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### Author Topic: Does a photon move through time?  (Read 9745 times)

#### amrit

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##### Does a photon move through time?
« on: 08/06/2010 22:28:31 »
If at the light speed time disappear how than that photon moves through space-time?
Photon should move through space only!

yours amrit

Edited your title to be a question - Mod
« Last Edit: 09/06/2010 10:16:21 by JP »

#### Geezer

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##### Re: Does a photon move through time?
« Reply #1 on: 09/06/2010 01:00:46 »
If at the light speed time disappear how than that photon moves through space-time?
Photon should move through space only!

How do you know it "moved" at all? If it arrived as soon as it departed, it was in two places at the same instant in time, so, in a sense, it didn't move through space and it didn't move through time.

Photons are very strange things.

#### JP

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##### Re: Does a photon move through time?
« Reply #2 on: 09/06/2010 02:50:47 »
Of course a photon moves through time.  If I get a very long length of optical fiber and send a pulse of light down it, the pulse will arrive after some time has passed.  I can measure this.  The photon has moved from one point in space and time to the same point in space, at a later time.  Its net motion has only been in time!

#### Geezer

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##### Re: Does a photon move through time?
« Reply #3 on: 09/06/2010 04:45:43 »
Of course a photon moves through time.  If I get a very long length of optical fiber and send a pulse of light down it, the pulse will arrive after some time has passed.  I can measure this.  The photon has moved from one point in space and time to the same point in space, at a later time.  Its net motion has only been in time!

JP, Is it incorrect to say that (from the "perspective" of the photon - if a photon could have a perspective) that no time elapses between its departure and arrival, or do I have that wrong?

We would certainly observe time elapse during a photon's journey. As you point out, it's not difficult to measure.

#### JP

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##### Re: Does a photon move through time?
« Reply #4 on: 09/06/2010 06:59:56 »
It's natural (but wrong) to think that the equations of SR tell you what light "experiences" if you just take the limit as the observer's speed approaches the speed of light.  After all, light moves at the speed of light.  However, there's a big mistake in doing this.  In order to ask what light experiences, you would have to be riding along with the light and it would have to be stationary in your reference frame.  SR assumes that no matter how fast you're going, light is always moving at the speed of light with respect to you.

More mathematically put, although you can take the limit as your velocity approaches the speed of light and get out answers, these answers can't describe what a photon sees, since you're still describing a frame in which the photon is moving at the speed of light.

#### Geezer

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##### Re: Does a photon move through time?
« Reply #5 on: 09/06/2010 07:28:21 »
It's natural (but wrong) to think that the equations of SR tell you what light "experiences" if you just take the limit as the observer's speed approaches the speed of light.  After all, light moves at the speed of light.  However, there's a big mistake in doing this.  In order to ask what light experiences, you would have to be riding along with the light and it would have to be stationary in your reference frame.  SR assumes that no matter how fast you're going, light is always moving at the speed of light with respect to you.

More mathematically put, although you can take the limit as your velocity approaches the speed of light and get out answers, these answers can't describe what a photon sees, since you're still describing a frame in which the photon is moving at the speed of light.

I thought the distance contracts to zero at C. Doesn't that mean the photon travels zero distance, and therefore, requires no time? (I suspect I'm missing something here  )

#### amrit

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##### Re: Does a photon move through time?
« Reply #6 on: 09/06/2010 07:32:41 »
If at the light speed time disappear how than that photon moves through space-time?
Photon should move through space only!

How do you know it "moved" at all? If it arrived as soon as it departed, it was in two places at the same instant in time, so, in a sense, it didn't move through space and it didn't move through time.

Photons are very strange things.

- not so strange, photon move with a light speed. So my question is clear: does photon move in time or not ?

#### JP

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##### Re: Does a photon move through time?
« Reply #7 on: 09/06/2010 08:00:54 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

#### Geezer

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##### Re: Does a photon move through time?
« Reply #8 on: 09/06/2010 08:27:43 »
If at the light speed time disappear how than that photon moves through space-time?
Photon should move through space only!

How do you know it "moved" at all? If it arrived as soon as it departed, it was in two places at the same instant in time, so, in a sense, it didn't move through space and it didn't move through time.

Photons are very strange things.

- not so strange, photon move with a light speed. So my question is clear: does photon move in time or not ?

From our perspective, it seems that photons change their position in time. If we agree that's the same as moving in time, then yes, photons move in time.

EDIT: It might be safer to say that photons simply "move". "Move" already includes the concept of time, so "moving in time" might mean something else. That's why I prefer to say "change position in time".
« Last Edit: 09/06/2010 08:52:13 by Geezer »

#### Geezer

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##### Re: Does a photon move through time?
« Reply #9 on: 09/06/2010 09:03:24 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

I was simply going with the math. At C the distance seems to resolve to zero. If that is true, I would have thought the time would also be zero.

