Am I misunderstanding something?

Recommended Posts

If something is moving at the speed of light relative to me (I know this isn't possible, but for my purposes it doesn't really matter), it will have its time slowed significantly.

Since velocity is defined as distance/time, the time will be slowed so the object will appear to travel a farther distance in the same time, correct? That would mean it would have to be going faster than the speed of light...

There has to be some gap in my understanding but I'm not sure what.

Share on other sites

8 minutes ago, Herzy said:

If something is moving at the speed of light relative to me (I know this isn't possible, but for my purposes it doesn't really matter), it will have its time slowed significantly.

Since velocity is defined as distance/time, the time will be slowed so the object will appear to travel a farther distance in the same time, correct? That would mean it would have to be going faster than the speed of light...

There has to be some gap in my understanding but I'm not sure what.

Thats relativity!

In reality, the object is in its own space/time and what you see has no effect on it. You "see" the relative speed but this is not the actual speed.

Edited by alanjgreen
• 1
Share on other sites

The only thing that can move at the speed of light is, well, light (electromagnetic radiation).  So time effectively stops for a photon - a clock on a photon would not tick - and if you could "ride a photon" (how cool would that be), you would make a journey from a distant galaxy to Earth instantaneously.  There is no passage of time, and distance is contracted to zero.  (In that frame of reference.)

Doug.

Share on other sites

Just a couple of clarifications:

45 minutes ago, alanjgreen said:

You "see" the relative speed but this is not the actual speed.

There is of course no such thing as the actual speed all speeds/velocities are relative.

16 minutes ago, cloudsweeper said:

The only thing that can move at the speed of light is, well, light

It is also thought that the gluon and graviton (if it is ever observed) also have zero rest mass (strictly their energy momentum 4 vector is identically zero).

They do not have a rest frame so the concept of a rest mass is a bit of an oxymoron!

Regards Andrew

Share on other sites

Suppose I am blinded by light from the sun. From the lights  perspective, it will reach the Earth instantly and might not even hit my eyes. From my perspective it will take 8 minutes to get here. How do you account for this 8 min disagreement?

Share on other sites

18 minutes ago, andrew s said:

It is also thought that the gluon and graviton (if it is ever observed) also have zero rest mass (strictly their energy momentum 4 vector is identically zero).

Regards Andrew

Thanks Andrew - Yes - I'd overlooked the fact that gravitational waves (alternatively viewed as gravitons) travel at c.

Doug.

Share on other sites

The only fact is that at a specific point in space/time, you and the photon were in the same position.

As for anything else, then its fair to say that we know less than we think we know about physics and all statements made are not based on fact

• 1
Share on other sites

5 minutes ago, Herzy said:

How do you account for this 8 min disagreement?

There is no disagreement to account for, because there is no 'standard' or 'common' time with which to measure the two. Your stopwatch is measuring your time,  the stopwatch carried by the photon measures no time. The two cannot be compared, because that would require instantaneous communication between the two stopwatches in order to synchronise them.

• 1
Share on other sites

11 minutes ago, alanjgreen said:

The only fact is that at a specific point in space/time, you and the photon were in the same position.

Why is this the only allowed fact ?

11 minutes ago, alanjgreen said:

As for anything else, then its fair to say that we know less than we think we know about physics and all statements made are not based on fact

I just don't agree with is. While we will never know everything we know a great deal about physics and can predict and postdict many events not just those directly experienced.

Regards andrew

Edited by andrew s
• 1
Share on other sites

29 minutes ago, andrew s said:

It is also thought that the gluon and graviton (if it is ever observed) also have zero rest mass

For a long time it was debated if the neutrino also had no rest mass, amongst other reasons being that there were so many of the little blighters littering the universe that even the most miniscule of rest mass would gravitationally collapse the universe into a Big Crunch. I must be getting old, I cant remember if the current thinking that it (they, the 3) have a small rest mass is beyond doubt ? ( I think it has to be to account for the oscillation between them ?? )

Share on other sites

1 minute ago, SilverAstro said:

I cant remember if the current thinking that it (they, the 3) have a small rest mass is beyond doubt ? ( I think it has to be to account for the oscillation between them ?? )

Yes the fact they can oscillate between the 3 types means, in the standard model of particle physics, they must have some rest mass.

Regards andrew

• 1
Share on other sites

12 minutes ago, andrew s said:

Why is this the only allowed fact ?

I just don't agree with is. While we will never know everything we know a great deal about physics and can predict and postdict many events not just those directly experienced.

Regards andrew

"Suppose I am blinded by light from the sun. From the lights  perspective, it will reach the Earth instantly and might not even hit my eyes. From my perspective it will take 8 minutes to get here. How do you account for this 8 min disagreement?  "

Its a fact because the photon was registered in his retina. There is proof that it was there and he was there, they were in the same place for a brief moment.

