One of Many

sam_handelman writes "The nytimes has another astrophysics article up. Free subscription etc. It talks about how inflation predicts multiple universes, this week. Dennis Overbye wrote the article, which is nice if lightweight. More info on the theory of inflation. Inflation, which is harebrained on first examination, actually predicts stuff, giving it credibility. Want to be the Right Pinky of God? It may yet be possible."

Comments

Re:theory, schmory

[mumblestheclown]

In the American vernacular, "theory" often means "imperfect fact" - part of a hierarchy of confidence running downhill from fact to theory to hypothesis to guess. Thus the power of the creationist argument: evolution is "only" a theory and intense debate now rages about many aspects of the theory. If evolution is worse than a fact, and scientists can't even make up their minds about the theory, then what confidence can we have in it? Indeed, President Reagan echoed this argument before an evangelical group in Dallas when he said (in what I devoutly hope was campaign rhetoric): "Well, it is a theory. It is a scientific theory only, and it has in recent years been challenged in the world of science - that is, not believed in the scientific community to be as infallible as it once was." Well evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts don't go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's in this century, but apples didn't suspend themselves in midair, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered.

Moreover, "fact" doesn't mean "absolute certainty"; there ain't no such animal in an exciting and complex world. The final proofs of logic and mathematics flow deductively from stated premises and achieve certainty only because they are NOT about the empirical world. Evolutionists make no claim for perpetual truth, though creationists often do (and then attack us falsely for a style of argument that they themselves favor). In science "fact" can only mean "confirmed to such a degree that it would be perverse to withhold provisional consent." I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms.

Evolutionists have been very clear about this distinction of fact and theory from the very beginning, if only because we have always acknowledged how far we are from completely understanding the mechanisms (theory) by which evolution (fact) occurred. Darwin continually emphasized the difference between his two great and separate accomplishments: establishing the fact of evolution, and proposing a theory - natural selection - to explain the mechanism of evolution.

- Stephen J. Gould, "Evolution as Fact and Theory"; Discover, May 1981

What about...?

[cordsie]

Personally, I'm having trouble reconciling the theory of inflation with a few well established notions about the universe. Does this mean that there are many turtles supporting other planets almost identical to our own?

Re: theory, schmory

[Black Parrot]

> 50 years from now high school physics students will laugh at us. "Ha, these idiots believed in all sorts of kooky stuff".

Do today's highschool physics students laugh at the scientists of 50 years ago?

> This theory is just that, a theory.

And that's all a theory is supposed to be.

Re:JUSES FAKING CHRISTO!!!

[bradkittenbrink]

Can anyone explain why I keep coming here? Every day at work, probably a dozen times. I hate the stories, I hate the editors. I'm not a big fan of Linux. I hate almost all of you, and I loathe the group-think that goes on here. It oozes out of all the highly modded comments... the /. party line.
Because we're mind control experts. We know you hate us, but we just love to have you around telling us how much you hate us, so we force you to come back. insert obligatory "all your base are belong to us" joke here

You can be the pinky....

[Sn4xx0r]

I'll be the brain :)

Inflation != Multiple Universes

[c_de_bugger]

From the article.
In fact, Dr. Guth said, "Inflation pretty much forces the idea of multiple universes upon us."
I read the article. Can anyone see where he justifies this statement with anything resembling logic?
I accept inflation and the 'anthropic principle' as well argued theories. Inflation=multiple universes is not (or not here).

Re:Inflation != Multiple Universes

[bradkittenbrink]

I didn't see the explanation in the article, but from what I've heard the explanation is pretty simple. I think I read it in A Breif History of Time or something like that. I probably don't remember it correctly but here goes nothing...

The trick is that the collapse from an inflationary situation to normal spacetime can't happen instantaneously. By the time the collapse has happened and created a universe of normal spacetime, the inflation has already created more than enough (inflating) space/spacetime/cosmicstuff to replace it. So there will always be inflating stuff left over. Eventually this new inflating stuff will start collapsing into pockets of normal spacetime, creating new universes each time. The point is that the inflating stuff inflates too quickly to be consumed by the collapse process, so the process continues indefinitely.

