## Relativity?

How does science work? And what's all this about quantum mechanics?

Moderators: AMod, iMod

uwot
Posts: 4973
Joined: Mon Jul 23, 2012 7:21 am

### Re: Relativity?

Viveka wrote: Tue Nov 07, 2017 6:38 pmOkay. I think I have an argument that works:
1, As the embankment observer sees this contraction and dilation of the train moving appreciably close to c, and the train looking at the embankment observer sees this contraction and dilation when moving appreciably close to c. However, how can both be at different rates of ticking on their light-clocks? Embankment>train, and train>embankment.  Thus there is a contradiction.
Well, as I said, the example of the light clock only applies to the moment when two inertial frames pass each other. The rest of the experience is a bit different. If you imagine a train coming down the tracks towards you, if it were made of glass, to use your example, and you could see a light clock on it; when it is a long way away, because of the angle, the pulse of light looks as if it is bouncing straight up and down.
Suppose the pulse of light is up when you first see it. For you to see it, the light from that pulse has to travel a certain distance. By the time the pulse is down, the light doesn't have to travel as far to reach you, because the train is closer to you. But whether the pulse is up or down, the light travels towards you at the same speed. Because the light from the down pulse doesn't take as long to reach you, it arrives sooner than it would have if the train was at rest (relative to you). So your experience of the ups and downs of the light clock are closer together. It looks to you as if the clock is ticking faster than your own. To the person on the train, exactly the same happens if they look at your light clock. In other words, both of you see the others light clock 'ticking' faster than your own.
Once the train has passed you, as the pulse bounces, every time, up and down, the train is further away, so the clock appears to be ticking slower, compared to your own. Again, it doesn't matter whether you are on the train or on the bank, you both see exactly the same. As davidm, myself and others have pointed out, it would only be a contradiction if the claim was that both clocks are in fact ticking slower than the other.
What the example of the 'twins paradox' is meant to demonstrate is that, in fact, one of the clocks is ticking faster than the other. This has been confirmed by experiments such as Hafele-Keating, so if some instantaneous means of communication were possible, then both parties would be able to tell which clock was ticking faster, even though, according to the premises of special relativity, they are getting further apart. But you don't need to posit superluminal communication. Superhuman visual acuity will do the trick. If someone so blessed could have watched the atomic clocks ticking in the Hafele-Keating experiment, from the surface of Earth, they would have seen the clocks on the planes ticking slower than the one in Washington, because that is what they actually did.
uwot
Posts: 4973
Joined: Mon Jul 23, 2012 7:21 am

### Re: Relativity?

Actually, I should qualify the above. It depends which way round the Earth the clocks are flying. Clocks that fly eastwards tick slower, compared to one on the ground; whereas they tick faster when flying westwards. There's a perfectly simple explanation for this in the blog/book. https://willijbouwman.blogspot.co.uk
Viveka
Posts: 369
Joined: Wed Sep 27, 2017 9:06 pm

### Re: Relativity?

uwot wrote: Fri Nov 10, 2017 7:46 am
Viveka wrote: Tue Nov 07, 2017 6:38 pmOkay. I think I have an argument that works:
1, As the embankment observer sees this contraction and dilation of the train moving appreciably close to c, and the train looking at the embankment observer sees this contraction and dilation when moving appreciably close to c. However, how can both be at different rates of ticking on their light-clocks? Embankment>train, and train>embankment.  Thus there is a contradiction.
Well, as I said, the example of the light clock only applies to the moment when two inertial frames pass each other. The rest of the experience is a bit different. If you imagine a train coming down the tracks towards you, if it were made of glass, to use your example, and you could see a light clock on it; when it is a long way away, because of the angle, the pulse of light looks as if it is bouncing straight up and down.
Suppose the pulse of light is up when you first see it. For you to see it, the light from that pulse has to travel a certain distance. By the time the pulse is down, the light doesn't have to travel as far to reach you, because the train is closer to you. But whether the pulse is up or down, the light travels towards you at the same speed. Because the light from the down pulse doesn't take as long to reach you, it arrives sooner than it would have if the train was at rest (relative to you). So your experience of the ups and downs of the light clock are closer together. It looks to you as if the clock is ticking faster than your own. To the person on the train, exactly the same happens if they look at your light clock. In other words, both of you see the others light clock 'ticking' faster than your own.
Which is a>b, b>a, and thus a contradiction.
uwot wrote: Fri Nov 10, 2017 7:46 am Once the train has passed you, as the pulse bounces, every time, up and down, the train is further away, so the clock appears to be ticking slower, compared to your own. Again, it doesn't matter whether you are on the train or on the bank, you both see exactly the same. As davidm, myself and others have pointed out, it would only be a contradiction if the claim was that both clocks are in fact ticking slower than the other.
Yes.
uwot wrote: Fri Nov 10, 2017 7:46 am What the example of the 'twins paradox' is meant to demonstrate is that, in fact, one of the clocks is ticking faster than the other. This has been confirmed by experiments such as Hafele-Keating, so if some instantaneous means of communication were possible, then both parties would be able to tell which clock was ticking faster, even though, according to the premises of special relativity, they are getting further apart. But you don't need to posit superluminal communication. Superhuman visual acuity will do the trick. If someone so blessed could have watched the atomic clocks ticking in the Hafele-Keating experiment, from the surface of Earth, they would have seen the clocks on the planes ticking slower than the one in Washington, because that is what they actually did.
But that would require a non-inertial frame of reference as it must 'turn around' to compare clocks.
OuterLimits
Posts: 238
Joined: Wed Sep 07, 2016 11:54 pm

