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Offline chris

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We think that the early Universe expanded very rapidly - known as rapid inflation - exceeding the speed of light, which the expansion of the Universe today continues to do.

How is this compatible with light being the fastest thing in the Universe?

Chris


 

Offline lightarrow

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How is the Universe able to expand faster than light?
« Reply #1 on: 06/03/2009 14:52:42 »
Because it doesn't expand in space.
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #2 on: 06/03/2009 15:07:11 »
Because it doesn't expand in space.
Do you mean that space expands, but the light in that space doesn't expand with it? I have trouble getting hold of the expanding space concept. For example, as space expands, do stars become farther apart? Do galaxies become farther apart? Is the expansion uniform everywhere? Do the more distant galaxies seem to expand more rapidly simply because there is more expanding space between us and them?

It hurts my brain just thinking about it. I kinda hope someone comes up with a better explanation for the apparent expansion.
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #3 on: 06/03/2009 15:36:20 »
A very tricky question indeed :)

There is no real relation at all, and that's why 'inflation' is introduced as a explanation.

If you were standing on a very high mountain at night time and first looked to your left and then to your right, you would notice that the starry sky would look 'the same'. The galaxies as well as the stars would seem like 'mirrored' in both directions, with the same type of displacement in 'space'.

When you take those two 'looks', remembering that the universe is said to be 13.7 billion years old, any direction you choose to look, then your combined age will be two times that, right. So you, by sight, have now 'ftl' encompassed 27.4 billions years:) But the light that comes to you from any direction have only been able to travel at most 13,7 billion years, not 27.4 billion.

If the Universe is limited by lights speed 'c', which we count in light years, then why is it that those two observations you made is so extremly 'similar' in matter of size and distribution of heavenly bodies? It have been given a name now btw.
It's called 'The Cosmological Principle'.

It's like they are 'mirror images' of each other?
But there is no way light or gravity could have 'communicated' any 'information' between them as both travel at 'c'?? And 'Information' as written here should be seen as 'any sort of physical interaction'.

So why would our universe be 'homogeneous' in appearance?
We have the uncertainty principle in QM stating that "increasing the accuracy of measurement of one observable quantity increases the uncertainty with which another conjugate quantity may be known". looking at it that way, how can everything be the 'same' as the 'conjugate quantity's' here is those two realities to the right and left of you on that mountaintop, not ever being able to 'exchange any information' as light haven't yet reached both sides. And, then there is the fact that 'CMB' the cosmic microwave background radiation is almost precisely the same temperature everywhere, about 2.725 K.

There is another problem too. That's called the 'flatness problem'.
It questions how the average density parameter can be of the order of 1?

The 'density parameter' is related to the ratio of the amount of matter in the universe and the amount needed to stop expansion. "The standard big-bang theory suggests that once this parameter deviates even slightly from 1 it very quickly approaches an asymptotic value far away from 1 for open or closed universes." Another explanation would be that when the universe is at '1' the current density of the universe is very close to its critical value at which space is perfectly flat.

A density parameter between 0 and 1 would mean an open universe that would continue expanding forever and a density parameter of 1 would mean a flat universe in which expansion slows but never truly stops. Would it be greater than 1 it would mean a closed universe. A density parameter of 5 for example would mean that the Universe should be younger than its oldest rocks:)

So how come it's at 1?

"According to Einstein's field equations of general relativity, the structure of spacetime is affected by the presence of matter and energy. On small scales space appears flat – as does the surface of the Earth if one looks at a small area.

On large scales however, space is bent by the gravitational effect of matter. Since relativity indicates that matter and energy are equivalent, this effect is also produced by the presence of energy (such as light and other electromagnetic radiation) in addition to matter.

The amount of bending (or curvature) of the universe depends on the density of matter/energy present."

We can measure this by looking at how light 'bends' around massive objects like stars giving us an idea of the current density. We can also use the Cosmic Microwave Background (CMB) and the relative frequencys of Type-Ia supernovae at different distances from Earth as measurements.

"Data from the Wilkinson Microwave Anisotropy Probe (measuring CMB anisotropies) combined with that from the Sloan Digital Sky Survey (observing Ia supernovae) constrain Ω0 to be 1 within 1%"

"Indeed, a very small departure of Ω from 1 in the early universe would have been magnified during billions of years of expansion to create a current density very far from critical. In the case of an overdensity (ρ > ρc) this would lead to a universe so dense it would collapse into a Big Crunch in a few years or less; in the case of an underdensity (ρ < ρc) it would expand so quickly and become so sparse it would soon seem essentially empty, and gravity would not be strong enough by comparison to cause matter to collapse and form galaxies. In either case the universe would contain no complex structures such as galaxies, stars, planets and people."