Re:Inflation != Multiple Universes

[AntiFreeze]

From reading the article, the following is my understanding of why inflation predicts multiple universes:

• Inflation is predicated upon certain conditions within the universe just a few planck times after the big bang (a planck time is on the order of 10^-32 or so seconds, I can't remember exactly off the top of my head).
• If these conditions hold, inflation will occur. People pretty much believe that inflation did occur, for there is no other current way to accurately explain the rapid expansion of the universe in the first few planck times after the big bang.
• Now, assuming inflation did occur, that means the conditions for inflation must have been met. Here is where "inflation=multiple universes" as you put, it comes into play. Those conditions necessary to create inflation exist in certain pockets of space-time (most notably at singularities, such as in the center of a black hole) in our universe.
• Hence, if the conditions for inflation are met, surley something must be inflating. But we can't see results of such inflation in our universe, and therefore it probably means that the inflation is occuring in another universe. This is where the article is weak, and you are probably having your problem. They did not speak about the theories which allow for "new" universes to be created with different laws of physics, and how the preconditions for inflation meet these criteria. These theories have been around for quite some time, and are generally regarded as possible. That said, conditions which would cause these new universes are theoretical, and whether or not they exist are under debate. It just so happens that inflation theory forces some of these alternate universes to exist.
• So if there are random points in our universe which cause inflation and the creation of new universes, then it is very possible that our universe is one such inflation due to circumstances within another universe. And so on, creating a "web" of inflated universes: the multiverse.

I hope I've done some justice to the theories (sorry for the lack of links, I'll rumage through my books and try and post a followup later). If I'm wrong, or remembering things poorly, don't flame me, just reply and set things straight.

Re:Inflation != Multiple Universes

[AntiFreeze]

Yup. That's the theory.

The laws of physics as we know them are the laws of physics for this universe and this universe alone. A different universe would have different laws of physics altogether.

The theories and the article both state this very clearly. That's one of the fascinating things about our universe: that it's laws are so precise as to allow stars, and subsequently life, to form. Only a narrow range of laws allow such formations, and our universe is one of the few (although possibly infinite) number of universes with laws capable of creating and sustaining life.

Re:Inflation != Multiple Universes

[guybarr]

but this would mean that the laws of physics would no longer be laws ..

It certainly, IMHO, means that the laws we know break. Very probably it means the laws we can conceivably test also do not apply.

This does not mean there isn't any generalization of the basic theories which do apply. In fact physicists predict properties such a theory must have, which may lead to hypothesis of this kind.

wether such hypothesis are true, or can even be tested, again, is a leap of faith IMHO.

If I lived on a proto-planet then I would be a creature that was much smaller than an electron and therefore must be made up of things that don't apply to the current physics

Here I think you may have a misconception of the notion of size. General Relativity tells us you cannot directly compare sizes over great distances. This means that the world we live in is a Riemann manifold ( a patchwork of local non congruent euclidian approximations )

What all this means, is that comparing sizes inside a black hole (the above approximations break on the way) and outside is not only impossible, it is meaningless. It does NOT mean the laws of physics must be different in flat areas inside. (or that they aren't)

Besides... I'd would be darn horrible to find out that we have been preforming planicide on entire civilizations and races every time a cyclotron or particle accelerator is fired up

wrong. this may have conceivably been possible if current experiments would heve been close to the plank scale. However we're many many orders of magnitude away from achieving such cataclysmic energies.
AFAIK we know pretty well the basics of what is happening in the sub-TeV scale.

Why harebrained?

[Mr_Dyqik]

Why is inflation harebrained on first examination?

It was originally proposed to address one of the big problems in the old big bang theory, namely that parts of the universe visible from Earth, that were so far apart that light couldn't have travelled between them since the big bang, looked pretty much the same. For this too happen, they must have been some sort of communication between them at some point in the past, but a fixed, unbreakable speed of light prevents this happening. This assumes that the universe has always been expanding, with the expansion being slowed by gravity only.

