Does Light Have Mass or Not?

[adimantium]

Einstein said it would take an infinite amount of energy to move something at the speed of light. Photons move at the speed of light every day, so we can infer that photons have no mass. However, a black hole has so much gravity (gravity only affects matter) even light is sucked in. Because light is sucked into a black hole, we can infer that photons have mass. WHAT? how can this be?
I assume either some how photons can be propelled without an infinite amount of energy (very unlikely). Or light is sucked into a black hole for another reason besides gravity.

 

[Drakkith]

However, a black hole has so much gravity (gravity only affects matter)

This is not true. Gravity affects light too.

I assume either some how photons can be propelled without an infinite amount of energy (very unlikely). Or light is sucked into a black hole for another reason besides gravity.

Nope, it's just gravity.

 

[ModestyKing]

It's because gravity isn't just a field force; it's the curvature of space-time, according to Einstein. When light is traveling across space-time, it must follow this curvature whether or not it has mass, and the curvature is caused by objects with mass/a gravitational force.
At least, that's how I interpret it.

 

[jtbell]

Because light is sucked into a black hole, we can infer that photons have mass.

No, we don't. From the FAQ section of our relativity forum:

If photons don't have mass, why do their paths "bend" in a gravitational field?

 

[namanjain]

depends on question also
what i know is that light is made of photons and mass less electric and magnetic fields.


photons have zero rest mass and its mass_{while moving} = h/λc (by the de brogle)
mind me to saying it may be wrong

 

[harrylin]

You can find a longer explanation of the fact that gravity affects light here :
http://www.bartleby.com/173/22.html

Note that no rest mass is required for bending.

 

[Greg Bernhardt]

Do photons have mass?
https://www.physicsforums.com/showthread.php?t=511175