Why does light and gravity travel at the same speed?

[Naty1]

So I'm wondering how you might go about finding the wavelength of a graviton, if there is such a thing. I'd think if there was a way we would have found one by now.

From
http://en.wikipedia.org/wiki/Graviton#Experimental_observation

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector.[12] The reason is the extremely low cross section for the interaction of gravitons with matter. ...

However, experiments to detect gravitational waves, which may be viewed as coherent states of many gravitons, are underway (e.g., LIGO and VIRGO). Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton...

No results that I have seen; some discussions here in the forums.

I am unsure about whether or not a graviton is a gravitational wave like how a photon is an EM wave.

I think that's a really tough one to answer...some clues...
There are some basic issues which are unresolved:

One thing we think we know is that gravity and EM have some [mathematical] differences: This is because the source of gravitation is the Einstein stress-energy tensor, a second-rank tensor, the source of electromagnetism is the four-current, a first-rank tensor.

Can gravitons be polarized like photons? is dependent on helicity...
Isn't the photon it's own antiparticle; how about the graviton?
How much more do we know about the mass of a photon than graviton? [We know the photon is massless down to some tiny,tiny figure; we haven't even found a graviton yet.]

As I understand things, there is not even wide agreement among QM people about exactly how a photon derives from or creates EM waves...apparently the latter is current thinking...
edit: found this in PHOTONarticle:

", the photon is not a point-like particle whose trajectory is shaped probabilistically by the electromagnetic field, as conceived by Einstein and others; that hypothesis was also refuted ... According to our present understanding, the electromagnetic field itself is produced by photons, which in turn result from a local gauge symmetry and the laws of quantum field theory..."

Here is one description of uncertainties (unknowns):

Gravitons and renormalization

When describing graviton interactions, the classical theory (i.e., the tree diagrams) and semiclassical corrections (one-loop diagrams) behave normally, but Feynman diagrams with two (or more) loops lead to ultraviolet divergences; that is, infinite results that cannot be removed because the quantized general relativity is not renormalizable, unlike quantum electrodynamics. That is, the usual ways physicists calculate the probability that a particle will emit or absorb a graviton give nonsensical answers and the theory loses its predictive power. These problems, together with some conceptual puzzles, led many physicists to believe that a theory more complete than just general relativity must regulate the behavior near the Planck scale.

Anyway,if interested, check Wikipedia here for a LOT on photons:
http://en.wikipedia.org/wiki/Photon

 

[zhermes]

So would a graviton have a wavelength? Or would that just be speculation.

Presumably a graviton would have a wavelength just like a photon does. It would be more appropriate to talk about the wavelength of the gravitational wave, and the energy of the graviton.

 

[Naty1]

There was another thread that discussed these issues...I can't find it... I did copy one post that I thought interesting...draw your own conclusions:

Phyzguy:
We really use the word photon to describe two things. On the one hand, we refer to a photon as being an elementary excitation of the EM field, which has a definite: energy, wavelength, and frequency. These photons are the eigenstates of the EM field, and extend to +/- infinity.
On the other hand, we also use the word photon to refer to the wave packet emitted by an atom when it drops from one energy level to another. But this latter photon is not an energy eigenstate. It does not have a definite frequency, because the atom is not in the upper and lower energy states for an infinite time, so there is a time uncertainty which leads to an energy uncertainty. So the wave packet contains a range of frequencies, and multiple measurements of its energy would lead to a distribution of probable values. Because there is a range of frequencies and wavelengths, the wave packet is also bounded in space and time. The "size" of the wave packet (let's say the duration in time) depends on how long the atom is undisturbed. If the atom is in a very undisturbed environment, with a long time between collisions, then the wave packet is very sharp, with a long duration (Delta-t), and a small distribution of energies (Delta-E). If the atom is in an environment where collisions are frequent, then the wave packet is more spread out, with a short duration (Delta-t), and a broad distribution of energies (Delta-E).

Any interpretations of the above comparison would be appreciated.

 

[Naty1]

I just noticed:

Originally Posted by Naty1
Where does that reference say ANYTHING about plasmas within black holes?

Sorry page not found. Try http://www.physorg.com/news/2010-11-...lasma-lab.html

Once again, that source says NOTHING about plasmas within black holes.

What the described experiments are doing is reproducing the high energies [used to create plasmas] OUTSIDE black holes as matter is accelerated towards the horizon of a black hole.

[Any jets of matter and radiation 'emitted' from a black hole are accelerated out from the external accretion disk, not the interior of the black hole.]

 

[ynot1]

What the described experiments are doing is reproducing the high energies [used to create plasmas] OUTSIDE black holes as matter is accelerated towards the horizon of a black hole.]

Interesting. So plasmas are created outside the event horizon.

[Any jets of matter and radiation 'emitted' from a black hole are accelerated out from the external accretion disk, not the interior of the black hole.]

So black holes would never evaporate. I see.

 

[ynot1]

Presumably a graviton would have a wavelength just like a photon does. It would be more appropriate to talk about the wavelength of the gravitational wave, and the energy of the graviton.

I recall something about the frequency of the gravitational radiation from a binary star would be twice its rotational frequency. So I guess we could go from there to calculate its wavelength.

 

[EdLorentz]

Except for Hawing radiation I don't believe gravity does escape from a black hole. Note if too much gravity escapes the black hole it seems it wouldn't be a black hole anymore.

A minor point, but isn't Hawking Radiation (which Hawking was originally against, original proposed by Jacob Bekenstein when his discussed black holes having a well defined entropy in 1972) just merely emitted near the Event Horizon? It is not necessarily "escaping" anything, it is a quantum-level effect that can become a macroscopic event, theoretically.

 

[zhermes]

Interesting. So plasmas are created outside the event horizon.So black holes would never evaporate. I see.

Particles are created outside of the event horizon. Not necessarily plasmas---which do often exist outside black-holes.
Black holes still evaporate, as the particles created extract energy from the black hole (according to theory).

I recall something about the frequency of the gravitational radiation from a binary star would be twice its rotational frequency. So I guess we could go from there to calculate its wavelength.

That is exactly correct.


As none of the current topics/discussions/points have anything to do with the original post; I suggest this thread be left. Any ongoing subjects should be brought up in new threads.