much

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of the philosophy of
cosmology in connection

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with the multiverse does,
the topic of selection effects.

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So about the
possible worlds of the

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philosophers, of course,
everyone here will

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recognise the great
man and his masterpiece.

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And my admiration
and indeed affection for

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him is evident in the
book. And I would also

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here like to thank Helen
Beebe for her outstanding

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editorial work in
bringing to fruition his

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correspondence in OUP
volumes back in, I think,

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22. And what a labour
of, I mean, immense

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labour, but labour of love
and admiration that was.

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And as your
editorial intro says,

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I mean, it is one of
the great philosophical

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correspondences,
because the man writes with

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a very colloquial and
lively English style,

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but with complete
academic precision.

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You know exactly
what he's saying.

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And there is a good sense
of humour in his writing, which

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comes up at the end of my
chapter about that, where,

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thanks to Helen's
philosophical correspondence,

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I discovered that
Lewis had written to the

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well-known New Yorker
cartoonist, Ros Chast,

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and asked permission
for the use of a cartoon

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for this very book. In
fact, that permission

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didn't work out for reasons
I know nothing about.

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But here's the
cartoon in case you

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haven't seen it. And
this is at least a sufficient

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reason to download
the book from University

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of Calgary, is it
not? So there we are.

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As you see,
worlds can be weird.

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And so this is Ros Chast
had obviously, unbeknownst to

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herself, rediscovered
Lewis's idea of comparative

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similarity between
possible worlds with

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which to understand
counterfactuals.

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So Everett,
well, there he is.

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As you see, there are two
cats. And that's the idea in

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the last part of the
Everett chapter where,

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following Saunders and
Wallace, Oxford colleagues,

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I emphasise the role
of decoherence and as

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sustaining the idea
that you can really speak

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of there being two
cats without getting into

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a deep worry that, oh,
hang on, in that case

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doesn't the mass double
and isn't mass meant

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to be conserved? So
that and the topic of

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probability were
the themes there.

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And when it comes to
cosmological multiverse, I broke

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out of the single hero
format for the slides.

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And across the top, there's
Starobinsky, Guth, and Linde.

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And then on the
bottom, I want a

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bit of a book plug for
Bernard Carr, bottom

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left, in his outstanding
15 years ago anthology,

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still available, with both
critical and advocating

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essays, which are
very well written.

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And in the middle, perhaps
the hero of the sceptics

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and all-round wonderful
philosopher as well

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as physicist, George
Ellis, one of the most

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profound and productive
relativists and cosmologists

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of our age, which as
we all know, is a golden

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age of cosmology. So
the book contains actually

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Wilczek and Hartle, and
they are saying things

00:10:44.681 --> 00:10:47.708
like beware of biased
sampling. And so Hartle,

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for example, says,
what is most probable to

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happen need not be what is
most probable to be observed.

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And Wilczek says
much the same.

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So that's the idea
of bias sampling.

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But the fine tuning that
is so remarkable about the

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modern understanding
in physical science of

00:11:08.258 --> 00:11:12.040
cosmology and its
relation to local physics,

00:11:12.041 --> 00:11:15.705
as in kind of physics
and chemistry on a single

00:11:15.717 --> 00:11:19.080
planet, is shown in
this picture that I got

00:11:19.081 --> 00:11:23.159
from Mauro Caffaro,
a colleague of Ellis's at

00:11:23.171 --> 00:11:26.003
Pavia, copied
from another one.

00:11:27.203 --> 00:11:32.268
It is quite striking how, if
you just look at so-called

00:11:32.280 --> 00:11:36.032
parameter space,
we're lucky to be here.

00:11:36.033 --> 00:11:39.394
So I won't go on
about that. I'd like to say

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thank you very much,
especially to BSPS Open

00:11:42.761 --> 00:11:47.996
and its initiators and to the
University of Calgary Press.

00:11:48.008 --> 00:11:51.680
So thank you. And
I will stop sharing.

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Thank you, Jeremy. And
now we are going to Richard.

00:11:55.439 --> 00:11:59.520
I don't know whether you have
slides that you need to put up.

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No, I don't have slides.

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On you go then.

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Yeah, thank you. Thank
you very much for the

00:12:06.055 --> 00:12:09.000
invitation to be part
of this, to celebrate

00:12:09.585 --> 00:12:13.284
Jeremy's book, which
is a really beautiful

00:12:13.296 --> 00:12:17.360
book on a very important
topic in contemporary

00:12:17.560 --> 00:12:21.548
physics and also
probably one of the most

00:12:21.560 --> 00:12:25.560
philosophically rich
topics one can have.

00:12:25.561 --> 00:12:28.210
So it's very exciting
to have the book.

00:12:28.222 --> 00:12:31.680
And I think, one, it is on
the one hand, of course,

00:12:32.210 --> 00:12:36.085
extremely well
informed. But it is also it's

00:12:36.097 --> 00:12:40.160
not easy to write a book
of that kind, because

00:12:40.161 --> 00:12:42.709
those are quite
controversial topics with a

00:12:42.721 --> 00:12:45.780
wide range of fairly
different perspectives on it.

00:12:45.860 --> 00:12:49.305
And Jeremy is very
successful in on the

00:12:49.317 --> 00:12:53.360
one hand, being even
handed in the presentation

00:12:53.480 --> 00:12:57.603
of the positions. And
on the other hand, being

00:12:57.615 --> 00:13:01.480
quite opinionated in
the end. So it's quite

00:13:01.481 --> 00:13:04.654
clear in the end, he
is very explicit about

00:13:04.666 --> 00:13:08.000
his own views about
the various perspectives.

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And I must say, I enjoyed
very much Jeremy's

00:13:10.848 --> 00:13:13.760
clear commitment in
chapter six, with respect

00:13:15.000 --> 00:13:19.083
to yes on the
philosophical, no on Everett,

00:13:19.095 --> 00:13:23.000
and maybe on the
cosmological multiverse.

00:13:23.001 --> 00:13:26.447
And I would admit
that I would personally,

00:13:26.459 --> 00:13:30.414
by and large, tend to
share his assessment, too.

00:13:31.834 --> 00:13:35.158
One intriguing aspect
of Jeremy's book

00:13:35.170 --> 00:13:38.920
is that it opens up a
big perspectives that

00:13:38.921 --> 00:13:43.765
it covers both possible worlds
and philosophical multiverses.

00:13:43.777 --> 00:13:46.360
And I assume
that will also play

00:13:47.420 --> 00:13:52.426
a role a little later in what
what Al will be saying.

00:13:52.438 --> 00:13:55.320
I would in the
remainder of my

00:13:55.321 --> 00:13:58.577
10 minutes, I would
like to point at two facets

00:13:58.589 --> 00:14:01.440
of the relation between
between those two

00:14:01.441 --> 00:14:04.686
groups, and maybe the
way in which that relation

00:14:04.698 --> 00:14:08.171
may be viewed in light of
developments in physics.

00:14:10.211 --> 00:14:13.419
And both of those
facets have to do

00:14:13.431 --> 00:14:17.520
with probability. And as
as Jeremy emphasises,

00:14:17.521 --> 00:14:20.461
unlike possible worlds,
philosophical multiverse

00:14:20.473 --> 00:14:22.676
hypothesis are
empirically testable.

00:14:22.677 --> 00:14:26.952
In other words, they state
probabilities of measurement outcomes.

00:14:26.964 --> 00:14:29.320
In Everett, those
are probabilities

00:14:29.321 --> 00:14:31.729
for the outcomes of
quantum measurements.

00:14:31.741 --> 00:14:34.160
In the cosmological
multiverse, those are

00:14:34.161 --> 00:14:36.553
probabilities for the
selection of ground

00:14:36.565 --> 00:14:39.320
states, which corresponds
to specific parameter

00:14:40.250 --> 00:14:43.586
values that we
measure in our world.

00:14:43.598 --> 00:14:48.200
And here we come to
the first point, which is that

00:14:48.201 --> 00:14:51.474
our understanding of
probabilities faces serious

00:14:51.486 --> 00:14:55.802
problems in those very contexts
where multiverses are posited.

00:14:55.803 --> 00:14:58.957
So there is the long
standing general

00:14:58.969 --> 00:15:02.520
question, our
understanding of probability,

00:15:02.521 --> 00:15:05.457
which has been developed
from a local observers

00:15:05.469 --> 00:15:08.040
perspective, can be
generalised to global

00:15:08.041 --> 00:15:11.507
contexts where
probabilities are linked to

00:15:11.519 --> 00:15:15.080
the world at large.
And this problem can be

00:15:15.081 --> 00:15:18.601
or may be related in
different ways, of course,

00:15:18.613 --> 00:15:21.920
to the specific issues
that are faced by the

00:15:21.921 --> 00:15:24.717
two multiverse research
contexts, let's say,

00:15:24.729 --> 00:15:27.600
in Everettian quantum
mechanics, the question

00:15:27.601 --> 00:15:30.639
is how the Born rule
can be extracted in the

00:15:30.651 --> 00:15:33.840
absence of collapse
and in internal inflation,

00:15:33.841 --> 00:15:36.735
there is the measure
problem, how to specify

00:15:36.747 --> 00:15:39.720
probabilities for the
generation of universes

00:15:39.721 --> 00:15:44.298
on an internally expanding
infinite inflationary background.

00:15:44.310 --> 00:15:46.560
Now, there are
proposals that

00:15:46.561 --> 00:15:49.645
aim to fix those problems
in both cases, there's

00:15:49.657 --> 00:15:52.560
a lot of discussion
about them. But it's fair

00:15:52.561 --> 00:15:56.191
to say that there is
no universally accepted

00:15:56.203 --> 00:15:59.450
solution at this
point, in either case.

00:15:59.451 --> 00:16:02.951
So one might say that
while there seems to be a

00:16:02.963 --> 00:16:06.320
clear cut distinction
between possible worlds

00:16:06.321 --> 00:16:09.260
where probabilities have
no place, and physical

00:16:09.272 --> 00:16:12.600
multiverses where a clear
probabilistic understanding

00:16:12.601 --> 00:16:15.671
is central to the
physical schemes.

00:16:15.683 --> 00:16:20.040
But that distinction may
be actually trickier than

00:16:20.140 --> 00:16:23.078
one might expect,
because it's trickier to

00:16:23.090 --> 00:16:26.320
spell out what we actually
mean by probability

00:16:29.240 --> 00:16:32.785
in those contexts.
Now, the second aspect

00:16:32.797 --> 00:16:36.440
is the question of
measuring the effect of

00:16:36.441 --> 00:16:40.129
other universes. And
of course, in principle,

00:16:40.141 --> 00:16:43.840
they are measurable,
being physical theories.

00:16:43.841 --> 00:16:47.484
So there is an implication
of those hypotheses.

00:16:47.496 --> 00:16:50.840
But in practice,
measuring effects of those

00:16:50.841 --> 00:16:55.646
other universes seems extremely
difficult without going into any detail.

00:16:55.647 --> 00:17:00.480
And there is one peculiar
way, however, to in some sense,

00:17:00.492 --> 00:17:04.080
observe effects of
other universes, which

00:17:05.100 --> 00:17:08.897
is an entropic reading
of observed fine tuning.

00:17:08.909 --> 00:17:12.097
And that brings us
to the second point.

00:17:12.098 --> 00:17:16.408
Entropic reasoning is about
explaining an observed fine

00:17:16.420 --> 00:17:20.714
tuned parameter values such
as a cosmological constant.

00:17:22.764 --> 00:17:25.259
And one explains
this fine tuning

00:17:25.271 --> 00:17:28.760
by demonstrating that
based on a given theory,

00:17:28.761 --> 00:17:31.160
such a fine tuned
parameter value is very

00:17:31.172 --> 00:17:33.760
likely to exist somewhere
in the multiverse.

00:17:33.761 --> 00:17:36.614
And then the second
step is to argue that

00:17:36.626 --> 00:17:39.560
our existence depends
on that fine tuning,

00:17:39.710 --> 00:17:42.403
so the genuine
entropic element.

00:17:42.415 --> 00:17:46.760
And once again, we can
see a link to the distinction

00:17:46.761 --> 00:17:49.884
between possible worlds
on the one hand, and

00:17:49.896 --> 00:17:52.960
physical multiverses.
Because in principle,

00:17:52.961 --> 00:17:55.502
an entropic argument
can be formulated within

00:17:55.514 --> 00:17:57.840
the framework of
possible worlds, just by

00:17:57.841 --> 00:18:01.086
saying if the world was
a bit different, nothing

00:18:01.098 --> 00:18:03.880
similar to us could
exist. But that would

00:18:03.881 --> 00:18:06.457
not be a physics based
argument, it would

00:18:06.469 --> 00:18:09.120
not be part of physics.
And what makes the

00:18:09.121 --> 00:18:12.294
argument a physics based
argument is the element

00:18:12.306 --> 00:18:15.160
that allows us to
attribute the probability

00:18:15.200 --> 00:18:18.921
to degeneration of
a fine tuning solution,

00:18:18.933 --> 00:18:23.200
assuming that a given
physical theory is viable.

