# michel123456's relativity thread (from Time dilation dependence on direction)

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15 minutes ago, md65536 said:

It's only important if you want to be consistent with what we actually measure of reality.

It's a combination of the definition of speed being relative, and that measured speeds are consistent with that. If you have A moving at 0.8c relative to B, does it make sense that B is moving at a different speed relative to A? If you wanted that, you could define speed differently (eg. define speed to be absolute, and please call it something else), but you would end up with a system of measurements that is either inconsistent with measurement, or more cumbersome than what we have.

I think it's a 3rd option: I think you're determined not to accept relativity and so you're determined not to understand it. I think we could find out with a quiz! Do you think that a) you will accept relativity and understand it together, or b) you will eventually understand it, and then accept it after, or c) if you accept that it's correct first, that will make it easier to understand, or d) you will never accept it and it's more likely that you'll find a flaw in it before anyone convinces you that it's true. Or e) other: ______ ?

i do have some problems with Relativity;

-relativity is based on a principle that says that SOL is measured the same by all observers, no matter their state of motion. To me it does not go well with speed being relative. To me (but that must be me) it would be simplier to state that the phenomena that an observer observes moving at c is called "light". IOW that the observers will call "light' some different thing. As if light was an array of radiation traveling at all possible velocities.

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2 hours ago, michel123456 said:

But all clocks (including clock 3) are in a rest frame. If i understand correctly.

They are not in the same frame

1 hour ago, michel123456 said:

So if I understand correctly, in order for every observer to agree, you have changed everything in such a way that velocity (0.8 c) remains the same. You have changed the distance (if it was a rod it is measured a different length). You have changed the time (the ticking rate, the phase, the delay). You have kept velocity the same. why haven't you changed velocity and kept time & space as they are? Why is it so important to keep velocity the same for all observers?

Because that’s how relativity works, and relativity is how nature behaves.

We have lots of evidence that time and space (distance) are relative. It’s not an arbitrary choice.

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22 minutes ago, michel123456 said:

i do have some problems with Relativity;

-relativity is based on a principle that says that SOL is measured the same by all observers, no matter their state of motion. To me it does not go well with speed being relative. To me (but that must be me) it would be simplier to state that the phenomena that an observer observes moving at c is called "light". IOW that the observers will call "light' some different thing. As if light was an array of radiation traveling at all possible velocities.

Always I see the same pattern. Brush aside explanations and equations as if you didn't even read them, but always latch on to any idea that justifies a failure to understand relativity as if that's just another equally valid viewpoint. I think Asimov's "my ignorance is just as good as your knowledge" quote applies. You say your view is "simpler" but it's just a misunderstanding. It makes me think that people who put effort into trying to explain things to you over and over are just wasting their time. You ask questions as if you want to understand, and then reply to answers as if your questions were only meant to demonstrate what you see as "problems with Relativity" and you had no interest in understanding how they're resolved. If you were interested in understanding it, you'd spend more time talking about what relativity says that doesn't make sense to you, and less about how much sense an alternative makes.

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2 hours ago, michel123456 said:

You have kept velocity the same. why haven't you changed velocity and kept time & space as they are? Why is it so important to keep velocity the same for all observers?

But theory does keep the spacetime interval invariant, just like lightspeed.

This is because space and time are not independent (as you would have it)

Spacetime embodies the connection between them.

If you have X space and Y space they can be independent, in which case they define a plane.

But if, say,   X2 + Y2  =  R2 , then they are no longer independent and you no longer have a plan  -- you have a circle.
In this case since X and Y are essentially the same both spatial so they have the same characteristics or properties or effects on matter,  you can draw it in space.

But space and time have some characteristics and effects the same and some different so the condition of dependence is different, leading to different effects on  matter.

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1 hour ago, md65536 said:

Always I see the same pattern. Brush aside explanations and equations as if you didn't even read them, but always latch on to any idea that justifies a failure to understand relativity as if that's just another equally valid viewpoint. I think Asimov's "my ignorance is just as good as your knowledge" quote applies. You say your view is "simpler" but it's just a misunderstanding. It makes me think that people who put effort into trying to explain things to you over and over are just wasting their time. You ask questions as if you want to understand, and then reply to answers as if your questions were only meant to demonstrate what you see as "problems with Relativity" and you had no interest in understanding how they're resolved. If you were interested in understanding it, you'd spend more time talking about what relativity says that doesn't make sense to you, and less about how much sense an alternative makes.

Sorry but I am talking about what Relativity doesn't make sense to me:

Second problem is, as i wrote above, the concept of the incoming object chasing its own image. At 0,99c the object has its own image collated to his nose. That sounds bogus; how can he have his own image so close and measure that the same image goes away from him at c? i don't know how you can reconcile the 2 scenarios.

