TIME DILATION. WHY do clocks that are

[sisoev]

OK PAllen, I know where is the deceiving point in your thinking (no offence applied)

When you think SIMULTANEITY in your experiment, think that when the back(blue) light cease to exits the front(red) line die simultaneously with it

 

[ghwellsjr]

Thanks for extending the explanation, but those are just variations of the same principle. My last question about two objects in a system was just to satisfy a philosophical question and you did answer it (albeit i didn't formulate the question as properly as it was in my head :) ). In the extended example you give, if those two cars are isolated in a system with just themselves, when they are both moving with the same speed that would be equal to being stationary, so when the one "slows" down as it is in your example that would translate that it is actually accelerating towards the other "stationary" car. Doesn't mattet, i get the example :)

Great, now do you think you could explain the Twin Paradox to someone who doesn't understand it?

 

[PAllen]

You are building your experiment on wrong analogy, PAllen.

Imagine that sometime in the past a red light (in the front) and blue light (behind the red) were mixed for you.
Now we deal with two different information (red and blue) mixed into one information (let say purple)
Now imagine that both information(colors) are simultaneously extracted.
What will be left?
Non.

Taking this to a transparent doors (red and blue) you'll see a purple door which opens.
Behind it we will see what ever is behind the blue door

You write gibberish and deny reality. Truly no further discussion is possible.

 

[sisoev]

You write gibberish and deny reality. Truly no further discussion is possible.

Just in case you missed my previous post;
When you think SIMULTANEITY in your experiment, think that when the back(blue) light cease to exits the front(red) line die simultaneously with it.

Now it should make sense to you :)

 

[PAllen]

Just in case you missed my previous post;
When you think SIMULTANEITY in your experiment, think that when the back(blue) light cease to exits the front(red) line die simultaneously with it.

Now it should make sense to you :)

No this is total nonsense. Suppose each pulse is one femtosecond. Then there is no overlap at all between two simultaneously emitted pulses, one right behind the other. They will be received separately, and the receiver (having set up the experiment and measured everything) can easily determine that the delay between them verifies simultaneous emission.

Try to write clear English. That is a real problem - much of what you write is incomprehensible as English.

 

[Sandrix]

Can i say something here for first time :P
Time is derivative of mass :P
If mass dosent exist or = zero than there is no dimension Time :)
time not exist if M=0 or we have pure energy :)
have fun :)

 

[sisoev]

No this is total nonsense. Suppose each pulse in one femtosecond. Then there is no overlap at all between two simultaneously emitted pulses, one right behind the other. They will be received separately, and the receiver (having set up the experiment and measured everything) can easily determine that the delay between them verifies simultaneous emission.

Try to write clear English. That is a real problem - much of what you write is incomprehensible as English.

The femtosecond does not make you see red door and blue door behind it. You see purple door.
Your example with the pulses is not identical with the door experiment.
Remember that the front door is blocking the information for the back one, and if they are transparent, the colors are mix into one.
Your example does not set the front pulse as blockage for the back one.
There is time when we see only the front door.
Where in your experiment is the time when we see only the front pulse.

 

[PAllen]

The femtosecond does not make you see red door and blue door behind it. You see purple door.
Your example with the pulses is not identical with the door experiment.
Remember that the front door is blocking the information for the back one, and if they are transparent, the colors are mix into one.
Your example does not set the front pulse as blockage for the back one.
There is time when we see only the front door.
Where in your experiment is the time when we see only the front pulse.

A front transparent door doesn't cause mixing. If a signal from front and back door emitted simultaneously, they will arrive one after the other. If they arrive at the same time, that tells you they were not emitted simultaneously, and further (assuming you set up the experiment) it tells exactly what the difference in emission time is.

Repeating trivially false statements does not make them true.

 

[Dale]

The femtosecond does not make you see red door and blue door behind it. You see purple door.
Your example with the pulses is not identical with the door experiment.
Remember that the front door is blocking the information for the back one, and if they are transparent, the colors are mix into one.
Your example does not set the front pulse as blockage for the back one.
There is time when we see only the front door.
Where in your experiment is the time when we see only the front pulse.

None of which is in any way relevant for the ladder paradox.

 

[Dale]

When you think SIMULTANEITY in your experiment, think that when the back(blue) light cease to exits the front(red) line die simultaneously with it

It is hard to tell what you mean, but when a light source stops emitting light the light that it has already emitted does not suddenly cease to exist but instead continues to propagate onward at c. Otherwise you would violate the conservation of energy. So, if two sources stop emitting light simultaneously in some frame then an observer does not necessarily stop receiving the light simultaneously.

