Speed of light and mass

  • Thread starter madmike159
  • Start date
  • #1
madmike159
Gold Member
369
0
Einstein's theory of relativity means that the faster an object travels and the more mass it has the more it will curve space-time. This means something like a spaceship could never travel at the speed of light because it would take an infinite amount of energy to reach that speed. So obviously photons have no mass or else they wouldn’t travel at the speed of light and there would be no speed of light.

However we know from E=[tex]h[/tex]f that photons have a certain amount of energy.

So it should have a mass = E/c[tex]^{2}[/tex]

but that would mean that a photon couldn't travel at the speed of light. Does anyone know why they either don’t have mass or why they are excluded from this rule?
 

Answers and Replies

  • #2
ZapperZ
Staff Emeritus
Science Advisor
Education Advisor
Insights Author
35,847
4,670
Please read the FAQ in this section of PF.

Zz.
 
  • #3
HallsofIvy
Science Advisor
Homework Helper
41,833
961
No, E= mc2 refers to "rest" mass: mass measured in a reference frame where the velocity is 0. Since photons never "rest" it does not apply to them.
 

Related Threads on Speed of light and mass

Replies
6
Views
1K
  • Last Post
Replies
19
Views
819
  • Last Post
Replies
17
Views
3K
Replies
6
Views
2K
Replies
2
Views
1K
Replies
32
Views
10K
Replies
32
Views
4K
Top