You cant prove the photon's navigation on its journey or how long the little guy had been in existence. You can give an opinion based on what you believe, but that is not a fact until it is proven.

Share on other sites

19 minutes ago, alanjgreen said:

Its a fact because the photon was registered in his retina. There is proof that it was there and he was there, they were in the same place for a brief moment.

This is just as much a theory based description of events as one that postulates that a state transition in an atom in the sun emitted a photon in the first place. I for one have never experienced a photon hitting my retina.

We clearly have a very different perspective on what physics is so I propose we leave it here.

Regards Andrew

Edited by andrew s
typo
• 1
Share on other sites

Whether we agree with each other or not is not the problem ! The problem is that Herzy has a problem requiring assistance !!

So we can all chip in with our thoughts, if any of it helps Herzy then that is great,,,  reading all thoughts helps me with what I think is my understanding, which is great,, , posting my thoughts helps me also with my understanding because if I have got something wrong shure as buttercups are yellow someone will tell me where I have gone wrong in my attempt to help whomsoever which is even greater

Wasnt it the great E. who said something to the effect if you cant explain it you dont understand it well enough ?

How you doing so far  Herzy, more or less happy than when we all started    ?

EDIT : RonnieB. often said, of the 4 candles sketch, " I wish I had written 'knockers' ", , now I wish I had written "buttercups are red"    I wonder if the word-watcher will let me get away with that ?

Edited by SilverAstro
• 2
Share on other sites

17 hours ago, SilverAstro said:

Whether we agree with each other or not is not the problem ! The problem is that Herzy has a problem requiring assistance !!

SilverAstro, I was in no way trying to draw to a close the issue raised by the OP just the side discussion that I was having with alanjgreen on different views on what Physics is. This was in my opinion distracting from the OP's question.

Regards Andrew

Share on other sites

18 hours ago, alanjgreen said:

You cant prove the photon's navigation on its journey or how long the little guy had been in existence. You can give an opinion based on what you believe, but that is not a fact until it is proven.

Alan, I'm not sure that is the case, the nature of the photon and its modes of interaction are pretty well understood and supported by evidence.  I'm not really sure what aspect of the photon's existence you are labelling as not proven or lacking in fact. Could you explain further what you mean?

Jim

Share on other sites

Saac,

the point I'm taking exception with is the stated concept the the little photon travels at infinite speed through space (distance becomes zero as stated above)

this actually ties in neatly with the OPs question about how that means it must be travelling faster than the speed of light.

please point us to the evidence that a photon can travel faster than the speed of light.

It draws into question why we are looking back in time (using light from other Galaxies) when in fact that light is instantly here, there and everywhere.

or we can just say it's relativity (as I did) but that's because I don't know as much as Einstein.

Alan

Share on other sites

21 hours ago, Herzy said:

If something is moving at the speed of light relative to me (I know this isn't possible, but for my purposes it doesn't really matter), it will have its time slowed significantly.

Since velocity is defined as distance/time, the time will be slowed so the object will appear to travel a farther distance in the same time, correct? That would mean it would have to be going faster than the speed of light...

There has to be some gap in my understanding but I'm not sure what.

Herzy the problem is dealt with when you consider measurements taken in their relative frames. You and the "something" experience different passage of time and measurement of distance. When you do your calculation of distance/time you need to make sure that your distance and time are measured in the same frame of reference. The journey time recorded by the "something" and you the observer will not agree as there is no absolute (common) reference for measurement of time.

Jim

Edited by saac
Share on other sites

1 hour ago, alanjgreen said:

Saac,

the point I'm taking exception with is the stated concept the the little photon travels at infinite speed through space (distance becomes zero as stated above)

this actually ties in neatly with the OPs question about how that means it must be travelling faster than the speed of light.

please point us to the evidence that a photon can travel faster than the speed of light.

It draws into question why we are looking back in time (using light from other Galaxies) when in fact that light is instantly here, there and everywhere.

or we can just say it's relativity (as I did) but that's because I don't know as much as Einstein.

Alan

I think we are pushing against the same open door regarding the first part  of your reply  The photon is not travelling at infinite speed, nor faster than the speed of light.  The Universe is safe!

I'm not sure why you then go on to say that the light from distant galaxies arrives instantly - if that is what you are saying, my apology If I have misunderstood. We do have to consider relativistic effects - from our reference the light from say Andromeda (2.5 million light years distant) takes 2.5 million years to arrive. Hence we can consider that we are looking at Andromeda as it was 2.5 million years ago. However from the light's perspective it has travelled a much shorter distance and as far as it is concerned it will have a different journey time.  The times recorded by us, the observer, and the photon will not be the same as there is no absolute frame of reference for time. So we can consider that we are looking into the past. The Universe is safe again- I think

I would contest that there is no doubt, save for any interaction the photon may have had during its journey, about our understanding, I certainly don't consider it to be opinion as the governing physics is pretty much established and tested.

