
Why we think there's a Multiverse, not just our Universe - petercooper
http://scienceblogs.com/startswithabang/2011/10/why_we_think_theres_a_multiver.php
======
Confusion
As the only criticism on this article has been downvoted strongly, I feel
compelled to repeat my explanation of that criticism (that believing in the
multiverse is like believing in heaven or hell) at a higher level, in the
hopes that people will be somewhat more critical of what esteemed scientists
are peddling as truth:

There is not a shred of experimental evidence for the multiverse. In fact,
experimental evidence is not even possible. That places it firmly in the
pantheon of metaphysics.

That there is a multiverse could be an unescapable conclusion from an
otherwise very successful theory, with many experimental verifications, but
that isn't the case. The article neglects to mention that there are many
alternative interpretations and theories that can equally well explain 'how it
all started' and still result in inflation and all associated 'best' theories
for the experimental observations of the universe. This article is all
unwarranted extrapolation (back to the beginning of time and before).

The main pillar of the success of the multiverse theory is that it
successfully appeals to the imagination. The main reason that it is being
promoted is because the great physicists promoting the idea do not realize
they are not as great philosophers as they are physicists.

~~~
gizmo
Assertions that take the form "X is like religion" are not enlightening. When
it is prefaced with "get the facts straight" then _of course_ it's going to
get downvoted. There is nothing being "peddled" here, there is no hidden
agenda by "esteemed scientists".

We have experimentally demonstrated that the universe is a really, really
weird place. Time and space can bend. Whoah. But hey, we proved that beyond a
shadow of a doubt. Then there's quantum mechanics. Wave functions!
Entanglement! Turns out the universe really works that way. Then the universe
starts looking really non-deterministic. Then we figured out that the simplest
interpretation of QM implies Many Worlds, that the universe splits and splits
and splits into a bazillion near-copies. The quantum events just _look_ non-
deterministic from our perspective. Do we know everything? Hell no. But we
know that QM is true and that it uses some form of Many Worlds. We know that
the world is deterministic. We don't know for sure how the universe came into
being (but we are sure the universe is expanding). We don't know if there
really is such a thing as the multiverse, but as we figure out more about the
big bang, about background radiation, about black holes and dark matter and
the shape of our universe there's a good chance we'll figure it all out
eventually.

Physics is treading on the domain of philosophy because we're getting better
at physics. Philosophers debated since the dawn of time about free will and
didn't get anywhere. Now we know that non-reductionist or dualistic world
views make little sense. Philosophers debated for ages about morality. Now
neuroscience is starting to deliver concrete answers. Philosophers debated for
ages about religion and heaven/hell. And elementary Bayesian math shows the
questions are just nonsensical.

Philosophy is about reasoning about topics we don't really understand. As our
understanding of physics, math, neuroscience and biology grows philosophy has
to make way.

~~~
Confusion

      Then we figured out that the simplest interpretation of QM
      implies Many Worlds
    

Many physicists contend this point. They do not consider this interpretation
as 'the simplest'. Things hinge on such contentious points as the physical
reality of 'the collapse of the wavefunction'. Again, the major thing the Many
World interpretation has going for it is that it easily appeals to our
imagination -- even, or especially, to the imagination of non-physicists.

    
    
      We know that the world is deterministic.
    

Philosophers disagree. It's even the question whether this issue can possibly
be settled by any experimental evidence, because of the way we, and our math,
are wired to consider everything in causal chains. The evidence isn't really
very compelling if you consider the fundamental problems surrounding the
question.

    
    
      Now we know that non-reductionist or dualistic world views
      make little sense
    

Descartes has been critiqued extensively long before science could say
anything about mind-matter interactions, because the main shortcomings of the
duality argument do not depend on any experimental facts at all.

    
    
      Now neuroscience is starting to deliver concrete answers.
    