#### peppercorn

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##### Re: Does a photon move through time?
« Reply #10 on: 09/06/2010 09:35:45 »
From our perspective, it seems that photons change their position in time. If we agree that's the same as moving in time, then yes, photons move in time.

EDIT: It might be safer to say that photons simply "move". "Move" already includes the concept of time, so "moving in time" might mean something else. That's why I prefer to say "change position in time".

In a sense I think it can be considered that photons are independent of movement in either time or space.  Clearly from our frame of reference they can be considered to move at 'c' from from one point in space to another. However, this is only ever going to be a philosophical discussion as no conscious material structure (ie. reasoning matter like us) can ever travel at 'c'.

mmmm, makes one wonder if this rules out all those SciFi ideas about entities that 'live' as pure energy...

#### JP

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##### Does a photon move through time?
« Reply #11 on: 09/06/2010 10:18:46 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

I was simply going with the math. At C the distance seems to resolve to zero. If that is true, I would have thought the time would also be zero.

That's certainly true if you consider "what happens when I go near the speed of light?" to be the question.  However, just going fast isn't really moving like light, since you can never be riding alongside of a photon even at these speeds.

#### amrit

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##### Does a photon move through time?
« Reply #12 on: 09/06/2010 11:13:37 »
If at the light speed time disappear how than that photon moves through space-time?
Photon should move through space only!

How do you know it "moved" at all? If it arrived as soon as it departed, it was in two places at the same instant in time, so, in a sense, it didn't move through space and it didn't move through time.

Photons are very strange things.

- not so strange, photon move with a light speed. So my question is clear: does photon move in time or not ?

From our perspective, it seems that photons change their position in time. If we agree that's the same as moving in time, then yes, photons move in time.

EDIT: It might be safer to say that photons simply "move". "Move" already includes the concept of time, so "moving in time" might mean something else. That's why I prefer to say "change position in time".

change position in time
or
moving in time
is the same thing

#### Geezer

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##### Does a photon move through time?
« Reply #13 on: 09/06/2010 19:56:21 »

change position in time
or
moving in time
is the same thing

I think movement (x) would be expressed as a change of position in time, or;

x = dS/dt  (where S is distance)

I'm not sure how to express movement in time.

Would it be dx/dt? I don't think that's the same as dS/dt.

That's why I think they are different things.

#### Geezer

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##### Does a photon move through time?
« Reply #14 on: 09/06/2010 20:13:41 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

I was simply going with the math. At C the distance seems to resolve to zero. If that is true, I would have thought the time would also be zero.

That's certainly true if you consider "what happens when I go near the speed of light?" to be the question.  However, just going fast isn't really moving like light, since you can never be riding alongside of a photon even at these speeds.

I realize I'm probably bending things a bit here if the contraction is really an observed effect. If photons don't degrade over distance, does that tend to reinforce the notion that they are sort of immune to time? (I don't know how to express this without using words like "immune", "experience" etc, which are really not applicable.)

#### amrit

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##### Does a photon move through time?
« Reply #15 on: 09/06/2010 23:24:58 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

I was simply going with the math. At C the distance seems to resolve to zero. If that is true, I would have thought the time would also be zero.

That's certainly true if you consider "what happens when I go near the speed of light?" to be the question.  However, just going fast isn't really moving like light, since you can never be riding alongside of a photon even at these speeds.

I realize I'm probably bending things a bit here if the contraction is really an observed effect. If photons don't degrade over distance, does that tend to reinforce the notion that they are sort of immune to time? (I don't know how to express this without using words like "immune", "experience" etc, which are really not applicable.)

photon move in space only, time does not run anywhere at any speed, no photon speed, no bullock car speed, with clocks we measure directly speed and not time, change of speed happens in space only and not in time....
« Last Edit: 09/06/2010 23:30:20 by amrit »

#### Geezer

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##### Does a photon move through time?
« Reply #16 on: 10/06/2010 01:40:49 »

photon move in space only, time does not run anywhere at any speed, no photon speed, no bullock car speed, with clocks we measure directly speed and not time, change of speed happens in space only and not in time....

Yes, well you do say that a lot, but why are you asking the question if you are so sure you know the answer?

#### JP

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##### Does a photon move through time?
« Reply #17 on: 10/06/2010 03:39:07 »
How would you define what an object experiences in SR?  I would define it as what you experience when you are in the frame in which that object is at rest.  In the case of massive objects, as you accelerate to match the object's speed, it appears to slow down until it is eventually stationary in your reference frame.  In the case of light, you can accelerate all you want, but it won't slow down.  You can never be in the frame at which the light is at rest.

What does this mean for defining what a photon "experiences"?  I would say that it means that the question itself is ill-posed.