Inflation just says that if the universe initially expanded much much faster than the current rate suggests it did, then those parts of the universe that are too far apart to communicate now, might have been able to communicate in the past. All of the complexity of the theory is in producing the physics that allows for, and causes the inflation.

Re:Why harebrained?

[Effugas]

Dyqik, that doesn't make any sense. There's no need for communication between two clusters after the big bang in the situation you describe: Given a limited set of circumstances that creates stellar bodies detectable at such great range, either those circumstances occur -- and we detect something -- or they don't, and we see nothing.

With a limited set of circumstances, it's trivial to imagine a limited set of detectable outcomes, particularly if the laws of the universe are, well, universal. Stars too hot would have burned out billions of years ago; stars too cold we could not see. That leaves this very narrow region we're able to detect, and unsurprisingly everywhere we look we see the same thing. When there's something else, we're either too late or blind.

Even this logic is unnecessary, though -- given that the visible regions were once part of the same singularity, all the "information" they'd ever need to remain related could have been exchanged at the point of the Big Bang itself. Absolutely identical output is theoretically justifiable, if there's a quantum level pseudorandom number generator at work. (Oddly enough, if there was, we'd never be able to tell, except through its occasional bugs...like entanglement, perhaps.)

--Dan

Re:Why harebrained?

[Mr_Dyqik]

If you take two opposite directions, and look at the CMB spectrum in those directions, the temperature is the same to within 0.00001K. Since the CMB radiation was emitted from those points at a redshift of about 1000, the emitting points that we can see today are about 2ct apart, where t is the age of the universe

Due to the way in which the universe is currently expanding, extrapolating the motion of those two points back to the big bang shows that the two points were always further apart than ct, the maximum distance that light can have travelled since the big bang. The question then is: Why are two points in space, that can never have been in contact at the exact same temperature?

Inflation answers the question by saying that when t->0 the expansion of the universe was so fast that the two points 2ct apart now were closer than ct.

Flat universe

[little1973]

AFAIK, one of the advantages of this theory is that it explains why the universe seems to be "flat". And the answer is that we just percieve a tiny fraction of the universe, so it's not surprising we see the universe as if it was flat.

Re:Flat universe

[richie2000]

Great - and we thought the flat earthers were bad enough...

Re:Flat universe

[fuctape]

Actually, the theory says that during the inflationary period, the Universe was *driven* to be flat, as opposed to open or closed, because of the nature of inflation and vacuums. Once we understood that the Universe could be open, closed, or flat (1930s?), we were shocked to find that it had won the lottery -- it's flat (probably).

Google: no registration

[mrBlond]

Please link to the Google version which doesn't require registration.

Multiple universes?

[mccalli]

it talks about how inflation predicts multiple universes

This is one of my pet hates. By the very definition of the word, there can only be one universe. Or are the definitions now being changed?

Cheers,
Ian

Re:Multiple universes?

[Mr_Dyqik]

universe here means the area of the universe that we can (possibly) see, communicate with, and/or do physics experiments in. Since physics is limited to that region of the universe in which we can do physics experiments, then it is conceivable that there exist regions of spacetime that are inaccessible to us, by virtue of distance or some other parameter.

Whether it is meaningful for physicists to talk amount these regions as _seperate_ universes comes down to what you think universe means, and what the values of the cosmological parameters are this week.

Re:Multiple universes?

[SEWilco]

Note to God: Remember to make English better in next universe.

Re:Multiple universes?

[amorsen]

This is one of my pet hates. By the very definition of the word [m-w.com], there can only be one universe. Or are the definitions now being changed?

By the very nature of the word, an atom cannot be divided.

Re:Multiple universes?

[bogado]

This definition was created when we discovered that they in fact could be divided. Words mean whatever you understand of them. Dictionary can, and will be, changed. Language is a changing beast, and you can screem all you want that "hacker" is not an evil computer genius, that people will continue to use the word as they learned. This is culture. :-)

Re:Multiple universes?

[mccalli]

Not a single one of the five different senses of the word gives even the suggestion that there can not be more than one.

