Why is the universe expanding?

after reading the thread on the center of the universe ( http://boards.straightdope.com/sdmb/showthread.php?threadid=58290 ), I realized that I’ve never thought or heard anything about the cause–WHY is space expanding?

So you’ve got the Big Bang, which is not an explosion as we think of it, and you’ve got the stuff in the universe, which is not really being propelled outward from the center of the explosion, but is rather, in a sense, sitting still while space gets larger and larger around it.

So what drives the expansion of space?

The Big Bang was the creation of time and space. It started as a rapid expansion of space (inflationary period) which has been coasting ever since. Recent evidence suggests that the expansion may be accelerating (due to the cosmological constant…or a kind-of anti-gravity force that only becomes significant over HUGE distances).

What caused the Big Bang is unknown. So, it appears that is just how the universe started out and some inertia-like quality has kept it going ever since.

Phobos, couldn’t we call the Big Bang just a regular quantum fluctuation of which there might have been kazillions. The truly unique event, to which we owe the Universe, would be the inflationary period.

I am speaking from memory because I have no references here but don’t quantum fluctuations have the complementary properties of delta time and delta energy. So an enormous Universe massing/energying fluctuation could occur for an almost infinitely short time. For some reason, during that almost infinitely short period, the fluctuation inflated and could not collapse like it should have.

Old age–just like me.

Phobos said that the Big Bang was the creatiun of time and space.

It’s a common error. The Big Bang tells us nothing about creation. It tells us about the evolution of space and time.

It’s a very compelling scenario, and I, for one, believe in it completely.

It does not, however, say anything about creation.

The physicists wisely leave that to the theologians and philosophers.

In any theory in mathematics or physics, some things, called axioms or postulates, are simply assumed. In physics if the assumptions make predictions that are supported by experiments, then the theory is supported. The answer to drives the expansion of space is the Big Bang. As to what caused the Big Bang, well, it is just assumed.

** Clairmont**, I have always read that the Big Bang was the moment of creation of space and time, and that physicists left the notion of cause to theologians and philosophers. Where did you hear that the Big Bang refers to evolution, but not the creation of space and time?

How do the religion people explain why the Almighty
would create by way of random quantum fluctuations, whatever that is? In many stories in different religions he just decrees existence into existence, more or less the way “we” do with our words and mathematics symbols. And we create OURSELVES into existence in the same way when we learn and use words and symbols. Thus not only can’t we ever explain creation but we can’t get past our languages, or as Protagoras once said, “MAN is the measure of all things.”

mipsman - It’s possible, but not known. The “quantum foam” idea seems to be one of the better speculations about the source of the Big Bang seed.

Clairmont - Let me clarify. Time and space had a beginning. Astronomers/physicists call that beginning the Big Bang (event). The subsequent evolution of the universe is described under Big Bang cosmology (i.e., Big Bang Theory makes certain explanations and predictions about the evolution of the universe - - several of which have been confirmed with observational data such as background radiation, abundance of elements, temperature of space, etc.). As I said, what caused the Big Bang (i.e., what caused the creation) is unknown. Whatever the cause, the event was called the Big Bang and the unfolding evolution/cosmology is explained based on the Big Bang Theory.

don - Most either do not consider the possibility (i.e., they never even heard of it or pay attention to such ideas) or do not accept the possibility (i.e., automatically reject all speculations that are not from scripture) that the universe was created from random quantum fluctuations. Of course, some religious people have no problem with such a detail as long as God is the cause of it all. IMHO, Protagoras had a very limited worldview (not necessarily his fault, of course, given the time in which he lived…480-411 BCE). The world and whole universe existed just fine for billions of years before Man was around to start measuring things.

Not really, I think it would just be the probability of the action. As well, that would mean we have an anti-universe pair with which we will annihilate with. I don’t know, though. There is no quantum theory of space, only particles themselves, so its not the best judge of things cosmological.

