Question about photons

@metal-brain said
I'm not convinced light is bent by gravity.

Then you are completely ignorant of physics.
The massive evidence of gravity bending (relative deflecting) light doesn't JUST come from solar eclipse but from MULTIPLE sources of evidence from hundreds of observations that cannot be sensibly explained in any other way and that leave no reasonable doubt of its existence.

https://en.wikipedia.org/wiki/Gravitational_lens

And gravitational lensing is observed around black holes;

https://en.wikipedia.org/wiki/Black_hole

Why would gravity affect something without mass?

Why would gravity affect something WITH mass? Until you know the answer to this second question you cannot know the answer to your first question. (Hint: GR)

@Metal-Brain
OF COURSE you doubt relativity. Fortunately the REAL world knows light is bent by gravity. But you, being a card carrying contrarian, would doubt the existence of your own feet if you got too fat to see them just bending down.
Do you know, for instance, a radio wave or TV wave, the broadcasts we pick up with antennae, they are also photons? Just bigger. It turns out the energy of a photon can be specified by its size. Smaller photon, more energetic and the more momentum it will impart upon impacting with some surface or other and there is a difference in that momentum imparted depending on whether it absorbs or reflects.
Also BTW, the whole deal with light following gravity, it is simply following the path in spacetime gravity generates, it is the curvature of space itself that makes light change direction. If there was zero gravity and a photon was let loose it would never change direction.
So also BTW, that bending of the path of photons due to gravity has been proven by RADIO TELESCOPE data also. Since a 1 gigahertz radio signal is in fact a photon and would follow the EXACT same path a 1 nanometer wavelength photon, radio telescopes can be used to verify the reaction of photons to gravity.
You ever hear of gravitational lensing? What the HELL do you think that is? Ever see the astronomy images of distant galaxies seen only because the light coming from that galaxy has been more or less focused by an intervening galaxy?
If you don't believe even that, google it. Do your own research for a change.

@humy said
Then you are completely ignorant of physics.
The massive evidence of gravity bending (relative deflecting) light doesn't JUST come from solar eclipse but from MULTIPLE sources of evidence from hundreds of observations that cannot be sensibly explained in any other way and that leave no reasonable doubt of its existence.

https://en.wikipedia.org/wiki/Gravitational_lens

And ...[text shortened]... now the answer to this second question you cannot know the answer to your first question. (Hint: GR)

https://science-andinfo.blogspot.com/2019/12/nasa-saw-something-come-out-of-black.html?fbclid=IwAR1zpVHJNozRTCgI790LAIojcnguIYDUm3XRMfrg2u9IIo9B3-MOMezfYF4

https://getpocket.com/explore/item/are-black-holes-actually-dark-energy-stars?utm_source=pocket-newtab

@sonhouse said
@Metal-Brain
OF COURSE you doubt relativity. Fortunately the REAL world knows light is bent by gravity. But you, being a card carrying contrarian, would doubt the existence of your own feet if you got too fat to see them just bending down.
Do you know, for instance, a radio wave or TV wave, the broadcasts we pick up with antennae, they are also photons? Just bigger. It tur ...[text shortened]... n intervening galaxy?
If you don't believe even that, google it. Do your own research for a change.

Classical physics also predicts the bending of light.

If nothing can escape a black hole explain this.

https://science-andinfo.blogspot.com/2019/12/nasa-saw-something-come-out-of-black.html?fbclid=IwAR1zpVHJNozRTCgI790LAIojcnguIYDUm3XRMfrg2u9IIo9B3-MOMezfYF4

@metal-brain said
Classical physics also predicts the bending of light.

If nothing can escape a black hole explain this.

https://science-andinfo.blogspot.com/2019/12/nasa-saw-something-come-out-of-black.html?fbclid=IwAR1zpVHJNozRTCgI790LAIojcnguIYDUm3XRMfrg2u9IIo9B3-MOMezfYF4

Classical physics also predicts the bending of light.

From gravity? Links please...

If nothing can escape a black hole explain this.

https://science-andinfo.blogspot.com/2019/12/nasa-saw-something-come-out-of-black.html?fbclid=IwAR1zpVHJNozRTCgI790LAIojcnguIYDUm3XRMfrg2u9IIo9B3-MOMezfYF4

Obviously, when the link said "Come Out Of A Black Hole" they didn't mean from below its event horizon thus you are just arguing the toss over grammar and semantics here.
When somebody says "nothing can escape a black hole", obviously, what they nearly always mean is nothing can escape from specifically BELOW its event horizon.
In other contexts, if somebody says says "something escaped a black hole", obviously, what they nearly always mean is something escaped from specifically ABOVE its event horizon.
You are going nowhere with this.

@metal-brain said
https://science-andinfo.blogspot.com/2019/12/nasa-saw-something-come-out-of-black.html?fbclid=IwAR1zpVHJNozRTCgI790LAIojcnguIYDUm3XRMfrg2u9IIo9B3-MOMezfYF4

https://getpocket.com/explore/item/are-black-holes-actually-dark-energy-stars?utm_source=pocket-newtab

I have read both of the above links and found both of some interest but neither says/implies gravity does NOT bending light thus neither contradicts anything I just said. NEITHER says/implies anything about gravity bending light and the latter is about an interesting but highly speculative and unproven theory that the apparent black holes aren't 'true' black holes because they are "dark energy stars" and the latter link says of this theory "The idea has found no support in the astrophysical community" because so far there has been absolutely NO evidence to support it; -Not that that wild theory would have any relevance to the argument here even if it hypothetically were to ever be proven correct.

