# Thread: From where the photon get the energy to travel?

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Mar 2006
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## From where the photons get the energy to travel?

From where does the photon supply itself with the energy needed to travel for billions of years?

2. Order of Kilopi
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May 2004
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From what I understand a photon is energy...

Photons have no mass either, so I don't see how they'd need energy to move.

3. A photon has 0 invariant mass, and in a vaccum doesn't suffer from a loss of speed, so once it is emitted, say, for instance, when a nucleus goes from a higher to a lower energy level, it travels at the constant rate of C, unless/until it interacts with matter. So, it doesn't need to supply itself with energy once accelerated, just like a spaceship doesn't need to use propulsion to maintain momentum in a vacuum.

Edit: This is a very simplistic answer, but I can supply you with links if you require a more complicated explanation or the maths behind it
Last edited by Serenitude; 2006-Nov-04 at 09:15 AM. Reason: Clarifying simple answer

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