Third problem is length contraction happening only in the direction of movement. I wonder how that can happen, while time dilation has no direction. How are the 2 effects compatible? (it would make more sense if length contraction happened in all directions. More sense if length contraction was a kind of illusion, a kind of perspective effect and not a real thing.

Fourth problem is with multiple realities; how is it possible for all observers to measure different realities (different times & lengths) and that these realities are all existing at the same time: aka you have a rod 1 meter long in your hand but some other observer in a moving car tells you that you are wrong, the rod is 90 centimeters. If someone told you that you would probably answer that you know better, the rod is 1meter long, point. What the other observer is measuring is a distorted image, it is not a 2nd reality.

Fifth problem: I cannot remember right now, my wife just cut the flow.

.......

Ah yes, fifth problem: the twin paradox. The paradox is not about one twin aging more or less than the other. The paradox is that there is a broken symmetry: the traveling twin is aging less than the twin who stays at rest. But since the traveling twin is also in a resting FOR (a different one), who is the traveling twin? twin A or twin B? Which of the 2 twins will age less than the other? It is not logically acceptable that both twins will age less than the other. That is the paradox. And there is something wrong in it.(and not endless conversations about accelerations in order to determine who is the traveler & who is at rest, that is not the problem)

And maybe more.

OTOH I would accept an explanation that would keep Galilean relativity, the absence of aether and generally some symmetry (as the one that states that the laws of physics are the same for all). But with only one reality, and one preferred observer: the observer that is in the same FOR as the observed object.

51 minutes ago, studiot said:

But theory does keep the spacetime interval invariant, just like lightspeed.

This is because space and time are not independent (as you would have it)

Spacetime embodies the connection between them.

If you have X space and Y space they can be independent, in which case they define a plane.

But if, say,   X2 + Y2  =  R2 , then they are no longer independent and you no longer have a plan  -- you have a circle.
In this case since X and Y are essentially the same both spatial so they have the same characteristics or properties or effects on matter,  you can draw it in space.

But space and time have some characteristics and effects the same and some different so the condition of dependence is different, leading to different effects on  matter.

But you have NO CLUE about what is space & what is time. It's not you, no one has.

Relativists keep talking about 'the fabric of spacetime" and 'expanding space" and "space being created' while expanding, and at te same time negating any notion of aether. To me, sure there is no aether, and the concept of "expansion" & "space being created" is ultimate bogus. I wonder how people with some intelligence can swallow that. Maybe i lack of intelligence that's the reason why I cannot swallow that. That was the sixth problem, more cosmological, but still related to Relativity.

Edited by michel123456
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24 minutes ago, michel123456 said:

Sorry but I am talking about what Relativity doesn't make sense to me:

[...](it would make more sense if length contraction happened in all directions. More sense if length contraction was a kind of illusion, a kind of perspective effect and not a real thing.

[...] What the other observer is measuring is a distorted image, it is not a 2nd reality.

[...]And there is something wrong in it.(and not endless conversations about accelerations in order to determine who is the traveler & who is at rest, that is not the problem)

That's not talking about relativity. Why not work through the explanations given, instead of ignoring them and always falling back to accepting some alternative, accepting that relativity is wrong?

All of your problems have been explained to you before. They all have examples that you *could* work through. You *could* work through them and see how you arrive at the answers that SR predicts, or find where you're getting hung up. You *could*!...

I gave you an example that *showed* the effect of time dilation without length-contraction perpendicular to the direction of travel. You expressed incredulity and moved on. Go through the example. We can show you what you're missing. Don't look at any of the details, and the answer's simple: You're missing everything.

However I think you're opposed to understanding relativity and are wasting people's time repeating the same questions about it while ignoring the answers. Go through the mathematical details of an example.

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52 minutes ago, michel123456 said:

But you have NO CLUE about what is space & what is time. It's not you, no one has.

Relativists keep talking about 'the fabric of spacetime" and 'expanding space" and "space being created' while expanding, and at te same time negating any notion of aether. To me, sure there is no aether, and the concept of "expansion" & "space being created" is ultimate bogus. I wonder how people with some intelligence can swallow that. Maybe i lack of intelligence that's the reason why I cannot swallow that. That was the sixth problem, more cosmological, but still related to Relativity.

I don't recall saying any of this, it certainly has little to do with what I wrote.

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1 hour ago, michel123456 said:

Third problem is length contraction happening only in the direction of movement. I wonder how that can happen, while time dilation has no direction. How are the 2 effects compatible? (it would make more sense if length contraction happened in all directions. More sense if length contraction was a kind of illusion, a kind of perspective effect and not a real thing.

As I recall you brought this up elsewhere, earlier. Perhaps you could not act like this issue wasn’t addressed?