1 : the whole body of things and phenomena observed or postulated

ie. everything. Can't have more than one of those. If more 'things' are being postulated that match what previously we called the universe, then by definition they are subsumed into the current universe and we need a different word to describe what we used to have.

Cheers,
Ian

Re:Multiple universes?

[Alsee]

1 : the whole body of things and phenomena observed or postulated

And then of course there is everything that has NOT been observed or postulated. So that usage does clearly imply that "universe" is not "everything".

Including everything "postulated" is not a requirement of all usages of the word. In most cases it is a pretty poor usage. You usualy don't want to consider non-existant things that have been postulated to be part of the universe.

In this case we are talking about something that has been postulated but not observed. It is not part of our universe because it can never be observed. It is part of a seperate whole.

Considering all of the "universes" to all be part of one universe is A valid usage, but it is not the only one.

The different senses listed pretty much revolve a "whole body" of things that are in some way connected. If there is a second "whole body" of things that are connected with each other, and there is no connection between the two "whole bodies", then they can be reasonably be called two universes.

-

Alan Greenspan

[invid]

Don't tell Alan Greenspan about the inflationary universe. He'll try to control it with interest rates.

Re:Alan Greenspan

[Rayonic]

And he'll suceed, by most accounts. ;-)

Multiverse Schmultiverse

[wiggys]

Dr Lee Smolin wrote an interesting (although difficult) book about the multiple universe theory.

He theorised that all of the universe's parameters (light, gravity, strong and weak nuclear etc) were self-tuned in much the same way that life is tuned for survival. Universes where the gravity was too strong, or the charge of a particle was too weak, didn't develop black holes. Our universe appears to have thousands of black holes, and we know for a fact our universe is tuned to support life, ergo, our universe will have "off-spring", with black holes being the mothers.

He's basically doing what Creationists do - merging biological evolutionary theory with cosmological evolution, something which most scientists are quick to separate. I think he might be onto something...

_______________

Why oh Why!!!

[phunhippy]

Why oh Why must the [editors] post these type of articles early in the morning! My head is going to hurt all day now!

thanks slashdot!

Re: You've got it backwards.

[guybarr]

Unfortunately, the big-brained ones have now copped onto the Sci-Fi idea of these alternate universes

I think you have a wrong picture: although the notion of different choices and their consequences is an ancient one, the notion of parallel universes came from science (everett interpretation, feynman-multiple-path approach to quantum mechanics) to SciFi and philosophy.

As usual, the ideas flow from science to science-fiction. I asume this is because usually, nature is more bizare than what our imagination can predict. (and also because the best scientists are among the most creative people ...)

How dense can you get?

[PigleT]

The second article, `inflation for beginners' says:

the density was not infinite but "only" some 1094 grams per cubic centimetre. These are the absolute limits on size and density allowed by quantum physics.

On that picture, the first puzzle is how anything that dense could ever expand -- it would have an enormously strong gravitational field, turning it into a black hole and snuffing it out of existence (back into the singularity) as soon as it was born.

Erm, could someone explain to me just how dense 1094g/cm^3 really is? I'm trying to picture a bag of sugar and a small cube of steel here... and I'm thinking maybe there's a scaling problem somwhere...

Infinite universes?...

[Anonymous Coward]

If there were an infinite number of universes in which each and every chance outcome is played out, would there be a universe where someone invents a universe destroying machine and destroys all the other universes without being stopped by anyone?

an example we can all understand

[el_gregorio]

to understand this theory, all you have to do is visit your favorite pr0n site using IE. you see the way your screen fills with an endless swarm of pop-up windows, each with their own content? think of those as little universes, each separate from the others, but united in their love of barely legal asian teens.

This is so incredibly scary...

[CSG_SurferDude]

Multiverses?

You mean this might mean that somewhere in the multiverse there might be a universe comprised entirely of "people" that look exactly like Lance and Britney?

Excuse me while I (and the rest of the "me's" in the multiverse) go out and hang ourselves....

