A Skeptical Look At The Multiverse

sjanich writes "The NY Times has a short, interesting article on multiverse theory. The author, Paul Davies, writes: 'This idea of multiple universes, or multiple realities, has been around in philosophical circles for centuries. The scientific justification for it, however, is new.' It is quite an interesting read. The author is a Physicist and pretty good science writer." Davies is not kind to the multiverse theory.

Comments

theory that makes no predictions is meaningless

[obtuse]

Davies refers to, but never explicitly states one particular point: Most of the multiverse theories are inherently untestable, because we're completely isolated from the other universes. These are theories that don't predict or even suggest anything. How meaningless can you get?

This is a good general point. Solipsism is uninteresting. Subjectivism & deconstructivism are often taken to similar absurd extremes by stupid people, including respected critics.

He makes the analogy between theology & these scientific non-explanations. Religion is personally very meaningful, but metaphysics isn't science. Consequently a classic metaphysical question, "How many angels can dance on the head of a pin?" is the canonical meaningless question.

The word that springs to mind is sophomoric. It reminds me of High School, when one friend asked another "What if you're really insane & just dreaming all of this?" The answer was of course, "So what? You've gotta pretty much live your life the same way anyway."

Re:theory that makes no predictions is meaningless

[aminorex]

Oh but they are not unfalsifiable in principle,
only in current practice. This is a crucial
distinction between a physical and a metaphysical
theory. The Higgs boson, when postulated, was
an hypothesis unfalsifiable in practice. But
clearly it is a physical, rather than a metaphysical,
hypothesis.

Now suppose that someone, let's call him Zweistein,
proposes a theory of multiple universes which
is incapable of producing a falsifiable prediction.
We may say that the good Zweistein's theory is a
metaphysical theory. But suppose that it is
subsequently elaborated by his intellectual
descendent, Dreistein. Suppose further that the
specific elaborations of Dreistein provide the
basis for constructing an experiment which is
capable of disproving his elaboration of the
original work of Zweistein.

Clearly Dreistein's theory is a physical theory.
If it's predictive power proves out in experiment,
not only is it a physical theory, but it becomes
then an operational hypothesis and the basis for
further science. Should we then discount the
prior work of Zweistein which was necessary for
the later, more practically useful results?
Of course not.

Yes, some ideas may not be sufficiently precise
to be falsified. But their future elaborations
may not fall into the same category. We should not
discount or discard speculation which is consistent
with observation, but rather let it live on in
its proper domain, to produce what useful future
results that it can produce.

Re:theory that makes no predictions is meaningless

[Jerf]

No dice. Appeals to the future don't get you out of that bind. We can't evaluate future theories, we can only evaluate current theories, because "somebody might figure it out in the future!" goes for everything.

I might also add that "somebody might figure it out in the future!", as a theory, is also untestable, except by waiting for said theory, at which point we can just evaluate the theory directly, so "somebody might figure it out in the future!" is not useful.

Warning: Not a Science article

[zenyu]

I was just reading the "article" and getting more and more annoyed with how clueless and full of unfounded and dumb opinions it was. . . Then I looked at the big warning label on top, "Op-Ed" this is an Editorial! This should not be in the "Science" heading it's just creationist political opinion. It's by a philosophy professor not a scientist. As an op-ed it isn't even a well argued one, no facts no educated opinion even.

Everett interpretation

[aminorex]

It is worthwhile to point out that cosmological
diversity is only one kind of "multiverse" theory.
In it, all of the various universes are embedded
in a larger space. Such theories are not therefore
unscientific, in the sense of being intrinsically
unfalsifiable, or unverifiable: Because the various
universes have topological relation to one another,
there is a continuum of existence connecting them,
and they may interact in yet unforseen ways. Our
current inability to design experiments to detect
such interactions is merely an artifact of
ignorance.

But there are many other forms of ontological
multiplicity which do not involve topological
continuum. The outstanding example is the
Everett interpretation of quantum mechanics.
In that theory, rather than the actual state of
affairs in the universe being the sole real
instantiation of the phi wavefunction, created
by the act of observation (as in the classical
Copenhagen interpretation of Bohr et al), the
quantum wave function is considered to be a
representation of the distribution of an infinite
multiplicity of alternatives, all equally "real".

I find the Everett interpretation to be much
preferrable, on several grounds, not the least
of which is that it is consistent with the
mathematical concept of probability distribution
in a way which the Copenhagen interpretation is
not, but others disdain
it because it implies the real existence of
entities which are not, so they say, in principle,
detectable. Again, this complaint fails because
it is an argument from ignorance: The current
inability, at a given level of human understanding
and technology, to design a verifying or falsifying
experiment, does not relate to the truth or falsity
of the hypothesis. Cophenhagenists are quite
comfortable supposing that unseen cats are undead,
and any truth not currently known is not yet true.
I think this is a much larger leap of faith than
is needed to create a working understanding.

Re:I guess he didn't like the Matrix either...

[CaptainStormfield]

You're absolutely correct. Davies reasons as follows -- see if you can spot the false (implicit) premise:

(1) If the multiverse theory is correct, there are a lot of "universes" that are the product of simulations run by intelligent beings.

(2) If (1) is true, then our "universe" might be the product of a siumulation run by intelligent beings.

(3) I do not believe that it is possible that I live in a universe that is the product of a siumlation run by intelligent beings.