1 hour ago, michel123456 said:

Fourth problem is with multiple realities; how is it possible for all observers to measure different realities (different times & lengths) and that these realities are all existing at the same time: aka you have a rod 1 meter long in your hand but some other observer in a moving car tells you that you are wrong, the rod is 90 centimeters. If someone told you that you would probably answer that you know better, the rod is 1meter long, point. What the other observer is measuring is a distorted image, it is not a 2nd reality.

“Reality“ is an issue for philosophy

What physics tells you is that the measurement value depends on who is doing the measurement

1 hour ago, michel123456 said:

Ah yes, fifth problem: the twin paradox. The paradox is not about one twin aging more or less than the other.

Yes, it is.

1 hour ago, michel123456 said:

The paradox is that there is a broken symmetry:

The lack of actual paradox is because of this

1 hour ago, michel123456 said:

the traveling twin is aging less than the twin who stays at rest. But since the traveling twin is also in a resting FOR (a different one), who is the traveling twin? twin A or twin B? Which of the 2 twins will age less than the other? It is not logically acceptable that both twins will age less than the other. That is the paradox. And there is something wrong in it.(and not endless conversations about accelerations in order to determine who is the traveler & who is at rest, that is not the problem)

The broken symmetry tells you who actually ages less.

1 hour ago, michel123456 said:

OTOH I would accept an explanation that would keep Galilean relativity, the absence of aether and generally some symmetry (as the one that states that the laws of physics are the same for all). But with only one reality, and one preferred observer: the observer that is in the same FOR as the observed object.

Why would you accept an explanation that is contradicted by experiments?

1 hour ago, michel123456 said:

But you have NO CLUE about what is space & what is time. It's not you, no one has.

Again, a matter for philosophy

1 hour ago, michel123456 said:

Relativists keep talking about 'the fabric of spacetime" and 'expanding space" and "space being created' while expanding, and at te same time negating any notion of aether. To me, sure there is no aether, and the concept of "expansion" & "space being created" is ultimate bogus. I wonder how people with some intelligence can swallow that. Maybe i lack of intelligence that's the reason why I cannot swallow that. That was the sixth problem, more cosmological, but still related to Relativity.

So you don’t understand it, and therefore nobody can?

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10 hours ago, michel123456 said:

Sorry but I am talking about what Relativity doesn't make sense to me

That is (nearly) fair. If you do not understand it, that's fine. You are surely not the only one. But as others already said, loads of people here try to explain it to you, but you keep sticking to your own, wrong, mental pictures. And really, you not understanding a counter-intuitive theory, does not mean in any way that the theory is wrong. All the experimental confirmations of special relativity should show you that the problem is your understanding, not the theory.

10 hours ago, michel123456 said:

Second problem is, as i wrote above, the concept of the incoming object chasing its own image. At 0,99c the object has its own image collated to his nose. That sounds bogus; how can he have his own image so close and measure that the same image goes away from him at c? i don't know how you can reconcile the 2 scenarios.

Special relativity is the reconciliation!

10 hours ago, michel123456 said:

Third problem is length contraction happening only in the direction of movement. I wonder how that can happen, while time dilation has no direction. How are the 2 effects compatible? (it would make more sense if length contraction happened in all directions. More sense if length contraction was a kind of illusion, a kind of perspective effect and not a real thing.

So everything should shrink, independent of the direction? And do not forget that space and time do not play the same role in spacetime. Where one second on a spaceship passing me is 10 seconds for me, 10 meters (yes, in the direction of flight) becomes one meter. Time 'expands', but length contracts. The time dimension in spacetime has the opposite sign as the space dimensions in the 'spacetime-distance' formula.

10 hours ago, michel123456 said:

Fourth problem is with multiple realities; how is it possible for all observers to measure different realities (different times & lengths) and that these realities are all existing at the same time: aka you have a rod 1 meter long in your hand but some other observer in a moving car tells you that you are wrong, the rod is 90 centimeters. If someone told you that you would probably answer that you know better, the rod is 1meter long, point. What the other observer is measuring is a distorted image, it is not a 2nd reality.

Another confusion of yours. In SR nobody is wrong. It is just that you must take the velocity between 2 flying systems into account (and this is not about signal delay!). For a muon produced in earth's higher atmosphere the distance it travels to the surface is shorter than for us, therefore it can reach us. From our view it travels the 'longer distance' but its time is slower, and therefore it can reach us. That makes one consistent reality: muons detected in our detectors at the earth's surface.

