
Complications in Physics Lend Support to Multiverse Hypothesis - ghosh
https://www.quantamagazine.org/20130524-is-nature-unnatural/
======
Steuard
I used to believe that the history of physics gave unwavering evidence that
there is always a deep reason for the patterns and phenomena we observe: maybe
not for the specifics of everyday life, but certainly for _fundamental_ facts.
(Think of how atomic theory made sense of the elements, or how nuclear physics
explained how the sun could shine for so long, or how the unification of
electricity and magnetism miraculously turned out to explain optics as well.)
So I was convinced that we would someday find a fundamental theory that would
be able to _predict_ things like the fine structure constant or the charge to
mass ratio of the electron.

But eventually someone pointed out that before we understood the history and
nature of the solar system, natural philosophers looked for similarly deep
explanations for the orbits of the planets. Kepler once proposed a deep
connection between the (five) gaps between the six known planets and the five
platonic solids (see, e.g.
[http://www.pbs.org/wgbh/nova/blogs/physics/2011/12/beautiful...](http://www.pbs.org/wgbh/nova/blogs/physics/2011/12/beautiful-
losers-keplers-harmonic-spheres/)), and Bode's law for planetary orbits was
widely accepted until Neptune was discovered in the "wrong" place in 1846 (see
[http://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law](http://en.wikipedia.org/wiki/Titius%E2%80%93Bode_law)).

Today, we understand that there is no reason to expect any particular pattern
of planetary orbits: solar systems are a dime a dozen in the galaxy, and their
details are accidents of history. So while I don't like the idea, I've
gradually come to accept that the "fundamental physical constants" of our
universe could conceivably turn out to be just as arbitrary as the ratio of
Jupiter's major orbital axis to Saturn's.

~~~
rndn
That’s the idea of an infinite number of onion layers [1]. What I find
intriguing is that if you assume that everything is based on cause and effect,
then (I think) you necessarily run into an infinite regress problem (the cause
of a cause of a cause …) unless you define some "uncaused cause", or the
concept of causation breaks down at some point.

[1]
[https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_...](https://en.wikipedia.org/wiki/Theory_of_everything#Infinite_number_of_onion_layers)

~~~
JadeNB
> What I find intriguing is that if you assume that everything is based on
> cause and effect, then (I think) you necessarily run into an infinite
> regress problem (the cause of a cause of a cause …) unless you define some
> "uncaused cause", or the concept of causation breaks down at some point.

Another possible resolution is a cyclic picture (something like
[https://en.wikipedia.org/wiki/Cyclic_model](https://en.wikipedia.org/wiki/Cyclic_model)),
in which the cause of the cause of the cause of … may be the original event.

~~~
hasenj
Cyclic causality is even more troublesome than infinite regress.

I find myself leaning towards causation breaking down at some point. Just like
our concepts of "position" and "momentum" break down at the quantum level.

~~~
noobermin
You say that causa sui or at least cyclic cause is troublesome without saying
why. I'm curious for your reasoning.

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Animats
The cosmology end of physics is kind of stuck right now. Many-worlds and the
anthropic principle are back again. What they're theorizing about has way too
much stuff that can't be observed or tested experimentally. Some people
question whether this is even science.

 _" Science is prediction, not explanation."_ \- Fred Hoyle.

~~~
jacquesm
It wouldn't surprise me at all if there are very hard limits to what science
can prove when it comes to questions like these. After all some experiments
can't be done from within the box and the box that we're in is made of the
very laws that we're trying to escape from in order to do the experiments.

It's almost the physical equivalent of Gödel's incompleteness theorem.

~~~
yborg
As with Gödel's proofs, proving that it is impossible to come up with an
experimentally verifiable demonstration that the multiverse theory is correct
would be a major achievement. And Gödel didn't end mathematics with his
theorems. It simply moved on, as would physics.

~~~
ccvannorman
Along similar lines, I've wondered if it's possible to prove "any observing
entity (e.g. a human) cannot possibly fully understand the system within which
it is contained" .. any complete knowledge of a system should necessitate a
larger system.