Would you like a mathematical derivation to back that up?

 

[Denius1704]

Great, now do you think you could explain the Twin Paradox to someone who doesn't understand it?

Yeahp i believe i can, because after your example the way i had to translate it to myself so i can picture it better was with a sonar given out between two whales... Then the picture became quite clear :)

 

[sisoev]

A front transparent door doesn't cause mixing. If a signal from front and back door emitted simultaneously, they will arrive one after the other. If they arrive at the same time, that tells you they were not emitted simultaneously, and further (assuming you set up the experiment) it tells exactly what the difference in emission time is.

Repeating trivially false statements does not make them true.

First of all in the garage door experiment we are dealing with the reflected light of the front door, which blocks us from seeing the back door.
We made them transparent for the sake of the argument.
We can make them transparent and emitting light, but that will not change anything.
If the back door is blue, we will have to see it through the front red transparent door, and we will see purple.
(I don't know how do you imagine a blue light to arrive unchanged trough red door.)
Now stop the back blue emission and the front red one at the same time.
What do you see?

Stop thinking about your opponent as an idiot and you may start seeing his point.

 

[PAllen]

First of all in the garage door experiment we are dealing with the reflected light of the front door, which blocks us from seeing the back door.
We made them transparent for the sake of the argument.
We can make them transparent and emitting light, but that will not change anything.
If the back door is blue, we will have to see it through the front red transparent door, and we will see purple.
(I don't know how do you imagine a blue light to arrive unchanged trough red door.)
Now stop the back blue emission and the front red one at the same time.
What do you see?

Stop thinking about your opponent as an idiot and you may start seeing his point.

Who says the front door is red? Transparent and clear, with flashing red light source would make sense. Backdoor would have synchronized flashing blue source.

Anyway, what I was responding to was your claim that you can't determine collinear simultaneity as a general principle.

 

[Dale]

First of all in the garage door experiment we are dealing with the reflected light of the front door, which blocks us from seeing the back door.
We made them transparent for the sake of the argument.
We can make them transparent and emitting light, but that will not change anything.
If the back door is blue, we will have to see it through the front red transparent door, and we will see purple.
(I don't know how do you imagine a blue light to arrive unchanged trough red door.)
Now stop the back blue emission and the front red one at the same time.
What do you see?

Why does what you see matter? If the door is closed when the ladder is in the doorway then it crashes regardless of what is seen. If the door is open when the ladder is in the doorway then it passes regardless of what is seen.

It is a red herring, not a red door.

 

[sisoev]

I'm taking a little brake to clear my mind :)

 

[sisoev]

OK.
Let's see it differently in order for me to understand you and you to get my point.
It will be easy for us to imagine the doors as transparent red (front) and blue(back) doors.
The light reflected from the front door will show it to us as red, but it will go trough it, reflect in the back door and will bring to us information for purple back door.
Am I correct?

When the doors open simultaneously, we will see purple door which is not open, but since we know that the actual door is blue, that will tell us that the door is open and we see false image of it.
The explanation of the ladder experiment still fails for me :)

Please tell me where am I wrong.

 

[Dale]

When the doors open simultaneously, we will see purple door which is not open, but since we know that the actual door is blue, that will tell us that the door is open and we see false image of it.
The explanation of the ladder experiment still fails for me :)

Please tell me where am I wrong.

You are wrong in thinking that the color of the door has any relevance whatsoever to whether or not the ladder hits the door. If the color mattered then we could just paint all cars some collision-proof color and greatly enhance road safety.

 

[sisoev]

You are wrong in thinking that the color of the door has any relevance whatsoever to whether or not the ladder hits the door.

You are right, but in the proposed experiment, the color which we see proves that the door is actually not there.
Aren't the experiments set to prove or disprove something?

 

[Dale]

You are right, but in the proposed experiment, the color which we see proves that the door is actually not there.

No it doesn't. Let me see if I understand your set-up for complete clarity. You are proposing a red transparent front door and a blue opaque back door with ambient white lighting from outside and no light sources either on the door or in the garage, correct?

 

[sisoev]

No it doesn't.

Ha-ha :D
OK...
I'm done with this topic.
I'll come back with the experiment I mentioned earlier.