10 hours ago, michel123456 said:

Ah yes, fifth problem: the twin paradox. The paradox is not about one twin aging more or less than the other. The paradox is that there is a broken symmetry: the traveling twin is aging less than the twin who stays at rest. But since the traveling twin is also in a resting FOR (a different one), who is the traveling twin? twin A or twin B? Which of the 2 twins will age less than the other? It is not logically acceptable that both twins will age less than the other. That is the paradox. And there is something wrong in it.(and not endless conversations about accelerations in order to determine who is the traveler & who is at rest, that is not the problem)

There is no symmetry. The travelling twin changes direction, i.e. it changes its reference frame, in order to return to earth. The home-staying twin doesn't. No symmetry, no paradox. And the 'twin paradox' is empirically confirmed, not with twins of course, but with travelling atomic clocks. 'Acceptability' by one person is not really an argument. Your logic is wrong, and as long as you stick to your, again wrong, mental pictures, you will never understand.

10 hours ago, michel123456 said:

OTOH I would accept an explanation that would keep Galilean relativity, the absence of aether and generally some symmetry (as the one that states that the laws of physics are the same for all). But with only one reality, and one preferred observer: the observer that is in the same FOR as the observed object.

This makes no sense. Special relativity is about how observers in different frames of reference see distance and time measurements in each other's frames. The symmetry is that of constant velocity, and therefore not existing preferred frame of reference.

11 hours ago, michel123456 said:

I wonder how people with some intelligence can swallow that. Maybe i lack of intelligence that's the reason why I cannot swallow that.

No, it is your stubbornness.

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49 minutes ago, Eise said:

No, it is your stubbornness.

Sure, I am stubborn. What I don't understand I say "I don't understand". The fact that I don't accept it is a simple consequence: i will never say "drop it Michel, others understand it in your place so you must accept it". No I prefer being stubborn. And being ridicule if necessary, I really don't care.

Thank you all anyway for the polite replies & sorry if you feel wasting your time.

49 minutes ago, Eise said:

So everything should shrink, independent of the direction?

That is what happens when you look around you. Things are observed getting smaller & smaller according to distance and of course things are NOT getting smaller, it is an effect of perspective. This effect is taking place in all directions. You don't observe the objects reducing only radially, or only tangentially. Isotropy is conserved.

Not to say that the laws of optics should be derived from Relativity, since it is a theory that deals with what is being observed.

Edited by michel123456
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55 minutes ago, michel123456 said:

Sure, I am stubborn. What I don't understand I say "I don't understand". The fact that I don't accept it is a simple consequence: i will never say "drop it Michel, others understand it in your place so you must accept it". No I prefer being stubborn. And being ridicule if necessary, I really don't care.

The lack of understanding is perfectly acceptable; you are making an effort to learn. The problem is when you insist that other things are or must be true.

Whether or not you understand, you must at least acknowledge what people tell you is mainstream physics. You have no basis to say that it's wrong and/or some other position is right.

55 minutes ago, michel123456 said:

That is what happens when you look around you. Things are observed getting smaller & smaller according to distance and of course things are NOT getting smaller, it is an effect of perspective. This effect is taking place in all directions. You don't observe the objects reducing only radially, or only tangentially. Isotropy is conserved.

Not to say that the laws of optics should be derived from Relativity, since it is a theory that deals with what is being observed.

Again, what you see and what you measure are not the same thing. Perspective is something you would account for if you were measuring the size of an object. If you look through a telescope and measure the angular size, you would need to know how far away it is. Nobody looks at the moon and insists that it is, in actuality, a few cm in diameter, or that the moon and the sun are physically the same size.

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1 hour ago, michel123456 said:

Sure, I am stubborn. What I don't understand I say "I don't understand".

Again, that is fair. But this is not:

1 hour ago, michel123456 said:

The fact that I don't accept it is a simple consequence

That is just logically wrong. Should I suppose that everything I do not understand is wrong, and therefore I should not accept it?

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28 minutes ago, Eise said:

That is just logically wrong. Should I suppose that everything I do not understand is wrong, and therefore I should not accept it?

Not everything. But something you are struggling with a sufficient time, yes. The same questions arise all the time, the same answers, no satisfaction.

45 minutes ago, swansont said:

Again, what you see and what you measure are not the same thing. Perspective is something you would account for if you were measuring the size of an object. If you look through a telescope and measure the angular size, you would need to know how far away it is. Nobody looks at the moon and insists that it is, in actuality, a few cm in diameter, or that the moon and the sun are physically the same size.

And all understand that the moon is round, because isotropy is conserved. The moon does not change shape because it is observed through angular size. In Relativity, length contraction is supposed provoking a change of shape. I don't know where it comes from.

What is the physical force involved that provokes  this change of shape? since it is firmly believed that length contraction do happen.

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53 minutes ago, michel123456 said:

Not everything. But something you are struggling with a sufficient time, yes. The same questions arise all the time, the same answers, no satisfaction.

Even that you know that special relativity is tested to the bone, and forms the basics of nearly all of physics? Quantum Field Theory would be wrong if relativity is wrong! The relationship between electrical and magnetic fields could not be understood if SR was wrong, etc etc.