~~~
Xcelerate
I've always wondered this as well.

Consider a finite collection of atoms consisting of a human and an
environment. For simplicity, assume these atoms move classically. The human is
a subsystem, and since the entire system involves deterministically, there is
only a limited number of configurations that the human subsystem can realize
within the environment. If a "human" is what is necessary to comprehend
reality, then there are aspects of the system that cannot be realized by the
subsystem, since there are far more states available to the total system.

Then again, I could just be rambling.

~~~
danbruc
I would argue it depends on the nature of the system. If the system follows
(simple) rules then you can likely compress the description of the system into
something that fits into a (small) subsystem. If the system and its behavior
is a uncompressible mess this will not work out. Up to now, I would say, our
universe with all its relatively simple laws of physics looks pretty
structured and easily compressible.

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kghose
[https://en.wikipedia.org/wiki/Anthropic_principle](https://en.wikipedia.org/wiki/Anthropic_principle)

I can find nothing unnatural about the existence of a single universe with
particular constants that give rise to life that then studies the universe.
There is nothing in this that leads inevitably to the conclusion someone has
been rolling the dice many times until this came about.

~~~
tim333
It sounds like you're thinking of the "strong anthropic principle" where the
constants have to be set so as to produce life at some point in the future. It
leaves the question as to how that worked unless you cite devine intervention.
I find the multiverse idea easier to believe.

~~~
vorg
Most large religions today require not a weak or strong anthropic principle,
but a "doubly strong" one, so that not only the initial constants of the
Universe and the subsequent random events leading to intelligent life on Earth
are somehow fine-tuned, but also various historical events after intelligence
emerged. Which events would depend on which particular religion, e.g. parting
the Red Sea for Christianity, the revelations to Mohammed for Islam, etc.

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TrainedMonkey
We developed highly accurate instruments that measure incredibly small and
large things. Yet all of our scientific progress is biased, because we have
evolved in a very specific environment that we handle well. Virtually all of
our scientific measurements had been done in a relatively small time frame[1]
and on one very specific planet with certain conditions [2].

I think it is way to early to call universe unnatural. Sure there is a chance
that it might be true, but we are not going to find out until we have way more
data. For one there is so much in cosmology that we cannot explain yet, such
as dark matter and accelerating expansion.

[1] Last 250 years or so.

[2] Gravity, magnetic field, stable trajectory around the sun (sun's gravity
is more or less unchanging)... I do know there are variations and experiments
in microgravity, but all high-energy particle acceleration experiments had
been done in relatively same conditions.

~~~
granfalloon
"Yet all of our scientific progress is biased, because we have evolved in a
very specific environment that we handle well."

I often get discouraged thinking about this. Our entire body of scientific
knowledge consists of inferences drawn from human observation, but our sensory
apparatus is only sensitive to a few different things/processes. And the
mental processes we apply to our observations evolved to simply help us
survive our physical environment. We could be fatally under-equipped to ever
come close to "understanding" the universe, right?

Also, I'm WAY out of my depth here, but is it at least _possible_ to imagine a
system where there are multiple sets of elementary particles, with each set
not interacting with the rest? I'm imagining an arbitrary number of sets of
particles that are each identical in function to the particles comprising our
physical world, but the states of the particles in Set 1 have no effect on the
states of the particles in Set 2, and so on. The result could be many
intertwined or overlaid physical universes, all occupying the same "space."
Could something like this ever be disproved?

~~~
TrainedMonkey
That is basically string theory^^

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ccvannorman
The deeper we go, the stranger things get. But I doubt scientists will "lose
the desire to continue looking for new physics" as is warned by this article!
We'll go deeper and things will get stranger, and that's just the way of human
exploration.

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jkbyc
Check out The Reference Frame blog if you want to read more (and more in-
depth) about naturalness. For example:
[http://motls.blogspot.cz/2012/07/diphoton-higgs-
enhancement-...](http://motls.blogspot.cz/2012/07/diphoton-higgs-enhancement-
as-proof-of.html) [http://motls.blogspot.cz/2013/12/doubly-protected-higgs-
is-n...](http://motls.blogspot.cz/2013/12/doubly-protected-higgs-is-
naturally.html)

Otherwise:
[https://www.google.com/?q=site:motls.blogspot.com+naturalnes...](https://www.google.com/?q=site:motls.blogspot.com+naturalness)

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elberto34
End of science? Hardly. just because we may be in a multiverse doesn't mean we
should stop trying to figure out how our particular universe works, and this
info may yield insight into the other universes. There is still so much to
learn

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gregonicus
"Parallel universes cannot be tested for" The multiverse idea just sounds like
a more respectable version of "turtles all the way down"

