michel123456

1.You didn't have the same comments on SwansonT post. 2. Is SwansonT post correct, or no? 3. Is my post correct, or no? Your post was slippery like a fish, you are avoiding the question.

My post was also about Swansont comment.

Tragic. Minus one. I am getting angry.

I really don't understand. Because if you take it like this, neither time dilation was observed. And i think that since the path as seen from Earth is 10km, neither the particle would have been observed length contracted. It is not compatible to observe a contracted muon traveling 10 km. -------------- After more thinking, if the muon is a sphere in its own frame, the earthling would have to observe the muon elongated 5 times, not contracted.

I went looking your link (as I always do) Please explain the following: What bothers me is the comment green underlined From what I understand As seen from Earth, the muon traveled 10 km in 34μs As seen from the muon, the muon traveled 2km in 6.8 μs There is a factor γ of 5 that is applied for converting one frame to the other. The velocity is the same for both observers.10 km/34μs=2km/6.8 μs BUT From the Earth frame, the muon is calculated to have been time dilated, and thus it must have been contracted too, and its path too. IOW from the Earth both effects must have been observed calculated. I don't understand the comment underlined in green.

And where is length contraction?

This is enlightenment! (the bold part above). I agree 100%. That is fully more understandable. Thank you. But is that Relativity? Because that is not what I have understood from this long conversation. The exact contrary to speak frankly. -------------------------------------------- Edited for enabling 2nd thoughts...after enthusiasm rebound. Your question suggests that my description is correct. I guess not. But if she wants to embark merchandise, she should use proper length. IOW it depends on the question.

Because they are anthropomorphic. However, good point. +1 Purpose built robots exist from the beginning of the industrial epoch* and used to be fascinating but are not so much these days. The struggle to make a robot that looks like a human and eventually surpasses him is the goal today. *sinple machine tools , then automated, then CNC machines or todays industrial robots ------------------------- And also maybe because our entire developed world is made upon the specifications of the human body. Our cars, our buildings, tables & chairs are made for us. An anthropomorphic robot could drive a car, or step a staircase, or use a kitchen. It is a parallel evolution to that of the automated kitchen & car. Automated staircase exist from long ago.

OK let's discuss length only. When the observer extends his hands and physically feels the length of the car being contracted, we are talking about the following (please correct me if I get it wrong) _the fact of touching simultaneously the 2 ends of the car is in fact 2 different events. That is because the left end of the car has a different 4D coordinate than the right end of the car. The T coordinate, as observed by you, is the same for both events, but the spatial coordinates are different. So we have a set of 2 events. For the moving observer, the 2 events are simultaneous For the observer in the car, the 2 events are not simultaneous. What about the length of the car? For the observer in the car, as measured at rest, the car has its own proper length. For the observer moving , the measured length correspond to the projection of a rotation of this length: it is contracted. Think of a circle with diameter=length. According to the angle of the diameter, its orthogonal projection will be less or equal, never larger. Anyway, what the moving observer measures is the projection of the length, not the proper length. The 3D length between the two 4D events doesn't change.

I don't understand, please clarify. Accepting and understanding are 2 different things. And it is not a "stupid optical illusion" effect. It is an effect that rules the laws of physics. The question here is to convince me (& others) that the effect of contracting is real, not in the sensibility of the observer (nobody is arguing against that), but in the sensibility of the observed. I keep saying that the observed doesn't change because it is been observed and measured by an hilarious number of comic heroes. And reversely the comic heroes are not contracting because they are been measured by the guy in the car.

Oh I thought naively that when you said Mr Magoo was moving, he was moving with the car... So you say that Mr Magoo moves and still can reach with his hands the car still at rest. That is quite a challenge. Usually when you move, you know, distance increases... But even in this case of extending his arms like Mr Fantastic, I guess his hands must join the frame of the car in order to measure it. For example putting a solid ruler next to the car. And you will tell me then that the solid ruler will contract. Because the ruler, the hands, Mr Magoo are under the laws of physics. I am afraid this example leads nowhere.

Mr Magoo is also under the laws of physics.

Question: We must be aware of 2 effects, time dilation and length contraction. The 2 effects are linked together. So when I observe an object time dilated, he is also length contracted. Doesn't that mean that its path is also length contracted? IOW that the object will take less time to travel a smaller distance, which looks perfectly sensible (it happens to me all the time ) IOW that the 2 effects should cancel each other? -------------- Because, now that I am thinking about it, if they don't cancel exactly, the velocity as measured by the traveler will not be the same as the velocity measured by the staying at rest observer.