Instead of protesting against the arguments given in this (and other...) threads, you should point to the places where you do not follow the argument; but your only reaction is taking your wrong mental pictures and say that the argument's conclusion does not fit them.

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1 hour ago, michel123456 said:

And all understand that the moon is round, because isotropy is conserved. The moon does not change shape because it is observed through angular size. In Relativity, length contraction is supposed provoking a change of shape. I don't know where it comes from.

So look at a situation where you don’t have a round object. Do railroad tracks get closer together in the distance? No, it’s perspective. We don’t worry that the train will derail.

Let’s say you have a siren, at some frequency. It’s moving. If it’s moving toward you, the frequency is higher. If it’s moving away, it’s lower. You can hear this. The frequency is actually higher or lower, depending on your situation. It’s not an illusion. So the concept of some measurement being relative is not new.

In relativity, length contraction comes from the invariance of c. The invariance is the new part. The derivation is pretty straightforward.

In most situations, a moving object that ejects/emits something, you expect the speeds to add linearly. If you can throw an object 20 m/s and are on a platform moving 10 m/s, and throw the object in the direction of travel, it will go 30 m/s

Light doesn’t behave that way, though. One consequence of c being invariant is that time and distance are not. If we “throw” this light from a moving platform and we both agree it moves at c (as we must) the only way for us to agree on measurements is if time and distance depend on our frame of reference

1 hour ago, michel123456 said:

What is the physical force involved that provokes  this change of shape? since it is firmly believed that length contraction do happen.

There is no force. The measurement depends on the frame of reference. In the object’s own frame, nothing is different. There is no physics one can point to that says one frame is correct and the other is wrong.

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17 hours ago, michel123456 said:

relativity is based on a principle that says that SOL is measured the same by all observers, no matter their state of motion.

Actually, it is based on the principle that the spacetime interval between two events is invariant (as others here have already pointed out). The invariance of SOL is a consequence of that.

15 hours ago, michel123456 said:

how can he have his own image so close and measure that the same image goes away from him at c?

Because the spacetime interval is an invariant.

15 hours ago, michel123456 said:

How are the 2 effects compatible?

Because the spacetime interval is invariant.

15 hours ago, michel123456 said:

how is it possible for all observers to measure different realities (different times & lengths) and that these realities are all existing at the same time

All observers agree on the same reality - being the invariant spacetime interval.

15 hours ago, michel123456 said:

Fifth problem: I cannot remember right now, my wife just cut the flow.

I don’t know what number five was meant to be, but it’s almost certainly addressed by the fact that - you guessed it - the spacetime interval is invariant.

15 hours ago, michel123456 said:

The paradox is that there is a broken symmetry:

One twin is inertial, the other one isn’t, so obviously there is no symmetry, because the frames aren’t related by a Lorentz transformation, but by something a little more complicated.

15 hours ago, michel123456 said:

who is the traveling twin?

The one who physically measures a non-zero value on his accelerometer at some point on his journey.

15 hours ago, michel123456 said:

OTOH I would accept an explanation that would keep Galilean relativity

So you would accept a model that precludes elementary particles from having the property of spin, and where the strong, weak, and EM interactions do not exist? Because all of these things are intrinsically relativistic phenomena.
I presume you hold this view because you are not aware of the crucial role relativity plays for the dynamics - and even mere existence - of the particles we observe, never even mind how those particles move under the influence of gravity.

15 hours ago, michel123456 said:

I wonder how people with some intelligence can swallow that.

There is no ‘space being created’, not sure where you got that from. Apart from that, intelligent people use relativity because they are intelligent enough to realise that it works very well within its domain of applicability.
But intelligence isn’t the problem, because you are evidently very intelligent as well, in your own way. The problem is that you equate it (the model) not making sense to you with it having to be wrong. But that’s just a common logical fallacy. Relativity is very much “true”, in the sense that it is a model that works extremely well; whether it makes “sense” (what does that even mean?) to you as an individual person or not is entirely irrelevant to this. Quantum field theory (e.g.) makes little sense to me, it feels like an odd jumble of ad-hoc made-up bits, which are made to fit using even more ad-hoc made-up bits. Nonetheless, I acknowledge that it works really well within its domain, and right now it is the best description of the microscopic world that we have, so I choose to accept it for what it is and study it to the best of my ability. But let’s just say you won’t see me loosing any sleep should it one day be augmented/replaced by something different.

This is why we have the scientific method - to minimise subjective measures such as “making sense”. “It doesn’t make sense to me” is simply not a scientific argument.

The other problem I see on this thread is that you are rejecting something that you evidently don’t understand very well, judging by some of the statements you have made here. That would be like me fighting tooth and nail against some particular design for a building, even though I know absolutely nothing about design principles, very little about structural mechanics, and even less about how it all fits into the surrounding cityscape. My arguments would thus just be personal opinions without any objective basis, and thus pretty much meaningless to any architect worth their salt.