Love to all you guys :)

 

[Dale]

I'll come back with the experiment I mentioned earlier.

Still looking forward to it.

 

[Janus]

OK PAllen, I know where is the deceiving point in your thinking (no offence applied)

When you think SIMULTANEITY in your experiment, think that when the back(blue) light cease to exits the front(red) line die simultaneously with it

Here's the experiment shown by animation. The white dot is the observer, the red and blue dots are the light sources. Each light source turns on and off simultaneously. The light that was emitted before this continues on its way.

Thus the observer sees in order:
1.No light
2.Red light only
3. Blue and Red light mixed(purple light)
4. Blue light only
5. No light.

[PLAIN]http://home.earthlink.net/~jparvey/sitebuildercontent/sitebuilderpictures/red-blue.gif

 

[sisoev]

Here's the experiment shown by animation. The white dot is the observer, the red and blue dots are the light sources. Each light source turns on and off simultaneously. The light that was emitted before this continues on its way.

Thus the observer sees in order:
1.No light
2.Red light only
3. Blue and Red light mixed(purple light)
4. Blue light only
5. No light.

[PLAIN]http://home.earthlink.net/~jparvey/sitebuildercontent/sitebuilderpictures/red-blue.gif[/QUOTE]
Thank You, Janus.
Thank You very much.
I abandoned this argument.
I was quick to use it and it wasn't in my favor :)
But thanks any way.

My last standing argument was few posts earlier, with the "purple door" experiment.

Once again Thank You :)

 

[sisoev]

No, it's not a matter of which one is moving, it's a matter of which one is changing speed or direction and where the two are in relation to each other when this happens.

So let's extend the analogy a little bit to include your question:

Suppose you are stopped and the vehicle with the siren passes you and you hear the sound drop in pitch from the high rate to the low rate and after it is a mile down the road, you take off after it at the same speed it is going. Now you will hear the pitch go from the low rate to the actual pitch of the siren, won't you? So there you both are separated by a mile, both moving and it's just like you were both stationary in terms of what you are hearing. But now if you increase your speed, you will immediately hear the pitch go higher, right? But instead of that, suppose the other vehicle slows down, will you immediately hear the pitch get higher? No, not until five seconds goes by.

Once you grasp the idea that distance causes a delay in what you observe if the other person changes speed but no delay if you are the one that changes speed, then you can easily understand the Twin Paradox with no math, no equations, no formulas.

Does this make perfect sense to you now?

ghwellsjr, I'd like to give you credit for the explanations you gave in this topic.
Earlier I said that the change of direction is not of any importance for the difference in the observations.
I see now that I was wrong.
Thank You :)

Now I guess I'll have to figure out how that affects the difference in the ageing.

 

[sisoev]

Still looking forward to it.

https://www.physicsforums.com/showthread.php?p=3498549#post3498549"

 

[Buckleymanor]

The period of a pendulum is approximately 2\pi\sqrt{L/g} so the dependence is very explicit. The period of an atomic clock is proportional to (m/M)\alpha^4mc^2, so I am not aware of any dependence on gravity or acceleration. A mechanical clock could probably be constructed either way, but I don't know a general formula for mechanical clocks.

Sorry for the late reply.
I don't see how the dependence is explicit for a pendulem clock could you elude to a more simple explanation as there seems to me to be an exclusion with regards atomic clocks.
Imagine a black hole with your atomic clock being sucked in and spagetification.Gravity and acceleration must play there part.
As for mechanical clocks is there any basic difference to pendulem ones.

 

[Dale]

I don't see how the dependence is explicit for a pendulem

g is the gravitational field, or more precisely, the proper acceleration.

Imagine a black hole with your atomic clock being sucked in and spagetification.

I don't get your point. You could smash it with a hammer too. Once it is broken it is no longer an identically constructed clock.

 

[ThomasT]

Why do clocks that are moving closer to light speed relative to another clock tick slower? I understand that the waves take longer to reach the stationary observer on the turn around, but that's just appearance. It still seems the clocks would be in sync upon the return. What is making time actually slow down (comparatively in that frame) by moving faster??

I'm not clear on what kind of answer you want. My reaction would be to say "that's the way the universe is". But you seem to want some kind of "mechanistic" answer.

It isn't really due to any effect that traveling at high speed has on your clocks, it has to do with the fact that observers moving relative to each other measure time differently.