Jim

Edited by saac
Share on other sites

45 minutes ago, alanjgreen said:

the point I'm taking exception with is the stated concept the the little photon travels at infinite speed through space (distance becomes zero as stated above)

Light always travels a speed c as measured by all inertial observers irrespective of their relative motion. That is why special relativity has the strange (to common sense) properties it does. The concept of little photon moving along a trajectory from A to B is just a loose analogy. In QM the photon does not have a position operator and so it make no sense to ask where it is or what speed it has. All QM can say is that given a photon is created (emitted) at A then the probability that it will be destroyed (detected) at B is such and such. If the two events do occur all inertial observes will agree it "moved" as if its speed were c even if they think it traveled different distances and took different times. QM offers no explanation about what happens in between the two events.

For the in between bit the best theory we have is Maxwell's equations which are compatible with QM as they are Lorentz invariant but describe classical waves not photons.

For an electromagnetic classical wave it propagates at speed c in a vacuum.

I hope this clarifies things a bit?

Regards Andrew

Edited by andrew s
Share on other sites

5 minutes ago, andrew s said:

The concept of little photon moving along a trajectory from A to B is just a loose analogy. In QM the photon does not have a position operator and so it make no sense to ask where it is or what speed it has. All QM can say is that given a photon is created (emitted) at A then the probability that it will be destroyed (detected) at B is such and such. If the two events do occur all inertial observes will agree it moved as if its speed were c even if the think it traveled different distances and took different times. QM offers no explanation about what happens in between the two events.

I think you have identified the root of the problem Andrew.  The very counter intuitive nature of light in its quantum realm means that many of our questions are invalid from the outset. We end up chasing ourselves down rabbit holes in search for an explanation rather than consider we may need to reconsider the question.

Jim

Share on other sites

Let me get this straight. I did a bunch of reading and I'll offer my explanation based on that reading for you all to correct.

If someone is traveling at 90% of c, then I'll see their time as being dilated or slowed.

However, there is no absolute motion (meaning it is impossible to experiment whether you are moving or not provided you don't accelerate) in the universe for inertial reference frames. So, the observer we thought was moving will actually see us as the ones moving and will see our times as slowed.

So, for example, suppose I travel to a distant galaxy and it takes me 2 million years to get there. Because there is no absolute motion, I could rightly say the Galaxy is moving towards me, and therefor it's time will be slowed. It will appear as if I get there very fast relative to their reference frame (that is why the photon reaches its destination instantly?). This difference in time dilation accounts for the disagreement in timing. If I got anything wrong please point it out.

Edited by Herzy
Share on other sites

If I want to use this same logic for my previous question:

Suppose I am blinded by light from the sun. From the lights  perspective, it will reach the Earth instantly and might not even hit my eyes. From my perspective it will take 8 minutes to get here. How do you account for this 8 min disagreement?

The difference is accounted for because the light can rightly say that I am moving, so it will see my time as slowed by 8 minutes and the two reference frames will both agree that I'm blinded by the suns light.

Share on other sites

*ignore accidently double posted and I'm not sure how to delete posts.

Edited by Herzy
Share on other sites

9 hours ago, Herzy said:

From the lights  perspective, it will reach the Earth instantly

Hi Herzy, I think you have now a much better understanding of relativity. The one thing you still need to grasp is that in SR "light" can't have a perspective. SR describes how observers in inertial frames of reference see the world and all inertial frame have relative velocities less than c. An observer can, in principle, be at rest in any inertial frame but light does not have a rest frame as you can't catch up with a light beam. Concepts like time proper time, time dilation and length contraction apply to observers in inertial frames.

I found this which reflects the situation and is quite readable: https://www.quora.com/If-a-photon-travels-at-the-speed-of-light-and-time-dilation-at-the-speed-of-light-is-infinite-does-this-mean-that-from-the-photons-perspective-it-takes-no-time-at-all-to-cross-the-entire-universe

Regards Andrew

PS I was pointing to the initial contribution not the following discussion which while interesting could just confuse as some of it goes back to referring to the lights (photons) perspective!

Edited by andrew s

Create an account

Register a new account

• Similar Content

• collimation woes, or is it something else?

By bomberbaz,

• 9 replies
• 297 views
• Something to look forward to!

By assouptro,

• 5 replies
• 367 views
• Something is going wrong with my flats

By Jerry Barnes,

• 4 replies
• 278 views
• Chasing down a Flat issue or something else ?

By mgirdwood,

• 0 replies
• 205 views
• AR2975, AR2976 and a taste of something to come?

By zcapp96,