### Re: Relativity?

Viveka wrote: Fri Nov 10, 2017 7:45 pm Which is a>b, b>a, and thus a contradiction.
It is not a contradiction if I think you are receding into the distance but you think I am, because neither of our perspectives is taken to be "objective".

So it is with relativity, if I find your clock to be ticking slow as it travels in my inertial frame and you find my clock to tick slower in your inertial frame.

There is no contradiction since neither of these is "objectively true". If the speed of light is not constrained to be the same in all inertial frames, you have the thorny question of the person following after the mirror and not seeing themselves in it.
uwot
Posts: 4973
Joined: Mon Jul 23, 2012 7:21 am

### Re: Relativity?

Viveka wrote: Fri Nov 10, 2017 7:45 pm
uwot wrote: Fri Nov 10, 2017 7:46 amIt looks to you as if the clock is ticking faster than your own. To the person on the train, exactly the same happens if they look at your light clock. In other words, both of you see the others light clock 'ticking' faster than your own.
Which is a>b, b>a, and thus a contradiction.
Do you understand the the difference between 'looks like' and 'is'?
OuterLimits
Posts: 238
Joined: Wed Sep 07, 2016 11:54 pm

### Re: Relativity?

Here's an interesting implication of SR that I'd never heard of before asking about it in a forum a few years ago:

A train is going by one person, at a high % of the speed of light.

The one person on the land is holding his clock by his face. Throughout the train, by the windows, watching the man as the train passes, are many people from the front of the train to the back, each holding a clock by his/her face. The man is so close to the train that he can only see the clock that is passing right by him on the train, and each person on the train can only see the man in the moment he is right outside the train next to them.

The people on the train are confident that their clocks are synchronized. As they pass the man, each person marks down what time on his/her own clock that was, and what the outside man's clock said. When they compare notes, they will decide that the outside man's clock was ticking slow, just as we now expect from SR. What will be the experience of the outside man? The succession of clocks going right past him appear to create a flip-animation of a clock which is ticking fast. He will conclude that time is ticking faster on the train, or that the clocks on the train are not synchronized correctly.
Viveka
Posts: 369
Joined: Wed Sep 27, 2017 9:06 pm

### Re: Relativity?

OuterLimits wrote: Fri Nov 10, 2017 8:22 pm
Viveka wrote: Fri Nov 10, 2017 7:45 pm Which is a>b, b>a, and thus a contradiction.
It is not a contradiction if I think you are receding into the distance but you think I am, because neither of our perspectives is taken to be "objective".

So it is with relativity, if I find your clock to be ticking slow as it travels in my inertial frame and you find my clock to tick slower in your inertial frame.

There is no contradiction since neither of these is "objectively true". If the speed of light is not constrained to be the same in all inertial frames, you have the thorny question of the person following after the mirror and not seeing themselves in it.
But that's the whole point. If they are not 'objectively true' then it's not science. And a problem with seeing oneself in mirrors in SRT is the light wouldn't move with the mirror to 'hit the target' of the mirrors of the light-clock, so to speak, while Galilean relativity has no such problem. The person following after the mirror and not seeing themselves in it, in another sense (Not in the previous) is a problem with both SRT and Galilean relativity, as when the train starts moving at light-speed, which is impossible for both theories when taking into account James Clerk Maxwell's Electromagnetic Theory, then one looking at a mirror wouldn't see oneself in it due to light moving at light-speed and thus at rest with respect to Light's frame of reference, which means that light moving after light would be moving at 0 with respect to one another.
OuterLimits
Posts: 238
Joined: Wed Sep 07, 2016 11:54 pm

