light & energy

[Michael Garrity]

Let us assume that it is possible to decerlate a photon to zero velocity instantaneously. How much energy would be released?

Mike Garrity

[SilverWingedSeraph]

Photons are energy, so... presumably all the energy they're made up of would be released as heat. So uh... the amount of energy an individual photon contains is about 3.58E-19 Joules, I think, though I think the wavelength can affect things slightly. Which is a teeny tiny miniscule amount of energy. One photon is nothing.

[Michael Garrity]

Seraph:

Now that you have given a specific figure for the energy of a photon of light, how could it be used to determine the energy that would be released if a beam of light were to be stopped instantaneously?

Mike Garrity

[Sarevok]

I think you guys are forgetting that classical mechanics don't apply strictly to photons. They have no "kinetic energy".

[GrandMasterTerwynn]

Let us assume that it is possible to decerlate a photon to zero velocity instantaneously. How much energy would be released?

Mike Garrity

Depends on the photon. As has been mentioned, you can stop a photon instantly. You stop photons instantly all the time. The energy imparted is expressed by the formula of Energy = (Planck's constant * the speed of light) / wavelength of the photon, and is expressed in terms of electron-volts.

[starslayer]

I think you guys are forgetting that classical mechanics don't apply strictly to photons. They have no "kinetic energy".

Yeah they do. Their energy is entirely kinetic. They also have momentum. Photons may also have energy you want them to have, although the vast majority, even most gamma rays, have macroscopically minuscule amounts.

[PeZook]

You can stop a photon instantly - let it hit you and it gets absorbed by your atoms.

Stand in the sun and you can feel the energy released. The amount varies with the type and intensity of the light.

A lot of them get reflected, though.

[Darth Tedious]

You can stop a photon instantly - let it hit you and it gets absorbed by your atoms.

Stand in the sun and you can feel the energy released. The amount varies with the type and intensity of the light.

A lot of them get reflected, though.

He didn't say you'd stop all of them. Another variable with a considerable bearing on the amount of reflection would be what colour you're wearing (assuming you're clothed).

[SCRawl]

Once photons are absorbed, they aren't photons anymore -- they release some portion of their energy into their target. Is it possible that the OP wanted to know if a photon could be "stopped" relative to some other non-photon, becoming a photon at rest? The very concept makes no sense to me, but it might not offend the sensibilities of a person without a background in science.

[Simon_Jester]

Yeah.

It's a bit closer to the underlying reality to imagine a "photon" as a little packet of standing waves- electric and magnetic fields tangled up together and zipping along in a straight line like waves on a string.

Trying to make one stand still is an impossibility; it's like trying to make an ocean wave stand still. Try it and you get a lump of water piled up above the surface of the rest of the water; it'll just collapse under its own weight and you have nothing.

[Eleas]

Trying to make one stand still is an impossibility; it's like trying to make an ocean wave stand still. Try it and you get a lump of water piled up above the surface of the rest of the water; it'll just collapse under its own weight and you have nothing.

Wow. That may be the best analogy on the subject I've heard.

[Simon_Jester]

Mathematically rigorous, to, up to a point; the classical-physics treatment of electromagnetic waves uses the same partial differential equation (known, imaginatively, as "the wave equation") as the one for water waves.

I could equally well have used sound waves: a sound wave that's standing still isn't a sound wave; it's just a region of high-pressure air, which won't last long at all before the pressure equalizes.

[Eleas]

True, but water is a lot more visceral, which adds to the effect. I don't know many people who don't recall trying to touch or preserve a wave when they were little.