What are the explanations for greater than C space-time expansion?

[wucko]

The universe is expanding as observed by cosmological redshift - faster than the speed of light, and the speed of expansion is increasing.

 

How exactly is this reconciled with the speed limit of C?

 

 

Here is a proposal:http://www.scienceforums.net/topic/66209-the-speed-of-light-and-discrete-notions-of-space-and-time/page__p__675852#entry675852

[StringJunky]

No laws are violated because space is being created between non-gravitationally bound objects ie the objects themselves are not actually experiencing any acceleration due to the expansion.

[wucko]

i like the idea that infact only time is being "created" (and had been forever), but space is discrete.

[swansont]

i like the idea that infact only time is being "created" (and had been forever), but space is discrete.

!

Moderator Note

You can ask questions or hypothesize and answer, but you can't do both. Mainstream science is what's discussed in the science sections. Speculative material belongs in Speculations.

[questionposter]

What is it being created from?

[ajb]

What is it being created from?

 

You maybe better off thinking 4 dimensional in the first place. That way space-time is not created, nor does it need anything to expand into. By expansion we are talking about the "size" of the 3-spaces embedded in the space-time. You can think of our Universe as a series of 3-spaces all piled on to of each other paramaterised by time. There are technicalities here and you cannot always do this in a meaningful way for general space-times.

 

Anyway, there is no violation of any of the rules of relativity when you have expansion of the 3-space at at rate faster that the speed of light. No physical objects are going past each other faster than the speed of light.

[khaled]

is it possible that this universe is a huge quantum environment, that since it was created, its physics laws were adjusted ?

[mindless]

In my experience as a scientist once an hypothesis has more than one speculative connection your chances of being wrong rise horrendously. If I have an hypothesis that says "suppose A gives rise to B according to my hypothesis" I have a reasonable chance of a successful theory, if I then add another "suppose B gives rise to C..." my chances of being right are, for various reasons, much worse than the product of the two probabilities. The main reason that chains of hypotheses are not worth anything is that the result of any hypothesis in the chain is always ill defined. A does not give rise to B, it gives rise to something that is almost like B, the next step in the chain is then a hypothesis that "something almost like B gives rise to C"...

 

So what are the chances of cosmological speculations involving multiple steps, that cannot by definition ever be tested, being right?

 

That said, four dimensional pseudo-Riemannian geometry is worth studying.

[juanrga]

The universe is expanding as observed by cosmological redshift - faster than the speed of light, and the speed of expansion is increasing.

 

How exactly is this reconciled with the speed limit of C?

 

 

Here is a proposal:http://www.sciencefo...852#entry675852

 

The speed limit of c refers to the ordinary velocity of a body moving in spacetime. The cosmological speed of expansion is not related with an ordinary velocity but it is the rate of metric 'creation' of space itself and can be larger than c without violating any known law.

[michel123456]

You maybe better off thinking 4 dimensional in the first place. That way space-time is not created, nor does it need anything to expand into. By expansion we are talking about the "size" of the 3-spaces embedded in the space-time. You can think of our Universe as a series of 3-spaces all piled on to of each other paramaterised by time. There are technicalities here and you cannot always do this in a meaningful way for general space-times.

 

Anyway, there is no violation of any of the rules of relativity when you have expansion of the 3-space at at rate faster that the speed of light. No physical objects are going past each other faster than the speed of light.

 

Bolded mine

 

Does that mean that when space expands, time expands too? so that the ratio space/time remains equal?

[pmb]

i like the idea that infact only time is being "created" (and had been forever), but space is discrete.

There is no basis on saying that time is being created is if time had that property. When you say that you must change the definition of time since the current one won't get you to your notion of it. Time is a measure of how things in our world change. The property of creation doesn't belong to that definition. And the idea of space being discrete is also meaningless.

 

What you've said here just cannot be given a meaning

 

!

Moderator Note

You can ask questions or hypothesize and answer, but you can't do both. Mainstream science is what's discussed in the science sections. Speculative material belongs in Speculations.

 

swansont - You're being too gracious. Nothing of what he said can be given a meaning so it doesn't belong in speculations.

 

And I'm saying that from a point of view of a physicist who enjoys and appreciates that forum. It is hopeful that someday someone will come up with something useful. I'd hate to see that forum littered with nonsense pseudo-science and crackpottery. Is that a word?

 

Does that mean that when space expands, time expands too? so that the ratio space/time remains equal?

Not in my opinion.

 

It's easier to sit on these things a while and tell yourself that you're in the position to answer that yourself before you need to bounce it offsomeone. E.g. What possible meaning can "time expands" be given? What does "expand" mean? Does it, or can it, apply to time? If so then try t think of an example of how to measure expand and ask yourself does spatial expansion need to be there in order for time to expand. Etc. etc. etc. I think that eventually you'l be in a much better position to ask your question at that point.

