Does light have mass?

  • Thread starter adimantium
  • Start date
  • #1
13
0

Main Question or Discussion Point

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.
 

Answers and Replies

  • #2
Drakkith
Staff Emeritus
Science Advisor
20,737
4,442
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.
 
  • #3
142
17
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.
 
  • #5
70
0
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 masswhile moving = h/λc (by the de brogle)
mind me to saying it may be wrong
 
  • #6
3,872
88
Last edited:
  • #7
18,076
7,496
Do photons have mass?
https://www.physicsforums.com/showthread.php?t=511175 [Broken]
 
Last edited:

Related Threads for: Does light have mass?

  • Last Post
3
Replies
59
Views
3K
  • Last Post
3
Replies
54
Views
10K
  • Last Post
Replies
4
Views
10K
  • Last Post
Replies
19
Views
3K
Top