Expansion speeds can be faster than light--T or F?

[losfomot]

It's not limited by relativity, because the motion is due to the expansion of the space, not the motion of the galaxy.

 

Not limited by, but still subject to the effects of?

 

I understand that the expansion velocities can be greater than c. But are those velocities still subject to the effects of special relativity?

 

For example, a galaxy moving away from us at .99c (due to expansion) is subject to time dilation and length contraction by a factor of 7 relative to us?

 

EDIT-

 

Wait, I think I am coming to a realization... because the two galaxies are co-moving, neither one has undergone an acceleration relative to the other one (disregarding Lambda), so neither galaxy could be subject to time dilation (and length contraction, and mass increase) relative to the other. Is that sort of right?

[Mr Skeptic]

It's not limited by relativity, because the motion is due to the expansion of the space, not the motion of the galaxy.

 

If the galaxy is not actually moving, where does the Doppler shift come from?

[Martin]

If the galaxy is not actually moving, where does the Doppler shift come from?

 

the cosmological redshift is NOT A DOPPLER SHIFT

 

this is what you learn on day one in a general astronomy or beginning cosmology course, so this is really really important for you to assimilate, Skeptic

 

doppler shift is the result of speed, of relative motion in some reference frame

of either the emitter (at the time of emission) or the receiver (at the time of reception)

 

the redshift is not caused by speed of relative motion at either the time of emission or time of reception

it is caused by the STRETCHING that occurs all during the flight.

 

so if I just tell you the recession speed at the time the light was emitted, you cannot calculate the redshift!

If all you know are recession speeds, you cant figure it out, because redshift doesnt depend on them!

 

For example, the CMB was emitted by matter which was receding from our matter at the rate of 66 c

at the moment it was emitted

but just from that you can't calculate anything

 

what you have to know is that during the time the light has been on its way to us, the universe has expanded by a factor of 1100.

this has stretched out the lightwaves.

so naturally when we get the light it is redshifted by a factor of 1100.

 

be very clear about that, that is not how doppler effect works and that this not the doppler formula

 

on day one the teacher gives you the REDSHIFT formula which is that the z + 1 = expansion factor during time of flight

and he or she points out that this is not the doppler formula and redshift is not a doppler effect

 

if by the end of the semester you have not gotten this clear, and assimilated it, you are apt to fail the course

=========

 

there can be a little add-on effect due to the galaxy's indidual motion thru its own local space, which is not part of the expansion

so there can be a small percent add-on effect that is doppler, but most of the time that can be ignored because such a small almost unmeasurable part of the whole.

[antimatter]

Everything has a speed limit, C, known a little better as the speed of light, as my science teacher says.

[Klaynos]

Everything has a speed limit, C, known a little better as the speed of light, as my science teacher says.

 

Firstly it's lower case c, secondly this may not hold for the universe expansion.

[Riogho]

Everything has a speed limit, C, known a little better as the speed of light, as my science teacher says.

 

Well, for one, we are watching it move faster then c, a LOT faster, and ACCELERATING.

 

And, nothing with MASS can exceed c.

 

Besides, Einsteins mass-energy equation breaks down near lightspeed anyway.

[Dark matter]

I now realize I totally made the wrong vote ( I voted false)

 

Because, Einstein stated that you cannot reach the speed of light because you would instantly reach your destination. That would not be true though when space is expanding, because it's expanding into nothing.

[Riogho]

Einstein said that?

[antimatter]

Well, I suppose you're right, but I don't think it's expanded that quickly since the Big Bang.

 

By the way, my bad for making the c uppercase, it was an accident that I unfortunatly make quite often.

[Farsight]

And you picked totally the wrong username too!

 

If anybody still doubts Martin's point, see Davis, T. M. ; Lineweaver, C. H. ; Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe, Publications of the Astronomical Society of Australia, 21, 97—109. URL: http://arxiv.org/abs/astro-ph/0310808v2

[antimatter]

How did I pick the wrong username...?