 

People want to apply similar meanings to time as they do to time and vice versa. This is Minkowski's fault with his famous article where he says space and time will dsappear and only a kind of union will remain. He never hinted on how to do it or what'd mean. What remained after his paper was a clear notion that time and space play a role where they are analogous, not the same. Even the metric tells us that. Measurment and obsvation area all quite different for space as they are for time.

 

Let me relay the following. From Nature No. 2677, Vol. 106, page 783

From this it follows that, in respect of its role in the equations of physice, though not with regard to its physical significance, time is equivalent to the space co-ordinates (apart from the relations of reality).

People have a talent for not getting this part. I think its because certain people get turned on by understanding things that others don't understand. And the properties of spacetime is one thing that people just don't understand so accepting without query what Minkowski stated causes all sorts of misleading things. (sigh)

 

I can also send this article to those who wish to read it in e-mail if I've already scanned it into a PDF file alreadt. If not then I can't do that anytime soon.I just can't take sitting in front of my computer anymore this weekend ery much. So off I go to the couch for the rest of today. More tommorow.

[mindless]

Time is a measure of how things in our world change.

 

Time is a hugely complex subject. The Time of Relativity theory is undoubtedly akin to a negative spacial dimension (cf Weyl's analysis), recent experiments on quantum interference through time reinforce this view (see Lindner et al 2005). The time of Change is highly correlated with the dimensional time of Relativity but may not be exactly the same, for instance according to Multiverse theories two differing outcomes may coexist and be derived at the same location in a common spacetime. The time of causation is also problematical, as Reichenbach pointed out, the spherical symmetry of spacetime means that although chains of cause and effect can be pursued into the future it is difficult to pursue them into the past - for instance try to calculate the inverse of a spreading ripple from a needle dipped into a pond so that the disturbance at the edge of the pond ends up as a dip in the water surface at the exact place that the needle entered. Even more complex, try to think of something that exists for no time at all. Can an object have no temporal parts?

 

Lindner, F., Schaetzel, F.G., Walther, H., Baltuska, A., Goulielmakis, E., Krausz, F., Milosevic, D.B., Bauer, D., Becker, W., and Paulus, G.G.. (2005) Attosecond double-slit experiment. Phys.Rev.Lett. 95,040401 (2005)

Edited May 20, 2012 by mindless

[IM Egdall]

The universe is expanding as observed by cosmological redshift - faster than the speed of light, and the speed of expansion is increasing.

 

How exactly is this reconciled with the speed limit of C?

 

 

Here is a proposal:http://www.sciencefo...852#entry675852

 

There is no need to reconcile. Special relativity says nothing (no information) can travel faster than the speed of light through space. General relativity says there is no limit to how fast space itself can expand.

[michel123456]

There is no need to reconcile. Special relativity says nothing (no information) can travel faster than the speed of light through space. General relativity says there is no limit to how fast space itself can expand.

 

So there is no limit to how fast space-itself can expand? Can space expand at infinite rate?

 

And after some more thinking:

The word "fast" refers to speed. Speed refers to an amount of space divided by an amount of time. Since space-itself is expanding, can we talk about the speed of expansion? Is this an expansion of 1 meter/sec? Or 500000 km/sec? Can one ask "how fast" does space-itself (the metric) expand?

Edited May 23, 2012 by michel123456

[zapatos]

So there is no limit to how fast space-itself can expand? Can space expand at infinite rate?

 

And after some more thinking:

The word "fast" refers to speed. Speed refers to an amount of space divided by an amount of time. Since space-itself is expanding, can we talk about the speed of expansion? Is this an expansion of 1 meter/sec? Or 500000 km/sec? Can one ask "how fast" does space-itself (the metric) expand?

A recent 2011 estimate of the Hubble constant, which used a new infrared camera on the Hubble Space Telescope (HST) to measure the distance and redshift for a collection of astronomical objects, gives a value of H0 = 73.8 ± 2.4 (km/s)/Mpc.[9][10] An alternate approach using data from galactic clusters gave a value of H0 = 67.0 ± 3.2 (km/s)/Mpc.[11][12]

http://en.wikipedia.org/wiki/Hubble's_law

[michel123456]

http://en.wikipedia.org/wiki/Hubble's_law

 

Hm.

at the question "how fast is space-itself expanding"?

the answer is:

2.3×10−18 inverse seconds.

 

Ref: The Hubble constant has units of inverse time, i.e. ~ 2.3×10−18 s−1

Edited May 23, 2012 by michel123456

[IM Egdall]

So there is no limit to how fast space-itself can expand? Can space expand at infinite rate?

 

Hmmm. Interesting. Recent observations say the expansion of space is accelerating. No one knows what is causing the expansion to speed up -- its been given the name dark energy. If we assume this mysterious dark energy stays the same over time (a big assumption since we don't know what it is) and we assume the universe will exist for an infinite amount of time, then I guess this says the expansion of the univere will reach an infinite rate.

 

Have I missed something here? Comments?

 

.

[imatfaal]

Hm.

at the question "how fast is space-itself expanding"?

the answer is:

2.3×10−18 inverse seconds.

