[geordief]

When it is said that time does not pass for a photon as it moves in a vacuum does that imply  that no internal  activity is possible? (or does this description only apply to observations upon the photon moving  in a vacuum?)

Is there such a concept as a potential  internal structure of a photon that would be  subject to change?

If any particle is massless does it necessarily lack an internal structure?

[Bill S]

If any particle is massless does it necessarily lack an internal structure?

That might depend on whether or not you consider things like frequency, amplitude and energy as internal attributes/structure.

[geordief]

That might depend on whether or not you consider things like frequency, amplitude and energy as internal attributes/structure

I don't think that.I thought its(ie a photon's)  energy came from its relationship to its environment.
I thought the frequency and amplitude were similarly a function of its relation to its environment.

So not internal.

I am not clear whether a  proton is supposed to not experience   proper time**  or whether it is simply  a question that cannot be asked (a bit like the singularity  scenario(s?)  which just seems to show that the present model has run out of road)

**no matter what speed a massive object travels at  it is always said that it experiences the same proper time  as any other object  in any other FoR (1 sec per sec as it is put simplistically), but with light  I get the feeling that this circumstance may no longer apply-unless I have misunderstood and all that is being said is that the question does not arise.

[jeffreyH]

How do we mark the passage of time? We observe things changing state. The hands of a watch moving, particle decay or interactions and so on. In a universe containing only one object with the only two states the object has are constant velocity and straight line motion and that is the only thing observable then how would the passage of time be marked?

In it's own inertial frame of reference nothing is happening.

[geordief]

Is this time stopping thing as banal as the way ,if you went to the shops and  took your time ,maybe dropping in at the Nag's Head and the bookie's  and then glanced at your smartphone to catch up on the news you would see that  by God that M'gabe F**er (and much more besides had also happened ) had resigned in the course of your journey.

If on the other hand you made a dash for it  as it was a rainy day  and similarly  took a check of the news ,practically nothing would have(had time to have)  happened.

Are we talking the same phenomenon , the faster you move the less happens over the course of your journey. With light  the same happens ,but to an infinite degree.

Or is there a lot,lot  more to it than that?Is that example even relevant and are these light related  effects entirely relativistic

[Bill S]

 Wheeler said: “Time is nature's way to keep everything from happening all at once”. This may sound like a flippant comment, but it is in fact quite a profound observation.  We might say that eternity is the absence of time, and that in eternity everything must happen at once.  However, even that statement is misleading: in order for something to happen there must be some passage of time.  In eternity, everything just is.  So Wheeler's assertion draws a distinction between "reality" as it might be, and "reality" as we perceive it.

[Bill S]

In a universe containing only one object with the only two states the object has are constant velocity and straight line motion and that is the only thing observable then how would the passage of time be marked?

In it's own inertial frame of reference nothing is happening.

Indeed, how would space or motion be measured.

I found this in my notes from a few years ago, when I was struggling with some basic ideas. 

I remind others that I write my notes as though I were trying to explain a point to someone with even less knowledge than I might have, so anything that sounds patronising is not intended as such.

“Imagine you are in a space craft at the “centre” of an infinite, void.   Nothingness stretches infinitely in every direction.  You perceive yourself as being stationary, but suppose you engage your engine and travel at fractionally below light speed for five seconds, then stop.  You review your position; are you 1,500,000 kilometres away from where you started?  Is there now more nothingness behind you than there is in front?  On reflection you conclude that there is still an infinity of nothingness in every direction.  There is in fact nothing to which your motion can be relative.  You have “moved”, but you are still in the same place - in the “centre” of an infinity of nothingness - your movement has no real meaning. 

You can argue that if you use your engine to propel your craft forward you will be able to detect your motion, as you will be accelerating, and accelerated motion can be felt by the person doing the accelerating. Undoubtedly this is so, but as you had no way of telling if you were in motion or not before you engaged your engine, you cannot tell if you have moved off from a standstill, if you have simply increased the speed at which you were already travelling, or if you have decreased your speed; which would be the case if you had already been travelling “backwards” without being aware of that fact. 

However, because no matter how far you move, you will still perceive yourself as being in the same place, the whole question of how far you might have travelled, and at what speed, is purely academic.”

[Bill S]

is this time stopping thing as banal as the way ,if you went to the shops and  took your time ,maybe dropping in at the Nag's Head and the bookie's  and then glanced at your smartphone to catch up on the news you would see that  by God that M'gabe F**er (and much more besides had also happened ) had resigned in the course of your journey.

If on the other hand you made a dash for it  as it was a rainy day  and similarly  took a check of the news ,practically nothing would have(had time to have)  happened.

Are we talking the same phenomenon , the faster you move the less happens over the course of your journey. With light  the same happens ,but to an infinite degree.

