What caused us to have relative time

[Dale]

E simply ignores this fact and declares that time is relative.

No, as I have told you several times already, he derives it from the two postulates.

 

[Ibix]

Isn't the relativity of simultaneity basically the x dependence of the Lorentz transform of time? If there were no x dependence then all observers would agree on the order of events.

Unfortunately, you can't remove the x dependence by letting c be non-constant. You can only do it by making both v and c proportional to x - in other words, rejecting the whole bourgeois notion of "velocity" as a useful concept. I think you can do that by a sufficiently crazy choice of curved coordinate systems but it wreaks havoc on every other aspect of physics, to the point that one needs some heavy duty maths just to work out how long a ruler is. Or, indeed, to define what length is in such a system.

Your only other option is to say that the Lorentz transforms are flat out wrong. Be careful! It'll get you banned, and you are also rejecting the theoretical basis for expecting nuclear reactors to work. Among other things.

Either option seems to me to be an awfully high price to pay for sweeping relativity of simultaneity under the carpet.

 

[pervect]

There is a lot of papers that mention that the choice of simultaneity is a convention - and while this is true, there is some fine print to this freedom.

The "fine print" is that if you want to apply Newton's laws in the low velocity limit, you can't just use whatever convention you like - your choice of conventions is restricted. You can't randomly choose a notion of simultaneity and expect Newton's laws to work.

In fact, it turns out that you're pretty much restricted to using Einstein's simulateity convention, if you require isotropy and linearity - though I haven't seen any paper that formally discusses this issue.

My quick informal argument for why this is true is below:

Newton's laws are isotropic, so any notion of simultaneity that is not isotropic won't be compatible with Newton's laws.

Similarly, applying a non-linear tranformation to space will "break" Newton's laws, so it is important that the transformation be linear.

 

[Sugdub]

I fully concur that:

...Each observer finds the other clock going slow. ...

But this is not the point. I was – explicitly – assessing whether the SR theory can or cannot demonstrate that clocks in relative motion to each other actually run at a different path, i.e. whether there is more than a simple (and reciprocal) “appearance”. And I demonstrated that SR cannot reach that conclusion: whereas relatively moving clocks appear to be running slow (this is reciprocal because there is no asymmetry between observers' roles), SR cannot conclude that they actually are running slow (because this would mean an asymmetry in the actual behavior of the clocks).
Conclusion: According to SR, relatively moving clocks actually don't run slow, this is just an appearance. In other words, and to remain plugged to the initial debate, my time flow is not relative, and if others' time flows appear to be relative to their state of motion in respect to me, this is only an appearance.

 

[Nugatory]

Conclusion: According to SR, relatively moving clocks actually don't run slow, this is just an appearance. In other words, and to remain plugged to the initial debate, my time flow is not relative, and if others' time flows appear to be relative to their state of motion in respect to me, this is only an appearance.

I don't see how you reconcile "just an appearance" with the fact of the muon lifetime measurements (and innumerable other examples observed in particle accelerators).

A question: is what you're calling "my time flow" any different than the proper time measured along your world-line? If so, how?

 

[Dale]

I was – explicitly – assessing whether the SR theory can or cannot demonstrate that clocks in relative motion to each other actually run at a different path

Do you have a scientific definition of "actually". If not, then I think you are talking about some irrelevant (to this forum) philosophical question and not a relevant scientific question.

 

[Mentz114]

I was – explicitly – assessing whether the SR theory can or cannot demonstrate that clocks in relative motion to each other actually run at a different path, i.e. whether there is more than a simple (and reciprocal) “appearance”. And I demonstrated that SR cannot reach that conclusion: whereas relatively moving clocks appear to be running slow (this is reciprocal because there is no asymmetry between observers' roles), SR cannot conclude that they actually are running slow (because this would mean an asymmetry in the actual behavior of the clocks).

This is wrong. I repeat what has been said before here - SR says that a clock shows the proper time along a worldline and provides a way to calculate the elapsed time between events on the worldline. This results in the 'clock paradox' ( Einsteins term) which is not a paradox but actually ensures that causal paradoxes do not happen.

