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Old 2014-01-02, 17:40   #1
jasong
 
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"Jason Goatcher"
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Default What if dark matter is actually light?(emitted light)

Been thinking about the dark matter problem. What if the emitted light from a star retains some of gravitational pull of the atom it was emitted from. Wouldn't it make sense that the consevation laws should extend to gravity as well?

Could dark matter be explained by assuming light has a gravitational pull?

Sorry if this has been suggested previously.
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Old 2014-01-02, 17:45   #2
chalsall
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Sorry if this has been suggested previously.
Many of our smartest Physicists have been thinking about this problem for quite some time.

Do you not think they might have thought about this possibility already?
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Old 2014-01-02, 18:52   #3
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Wouldn't it make sense that the consevation laws should extend to gravity as well?
In what sense do you think it has not been?
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Old 2014-01-02, 23:18   #4
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In what sense do you think it has not been?
I'm suggesting the possibility that photons of light might exert a miniscule gravitational pull.
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Old 2014-01-02, 23:21   #5
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Originally Posted by chalsall View Post
Many of our smartest Physicists have been thinking about this problem for quite some time.

Do you not think they might have thought about this possibility already?
In that case, are there papers on this and I just didn't know? It wouldn't surprise me if this has been considered before.
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Old 2014-01-02, 23:27   #6
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Originally Posted by jasong View Post
I'm suggesting the possibility that photons of light might exert a miniscule gravitational pull.
Based on what theory?

Photons have empirically demonstrated their ability to provide pressure ("light sail, anyone"), but not a gravitational pull.

Really, Jason... You need to read more....
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Old 2014-01-02, 23:48   #7
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Quote:
Originally Posted by chalsall View Post
Based on what theory?

Photons have empirically demonstrated their ability to provide pressure ("light sail, anyone"), but not a gravitational pull.

Really, Jason... You need to read more....
Under general relativity, all forms of mass/energy act the same w.r.to gravity; the only real difference is dynamic effects due to movement of objects (and in this sense photons are special, in being able to achieve the "cosmic speed limit", unlike mass-nonzero objects).

For example, GR does not care if the stuff inside a black hole is baryonic or "trapped photons" - it only cares how that translates into the stress-energy tensor term of the Einstein equations.

I suggest a course of remedial reading for all correspondents in the above exchange.

And indeed the smart minds pondering dark matter are well aware of these things - "Wikipedia is your friend".

Last fiddled with by ewmayer on 2014-01-03 at 03:07
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Old 2014-01-03, 03:04   #8
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I googled it and people have considered the possibility. What I haven't determined is if anyone has run simulations to test the theory. It's possible that it's way more mathematically complex than it seems.
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Old 2014-01-03, 03:06   #9
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Originally Posted by chalsall View Post
Based on what theory?

Photons have empirically demonstrated their ability to provide pressure ("light sail, anyone"), but not a gravitational pull.

Really, Jason... You need to read more....
Lol, so do you, apparently. You trolled yourself this time.
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Old 2014-01-03, 09:14   #10
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For example, GR does not care if the stuff inside a black hole is baryonic or "trapped photons" - it only cares how that translates into the stress-energy tensor term of the Einstein equations.
Or trapped leptons for that matter. Nit-picking, I agree, but another interesting possibility is the formation of a BH from carefully focussed gravitational radiation.

More intriguing, and one I've not seen considered elsewhere is the possibility or otherwise of a pressure BH. Pressure contributes to the (off-diagonal terms of the) stress-energy tensor. So the question becomes, is it possible to find a physically realizable T for which the diagonal terms are all zero in some frame of reference? My guess is that it is not.

Another idea: could dark matter give itself away by falling into a black hole? If so, what would be the observational signature and what would be the physical mechanism? It would increase the mass of the BH and, perhaps, change its angular momentum. Perhaps these changes would be reflected in the energy output created by regular matter falling into the BH being different from that expected. What else might occur?
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Old 2014-01-03, 09:19   #11
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Originally Posted by jasong View Post
Lol, so do you, apparently. You trolled yourself this time.
Be very, very careful. Chalsall wrote

Photons have empirically demonstrated their ability to provide pressure ("light sail, anyone"), but not a gravitational pull.

To the best of my knowledge, that statement is true. Almost all physicists believe in the equivalence principle and so believe that photons have gravitational mass because it has been empirically demonstrated that they have inertial mass. However, it is only a belief and no experiment has yet directly demonstrated the gravitational mass of a photon.

Last fiddled with by xilman on 2014-01-03 at 09:21
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