Long story short - if your opinion about relativity is not based on thorough and intensive study of the model itself (which it isn’t - no offence intended at all), and how it fits into the overall framework of physics, then it is scientifically unreliable and you need to question it.

2 hours ago, michel123456 said:

What is the physical force involved that provokes  this change of shape? since it is firmly believed that length contraction do happen.

This is the core issue that you haven’t grasped in all this - relativistic effects are relationships between frames/observers in spacetime, not things that happen “to” or “in” a single frame. So there is no force contracting anything, and nothing slowing down any clocks. It is only when you take two clocks or two rulers from different frames, and compare them in some suitable manner, that you find that the relationship between them is such that one is dilated/contracted with respect to the other.
So for example, when we collide heavy gold ions in the RHIC, then the resulting shower of particles after the collision as seen in the lab frame is consistent only with the gold ions having the shape of flattened disks (due to length contraction in the direction of motion only), not with them being spherical - we can easily tell, because the transition amplitudes of the various scattering and decay processes seen in the lab frame explicitly depend on the spatial distribution of the original ensemble (the ion). The necessary calculations are complicated, but the result is not only consistent with, but mandated by relativity. The same is true in the ion frame (in the sense that the exact same outcome is predicted) - now the ion itself is seen as spherical, but distances in the accelerator are length-contracted, and the oncoming ion is more heavily time-dilated and contracted. But the eventual outcome is the same, so there is perfect symmetry (at the time of collision, i.e. after the acceleration phase).

This is a real-world experiment, so we know experimentally that it all checks out.

Edited by Markus Hanke
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2 hours ago, swansont said:

So look at a situation where you don’t have a round object. Do railroad tracks get closer together in the distance? No, it’s perspective. We don’t worry that the train will derail.

Let’s say you have a siren, at some frequency. It’s moving. If it’s moving toward you, the frequency is higher. If it’s moving away, it’s lower. You can hear this. The frequency is actually higher or lower, depending on your situation. It’s not an illusion. So the concept of some measurement being relative is not new.

In relativity, length contraction comes from the invariance of c. The invariance is the new part. The derivation is pretty straightforward.

In most situations, a moving object that ejects/emits something, you expect the speeds to add linearly. If you can throw an object 20 m/s and are on a platform moving 10 m/s, and throw the object in the direction of travel, it will go 30 m/s

Light doesn’t behave that way, though. One consequence of c being invariant is that time and distance are not. If we “throw” this light from a moving platform and we both agree it moves at c (as we must) the only way for us to agree on measurements is if time and distance depend on our frame of reference

There is no force. The measurement depends on the frame of reference. In the object’s own frame, nothing is different. There is no physics one can point to that says one frame is correct and the other is wrong.

Surprisingly I am OK with all of that.

Where I am not ok is when someone argues that the measurement is really happening. For example when the twin comes back and is younger than his brother. Is he length contracted too? (If you answer yes you will drive me crazy).

You wrote: "There is no force". What a relief. Of course not, because in reality (what I consider Reality i.e. the FOR of the object itself), in reality nothing happened, no length contraction, no time dilation. Those things cannot happen just because someone is observing you! Yes someone may measure length contraction & time dilation. It may even happen that billion observers in billion different FOR will measure different lengths and times, but there is only one reality. In the FOR of the object, things are rigid & time ticks as usual. And when the twin comes back, he is not length contracted according to his position (upright or sitting) in the spacecraft. It is insane to believe such a thing.

There is an awfull mess between what one measures & what reality is made of. This is not philosophy, this is about the interpretation of Relativity.

2 hours ago, Markus Hanke said:

This is the core issue that you haven’t grasped in all this - relativistic effects are relationships between frames/observers in spacetime, not things that happen “to” or “in” a single frame. So there is no force contracting anything, and nothing slowing down any clocks

I agree, but that is NOT what I read about Relativity. Usually it is explained that the effects of relativity are real. Taking Swansont example, in Relativity  it is like the parallel train tracks do join together at the horizon. The twin that comes back younger is like a train derailing at the horizon: it is the same flawed concept.

Edited by michel123456
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8 hours ago, swansont said:

The lack of understanding is perfectly acceptable; you are making an effort to learn.

I don't think that's true. I don't see a single reply here from michel123456 that relates to trying to understand any of the answers and explanations given. No asking for further details. No working through a solution. Every reply is a justification of not making an effort to learn, an argument of why the explanations can be ignored.

Literally 10 years ago he was asking about the same "problems" he had with relativity. 10 years from now, he'll have a similar list of "problems", after thousands of attempts by people to explain it to him, after 0 attempts to work through it.