Thats the hard part. I totally understand why people would measure times differently, (The ball in motion moving farther from a side "still" F.O.R.) but its due to appearance. Why someone would actually age less and why the clocks would not be in sync upon return totally fail me.

As HallsofIvy indicated, the OP seems to want a mechanistic explanation of relativistic differential aging. Janus seems to be saying that differential aging isn't a mechanistic effect, or at least that it doesn't require a mechanistic explanation.

So I'm wondering along with the OP: (1) is relativistic differential aging a mechanistic effect?, and (2) if it is a mechanistic effect, then is there a mechanistic explanation for the effect?

If it isn't a mechanistic effect, then it would follow that the periods of oscillators are not affected by the speed at which they travel. But that would contradict the results of numerous experiments.

Thus it would seem to be the case that relativistic differential aging is an interactional (mechanistic) phenomenon that isn't yet well understood.

So, my answer to the OP for (1) is yes, the speed at which an oscillator is moving is directly affecting the period of the oscillator, and for (2) is no (afaik).

 

[Dale]

I would say it is a geometric effect and that the geometry is well understood.

 

[ThomasT]

I would say it is a geometric effect and that the geometry is well understood.

I agree. But I'm still wondering if (even the beginnings of) a mechanistic (interactional) explanation exists, or if it might be possible. Like, say, something along the line of a quantum mechanical description of relativistic differential aging. Saying that differential aging is a consequence of the speed of light being the same for all observers doesn't quite do it for me, because clocks undergo real physical changes based on their movement. Something measurable happens to oscillators when they're significantly speeded up, and the geometric explanation doesn't really account for this. Does it?

 

[Dale]

Something measurable happens to oscillators when they're significantly speeded up, and the geometric explanation doesn't really account for this. Does it?

It does, completely. In addition, any mechanistic explanation would be hampered by the question "why don't the co-moving observers measure any difference". The geometric explanation accounts for that also.

 

[harrylin]

I agree. But I'm still wondering if (even the beginnings of) a mechanistic (interactional) explanation exists, or if it might be possible. Like, say, something along the line of a quantum mechanical description of relativistic differential aging. Saying that differential aging is a consequence of the speed of light being the same for all observers doesn't quite do it for me, because clocks undergo real physical changes based on their movement. Something measurable happens to oscillators when they're significantly speeded up, and the geometric explanation doesn't really account for this. Does it?

Sure, as most people here know an interactional explanation existed from the very start - the Lorentz ether. It just happens to be currently not a popular concept. The geometric explanation is now the most popular and it surely does account for the effects, but on another, more mathematical level. Geometrical and physical explanations are not necessarily mutually exclusive, they are different ways of looking at the same.

 

[ThomasT]

It does, completely.

I thought that it explained it as a function of changes in the distance/time ratio. But oscillators actually slow down as their speed increases. That is, they actually undergo physical changes. Don't they? How does the geometric description explain that?

In addition, any mechanistic explanation would be hampered by the question "why don't the co-moving observers measure any difference". The geometric explanation accounts for that also.

I'm not sure what you're referring to. You mean the symmetric time-dilation effect?

 

[ThomasT]

Geometrical and physical explanations are not necessarily mutually exclusive, they are different ways of looking at the same.

I agree. I didn't mean to suggest that one contradicts or excludes the other. Just that one, the mechanistic (interactional) description is the deeper sort of explanation. The sort of thing we appeal to for real understanding of a phenomenon.

 

[Dale]

Just that one, the mechanistic (interactional) description is the deeper sort of explanation.

That is entirely a matter of personal preference, and one I happen to disagree with completely.

 

[ketoret]

on op648's post, I think Einstein said something like that! He said something along the lines that sitting with a pretty girl at a cafe, 3 hrs seems like 3 minutes, but sitting on a hot stove, 3 minutes seems like 3 hrs, and if you understand that, you understand relativity. It was probably his humorous way of trying to explain relativity to people unschooled in physics :-), and likely too that many people took him seriously. Perhaps the one sitting on the stove jumps off at a good fraction of the speed of light...

 

[A.T.]

But I'm still wondering if (even the beginnings of) a mechanistic (interactional) explanation exists, or if it might be possible. Like, say, something along the line of a quantum mechanical description of relativistic differential aging.

Not sure what you mean by "mechanistic (interactional)", but all the interactions within a mechanical clock are also based on electromagnetic fields, in which changes propagate at the same speed for every observer.

