Understanding the Expansion of Space: A Scientific Perspective

[InfinityDelta]

Yes, the universe is, because the average density of space is less than 3 hydrogen atoms per cubic meter, so the universe will keep expanding forever.

 

[dad]

Yes, the universe is, because the average density of space is less than 3 hydrogen atoms per cubic meter, so the universe will keep expanding forever.

You sound fairly certain of that. Russ seems a little less certain. So, what is it you think that that the present spacing out of hydrogen atoms per cubic meter has to mean, and why?

 

[MeJennifer]

We cannot evidence that, or say true or false. It is out of the scope and concern of science. If there were such a state in the far past, basically a different universe, we likewise could not tell. In other words, we cannot prove with science that the state of the universe in the past was as it now is!
Personally, I suspect the universe was in a different state, one that included the spiritual, and physical. Something changed, and we were left in this physical only state, separated from the spiritual. A state that is literally, temporary.
That is why, looking at light far away, or redshift, or the CMB, etc. is not looking in the far past after all. It is simply looking far away. We have assumed that light coming from there, taking billions of years meant that it took that long for the light to get here. In effect, that is simply assuming that it was always as it now is.
Light in the former state could have gotten here in days, for example. A different light, in a different state universe. As it was changed, we were left with the slow light we now have. Similarly, such a universal state change could leave light redshifted, in a pattern as we now see (more shifted the further we get out). Same thing with the CMB.
Far as I know, there is nothing science can do to prove, or support, observe, evidence, etc that the past was this same state. That is nothing but an assumption.
So, that would leave us in a temporary present state, with the future, and past being in different states. Anything but a 'steady state'. This could explain a lot, even things quantum. (If waves do go to and from the different past and future, we in the present would consider their behaviour hard to understand)
So, yes I know full well that the past state is but assumed. -No?

Let me ask you this: would you agree that if we had a universe without mass and energy that such universe would expand?

Think of a very simple model of a universe that starts with a point where we emit photons in all directions, so that we get an expanding sphere.

Then consider the following situations:

A universe without mass and energy will expand forever, since the area of the expanding sphere will continue to increase.

A universe with some mass and energy will expand forever as well but the area of the sphere increases slower than in the first case. The decreasingly negative contribution to the area of the sphere by the curvature of space-time reduces the rate of increase of the area of the expanding sphere but overall the area still increases. Effectively the expansion accelerates here since the negative contribution to the area of the sphere decreases over time.

A universe with exactly a critical amount of mass and energy will seize to expand, the area of the sphere remains constant. The negative contribution to the area of the sphere by the curvature of space-time completely compensates for the expansion of the sphere.

A universe with more than a critical amount of mass and energy will seize to expand, the area of the expanding sphere decreases. The negative contribution to the area of the sphere by the curvature of space-time actually reduces the area of the expanding sphere and the surface is trapped, it can only get smaller.

 

[dad]

E=MeJennifer;1279000]Let me ask you this: would you agree that if we had a universe without mass and energy that such universe would expand?

Think of a very simple model of a universe that starts with a point where we emit photons in all directions, so that we get an expanding sphere.

Then consider the following situations:

A universe without mass and energy will expand forever, since the area of the expanding sphere will continue to increase.

A universe with some mass and energy will expand forever as well but the area of the sphere increases slower than in the first case. The decreasingly negative contribution to the area of the sphere by the curvature of space-time reduces the rate of increase of the area of the expanding sphere but overall the area still increases. Effectively the expansion accelerates here since the negative contribution to the area of the sphere decreases over time.

Hypothetical questions, all. The basic assumption is here, that all we had to begin with was matter similar to the kind we now have. Then, you imagine how it 'must' have worked. But stick to what we know. Do you think you know that matter in the past was as now? What if the state of the universe was different then? In the example I gave, with BOTH, the spiritual, and physical together. If that 'forever state' did exist, rather than the physical only state we now see, none of your ideas apply.

A universe with exactly a critical amount of mass and energy will seize to expand, the area of the sphere remains constant.

Again you are talking of physical only matter, as we are familiar with. Wouda, could have shoulda, and what if.

The negative contribution to the area of the sphere by the curvature of space-time completely compensates for the expansion of the sphere.

Our present space time. What can you offer to prove that the state of the universe will be, or was the same? Let me answer for you. NOTHING. Therefore your whole scenario is based on a same state past. It is based, in other words, on something that is nothing at all more than an assumption. An assumption that cannot be supported by fact, observation of man, evidence, or science.

A universe with more than a critical amount of mass and energy will seize to expand, the area of the expanding sphere decreases.

No! A physical only state universe as we now know it, would expand...etc.

The negative contribution to the area of the sphere by the curvature of space-time actually reduces the area of the expanding sphere and the surface is trapped, it can only get smaller.

So, what are you saying? Do you think that the universe is really getting smaller?

 

[MeJennifer]

Hmm, I actually attempted for you to understand by giving some examples, I seem to have failed miserably.

 

[Garth]

Hmm, I actually attempted for you to understand by giving some examples, I seem to have failed miserably.

Don't waste your time MeJennifer, you tried.

 

[dad]

Hmm, I actually attempted for you to understand by giving some examples, I seem to have failed miserably.

Well, in the context of normal physics, assuming that it was this state that existed at creation, your scenario is good. But what can get us from here to there??
"a very simple model of a universe that starts with a point where we emit photons in all directions, so that we get an expanding sphere."
If we look at claims of the future, where some envision a new universe, where there is no state of decay, and a different light, etc etc,- how would that be measured by this temporary universe? In other words, of course we really don't know the state of the universe in the future.
Like you have tried to do with the past, one can say, IF it were the same in the future, then we would see the sun burn out, galaxies crash, etc etc.
Same with the far past. IF the universe were just physical at the time, it had to have come from ..such and such.
So, how do you know it was in this same state, any more than the future will be?? My point is that all we really know is the present state of the universe. (some thousands of years of observation). The rest is pure belief. How could anyone really call that science??

Science, in other words, has real limits. Dreams of what the future would be like, or what a far past was like cannot be proved, supported, observed, tested, etc.

 

[russ_watters]

This thread is done.

Dad, this is a physics site. As such, discussions must be grounded in physics. This is not a place for religious speculation, or worse, religiously motivated attacks on science.