On the subject of morality, neuroscience cannot possibly deliver any concrete
answers at all. You're engaging in the naturalistic fallacy if you think it
does. What is the case in the world is not argument for what should be the
case in the world. Neuroscience may explain why people hold certain ethical
views. It can _never_ explain what ethical view they should hold. What view is
'acceptable', 'the best', 'right'. The answer to that question cannot be
reduced to physical facts about the universe.

    
    
      Philosophy is about reasoning about topics we don't really
      understand.
    

Then we don't really understand logic and math either, do we? The foundations
of logic and math are still part of philosophy after all.

And, well, Hume didn't really understand causality, did he? But fortunately,
thanks to modern physics, now we do?

~~~
gizmo
> Many physicists contend this point [ ... ] appeal to imagination.

Not so. The vast majority of quantum physicists now agree Many Worlds has won,
including Feynman, Gell-Mann and Hawking. The concept of 'collapse of the
wavefunction' is silly and shouldn't even be considered for reasons outlined
here: <http://lesswrong.com/lw/q8/many_worlds_one_best_guess/>

> Determinism; Philosophers disagree.

It's just basic reductionism. There are absolutely no fundamental problems
surrounding this.

> On the subject of morality, neuroscience cannot possibly deliver any
> concrete answers at all.

All moral thought and all moral beliefs up to now have happened inside the
human brain. Most moral thought is confused and self-contradictory. If we want
to figure out why we are moral the way we are, what our "true" moral beliefs
are, and how to build societies that flourish, we have to look inside the
brain to see how it all works. Either morality has bearing on the real world
and is therefore subject to measurement or it has no bearing on the real world
and is therefore irrelevant.

> Then we don't really understand logic and math either, do we? The
> foundations of logic and math are still part of philosophy after all.

Where the line is drawn between math/philosophy isn't a very interesting
question.

> And, well, Hume didn't really understand causality, did he? But fortunately,
> thanks to modern physics, now we do?

Nope. And yep. And thanks to Bayesian reasoning.

~~~
Confusion
Concerning Many Worlds:

Firstly, [1] disagrees with you. Secondly, there is a difference between
accepting MWI above other interpretations and actually believing in multiple
parallel universes. A difference between accepting the physical and the
metaphysical consequences. Thirdly and crucially, MWI depends on QM. Everyone
acknowledges QM is probably not a definite description of the universe and
non-locality, non-contextuality or another kind of modification would wreak
havoc on MWI. If physicists subscribe to MWI but also acknowledge QM seems
incomplete, they are being inconsistent.

Concerning determinism:

You say "it's just basic reductionism". But in fact it _presupposes_
reductionism as a viable strategy to determine 'the truth' about determinism.
It isn't [2]. Specifically, the question whether we can even determine whether
our fundamental theories are deterministic is still wide open. None of the
theories, from classical mechanics to quantum mechanics, is clearly
deterministic and it remains a question whether it can even be determined
whether they are deterministic.

Concerning morality:

No matter how well you can 'measure' my 'true' ethical views on abortion: no
measurement will ever tell you what my ethical view on abortion should be. No
collection of measurements will ever tell you what a governments policy on
abortion should be. At most you can hope to be able to say: in this particular
case we should allow it, because that will be best for everyone: the average
happiness, productivity and insert-factor-of-importance will be highest if we
allow it. However, that kind of judgment presupposes a certain moral system.
You can never determine which factors should be important. At most you can
measure which factors people rate as most important on average. But again, you
presuppose a certain moral system if you _choose_ to use that measurement to
determine what to do. If you feel otherwise, there's a large philosophical nut
left for you to crack.

I think you underestimate the complexity of these subjects and that your
verdicts are premature.

