If photons have no mass,why would black holes attract light?

In summary, the question of why black holes attract light despite photons having no mass has been addressed in a previous entry on the Physics Forums website. It is explained that mass is not necessary for attraction, and the concept of gravity is independent from mass. The entry also provides further reading for a deeper understanding of the topic.
  • #1
If photons have no mass, why would black holes attract light?
I was told that photons have no mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is just photons, then it should not be affected by gravity. Hence black holes could catch everything but light.

Do I miss something? Is light more than a bunch of photons? Or maybe black holes are not exactly what I think.
 
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  • #2
Murtuza Tipu said:
If photons have no mass, why would black holes attract light?

Mass is not necessary to be attracted. The trajectory is independent from mass (both in classical mechanics and relativity).
 
  • #3
What makes a black hole to attract anybody ? Gravitational force and it depends on mass
 
  • #4
Murtuza Tipu said:
If photons have no mass, why would black holes attract light?
I was told that photons have no mass. However I thought that black holes are called "black" because no light can go escape the gravity force in their vicinity. I somehow think that, if light is just photons, then it should not be affected by gravity. Hence black holes could catch everything but light.

Do I miss something? Is light more than a bunch of photons? Or maybe black holes are not exactly what I think.

What you missed is reading our Relativity FAQ on this entry:

https://www.physicsforums.com/threads/why-are-massless-photons-affected-by-gravity.511173/

This question has been asked many times and it is sufficiently addressed at the simplest level in that entry.

Zz.
 
  • #5
What ZapperZ said. This thread is closed.
 

1. Why do black holes attract light if photons have no mass?

Black holes do not attract light because of the mass of photons, but rather because of their extreme gravity. According to Einstein's theory of general relativity, gravity is the result of the curvature of spacetime caused by the presence of massive objects. Since black holes have a tremendous amount of mass, they create a strong gravitational pull that can even trap light.

2. Does this mean that photons are affected by gravity despite having no mass?

Yes, photons are affected by gravity because they have energy and momentum, even though they have no mass. This is known as the principle of equivalence, which states that all objects, regardless of their mass, are affected by gravity in the same way.

3. How does the gravitational pull of a black hole affect the path of light?

The gravitational pull of a black hole bends the path of light, causing it to follow a curved trajectory. This is known as gravitational lensing and can be observed when light from distant objects passes near a black hole, causing it to appear distorted or magnified.

4. If photons have no mass, why can't they escape a black hole?

The reason photons cannot escape a black hole is not due to their mass, but because of the intense gravitational pull of the black hole. As light travels towards a black hole, it loses energy due to the gravitational redshift, eventually reaching a point where it does not have enough energy to escape the black hole's gravitational pull.

5. Can anything escape the event horizon of a black hole?

The event horizon of a black hole is the point of no return, beyond which nothing, including light, can escape. This is because the gravitational pull of a black hole becomes infinitely strong at the event horizon, making it impossible for anything to escape.

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