00:18:23.201 --> 00:18:26.993
Now as an aside,
normally, entropic reasoning

00:18:27.005 --> 00:18:30.640
is embedded in
cosmological multiverse, but

00:18:30.915 --> 00:18:33.396
in principle, there
may also be options if

00:18:33.408 --> 00:18:36.080
one assumes that
Everettian quantum mechanics

00:18:36.180 --> 00:18:39.778
can underlie string
theory to have entropic

00:18:39.790 --> 00:18:42.830
reasoning in the
context of Everett.

00:18:43.860 --> 00:18:48.474
In any case, on the basis
of a physical theory, entropic

00:18:48.486 --> 00:18:53.018
reasoning provides a physical
explanation of fine tuning.

00:18:53.168 --> 00:18:55.035
And it can even
make successful

00:18:55.047 --> 00:18:58.573
predictions if the fine
tuning is of the right amount.

00:18:58.574 --> 00:19:01.561
That is, does not
go beyond what is

00:19:01.573 --> 00:19:05.560
entropically required, as
suggested by Weinberg.

00:19:05.920 --> 00:19:09.767
However, there is a
catch. In some sense,

00:19:09.779 --> 00:19:13.920
the multiverse only
seems to solve a problem

00:19:13.921 --> 00:19:17.142
it has itself generated.
The problem is that

00:19:17.154 --> 00:19:21.583
fine tuning is considered
unsatisfactory without explanation.

00:19:21.783 --> 00:19:26.640
And if we have a probabilistic
understanding of fine tuning, we know why

00:19:26.641 --> 00:19:29.619
this is unsatisfactory.
It's unsatisfactory

00:19:29.631 --> 00:19:32.760
because the type of
outcome we see just looks

00:19:34.880 --> 00:19:38.468
very improbable.
However, if we don't think

00:19:38.480 --> 00:19:42.080
that there is a
fundamental theory that can

00:19:42.820 --> 00:19:46.716
give us such a probabilistic
understanding, why

00:19:46.728 --> 00:19:50.720
should we take fine
tuning to be unsatisfactory?

00:19:50.721 --> 00:19:53.645
There may of course
be other reasons, but

00:19:53.657 --> 00:19:56.880
it's not a trivial question.
And one may say,

00:19:56.881 --> 00:19:59.724
if there is no fundamental
theory that gives

00:19:59.736 --> 00:20:02.720
us probabilistic
understanding, it's not clear

00:20:02.870 --> 00:20:05.922
whether there is a
fine tuning problem.

00:20:05.934 --> 00:20:09.840
Now, string theory
introduces such a probabilistic

00:20:09.841 --> 00:20:12.298
understanding based
on the landscape, and

00:20:12.310 --> 00:20:14.840
in combination with
internal inflation, it

00:20:15.360 --> 00:20:19.139
leads to the multiverse
that then solves it.

00:20:19.151 --> 00:20:23.360
So one might say the
following about the relation

00:20:24.240 --> 00:20:28.599
between possible worlds
and the physical multiverses.

00:20:28.611 --> 00:20:32.240
Even in the context of
possible worlds, such

00:20:32.241 --> 00:20:35.688
as, for example, possible
values of the cosmological

00:20:35.700 --> 00:20:38.960
constant, many of us
seem to have a probabilistic

00:20:38.961 --> 00:20:42.206
intuition, which is why
we tend to view fine

00:20:42.218 --> 00:20:45.400
tuning as a problem.
Now the multiverse, or

00:20:45.401 --> 00:20:48.926
more precisely its
string theory component,

00:20:48.938 --> 00:20:52.640
provides a physical
basis for that intuition.

00:20:52.641 --> 00:20:56.208
And the multiverse can
at the same time offer

00:20:56.220 --> 00:20:59.560
an entropic solution.
In other words, even

00:20:59.561 --> 00:21:01.848
if there was a
fundamental difference, or

00:21:01.860 --> 00:21:04.440
even though there is a
fundamental difference,

00:21:04.441 --> 00:21:07.539
let's say, formally,
between possible worlds

00:21:07.551 --> 00:21:10.520
and the multiverse,
our intuitive thinking

00:21:15.100 --> 00:21:18.996
about possibility may
have implicitly factored

00:21:19.008 --> 00:21:23.000
in the multiverse all
along. And that, I think,

00:21:23.001 --> 00:21:26.074
makes it so important
to follow Jeremy's

00:21:26.086 --> 00:21:29.480
route to compare, to
have those, even though

00:21:29.530 --> 00:21:32.346
he very clearly
distinguishes between those

00:21:32.358 --> 00:21:35.508
different groups, to have
them in the same book.

00:21:35.509 --> 00:21:37.922
Because in some
way, and in some way

00:21:37.934 --> 00:21:40.680
that is not entirely
understood, maybe at

00:21:40.980 --> 00:21:48.880
this point, they nevertheless
belong together. Thank you.

00:21:48.881 --> 00:21:50.834
Thank you, Rikard.
That was great.

00:21:50.846 --> 00:21:53.760
And now, Jeremy, I'm
going to give you a little bit

00:21:53.761 --> 00:21:57.483
of a right to reply
after Al has said his

00:21:57.495 --> 00:22:01.026
piece, should you
wish to say anything.

00:22:01.027 --> 00:22:04.560
So yes, Al Wilson,
over to you.

00:22:05.230 --> 00:22:09.043
Yeah, thank you, Helen.
I do have some slides

00:22:09.055 --> 00:22:11.887
which I'll talk
to very briefly.

00:22:11.888 --> 00:22:16.004
In a minute, I wanted to say
thank you to the organizers,

00:22:16.016 --> 00:22:19.080
most of all to Jeremy
for writing this book

00:22:19.081 --> 00:22:22.673
and occasioning this
occasion. It's a privilege

00:22:22.685 --> 00:22:26.520
to be part of it. It was
even more of a privilege,

00:22:26.521 --> 00:22:29.027
I have to say, to be
taught philosophy of

00:22:29.039 --> 00:22:32.547
quantum theory by Jeremy
back in the day in about 2002.

00:22:34.397 --> 00:22:37.393
And it was a
large part, thinking

00:22:37.405 --> 00:22:41.280
through Everett with
him, and other than this

00:22:41.405 --> 00:22:45.977
call that led me to want to
be a philosopher of physics.

00:22:45.989 --> 00:22:48.400
And yeah, so
this is somewhat

00:22:49.495 --> 00:22:53.530
personal as well. So,
I mean, obviously, it's

00:22:53.542 --> 00:22:57.320
a very rich book, and
one I think that was

00:22:57.321 --> 00:22:59.969
kind of badly needed
because of the sort of

00:22:59.981 --> 00:23:02.640
chaos that accompanies
multiverse thinking.

00:23:02.690 --> 00:23:06.496
It's a multiverse of
proliferate worlds, but

00:23:06.508 --> 00:23:10.240
versions of the
multiverse also proliferate

00:23:10.290 --> 00:23:12.493
nearly every multiverse
theorist has some

00:23:12.505 --> 00:23:14.720
difference in their
multiverse from every

00:23:14.721 --> 00:23:16.622
other multiverse
theorist. And one of the

00:23:16.634 --> 00:23:18.640
great achievements
of this book is to bring

00:23:21.440 --> 00:23:25.287
a kind of coherent
order to that variety.

00:23:25.299 --> 00:23:29.440
I'm going to talk about
three aspects of the

00:23:29.441 --> 00:23:32.946
discussion, not quite
following the three

00:23:32.958 --> 00:23:36.560
multiverses in the
book, but close enough.

00:23:36.660 --> 00:23:38.904
So, first about the
possible worlds, and I'm

00:23:38.916 --> 00:23:41.120
going to scrutinize
a little bit the notion

00:23:41.320 --> 00:23:45.218
of logical possibility
that Jeremy talks about

00:23:45.230 --> 00:23:49.633
and he associates with
the possible worlds of Lewis.

00:23:49.783 --> 00:23:52.543
Then I'll talk
about the quantum

00:23:52.555 --> 00:23:56.160
multiverse, in
particular, the probability

00:23:56.260 --> 00:23:59.958
problem for Everettian
quantum mechanics.

00:23:59.970 --> 00:24:03.680
And here I'm really
kind of curious about

00:24:03.681 --> 00:24:08.267
the kind of state of play
as Jeremy and others see it.

00:24:08.279 --> 00:24:11.200
What really is
kind of needs to be

00:24:11.201 --> 00:24:14.781
done by Everettians
to really to shore up

00:24:14.793 --> 00:24:18.560
their position here.
And finally, I'll talk

00:24:20.660 --> 00:24:24.642
about a point that Jeremy
makes in discussion

00:24:24.654 --> 00:24:28.560
of my own work on the
connection between the

00:24:28.710 --> 00:24:31.599
possible worlds and
the quantum multiverse

00:24:31.611 --> 00:24:35.244
relating to the contingency
of quantum theory itself.

00:24:35.444 --> 00:24:37.841
This is a kind of
a identified in the

00:24:37.853 --> 00:24:40.720
book at a core point of
disagreement between

00:24:42.140 --> 00:24:45.851
us that endures. And
I'm really curious kind

00:24:45.863 --> 00:24:49.840
of where Jeremy's
ultimate motivation is coming

00:24:49.841 --> 00:24:53.629
from there, because he
explains what he thinks.

00:24:53.641 --> 00:24:58.123
One can still ask kind of
why I think a little bit more.

00:24:58.124 --> 00:25:00.429
And this will
actually bring us

00:25:00.441 --> 00:25:03.520
back to Lewis and his
correspondence that

00:25:03.600 --> 00:25:06.544
Jeremy was talking
about as well.

00:25:06.556 --> 00:25:11.600
So logical possibility. I
mean, I don't know if this is a

00:25:11.601 --> 00:25:15.146
sort of confabulated
memory, but my memory when

00:25:15.158 --> 00:25:18.640
I was studying metaphysics
of modality for the

00:25:18.641 --> 00:25:21.279
first time was that
logical possibility was a

00:25:21.291 --> 00:25:24.000
very common term, and I
think much more common

00:25:25.620 --> 00:25:30.038
than it is today. So Lewis
used the term logical possibility.

00:25:30.050 --> 00:25:32.480
He talked about
broad and narrow,

00:25:32.655 --> 00:25:36.151
but focused on what he
called broad. But it was it

00:25:36.163 --> 00:25:39.600
was widely used and sort
of common parlance and a

00:25:39.760 --> 00:25:44.843
sort of common language
for a lot of metaphysicians.

00:25:44.855 --> 00:25:50.430
And my suspicion is that kind of
Jeremy harkened back to those days.

00:25:50.442 --> 00:25:54.080
There's been sort of
diversification in the way that

00:25:54.081 --> 00:25:56.397
analytic philosophers
talk about modality.

00:25:56.409 --> 00:25:59.280
And I'm going to speculate
here that there's kind of

00:25:59.430 --> 00:26:02.134
two intellectual trends
that have moved people

00:26:02.146 --> 00:26:05.040
away from so much focus
on a thing called logical

00:26:06.440 --> 00:26:08.970
modality, a
logical possibility.

00:26:08.982 --> 00:26:13.840
One, perhaps David Chalmers
is the most directly implicated in

00:26:15.000 --> 00:26:18.651
the emergence of two
dimensional modal semantics.

00:26:18.663 --> 00:26:22.400
And instead of just
logically possible worlds now,

00:26:24.585 --> 00:26:27.580
we have kind of two
sets of world like things

00:26:27.592 --> 00:26:30.800
associated with primary
and secondary intentions

00:26:31.920 --> 00:26:34.665
in two dimensional
semantics.

00:26:34.677 --> 00:26:39.920
And broadly speaking, the
way I see this is that primary

00:26:39.921 --> 00:26:42.909
intentions are more like
analyticity and secondary

00:26:42.921 --> 00:26:45.920
intentions are more like
metaphysical possibility.

00:26:46.945 --> 00:26:49.518
But whether or not
that speculation is right,

00:26:49.530 --> 00:26:52.000
there does seem to
have been a move in that

00:26:52.150 --> 00:26:53.999
analytic philosophy
from talking about logical

00:26:54.011 --> 00:26:56.437
possibility to talking about
metaphysical possibility.

00:26:59.837 --> 00:27:02.484
A perhaps
related trend that I

00:27:02.496 --> 00:27:06.320
think I've observed
relates to grounding theory,

00:27:06.470 --> 00:27:09.292
which is increasingly
used in metaphysics

00:27:09.304 --> 00:27:12.000
and sometimes even
increasingly used in

00:27:12.650 --> 00:27:16.073
philosophy of physics,
where there's a sort of

00:27:16.085 --> 00:27:19.520
explicit deviation
between logical possibility

00:27:19.521 --> 00:27:23.597
and metaphysical possibility
and the corresponding necessities.

00:27:23.609 --> 00:27:25.520
Something like
A grounds B is

00:27:25.521 --> 00:27:28.137
logically contingent.
There's nothing in logic

00:27:28.149 --> 00:27:30.720
that is going to ensure
that a true grounding

00:27:30.845 --> 00:27:34.097
statement is true. But
at least in some important

00:27:34.109 --> 00:27:38.160
sense, those claims are meant
to be metaphysically necessary.