Your point?

@Metal-Brain
NASA is not saying it came from beyond the event horizon. But radiation can escape, it was shown by Hawking, called Hawking radiation:

https://en.wikipedia.org/wiki/Hawking_radiation

@humy said
but neither says/implies gravity does NOT bending light

My misedit;
That should be;
"...but neither says/implies gravity does NOT bend light ..."

@humy
One question, if light simply follows the path of spacetime, is that really bending?

@sonhouse said
So if you have a lot of photons in one place, can they generate a gravity well?

Yes, the Einstein Field equations have the energy-momentum density tensor on the right hand side, the left hand side is the Einstein tensor. Photons have energy so they gravitate.

@metal-brain said
I'm not convinced light is bent by gravity. I am considering the possibility that the solar eclipse experiment was flawed that supposedly confirmed it. Why would gravity affect something without mass? I didn't see anything in Einstein's GR equations that indicated that. I have always been puzzled by that.

On empirical grounds we think that light consists of photons which are quantum particles and that they are massless. The possibility that photons may have a tiny mass is something the experimentalists check for, according to Wikipedia [1] observation of the galactic plasma indicates a mass less than 3.0E−27 eV, for comparison the mass of the electron is about 500keV, thirty orders of magnitude larger.

However, because Einstein's theory of General Relativity has particles travelling along geodesics it doesn't matter for this whether light is a particle or not, we can use any theory where light is massless or has a small mass, and where our theory has light as a quantum particle massless or otherwise, a classical particle (with a small mass) or a classical wave. In each case the propagation of the particle or wave is determined by the geometry of space-time.

That the path of light should be bent to a detectable degree by very massive objects is a prediction of general relativity that is not present in classical theories of gravitation combined with light as a classical wave. Evidence for the presence or absence of the bending of light is a make or break test of General Relativity. The use of gravitational lensing of light in astronomy presents sufficient evidence for bending of light, so I don't think that GR can be attacked on those grounds.

[1] https://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass

@deepthought said
On empirical grounds we think that light consists of photons which are quantum particles and that they are massless. The possibility that photons may have a tiny mass is something the experimentalists check for, according to Wikipedia [1] observation of the galactic plasma indicates a mass less than 3.0E−27 eV, for comparison the mass of the electron is about 500keV, thi ...[text shortened]... ked on those grounds.

[1] https://en.wikipedia.org/wiki/Photon#Experimental_checks_on_photon_mass

Is this wikipedia info wrong?

"Classical physics also predicts the bending of light, but only half of that predicted by general relativity."

https://en.wikipedia.org/wiki/Gravitational_lens

@metal-brain said
Is this wikipedia info wrong?

"Classical physics also predicts the bending of light, but only half of that predicted by general relativity."

https://en.wikipedia.org/wiki/Gravitational_lens

Lets say it isn't wrong. What's your point? GR would be correct either way.

@DeepThought

So any form of energy has gravitation? So photons, RF and such are electromagnetic propagating fields.
So if you split apart the electric field, and the magnetic field, I think magnetic fields have energy, so a magnet that has been demagnetized and the same mass magnet that has a full magnetic field would have a slightly different gravitational field? Or would the internal magnetic moments of the non magnetized magnet still have the same magnetic energy but just not an overall field, therefore the same gravity field?

@metal-brain said
Is this wikipedia info wrong?

"Classical physics also predicts the bending of light, but only half of that predicted by general relativity."

https://en.wikipedia.org/wiki/Gravitational_lens

It depends on what the theory of light in play is. What the Wikipedia page is referring to is a game one can play where one takes the Newtonian formula for the gravitational potential:

V = -GMm/r

and claims that a photon in a gravitational well loses that much energy escaping. Since it's energy is given by Einstein's formula E = mc^2 one can get a formula for the radius from which no light can escape:

r = GM/c^2.

Which isn't amazingly convincing since we're using Einstein's special theory of relativity for the energy of the photon and Newton's for the gravitational potential and these theories are incompatible. Newton's theory requires instantaneous signalling and relativity rules that out. It's a bit of a dreadful hodgepodge, I don't understand why one shouldn't just use the standard classical formula for escape velocity. So I'm not particularly convinced by the statement that classical (i.e. Newtonian) physics produces a factor of 2 relative to what one obtains by solving the Einstein Field equations:

r = 2GM/c^2.

and this is just the classical formula for escape velocity rearranged with the speed of light substituted into it.

Overall though, what matters for the argument is whether light ought to be affected by gravity in a theory. Newton had a particle theory of light, so this type of argument works. By the time of the Michelson-Morley experiment they had Maxwell's theory and so the theory of light was a wave theory. It's not obvious to me how electromagnetic waves would be affected by gravity in Newton's theory. The point I'm making is that the result that light should be deflected by massive objects is not sensitive to the theory of light in Einstein's theory.