 

[harrylin]

Not sure what you mean by "mechanistic (interactional)", but all the interactions within a mechanical clock are also based on electromagnetic fields, in which changes propagate at the same speed for every observer.

Yes, and that provides at least intuitively a nice "mechanistic" (or physical) answer to the OP's question of "What is making time actually slow down (comparatively in that frame) by moving faster??";
In particular with the help of such animations as this one:
[URL]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/length_con2.gif[/URL]
I think that Janus made that animation; Janus how did you do it? they are very useful.

 

[Dale]

I thought that it explained it as a function of changes in the distance/time ratio. But oscillators actually slow down as their speed increases. That is, they actually undergo physical changes. Don't they? How does the geometric description explain that?

The same way that the side of a right triangle is actually physically shorter than the hypotenuse. It is just geometry, only using the Minkowski metric instead of the Euclidean metric.

 

[ghwellsjr]

I think that Janus made that animation; Janus how did you do it? they are very useful.

He explained how he did it in post #6:

The frame are drawn with POV-Ray, then assembled by a GIF animator (I use Animation Shop 3).

 

[harrylin]

The same way that the side of a right triangle is actually physically shorter than the hypotenuse. It is just geometry, only using the Minkowski metric instead of the Euclidean metric.

For comparison with post #138, here's an illustration of that geometric explanation why oscillators actually slow down as their speed increases:
[PLAIN]http://images.blogstream.com/i/userImages/26/26371_18688.jpg
(a basic but neat Minkowski diagram that I hijacked from a web blog by L.G. Sims)

 

[harrylin]

He explained how he did it in post #6:
'The frame are drawn with POV-Ray, then assembled by a GIF animator (I use Animation Shop 3).'

Thanks, I forgot! Regretfully Animation Shop 3 isn't freeware...

 

[Janus]

Thanks, I forgot! Regretfully Animation Shop 3 isn't freeware...

I'm sure that that are a number of freeware programs that would do the job. Assembling the individual frames into an animated GIF is the easy part.

 

[Ernst Jan]

I'm trying to understand this

I understand the picture where Zoe is stationary in front of the veranda, but I do not understand the animation.

If it’s an object like a ping-pong ball going from one side of the car to the other, I would assume the ball would get the forward speed of the car. Since all objects can be pushed by the car, it would be strange to even ask why the ping-pong ball would go like the light ray in the animation. Light however doesn’t get pushed by the car, so this makes me question that it gets the forward motion of the car.

In case Zoe moves, the angle in which the light ray is being sent will have to change, or the light will no longer reach the mirror. (for Zoe it will seem to go backwards in her car)
If she does change it however, there wouldn’t be any need to change her time. Instead she could just calculate the same distance as Jasper does.

My problem with the animation comes down to this:
If a light source moves from back to front it has no effect on the speed of the light, but if a light source moves sideways there suddenly is some mysterious sideways velocity of the light.

If I assume the light ray gets the forward velocity from the moving lightsource then the calculation is correct and time for Zoe has to change. For me this seems like a good reason to say the assumption is false.

If I assume the light ray doesn't get the forward motion, then time stays the same. For me this makes sense.

There’s a light source of yellow light with a wavelength of 580nm in the back of a car and an observer 2m from the light source in the front of the car.

If the car is standing still it takes 1/517x1012 s for the light wave to appear. The light wave with a wavelength of 580nm will travel to the observer in 6.67x10-9 s. It will take the observer 1/517x1012 s to detect the light wave from front to end. The observer will see this as yellow light with a wavelength of 580nm.

If the car is traveling with a speed of 0.8c it will take 1/517x1012 s for the light wave to appear. In this time the light source has moved 464nm. So the distance between the front of the wave and the end is now 116nm (instead of 580nm) The light wave with a wavelength of 116nm will travel to the observer in 33.3 x10-9 s The observer will move a length L between detecting the front of the 116nm wave and the end. (L+116nm)/c = L / 0.8 so L=464nm making the observer see the light with a wave length of (464+116=) 580nm.

To prove this is right I’d need something that uses some kind of electro-magnetic wave and show it takes the waves longer at higher speeds. So I’d need a thing like an atomic clock and show it runs slower at higher speeds or I’d need a particle like a muon and show the information traveling within about its decay will take longer to reach its outer edges at high speeds. Funny thing is those are exactly the same things as are being used to proof time dilation.

My question is, what am I doing wrong or what experiment does time dilation explain that can't be explained by my view?

