Complications in Physics Lend Support to Multiverse Hypothesis

https://www.quantamagazine.org/20130524-is-nature-unnatural/

by ghosh • 12 years ago

45 59 12 years ago

Animats• 12 years ago

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• 12 years ago

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• 12 years ago

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.

danbruc2• 12 years ago

[...] some experiments can't be done from within the box [...]

Only true if the box is not everything.

ccvannorman2• 12 years ago

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.

trhway• 12 years ago

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 :)

TrainedMonkey2• 12 years ago

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.

noobermin2• 12 years ago

WRT HEP experiments, I'm hoping the developments in laser acceleration of charged particles leads to accelerator-like experiments being much cheaper and thus more easily doable for smaller groups and labs, it would at least increase the number of variations in conditions.

But, you're right about scientists assuming a lot about the universe. In cosmology, this is known as the Cosmological Principle[0], which is expressed in the language of the field as homogeneity of the matter distribution of the universe. Implicit hypotheses with this is that fundamental constants are constant and the laws of physics are the same. The basic idea is the assumption that the Earth is not special, therefore, experiments done here, while accounting for particular effects like earth's gravity, being a non-inertial frame, etc., would be representative of any point other point of space.

And it's not that this is a bad assumption. For example, spectra analysis of elements on earth has given us good ways to figure out the elements of stars far out of reach, and it is one hell of a coincidence that the spectra we see in stars is so similar to elements here like hydrogen and helium that one can't assume that earth was just gifted with these elements while other parts weren't. This is just one example of the success of this assumption.

[0] https://en.wikipedia.org/wiki/Cosmological_principle

granfalloon• 12 years ago

"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?

TrainedMonkey2• 12 years ago

That is basically string theory^^

Steuard3• 12 years ago

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...), 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).

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.

placebo• 12 years ago

Not sure this analogy holds. Although the ratio of Jupiter's and Saturn's major orbital axis might seem arbitrary, given all the prior conditions to the orbit formations, current physics theories perhaps could have theoretically predicted this ratio long before it came to be. In the same way, physicists would like an elegant model that would predict or explain the constants in a way that makes more sense in a larger picture rather than having them as some magic numbers.

Steuard3• 12 years ago

Exactly. That's pretty much what multiverse models suggest might be true for "fundamental constants": if you somehow knew the precise conditions of our part of the universe in the moments leading up to our big bang (and the parameters of whatever process triggered it: quantum fluctuations or whatever), you could in principle predict things like the charge to mass ratio of the electron. (E.g. if you knew the precise shape and fluxes of our 6-dimensional Calabi-Yau compactification manifold in string theory, you could work out the low-energy field content and coupling constants of the resulting universe.)

[String phenomenology isn't really my field, but I certainly haven't had a lot of luck deriving a unique background from pure theory. I did once think that I'd found a model that predicted the cosmological constant to within an order of magnitude or two, but that obviously didn't pan out.]

rndn3• 12 years ago

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_...

JadeNB2• 12 years ago

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), in which the cause of the cause of the cause of … may be the original event.

Steuard3• 12 years ago

I certainly didn't intend to suggest that an infinite number of theoretical layers might be necessary to explain nature (though I suppose I can't rule it out). Everything in my comment was meant to be compatible with (to take one example) the possibility that some particular well-defined refinement of string theory turns out to be the ultimate theory of nature, and only variations in local conditions are unpredictable. (This is meant in much the same way that the well established laws of gravitation, electromagnetism, and nuclear physics will give rise to very diverse solar systems.)

There are interesting questions in many multiverse models about the history and origin of the universe, and I've seen people express concerns about the possibility of "infinite history" in much the same words you've used here. But that's a different issue than Smolin's notion of infinitely many layers of theory being needed to keep the cosmic machinery running.

Personally, I'm not overly bothered by the notion of space and time existing forever in both directions, with new bubbles of interesting reality occasionally spawning themselves from the remnants of the old ones at random after uncounted eons of darkness. I don't know why that structure might exist rather than something else (or why there is something rather than nothing), but positing a "first cause" wouldn't make me any more satisfied (and would raise additional questions). I think modern math and science are more comfortable with the possibility of infinity than folks used to be, and that our notion of a "cause" is rather different. (When I think of "causality", all I think about are light cones and Cauchy problems: http://en.wikipedia.org/wiki/Cauchy_problem .)

gregonicus• 12 years ago

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

Houshalter3• 12 years ago

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• 12 years ago

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.

kghose• 12 years ago

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.

jmcqk6• 12 years ago

This is exactly the way I think about it too. it doesn't seem reasonable to assume vastly more complicated universal structure based on nothing more than our own existence.

tim333• 12 years ago

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.

vorg2• 12 years ago

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.

onnoonno• 12 years ago

The funny thing is that the Antrophic principle believes in some kind of 'true randomness' in this way - even if it is just about the constants for the otherwise deterministic universe :-)

elberto34• 12 years ago

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

kazinator10• 12 years ago

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.

stefantalpalaru2• 12 years ago

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

But as long as there is no proof of the existence of these multiple universes it's still magical thinking.

AnimalMuppet2• 12 years ago

Worse: Why do you consider the multiple universe hypothesis as more probable than the God hypothesis?

On the basis of data? No. (If you think otherwise, show us the data.)

On the basis of philosophical prejudice? Yes, I think that's the reason.

But if you say that, given no evidence for God, one should be an atheist, then given no evidence for multiple universes...

dragonwriter• 12 years ago

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.

jkbyc• 12 years ago

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/2013/12/doubly-protected-higgs-is-n...

Otherwise: https://www.google.com/?q=site:motls.blogspot.com+naturalnes...

Complications in Physics Lend Support to Multiverse Hypothesis

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