### Re: Relativity?

Viveka wrote: Fri Nov 10, 2017 8:42 pm
OuterLimits wrote: Fri Nov 10, 2017 8:22 pm
Viveka wrote: Fri Nov 10, 2017 7:45 pm Which is a>b, b>a, and thus a contradiction.
It is not a contradiction if I think you are receding into the distance but you think I am, because neither of our perspectives is taken to be "objective".

So it is with relativity, if I find your clock to be ticking slow as it travels in my inertial frame and you find my clock to tick slower in your inertial frame.

There is no contradiction since neither of these is "objectively true". If the speed of light is not constrained to be the same in all inertial frames, you have the thorny question of the person following after the mirror and not seeing themselves in it.
But that's the whole point. If they are not 'objectively true' then it's not science. And a problem with seeing oneself in mirrors in SRT is the light wouldn't move with the mirror to 'hit the target' of the mirrors of the light-clock, so to speak, while Galilean relativity has no such problem. The person following after the mirror and not seeing themselves in it, in another sense (Not in the previous) is a problem with both SRT and Galilean relativity, as when the train starts moving at light-speed, which is impossible for both theories when taking into account James Clerk Maxwell's Electromagnetic Theory, then one looking at a mirror wouldn't see oneself in it due to light moving at light-speed and thus at rest with respect to Light's frame of reference, which means that light moving after light would be moving at 0 with respect to one another.
Just as science predicts that my perspective and yours are different, and explains why, and predicts what we will see, then so does the science of relativity predict how a person in one IF will measure another IF's clock to seem slow. In relativity, light has no "frame of reference" and all experimentation regarding light and clocks bears this out. You can rail against that all day, but it's the reason everybody cares about relativity: results.
Noax
Posts: 670
Joined: Wed Aug 10, 2016 3:25 am

### Re: Relativity?

OuterLimits wrote: Fri Nov 10, 2017 8:36 pm Here's an interesting implication of SR that I'd never heard of before asking about it in a forum a few years ago:

A train is going by one person, at a high % of the speed of light.

The one person on the land is holding his clock by his face. Throughout the train, by the windows, watching the man as the train passes, are many people from the front of the train to the back, each holding a clock by his/her face. The man is so close to the train that he can only see the clock that is passing right by him on the train, and each person on the train can only see the man in the moment he is right outside the train next to them.

The people on the train are confident that their clocks are synchronized. As they pass the man, each person marks down what time on his/her own clock that was, and what the outside man's clock said. When they compare notes, they will decide that the outside man's clock was ticking slow, just as we now expect from SR. What will be the experience of the outside man? The succession of clocks going right past him appear to create a flip-animation of a clock which is ticking fast. He will conclude that time is ticking faster on the train, or that the clocks on the train are not synchronized correctly.
A good question. The flip animation would indeed appear to be a clock going fast. But the clocks on the train are not synchronized in the frame of the platform. They're synced (presumably) in the train frame. So the guy views a fast animation of clock faces that appear to go fast because they're all out of sync.

As for what one clock on the train looks like to somebody on the platform (Viveka asked about something like this), the clock on an approaching train is going to appear to run fast due to blue shift, and slower as it recedes due to red shift. This effect will completely outweigh the relativistic effects. As uwot says, one must distinguish between "looks like" and "is".
OuterLimits
Posts: 238
Joined: Wed Sep 07, 2016 11:54 pm

### Re: Relativity?

Noax wrote: Sat Nov 11, 2017 6:04 am
OuterLimits wrote: Fri Nov 10, 2017 8:36 pm Here's an interesting implication of SR that I'd never heard of before asking about it in a forum a few years ago:

A train is going by one person, at a high % of the speed of light.

The one person on the land is holding his clock by his face. Throughout the train, by the windows, watching the man as the train passes, are many people from the front of the train to the back, each holding a clock by his/her face. The man is so close to the train that he can only see the clock that is passing right by him on the train, and each person on the train can only see the man in the moment he is right outside the train next to them.