 

Ref: The Hubble constant has units of inverse time, i.e. ~ 2.3×10−18 s−1

 

The inverse seconds units can be thought of as (meters per meter) per second: ie a ratio of growth in size per second. The two length measurements are in the same units so they cancel out to leave only a ratio. Because the rate of growth is so small - most usage will be in kilometres growth per megaparsec per second; ie each second what was a megaparsec is increased by a kilometre.

[wucko]

What is it being created from?

 

if you mean time, its not created of anything. it builds up.

The speed limit of c refers to the ordinary velocity of a body moving in spacetime. The cosmological speed of expansion is not related with an ordinary velocity but it is the rate of metric 'creation' of space itself and can be larger than c without violating any known law.

 

@'creation' of space: i like to think about creation of 'time' only. the expansion thus becomes an effect of time solely. (as an hypothesis (@moderators))

my explanation is this:

 

space-time is expanding faster than C because only time is expanding it. No space is created, only time causes this. its a hypothesis yes. and it works splendidly if you reverse t.

Hmmm. Interesting. Recent observations say the expansion of space is accelerating. No one knows what is causing the expansion to speed up -- its been given the name dark energy. If we assume this mysterious dark energy stays the same over time (a big assumption since we don't know what it is) and we assume the universe will exist for an infinite amount of time, then I guess this says the expansion of the univere will reach an infinite rate.

 

Have I missed something here? Comments?

 

.

 

my hypothesis is: acceleration is apparent, what couses expansion is time. (not space-time expansion, only time expansion). it then appears that events 'further away' (in time), are 'mooving away' faster, because any given non-local time-point has a history-line of its own, so the discrete 'time-points' add up uppon each other so that the observable dillation is an acceleration.

[Strange]

 

space-time is expanding faster than C

 

Note that expansion is not measured by velocity, so this statement is meaningless. Expansion is a proportional increase in distance between two points. This is why the separation speed is proportional to distance.

 

As a result there are inevitably points that are far enough apart that their speed of separation will be greater than c. We can see galaxies that are receding at more than the speed of light.

 

Also worth noting that the light speed limit comes from the (special) theory of relativity while the expansion of the univers is described by the (general) theory of relativity. Therefore there cannot be any conflict.

[Schneibster]

What is it being created from?

 

There is no requirement to create spacetime from anything. Since it's empty, i.e. nothing, it can be created from nothing.

 

It's more correct to ask "what creates it," and the answer is the Casimir effect/cosmological constant/dark energy. Just as it pushes two plates together in the laboratory, it pushes space apart.

 

And in answer to the OP, since spacetime is nothing, it's massless and can exceed the speed of light.

 

Also there is an error in your question: we cannot see anything going faster than light. The point beyond which galaxies are receding faster than light is called the "horizon" and we can see nothing beyond it.

Edited April 6, 2014 by Schneibster

[Strange]

Also there is an error in your question: we cannot see anything going faster than light. The point beyond which galaxies are receding faster than light is called the "horizon" and we can see nothing beyond it.

 

Actually, its not that simple (which is one reason we know that red shift is due to the expansion of space and not the Doppler effect, which would give different results.

 

http://arxiv.org/abs/astro-ph/0310808

 

We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light.

[Schneibster]

 

http://arxiv.org/abs/astro-ph/0310808

 

I learn something new every day. Thank you.

 

However, I'll also point out that there is still a horizon.

Also, its worth saying that another explanation for greater-than-c-spacetime-expansion is that it is empty space being created everywhere between, somewhat offset by other geometric effects. This is clear from the Einstein Equation, which is the master equation from which the ten equations of the gravity field are derived:

 

G_uv + Λg_uv = 8πG/c^{4 x}T_uv

 

Lambda, then, Λ, is pushing space apart, except where it is opposed by g_uv, the metric tensor.

[Mordred]

The terms created, stretched etc is VERY misleading. Space itself has no substance, fabric or energy. Space is simply geometric volume that is simply filled with the contents of the universe. However an important consequence of having a region of volume is that you will have a vacuum energy-density at the very least. This does not mean that the volume has a fabric or energy property. A volume of space is simply a filled region. Space geometry changes due to gravity is simply a descriptive of its energy-density distributions. The term warping of space is also a poor and misleading descriptive.

[michel123456]

The terms created, stretched etc is VERY misleading. Space itself has no substance, fabric or energy. Space is simply geometric volume that is simply filled with the contents of the universe. However an important consequence of having a region of volume is that you will have a vacuum energy-density at the very least. This does not mean that the volume has a fabric or energy property. A volume of space is simply a filled region. Space geometry changes due to gravity is simply a descriptive of its energy-density distributions. The term warping of space is also a poor and misleading descriptive.

I agree that it is VERY misleading. You have explained why it is misleading.

Now it remains to explain clearly what the expansion of space means.

If a volume of space is simply a filled region, it means, as I naively understand, that when space expands there is a larger volume of space with more stuff inside it.

Not that anything else happens.