Black Holes & Gravity: Exploring Photons & the Singularity

[Cosmo Novice]

From reading various articles my understanding is that BH are gravitationally extreme - although from a distance they are gravitationally the same as any other object it is inside the Schwarzschild Radius EH where BH's differ from other large masses.

The "singularity" is the point at which current physics fails to offer theoretical proofs as the singularity mathematically moves towards infinity.


My question is this:

If photons are bosonic particles, how can they be affected by Gravity, assuming they are massless?

 

[WannabeNewton]

There is a momentum associated with moving photons and they can be affected by arbitrarily curved space - times. They start moving along the geodesics of the curvature; remember gravity isn't really the same "force" kind of entity in GR as it was in Newton's framework.

 

[bcrowell]

If photons are bosonic particles, how can they be affected by Gravity, assuming they are massless?

GR describes gravity as curvature of spacetime. Any sufficiently small particle (massive or massless) traveling through a curved spacetime moves along a geodesic, which means a "line" that is as straight as possible.

Another thing to realize is that "mass" has a specialized technical meaning in relativity; it means $m=\sqrt{E^2-p^2}$ (in units where c=1). When we say that a photon is massless, that's what we mean. But mass in GR doesn't have all the properties you might think. For example, mass isn't additive. For example, a box full of photons has a nonzero contribution to its mass coming from the photons, even though the photons individually have zero mass.

 

[Chalnoth]

If photons are bosonic particles, how can they be affected by Gravity, assuming they are massless?

Gravity responds to energy, pressure, momentum, and shear, not just mass. Photons have energy, pressure, and momentum, and so interact with gravitational fields.

 

[Cosmo Novice]

Thanks for your answers