~~~
Houshalter
Why? "Turtles" is a bad hypothesis because it's so arbitrary. It is no more
likely than "ducks all the way down", etc. The fact that it's not testable is
the least of it's problems.

Whereas a multiverse is a much higher prior probability. In fact believing we
are the only universe is just as untestable a hypothesis, and even more silly.

~~~
julius
Please stop with the probabilities.

We can demonstrate, our universe exists. Claims about the number of universes
(>= 1) are untestable (for now) and should therefore be considered
speculation.

~~~
Houshalter
I'm not saying that there isn't any evidence our universe exists. That would
be silly. I'm saying there is no evidence that our universe is alone and it
would be incredibly surprising if it was. I don't know why "number of
universes = 1" should be a default hypothesis.

~~~
mratzloff
There is no evidence for unicorns, but I don't know why everyone assumes they
don't exist. Isn't it equally likely that they are just really good at hiding?

~~~
Houshalter
You are making my argument for me. The hypothesis "unicorns don't exist" has
zero proof. You can never ever prove that unicorns don't exist. Therefore, the
statement "unicorns don't exist" is just wild speculation and outside the
realm of science. Therefore, until someone shows proof we will assume that
unicorns do exist.

The idea that our universe is the only universe is just as crazy to me as
saying unicorns exist. The laws of physics are incredibly arbitrary, and the
probability of a random set of laws of physics supporting intelligent life is
ridiculously small.

More formally, via Solomonoff induction, the hypothesis of multiple universes
should be more likely by several orders of magnitude, since it can necessarily
be expressed with fewer bits of complexity. E.g. "all computable programs" vs
"one specific program", or "all possible laws of physics", vs "one very
specific set of laws of physics."

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kazinator
The thing is, nothing you can discover in physics can refute the multiverse
hypothesis. It is not falsifiable in that way.

Even if you find that you're in a very special universe, you need an
explanation of why it is that way. The multiverse hypothesis helps, by giving
a plausible answer which avoids belief in gods.

~~~
dragonwriter
> Even if you find that you're in a very special universe, you need an
> explanation of why it is that way.

Emotionally "need", perhaps. Scientifically, not really.

> The multiverse hypothesis helps, by giving a plausible answer which avoids
> belief in gods.

The multiverse conjecture is -- by your own description -- not a hypothesis in
the scientific sense, because, as you say, it cannot be falsified empirically.
Like any belief in God that is compatible with science, its simply -- from a
scientific perspective -- superfluous. It has no advantage, except the
emotional advantage it provides to someone with an emotional bias to (1) have
an explanation even if it is untestable, and (2) to avoid that explanation
relying on belief in God.

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trhway
>Physicists reason that if the universe is unnatural, with extremely unlikely
fundamental constants that make life possible, then an enormous number of
universes must exist for our improbable case to have been realized.

somewhat reminds about what physics must have been before Newton's laws - the
cannon ball flies this strange seemingly unnatural trajectory what it would
sound reasonable to suppose that "enormous number of universes must exist for
our improbable case to have been realized." Though they were lucky back then
to have God's will as an easy always available tool for explanation. We're not
that lucky today. We have to continue digging :)