[1] [http://en.wikipedia.org/wiki/Many-
worlds_interpretation#Rece...](http://en.wikipedia.org/wiki/Many-
worlds_interpretation#Reception)

[2] <http://plato.stanford.edu/entries/determinism-causal/>

~~~
Umofomia
BTW, you guys keep talking about MWI, while the original article is
categorically not about MWI. The author describes a Tegmark Level I
Multiverse[1], the most conservative of the multiverse models. MWI is Level
III, and the author himself says in a subsequent comment[2]:

    
    
      What I've presented, above, is the argument for the first
      type of Multiverse, which I think is correct, and hence,
      which I believe in.
      
      I think that anything beyond that is too speculative to be
      believed at this point, at least with any sort of
      confidence. At least, by me.
    

[1]
[http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_...](http://en.wikipedia.org/wiki/Multiverse#Level_I:_Beyond_our_cosmological_horizon)

[2]
[http://scienceblogs.com/startswithabang/2011/10/why_we_think...](http://scienceblogs.com/startswithabang/2011/10/why_we_think_theres_a_multiver.php#comment-5674646)

------
sendos
Isn't this like having a function that explains very well data that is within
an observable range, and then stating with confidence that that function also
applies to data in a range that is unobservable to you?

Yes, that function may hold outside your observable space, but it may not. We
can't simply state as fact the predictions that come from assuming that this
function applies outside our observable space.

~~~
redwood
Spot on, and even much of what is 'observable' here is not even close to
understood. Inflation and dark energy/matter are both concepts that have been
built to explain observation but which are themselves not yet explained at
least not with much consensus.

------
lionhearted
Potentially a stupid question -

How can the universe get "colder"? Does it just mean that the average energy-
per-square-meter (or whatever unit) is less? If so, wouldn't that mean that
saying "less dense" and "colder" mean basically the same thing at that scale?

Maybe I'm asking something stupid and obvious, but I keep thinking that energy
can't be destroyed, ergo, there's exactly as much energy (and thus heat?) as
before. Or is heat energy density? But doesn't that make "less dense and
colder" a redundant statement, since they'd be the same thing?

~~~
count
Less dense implies colder, as the volume is not constant, but expanding.
Temperature and density are different things though - one is how much energy
something has, the other is how far away from other things it is. Related, but
different.

With respect to destroying energy - energy converted into matter is 'colder'.
There's not the exact same amount of energy - it's not that it can't be
destroyed, it must be conserved with matter (E=MC^2). Great example - kinetic
energy is used in a particle accelerator to create new particles, and it takes
a ton of energy to make even a tiny bit of mass, so the average temperature
would go down as more mass is created (heat being the transfer of energy -
once it's trapped in a particle, it's not transferred as freely).

(Caveat - I'm not a cosmologist...)

~~~
30thElement
How does converting energy into mass make it "colder"? If you have 1 protons
worth of energy in a volume, and you have 1 nonmoving proton in another area
with the same volume, isn't there the same amount of energy in both regions?
Or is it "colder" because you can't have a region with energy and nothing
else, it must be something like kinetic energy, which gives heat?

~~~
sp332
Temperature is the average energy of the particles in a space. So if the
proton isn't moving, it is at absolute 0 temperature even though it has some
mass-energy left.

------
acak
A great TED talk on the design of the Universe, if any one is wondering about
the glass shaped picture (the 5th image) in the essay:

[http://www.ted.com/talks/george_smoot_on_the_design_of_the_u...](http://www.ted.com/talks/george_smoot_on_the_design_of_the_universe.html)

------
TheBurningOr
Fascinating article, but I'd still like to know more about that 8th figure on
the inflation model. We are told that the y-axis represents energy, but what
is the x-axis? It clearly isn't time because it's being measured in phi over
something measured in GeV.

~~~
fl3tch
The attribution to Ned Wright takes you here:

<http://ned.ipac.caltech.edu/level5/Narlikar/Narlikar3_2.html>

which has a lot more information. Phi is defined as the Higgs scalar field.

------
anakanemison
This kind of science has always been hard for me to integrate. Thinking as a
Bayesian, these arguments seem to be meant to influence my "prior" over
possible initial states or natures of the universe. I'm not accustomed to
that.

