Why does light and gravity travel at the same speed?

ynot1

Gravitons are the gravitational equivalent to photons for the electromagnetic fields. Gravitons spread the gravitational field of a particle at its creation. The gravitational field of the particle then becomes attached to the particle as long as it's not acceerated. If that happens then the gravitons come into play again to update the gravitational field. But gravitons play no part in a static gravitational field for a particle moving with no acceleration.

Radiation escapes black holes when its wavelength is greater than the diameter of the event horizon. I don't think gravitons are part of a black hole. They only update the gravitational field, as when the black holes lose mass by Hawing radiation.

ynot1

Per Einstein gravity is curvature of spacetime. The gravitational field of the black hole is the sum of the individual contributions from each particle in the black hole. If I understand Hawking radiation it annihilates particles in the black hole, and so the contribution of their gravitational field to that of the black hole will be lost, reducing the gravitational field of the black hole itself and reducing the curvature of spacetime.

Chronos

You don't need 'gravitons' if gravity is a scalar field. See also http://imagine.gsfc.nasa.gov/docs/as...s/980601a.html

universe21!

Gravitons don't exist because a theory out there says space time effects everything even where it doesn't exist. This means space-time doesn't exist where a planet is but does effect it. the effect is space-time pushes towards the (physical) Centre of the planet, as gravity.

and we know space doesn't have force carriers to meditate its range so the same applies to gravity. Since it (gravity) is Space time pushing against a Object it doesn't need the Graviton Boson hence why we have never found one. but this doesn't violate QM.

I find this a very interesting and simple theory because we know space-time and gravity is around. and we have never seen a graviton during an experiment. sounds like a very plausible theory.

What i can say about your question is gravity requires 0 mass to operate and light operates at 0 mass. so the laws of physics consern their speed should be identical.

Drakkith

Universe21, spacetime most certainly exists everywhere in the universe. And we don't know that gravity DOESN'T have a force carrier, we simply haven't been able to find one yet.

ynot1

looks like whatever force carrier gravity has would be the same as that for light if they both propagate at the same speed.

ynot1

So the propagator (for both), i guess, has no mass, so must be spacetime, unless there is something strange going on.

alphachapmtl

The photon are massless, so (it is believe) are the gravitons (which have never been observed). So they both travel at the speed of light.

coelho

I have a question, and it seems this is the most apropriate place and time to ask it.

From what i remember, black holes are created when a very massive star shrinks itself to a radius smaller than the so-called Schwarzschild radius. But, from a observer far away from it (like us, for example), as closer the radius of the star gets to the Schwarzschild radius, slower the shrinking gets, so from a observer far away, it takes an infinite time to a star became a black hole, and so, from a observer far away (like us), there are still no actual black holes in the universe, but only stars in the process of becoming one.

It is right?

ynot1

It seems as long as there is gravity the mass falling in will accelerate until the compressive force of matter inside the black hole balances the force of gravity. Of course the force of impact of infalling matter with matter inside the black hole is going to create heat and of turbulence depending on the compressibility and rebound effects of the mixture of matter inside. The spin of the star also effects the dynamics inside the black hole. For example if the radius of the star collapses by a factor of 1000 the spin of the black hole would increase by about 1000. So stars with spin will be spinning off all kinds of matter as it collapses. If we had data on the high pressure impacts we could do some very interesting theory about what's really going on inside for various spin rates.

ynot1

True. But note this depends not only on the mass of the star but also its spin. That is, the higher the spin, the more heavy matter will be thrown off the star before it completely collapses, reducing the probability of the star forming a black hole.

zhermes

I think that that is correct. An observer will never see an infalling shell cross an event horizon.
At the same time, however, infalling material becomes increasingly redshifted (quite rapidly), and thus an observer will stop 'seeing' any of that outside material. I guess the infalling matter would appear to dim/fade as it asymptotically approaches the event horizon (which also grows as additional matter falls in).

See: http://adsabs.harvard.edu/abs/2012PhLB..707..233P

ynot1

This reference applies to a pre-existing black hole but the question is creation of a black hole from a massive star, not collapse of a shell onto a pre-existing black hole.

zhermes

It seems like it should apply as soon as an event horizon forms---i.e. as soon as you pass critical density.

Naty1

This seems preposterous....but then, again, some things are so!

For example, there are few if any 'particles' within a black hole.
Except for recent infalls, all are destroyed at the singularity.

Hawking radiation is formed outside the horizon; Perhaps you mean infalling particles with negative energy combine with recent particles of positive energy...even that doesn't seem
likely ....how would one catch up with the other, or slow down, to affect annihilation...?

Have you any references that describe black holes as you posted??

Naty1

This has been discussed before and I am not positive, but what I concluded from conflicting posts is that such an 'infinite' time is an 'ideal' perspective from infinity in flat spacetime....in our real universe, such a frame does not exist...so dilation IS extended but not infinite.
If it were, how could we observe ANY black hole??

Naty1

ok I found the source which I have on the preceding issue:

From Kip Thorne in BLACK HOLES AND TIME WARPS

when the star forms a black hole:

I think the guy who 'accidently' discovered this is David Finkelstein...

I just checked Wikipedia...looks like THIS is what he discovered with Misner:

But what does it mean??