00:27:38.161 --> 00:27:40.397
So we've got a
divergence between

00:27:40.409 --> 00:27:43.040
logical and metaphysical
modalities and

00:27:43.041 --> 00:27:45.154
metaphysicians,
largely, as I see it, started

00:27:45.166 --> 00:27:46.960
to focus on the
metaphysical modality.

00:27:47.620 --> 00:27:50.513
So my question here
for Jeremy is whether

00:27:50.525 --> 00:27:53.360
or not this is a kind
of these are good,

00:27:53.960 --> 00:27:56.500
whether he agrees that
these trends exist and

00:27:56.512 --> 00:27:58.655
whether he thinks
they're good trends.

00:27:58.656 --> 00:28:02.884
I mean, has there been a net gain
as we've shifted focus in this way?

00:28:02.896 --> 00:28:05.280
And when I say we,
I guess I'm talking

00:28:05.281 --> 00:28:08.011
about metaphysicians.
The question as to whether

00:28:08.023 --> 00:28:10.480
philosophy of physics
should follow that or

00:28:10.481 --> 00:28:12.724
whether they're good
reasons for philosophy of

00:28:12.736 --> 00:28:15.040
physics in particular,
to kind of cleave to the

00:28:16.890 --> 00:28:20.835
more traditional kind
of logical possibility, as

00:28:20.847 --> 00:28:24.640
Jeremy largely does.
That's the first comment.

00:28:26.200 --> 00:28:29.104
The next one is
going to be briefer.

00:28:29.116 --> 00:28:33.600
It's about Everett and
probability. Again, rich chapter,

00:28:33.601 --> 00:28:37.469
there's lots to say.
Three traditional questions

00:28:37.481 --> 00:28:41.200
about Everettian
probability. Jeremy calls two

00:28:41.670 --> 00:28:45.747
of them the qualitative
and quantitative problems.

00:28:45.759 --> 00:28:48.498
What even are
Everettian chances?

00:28:48.499 --> 00:28:52.375
And then why should they
be set by the Born rule?

00:28:52.387 --> 00:28:56.560
Why should we take the
Born rule to kind of guide our

00:28:56.561 --> 00:28:59.244
expectations and
actions? And then there's

00:28:59.256 --> 00:29:02.080
this further problem,
the epistemic problem.

00:29:02.180 --> 00:29:05.198
How can we use probabilistic
evidence as we get

00:29:05.210 --> 00:29:08.240
statistical evidence
that we collect to confirm

00:29:08.241 --> 00:29:10.893
quantum theory
itself? And it's really the

00:29:10.905 --> 00:29:13.760
quantitative problem
that gets most attention

00:29:15.910 --> 00:29:19.782
in the multiverse. Volume,
epistemic problem is

00:29:19.794 --> 00:29:23.760
mentioned in further
reading and the qualitative

00:29:23.761 --> 00:29:26.243
problem is, it gets a
bit of discussion and

00:29:26.255 --> 00:29:29.040
it's said to raise certain
issues. But I get the

00:29:29.041 --> 00:29:31.714
impression Jeremy doesn't
see those as very pressing.

00:29:31.726 --> 00:29:33.520
It would be sort
of the interesting

00:29:33.521 --> 00:29:35.797
issues that are raised,
but they're not kind of

00:29:35.809 --> 00:29:38.455
clear and present threats
to the viability of Everett.

00:29:38.456 --> 00:29:40.509
Whereas the
quantitative problem does

00:29:40.521 --> 00:29:43.040
seem to be seen as a
clear and present threat.

00:29:43.890 --> 00:29:47.253
So really my question
here is just, is that

00:29:47.265 --> 00:29:50.640
a good reading of
Jeremy's view? Is it that

00:29:50.641 --> 00:29:54.720
things are going to stand and fall
on solving the quantitative problem?

00:29:55.570 --> 00:29:58.409
I ask this because I
think a lot of people are

00:29:58.421 --> 00:30:01.058
still bothered by the
qualitative problem.

00:30:01.059 --> 00:30:04.084
I think that like Everettianism
just can't get off the

00:30:04.096 --> 00:30:06.560
ground at all because
there's nothing in the

00:30:06.561 --> 00:30:08.992
theory that could
possibly be a probability.

00:30:09.004 --> 00:30:11.280
That seems to be a
big sticking point for

00:30:11.281 --> 00:30:13.756
outsiders, maybe
less than insiders.

00:30:13.768 --> 00:30:17.600
Insiders are very motivated
by the quantitative problem.

00:30:17.725 --> 00:30:20.817
But if we're going to
appeal more to outsiders

00:30:20.829 --> 00:30:24.000
with this sort of view,
I think the qualitative

00:30:24.001 --> 00:30:26.591
problem still
looms pretty large.

00:30:26.603 --> 00:30:30.880
And for the last point, and
again, this will be perhaps

00:30:30.980 --> 00:30:33.798
briefer, is about the
contingency of the laws

00:30:33.810 --> 00:30:36.640
of physics, the
fundamental laws, not kind of

00:30:36.641 --> 00:30:39.309
emergent laws that
are obtained here in the

00:30:39.321 --> 00:30:42.000
universe or perhaps
here in the multiverse,

00:30:45.680 --> 00:30:49.668
but laws that obtain
across the whole thing.

00:30:49.680 --> 00:30:53.680
And Jeremy confesses
that he is committed to

00:30:53.681 --> 00:30:56.089
the view in the
Humean tradition that the

00:30:56.101 --> 00:30:58.640
fundamental laws of
physics are contingent.

00:31:00.450 --> 00:31:03.541
And this comes out at
various stages in the book,

00:31:03.553 --> 00:31:06.720
but one of them is in his
primary objection to the

00:31:06.920 --> 00:31:10.564
view that I defend, the
identification of objective

00:31:10.576 --> 00:31:14.160
modality of what I call
metaphysical modality with

00:31:15.945 --> 00:31:19.876
Everettian worlds.
Because it would make the

00:31:19.888 --> 00:31:23.920
basic principle of quantum
theory and perhaps

00:31:23.921 --> 00:31:27.277
also the initial quantum
state into necessary truths.

00:31:27.289 --> 00:31:29.280
Jeremy finds
that unbelievable.

00:31:31.350 --> 00:31:34.183
I guess I'm curious
as to where that core

00:31:34.195 --> 00:31:37.040
motivation is coming
from. Why is it that

00:31:43.720 --> 00:31:46.834
laws have to be
contingent? And one option is

00:31:46.846 --> 00:31:50.320
just kind of something
like philosophical bedrock,

00:31:50.345 --> 00:31:52.895
this pure intuition that
we can't give any further

00:31:52.907 --> 00:31:55.520
justification for. And
Jeremy shares that intuition

00:31:55.620 --> 00:31:58.960
and that's where we
stop. Or is it something

00:31:58.972 --> 00:32:02.400
more methodological,
something like a sort of

00:32:02.560 --> 00:32:06.504
Kantian regulative
ideal that we should treat

00:32:06.516 --> 00:32:10.560
laws of physics as
contingent for kind of good

00:32:10.561 --> 00:32:13.418
methodological reasons?
We always have reason to

00:32:13.430 --> 00:32:16.240
treat them as contingent.
And that's the source

00:32:16.340 --> 00:32:20.861
of the judgment. Maybe
those aren't exclusive options.

00:32:20.873 --> 00:32:23.840
But this brings
me back then to the

00:32:23.841 --> 00:32:26.147
Lewis correspondence,
because I'd always wondered

00:32:26.159 --> 00:32:28.240
what Lewis thought of
this, why Lewis was so

00:32:28.241 --> 00:32:32.228
convinced of the contingency of
the fundamental laws of physics.

00:32:32.240 --> 00:32:34.640
And it comes out in
the correspondence

00:32:34.740 --> 00:32:36.991
in a letter to a
non-philosopher, interestingly.

00:32:37.003 --> 00:32:39.360
He was never as explicit
to philosophers as he was

00:32:39.510 --> 00:32:43.303
to this non-philosopher that
was writing to him about this.

00:32:43.315 --> 00:32:45.600
And he says that
he wants the world

00:32:45.750 --> 00:32:49.348
to play the role of a
logic for science, whereby

00:32:49.360 --> 00:32:53.120
we make scientific progress
by successively ruling

00:32:54.160 --> 00:32:57.823
out the possibilities.
And that if the laws were,

00:32:57.835 --> 00:33:01.360
if they were non-contingent
law of the physics,

00:33:01.885 --> 00:33:05.166
then the possible world
just couldn't play that

00:33:05.178 --> 00:33:07.500
role of being a
logic for science.

00:33:08.200 --> 00:33:12.854
So I wonder whether Jeremy
shares that view with Lewis or

00:33:12.866 --> 00:33:16.103
maybe has some
other reason for this.

00:33:16.104 --> 00:33:18.961
But these are all the
things I'm curious about.

00:33:18.973 --> 00:33:22.080
I'm very grateful again
for the writing of this book.

00:33:22.205 --> 00:33:27.440
Thanks, Jeremy. And thank you all
for coming into David for organizing.

00:33:29.490 --> 00:33:32.585
Thank you, Al. Thank
you both to Jeremy and Al

00:33:32.597 --> 00:33:35.476
for name checking the
Lewis correspondence.

00:33:35.477 --> 00:33:40.619
That makes me very happy. And
for showing that Roz Chas cartoon.

00:33:40.631 --> 00:33:43.440
So Jeremy, if you
want to say some

00:33:43.441 --> 00:33:45.464
stuff at this point in
response, go ahead.

00:33:45.476 --> 00:33:47.840
And after that, we'll go
to Q&A. But if you don't

00:33:47.841 --> 00:33:53.360
want to, you don't have to. Thank
you. And indeed, thank you very much,

00:33:53.410 --> 00:34:00.577
Ricard and Al for those
splendid comments. I will say a bit.

00:34:04.497 --> 00:34:09.188
I know ping pong between
the invited lot is bad news for

00:34:09.200 --> 00:34:13.200
this audience who are
getting ever more agitated.

00:34:14.880 --> 00:34:18.868
The truth is that I, to
the extent I got, I want

00:34:18.880 --> 00:34:22.880
to announce to the
invited audience that this is

00:34:22.881 --> 00:34:25.415
ordeal by fire for the
author because I have not

00:34:25.427 --> 00:34:28.691
colluded with Ricard and Al at
all about what they would say.

00:34:28.692 --> 00:34:31.242
So I have been punched
in various places.

00:34:31.254 --> 00:34:33.280
And I would like
to report to the

00:34:34.320 --> 00:34:38.266
audience that I actually
agree with the punches

00:34:38.278 --> 00:34:42.320
of Ricard wholly, I believe,
and Al roughly 50%.

00:34:43.700 --> 00:34:50.640
And without going on about it,
I'd say my humanism is deep.

00:34:52.915 --> 00:34:56.527
It's the denial of the
necessary connections in

00:34:56.539 --> 00:34:59.470
the world due to
the conceivability.

00:34:59.471 --> 00:35:02.896
And it goes with thinking,
well, it just seems a possibility,

00:35:02.908 --> 00:35:05.520
call it logical, metaphysical,
whatever you want

00:35:05.521 --> 00:35:08.657
to call it, just seems
plain possible that the

00:35:08.669 --> 00:35:11.680
cosmos could consist
of a vacuum solution of

00:35:11.681 --> 00:35:15.387
Maxwell electromagnetism.
And this is my kind of

00:35:15.399 --> 00:35:19.040
we are up to our necks
in modality stick in the

00:35:19.041 --> 00:35:21.719
possible world chapter.
And so the truth is, I

00:35:21.731 --> 00:35:24.480
did intend to write a
book that was meant to be

00:35:25.440 --> 00:35:29.345
an introduction to the
ardent student newcomer.

00:35:29.357 --> 00:35:33.440
I realised as I was
writing it that I'm incapable

00:35:33.540 --> 00:35:37.429
of softening the
relentlessly humorless,

00:35:37.441 --> 00:35:41.440
pedagogic, concise
prose, and that it was

00:35:41.441 --> 00:35:44.521
not going to be much
good to anyone, unless

00:35:44.533 --> 00:35:47.531
you already, you know,
drunk the Kool-Aid.

00:35:51.131 --> 00:35:55.557
But my answers to Al's
more specific questions then,

00:35:55.569 --> 00:35:59.440
especially about the
first and third aspects,

00:35:59.590 --> 00:36:05.040
would be along the lines of,
sorry, Al, grew up a Humean.

00:36:07.820 --> 00:36:14.720
Well said, Jeremy.

00:36:14.721 --> 00:36:19.440
Okay, and we'll have to... People
should read more David Hume.

00:36:20.155 --> 00:36:27.680
Quite so. I think we're scheduled
to go on to 6.30, are we, David?

00:36:28.240 --> 00:36:30.400
No, you can, I mean,
we can stop at 6.

00:36:30.401 --> 00:36:34.240
Well, let's just see...
Sorry, at 7. Sorry.

00:36:35.280 --> 00:36:38.618
Oh, sorry. 6.30 my
time. 7. Right. Okay.

00:36:38.630 --> 00:36:43.280
So we'll see how we go. And
if there are more questions,

00:36:43.281 --> 00:36:45.209
I take it we can just
kind of carry on for a bit

00:36:45.221 --> 00:36:47.081
and anyone that needs
to leave can just leave.

