Understanding the Speed of Space in Relativity

[Tenunbow]

Hello, we know that according to special relativity nothing in the universe go faster than speed of light,but space can.Now according to E=mc^2 entity with mass can not reach speed of light and photon is mass less with mass=0.So it can reach speed of light so its meaning that space contain negative mass so it has speed greater than speed of light,and why special relativity does not put any constrain on speed of space.Thanks in advance.

The simple answer is that a negative mass would have the same constraints as a positive mass, neither of which can travel faster than c.
The difference is that a positive mass will move with the force applied and the negative mass will move opposite to the force applied.

 

[my2cts]

I'm not quite sure what you mean here. What effects are being wiped out?

I mean that thermalisation would wipe out the memory of a specific state of motion at a certain timescale. That timescale should follow from dynamics.

 

[my2cts]

Read the OP again, there is a severe misunderstanding here. This isn't just a topic about the expansion of space. If it is, it belongs in the astrophysics forum. Rather, it is the assertion that the apparent super luminal expansion of space is DUE to a "negative mass" of space! It is VERY specific!

Zz.

I agree. But this thread is at least partly about superluminal expansion.

 

[dauto]

So the object at 1 billion ly moves at v=c away from us. An object further away would move faster than c relative to us. That contradicts SR.

No it doesn't. You are missing a very very very important point here. The distance we're are talking about here is the comoving distance. That means the distance is not measured the same way it would usually be measured in special relativity and any receding rate cannot be directly used to find how fast an object is moving with respect to another. Note that that is possible to do even within Special relativity. There is no need to use General relativity.

 

[my2cts]

No it doesn't. You are missing a very very very important point here. The distance we're are talking about here is the comoving distance. That means the distance is not measured the same way it would usually be measured in special relativity and any receding rate cannot be directly used to find how fast an object is moving with respect to another. Note that that is possible to do even within Special relativity. There is no need to use General relativity.

I am not missing the point. I use Fizeau-Doppler. GRT tells me that the rate of change of distance is not related to velocity and frankly I do not know what to think of that.

 

[BruceW]

I agree with 2cts, that we only get objects moving at relative velocities greater than c because we are using general relativity. I can't think of any situation in special relativity where two objects would have relative velocity which is greater than c...

edit: I guess it depends on where you draw the line between special relativity and general relativity...?

 

[us40]

The simple answer is that a negative mass would have the same constraints as a positive mass, neither of which can travel faster than c.
The difference is that a positive mass will move with the force applied and the negative mass will move opposite to the force applied.

This link may help to understand my view:

http://www.livescience.com/38533-photons-may-emit-faster-than-light-particles.html

 

[BruceW]

It essentially is saying that if photons were not massless, then other objects could move faster than photons. Yep, but that's not very interesting in my opinion. c would still be the upper speed limit, and relativity would still work the same, but photons would be massive particles instead.

 

[ZapperZ]

This link may help to understand my view:

http://www.livescience.com/38533-photons-may-emit-faster-than-light-particles.html

You need to be very careful here. The paper in question (not this news report) is similar to the investigation on the UPPER LIMIT of photon mass. It does NOT imply that it has a mass. The same goes with this particular study. It is saying that if a photon has a mass, then it must have a lifetime and decay to other particles. So they estimated the LOWER LIMIT of the decay lifetime of a photon. It doesn't mean that they have actually found it! Furthermore, look at the lifetime that they computed, and compare that to the age of the universe!

a visible wavelength photon in our reference frame would be stable for 10^18 years or more

There's a lot of "If's" here and there's a lot of "sensationalistic noise" that you have to overcome to get the actual physics.

Zz.

 

[us40]

It essentially is saying that if photons were not massless, then other objects could move faster than photons. Yep, but that's not very interesting in my opinion. c would still be the upper speed limit, and relativity would still work the same, but photons would be massive particles instead.