So both  of those phenomena need an explanation and there is where 'Inflation' comes in. "Currently, inflation is the only theory that explains why the observable Universe is both homogeneous and causally connected. During inflation the Universe expanded a factor of 10^54, so that our horizon now only sees a small piece of what was the total Universe from the Big Bang."

And all of this goes into (with the later seen 'expansion') why our universe can be 'bigger' than it 'age' 13.7 billions year. There are different numbers for its possible size, but this wiki http://en.wikipedia.org/wiki/Observable_universe gives it as about 93 billion light-years.

So that's how I understand we have come to the idea of 'inflation'.


--------

It's like a very big puzzle, and to get the real 'volume' of it you will need to look at redshift too.

Here is an alternative view of it :)
http://metaresearch.org/cosmology/DidTheUniverseHaveABeginning.asp
« Last Edit: 06/03/2009 20:08:47 by yor_on »
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #4 on: 06/03/2009 17:28:51 »
That is a very interesting paper yor_on; it is a little dated; it seems to be about 20 years old.

The one thing I find most difficult to explain in opposition the the BB theory is the time dilation observed in type 1A supernovas. But I used to do experiments at Bell Labs, and I remember how difficult it was to arrive at any outcome that was not in agreement with prevailing thought. When the outcome agreed, the experiment was over quickly and reported. When the outcome didn't agree, the experiment lasted much longer, and sometimes didn't get reported at all.
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #5 on: 06/03/2009 17:55:46 »
Sorry Vern :)
I read it and I liked it.
And I should have looked on the sources perhaps, I definitely missed the 'best of' date here.

I introduced it hoping for a discussion though.
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #6 on: 06/03/2009 18:36:34 »
It was interesting as I said. It didn't have the latest 1A supernova studies in it and these, if they are real, are very damning to ideas trying to avoid the expanding universe concept.

This is the sentence that dated the material:
Quote from: the link
In 1993, another supernova was seen in a galaxy at redshift z = 0.43. Details of an analysis of those observations are eagerly awaited.
« Last Edit: 06/03/2009 18:40:44 by Vern »
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #7 on: 06/03/2009 18:42:43 »
So do you have a good link to those studies?
 

Offline swansont

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How is the Universe able to expand faster than light?
« Reply #8 on: 06/03/2009 18:59:22 »
We think that the early Universe expanded very rapidly - known as rapid inflation - exceeding the speed of light, which the expansion of the Universe today continues to do.

How is this compatible with light being the fastest thing in the Universe?

Chris

c is the speed limit of motion through flat space (i.e. where special relativity applies).  The expansion of space itself is not motion through space, and is not constrained by this limit.  Nothing overtakes the photon, though — it still wins the race.
 

Offline lightarrow

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How is the Universe able to expand faster than light?
« Reply #9 on: 06/03/2009 20:00:54 »
Because it doesn't expand in space.
Do you mean that space expands, but the light in that space doesn't expand with it?
What do you mean? Light moves *in* the space while space doesn't.
Quote
I have trouble getting hold of the expanding space concept.
We are talking of the behaviour of the entire universe and you pretend to have these concepts as clear as the billiards' physics?  :)
Quote
For example, as space expands, do stars become farther apart? Do galaxies become farther apart?
Yes.
Quote
Is the expansion uniform everywhere?
Don't know.
Quote
Do the more distant galaxies seem to expand more rapidly simply because there is more expanding space between us and them?
It seems so, but surely, one day we'll find some little deviations from this rule and so we will have to look for another model of the universe... :)
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #10 on: 06/03/2009 20:16:32 »
You display your usual brilliance lightarrow :) The thing I was trying to understand is: The expanding space contains photons whose wavelengths occupy spacial areas. How can the wavelength not increase as space expands?

We know the wavelength of light does increase with distance, but we attribute that to the Doppler effect.

Edit: Maybe space is expanding and the stuff in it is just going along for the free ride, and not really moving away through space. But if that is true, should we not be able to see that same effect within our own galaxy; after all, it is about a hundred thousand light years across.
« Last Edit: 07/03/2009 02:58:43 by Vern »
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #11 on: 06/03/2009 21:41:40 »
Hmm reading you Vern I got to admit that this also puzzles me. If we by expanding assume that a point in space either somehow becomes more points (Plank sized or:) or that this 'point' just expands doesn't really matters. The question will still be how the wave keeps its 'spatial' form in space. But that is only if we see that wave as something consisting of a entity having a physical locality in space and moving in it the same way 'matter' does.

If the propagation is a 'vibration'  oscillating vertically, touching 'points' in spacetime, and just 'seemingly' traveling a 'real' 3D path in spacetime then the question becomes moot. So that would be a favorite choice for me if it is so. That idea may wreck havoc with a lot of other ideas though :)

I wonder how such an idea could be expressed in a two slit experiment for example?
And why light would follow spacetime's geodesics if so?
 