00:36:47.290 --> 00:36:53.120
So if you would like to ask a
question, raise your virtual hand.

00:36:54.640 --> 00:36:57.216
Yeah, put a question
in the chat if you prefer,

00:36:57.228 --> 00:36:59.760
for some reason, and
David will monitor it and

00:36:59.761 --> 00:37:03.288
somehow interpose your
question as and when he sees fit.

00:37:03.300 --> 00:37:05.600
And I'm just going
to take the hands

00:37:05.700 --> 00:37:08.438
in the order in
which I see them.

00:37:08.450 --> 00:37:11.767
Of which there are
none so far, because

00:37:11.768 --> 00:37:14.400
Jeremy, you've convinced
absolutely everyone.

00:37:14.401 --> 00:37:18.720
All Alded.

00:37:21.405 --> 00:37:25.280
This seems most unusual that
nobody wants to ask a question.

00:37:25.281 --> 00:37:29.440
That's okay.

00:37:29.441 --> 00:37:32.400
It's very odd.

00:37:33.680 --> 00:37:36.567
The book gallops
through a lot.

00:37:36.579 --> 00:37:41.680
I feel underprepared myself
to remember what it claims.

00:37:42.580 --> 00:37:46.151
Alan, Richard, if you
want to, you know, press...

00:37:46.163 --> 00:37:49.096
Oh, we have a question
from Dan Linford.

00:37:49.097 --> 00:37:53.220
On you go. Yeah, okay. I
mean, so there's this objection

00:37:53.232 --> 00:37:56.640
that sometimes gets
raised to various sorts of

00:37:56.715 --> 00:37:59.062
multiverses, but
particularly the inflationary

00:37:59.074 --> 00:38:01.985
multiverse or other sorts
of like anthropic proposals.

00:38:02.675 --> 00:38:06.704
It's what people call the
this universe objection.

00:38:06.716 --> 00:38:09.520
So for people who
don't know the way

00:38:09.521 --> 00:38:12.878
the objection is supposed
to go is that when you

00:38:12.890 --> 00:38:16.400
evaluate your hypothesis
in light of the evidence,

00:38:16.600 --> 00:38:18.528
you should take into
account the most specific

00:38:18.540 --> 00:38:20.480
version, most specific
evidence that you have.

00:38:20.481 --> 00:38:23.621
And the most specific
evidence that we

00:38:23.633 --> 00:38:27.200
have is not just that
life exists, but that

00:38:28.080 --> 00:38:32.584
this universe is a
universe that contains life.

00:38:32.596 --> 00:38:36.080
And the objection
is supposed to be,

00:38:36.230 --> 00:38:37.998
this is not an objection
that I endorse, but

00:38:38.010 --> 00:38:39.790
it's one that's out
there in the literature.

00:38:41.910 --> 00:38:45.910
The objection is supposed
to go that while the

00:38:45.922 --> 00:38:49.760
anthropic selection
might give you that life

00:38:49.761 --> 00:38:52.000
exists somewhere,
it doesn't help with a

00:38:52.012 --> 00:38:54.320
question about why
life should exist here

00:38:54.321 --> 00:38:56.466
in the universe that
we inhabit, right?

00:38:56.478 --> 00:38:59.440
Because like that's the
most specific evidence that we

00:38:59.441 --> 00:39:01.699
have according
to the objection.

00:39:01.711 --> 00:39:05.840
So I wonder what you make
of that sort of objection to like

00:39:10.220 --> 00:39:17.120
anthropic arguments, but yeah.
>> Jeremy, do we want to?

00:39:17.121 --> 00:39:23.360
>> You go ahead, Rikard.
>> Well, it seems to me that

00:39:27.900 --> 00:39:31.268
this reasoning does not
do justice to the second

00:39:31.280 --> 00:39:34.800
part of anthropic reasoning,
which is pointing at,

00:39:37.650 --> 00:39:41.440
so the first part just
tells us, given these

00:39:41.452 --> 00:39:45.600
laws of physics, it is
very probable that in the

00:39:45.601 --> 00:39:49.071
multiverse, there is at
least one universe that

00:39:49.083 --> 00:39:52.640
has those fine tuned
values that allow for life.

00:39:57.715 --> 00:40:01.093
The second aspect then
is the genuine anthropic

00:40:01.105 --> 00:40:04.640
step, which says, assuming
that there is this one

00:40:05.280 --> 00:40:09.179
universe where life
developed, there will be

00:40:09.191 --> 00:40:13.280
observation, or where
observational, observing

00:40:13.281 --> 00:40:16.302
life has developed,
there will be observations.

00:40:16.314 --> 00:40:18.960
And of course, those
observations will be

00:40:23.985 --> 00:40:27.293
observations that
witness a fine tuned

00:40:27.305 --> 00:40:31.760
cosmological constant.
So, any observer, therefore,

00:40:32.810 --> 00:40:36.596
can on that basis explain
why they observe a fine

00:40:36.608 --> 00:40:40.560
tuned cosmological
constant. And I don't think that

00:40:40.880 --> 00:40:45.135
there is any problematic
aspect of the anthropic

00:40:45.147 --> 00:40:48.880
reasoning in that
respect. There are other

00:40:48.881 --> 00:40:52.115
worries about anthropic
reasoning, which go more

00:40:52.127 --> 00:40:55.440
in the direction of asking,
okay, what exactly do

00:40:55.441 --> 00:40:59.710
you want to explain? Do you
explain your own existence?

00:40:59.722 --> 00:41:02.480
In that case, then
you fall back to

00:41:02.930 --> 00:41:07.164
a full-fledged strong
anthropic argument saying

00:41:07.176 --> 00:41:10.880
I exist, therefore,
and I exist observing

00:41:10.881 --> 00:41:13.193
a fine tuned
cosmological constant.

00:41:13.205 --> 00:41:17.598
And that's why I was observing a
fine tuned cosmological constant.

00:41:19.638 --> 00:41:22.642
In order to avoid
that problem, one

00:41:22.654 --> 00:41:27.242
needs to have a wider concept
of what is selected there.

00:41:27.243 --> 00:41:29.959
And then, of course,
the question is how

00:41:29.971 --> 00:41:33.360
do we then specify what
is selected based on this

00:41:34.740 --> 00:41:38.602
anthropic argument?
So, I think there are other

00:41:38.614 --> 00:41:43.016
problems that are quite
difficult to handle, actually.

00:41:43.041 --> 00:41:47.840
But yes, but they go in a slightly
different direction, I think.

00:41:51.140 --> 00:41:52.560
>> JANE: Jeremy, do you
want to add anything to that?

00:41:52.561 --> 00:41:55.204
>> JEREMY: I agree
with what Ricard said.

00:41:55.216 --> 00:41:58.000
I mean, I would thank
Dan very much for the

00:41:58.001 --> 00:42:04.240
objection, but I do think that
Ricard's line was exactly right.

00:42:06.710 --> 00:42:11.412
You must condition on
all you know sounds right.

00:42:11.424 --> 00:42:13.840
Like I said
in my slide,

00:42:18.080 --> 00:42:21.981
take into account the
process of observation,

00:42:21.993 --> 00:42:26.080
but you'll get scientifically
unusable measures

00:42:28.870 --> 00:42:32.583
if you condition on every
detail of what you know,

00:42:32.595 --> 00:42:36.320
just in the way that Ricard
was saying at the end.

00:42:40.530 --> 00:42:43.440
>> JANE: Okay.
We have a question from Julius.

00:42:48.525 --> 00:42:51.437
>> JULIUS: Sorry,
permission issue.

00:42:51.449 --> 00:42:55.623
Hey, so, yes, I haven't
read the book. I'm sorry.

00:42:55.624 --> 00:42:58.174
And I see from the number
of questions that you had that

00:42:58.186 --> 00:43:00.240
if I did, my question
would surely be answered.

00:43:00.440 --> 00:43:03.019
And I would just not
ask silly questions on a

00:43:03.031 --> 00:43:05.680
forum like this. But
anyway, so it seems to me

00:43:06.420 --> 00:43:08.781
that one way of looking
at the variety of 20th

00:43:08.793 --> 00:43:10.960
century developments
of different types of

00:43:10.961 --> 00:43:14.263
multiverses is kind of,
oh, we actually discover

00:43:14.275 --> 00:43:17.520
new multiverses when
we control them better and

00:43:17.521 --> 00:43:21.187
better with similarity
relations or with this

00:43:21.199 --> 00:43:24.480
or that probability
measures and so on.

00:43:24.630 --> 00:43:27.571
And so, I wanted to ask
an open-ended question.

00:43:27.583 --> 00:43:30.640
Is the philosophical misery
or slash excitement of

00:43:30.740 --> 00:43:34.065
dealing with them nearly
done? Have we discovered,

00:43:34.077 --> 00:43:37.280
Jeremy, in your opinion,
most of the multiverses

00:43:37.281 --> 00:43:40.867
that we might encounter
in the near future?

00:43:40.879 --> 00:43:44.800
Or perhaps you see some
prospects for even more

00:43:44.801 --> 00:43:47.185
multiverses that we
should do and therefore

00:43:47.197 --> 00:43:49.760
perhaps you would have
to do a revised version

00:43:49.960 --> 00:43:56.184
of the book in 20 or 50 years?
>> JANE: What a fun question.

00:43:56.824 --> 00:44:01.869
Thank you, Julius. I guess
it's a great question even if one

00:44:01.881 --> 00:44:05.840
has read the book. So
I'm enjoying the question.

00:44:06.390 --> 00:44:09.575
Of course, it goes
back in a way to my

00:44:09.587 --> 00:44:13.120
catchphrase, which I
used in answer to Al,

00:44:14.020 --> 00:44:16.568
we are up to our
necks in modality, in all

00:44:16.580 --> 00:44:19.200
our thought and talk,
both in everyday life

00:44:20.000 --> 00:44:22.516
and in technical
science.

00:44:22.528 --> 00:44:28.000
So I think alternatives/options/other
possibilities are

00:44:28.750 --> 00:44:33.497
kind of cognitively mandatory.
It's what you work with.

00:44:33.509 --> 00:44:36.400
It's what the dog
works with when

00:44:37.600 --> 00:44:41.467
in its behaviour showing
how it's deciding where

00:44:41.479 --> 00:44:46.865
to dig up the forgotten, the bone
whose location is half forgotten.

00:44:48.785 --> 00:44:51.308
So philosophical
refinement and

00:44:51.320 --> 00:44:55.120
also refinement of ideas
from technical science

00:44:56.840 --> 00:45:01.511
will march on with luck if
funding survives long enough.

00:45:01.523 --> 00:45:04.240
And in that
sense, there will be

00:45:05.110 --> 00:45:09.071
rather like restaurants
lengthening their

00:45:09.083 --> 00:45:12.960
menu for ever more
discerning customers.

00:45:13.830 --> 00:45:17.138
There will be for the
philosopher or physicist,

00:45:17.150 --> 00:45:20.400
you know, more
multiverses. But I don't think,

00:45:20.550 --> 00:45:23.161
so to speak, if I reach
for another sector

00:45:23.173 --> 00:45:25.920
of physics than quantum
theory or cosmology,

00:45:26.880 --> 00:45:30.786
I'm not going to find in
material science or the

00:45:30.798 --> 00:45:34.880
details of classical
electromagnetism a completely

00:45:36.170 --> 00:45:40.815
other display of options that
deserve the word universe.

00:45:40.827 --> 00:45:47.140
I think indeterminism in physics
obviously involves future alternatives.

00:45:47.152 --> 00:45:50.800
And so even before
quantum or cosmology,

00:45:52.200 --> 00:45:54.354
there's a lot of physics
and philosophy to

00:45:54.366 --> 00:45:56.480
say about the status
of possible futures.

00:45:57.480 --> 00:46:00.735
As we tend to learn a
lot in philosophy class, in

00:46:00.747 --> 00:46:04.080
philosophy of space and
time or metaphysics class,

00:46:04.230 --> 00:46:07.120
but not at all in academic
physics education.

00:46:12.150 --> 00:46:15.200
Thanks, Jeremy.
A question from Sandra.

00:46:19.600 --> 00:46:24.838
Hi, I haven't read the book,
but I was listening to everybody.

00:46:24.850 --> 00:46:27.365
I am in my first
year of PhD.

00:46:28.085 --> 00:46:32.270
So I was just curious. I was
working on laws of nature.

00:46:32.282 --> 00:46:35.200
And I think Alasdair
did point out the

00:46:35.201 --> 00:46:36.821
fact that laws
could be different.

00:46:36.833 --> 00:46:39.440
And how do we see that? I
think there was a question or

00:46:39.441 --> 00:46:42.542
some idea like that.
And I was thinking that if

00:46:42.554 --> 00:46:45.600
one is a human, how do
we go about maintaining

00:46:45.601 --> 00:46:47.685
the position that well,
laws could have been

00:46:47.697 --> 00:46:49.840
different in possible
worlds. But then at the

00:46:49.841 --> 00:46:52.819
same time, in the worlds
that are closer to ours,

00:46:52.831 --> 00:46:55.760
they are going to be
same. But at the same time,

00:46:55.761 --> 00:46:58.650
when you look around,
what basically human

00:46:58.662 --> 00:47:01.840
account is, it is
basically saying that, well,

00:47:01.841 --> 00:47:05.069
laws are just descriptions.
So I was wondering,

00:47:05.081 --> 00:47:08.320
how does law get their
predictive powers in the

00:47:08.321 --> 00:47:10.694
sense that they tell
us what sort of protein

00:47:10.706 --> 00:47:13.200
foldings would happen
and what sort of protein

00:47:13.201 --> 00:47:16.553
foldings would not? And
then pragmatists do have

00:47:16.565 --> 00:47:20.000
a sort of critique of human
accounts of laws such

00:47:20.001 --> 00:47:22.482
that they are unable to
just explain where does

00:47:22.494 --> 00:47:25.399
law get its predictive powers
and explanatory powers.

