Is there anything faster than light?

I'm curious what offended you so much.

 

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Relative to an observer here or on the distant galaxy.

There is no claim that is an exception to SR because it is not an exception to SR.

Sure, they appear fixed due to the distances and short time frames measured.

First objects cannot move through space at FTL so discussing what the doppler shift would look like is moot. However, for an object that has an increasing recession velocity the wavelength of light from that object would shift farther and farther to the red until the object was unobservable in ANY wavelength. For all intents and purposes it is gone; it is no longer in our observable universe. The galaxies that are very far from us will continue to red shift more and more until they dissapear from our sight.

Nothing can move through space FTL, we agree on that. I also agree that you would probably produce cherenkov raditation if you somehow could move through space FTL. But no one has suggested that distance galaxies move through space at FTL speeds or even close to c.
What is believed is that areas of space at great distances (any space greater than 15 bly or so) is moving away from our area of space at speeds >c. The galaxies carried along in those areas of space are red shifted and the movement of that area of space relative to us is called recession velocity. Recession velocity is not a movement through space.

 

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Sean Carroll recommended his blog readers to read the following paper...it seems to have quite a lot to do with recent threads here.
“Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe”.

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

3.1 Misconception #1: Recession velocities cannot exceed the speed of ligh

My bold.
Ps. I neary went blind cutting and pasting that...kept losing it.

 

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Nice, sweetpea. I've been trying to figure out how to understand that for years, in a way that would allow me to properly explain it. Thanks very much.

 

Well, maybe Danshaven will see this, maybe he won't.

 

Bizarre.

A Russell's teapot by any other name...

 

danshawen, I really, really recommend the article that sweetpea linked.

For example, did you know that all galaxies that we see at redshift z= ~1.46 or so or greater are currently moving away from us at greater than c? That's because we're seeing the past, not the present. When they emitted the light we see now, they were still visible.

And it's actually even more complicated than that; but you should read the paper.

 

Yes, we infer that they are receding at >c because of our understanding of the Hubble constant and present day observation.

 

Yep, and it is an extremely reasonable inference.

 

Worth noting that z=1.46 is about 6,250 megaparsecs, or about 20 billion light years, and note also that this is the current distance, not the distance when the light was emitted.

Formula: d = zc/H
Where,
d is the distance in Mpc (megaparsecs)
z is the redshift factor, 1.46, a dimensionless number
c is the speed of light, 2.997925 e+5 km/s, and
H is the Hubble constant, currently estimated at about 70 km/s/Mpc

The conversion factor from megaparsecs to light years is available online and trivial to find. It's about 1:3.26.

The formula is not exact, but for z < 2 it's within 5%.

 

http://curious.astro.cornell.edu/ab...rom-each-other-faster-than-light-intermediate

"The second question is an interesting one that confuses many people. The theory of relativity does indeed state that nothing can travel faster than light, however this refers to motion in the traditional sense, meaning you can't launch a spaceship and travel through space faster than light. The two galaxies we've been discussing are not travelling through space, it is the space between them that is expanding. Or put in another way, they are stationary and all the space around them is being stretched out. This is why it doesn't violate the theory of relativity, because it is not motion in the traditional sense."

Can no one else here detect the teeniest bit of inconsistent BS being ladled out in large quantities here?

Show me space that stretches. Not out there. Right here. Right now. Didn't think so. If there isn't even a theory to explain this "non-traditional" sort of motion, maybe, just maybe, it doesn't really exist. If it didn't, what would change, exactly? What would become inconsistent without the theory that space stretches that would be consistent with it?

I'm telling you, "stretching space" is a YEC artifact. Here it is:

http://www.icr.org/article/new-creationist-cosmology-no-time-at/

Isaiah 40:22: “[God] stretches out the heavens like a [tent] curtain” (NASB)

Space does not stretch, or if it does, not in a manner that renders the speed of light no longer an invariant. There are severe consequences to that line of thinking by articles like this one that aren't even being considered.

You can't have it both ways. If it is happening (space stretching) "out there", then either it must be happening here as well or else it isn't happening. There is no preferred frame of reference. The bible and what the creationists use it for here is not science or mainstream cosmology by any stretch.

 

You really better read that paper. It's not BS at all. By "motion in the traditional sense" they mean precisely that it is not motion in the SRT sense, but in a sense that only can be understood in GRT. That's because we're not talking about something moving in its local frame, but something moving because spacetime is expanding

De Sitter space. It's a valid solution to the EFE. Puzzled heck out of Einstein when he came across it, too. Not for long, though; it made him add the cosmological constant to GRT. Turns out he was right, although later he thought he was wrong.

