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from where does light get its kinetic energy to travel these much long distances? Answered

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kelseymh (author)2011-12-07

Photon's don't have "kinetic energy" in the sense of some energy different from their mass. Since real (as opposed to virtual) photons have zero rest-mass, all their energy is "kinetic," and hence the adjective is redundant. The energy of a photon is determined solely by the process which produced it.

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gruffalo child (author)kelseymh2011-12-07

And what are virtual photons???

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kelseymh (author)gruffalo child2011-12-07

(I'm guessing you have already typed "virtual photons" into Wikipedia, and want more information...).

Virtual photons are exchanged between charged or magnetic particles, and are the quanta of the electric and magnetic forces. In terms of Feynman diagrams, virtual photons only connect vertices, and do not appear as external lines (incoming or outgoing observables).

Because virtual photons are not directly observable, when calculating an interaction involving them you must integrate over all possible four-momenta, including both massless and massive cases.

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gruffalo child (author)kelseymh2011-12-08

Oh, THOSE photons... I simply never thought you have a special name for them, I think I could have guessed, but I somehow didn't... I remember sitting in the grass almost as tall as I am and asking if you could see the shining between particles if you get small enough.

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lemonie (author)2011-12-07

Light is energy.

L

You may as well ask "where does love get it's energy from?"

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BrazenRain (author)2011-12-07

Traveling across a longer distance does not require more energy.
Energy (conventionally) correlates with mass and speed.

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kelseymh (author)BrazenRain2011-12-07

Except that photons have no mass, and travel at a fixed speed through vacuum. In this case, energy correlates with frequency.

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Kiteman (author)2011-12-07

The photons of light from a candle on a cake do not have much difference to the photons of light from an exploding supernova (wavelength ("colour") is the only difference).

The reason that the supernova can be seen across the universe, when a candle can only illuminate a room, is the sheer number of photons involved.

A photon from a candle will travel as far and as fast as a supernova photon, but will arrive alone and barely detectable, rather than in the company of many.

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