[Dark matter]

Einstein said that?

 

Clarification: I believe Einstein said "you cannot travel at the speed of light because if you did, you would instantly reach your destination." (Theory of relativity) My theory, which is based off that, is that since space expands into nothingness, space may be expanding faster than the speed of light.

 

By the way, awesome signature.

[antimatter]

There is one answer to this whole thing. I'm warning you, it's very vague.

It's very possible for the universe to have expanded faster than the speed of light, but there is no way of knowing for sure.

[Martin]

Einstein never denied that stuff could recede from us faster than light. His theory of general relativity PREDICTS that this can happen and provides the model used in expansion cosmology. This has been confirmed.

 

Long after the big bang, matter which we are now seeing (its light redshifted to microwave, now being received) was receding at 60 times c.

 

We are seeing that matter as it was when it was receding at 60c.

 

this was over a third of a million years after the big bang. So FTL recession speeds are not restricted to the big bang (as someone mistakenly claimed.)

 

If you think this contradicts Einstein's theory then you have a problem. Probably you should read Lineweaver---the simplest way to correct misperceptions about standard cosmology.

[raf]

I believe Einstein said "you cannot travel at the speed of light because if you did, you would instantly reach your destination.

 

but if the distance is 10 light years away ...even if you travelled at the speed of light you would not reach your destination instantly.

[iNow]

I believe Einstein said "you cannot travel at the speed of light because if you did, you would instantly reach your destination.

 

but if the distance is 10 light years away ...even if you travelled at the speed of light you would not reach your destination instantly.

 

You have to remember to what that velocity is relative. A photon travelling at c will, from it's own perspective (photons don't have a perspective or reference frame, but for purposes of answering your question, this is how I'll say it) experience infinite length contraction and time dilation. This is why the statement that a photon instantly reaches it's destination, from the perspective of the photon, is completely valid.

 

However, from an outside observerer like you or me, the photon would take 10 light years to cross that distance... relative to us.

 

Mind boggling, but true.

[kaneda]

iNow. We know that photons can change wavelength so they do experience time. As they are waves and come in a huge variety of wavelengths, they do not experience length contraction as that would change their wavelength.

[iNow]

iNow. We know that photons can change wavelength so they do experience time. As they are waves and come in a huge variety of wavelengths, they do not experience length contraction as that would change their wavelength.

 

Again... that's relative to an observer in a different reference frame... namely, us. What's your point exactly?

[swansont]

Following Martin's earlier suggestion and the recent explosion of posts, a whole bunch of OT speculative discussion about the big bang and relativity has been moved

 

http://www.scienceforums.net/forum/showthread.php?t=31714

[Dark matter]

I am curious, what type of matter is it?

 

(responding to martin)

[Martin]

I am curious, what type of matter is it?

 

(responding to martin)

 

Please use the quote button if you want to ask about something I said. It makes it a lot more efficient because I don't have to sift through my earlier posts and guess as to what you are asking.

 

Just go back to whichever post of mine you have questions about, and click on the quote button below it. If it's a long post you can highlight the part you have questions about, or erase the rest.

 

Thanks.

[J.C.MacSwell]

I believe Einstein said "you cannot travel at the speed of light because if you did, you would instantly reach your destination.

 

but if the distance is 10 light years away ...even if you travelled at the speed of light you would not reach your destination instantly.

 

By your new reference frame the distance would contract to zero and the time lapse would be zero...thus instantaneous.

[Eureko]

Hell. I have always wondered about this!

Somebody with the answer?

[antimatter]

Really the only answer I think there is, is that, it's very possible, but there is just no way of knowing with our current knowledge of the Universe.

Sorry if that wasn't a very sastisfying answer, maybe somebody else will give a better one.

[Klaynos]

Hell. I have always wondered about this!

Somebody with the answer?

 

Reading the posts will show you the side of opinion, Martin and Swansont's posts are probably the ones to pay particular attention to.