 

[harrylin]

I'm trying to understand this

I understand the picture where Zoe is stationary in front of the veranda, but I do not understand the animation.

The animation of Janus (if that's the one you mean) is certainly about EM wave propagation, bouncing from mirrors; the dots make it easy to follow the reflections.

If it’s an object like a ping-pong ball going from one side of the car to the other, I would assume the ball would get the forward speed of the car. Since all objects can be pushed by the car, it would be strange to even ask why the ping-pong ball would go like the light ray in the animation. Light however doesn’t get pushed by the car, so this makes me question that it gets the forward motion of the car.

Light rays are not affected by the forward motion of the car (at least that is the second postulate, and experiments apparently confirm it).

In case Zoe moves, the angle in which the light ray is being sent will have to change, or the light will no longer reach the mirror. (for Zoe it will seem to go backwards in her car)
If she does change it however, there wouldn’t be any need to change her time. Instead she could just calculate the same distance as Jasper does.

My problem with the animation comes down to this:
If a light source moves from back to front it has no effect on the speed of the light, but if a light source moves sideways there suddenly is some mysterious sideways velocity of the light. [..]

In SR there is a difference between quantity of motion and speed; as a result, speed and direction do not relate to each other like in Newton's mechanics. But I'm sure we had a thread about your question not long ago... OK I found it back with Google:

https://www.physicsforums.com/showthread.php?t=503207

There’s a light source of yellow light with a wavelength of 580nm in the back of a car and an observer 2m from the light source in the front of the car.

If the car is standing still it takes 1/517x1012 s for the light wave to appear. The light wave with a wavelength of 580nm will travel to the observer in 6.67x10-9 s. It will take the observer 1/517x1012 s to detect the light wave from front to end. The observer will see this as yellow light with a wavelength of 580nm.

If the car is traveling with a speed of 0.8c it will take 1/517x1012 s for the light wave to appear. In this time the light source has moved 464nm. So the distance between the front of the wave and the end is now 116nm (instead of 580nm) The light wave with a wavelength of 116nm will travel to the observer in 33.3 x10-9 s The observer will move a length L between detecting the front of the 116nm wave and the end. (L+116nm)/c = L / 0.8 so L=464nm making the observer see the light with a wave length of (464+116=) 580nm.

To prove this is right I’d need something that uses some kind of electro-magnetic wave and show it takes the waves longer at higher speeds. So I’d need a thing like an atomic clock and show it runs slower at higher speeds or I’d need a particle like a muon and show the information traveling within about its decay will take longer to reach its outer edges at high speeds. Funny thing is those are exactly the same things as are being used to proof time dilation.

My question is, what am I doing wrong or what experiment does time dilation explain that can't be explained by my view?

If I understand you correctly, you do not use SR but another theory according to which the speed of light adds to the speed of the source. There can be no Doppler effect if the source and receiver have the same velocity (see http://en.wikipedia.org/wiki/Doppler_effect);
and in particular for this thread, if you'd make a similar animation as here above, you should not obtain time dilation. It thus seems that you made a calculation error.

Note also that you seem to suggest an imposed source frequency with a receiver; while the animation suggests a source such as a laser with a resonance frequency that is created by an optical cavity.

 

[Dale]

If a light source moves from back to front it has no effect on the speed of the light, but if a light source moves sideways there suddenly is some mysterious sideways velocity of the light.

Nothing mysterious about it. It comes directly from Maxwell's equations for a given set of boundary conditions in different frames.

If I assume the light ray gets the forward velocity from the moving lightsource then the calculation is correct and time for Zoe has to change. For me this seems like a good reason to say the assumption is false.

If I assume the light ray doesn't get the forward motion, then time stays the same. For me this makes sense.

Except that if it doesn't get the forward motion then you get real paradoxes. Like the light hitting a detector in one frame and not hitting the same detector in another frame.

 

[Ernst Jan]

Thank you for answering!

The animation of Janus (if that's the one you mean) is certainly about EM wave propagation, bouncing from mirrors; the dots make it easy to follow the reflections.

Indeed, clearly it shows how the situation IS for them, and not how they "see" it. Note that if the derived time dilation is TRUE, the animation is NOT correct.

Light rays are not affected by the forward motion of the car (at least that is the second postulate, and experiments apparently confirm it).

Indeed, that's what I said.

