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Myndecho's avatar

How can photons move when at the speed of light there is no time for photons?

Asked by Myndecho (948points) May 18th, 2009

And another question: In the double split experiment, do the photons act randomly when going through the split? If so why do they always choose to go through as a wave and not as a particle?

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16 Answers

RareDenver's avatar

I guess as photon has no mass then time has no real meaning for it, however we do have mass so relative to us the photon does move?

My head hurts…

robmandu's avatar

“Time is an illusion. Lunchtime doubly so.”

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Myndecho's avatar

I’ve posed this onto many people and it normally stumps them just as it has me. Reads a brief history of time again because there’s something I’m missing

RareDenver's avatar

@Myndecho I’ve read that like 4 times now and stuff like this still plays with my head. Maybe I need to read The Universe In A Nutshell again.

wundayatta's avatar

Clearly, you’r not a photon. We photons might as the same about you. How come when you move across time, you can’t reach the speed of light? Huh?

For us, there is only one moment: now. We are everywhere we will be or have been, all at once. We are constant as time flows around us. We travel not. We have been here forever and yet, we are not yet here. When it becomes obvious, you ask yourself how you could not have seen it before. Well, it’s because we were not there. You had no light, and with no light, no time, and no existence.

If we are there, or here, or everywhere, then you can have time. If we slow down for time, you all disappear. Time moves at the speed of light; that is, at the same speed as we. It can not catch up to us, or pass us, nor we it. Wherever we are, we are constant, availing any with photo-receptors to perceive.

Yet you persist in your silly fantasies. You believe in causality. You act as if everything is new, when in fact nothing is new or old. There is only is-ness. When you decide to be, you will know the answer to your question…. and every other question, too.

quarkquarkquark's avatar

It’s relativity! They move—and have time—relative to us, the observers. You’re probably “imagining” yourself as a photon. This is something to which we are all prone. It is a pointless and unhelpful pursuit.

As for your other question, the basic explanation is that light is made up of particles that act as a wave. Photons don’t act randomly, exactly, when going through the split. They spread in a pattern predicted probabilistically by the Schrodinger wave function. They “choose” nothing—beware of that kind of pseudoscientific terminology. There is a path photons are most likely to follow, and deviations from this path are predicted statistically by, well, math. As such, they behave as a wave.

FireMadeFlesh's avatar

Photons are light. What we commonly call light is a stream of photons in the visible portion of the energy spectrum. Since they are the same thing, they must travel at the same speed.

In the double slit experiment, we are conducting a wave experiment, and so see wave properties of the photons. Every particle/wave is a particle AND a wave, and the experiment we perform simply determines which properties we measure.

andrew's avatar

Remind me again, then, photons have no mass? Is that correct?

RareDenver's avatar

@andrew I think it might be more correct to say “they have negligible mass” but I’m no expert. I’m guessing that they must have some mass if they can be affected by the gravitational pull of a singularity, for instance in a black hole.

Although then again is it just the infinite curvature of space time around a singularity that causes photons to fall into it? They wouldn’t necessarily need a mass then would they?

FireMadeFlesh's avatar

@andrew That is correct, they have no mass. Anything of zero mass travels at the speed of light. This is part of the reason we know neutrinos have mass, although it is too small to measure with current technology.

FireMadeFlesh's avatar

@RareDenver Photons are affected by gravity because they travel in straight lines through curved space. They have no mass, but must still travel through warped space (take a look at gravitational lensing. This looks like a good book, but try Wiki first). Photons cannot escape a singularity because of the warped spacetime, which is warped tightly enough that the photons travel ever closer to the singularity. Accretion discs around black holes radiate strong gamma radiation, and hard x-rays. This shows that photons can escape from outside the event horizon.

andrew's avatar

@FireMadeFlesh Outside the event horizon (just making sure), since anything within the event horizon is in a hot mess.

FireMadeFlesh's avatar

@andrew Yes, outside the event horizon. Anything within the event horizon we cannot know for sure because Quantum and General Relativity contradict each other. Our best guesses are spaghettification and/or obliteration by radiation.

FireMadeFlesh's avatar

To all: sorry about my link above, that book contains a lot of mathematical content far above my level (which is effectively the highest level taught in Australian high schools). Try Wikipedia for good explanations on gravitational lensing.

RareDenver's avatar


Yes that’s what I was getting at when I said

“Although then again is it just the infinite curvature of space time around a singularity that causes photons to fall into it? They wouldn’t necessarily need a mass then would they?”

You though said it far eloquently than I ever could, and more authoritatively, not my wishy washy way of putting a question mark at the end of everything!

FireMadeFlesh's avatar

@RareDenver Thank you! I guessed you were right, but though I might clarify because you seemed unsure of yourself thanks to the first paragraph.

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