I'm used to science presenting me with evidence meant to influence my
"posterior". I can handle that.

~~~
xenophanes
Are you aware that's irrational? Your assumptions about priors contain plenty
of mistakes (all ideas do, mine too) and you should find a way of thinking
which better allows for correcting those mistakes.

~~~
anakanemison
I think it's more unfortunate than irrational. I'd like to think I'm open to
changing them--my priors started out (a couple of decades ago) pretty
terrible. The process of how to do it well in response to arguments without
experimental results is the challenging part.

~~~
xenophanes
Bayesianism is in the empiricist tradition where it's focussed on how to
update ideas in response to evidence, but it doesn't actually provide guidance
for how to deal with non-empirical ideas that can't be judged by evidence.

This (empiricism) has driven philosophers to things like positivism (where
they declare everything non-empirical to be worthless or even meaningless).
It's a problematic tradition.

The problems are made worse because it turns out that the large majority of
ideas are assessed in a non-empirical way (not due to people being idiots;
this is correct). Using evidence is the less common case (though it is quite
important when relevant).

In _The Fabric of Reality_ by David Deutsch, he gives an example of the theory
that eating a kilogram of grass will cure the common cold. This, he points
out, _should not be empirically tested_ , and will not be. Rather it is
rejected without evidence because it is a bad explanation. Only good
explanations are worth testing. (This does not make us miss out on any truths.
If it really was true, someone could figure out some explanation of how it
works, and then we'd test it.)

In his recent book, _The Beginning of Infinity_, Deutsch further explains that
there's no point in testing any theory for which its details can easily be
changed around in an ad hoc way, because you can never refute such things with
evidence since they will just revise themselves endlessly. The only thing that
can refute that sort of approach is philosophical criticism. Only ideas which
survive some philosophical criticism and are therefore of higher quality are
worthwhile to empirically test.

What makes it hard to change a theory around, ad hoc, to avoid refutation, is
if there is some actual connection between the content of the theory and the
problem it's trying to solve, so most changes to it would make it no longer
address the problem as well.

Deutsch calls that quality "hard to vary" and says it is what makes
explanations good. His books expand on this, and offer a version of Popperian
epistemology with (relatively small) improvements.

Popperian epistemology, focussed on criticism not justification (which is
impossible), and which applies to all types of knowledge without difficulty
rather than being narrowly focussed on empiricism, is the solution.

One of the Popperian ideas is that because we are fallible and make lots of
mistakes, and need to improve on them (by criticism), irrationality has to do
with anything that hampers this process of correcting errors. So that's why I
regard difficulty error-correcting priors as irrational. Deutsch even proposes
that hampering the correction of mistakes is the most important criterion of
_immorality_.

~~~
anakanemison
Your response is really exciting! I'm grateful--it's pointing at exactly what
I was hoping to find. Deutsch seems to be talking about how to evaluate
challenging arguments that come before evidence.

To contribute something, other than my thanks, here's a link to Deutsch
talking about knowledge, evidence, and incredible cosmic relationships:

[http://www.ted.com/talks/david_deutsch_on_our_place_in_the_c...](http://www.ted.com/talks/david_deutsch_on_our_place_in_the_cosmos.html)

~~~
xenophanes
If you'd like to contribute more, you could contribute any thoughts you have
while looking into it at the discussion group:

<http://groups.google.com/group/beginning-of-infinity/>

Thanks for the positive response! Good luck.

------
knodi
Sometimes I think I was born too soon. To think the new knowledge we well
discover with in the next 100, 200, 1000 years is really exciting.

I wouldn't be surprised if in the next 20-50 years with all the genetic
engineer going on one could live for ever. Of cause as long as you can afford
it.

~~~
powertower
I envision a world where, due to technology and science, everyone stops aging
after 25.

A clock will be constantly visible on your forearm and time will be the only
commodity in the world, in which you'll get paid and make payments in.