The people on the train are confident that their clocks are synchronized. As they pass the man, each person marks down what time on his/her own clock that was, and what the outside man's clock said. When they compare notes, they will decide that the outside man's clock was ticking slow, just as we now expect from SR. What will be the experience of the outside man? The succession of clocks going right past him appear to create a flip-animation of a clock which is ticking fast. He will conclude that time is ticking faster on the train, or that the clocks on the train are not synchronized correctly.
A good question. The flip animation would indeed appear to be a clock going fast. But the clocks on the train are not synchronized in the frame of the platform. They're synced (presumably) in the train frame. So the guy views a fast animation of clock faces that appear to go fast because they're all out of sync.

As for what one clock on the train looks like to somebody on the platform (Viveka asked about something like this), the clock on an approaching train is going to appear to run fast due to blue shift, and slower as it recedes due to red shift. This effect will completely outweigh the relativistic effects. As uwot says, one must distinguish between "looks like" and "is".
The problem is specifically set up so that the platform clock is only seen by a train observer as they are minimal distance. so that the issues of "measuring a moving clock in one's own inertial frame" and whether that is illusory are circumvented.
Noax
Posts: 670
Joined: Wed Aug 10, 2016 3:25 am

### Re: Relativity?

OuterLimits wrote: Sat Nov 11, 2017 2:36 pm The problem is specifically set up so that the platform clock is only seen by a train observer as they are minimal distance. so that the issues of "measuring a moving clock in one's own inertial frame" and whether that is illusory are circumvented.
Yes, the only cases where clocks can be legally (frame independent) compared is when they are in each other's presence, which is what you've set up in your scenario. That's what made it a good example.
ken
Posts: 2075
Joined: Mon May 09, 2016 4:14 am

### Re: Relativity?

surreptitious57 wrote: Sun Nov 05, 2017 4:21 pm
ken wrote:
surreptitious57 wrote:

No is the answer to both of those questions and so saying photons do not experience time is more a figure of speech than anything else
In a story book or in general conversation then figure of speech might be fine
But in philosophy and /or matters of science is figure of speech really the best way to speak and communicate
As long as the figure of speech in question is clearly understood there is no problem. And saying that photons
do not experience time
is a perfectly acceptable term to use because it obviously is not to be taken literally
So, to you, figure of speech can be used countless times in philosophy and science and there is NO problem as long as the figure of speech is clearly understood. How do you KNOW when, and if, a figure of speech WILL BE clearly understood, and by how many people it WILL BE clearly understood by?
ken
Posts: 2075
Joined: Mon May 09, 2016 4:14 am

### Re: Relativity?

surreptitious57 wrote: Sun Nov 05, 2017 4:31 pm
ken wrote:
A part of philosophy is about how to find meaning in things. The truth of ALL things is found in the communication we use. If words are not to be taken literally especially while doing science and more so philosophy then the truth and the meaning of things will never be discovered or revealed
Dictionaries are descriptive not prescriptive and so the meaning of words is referenced in the way the are actually used
Can the way words are actually used be taken out of context?
surreptitious57 wrote: Sun Nov 05, 2017 4:31 pmThe dictionary definition of a word is only a guide to how it can be used not an absolute rule set in stone for all of time
I hope you, and others, will remember this.
ken
Posts: 2075
Joined: Mon May 09, 2016 4:14 am

### Re: Relativity?

davidm wrote: Sun Nov 05, 2017 5:23 pm
ken wrote: Sun Nov 05, 2017 5:16 am
thedoc wrote: Sun Oct 29, 2017 10:10 pm

As has been stated numerous times, clocks will measure different times when moving relative to each other, why is that so hard to understand.
WHY? Because if human beings state that it takes four years to travel a distance of four light years, traveling at the speed of light, then do not also state that it takes no time at all.

WHY do you human beings state contradictory things and expect others to understand?

If it takes four years to travel a distance, then it takes four years. NOT no time at all. If it takes no time at all, then it does NOT take four years. What IS actually true can be discovered, learned, seen, and understood from the a Universal perspective, if any one is really interested.
Good lord, you are thick!
Absolutely everything is relative to the observer.
ken
Posts: 2075
Joined: Mon May 09, 2016 4:14 am

### Re: Relativity?

davidm wrote: Sun Nov 05, 2017 5:24 pm
ken wrote: Sun Nov 05, 2017 5:16 am
What CAUSES a clock, like a digital watch, which is programmed to change at certain intervals and has the exact same continual power source, to supposedly slow down when traveling faster than another one with the exact same mechanisms and power source?
The CAUSE has already been explained to you!
What has been explained is WHY a light clock would slow down.

A digital clock has NOT yet been proven to slow down.