Or is there a lot,lot  more to it than that?Is that example even relevant and are these light related  effects entirely relativistic

The distinction must be that, in your example, time has remained unchanged, you have simply experienced more of it in one scenario than in the other.

BTW, the whole idea of stopping time assumes that time is moving.  This must mean that time is something in its own right.  Could be safer to think in terms of our moving through time. 

This introduces the ideas of “tensed” and “untensed” time.  That’s fun.

[Colin2B]

Is this time stopping thing as banal as the way ,if you went to the shops and  took your time ,maybe dropping in at the Nag's Head and the bookie's  and then glanced at your smartphone to catch up on the news you would see that  by God that M'gabe F**er (and much more besides had also happened ) had resigned in the course of your journey.

If on the other hand you made a dash for it  as it was a rainy day  and similarly  took a check of the news ,practically nothing would have(had time to have)  happened.

What you are talking about here is the difference between perceptual time ie internal brain memory etc, and measured time ie clock time.

Are we talking the same phenomenon , the faster you move the less happens over the course of your journey. With light  the same happens ,but to an infinite degree.

Or is there a lot,lot  more to it than that?Is that example even relevant and are these light related  effects entirely relativistic

They are relativistic.
If you could travel say from earth to a point 1lightyear away, the faster you travelled the shorter the distance would appear – length contraction – so the less time you would spend getting there. However, someone on earth would measure the distance as one light year so conclude that time is dilated for you.

When it is said that time does not pass for a photon as it moves in a vacuum does that imply  that no internal  activity is possible? (or does this description only apply to observations upon the photon moving  in a vacuum?)

Is there such a concept as a potential  internal structure of a photon that would be  subject to change?

If any particle is massless does it necessarily lack an internal structure?

What do you mean by internal activity or internal structure?
The photon is a travelling/propagating variation of the electromagnetic field, as such it will have a fundamental frequency and harmonics and hence has wavelike/pulselike properties. Because the varying fields can interact with certain materials eg dielectrics it can transfer momentum and hence has particle like properties.
So I don't tend to think in terms on internal structure or internal activity.

[Bill S]

The photon is a travelling/propagating variation of the electromagnetic field, as such it will have a fundamental frequency and harmonics and hence has wavelike/pulselike properties. Because the varying fields can interact with certain materials eg dielectrics it can transfer momentum and hence has particle like properties.
So I don't tend to think in terms on internal structure or internal activity.

That makes sense to me, but seems to bring us back to the "not a wave...not a particle" idea.

[Colin2B]

That makes sense to me, but seems to bring us back to the "not a wave...not a particle" idea.

I’m not sure it does.
The way I look at it is that sound waves can transfer momentum, but we never get into a discussion as to whether sound is a wave or particle. The reality is that with sound - as with other macro phenomena - the energy is effectively continuous and there is no value in considering quanta. That isn’t the case with atomic and sub atomic interactions, quanta become important, so if you are looking at light in the macro way (lots of photons) its best to treat it as a wave, but at the level of individual quanta it can be useful to do calculations as if it were a particle. But doing that doesn’t imply anything about the structure of light, the variations of E&B are very much a wave.

[geordief]

If you could travel say from earth to a point 1lightyear away, the faster you travelled the shorter the distance would appear – length contraction – so the less time you would spend getting there. However, someone on earth would measure the distance as one light year so conclude that time is dilated for you.

So,for the sake of example if we discovered a promising  exoplanet  a thousand  light years from Earth and were able to send a spacecraft in its direction at .99c with a nuclear family or two on board how much would they have aged by the time they reached their destination?**

I take it that ,if they returned to Earth it would be a little over 2000 years later....

**not so good at maths ...it wouldn't be 140 years  would it  ;-)

[Kryptid]

So,for the sake of example if we discovered a promising  exoplanet  a thousand  light years from Earth and were able to send a spacecraft in its direction at .99c with a nuclear family or two on board how much would they have aged by the time they reached their destination?**

I take it that ,if they returned to Earth it would be a little over 2000 years later....

**not so good at maths ...it wouldn't be 140 years  would it  ;-)

http://www.emc2-explained.info/Dilation-Calc/#.WhZHYFWnHrc

[jeffreyH]

If you could travel say from earth to a point 1lightyear away, the faster you travelled the shorter the distance would appear – length contraction – so the less time you would spend getting there. However, someone on earth would measure the distance as one light year so conclude that time is dilated for you.

So,for the sake of example if we discovered a promising  exoplanet  a thousand  light years from Earth and were able to send a spacecraft in its direction at .99c with a nuclear family or two on board how much would they have aged by the time they reached their destination?**

I take it that ,if they returned to Earth it would be a little over 2000 years later....

**not so good at maths ...it wouldn't be 140 years  would it  ;-)

Don't underestimate yourself.