00:47:25.400 --> 00:47:31.280
So I was wondering if you could just
maybe speak on it a bit. So, yeah.

00:47:31.281 --> 00:47:38.028
Yes. Well, Al may want to come
in on this, or would you, Rikard?

00:47:41.298 --> 00:47:43.754
But thank you
for the question.

00:47:43.766 --> 00:47:47.920
I'm afraid you're going to
get a human answer that you

00:47:54.575 --> 00:47:57.506
probably heard before.
And that is, I agree that

00:47:57.518 --> 00:48:00.400
on my conception, I think
the human conception,

00:48:00.401 --> 00:48:04.146
humans vary, of course,
but I think Helen will

00:48:04.158 --> 00:48:08.160
join me in this. I mean,
on the human conception,

00:48:10.480 --> 00:48:14.635
the laws describe patterns.
And of course, there's

00:48:14.647 --> 00:48:19.777
the question, what, every
possible pattern you could pick out?

00:48:19.778 --> 00:48:22.749
And the answer is
no, not every one.

00:48:22.761 --> 00:48:26.400
It's not true that every
true generalization

00:48:27.760 --> 00:48:31.790
or every true contingent
generalization is to be

00:48:31.802 --> 00:48:35.760
a law of nature. It's
some that are selected by

00:48:37.120 --> 00:48:41.240
their fruitfulness,
fecundity, depth, fertility,

00:48:41.252 --> 00:48:45.040
whatever it's going.
Of course, Lewis, as it

00:48:45.041 --> 00:48:47.823
happens, has
established a long tradition

00:48:47.835 --> 00:48:50.560
following a one-liner
from Frank Ramsey,

00:48:53.440 --> 00:48:58.582
actually, whom he credits in
a footnote for having said it.

00:48:58.594 --> 00:49:01.440
So that's the basic
human answer

00:49:01.515 --> 00:49:03.891
about what the laws are.
And your challenge on

00:49:03.903 --> 00:49:06.240
that, how can you be
confident of prediction?

00:49:12.240 --> 00:49:16.331
That is, as a question
of justification,

00:49:16.343 --> 00:49:20.240
in a very rationally
satisfying sense,

00:49:22.160 --> 00:49:25.482
I think that is an
unanswered question.

00:49:25.494 --> 00:49:30.160
That is to say, Hume
replies, the only justification is

00:49:30.161 --> 00:49:33.101
custom or habit or
instinct, which, of course,

00:49:33.113 --> 00:49:36.000
sounds like a psychological
description of an

00:49:36.880 --> 00:49:42.462
inevitable tendency of the human
mind, or indeed the dog's mind.

00:49:42.474 --> 00:49:44.880
And I think
it is true as a

00:49:49.360 --> 00:49:53.903
psychological description
of how we go about things.

00:49:53.915 --> 00:49:57.360
And I am worried,
sad, ashamed that 300

00:49:57.361 --> 00:50:00.483
years of philosophy
hasn't yet given a good

00:50:00.495 --> 00:50:03.920
answer to Hume's
predicament about a more fully

00:50:05.280 --> 00:50:11.760
stand on two feet rational
reassurance about why.

00:50:14.350 --> 00:50:18.735
But I'm just feeling the pain
about the problem of induction.

00:50:18.747 --> 00:50:20.800
As you may
know, Sandra, the

00:50:20.950 --> 00:50:24.587
Cambridge philosopher
C.D. Broad called induction,

00:50:24.599 --> 00:50:28.320
the glory of science and
the scandal of philosophy.

00:50:28.470 --> 00:50:30.699
And I don't know
whether Helen would

00:50:30.711 --> 00:50:33.200
agree, but I think
it is still unsolved.

00:50:35.270 --> 00:50:36.841
I think we're just
going to have to learn

00:50:36.853 --> 00:50:38.320
to live with it,
Jeremy. It's my view.

00:50:38.321 --> 00:50:42.720
Suck it up. Question from Michael.

00:50:45.120 --> 00:50:49.232
Hi, Jeremy. I was just
continuing this speculation

00:50:49.244 --> 00:50:53.120
that you had with Julius,
what kind of order we

00:50:53.220 --> 00:50:56.362
could get in the many
possibilities that our

00:50:56.374 --> 00:50:59.600
theories produce in the
future? Because if we

00:50:59.750 --> 00:51:01.881
don't have much of
an order, then we're as

00:51:01.893 --> 00:51:04.240
helpless as Newton is
with respect to Bentley.

00:51:06.880 --> 00:51:11.201
Well, God picks it or we
call it an anthropic argument.

00:51:11.213 --> 00:51:14.080
And I mean, 20
years ago, I think we

00:51:14.081 --> 00:51:16.706
had many discussions
about Lewis spheres of

00:51:16.718 --> 00:51:19.401
possible world and
Hamilton-Yacobi theories.

00:51:19.402 --> 00:51:22.680
So there are scenarios
where you can put the

00:51:22.692 --> 00:51:25.315
modalities in a
pretty good order.

00:51:25.465 --> 00:51:29.600
Statistical theories, at least,
let you say, well, this is a

00:51:29.612 --> 00:51:33.120
phase transition. So
somehow it had to be expected.

00:51:33.121 --> 00:51:38.480
But what would we
expect as a sort of order

00:51:40.560 --> 00:51:43.920
stating the place of the
sphere of possible world

00:51:43.932 --> 00:51:46.960
or a probabilistic
framework? What should we

00:51:49.600 --> 00:51:54.205
expect of cosmology or
multiverse theory in the future?

00:51:54.217 --> 00:51:57.600
When would you be
happy to have an order

00:52:00.250 --> 00:52:02.871
on the possibilities?
Yes, I'm not.

00:52:02.883 --> 00:52:07.665
I think I won't answer this at
all. I'll be able to answer this.

00:52:09.835 --> 00:52:12.436
It's kind of too
multifaceted.

00:52:12.448 --> 00:52:17.120
I think that your mention of
Hamilton-Yacobi theory and

00:52:20.080 --> 00:52:23.986
statistical physics does
echo something that the

00:52:23.998 --> 00:52:27.448
book, as you may know,
makes a deal about.

00:52:27.598 --> 00:52:31.343
Namely, I illustrate my,
we are up to our necks

00:52:31.355 --> 00:52:34.720
in modality in all our
cognition by saying

00:52:36.400 --> 00:52:40.268
physical theories use
indispensably spaces of

00:52:40.280 --> 00:52:44.160
possible states of the
objects they describe.

00:52:45.430 --> 00:52:48.861
So even if you say
your philosophy will be

00:52:48.873 --> 00:52:52.480
focused only on what
you might call the best

00:52:52.481 --> 00:52:58.560
deliverances of human inquiry,
technical science with its precision and

00:53:04.080 --> 00:53:08.746
success, modular, the
problem of induction.

00:53:08.758 --> 00:53:12.080
So I think it's
easy enough to

00:53:16.960 --> 00:53:20.693
survey the variety of
state spaces and their

00:53:20.705 --> 00:53:24.960
endemic indispensability
across technical science.

00:53:25.160 --> 00:53:28.208
So in that sense,
one can bring order to

00:53:28.220 --> 00:53:31.280
the multiverses.
It's along the lines of

00:53:35.480 --> 00:53:39.582
fly like an eagle over
the legacy of established

00:53:39.594 --> 00:53:43.280
science and see what
possibility spaces are

00:53:44.920 --> 00:53:52.720
widely appealed to. But the deep
question of what is a proposition,

00:53:53.440 --> 00:53:56.327
I said this in the book
here and there, that

00:53:56.339 --> 00:53:59.040
I work with the jargon
of possible world,

00:53:59.041 --> 00:54:03.125
but I believe that one
can instead talk about

00:54:03.137 --> 00:54:06.960
propositions which
are less than maximally

00:54:11.670 --> 00:54:15.383
specific in how they
portray the world as being.

00:54:15.395 --> 00:54:19.899
And you can also talk Frugean,
I mean, the realm of sense.

00:54:24.539 --> 00:54:27.748
I believe that there
are these, as they

00:54:27.760 --> 00:54:31.760
say, abstract propositions,
senses. I should have

00:54:31.761 --> 00:54:34.838
perhaps said at the very
beginning, when Ricard

00:54:34.850 --> 00:54:38.400
kindly said that Jeremy has
a yes to the philosophers,

00:54:38.500 --> 00:54:41.923
a no to the average and
a maybe to the cosmology,

00:54:41.935 --> 00:54:44.880
and Ricard kindly said
he tended to agree,

00:54:45.910 --> 00:54:52.080
I should have clarified perhaps that
my yes is not to Lewis's yes. Right.

00:54:53.810 --> 00:54:57.688
There's a bit in the book
where I say the word

00:54:57.700 --> 00:55:01.760
concrete versus abstract
is a bad jargon because

00:55:01.761 --> 00:55:04.884
it means about four
or five different things.

00:55:04.896 --> 00:55:07.360
And Lewis, I follow
Lewis, he says,

00:55:07.361 --> 00:55:11.266
of the five, six things
it means, I agree that

00:55:11.278 --> 00:55:15.280
four out of the six, my
world as I believe them

00:55:15.281 --> 00:55:19.027
to be count as concrete.
So my friends are right

00:55:19.039 --> 00:55:22.640
to say, David, you
believe in concrete worlds.

00:55:22.715 --> 00:55:26.448
But since these
distinctions cut across one

00:55:26.460 --> 00:55:30.640
another, it's not really
intellectually accurate

00:55:32.415 --> 00:55:37.380
to paste it as concrete as if
there was a single notion there.

00:55:37.392 --> 00:55:40.240
I don't believe
that the worlds are

00:55:40.265 --> 00:55:43.034
concrete in the four
of the six senses in

00:55:43.046 --> 00:55:45.760
which he agrees his
worlds are concrete.

00:55:46.560 --> 00:55:50.224
That's the sense in which
I'm in an agony about

00:55:50.236 --> 00:55:53.520
what worlds are. But
I think it's almost a

00:55:53.521 --> 00:55:56.728
perennial agony since
the invention of logic and

00:55:56.740 --> 00:56:00.160
the philosophy of language
to get one's mind around

00:56:00.161 --> 00:56:03.794
what exactly is the
vehicle of representation.

00:56:03.806 --> 00:56:07.840
I mean, I think we have
naturalistic theories about

00:56:07.841 --> 00:56:14.480
how objects do represent, but what is
a proposition is for me a tough one.

00:56:17.380 --> 00:56:19.723
Yeah, I think you
have just a fascinating

00:56:19.735 --> 00:56:22.320
example that it took
one and a half centuries

00:56:22.470 --> 00:56:24.951
after the theory to
get the modality in

00:56:24.963 --> 00:56:27.840
order or to talk properly
about the modality.

00:56:27.841 --> 00:56:31.498
And then one could
wonder, there could be further

00:56:31.510 --> 00:56:34.880
theoretical development
about the modalities.

00:56:35.030 --> 00:56:36.720
Thank you. Thank you.

00:56:36.721 --> 00:56:41.680
And I'm sorry to interrupt you.
Somebody sent me a question directly.

00:56:41.880 --> 00:56:42.800
Okay, go for it.

00:56:42.801 --> 00:56:45.677
Before we just, so Mark
Nader Basafa asks, do you

00:56:45.689 --> 00:56:48.400
think the strongest
arguments for a multiverse

00:56:48.401 --> 00:56:51.683
justify believing that
other universes exist or

00:56:51.695 --> 00:56:55.200
primarily justify to
investigate that possibility?

00:56:58.490 --> 00:57:01.518
Do the most powerful
arguments justify that

00:57:01.530 --> 00:57:04.640
they exist or that
they justify only that it

00:57:11.590 --> 00:57:13.240
is worth
investigating? Yes.

00:57:13.252 --> 00:57:16.640
So they are arguments which
intend us to conclude that the

00:57:18.050 --> 00:57:22.056
universes in question
exist. In all three of my

00:57:22.068 --> 00:57:27.007
topics, that is the aim of the
advocate of the multiverse.

00:57:27.397 --> 00:57:30.346
So let me clarify
what the various

00:57:30.358 --> 00:57:34.240
participants to the
debate are trying to ask.

00:57:35.220 --> 00:57:38.046
But so this is an
easy answer, if you

00:57:38.058 --> 00:57:41.280
like, it's just a kind
of friendly answer.

00:57:42.005 --> 00:57:45.680
It's certainly true that even if you
think the arguments are unconvincing,

00:57:46.880 --> 00:57:50.841
they're very worthwhile
arguments to consider,

00:57:50.853 --> 00:57:54.480
because why they
stumble is worth knowing.

