Discussion in 'Astronomy, Exobiology, & Cosmology' started by amraam, Nov 12, 2001.
I do not disagree by your definition of the terms.
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A singularity has zero volume, and an infinite universe has infinite volume.
Keep in mind that the universe may also be finite.
The Universe has been shown to have an accelerating expansion thus defying the critical density and making it infinite.
The difference between calling the Universe a singularity or infinite is that a singularity is a single point, the Universe, from our dimensional viewpoint is a large spread/expanse.
But who is to say that a singularity does not, in some higher dimension, say the 11th dimension, have greater volume than the Universe? That is where this all gets complicated, under string, superstring and M-theory.
<i>The Universe has been shown to have an accelerating expansion thus defying the critical density and making it infinite.</i>
An accelerating universe does not have to be infinite. In fact, most astronomers think our universe is finite. The density of matter is thought to be greater than the critical density, but there's also "dark energy".
Yes but there is another way of looking at it. If the universe is infinite then it is all that there is with 'nothing' outside of it, if it is a singularity then likewise it is all there is with 'nothing' outside of it. From inside the universe the two conditions are indistinguishable.
The universe may be finite but in that case it exists in the cosmos, which is not. I think this is just a choice of definition.
They are quite distinguishable, because you're not likely to find anyone alive in a point of infinite temperature. Mathematically, there is a difference between zero and infinite volume, though we can't imagine either.
I don't know what you mean by cosmos. Are you implying there is some kind of multiverse outside our expanding universe, or do you just mean space-time as a whole?
Hmmm..."dark energy" is very much a flawed concept in astronomical terms, it relies very much on highly theoretical hypotheses, whereas astronomy is observational mainly. Because the Universe has an accelerating expansion it will never experience a Big Crunch to "close" the Universe, but it will remain in an "open" state and just expand forever, thus making it infinite. The major point missing here is a defintion of infinite. At the moment, the Universe is, in fact, infinite because we cannot define its edges because as soon as you do define those edges then they will have moved outwards. It is just like a road map, each time a new road map is commissioned, it becomes instantly out of date due to new building of roads etc. Also, defining the Universe also becomes subject to the Heisenberg Uncertainty Principle.
If the universe is all there is then it seems unreasonable to say that once it had zero volume and now it is infinite. Where did all that volume come from? Surely the universe is no more or less than it ever was (a closed system in other words). High temperatures damage human beings but lets not be anthropomorphic. Can you clarify what we should both be meaning when we say 'singularity'. Is it a non-point or a very small one? I ask because this may be what we disagree about.
I was trying to avoid a misunderstanding caused by our definition of universe. Some people mean this universe, one among many in a multiverse, and some people mean everything that there is.
Well you're running into the absurdity of a singularity. In the case of an infinite universe, the overall size is constant. Space is infinite now, and always will be. A t=0 this universe vanishes, but that is only because there is no quantum theory of gravity. The infinites of GR should be replaced by something finite, which should mean the infinite universe remains infinite even at the very beginning.
We're talking about infinite temperature here - where even atoms cannot form. But again, this is one of the absurdities of a singular universe. You have infinite temperature in a point of zero volume.
Ok, but "all that there is" could still be finite.
Agree with the rest of your post but not this. Is there a fence around it or what?
There is nothing logically inconsistant about a finite universe. The concept of infinite space is just more of what we're used to thinking of.
Are you sure? It seems to me that there is.
Well it might be my lack of imagination but I cannot conceive of there being an end to the cosmos. Why would it end? What would be 'outside' of it. What law of nature would detirmine that their were limits to its existence? How would we know if we reached the edge? How could it be both eternal and finite?
Also I have a problem with the idea that infinities can exist within a finite cosmos.
I also find it hard to imagine anything like that, but that isn't a logical inconsistancy. It is only a flaw of our limited human intuition.
If the universe is finite, there is no outside. It can be a hypersphere or have a hyperbolic shape, which means there would be no edge or center. I'm sure you've heard of the balloon analogy, and that applies here. The curved 2D surface represents the universe, with no inside or outside space. A 2D person could go in a straight line and if he went far enough, he would wind up right back where he started. The problem is that this is only a 2D analogy, and we cannot possibly imagine what a curved 3D surface looks like. But we can mathematically define it, and this the picture cosmology paints for our universe.
But it does seem hard to believe that space could be finite. When we consider that infinity is the only alternative, it seems somewhat easier to believe.
I agree generally with what you said but still wonder what it means, what it tells us, that we cannot conceive of a cosmos that is finite without invoking all sorts of intellectual complications. Also Mr. Occam's razor suggests that the pragmatic and sensible hypothesis is that it is infinite.
I disgree with the bit of your post I have quoted. By some quirk of my neurons I find it easier to believe in infinity.
<i>Hmmm..."dark energy" is very much a flawed concept in astronomical terms, it relies very much on highly theoretical hypotheses, whereas astronomy is observational mainly.</i>
Astronomy is observation. Astrophysics is very much theoretical.
What is flawed about dark energy, in particular?
<i>Because the Universe has an accelerating expansion it will never experience a Big Crunch to "close" the Universe, but it will remain in an "open" state and just expand forever, thus making it infinite.</i>
The terms "closed" and "open" have very specific meanings in cosmology. As I said before, most astronomers currently believe the universe is closed, despite the fact that the expansion seems to be accelerating. Whether the universe is closed or open depends only on the total mass density.
Well, when you accept that curved space is gravity, the notion of closed finite universes does not seem that complicated.
But I agree that an infinite universe is easier to grasp at first thought. That is, until you start to look at the concept in more detail. Infinite space. Infinite galaxies. Infinite earths. Infinite people identical to yourself. No wonder such a concept has driven people mad. It's too bad there are only 2 options - as both an infinite and finite space seem difficult to swallow.
Infinite space yes, (although bounded , as in foamy-space).
Infinite Galaxy's and planets etc , no.
there was only so much matter made during the big-bang.
I you look at the baryon density and photonic density there is a ratio of 1 billion to one.
This gives a upper mass limit to the production of baryonic matter in the universe. ( lets say 10 ^80) So there can only be a limited number (although astronomical).
The recent findings of the MAP probe have shown that there is not enough mass in the universe to close it, therefore it is open.
There are other lines of research that show that the number of `omega`(i wont explain) is within 10^60 decimal places of being flat!
For all intents and reasons i would imagine that the universe IS flat (with not one electron more or less) so that the universe will expand forever....
An infinite universe has an infinite amount of energy, hence an infinite number of galaxies.
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