After the age of 25, you'll get 1 to 75 years of "time" deposited in your
account. The clock on your arm will decrement by default as time passes, and
increase/decrease as you earn/spend.

When your time expires (the clock reaches zero), you die.

Most people will live day-to-day, only having 24 hours of time in any given
moment. Others will have millions of years on their clocks.

~~~
trafficlight
This plot doesn't make any sense.

~~~
powertower
Time is the ultimate currency.

Gold is only backed by the agreement of its scarcity; otherwise, it has no
value (outside its physical usefulness as a material).

Fiat currency is only backed by the confidence of a nation; otherwise, it has
no value.

Time is a currency that's backed by your life.

It is as real as it gets.

~~~
borism
Why would time be of any value if nobody is ageing after 25?

~~~
lftl
I'm trying to fill in the gaps in the author's thinking, but I imagine it
something along the lines that keeping you "aged" 25 requires resources. So
time is sort of a proxy currency for the resources required to keep you alive.
If you run out of time you don't have anything to purchase the resources to
keep you living.

------
rms
I cannot recommend the writings of Max Tegmark on the multiverse enough. Among
people doing science at the heights of their fields, he is perhaps a uniquely
talented popular writer. He even keeps it readable on his scientific papers,
which read mostly just like his popular papers except shorter and with more
math.

<http://arxiv.org/PS_cache/arxiv/pdf/0905/0905.1283v1.pdf> is his overview of
the levels of multiverses.

If that properly blows your mind, see Bostrom's Infinite Ethics.
<http://www.nickbostrom.com/ethics/infinite.pdf>

------
xenophanes
If you're interested in MWI you should read David Deutsch's books:

<http://beginningofinfinity.com/>

~~~
gjm11
I agree -- if you're interested in MWI then you should read Deutsch (in fact,
you should read Deutsch anyway) -- but the OP isn't about MWI, it's about a
different sort of multiverse, with lots of "pocket universes" even on a single
Everett branch because of inflation. Many of the implications are pretty
similar, though.

~~~
xenophanes
I did read the original link but honestly don't really understand. Seemed to
be some kind of argument there has to be a multiverse to account for the
expansion of the universe. That seems like a weak argument to me because in my
understanding we're not that sure about what's happening to the universe and
cosmologists keep changing their minds. Regardless, I didn't quite follow what
sort of multiverse they said it implied and how it differs from MWI.

Going by your comment, I'm not sure there's as much difference as you may be
suggesting. Deutsch's MWI is full of what we might (or might not) call "pocket
universes", it's not focussed on just big universe sized branches.

I saw the article talking about the wave function spreading out which I think
is the same concept Deutsch talks about in BoI with fungible instances of
particles spreading out (a multiversal object is a collection of instances).

------
trocker
hah, its like a variable in a function making theories about what the whole
program is all about, and that there might be many other functions similar to
it. :D

take a look at this one too - <http://en.wikipedia.org/wiki/Many-
worlds_interpretation>

~~~
powertower
I've always been put off by the many-worlds interpretation.

They take something that's perfectly explainable with a probability wave, and
turn it into fantasy.

<http://en.wikipedia.org/wiki/Wave_packet>

------
jaequery
Let's get the facts straight. Believing in a multiverse is no different than
believing in heaven/hell.

~~~
borism
* _for a similar enough definition of heaven, hell and multiverse._

Have you read the article?

~~~
Confusion
He may very well have. There is not a shred of experimental evidence for the
multiverse. In fact, experimental evidence is not even possible. That places
it firmly in the pantheon of metaphysics.

Now it could be an unescapable conclusion from an otherwise very successful
theory with many experimental verifications, but unfortunately the article
neglects to mention that there are many alternative interpretations and
theories that can equally well explain 'how it all started' and still result
in inflation and all associated theories.

That the multiverse theory successfully appeals to the imagination is the main
pillar of its succes.

It's a shame he is being downvoted for succinctly stating a plain truth.