If you could only grasp this it would remove all your (big) misunderstandings.

 

[Sugdub]

Do you have a scientific definition of "actually". If not, then I think you are talking about some irrelevant (to this forum) philosophical question and not a relevant scientific question.

You are welcome. Concerning clocks “actually" running slow I precisely mean what physicists indicate in the context of the “twins” thought experiment: the “moving twin”, when coming back, will be younger than the other one, because his/her clock ran slower all along the trip.
My statement is that SR cannot, from a pure logical standpoint, justify that the “moving clock” ran slower: all inputs being fully symmetrical, the conclusion cannot be non-symmetrical.
Thanks.

 

[PAllen]

You are welcome. Concerning clocks “actually" running slow I precisely mean what physicists indicate in the context of the “twins” thought experiment: the “moving twin”, when coming back, will be younger than the other one, because his/her clock ran slower all along the trip.
My statement is that SR cannot, from a pure logical standpoint, justify that the “moving clock” ran slower: all inputs being fully symmetrical, the conclusion cannot be non-symmetrical.
Thanks.

How about this as a demonstration of symmetric, "actual" time dilation.Alice and Betty each have a sample of the same type of radio-isotope. They are approaching each other rapidly. Alice has laid out an array of geiger counters at rest relative to her, that Betty is passing. Betty has arranged an array of geiger counters at rest relative to her that Alice passing. After they pass each other and each collects information from the geiger counters, Alice finds Betty's isotope was decaying slow compared to hers. Betty finds Alice's isotope was decaying slow compared to hers. Note there is no question of visual effects or Doppler going one here - only the passing of momentarily co-located geiger counters.

 

[Nugatory]

My statement is that SR cannot, from a pure logical standpoint, justify that the “moving clock” ran slower: all inputs being fully symmetrical, the conclusion cannot be non-symmetrical.
Thanks.

All inputs are not symmetrical in the SR version of the twin paradox, which is why it is at least logically possible that conclusion be non-symmetric.

The asymmetry is physically apparent in the fact that the twins experience different acceleration.

It will also show up quite clearly if you just try working the problem in a frame in which the traveling twin is at rest during either the outbound or the inbound leg of the trip (Try it! Don't just take my word for it).

 

[PAllen]

All inputs are not symmetrical in the SR version of the twin paradox, which is why it is at least logically possible that conclusion be non-symmetric.

The asymmetry is physically apparent in the fact that the twins experience different acceleration.

It will also show up quite clearly if you just try working the problem in a frame in which the traveling twin is at rest during either the outbound or the inbound leg of the trip (Try it! Don't just take my word for it).

I think sugdub doesn't dispute the twins scenario (because there is asymmetry). What he/she claims is that the symmetric time dilation is not 'real' or 'actual' precisely because it is symmetric.

 

[Dale]

You are welcome. Concerning clocks “actually" running slow I precisely mean what physicists indicate in the context of the “twins” thought experiment: the “moving twin”, when coming back, will be younger than the other one, because his/her clock ran slower all along the trip.

Then nature disagrees with you. Clocks do "actually" run slow according to your definition. This experiment has been done many times in many different ways, and the results agree with SR's predictions.

My statement is that SR cannot, from a pure logical standpoint, justify that the “moving clock” ran slower: all inputs being fully symmetrical, the conclusion cannot be non-symmetrical.

Your statement is irrelevant for two reasons.

First, it is irrelevant because the assertion that you are attributing to SR is not an assertion that SR makes for inertial clocks. I detailed the assertion that SR actually makes above, and that one is fully symmetrical for inertial clocks. Your objection is therefore simply a strawman fallacy.

Second, it is irrelevant because your definition of "actually" involves an asymmetric situation. So an argument from symmetry simply doesn't apply to whether or not clocks "actually" slow down.

 

[Dale]

I think sugdub doesn't dispute the twins scenario (because there is asymmetry). What he/she claims is that the symmetric time dilation is not 'real' or 'actual' precisely because it is symmetric.

That isn't what Sugdub mentioned as the definition of "actually".