Interestingly de Sitter space turns out to be an excellent model of our universe; it's what you get when the cosmological constant is positive: an infinitely expanding space. Cosmological models of the time were steady-state because Hubble had not yet discovered the Hubble Flow, so Einstein thought it was pathological and added cosmological constant to correct for it. When Hubble came along, it became clear exactly what cosmological constant really was.

There is a theory that explains it: GRT. You really, really need to read that paper. Trust me. Have I been nasty to you, trolled you, or lied to you yet? And I won't, either.

GRT.

No, for certain it's not. YECs aren't smart enough to understand GRT.

They're trying to explain the results of tensor mathematics and differential geometry to people who don't know what a derivative is. Give them a break.

 

It is, it is pure without further adulteration.

I though this issue would come up in that cosmological redshift thread, but that thread was completely hijacked by Schneibsetr with his alternative mainstream take......

See, everyone with basic knowledge of language and Physics can figure out what these guys are talking, those who support this are parrotising mainstream. Those who oppose will be termed as cranks and idiots.......But I am asking a honest question to all the supporters...well you have understood the language, but do you understand how stretching the intervening space will be termed as some special kind of speed rather no speed. Come on guys, accelarated rate of change of position with respect to time requires energy and that is speed in what we understand as speed. is there anybody who can say that no energy is involved in this so called stretching, if at all any stretching is there ?


PS: I do not dispute the observations, but interpretation is not right, unfortunately there is no other viable interpretation.

 

Ah. OK. Your responses make more sense now.

You are not highlighting any self-contradiction in the cosmological model, you are highlighting that you're not clear on how it works.

This, for example:

is an oft-cited source of confusion which is routinely corrected with a bit more knowledge.

Are you interested in knowing how it works??

 

Sorry, who exactly said no energy was involved?

 

Let's try to explain this. This is specifically for danshawen, but everyone else who's not a relativist will probably get something from it too.

"Motion" in the SRT sense means motion with respect to nearby bodies. But because SRT only deals with the limit case where spacetime is flat, it doesn't deal with the kinds of curvatures of spacetime that GRT deals with; SRT is totally incapable of describing things like that because it doesn't contain the math to describe them. Your understanding of "motion" is fine for SRT, but when GRT comes into the picture it adds this possibility for spacetime to warp; and you already know that, danshawen. You know it because you know that SRT doesn't work right in a gravity field, and because it also doesn't work right for an observer under acceleration. These are two of the ways spacetime can warp under GRT, but they're not the only ways; this "spacetime stretching" or "expansion" everyone is talking about is another.

There isn't any analogy anyone can give other than the old rubber sheet example, in which a gravity well is a dimple in the rubber sheet caused by the mass of something, and in that analogy it's stretching the rubber sheet so it's bigger. Unlike a real rubber sheet, however, that doesn't increase the tension, so the dimples don't get smoothed out by it, so that's where the analogy fails.

What we're talking about here simply doesn't happen over distances as small as our local galaxy group; that's why there's nothing that anyone can show you directly in front of you. The type of "motion" GRT talks about in this sense simply doesn't manifest itself measurably below scales of tens of millions of light years. And that's even only partially true; the main reason we don't see it in the Local Group is because across the Local Group, gravity is strong enough to overcome this "stretching of spacetime." You can't expect to have evidence for something that doesn't occur within millions of light years of here placed right in front of you; it's not a reasonable expectation.

 

very true, none said, so if energy (say DE) is involved what work it is doing ? Stretching ? Will the consumption of energy be more or less or same if lighter objects are present in that part of universe ? If presence of gravity can hold the expansion (in local group), then what does it suggest ?

Why accept things blindly ? I know nothing can be done, but do not accept things which appear illogical.. Eienstein himself said that theory should be explanable to a layman...do not take it literally, but thats how it should be.

 

This last statement is the crux.

Cosmological expansion is far, far weaker than gravity. It is unable to have an effect on gravitationally-bound systems.

Think of a balloon with pennies glued all over it. Blow up the balloon and the space between the pennies expands. Does anyone demand to know why the pennies are not ripped atom-from-atom by being glued to an expanding balloon? No. It is obvious that the glue is far weaker than the molecular bonds within the pennies. An ant standing on one of the pennies might argue the balloon is obviously not expanding, since it sees no pennies disintegrating.

@danshaven, this answers your question.

 

I love this. People who disagree with someone must obviously be "blindly" accepting things.
Perish the thought that they might have actually done the hard work to understand what they're talking about.

 

I have seen this weird cop out argument by most of the mainstream supporters..

Finally they will say it is spacetime that is expanding not the space.....and it is non intuitive type and cannot be explained.

They must realise that observation of the reality is in and around space, not in and around some mathematical spacetime.....