What he's good at, is asking questions that makes one think he's interested in learning about relativity. But look at the replies. The only interest is in what doesn't make sense to him. Anything making sense of it is ignored. That's the only answer he's interested in: that it doesn't make sense. All his questions are phrased as if the answer he expects is that it can't make sense, never a question about how the resolution to the problems work out correctly. So I think he's soapboxing, getting much better responses by stating "relativity is nonsense" as a question.

Edit: To be fair, page 1 of this thread is full of counter examples to what I said, including asking about specific examples and numbers and their explanations. I don't know how we got from that on page 1 to page 2 with:

2 hours ago, michel123456 said:

And when the twin comes back, he is not length contracted according to his position (upright or sitting) in the spacecraft. It is insane to believe such a thing. [...] The twin that comes back younger is like a train derailing at the horizon: it is the same flawed concept.

Edited by md65536
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re. "how can he have his own image so close and measure that the same image goes away from him at c? "

5 hours ago, Markus Hanke said:

Because the spacetime interval is an invariant.

So basically, say in an Earth frame, with a rocket approaching at near c, the image of the rocket when it began its journey can be very close to the rocket itself, for nearly the entire journey, but in the rocket frame the image reaches Earth less than half way through the journey (since the Earth is approaching at near c, Earth and the outbound image will meet near the halfway mark).

The spacetime interval is invariant implies for example that... if you consider some pair of events, one that the "image" passes through and one that the rockets passes through, that are spatially near each other (separated by x) in the Earth frame, they're also temporally near each other (separated by t) in the Earth frame, and you get a small interval (ct^2 - x^2). In the rocket frame, those events are far apart spatially, but also far apart in time, and you get the same small interval.

Is that all there is to it? Does that sufficiently explain it? It seems to, but normally I'd have to figure out the separate time dilation, length contraction, and relativity of simultaneity to reconcile the different reference frames. Are those still needed, separately (or combined like in Lorentz transformation), to calculate the components of the interval? It seems like the interval being invariant isn't enough to know the x and t in another frame, without calculating one or the other separately?

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3 hours ago, michel123456 said:

Surprisingly I am OK with all of that.

Where I am not ok is when someone argues that the measurement is really happening. For example when the twin comes back and is younger than his brother. Is he length contracted too? (If you answer yes you will drive me crazy).

When he returns the relative speed is zero, so no. Their clock run at the same rate, too, at that point. Length contraction and time dilation require motion (for SR). But during trip, yes, he is, according to the twin on earth. As is his spaceship.

3 hours ago, michel123456 said:

You wrote: "There is no force". What a relief. Of course not, because in reality (what I consider Reality i.e. the FOR of the object itself), in reality nothing happened, no length contraction, no time dilation. Those things cannot happen just because someone is observing you! Yes someone may measure length contraction & time dilation. It may even happen that billion observers in billion different FOR will measure different lengths and times, but there is only one reality. In the FOR of the object, things are rigid & time ticks as usual. And when the twin comes back, he is not length contracted according to his position (upright or sitting) in the spacecraft. It is insane to believe such a thing.

Reality has nothing to do with it. A billion different answers from a billion observers, and none of them can do a physics experiment that shows that “this is the ‘real‘ frame”

Each frame is as real as the next.

But I can’t cause a force to be exerted somewhere simply by moving. There’s so force, and rigidity is not an issue. Nothing is being crushed. A meter stick, or a length of a meter, is not a meter long when measured from a moving frame.

Energy isn’t invariant, either. If you’re on a train car moving 100 m/s and throw a 1 kg ball 10 m/s, you see the ball moving 10 m/s and have 50 joules of KE. That’s true for anyone on the train. But that ball hitting a wall affixed to the earth is moving 110 m/s and has 6050 joules.

Which one is “real”?

Values depending on which frame you’re in is nothing unusual in physics.

3 hours ago, michel123456 said:

There is an awfull mess between what one measures & what reality is made of. This is not philosophy, this is about the interpretation of Relativity.

No, it isn’t. “Reality” is not anything relativity distinguishes

3 hours ago, michel123456 said:

I agree, but that is NOT what I read about Relativity. Usually it is explained that the effects of relativity are real. Taking Swansont example, in Relativity  it is like the parallel train tracks do join together at the horizon. The twin that comes back younger is like a train derailing at the horizon: it is the same flawed concept.

Younger than his twin, because time ran slower for them. Not younger than when they started.

And yes, the effect is real, in that it is not an illusion. Clocks would read different times.

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16 hours ago, michel123456 said:

I agree, but that is NOT what I read about Relativity. Usually it is explained that the effects of relativity are real.