I think it has more to do with the need of empty space. It is like the famous 15 puzzle, If you fill the 16th square, you have locked the system, the squares cannot slide anymore. In your axis & hole example, the axis need some gap to enter the hole, otherwise it sticks. In the atom & electron example, again some void is needed, otherwise nothing could work.

I guess but we don't use the same phrasing. One of the problem of these discussions is language. I agree100% The "funny thing" is that talking about Relativity, then suddenly the length contraction & time dilation seems to become "real" in such way as if the object was changed by the observer. It is not changed by the observer. The other "funny thing" is that most physicists will shoot you if you dare to compare relativistic effects to optical effects, or even worse, to optical illusion. I have found an example. A cube is a geometric object with 6 sides. However, if you look at a cube you can only, at best, see 3 sides simultanately.(not counting eventual reflections) So Relativistic physicist say that when you observe 3 sides, the cube "has" 3 sides. That if I turn it exactly facing me, the cube changed and "has" one side. But all physicists in the world agree that in 4d, the cube has 6 faces. What I say is that the cube doesn't change, it always has 6 faces, even if you can see only 3, even when you catch it in your own hands. The cube doesn't change because it is observed.

Tim88 +1 for your very explicit and understandable posts. And I am glad that we agree that in no way an observer can make things happen in an object just by looking at it. Because sometimes I fell getting crazy reading some very knowledgeable posters seemingly stating otherwise (but that must be me who understands badly). IOW, I am an observer, I look in my telescope to some distant star. This has no effect upon the star. If the star looks length contracted to me, it is merely an effect of observation, nothing else. If I start running like the flash, the star will not change length.

This is wrong. Mr Magoo is (being observed) contracting as well. He feels nothing. I have a deal to propose for you: I will agree with that if you agree that in no way an observer can make things happen in an object just by looking at it. Excellent point about Newton mechanics: nobody is arguing that a body "has" kinetic energy. Nobody is asking "who is right?" because the simple answer is that kinetic energy is relative. But I argue that the body to which this kinetic energy is linked is a body that "exists" and "has" dimensions. It is not a body that "has" multiple lengths at the same time according to the state of motion of its observers. And if another observer arrives, the body doesn't change length. And exactly as in the case of kinetic energy, there is a "zero" point, which corresponds to the frame at rest. In this frame, kinetic energy is zero, the length is maximum, the ticking rate is minimum, and rest mass is defined.

It is profession, if I understand clearly what you are talking about https://en.wikipedia.org/wiki/Scientific_visualization

What blows my mind is this: _You have explained the thing with S0 and S1. but there can be millions of S (S2,S3,S4,S5,...) for which the contraction will be different. How in the hell can it be possible that all these contractions happen inside the same object at the same time (as you said,that the electromagnetic equilibrium positions of its atoms change in many ways at the same time)! ------------------------------------------------------------------ To me the situation is simple: there is only one object with a "zero configuration" as observed at rest. For all other FOR S1, S2, S3, there are different "configurations" of the object, that are relative. Like Kinetic energy is relative. And the observations must be symmetric: in your example of the mirror, is it also proved that the Earth was contracted as seen by the mirror? Because if it is not, you have a problem. "dials in" a quickly incrementing sequence of dates " is an euphemism for "ticking faster". I thought it was not possible.

Thank you. IOW (please correct me) time dilation is not about what one observes, because one cannot directly observes through simultaneity. edit I mean, the red observer at red 2015 cannot see the green guy at green 2013.4.

I didn't figure it was a so difficult question...

Your 2 first links are not available to me.

The blue triangle. It means for the red path that 2 years have passed for him while he sees only one year has passed for the green dot. IOW he is observing the clock on the green path ticking slower. Is that it?

Unfortunately for me a diagram is the alpha and the omega for understanding. An equation says much more when it is put into a graph. Yes the diagram on the left is more sensible and understandable. Thank you. It is perfectly symmetric, there is no preferred FOR, what observes the one is what observes the other. They are both moving relatively to each other. The numbers from the equation coincide. The gamma factor 1,25 appears somehow evidently. (edit) And also the difference between simultaneity and light ray is shown. However time dilation is not so evident to detect. I will post my understanding in a while. Please check if I missed the point again.

I will do that. And yes it is read as time dilation. And yes i am always interested.