(4) The nature of the universe corresponds to my beliefs about the nature of reality.

(5) Therefore, it is not possible that I live in a universe that is the product of a simulation run by intelligent beings.

(6) Therefore, the multiverse theory is false.

The bottom line: there is no way to prove that you're not a brain in a vat.

But it is an interesting argument

[apsmith]

and one I had not heard before.

I think the real point is, not that he finds the idea of us living in a "simulation" abhorrent or impossible, but that any theory from which such a conclusion logically follows is something that cannot be considered scientific - such a theory is exactly equivalent to a religious doctrine in which unexplained events are attributed to the supernatural (unexplained "miraculous" events in our universe could be just defects in the simulation, or even deliberate effects caused by the simulators, after all).

And that sort of thing just flies in the face of centuries of doctrine and methodology in science, about what science really is.

I think it's an interesting argument; I find myself somewhat inclined to agree - depending on the type of multiverse we're talking about, anyway.

Re:One question

[ralphclark]

Mathematicians say that some infinite sets can contain more members than other infinites sets, eg the set of real numbers is more highly populated than the set of natural numbers (effectively integers). This holds wherever one infinite set can be mapped onto a subset of another infinite set. Also in that particular case the set of real numbers that can't be mapped is larger than the set that can. So it's meaningful to postulate, on statistical grounds, that the number of sterile potential universes is larger than the number of fecund potential universes.

Re:How ridiculous,

[Alsee]

Thanks for posting an intelligent response, btw. You probably already know how rare this kind of thing is

Ditto :D

By the arguments outlined in my previous message, any such collection would have a very disorganized internal structure

Have you seen the incredible high-res photos of the sun that were on slashdot a few months ago? The sun contains higly complex structures. Complex, organized, and and stable structures often arise out of highly disorganized and disruptive lower level processes. Virtual particles are an increadibly "hot" boiling sea of energy. Our bodies are composed of "molten" molecules bouncing in a highly chaotic and disruptive manner. (It's always amusing to reffer to water as molten ice :grin:)

If a cubic foot of sun-stuff can have enough higher-level structure to yeild the equivilant structure an atom provides for us then the sun is perhaps a large enough enviornment to hold a "biosphere". It's a bit fantasical, but not inconceiveable. Who knows what would happen within a 4-d star?

Postulating about clusters of such matter collections doesn't work either, as any such cluster would be unstable

Actually I'm not convinced of that. For example the ring around saturn is a stable structure of multiple bodies, where as it would be unstable if it were a single solid ring. It could also be stablized by some other force. It only takes a tiny force to maintain some unstable orbits. That force could be radiation pressure, solar wind, magnetic field, static electric charge, some complex magneto-hydrodynamic interaction with the solar wind, thermal gas jets (like the jets that appear on coments that approach the sun), or more likely something I haven;t thought of.

Given an entire 4-d universe I find it unlikely that there would be no relatively stable regions of some sort. Just look at the absolutely miniscule percentage of our universe has a stable temperature for liquid water. An alien with different physics would probably conclude our physics were incapable of having that sort of stability anywhere.

Your arguments about emergent properties and patterns in our universe are a great illustration of how conducive our universe is to such organization. Universes with other dimensionalities seem to be less so.

As above, look at the miniscule percent of our universe is conductive to that sort of organization. The universe is 99.9999% empty space. Anything that isn't empty space is 99.9% solar fireball. The universe's matter is almost all hydrogen and helium. Anyone with different laws of physics would likely never realize that heavy elements like carbon could be produced. And even if they did realize it, they'd probably never realize a nova could release that matter to empty space where it could condense into a planet. It is an entire chain of absurdities. Life in our universe is impossible by any rational argument :D

The real question is how much complexity does the system support? If a universe has a rich complex set of physics then it probably results in useful structures of which we have no concept. Who needs stars and atoms? A complex universe will have complex and useful "things".

-

The Multiverse Theory of Auto-Repair

[SpeakingMute]

Imagine that your car begins making a strange knocking sound when you brake. You take your car into the autoshop to find out what's causing the problem. Without even looking under the hood, the mechanic explains that the reason your car is making the sound is because there are infinitely many universes with different versions of you and your car, and you just happen to live in the universe where the car began making a knocking sound. Odds are, you'd look for another mechanic. The multiverse theory essentially uses the same logic to explain (or explain away) features of the universe such as the gravitation or planck constant. As such, its basically a huge non-explanation. Regardless of Davies particular bias, his main point is that the theory is practically devoid of explanation and is about as meaningful as saying "God did it". When Davies invokes the term "falsifiable", he isn't claiming that there couldn't be evidence to support it, but rather there could never be a way to disprove the theory. The lack of criteria for falsifying multiverse theories is problematic because there could be other, more fruitful theories that explain the same observations as a particular version such as Brane Theory. Returning the above example with the mechanice, compare the two rivals theories for the noise: a) infintely many universes with different parameters for the car's noise level when brakes are applied. b) the brake-pads are worn out. A is just as valid a theory as B; the difference is, you can disprove B, and apply B to tell you something about the car (it needs new brake pads). Which theory do you think is better? For a final bit of flame; yeah, maybe people dislike multiverse theories because they mean are universe isn't "special"...but my feeling is that multiverse theories have such appeal is because they're a neat sci-fi prop, not because they have any real value.