As well as introduce the question of what it then would exist in except what we can observe. But then again, it seems to my unsophisticated mind not unlike the concept of 'distance' which also seems possible to take under scrutiny, even though we use it at a daily basis without hesitation :) But I'm not swearing by any of those ideas, I just kind of like them ::)) I think, I hope...


--
well, I do hope I do at times.
Ah, think that is:)

----
" If we imagine the wave profile as a solid rigid entity sliding to the right, then obviously the phase velocity is the ordinary speed with which the actual physical parts are moving. However, we could also imagine the quantity "A" as the position along a transverse space axis, and a sequence of tiny massive particles along the x axis, each oscillating vertically in accord with A0 cos(kx - wt). In this case the wave pattern propagates to the right with phase velocity vp, just as before, and yet no material particle has any lateral motion at all. This illustrates that the phase of a traveling wave form may or may not correspond to a particular physical entity. It's entirely possible for a wave to "precess" through a sequence of material entities, none of which is moving in the direction of the wave. In a sense this is similar to the phenomenon of aliasing in signal processing. What we perceive as a coherent wave may in fact be simply a sequence of causally disjoint processes (like the individual spring-mass systems) that happen to be aligned spatially and temporally, either by chance or design, so that their combined behavior exhibits a wavelike pattern, even though there is no actual propagation of energy or information along the sequence. "

Yeah I know :) I like this one
http://www.mathpages.com/HOME/kmath210/kmath210.htm
« Last Edit: 06/03/2009 22:41:03 by yor_on »
 

Offline chris

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How is the Universe able to expand faster than light?
« Reply #12 on: 06/03/2009 22:31:14 »
What is interesting to me is that as space i.e. the Universe expands it makes / creates more space which, in turn, makes / creates more dark energy. Therefore, if the thing that is making space is expanding more quickly than light travels, then whatever makes dark energy is also moveing faster than light, presumably...?
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #13 on: 06/03/2009 22:40:56 »
So do you have a good link to those studies?

This is to Berkley's 1997ff report. It is offered in support of the Big Bang theory. However, they say this supernova blasted forth 11.3 billion years ago. If the life cycle of stars is ten to twenty billion years, how did this thing have time to form since the big bang? Keep in mind that a supernova can not be a first generation star. It burns carbon which can only come from a used up star that lived out its life and died in a blast of its own.

Quote from: the link
With a redshift (or z) of about 1.7, says Nugent, "supernova 1997ff is some 11.3 billion years old, much older -- and much fainter -- than the previous record of z equals 1.2, which corresponds to an age of about 9.8 billion years old." He adds that a supernova at redshift 1.7 "is too far away to have been visible from the surface of the Earth. Only a space-based telescope could have found it."
« Last Edit: 06/03/2009 23:07:53 by Vern »
 

Offline JP

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How is the Universe able to expand faster than light?
« Reply #14 on: 06/03/2009 22:54:31 »
We know the wavelength of light does increase with distance, but we attribute that to the Doppler effect.

Actually, it's due to the expansion of the universe: http://en.wikipedia.org/wiki/Redshift#Expansion_of_space
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #15 on: 06/03/2009 22:59:50 »
Jesus Chris:)
I considered my ideas to be rather 'far out':)
Now you tell me that we have 'dark energy' moving FTL, sort of:)

But, why not, if we have an expanding 'empty' space 'containing' a large potential energy, then perhaps dark energy is a property of those minuscule 'rifts' that is created as space expands. Perhaps they could be a equivalent to 'virtual particles' creating a 'mass effect' while hiding under HUP (Heisenbergs uncertainty princiole).

If dark energy was 'moving' as you suggested, wouldn't that be noticeable for us?
« Last Edit: 06/03/2009 23:16:06 by yor_on »
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #16 on: 06/03/2009 23:05:07 »
Quote from: the link
The most distant objects exhibit larger redshifts corresponding to the Hubble flow of the universe. The largest observed redshift, corresponding to the greatest distance and furthest back in time, is that of the cosmic microwave background radiation; the numerical value of its redshift is about z = 1089 (z = 0 corresponds to present time), and it shows the state of the Universe about 13.7 billion years ago, and 379,000 years after the initial moments of the Big Bang.[50]

This brings up the curiosity; how do we determine the red shift of the CMBR? It is dark-body radiation. What frequencies would one consider if it is just a very narrow band of frequencies?
« Last Edit: 06/03/2009 23:08:51 by Vern »
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #17 on: 06/03/2009 23:08:16 »
We know the wavelength of light does increase with distance, but we attribute that to the Doppler effect.

Actually, it's due to the expansion of the universe: http://en.wikipedia.org/wiki/Redshift#Expansion_of_space


Does that mean that all observed redshift already gave been recalculated and adjusted for this phenomena, or is this a theory without experimental grounding?