What I trying to say is...
Photon is quantum of light.Now in loop quantum gravity(candidate theory for quantum gravity) physicist create quantum of space.(http://en.wikipedia.org/wiki/Quantum_loop_gravity).
Now say that quantum of space spaceon(sorry for wired name). Now according to article I have referenced in previous post if particle is lighter than photon it can go with greater velocity.So spaceon can go faster than speed of light.If photon has positive mass spaceon has mass somewhat lesser than photon and if photon has zero mass mass of spaceon is negative.That is my point.

 

[ZapperZ]

What I trying to say is...
Photon is quantum of light.Now in loop quantum gravity(candidate theory for quantum gravity) physicist create quantum of space.(http://en.wikipedia.org/wiki/Quantum_loop_gravity).
Now say that quantum of space spaceon(sorry for wired name). Now according to article I have referenced in previous post if particle is lighter than photon it can go with greater velocity.So spaceon can go faster than speed of light.If photon has positive mass spaceon has mass somewhat lesser than photon and if photon has zero mass mass of spaceon is negative.That is my point.

But what exactly is the physics that allows you to say that if a particle has v>c, it mass must be negative?

Look at tachyons, for example. One can arrive as the mass of these hypothetical particles quite directly from SR. See, for example:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html

Look at the criteria for M^2 to be negative. That is why I said earlier about mass being "imaginary" in this case. Nowhere in here is the requirement that mass has to be "negative" for this particle to have v>c!

Again, to repeat, we know and already have particles with negative mass. They have the opposite behavior as regular particles in a gravitational field, etc. But they certainly do not have superluminal behavior.

Zz.

 

[BruceW]

Now say that quantum of space spaceon(sorry for wired name). Now according to article I have referenced in previous post if particle is lighter than photon it can go with greater velocity.So spaceon can go faster than speed of light.If photon has positive mass spaceon has mass somewhat lesser than photon and if photon has zero mass mass of spaceon is negative.That is my point.

The article is saying if the photon has mass, then another particle might go with greater velocity. This is possible because this other particle could still have velocity less than c, but greater than the speed of the photon. The main thing is that massless particles move at c, and particles with mass move at less than c.

A (hypothetical) particle which travels at greater than c is called a tachyon, and would have imaginary mass, as ZapperZ was saying. Also, about the 'spaceon' I'm not sure what you mean. I don't know anything really about quantum gravity. But I think in string theory, a 'graviton' is predicted (which is a massless particle). But from what I read in the wikipedia page on quantum loop gravity, there is no particle like the graviton which is fundamental to quantum loop gravity.

 

[TurtleMeister]

Again, to repeat, we know and already have particles with negative mass. They have the opposite behavior as regular particles in a gravitational field, etc. But they certainly do not have superluminal behavior.

Zz.

underline by me

Sorry to butt in, but I would like to read more about this. Do you have a link or source?

 

[Dale]

What I trying to say is...
Photon is quantum of light.Now in loop quantum gravity(candidate theory for quantum gravity) physicist create quantum of space.(http://en.wikipedia.org/wiki/Quantum_loop_gravity).
Now say that quantum of space spaceon(sorry for wired name). Now according to article I have referenced in previous post if particle is lighter than photon it can go with greater velocity.So spaceon can go faster than speed of light.If photon has positive mass spaceon has mass somewhat lesser than photon and if photon has zero mass mass of spaceon is negative.That is my point.

OK, this is just getting weirdly speculative. Even in theories where the volume operator is discrete that doesn't mean that there are spaceons that travel anywhere. Please stop just making stuff up.

Also, your question wrt negative mass has been answered. To recap: the article you cited was talking about the possibility of photons having some non-zero (positive) mass. If that were true then photons would not travel at c and particles with (positive) mass could travel faster than photons but still slower than c. Hypothetical particles which would go faster than c are called tachyons and would have imaginary mass, not negative mass.

Thread closed.