00:57:56.160 --> 00:58:00.099
So inquire, thinking
of the arguments as

00:58:00.111 --> 00:58:04.160
prompts to us to
investigate is a way of,

00:58:06.330 --> 00:58:10.677
well, putting more
positively the conclusion,

00:58:10.689 --> 00:58:14.080
it's an argument
worth considering,

00:58:14.081 --> 00:58:19.360
even though it doesn't convince
of its announced conclusion.

00:58:21.760 --> 00:58:22.560
Yeah. Thank you.

00:58:22.710 --> 00:58:24.565
You've done a very
good job of warming up the

00:58:24.577 --> 00:58:26.320
audience, Jeremy,
because we now have four

00:58:26.321 --> 00:58:29.600
questions in a big queue.
So I'm going to go to Josh next.

00:58:30.500 --> 00:58:31.627
Well, thanks so
much, Jeremy.

00:58:31.639 --> 00:58:33.840
I've really enjoyed the parts
of the book that I've read,

00:58:33.841 --> 00:58:35.808
although it's true I haven't
managed to read the

00:58:35.820 --> 00:58:37.840
whole thing yet. But I
have a question going back

00:58:37.841 --> 00:58:41.292
to the explanation stuff. So I
guess chapter five of your book.

00:58:41.304 --> 00:58:43.200
And I'm kind of
curious about some

00:58:43.201 --> 00:58:45.806
possible answers
from the Humean view.

00:58:45.818 --> 00:58:49.440
So I'm kind of wondering,
would it be permissible for

00:58:49.441 --> 00:58:52.878
a Humean, perhaps of
your variety, to just say,

00:58:52.890 --> 00:58:56.560
we need not give an
explanation for why it is that

00:58:56.561 --> 00:58:58.844
our universe appears
to be fine-tuned?

00:58:58.856 --> 00:59:02.560
We need not explain the horizon
problem, the flatness problem.

00:59:02.735 --> 00:59:04.796
The putative explanation
for this kind of Humean

00:59:04.808 --> 00:59:06.880
would be something
like, that's just the way the

00:59:06.881 --> 00:59:10.063
contingent facts are. That's
the way the Humean mosaic is.

00:59:10.075 --> 00:59:12.080
There's nothing
further to say about

00:59:12.081 --> 00:59:14.829
it. It would be the answer
to the why question,

00:59:14.841 --> 00:59:17.600
for each of these why
questions is, that's just

00:59:17.601 --> 00:59:20.410
the way things are. So
I'm kind of wondering, is

00:59:20.422 --> 00:59:23.360
this a permitted answer
for a Humean of your kind?

00:59:23.361 --> 00:59:25.589
Or would you think
somebody giving this kind of

00:59:25.601 --> 00:59:28.447
answer is being irrational,
making some kind of mistake?

00:59:30.767 --> 00:59:35.176
>>No, I don't think
they're being irrational.

00:59:35.188 --> 00:59:38.160
And many people
will know, Josh,

00:59:38.320 --> 00:59:42.308
you yourself will know,
there was actually a

00:59:42.320 --> 00:59:46.320
Hugh Price and Craig
Callender 25 years ago,

00:59:47.760 --> 00:59:51.663
about assessing in what
sense a so-called past

00:59:51.675 --> 00:59:55.760
hypothesis, that is to
say an early cosmic state

00:59:57.600 --> 01:00:00.945
of the right type
to lead to etc.

01:00:00.957 --> 01:00:05.600
, to what extent it needed
to be explained. And

01:00:07.040 --> 01:00:14.240
the whole culture of early universe
cosmology by the practitioners is

01:00:17.360 --> 01:00:21.433
a... Well, I think Ricard
and others in the Zoom

01:00:21.445 --> 01:00:25.360
would agree with me,
that culture is dominated

01:00:28.320 --> 01:00:32.569
by people preferring to
have a causal explanation

01:00:32.581 --> 01:00:36.320
of the advocated early
state. And the best,

01:00:37.060 --> 01:00:40.838
and the causal
explanation shouldn't just be

01:00:40.850 --> 01:00:44.640
tracing the causal
antecedents of the state,

01:00:44.641 --> 01:00:47.789
no matter how highly
specific or peculiar it

01:00:47.801 --> 01:00:50.960
seems, please have a
framework in which this

01:00:50.961 --> 01:00:54.546
early state with its
special qualities turns

01:00:54.558 --> 01:00:58.400
out to be generic. And
so there's, I think it's

01:00:59.520 --> 01:01:03.595
scientifically fruitful
to... This goes back to

01:01:03.607 --> 01:01:07.520
the previous discussions,
including the thing

01:01:07.521 --> 01:01:11.392
about what to condition
on. It's scientifically

01:01:11.404 --> 01:01:15.040
fruitful to, and in that
way explanatory, to

01:01:19.790 --> 01:01:23.359
render the state typical.
So frameworks earn

01:01:23.371 --> 01:01:27.440
their adherence, earn our
adherence by showing the

01:01:27.600 --> 01:01:31.545
states to be typical.
But I do think a kind of

01:01:31.557 --> 01:01:35.102
that's the way it
is, is not irrational.

01:01:35.152 --> 01:01:37.961
And it must, at some
point, come for everyone.

01:01:37.973 --> 01:01:41.120
I mean, we're now not in
the philosophy of cosmology,

01:01:41.121 --> 01:01:44.057
but the philosophy
of cosmogony, right?

01:01:44.069 --> 01:01:47.760
So these origin questions
are really tough. Yeah.

01:01:47.761 --> 01:01:51.200
Thanks, Jeremy. Hassock?

01:01:53.890 --> 01:01:57.638
Yes, thank you. Thank
you so much, Jeremy.

01:01:57.650 --> 01:02:01.840
And congratulations. I
have ignorant questions,

01:02:01.990 --> 01:02:04.700
because I've not
read the book yet.

01:02:04.712 --> 01:02:09.141
But two coupled ones, one,
both about the Everettian side.

01:02:17.581 --> 01:02:20.446
One is, I mean, is the
Everettian multiverse

01:02:20.458 --> 01:02:23.360
the same kind of thing
in any sense from the

01:02:23.760 --> 01:02:27.877
cosmological one? And
if not, should we not just

01:02:27.889 --> 01:02:31.760
stop using the same
word to describe the two?

01:02:32.880 --> 01:02:36.595
The other is, I mean,
with your questions

01:02:36.607 --> 01:02:40.880
about, you know, what
even are these chances or

01:02:41.040 --> 01:02:44.768
probabilities of,
do the Everettians

01:02:44.780 --> 01:02:49.040
have standard answers
to those questions?

01:02:53.520 --> 01:02:57.548
Right, lovely pair of
questions. About the second,

01:02:57.560 --> 01:03:01.520
I think it's fair to say,
yes, the Everettians do

01:03:01.521 --> 01:03:05.516
have answers to what
propositions or events or

01:03:05.528 --> 01:03:09.360
items the probabilities
of probabilities of.

01:03:09.510 --> 01:03:12.087
But I also see that I
can see on the screen as

01:03:12.099 --> 01:03:15.746
many can, Simon is in the queue.
So I'm going to postpone that.

01:03:16.296 --> 01:03:18.580
But about the
first, again, I

01:03:18.592 --> 01:03:21.760
actually defer rather,
if I may, to Ricard.

01:03:22.730 --> 01:03:26.257
It was a delicate
issue in writing that

01:03:26.269 --> 01:03:30.080
chapter about the
cosmological multiverse,

01:03:30.230 --> 01:03:33.195
how to relate it
to the Everettian.

01:03:33.207 --> 01:03:37.440
And Ricard gave me
invaluable advice. But broadly,

01:03:37.540 --> 01:03:40.800
and I think this is compared with
what Ricard said out loud today,

01:03:48.760 --> 01:03:52.746
the string theories,
the cosmology folks,

01:03:52.758 --> 01:03:56.560
they are not obliged
to endorse Everett

01:03:57.520 --> 01:04:02.360
in the traditional main
central thesis sense of Everett.

01:04:02.372 --> 01:04:05.520
I, Everett, tell
you that a strictly

01:04:05.521 --> 01:04:08.256
isolated quantum
system will evolve towards,

01:04:08.268 --> 01:04:10.640
according to the
Schrodinger equation,

01:04:10.690 --> 01:04:12.976
so-called Schrodinger
evolution, and there is

01:04:12.988 --> 01:04:15.910
never a physical process of
collapse of the wave packet.

01:04:16.210 --> 01:04:18.462
They're not
obliged to do that.

01:04:18.474 --> 01:04:21.760
They can allow so-called
non-unitary evolution.

01:04:21.910 --> 01:04:24.605
But what is crucial to
them is that if you have

01:04:24.617 --> 01:04:27.440
a state in which in the
conventional quantum way,

01:04:27.590 --> 01:04:31.223
there is a complex
amplitude for more than one

01:04:31.235 --> 01:04:34.960
alternative, in order to
have their multiverse,

01:04:35.110 --> 01:04:38.152
you must say there is a
physical reality for both

01:04:38.164 --> 01:04:41.280
the alternatives that have
this complex amplitude.

01:04:42.380 --> 01:04:44.909
So the idea is over
time, there may be a

01:04:44.921 --> 01:04:48.160
non-Schrodinger-like
suppression of an alternative.

01:04:48.870 --> 01:04:51.725
That's perfectly
compatible with the general

01:04:51.737 --> 01:04:55.700
vision of eternal inflation
and a string theory multiverse.

01:04:56.100 --> 01:04:59.188
They're not
committed to what the

01:04:59.200 --> 01:05:03.200
average Everettian
exposition first stresses,

01:05:03.350 --> 01:05:06.092
Schrodinger evolution
always true for a strictly

01:05:06.104 --> 01:05:08.800
isolated system. But
what they are committed to

01:05:13.700 --> 01:05:17.758
is that there is physical
facts in the alternatives

01:05:17.770 --> 01:05:21.007
that get some non-zero
complex amplitude.

01:05:21.008 --> 01:05:25.737
That's the crucial thing.
And that physical reality

01:05:25.749 --> 01:05:29.520
underneath for each
such alternative is,

01:05:29.670 --> 01:05:35.600
you know, in toy form, one of the
worlds of the cosmological multiverse.

01:05:36.100 --> 01:05:37.120
Yeah.

01:05:37.670 --> 01:05:41.360
So you can't throw away the
interference terms as a kind of jargon.

01:05:43.160 --> 01:05:44.000
Yeah. Thank you.

01:05:44.001 --> 01:05:46.820
Simon.

01:05:48.320 --> 01:05:52.308
Oh, right. Well, thank
you. I seem to have a

01:05:52.320 --> 01:05:55.670
timely question or
perhaps answers.

01:05:55.671 --> 01:05:58.817
Hasluck, some lovely
questions for you. I do differ a

01:05:58.829 --> 01:06:00.860
little bit from
Jeremy in my reply.

01:06:00.861 --> 01:06:03.822
I mean, I think one point
about propositions and so forth,

01:06:03.834 --> 01:06:06.080
I don't really see
Everettian quantum theory

01:06:06.880 --> 01:06:11.083
as requiring or delivering,
you know, large scale

01:06:11.095 --> 01:06:14.880
detail on philosophical
problems or projects

01:06:14.930 --> 01:06:17.573
that maybe have been
going for centuries.

01:06:17.585 --> 01:06:21.120
I mean, absolutely not. In
fact, most of my recent work

01:06:21.121 --> 01:06:24.349
on Everettian quantum
theory has been trying to

01:06:24.361 --> 01:06:27.600
rid it of philosophy and
present it in the same

01:06:27.601 --> 01:06:30.606
framework or formulation
or similar formulations

01:06:30.618 --> 01:06:33.760
as one would say GR or
other fundamental theories.

01:06:34.235 --> 01:06:37.587
And on the other point,
I do agree with you,

01:06:37.599 --> 01:06:41.040
Hasluck, there is
something deeply dissimilar

01:06:41.041 --> 01:06:45.071
about the multiverse
part three, Jeremy, in your

01:06:45.083 --> 01:06:49.040
wonderful book and
multiverse part two, because

01:06:49.115 --> 01:06:52.934
after all, the
inflationary multiverse is,

01:06:52.946 --> 01:06:56.960
we've been there
before. It's like distance,

01:06:56.961 --> 01:07:00.792
but okay, some exponentiate
a distance to some

01:07:00.804 --> 01:07:05.499
sort of a limit, which is
deeply distinctive and different.

01:07:05.500 --> 01:07:07.334
But it is something
we've met before.

01:07:07.346 --> 01:07:09.440
We met the
enlargement of the size of

01:07:09.441 --> 01:07:12.319
the universe going from
planet to solar system to

01:07:12.331 --> 01:07:15.850
galaxy to multiverse, multi-galaxies
and so on and so forth.

01:07:15.851 --> 01:07:18.086
Is not the inflationary
multiverse just

01:07:18.098 --> 01:07:20.800
yet another similar step?
And I think one could

01:07:20.801 --> 01:07:22.869
make that claim.
And I don't think that's

01:07:22.881 --> 01:07:24.960
true of the Everettian
multiverse at all.

