Why are Photons affected by gravity?

In summary, a photon is affected by the curvature of space, and also causes space to be curved.time passes more slowly in a gravitational field.
  • #1
Commander8bal
2
0
Hi there,

I was wondering if anyone could tell me why a photon is affected by gravity? From my current understanding of gravity, only objects with mass are able interact with the warping of space time. Why then, would a photon or any other massless particles have there vectors be deviated by other objects around them?

Thanks for your time in feeding my hungry mind.
 
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  • #2
I think your current understanding of gravity needs to be revised. As lacking as my knowledge of general relativity is, I can nonetheless tell you that what your statement should have said was:

"...only objects with mass are able to *cause* the warping of spacetime"

The warping of spacetime, however, affects anything that travels through it, including photons. Photons in the vicinity of some object that *does* have mass and *is* warping spacetime will travel on curved paths simply by virtue of the fact that the region of spacetime in which they are traveling is curved.
 
  • #3
Because photons only have zero rest mass. But since they are never at rest, they do have mass.

Very strictly speaking, "photon" is a term from quantum theory, while the "gravitational mass of an electromagnetic field" is an idea from General relativity, and there is as yet no framework which incorporates both theories properly. So perhaps I should say that the electromagnetic field has a non-zero stress-energy tensor which enters into the Einstein field equation of General Relativity. However, lax language about the mass of a photon is traditional in physics:

Apparent Weight of Photons
R. V. Pound and G. A. Rebka
Phys. Rev. Lett. 4, 337 (1960)
http://prl.aps.org/50years/milestones [Broken]
http://focus.aps.org/story/v16/st1

See also Count Iblis's post #48 at:
https://www.physicsforums.com/showthread.php?t=251161
 
Last edited by a moderator:
  • #4
Thanks for the clarification on gravitational interaction of particles. Just one more question though, do Photons having mass or being massless give off gravity themselves?
 
  • #5
Commander8bal said:
Thanks for the clarification on gravitational interaction of particles. Just one more question though, do Photons having mass or being massless give off gravity themselves?

Yes, a photon is affected by the curvature of space, and also causes space to be curved.
 
  • #6
time passes more slowly in a gravitational field. a light wave passing through will slow down. the light refracts exactly as it does when passing through any material, like glass, which causes light to slow down.

thats my understanding of it anyway.
 

1. Why are photons affected by gravity?

Photons are affected by gravity because they have energy and mass, even though they have no rest mass. According to Einstein's theory of general relativity, gravity is the result of the curvature of spacetime caused by mass and energy. As photons travel through spacetime, they follow the curvature and are affected by the gravitational pull of massive objects.

2. Do photons have mass?

Yes, photons have energy and therefore have an equivalent mass. However, they have no rest mass, meaning they do not have a mass at rest. This is because photons travel at the speed of light, so they cannot be at rest.

3. How does gravity affect the speed of photons?

Gravity can affect the speed of photons by either increasing or decreasing their speed. As photons travel through curved spacetime, their path may be altered, causing them to speed up or slow down. This is known as gravitational lensing and has been observed in the bending of light around massive objects such as galaxies.

4. Can photons escape the gravitational pull of a black hole?

No, photons cannot escape the gravitational pull of a black hole. This is because black holes have an incredibly strong gravitational force, so strong that even light cannot escape from it. Once a photon crosses the event horizon of a black hole, it will be pulled into the singularity at the center.

5. How does the gravitational redshift of photons occur?

The gravitational redshift of photons occurs when they travel away from a massive object. As they move away, they lose energy due to the gravitational pull, causing their wavelength to increase and their frequency to decrease. This results in a shift towards the red end of the electromagnetic spectrum. This phenomenon has been observed in the redshift of light from distant galaxies, providing evidence for the existence of dark matter.

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