Why light travels

  • Thread starter ludi_srbin
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  • #1
ludi_srbin
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How does light travel? What gives the energy to the photons to travel at c? And if in order for something to travel at c you need an infintie amount of energy, how come photon travels at c?
 

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  • #2
yourdadonapogostick
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no, you don't. photons are massless. [tex]E=hf[/tex]
 
  • #3
εllipse
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To elaborate, it only takes an infinite amount of energy for something to travel the speed of light if it has a rest mass (a mass in its own frame of reference) because relativistic mass increases as speed increases. But for something that doesn't have a rest mass (such as a photon), it has to move at the speed of light in order to even exist at all. (Or atleast, that's what the equations seem to suggest to me. I posted my reasoning behind this here: https://www.physicsforums.com/showthread.php?t=79637 and nobody told me I was wrong so I assume it was correct.)
 
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  • #4
Chronos
Science Advisor
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ludi_srbin said:
How does light travel? What gives the energy to the photons to travel at c? And if in order for something to travel at c you need an infintie amount of energy, how come photon travels at c?
Here is a link to get you started:

Special Relativity as a Physical Theory
http://www.arxiv.org/abs/physics/0410124

And here:
http://physics.nyu.edu/hogg/sr/
 
  • #5
Igor_S
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εllipse said:
To elaborate, it only takes an infinite amount of energy for something to travel the speed of light if it has a rest mass (a mass in its own frame of reference) because relativistic mass increases as speed increases. But for something that doesn't have a rest mass (such as a photon), it has to move at the speed of light in order to even exist at all. (Or atleast, that's what the equations seem to suggest to me. I posted my reasoning behind this here: https://www.physicsforums.com/showthread.php?t=79637 and nobody told me I was wrong so I assume it was correct.)

I think modern interpretation is that mass doesn't change (it's the same in all inertial systems), but energy does according to formula:

[tex]E = \frac{mc^2}{\sqrt{1-(v/c)^2}}[/tex].

So mass is the same in the eyes of every intertial observer (the term "invariant" is commonly used).
 

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