01:07:26.400 --> 01:07:28.617
But anyway, sorry, I was
just so intrigued by these

01:07:28.629 --> 01:07:30.640
questions and answers,
I had to say something.

01:07:31.600 --> 01:07:35.547
But I do have a question
for Jeremy, quite apart

01:07:35.559 --> 01:07:39.600
from the 30 odd queries
I raised about part three

01:07:39.601 --> 01:07:43.068
of your book, which
you never got back to me

01:07:43.080 --> 01:07:46.480
about, nevermind.
Perhaps over dinner later

01:07:46.560 --> 01:07:50.591
tonight, we'll get round
to the. So, indeed, we

01:07:50.603 --> 01:07:54.560
disagree on your
verdicts. But I'm very struck

01:07:54.635 --> 01:07:58.066
by your stress on the,
that we are steeped in

01:07:58.078 --> 01:08:01.520
metaphysics in modality
in particular, sorry,

01:08:01.670 --> 01:08:04.129
I shouldn't have said
metaphysics, that we are

01:08:04.141 --> 01:08:06.720
steeped in modality in
science. And you repeated

01:08:06.721 --> 01:08:10.415
it two or three times
this last hour or so.

01:08:10.427 --> 01:08:14.720
But I have a question now,
are mathematicians also

01:08:15.780 --> 01:08:19.559
steeped in modality?
And I mean, it's a bit of

01:08:19.571 --> 01:08:23.280
a trick question,
because if you agree to it,

01:08:23.281 --> 01:08:25.457
then there's a big problem.
And if you disagree,

01:08:25.469 --> 01:08:27.520
there's a big problem.
So if you agree to it,

01:08:27.521 --> 01:08:30.873
then the big problem is,
I mean, coming back to

01:08:30.885 --> 01:08:34.320
something that Michael
Stoltz has now said, that

01:08:34.420 --> 01:08:36.558
it's not as though
mathematicians have been

01:08:36.570 --> 01:08:39.281
agonising about modality
for the last 50 or 100 years.

01:08:39.282 --> 01:08:43.120
So if they are steeped in it, they
don't seem to be bothered about it,

01:08:43.121 --> 01:08:45.527
or not remotely in the
way that scientists, well,

01:08:45.539 --> 01:08:47.760
you could say the same
of scientists as well,

01:08:47.761 --> 01:08:49.411
that they haven't
been bothered about it.

01:08:49.423 --> 01:08:51.440
But I think the point of
view of the philosophy of

01:08:51.441 --> 01:08:53.576
physics is, they jolly
well ought to acknowledge

01:08:53.588 --> 01:08:56.107
it, or that's, I think, the
point that you're making.

01:08:56.442 --> 01:08:59.878
So if you agree that
mathematicians are

01:08:59.890 --> 01:09:04.741
also steeped in modality,
then it raises a lot of questions.

01:09:04.742 --> 01:09:06.688
On the other hand,
if they are not,

01:09:06.700 --> 01:09:09.520
then when does the
thinking of the mathematical

01:09:09.521 --> 01:09:13.383
physicist free of modality
go over to the thinking

01:09:13.395 --> 01:09:16.960
of the physicist proper,
or the philosopher of

01:09:17.490 --> 01:09:21.019
physics where there
is now modality?

01:09:21.031 --> 01:09:25.440
So perhaps it's a third
way, but over to you.

01:09:30.210 --> 01:09:33.781
Yeah. Yes. I mean,
I'm going to just report

01:09:33.793 --> 01:09:36.960
briefly what I believe.
And of course,

01:09:36.961 --> 01:09:40.864
there's a massive
discussion. And one has to

01:09:40.876 --> 01:09:44.880
admit that, so to speak,
age 18 to 28 is when

01:09:44.881 --> 01:09:47.650
you form your philosophical
views, and then yuck,

01:09:47.662 --> 01:09:49.913
you may find yourself
not changing much.

01:09:50.038 --> 01:09:53.587
And it is true that between
the ages of 18 and 28, I

01:09:53.599 --> 01:09:57.120
came to believe and still
do that pure mathematics,

01:09:57.121 --> 01:10:00.628
in the sense used in
after the pure applied

01:10:00.640 --> 01:10:04.240
division got going in
the late 19th century,

01:10:05.065 --> 01:10:10.720
is analytic and necessary,
and has a special subject matter,

01:10:13.280 --> 01:10:17.103
not in space and time,
since I believe it true.

01:10:17.115 --> 01:10:20.320
But I am not assured
that the world has

01:10:21.070 --> 01:10:24.922
got infinitely many
objects in it. So this is all,

01:10:24.934 --> 01:10:28.720
you know, sophomore
philosophy of math by reading

01:10:28.800 --> 01:10:33.555
Frege, and so on. But it is
actually what I still believe.

01:10:33.567 --> 01:10:36.800
Upshot, the answer
to your question is,

01:10:36.900 --> 01:10:38.892
I think they're not
steeped in modality.

01:10:38.904 --> 01:10:41.200
So the challenge will
hang on. So what happens

01:10:41.201 --> 01:10:44.589
when a mathematical
physicist applies their

01:10:44.601 --> 01:10:48.000
work to the empirical
world? And I mean, my

01:10:48.400 --> 01:10:52.210
short answer will be
the notion of physical

01:10:52.222 --> 01:10:56.400
dimension, mass, length,
time, electric charge,

01:10:57.140 --> 01:11:01.020
are not in the topic
of pure mathematics.

01:11:01.032 --> 01:11:04.640
And it is the physical
dimensions that

01:11:05.280 --> 01:11:10.160
render the propositions about a
topic that lies in space and time.

01:11:12.535 --> 01:11:15.225
Now, I did, I mentioned
the traditional mass,

01:11:15.237 --> 01:11:18.000
length, and time, but
it doesn't really depend

01:11:18.001 --> 01:11:21.123
upon mentioning length
and time in order to make

01:11:21.135 --> 01:11:24.400
a link to the empirical
world. It seems to me that

01:11:24.550 --> 01:11:28.223
in a world with no space
and time, but in which

01:11:28.235 --> 01:11:31.651
the gospel of Hume
is still regnant, right?

01:11:31.652 --> 01:11:34.549
And there's contingency
and there's inquirers and

01:11:34.561 --> 01:11:37.200
there's guessing what
the laws of nature are.

01:11:37.201 --> 01:11:40.869
So I would still want
to say there might be

01:11:40.881 --> 01:11:44.560
a wizard, a late 19th
century mathematician

01:11:44.561 --> 01:11:48.720
in such a world who makes the
pure versus applied distinction,

01:11:48.721 --> 01:11:52.800
zooms off and does their
abstract group theory or whatnot.

01:11:54.600 --> 01:11:56.341
And it's still true
that a mathematical

01:11:56.353 --> 01:11:58.240
physicist in that world
would in some way,

01:11:59.700 --> 01:12:02.560
when they do, when they talk
to their empirical colleagues

01:12:04.210 --> 01:12:06.585
about the nature of
the world in which they

01:12:06.597 --> 01:12:09.040
are embodied, they'd
be going to be invoking

01:12:09.041 --> 01:12:14.000
some dimension, which wasn't
a topic of their pure maths book.

01:12:16.400 --> 01:12:18.387
Well, thank you,
Jeremy. I'd love to press

01:12:18.399 --> 01:12:20.160
you and guess
what? I will press you,

01:12:20.161 --> 01:12:23.040
but I will, there are other hands up.
So till later.

01:12:23.690 --> 01:12:28.080
Fantastic.
Thank you, Simon, for that. Colin?

01:12:30.830 --> 01:12:33.840
Great. Thanks for the talk,
Jeremy, and for the organizers.

01:12:33.841 --> 01:12:35.440
Thank you.

01:12:35.615 --> 01:12:40.082
My name is Colin Hamlin. I'm
also from Calgary, incidentally.

01:12:40.094 --> 01:12:42.480
I'm actually
starting a PhD with

01:12:42.481 --> 01:12:45.957
your coauthor, Sebastian
De Hero at the ILC.

01:12:45.969 --> 01:12:50.160
On the topic of the
mathematical universe hypothesis,

01:12:50.161 --> 01:12:53.955
one of the multiverse
theories you consider.

01:12:53.967 --> 01:12:57.600
I know you touch on
it in the book and you

01:12:57.601 --> 01:13:02.240
have a 2014 article about it, which
I found very helpful for my research.

01:13:02.820 --> 01:13:06.668
In that review, you
call yourself, I think,

01:13:06.680 --> 01:13:10.720
a reluctant Platonist
about pure mathematics,

01:13:10.721 --> 01:13:14.230
such that you would
be committed to a vast

01:13:14.242 --> 01:13:17.680
ontology of pure
mathematical structures.

01:13:17.681 --> 01:13:22.400
And you kind of pose the question,
and I do appreciate how you do so,

01:13:23.735 --> 01:13:26.960
that what is the relationship
between our physical

01:13:26.972 --> 01:13:30.080
universe and those
structures? And you mark this

01:13:30.081 --> 01:13:32.858
by instantiation versus
identification, which I

01:13:32.870 --> 01:13:34.808
think is a great
way to frame it.

01:13:35.033 --> 01:13:38.639
I think it's also similar to
how Muller frames it in his

01:13:38.651 --> 01:13:41.280
discussions of ontic
structural realism.

01:13:41.281 --> 01:13:46.000
And so given your realism
about these structures,

01:13:48.070 --> 01:13:50.485
the mathematical universe
hypothesis seems a

01:13:50.497 --> 01:13:53.200
little bit harder for you
to resist than it would

01:13:54.000 --> 01:13:57.559
be for an anti-realist
about mathematics.

01:13:57.571 --> 01:14:02.000
If the pure structures are
already in our ontology,

01:14:02.080 --> 01:14:06.328
then it seems very
tempting or even we're

01:14:06.340 --> 01:14:10.080
highly motivated
to put them to use.

01:14:11.520 --> 01:14:15.182
So rather than having
a dual ontology of

01:14:15.194 --> 01:14:18.960
pure structures and
our physical universe

01:14:18.961 --> 01:14:24.640
with its peculiar instantiation
relationship to one of those structures,

01:14:24.641 --> 01:14:27.801
we could instead have
a unified fundamental

01:14:27.813 --> 01:14:31.280
ontology of pure
mathematical structures alone.

01:14:31.281 --> 01:14:34.156
So I'm wondering
what you think of this,

01:14:34.168 --> 01:14:37.200
independent of the
other objections to the

01:14:37.760 --> 01:14:40.708
mathematical
universe hypothesis.

01:14:40.720 --> 01:14:45.760
Do you think that a commitment
to Platonism puts pressure

01:14:45.761 --> 01:14:49.760
to slide into Pythagoreanism?
Thank you.

01:14:50.965 --> 01:14:54.197
Right. The short
answer is yes, it does.

01:14:54.209 --> 01:14:57.950
And so you're right,
I'm a reluctant Platonist.

01:14:58.510 --> 01:15:03.139
I think it's a phrase from
Quine because, again,

01:15:03.151 --> 01:15:07.200
channeling the Hume,
our concepts and the

01:15:07.450 --> 01:15:11.153
beliefs that we express
or formulate with them

01:15:11.165 --> 01:15:14.800
and what we hope is
knowledge about the world

01:15:14.801 --> 01:15:17.781
is rooted largely in the
stream of experience.

01:15:17.793 --> 01:15:20.720
So that's the empiricism.
And then you worry,

01:15:20.721 --> 01:15:23.909
how on earth do I
know pure mathematics,

01:15:23.921 --> 01:15:27.440
especially when the
teacher is talking to me

01:15:27.760 --> 01:15:31.904
about infinity, which
I don't see in the

01:15:31.916 --> 01:15:35.590
invisible world.
So I am reluctant.

01:15:39.200 --> 01:15:43.183
I look fondly and enviously
back to the time of Euler

01:15:43.195 --> 01:15:46.720
when the pure applied
distinction didn't exist.

01:15:50.490 --> 01:15:54.400
And I, nevertheless,
you have to be honest

01:15:54.412 --> 01:15:58.240
about where we are
now. And it seems that

01:15:59.520 --> 01:16:03.595
this is very gallopingly
covered in the chapter

01:16:03.607 --> 01:16:07.520
two of the book. The
rise of pure mathematics

01:16:08.170 --> 01:16:15.280
just leads to what we consider a body
of knowledge that is detached from

01:16:17.380 --> 01:16:21.277
our knowledge of the
empirical world sufficiently

01:16:21.289 --> 01:16:24.640
to earn these phrases,
you know, abstract,

01:16:24.740 --> 01:16:27.452
not beholden to
the empirical world.

01:16:27.464 --> 01:16:32.455
And once you've got the distinction,
you can't think yourself back.

01:16:32.456 --> 01:16:34.909
But Colin, I'm
glad to think that

01:16:34.921 --> 01:16:38.480
you'll go to the Netherlands
because I'm glad to

01:16:38.560 --> 01:16:42.410
announce to everybody
that Klaas Landsman,

01:16:42.422 --> 01:16:46.560
Mathematical Physics
in Nijmegen, has written

01:16:46.561 --> 01:16:49.985
a book called The
Philosophy of Mathematical

01:16:49.997 --> 01:16:53.120
Physics, in which he
works together with

01:16:58.320 --> 01:17:03.348
Associated Papers to try and
get back to the glory of a unity.