Of course they are real. Them being relationships between reference frames doesn’t mean they aren’t real. To stay with the previous example, when we collide gold ions in the RHIC, they really are flattened disks in the lab frame, and their collision dynamics behave accordingly. Likewise, in the rest frame of the ion its shape really is spherical, and it is the accelerator and the oncoming ion that are contracted and time-dilated. The point is that the relationships between the frames are such that both frames agree on the outcome - they determine the same collision end products, even if they don’t agree on how it came about. Hence, even though different observers disagree on measurements of space and time, they always agree on the empirical outcome of the experiment (which is given by the spacetime interval, this being a relativistic field theory). So there is only one reality, which is what all observers agree upon.

As another example, if you put a muon into an accelerator, it really does ‘live’ much longer than a reference muon at rest. This is empirical reality, not just an observational artefact or illusion of some kind, and these effects are observed and measured every day in all areas of high energy physics.

16 hours ago, michel123456 said:

The twin that comes back younger is like a train derailing at the horizon: it is the same flawed concept.

It is not a flawed concept, it is empirical fact. The two twins evidently trace out geometrically different world lines in spacetime, and since total proper time is just the geometric length of a world line, they cannot be of the same age when they return to rest. This is just elementary geometry, there is nothing surprising, puzzling, or paradoxical about this at all, and both twins will agree on the outcome of this experiment (i.e. the difference in accumulated times on their clocks).

Why do you struggle so hard against something that has been tested and verified over and over again to the n-th degree for well over a century now? Lorentz invariance and all other principles of relativity are thoroughly established empirical facts, they aren’t just someone’s flights of fancy. You are flogging a dead horse here by rejecting this. If the idea doesn’t make sense to you, and you see all manner of paradoxes and contradictions, then that means only that you aren’t understanding the model - it doesn’t mean it isn’t true. Fundamentally, judging from the comments you made on this thread, you are thinking in terms of Euclidean geometry - so of course none of the principles make much sense to you, because they don’t work in a Euclidean world. However, relativistic spacetime is not Euclidean, and once you realise that, everything falls into place very nicely. But it is for yourself to make that conceptual shift, no one else can do this for you - we can only try and help by answering honest questions.

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12 hours ago, swansont said:

And yes, the effect is real, in that it is not an illusion. Clocks would read different times.

So you are saying that as the returning twin stops, all of a sudden he comes back to his original dimensions (length contraction stops because motion stops) but the accumulated time gap is still there. Is that it?

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13 hours ago, md65536 said:

Is that all there is to it? Does that sufficiently explain it? It seems to, but normally I'd have to figure out the separate time dilation, length contraction, and relativity of simultaneity to reconcile the different reference frames. Are those still needed, separately (or combined like in Lorentz transformation), to calculate the components of the interval? It seems like the interval being invariant isn't enough to know the x and t in another frame, without calculating one or the other separately?

I am not entirely sure what you mean. Basically, you’d calculate the interval in one frame first; you then apply Lorentz transformations to the time and space parts in order to “go” into the other frame, and check what this does to the overall interval. What you’ll find is that the interval remains the same - Lorentz transformations are just hyperbolic rotations in spacetime, so when you go from one frame to another, you essentially rotate some portion of the space part into the time part, or vice versa. This leaves the overall quantity unchanged.

1 minute ago, michel123456 said:

So you are saying that as the returning twin stops, all of a sudden he comes back to his original dimensions (length contraction stops because motion stops) but the accumulated time gap is still there. Is that it?

In the classical Twin Paradox setup, one of the frames is inertial, whereas the other one isn’t - so these frames are not symmetric, and they can be physically distinguished (by accelerometer readings). This asymmetry is what leads to the difference in total accumulated times. If both frames were inertial, then they would be physically indistinguishable, and there would be no residual difference in total accumulated times.

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8 minutes ago, Markus Hanke said:

But it is for yourself to make that conceptual shift, no one else can do this for you - we can only try and help by answering honest questions.

14 hours ago, md65536 said:

I don't think that's true. I don't see a single reply here from michel123456 that relates to trying to understand any of the answers and explanations given. No asking for further details. No working through a solution. Every reply is a justification of not making an effort to learn, an argument of why the explanations can be ignored.

Literally 10 years ago he was asking about the same "problems" he had with relativity. 10 years from now, he'll have a similar list of "problems", after thousands of attempts by people to explain it to him, after 0 attempts to work through it.

What he's good at, is asking questions that makes one think he's interested in learning about relativity. But look at the replies. The only interest is in what doesn't make sense to him. Anything making sense of it is ignored. That's the only answer he's interested in: that it doesn't make sense. All his questions are phrased as if the answer he expects is that it can't make sense, never a question about how the resolution to the problems work out correctly. So I think he's soapboxing, getting much better responses by stating "relativity is nonsense" as a question.

Edit: To be fair, page 1 of this thread is full of counter examples to what I said, including asking about specific examples and numbers and their explanations. I don't know how we got from that on page 1 to page 2 with:

.

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