Humanity's egocentrism

[Danny Rathjens]

How long will it take for humanity to learn that we aren't as special as we've always assumed?

• Some groups of people used to think they were the center of the world(e.g. Zhong Guo==Middle Kingdom)
• Bigger groups used to think that earth was the center of reality and everything literally revolved around humans.(A belief vigorously defended)
• Leewonhoek's microscope revealed a smaller scale of reality than we knew, and it was quite some time before people accepted it.
• Newton's theories seemed to describe how all reality worked until we realized different things were going on at very small and very large scales.
• Now we have a much greater understanding of things at the quantum scale and the universal scale, but it seems obvious that that is not the end of it.

Why do we seem to assume that the scale of reality is finite and coincidentally matches the same scale at which we exist? I think that based upon all of our prior fumblings we would be more likely to conclude that reality extends to a much smaller scale than the quantum and a much greater scale than that of the observible universe; even that it is infinite in both directions.

Re:Humanity's egocentrism

[opaqueice]

"Why do we seem to assume that the scale of reality is finite and coincidentally matches the same scale at which we exist? I think that based upon all of our prior fumblings we would be more likely to conclude that reality extends to a much smaller scale than the quantum and a much greater scale than that of the observible universe; even that it is infinite in both directions."

Why do you think scientists make this assumption? The quantum scale I think you're referring to is approximately 30 orders of magnitude (10^30) below the scale we are familiar with in every day life. The size of the observable universe is 30 orders above our scale. And no one is saying that's the end - you can easily construct models, which are consistent with observation, in which the final volume of the universe is infinite. As for the smallest scale, there is a natural length scale in nature. It's the only length you can make by combining the fundamental constants in nature (Planck's constant, the speed of light, and the gravitational constant), and it's the very short quantum scale I referred to above. We *do* think something special happens there, but it may or may not preclude shorter lengths from being a meaningful concept.

So certainly no practicing scientist who thinks about these issues would make the assumption that there's anything special about human scales - in fact, precisely the opposite. One of the powerful principles of modern cosmology is the idea that we do *not* live in a special time or place, and therefore that we have to explain why the conditions we inhabit are generic.

Re:Silly Humans

[falzer]

Silly humans, still debating simple things like evolution, astrophysics, and whether Star Trek or Star Wars is better(non-geeks: read that as "penis size"); and yet you still wonder why alien civilizations haven't contacted you yet.

We're still grappling with the galactic pickle matrix.

More ambitious multiverses

[SiliconEntity]

Max "Mad Max" Tegmark has a more ambitious multiverse theory. It goes way beyond inflation, black holes, and even the Many Worlds Interpretation of quantum mechanics.

His idea is that all possible mathematical structures exist, and that we live in one of them! At some level, physics can be considered a branch of mathematics. Hence our universe can be considered as an enormously complicated mathematical structure. The question is, why this structure instead of some other?

His answer is that all mathematical structures exist, but that most of them are unsuitable for life. The paper linked above analyzes many different possibilities in terms of numbers of dimensions, numbers of time dimensions (yes, you could conceive of a universe with two-dimensional time), various other parameters, and he shows that structures that we would think of as living would have a hard time existing in universes much different from our own.

The Tegmark model can be thought of as the simplest possible physical theory. If physics is reducible to mathematics, then saying that all mathematical structures exist can be put more simply: Everything exists.

A similar model based on computation is proposed by Juergen Schmidhuber. Rather than Tegmark's mathematical structures, Schmidhuber proposes that all computations exist. Given that any mathematical model of a universe can be simulated by a computer program, these two formulations are roughly equivalent.

But Schmidhuber's approach has the advantage that it provides a natural way to say that some universes are more probable than others: namely, universes with short programs have more "measure" than universes with long programs. It follows that our universe probably has a relatively short program, which therefore explains why we observe that physical laws are mathematically simple.

It's pretty heavy stuff, but certainly exciting to see that researchers are (somewhat reluctantly) beginning to entertain multiverse models. The more ambitious "everything exists" theories are still too extreme for the mainstream, but I suspect that they, too, will get increasing attention over the next few decades.