01:17:03.360 --> 01:17:06.320
So while my 2014
and my book summary

01:17:06.321 --> 01:17:09.527
of my view there was
critical of Max Tegmark, and

01:17:09.539 --> 01:17:12.560
this is what I was
summarizing in my answer to

01:17:14.240 --> 01:17:19.074
Simon, so the adjacency of
the questions is very fortunate.

01:17:19.086 --> 01:17:22.240
Nevertheless, yes,
I really sympathize

01:17:23.145 --> 01:17:31.120
with the aim of your project.
Thank you, Josh. Question from Ayaz.

01:17:39.100 --> 01:17:42.623
Hi. Yeah, am I audible?
Yeah. Actually, I have

01:17:42.635 --> 01:17:46.400
not read the book, but I
have one basic question.

01:17:46.401 --> 01:17:49.283
Since in our wave
function, when we design the

01:17:49.295 --> 01:17:52.000
wave function, we have
multiple components,

01:17:52.100 --> 01:17:55.421
and but we always
get a single outcome.

01:17:55.433 --> 01:17:59.840
So does that mean in the
many world interpretations,

01:17:59.841 --> 01:18:03.589
does that mean the rest
of the components are

01:18:03.601 --> 01:18:07.048
just empty waves, or
just empty outcomes?

01:18:07.573 --> 01:18:11.368
And if so, why we need to
introduce many outcomes,

01:18:11.380 --> 01:18:14.800
and then construct the
probability from them,

01:18:14.801 --> 01:18:18.030
when only one, this
actual configuration

01:18:18.042 --> 01:18:21.040
already gives one
distribution to us?

01:18:21.041 --> 01:18:27.280
Thank you. I didn't quite hear the
last words, but the short answer is

01:18:29.940 --> 01:18:33.406
the other outcomes that
you do not see are in no

01:18:33.418 --> 01:18:37.040
sense, the proposal is
by the Everettian that they

01:18:39.840 --> 01:18:43.739
are in no sense empty,
they are equally real

01:18:43.751 --> 01:18:47.840
with the one you see.
And you might say, well,

01:18:47.890 --> 01:18:51.421
why should I believe that?
And part of the answer,

01:18:51.433 --> 01:18:54.480
which is kind of close
to the technicality,

01:18:55.170 --> 01:19:03.120
which you're aware of, is that if
you say there is no physical reality

01:19:04.825 --> 01:19:07.966
associated with the
mathematics that describes

01:19:07.978 --> 01:19:12.290
those outcomes, you can get
the wrong answer in an experiment.

01:19:14.140 --> 01:19:16.953
And the double
slit is, of course,

01:19:16.965 --> 01:19:20.400
the toy example, where
you need to keep the

01:19:24.770 --> 01:19:28.442
interference terms
or as I use that jargon.

01:19:28.454 --> 01:19:32.720
But the Everett vision is
to have an equal reality

01:19:33.120 --> 01:19:36.463
to all the outcomes.
Okay, I got this.

01:19:36.475 --> 01:19:41.120
But if we have the equal
reality to all the outcomes,

01:19:41.121 --> 01:19:44.720
doesn't it disqualify
the bond distribution

01:19:44.732 --> 01:19:47.840
and bond rule of
equal probabilities?

01:19:50.190 --> 01:19:54.400
Does it refute that?
Does it refute the bond rule?

01:19:55.100 --> 01:19:57.678
Yeah. If we can see,
we are in the bond

01:19:57.690 --> 01:20:00.480
rule, the total
probability should be one.

01:20:01.220 --> 01:20:04.941
Yes. 100%. So, why
we are here giving the

01:20:04.953 --> 01:20:08.960
probability of one is
to two for each event,

01:20:08.961 --> 01:20:14.480
for example, if we have two events?
Yes. So, your criticism is that the

01:20:14.960 --> 01:20:18.813
Everettian seems to
require probability two

01:20:18.825 --> 01:20:22.960
for the pair taken
as... Yes, I think this is,

01:20:22.961 --> 01:20:26.130
you're saying in your
terms, the same as Al

01:20:26.142 --> 01:20:29.840
Wilson was stressing,
they call it the qualitative

01:20:30.800 --> 01:20:34.628
problem of probability.
And you've put a kind of

01:20:34.640 --> 01:20:38.800
numerical precision on
that query that Al mentioned.

01:20:39.590 --> 01:20:43.418
You're saying, how
can there be probabilities

01:20:43.430 --> 01:20:47.440
if all outcomes occur?
And you're saying, well,

01:20:47.441 --> 01:20:50.083
in particular, if all
outcomes occur, then

01:20:50.095 --> 01:20:52.560
they must all be
given probability one.

01:20:54.770 --> 01:20:58.486
Well, I won't try to
defend the Everettian,

01:20:58.498 --> 01:21:02.400
but as you can imagine,
they say all is well.

01:21:03.520 --> 01:21:08.092
And I believe actually,
that they're intellectually

01:21:08.104 --> 01:21:11.520
coherent, right, in
this matter. Yeah.

01:21:11.770 --> 01:21:15.600
I'm sorry not to help you more.
Okay. Okay. Thank you.

01:21:16.300 --> 01:21:19.738
Richard, do you mind
if I just quickly jump

01:21:19.750 --> 01:21:23.120
in because I must
give an immediate reply.

01:21:23.920 --> 01:21:26.358
So, one very natural
way of understanding

01:21:26.370 --> 01:21:28.640
what probability
means in this context

01:21:28.641 --> 01:21:33.360
is to write the quantum state in
terms of equi-amplitude branches.

01:21:35.860 --> 01:21:37.916
And then the greater
the proportion of

01:21:37.928 --> 01:21:40.160
equi-amplitude branches
with one outcome,

01:21:40.310 --> 01:21:45.040
the more probable that outcome. So,
there are fairly straightforward ways

01:21:45.165 --> 01:21:48.552
of responding to this
question of what exactly are

01:21:48.564 --> 01:21:51.760
these probabilities. We
add to that, of course,

01:21:51.910 --> 01:21:54.433
the very large
dimension of the decision

01:21:54.445 --> 01:21:57.360
theoretic route, which
shows that furthermore,

01:21:58.010 --> 01:22:00.073
those quantities thus
counted, which is the

01:22:00.085 --> 01:22:02.160
Born rule, gives you
the Born rule counting

01:22:02.161 --> 01:22:05.044
in the appropriate
limit, should, for an

01:22:05.056 --> 01:22:08.240
agent who is cognizant
of them and so forth,

01:22:09.920 --> 01:22:14.046
knows their physics,
dictate their credences.

01:22:14.058 --> 01:22:17.920
So, there's very
systematic answers to the

01:22:17.921 --> 01:22:20.378
question of what is
probability in Everettian

01:22:20.390 --> 01:22:22.640
quantum theory, both
in the physical side

01:22:22.740 --> 01:22:26.480
and its connection with epistemic
and normative considerations.

01:22:26.530 --> 01:22:30.320
Nothing remotely has been achieved
in any other physical theory.

01:22:31.370 --> 01:22:34.640
So, sorry, I did have to protest.
End of protest.

01:22:35.190 --> 01:22:40.080
Okay. Thank you. Okay. I'm going to
take a final question from Richard.

01:22:40.630 --> 01:22:42.613
It's not a
question, actually.

01:22:42.625 --> 01:22:46.160
It's just a very brief remark
because Simon and Hasser

01:22:47.670 --> 01:22:50.743
very rightly pointed out
the enormous differences

01:22:50.755 --> 01:22:53.840
between the Everettian
multiverse on the one hand

01:22:53.920 --> 01:22:57.741
and the cosmological
one. One might just point

01:22:57.753 --> 01:23:01.920
out, though, that there
are those very speculative

01:23:02.160 --> 01:23:05.966
thoughts by Susskind
and John Carroll that

01:23:05.978 --> 01:23:10.160
nevertheless, those
may just be very different

01:23:12.530 --> 01:23:16.377
perspectives on the
same thing. So, there are,

01:23:16.389 --> 01:23:20.080
it might still make
sense to think about it,

01:23:20.230 --> 01:23:23.175
let's say, along
comparable lines because

01:23:23.187 --> 01:23:26.000
it's not entirely
clear yet, let's say,

01:23:26.001 --> 01:23:28.843
both sides probably,
in particular the

01:23:28.855 --> 01:23:32.160
cosmological side
maybe, is not sufficiently

01:23:33.060 --> 01:23:36.900
well understood to have a
very stable understanding

01:23:36.912 --> 01:23:40.160
of the distance between
the two, let's say.

01:23:40.161 --> 01:23:44.960
Thank you.

01:23:44.961 --> 01:23:49.920
Having said no more questions, now Al
has put his hand up. So, I feel like,

01:23:50.870 --> 01:23:52.854
seeing as Rik has just
made a comment, I'm

01:23:52.866 --> 01:23:54.720
going to let Al make
a comment as well.

01:23:55.170 --> 01:23:57.644
If that's okay. I
mean, it's because I'm

01:23:57.656 --> 01:24:00.640
tempted to say something
on the very same point.

01:24:01.920 --> 01:24:04.805
And actually, it links
to a very memorable

01:24:04.817 --> 01:24:07.920
conversation with Rikard
in Exeter some years

01:24:07.921 --> 01:24:11.428
ago where I was
pressing him on the relation

01:24:11.440 --> 01:24:14.880
between these
multiverses. And I think even

01:24:14.881 --> 01:24:17.139
if we become convinced
that there is good reason

01:24:17.151 --> 01:24:19.280
to believe in any
individual multiverse, that

01:24:19.281 --> 01:24:21.922
shouldn't make us lose
sight of the fact that that

01:24:21.934 --> 01:24:25.165
was a somewhat surprising
thing to have ended up concluding.

01:24:25.315 --> 01:24:27.846
None of us started
out our intellectual

01:24:27.858 --> 01:24:31.634
career expecting to be
convinced of a multiverse, probably.

01:24:32.374 --> 01:24:34.728
And so, that
means, and I take

01:24:34.740 --> 01:24:38.160
that, some people take
kind of the precedent,

01:24:38.161 --> 01:24:41.474
if one, then why not
many? And I would rather go

01:24:41.486 --> 01:24:44.880
the other way, that if
one, that's already a lot.

01:24:44.980 --> 01:24:48.433
And it would be particularly
surprising, I think,

01:24:48.445 --> 01:24:51.840
if there should be somehow
enough multiverses to

01:24:51.841 --> 01:24:54.798
explain fine tuning
multiple times over.

01:24:54.810 --> 01:24:58.720
So, I think, you know,
explaining fine tuning once is

01:24:59.600 --> 01:25:03.804
impressive enough.
Explaining it twice is suspicious.

01:25:03.816 --> 01:25:06.320
And so, I'm
tempted towards the

01:25:06.321 --> 01:25:08.909
view that the Everett
and the cosmological

01:25:08.921 --> 01:25:11.520
multiverse have to be
combined in some way

01:25:12.130 --> 01:25:16.010
if they're to both be
sustained. There's got to

01:25:16.022 --> 01:25:20.080
be kind of one unified
account that explains fine

01:25:20.081 --> 01:25:22.442
tuning there and perhaps
gives us both sorts

01:25:22.454 --> 01:25:24.720
of multiplicities, but
it would have to be

01:25:24.920 --> 01:25:28.044
kind of rolled into a
single unified multiverse.

01:25:28.056 --> 01:25:30.800
That's just a hunch,
but it speaks to what

01:25:31.125 --> 01:25:33.605
Ricardo was saying and also
to what Julius was asking earlier.

01:25:35.750 --> 01:25:37.479
Jeremy, I'm going to
let you have the final

01:25:37.491 --> 01:25:39.110
word, if you would
like the final words.

01:25:40.000 --> 01:25:43.945
Helen, thank you very
much. My final words are

01:25:43.957 --> 01:25:48.000
to say a hearty thanks
to everybody for coming,

01:25:48.100 --> 01:25:51.516
and especially to BSPS
Open and yourselves

01:25:51.528 --> 01:25:55.200
and University of Calgary
and Ricardo now for

01:25:55.860 --> 01:25:58.623
so kindly spending
so much time.

01:25:58.635 --> 01:26:03.360
But the substantive answer
on the various controversies

01:26:03.361 --> 01:26:07.440
is to say, sorry, folks, it was
only meant to be an introduction.

01:26:12.400 --> 01:26:16.173
Good point. Well made.
Just to echo Jeremy's

01:26:16.185 --> 01:26:20.883
thanks to Al and Ricardo
and David for organising this.

01:26:20.884 --> 01:26:23.830
But especially thank
you to Jeremy for

01:26:23.842 --> 01:26:27.440
writing the book and
all your splendid answers

01:26:27.441 --> 01:26:29.686
to the questions. But also
all the questions were great.

01:26:29.698 --> 01:26:31.361
Thank you so much,
everyone, for chipping

01:26:31.795 --> 01:26:35.127
in. They really were. Yeah.
So, thank you very much.

01:26:35.139 --> 01:26:37.232
That's it. Enjoy the
book. Thank you.

01:26:37.233 --> 01:26:44.080
Thank you, David.
Thank you, everybody.