---

Or you mean that we don't have to change anything, we just in-cooperate 'expansion' in our current cosmological redshift, sorry I meant 'Doppler effect redshifts ' as 'cosmological' seems to be taken now by this new theory, without needing to change any parameters what so ever?

Didn't the 'expansion' move faster than light after a certain 'distance'?
If that is true we can't really say how big our universe is, can we?
As more and more light will be 'quenched' as space 'grows' faster than light.



« Last Edit: 06/03/2009 23:30:14 by yor_on »
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #18 on: 06/03/2009 23:57:45 »
This wrecks havoc with my new idea :)
If light is redshifted due both to the expansion and the Doppler redshift.
I knew that we had an accelerating expansion but I did not know that we had it incorporated in the redshift seen. What experiments have we done for distinguishing between Doppler redshift versus 'cosmological redshift'?
Is it even possible to construct such an experiment??

-------
But if I get it right this 'cosmological redshift' still , even if incorporated in 'redshift' as seen generally, is a theory? As I can't find any experimental evidence?

Although the accelerating expansion is corroborated by separate sources as "the cosmic microwave background, gravitational lensing, age of the universe and large scale structure, as well as improved measurements of the supernovae according to http://en.wikipedia.org/wiki/Cosmic_acceleration.

Or am I wrong?


« Last Edit: 07/03/2009 00:15:11 by yor_on »
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #19 on: 07/03/2009 00:02:42 »
I think they're going with all cosmological red shift, no Doppler. Remember, this all depends upon the thing, whatever it is, that we call space, having the property of elasticity. If suddenly we discover that space-time is actually inelastic, we will be back to Doppler.
« Last Edit: 07/03/2009 00:09:34 by Vern »
 

Offline yor_on

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How is the Universe able to expand faster than light?
« Reply #20 on: 07/03/2009 00:19:46 »
There's no need for spacetime to be inelastic for Doppler redshift to be correct and cosmological redshift to be wrong Vern :) Just accept that light don't travel same as matter do in spacetime :)
I really like that idea, and i absolutely refuse to leave my new 'child' out in the cold...

So, prove me wrong ::))

---

Maybe I will feel different tomorrow though.
:)
« Last Edit: 07/03/2009 00:22:32 by yor_on »
 

Offline Vern

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How is the Universe able to expand faster than light?
« Reply #21 on: 07/03/2009 01:32:26 »
I can see a real problem though. We assign a portion of the red shift to cosmological expansion, then we assign a portion to Doppler effect; how do we determine how much to assign to each phenomenon?

It seems that the way the cosmological red shift is explained, it demands to take all of the red shift and leave none for Doppler. :) It reminds me of the government.
 

Offline lightarrow

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How is the Universe able to expand faster than light?
« Reply #22 on: 07/03/2009 02:52:30 »
What is interesting to me is that as space i.e. the Universe expands it makes / creates more space which, in turn, makes / creates more dark energy.
Chris, do you have any link to papers/documents discussing this fact, that is the creation of more dark enenergy as Universe expands?
 

Offline JP

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How is the Universe able to expand faster than light?
« Reply #23 on: 07/03/2009 04:17:39 »
Lightarrow, I went hunting for sources on dark energy being linked to "how much" space there is, and I came up with a couple links:

http://en.wikipedia.org/wiki/Dark_energy#Cosmological_constant
http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/dark_energy.html

It sounds like dark energy is tied to the idea of the cosmological constant, and also to the idea of vacuum energy.  The more vacuum you have, the more dark energy there is. Strangely, according to these links, the vacuum energy predicted by particle physics is way way too high for the visible cosmological constant.  So there's obviously something we don't understand yet.
 

Offline JP

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How is the Universe able to expand faster than light?
« Reply #24 on: 07/03/2009 04:23:18 »
I can see a real problem though. We assign a portion of the red shift to cosmological expansion, then we assign a portion to Doppler effect; how do we determine how much to assign to each phenomenon?

It seems that the way the cosmological red shift is explained, it demands to take all of the red shift and leave none for Doppler. :) It reminds me of the government.

There's a pretty good theory that predicts how fast the universe is expanding, and how fast distant objects should appear to be moving away from us as a result of that expansion: i.e. it predicts the Hubble/expansion redshift.  On top of this general expansion, things can also be moving locally, which would introduce a regular Doppler shift.  I'm not sure how astronomers assign causes for their shifts, but I'm guessing there's a lot of detailed analysis that goes into it.  For example, a star in orbit very far away from us will be red shifted due to its distance, but on top of that it will have an oscillating Doppler shift depending on its orbit: it will be bluer when its moving towards us in its orbit and redder when moving away.
« Last Edit: 07/03/2009 04:26:34 by jpetruccelli »
 

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How is the Universe able to expand faster than light?
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