Understanding the Expansion of Space: A Scientific Perspective

[dad]

It does not depend on assumptions but the definition of the method of measurement.

We shall see.

What we actually do know is what we can observe and measure.

We shall see.

So, how do we measure mass, length and time at the far reaches of the universe to say whether we "actually really do know" that the universe is expanding or not?

That is the question, yes.

Measurements are a comparison of the properties of those far objects with some set of laboratory defined standard units of M, L, & T that does not change across the intervening millions of light years of space and millions of years of time. In other words we need a conservation principle, something that is conserved and does not change over cosmological distances.

I know. But you miss my point. The state of this present universe may not have been the same in the far past, therefore, using only present observation only tells us about the present.

The standard GR model conservation principle is that of energy-momentum, or in other words, 'rest' mass. The mass of an atom, and therefore its size and atomic frequencies, is defined to be constant and atomic rulers and clocks are thus defined to be standard 'rigid rulers' and 'regular clocks'. In this frame the universe expands around a fixed ruler.

So you seem to think. But, aside from redshift, and CMB, how do we actually know this??

However in a mass field theory, such as Hoyle's, the ruler itself changes size, and clocks 'speed up', relative to the laboratory standard. In SCC in the Jordan conformal frame where the conservation principle is that of energy, an eternal universe is static with exponentially shrinking rulers and 'speeding up' clocks. The ruler shrinks in a static universe.

Interesting speculation. I was more concerned about what we know.

"Is space really expanding?" - It depends on how you measure it.

So, is it possible to actually measure such a change in the standards of measurement? In SCC this is possible by comparing the atom against a representative photon, such as one sampled from the CMB.

Such a photon when measured by such an atom will appear to exhibit red shift, not because the photon has lost energy but because the atom has gained mass.

"Self-creation cosmology (SCC) theories are gravitational theories in which the mass of the universe is created out of its self-contained gravitational and scalar fields,"
Speculation, in other words on how mass came about in our universe.

Not a way we know that the universe is expanding. That is simply one of a number of theories quasi relating to the issue.

 

[dad]

To Dad:

I am not exactly sure what you are trying to dispute, perhaps you could organize your responses in a more logical manner? You seem to display the mentality that everything is assumed, speculated and conjectured without evidence. If one wants to dispute the notion of past and future, one should evaluate the logic.

Some feel that there is an afterlife, for example. A place, as we know, most call heaven. If there really were such a place, the universe would have to undergo a complete state change. Things here, we know, are not eternal, not even the sun. In fact, a new heavens and Earth are claimed to be on the way by some.

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?

It is perfectly natural to assume that the physics in the past are causally related to the physics of today and the physics of the future, because it requires an additional assumption to consider otherwise.

Well, if one did not want to use any other assumption, it matters not. The only thing that does matter is to be able to defend the ones we do use! That cannot be done by science for or against a same or different state past or future.

You would actually have to construct an additional postulate, in that the physics of the universe were some how different than they are today and then engineer a model which describes this. We are merely inducing from observation (from several different methods) that the physics are the same.

That is already done in a model where the spiritual and physical are together in an eternally stable state.

However, if you want to dispute the notion of causality altogether, that is a philosophical discussion of science initiated by the great David Hume and not relevant to the discussion of pure science.

No, under normal observed limits, the same past (recent) is very evidenced.

If you are merely asking for the causal relations between the scientific discoveries and theories, that is perfectly acceptable and I am sure you will receive more than enough information from our knowledgeable PFers!

I explained where I was coming from. I think it is impossible to prove a same past, that all science depends on, and assumes as a foundation for past ideas.
So, how do we know the universe is expanding?? (aside from redshift, and CMB, for the reasons I outlined)

 

[InfinityDelta]

The universe is gaining speed as it expands, yet I personally dislike this because it destroys my 2nd theory for the Big Bang, unless the last universe did collapse.

 

[dad]

The universe is gaining speed as it expands, yet I personally dislike this because it destroys my 2nd theory for the Big Bang, unless the last universe did collapse.

You think you know it is gaining speed how? Redshifted light??

 

[russ_watters]

You already know the answer to that question, dad. We only have the best information we have. No we aren't certain of anything, but we draw the most reasonable conclusions based on the available evidence.

 

[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.