Mass and Energy: Photons, Energy, and Light Speed

AI Thread Summary
Photons possess energy, quantified by the equation E = hf, but they have zero rest mass, allowing them to travel at the speed of light. The distinction between energy and mass is crucial; while energy can travel at light speed, matter with non-zero rest mass cannot. This is due to the principles of relativity, which state that only massless particles like photons can achieve light speed. The concept of relativistic mass does not change this fundamental limit for massive objects. Thus, while energy and mass are interchangeable, their behavior under the laws of physics differs significantly.
pnazari
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Ok I have some general questions about mass and energy. I was wondering if photons have any energy themselves? And if they do, why is it that energy can travel at the speed of light but mass can not (ie, if they are interchangeable why can't mass travel at light speed). Thanks for your time.
 
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Photons can have virtually any energy...But photons do not have rest mass,that's why they always travel at "c" in vacuum.The relativistic mass of the photon (given by Einstein's equation) has nothing to do with its rest mass and hence with its speed...

What do you mean,"energy can travel of the spped of light"...??PHOTON'S ENERGY TRAVELS AT THE SPEED OF LIGHT.It's also valid for any other massless particles...

Daniel.
 
What I mean is that if photon has energy and it is traveling at c then it's energy is also traveling at c...i don't even know if this is a valid statement...
 
Yes,in the case of the photon,its energy travels at "c",simply because the photon IS ENERGY.Quantum of energy for the electromagnetic field...

Daniel.
 
So then if the photon is just energy traveling at c, and since energy and matter are interchangeable, then why is it that matter can't travel at c? That was my original question.

If I understand what you said previously, it is because the photon has zero rest mass?
 
pnazari said:
So then if the photon is just energy traveling at c, and since energy and matter are interchangeablethen why is it that matter can't travel at c?



Matter which has nonzero rest mass cannot travel at "c".Period.

pnazari said:
If I understand what you said previously, it is because the photon has zero rest mass?

Yes.

Daniel.
 
pnazari said:
Ok I have some general questions about mass and energy. I was wondering if photons have any energy themselves? And if they do, why is it that energy can travel at the speed of light but mass can not (ie, if they are interchangeable why can't mass travel at light speed). Thanks for your time.
Yes. Photons have energy E = hf. A photon has zero proper mass m0 (aka "rest mass") but a non-zero inertial mass m = p/v = p/c = E/c2. If you'd like to then you can think of light as carrying mass with it.

Pete
 

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