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

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?

[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.

Google: no registration

[mrBlond]

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

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).

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.

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...

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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.