I was simply going with the math. At C the distance seems to resolve to zero. If that is true, I would have thought the time would also be zero.

That's certainly true if you consider "what happens when I go near the speed of light?" to be the question.  However, just going fast isn't really moving like light, since you can never be riding alongside of a photon even at these speeds.

I realize I'm probably bending things a bit here if the contraction is really an observed effect. If photons don't degrade over distance, does that tend to reinforce the notion that they are sort of immune to time? (I don't know how to express this without using words like "immune", "experience" etc, which are really not applicable.)

Hmm... it could be.  I admit that the mathematics of v->c for a massive object along with the fact that light doesn't decay does suggest something is special about it.  But remember that light is special, as it's the one thing in special relativity that always moves at a constant speed regardless of what the observer is doing.

However, I still would argue that answering "does light age?" requires you to define a rest-frame for the light and look at the effects of space and time in that rest frame.  Letting v->c isn't sufficient, since the light isn't at rest.  This might be a case where asking anything from light's "point of view" is ill-posed within our current theories.

#### Geezer

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##### Does a photon move through time?
« Reply #18 on: 10/06/2010 04:05:23 »

Hmm... it could be.  I admit that the mathematics of v->c for a massive object along with the fact that light doesn't decay does suggest something is special about it.  But remember that light is special, as it's the one thing in special relativity that always moves at a constant speed regardless of what the observer is doing.

However, I still would argue that answering "does light age?" requires you to define a rest-frame for the light and look at the effects of space and time in that rest frame.  Letting v->c isn't sufficient, since the light isn't at rest.  This might be a case where asking anything from light's "point of view" is ill-posed within our current theories.

Yes - it seems a bit silly to use terms like "point of view" in this context.

I think photons may be the only "things" that have zero rest-mass. If that is true, do all the "things" that have some rest-mass tend to degrade with distance? Would that provide a clue?

(Sorry about the "things". I'm trying to avoid defining what photons might be!)

#### JP

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##### Does a photon move through time?
« Reply #19 on: 10/06/2010 04:39:27 »
I'm not sure I follow what you mean by degrade with distance?  Do you mean that the particle decays at some time?

#### Geezer

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##### Does a photon move through time?
« Reply #20 on: 10/06/2010 04:54:48 »
I'm not sure I follow what you mean by degrade with distance?  Do you mean that the particle decays at some time?

Ah, yes (I think). Photons seem to retain their energy despite the distance/time that we perceive them to travel. I'm not sure that any other "things" can retain their energy in a similar fashion.

(Rats! You used the "p" word.)
« Last Edit: 10/06/2010 05:12:32 by Geezer »

#### JP

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##### Does a photon move through time?
« Reply #21 on: 10/06/2010 05:41:26 »
I'm not sure about that.  Photons and gluons both have zero mass and behave quite differently.  A photon is stable while a gluon quickly decays into a jet of particles.  http://en.wikipedia.org/wiki/Jet_(particle_physics)

Electrons have a mass, but as far as we know, they seem to be stable.

As for retaining their energy, which is different than decaying, conservation of energy should hold for any process, even if a particle decays, the decay products should show conservation of energy.

#### Geezer

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##### Does a photon move through time?
« Reply #22 on: 10/06/2010 06:31:01 »
I'm not sure about that.  Photons and gluons both have zero mass and behave quite differently.  A photon is stable while a gluon quickly decays into a jet of particles.  http://en.wikipedia.org/wiki/Jet_(particle_physics)

Electrons have a mass, but as far as we know, they seem to be stable.

As for retaining their energy, which is different than decaying, conservation of energy should hold for any process, even if a particle decays, the decay products should show conservation of energy.

I'm not in a strong position to argue, but I don't think electrons are capable of travelling for light-years in the way that photons do. I seem to remember that electron guns are a bit wimpy.

#### amrit

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##### Does a photon move through time?
« Reply #23 on: 10/06/2010 07:19:35 »

photon move in space only, time does not run anywhere at any speed, no photon speed, no bullock car speed, with clocks we measure directly speed and not time, change of speed happens in space only and not in time....

Yes, well you do say that a lot, but why are you asking the question if you are so sure you know the answer?

that is for you.....I already know it

#### Geezer

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##### Does a photon move through time?
« Reply #24 on: 10/06/2010 07:35:10 »

photon move in space only, time does not run anywhere at any speed, no photon speed, no bullock car speed, with clocks we measure directly speed and not time, change of speed happens in space only and not in time....

Yes, well you do say that a lot, but why are you asking the question if you are so sure you know the answer?

that is for you.....I already know it

Wow! I am humbled by your vast knowledge. BTW, you're banned.

#### The Naked Scientists Forum

##### Does a photon move through time?
« Reply #24 on: 10/06/2010 07:35:10 »