Can we try to stay a bit more on topic? Phobos’ first post was on the right track. Hence, I’ll rephrase:

What caused inflation, and what keeps it going?

Not what caused space and time to come into existence in the first place (and esp. not any discussion of divine creation…this ain’t GD), but what made it get so big.

If anyone has more to add to Phobos’ answer (which is, essentially, no one knows), please do so.

Some physicists have postulated a repulsive force, a kind of anti-gravity, to explain inflation.

I don’t know much about it, and I suspect there isn’t much to know anyway.

It’s just speculation. No one really knows. This force has not been demonstrated, either experimentally or mathematically.

In reference to cause versus creation, I’d like to again say that the Big Bang is an evolutionary and not a creation theory.

The smallest interval of time that is physically meaningful is the “jiffy”. That’s a portion of a second expressed as a decimal point followed by 43 zeros and a one.

Obviously, creation did not occur then, but at zero time.

Peter Medawar, the Nobel laureate, said it elegantly and concisely: “Science is not equipped to deal with first and last things.”

What happened at the moment of creation, no one knows, and the Big Bang theory says absolutely nothing about it.

You could suppose there is anti-gravity or inflation and if that fits the observations, then it is a good theory. But then you have answered the question with another question: What causes anti-gravity or inflation? Eventually, you reach the point where you just have to say that the theory says so because it agrees with observations.

First, the disclaimers:

  1. I’m not a cosmologist.
  2. This post may just confuse the issue.
  3. I’m working from memory.

Now that that’s out of the way-- there are two different ways that the universe is expanding, in a sense:

A) the universe is expanding because “space” is getting bigger.
B) the universe is expanding because we can see farther with each passing moment.

The outer edge of the observable universe is moving outward at the speed of light simply due to the passage of time. There may be galaxies 1000 billion light-years away, but the light travel time is so long, we cannot possibly know.
If the universe is 15 billion years old (for argument’s sake), we can only see 15 billion light-years out. In a billion years, we’ll be able to see 16 billion light-years, regardless if the space in the universe is actually expanding or not.

This apparent expansion is distinct from the expansion observed in the redshifts, which is actual expansion of space.

When Protagoras said man is the measure of all things he meant that humans can conceive of things (“measure” in the broad sense, that is) only in terms of themselves.
All these metaphors about how stars are “born” and then
“die,” with “youth” and “maturity” in between are examples of conceiving of the stars in human terms. We can’t get outside ourselves. Anaximander in the 6th-century BC, a
little BEFORE Protagoras, said that any particular thing that exists pays the price of existence by being taken down and replaced by another thing that comes into existence (at the first thing’s expense). This explains creation, decay, change. It is obviously a parallel to
the Greek idea of hubris: any PERSON who stands out from the crowd (“above himself”) risks having to pay the price when others want to drag him down. Empedocles said we live in an era of LOVE reigned over by goddess Aphrodite, in which atoms get together by chance, creating haphazardly various combinations of things, only some of which are viable. Then we live in an era of HATE, governed by Ares, in which things fall apart. Then the love goddess takes over again, etc.He referred to these two gods by way of explaining his cosmology. As for science, it is largely self-proving until another theory comes along prompted by thought or else keener observation. Thus you can predict the movements of the planets if you think they follow complicated epicycles, or you can predict their movements if they just move in elipses around the sun… The clumsiness of the epicycle theory probably motivated further thought and observation in the direction of simplification-economy-Occam’s Razor.
Having quarks and/or strings is about as clumsy as things get to the googol power and moves us over into mathematics.
That is, the scientific theory of physics seems to be talking about things coming out of nowhere, mathematical points, and of course there are the elaborate equations with enormous SIGMAS in them and lazy eights such that the line between mathematics and physics is blurred or shimmering, like the line between reality and fantasy. I think mathematics is the only exception to Pythagoras’ or the Deconstructionists’ ideas of our being bound by our language. However, mathematics is also a language, so maybe not, yet it does seem to have something transcendental about it… Which takes us to Pythagoras’ “All is number.”