In SR there is a difference between quantity of motion and speed; as a result, speed and direction do not relate to each other like in Newton's mechanics. But I'm sure we had a thread about your question not long ago... OK I found it back with Google:

https://www.physicsforums.com/showthread.php?t=503207

Thanks for the link. I read the thread and it's the same argument that you give here. SR is true and so everything that contradicts it is false. I agree with the conclusion under that premisse. My question was why would you assume something like that, since as I showed it makes more sense not to.

If I understand you correctly, you do not use SR but another theory according to which the speed of light adds to the speed of the source.

No, in my calculation all speeds are absolute and c is constant.

There can be no Doppler effect if the source and receiver have the same velocity (see http://en.wikipedia.org/wiki/Doppler_effect);

That's what I showed, the light has the same wave length for the observer, as long as his relative speed to the lightsource is the same. In my example the relative speed was zero and absolute speed was 0.8c.

and in particular for this thread, if you'd make a similar animation as here above, you should not obtain time dilation.

Indeed, I showed there is no need to explain things with time dilation.

It thus seems that you made a calculation error.

You know what... I actually believe you. I'm convinced there is a perfectly good explantion why so many people think SR is TRUE and I would very much like to be one of them.
A wise man once said that you don't really understand something until you can explain it to your grandmother. I want to understand SR, so that's why it's not enough for me to say that SR seems to be internally consistent as an argument that it must be TRUE. I need a reason why the assumptions made are TRUE or at least why those assumptions make sense.

Note also that you seem to suggest an imposed source frequency with a receiver; while the animation suggests a source such as a laser with a resonance frequency that is created by an optical cavity.

Sorry for the confusion. The calculation was to show that atomic clocks will run slow without the need to explain it with time dilation.

 

[Ernst Jan]

Except that if it doesn't get the forward motion then you get real paradoxes. Like the light hitting a detector in one frame and not hitting the same detector in another frame.

This makes no sense at all.

In my view there can be a "universal observer" , one that can see everything as it IS at one moment in the intuitive sense. This by pure definition means that there can be no real paradoxes like the one you describe. Note that if SR is true, such an observer is no longer possible.

 

[harrylin]

[..] Note that if the derived time dilation is TRUE, the animation is NOT correct.

Please elaborate; the animation seems to accurately describe Maxwell wave propagation, which is maintained in SR.

[..] Thanks for the link. I read the thread and it's the same argument that you give here. SR is true and so everything that contradicts it is false. I agree with the conclusion under that premisse.

??! No, that is not at all the argument there, nor here. The purpose of Physicsforums is to explain currently existing theory, that's all.

My question was why would you assume something like that, since as I showed it makes more sense not to. [quotation] No, in my calculation all speeds are absolute and c is constant.

If so, I don't understand the difference with the simulation; if you simply used Maxwell, that is also what the simulation does - it's standard ray tracing.

[..] Indeed, I showed there is no need to explain things with time dilation.

That's the question of this thread upside-down; time dilation was first predicted by SR and subsequently measured. The question that we try to answer in this thread is why it happens.

[..] I need a reason why the assumptions made are TRUE or at least why those assumptions make sense. [..] Sorry for the confusion. The calculation was to show that atomic clocks will run slow without the need to explain it with time dilation.

That is a misunderstanding: "time dilation" is just a common lable of the phenomenon; it's not an explanation of it. Other lables of the same are "clock retardation" and "running slow".

Now, the basic assumptions that need to make sense to you are the two postulates of Einstein, or the few starting assumptions of Lorentz-Poincare:

- we cannot measure our absolute motion (at constant velocity): this is the experimental outcome of very many failed attempts to detect absolute motion.

- the speed of light in vacuum is independent of that of the source and constant, similar to sound waves: this was at the time inferred by many experiments that supported Maxwell's theory; and later also direct experiments gave support to it.

The effects of clock slowdown as well as the shrinking of objects follow logically (by mathematical necessity) from those starting assumptions, as Einstein showed.

In later years, others (such as Ives) showed that the same follows, when starting from Maxwell's theory, from the conservation of momentum and energy.Harald

PS: please start a new thread if you want to elaborate on this deviation from the topic of this thread.

 

[harrylin]

This makes no sense at all.

In my view there can be a "universal observer" , one that can see everything as it IS at one moment in the intuitive sense. This by pure definition means that there can be no real paradoxes like the one you describe. Note that if SR is true, such an observer is no longer possible.

I don't think so; SR makes no claims about what "really is" and merely pretends that we cannot identify such an observer. Please show me wrong.