michel123456

As I wrote above: if he stopped, it is 60 minutes aka1 hour (because he is 1 HL away). If he makes the U-turn immediately it gets complicated because you have to count for the velocity after the U-turn. It is this instant that Janus describes when the traveler is going back but observer on the Earth haven't seen the U-turn yet. But we have not reached an agreement on what is happening. Basically I am the bad guy disagreeing with everybody.

When the traveler makes the U-turn, he sees the Earth still getting away from him. He will see the Earth stop going away and begin the rush at him some minutes after he made the U-turn, because there is a delay. The image of the Earth takes some time to go to the traveler. See it otherwise: if the traveler stopped for a drink at destination, he would see the image of the Earth stop getting away from him after 1 hour. (approx 4 beers in Belgian units)

Because what the traveler sees is the same (the mirror) of what the observer on earth sees. When the traveler goes out, as much the distance to the Earth increases, as much the delay increases too. And on the return trip, as much the distance reduces, so reduces the delay. The turning point will not be reached at the middle point (in time) of the travel. Although it will be the middle point in distance. If the clock makes the U-turn at the middle point in time, at the end of the travel the clock will miss the Earth by a distance corresponding to the delay (if I am correct, this is more a guess than an accurate calculation). Check with Janus example.

Galilean relativity yes., but not Relativity (because of SOL). But even with Galilean relativity, if the Earth is also moving in the direction of traveler B, but at a lower velocity (which is the equivalent of the delay caused by SOL), the outbound will not be the same with the inbound. Because of the delay, the outbound will look longer than the inbound, it appears in all examples posted by Janus.on page 1 of this thread.

Specifically Half the rate for one hour, so the outbound traveler sees Earths clock clicking only 30 minutes. Double the rate for returning: Earths click 60 minutes for a return travel of 30 minutes. The traveler sees at his clock that he traveled 1h30 minutes, the same as the observer on Earth. That is what I call "symmetry". The trip lasted the same time for the traveler & for the guy at rest on Earth. You have been fooled.

. (previous answer erased, obvious mistake) The half and double rate are observed from the Earth. From this FOR, the outbound & inbound travel will not be observed the same. I suspect that the same goes for the traveling twin, he will not measure the same time for the outbound & for the inbound, because of the Doppler shift taking place only in 1 direction (toward the Earth). So it is not "Half the rate for one hour, and double the rate for one hour" it is "Half the rate for one hour, and double the rate for less than an hour.

Fine. Why the relativistic scenario does not end to be symmetric? While presenting a totally symmetric equation for frequencies? see my post above. A sees B traveling 2 and 1/4 hrs while going away. And you say that A sees B traveling back in 15 minutes? Or 2 and 1/4hrs divided by 3 = 45 min? Why do you divide 45 minutes (as observed by the traveling clock)? instead of the time observed by A?

I have no problem with Bufofrog's example. I have no problem with A observing time dilation. I have no problem with A observing length contraction. I have a problem when the situation is not symmetric. In my view: what A observes must be the same as what B observes. If A observes B time dilated, then B must observe A as time dilated too, and of the exact same amount. Same for length contraction: length contraction as observed by A must be the same as length contraction observed by B. In the outbound travel and in the inbound. And when they meet together, A & B should have measured exactly the same thing concerning the other one. There is absolutely no reason why A should have a different age from B. No reason at all. The Frequency equation shows it. The jump in another FOR and arguments about accelerometer is not valid. Both are inertials. If you want add a 3rd observer (called C) that moves parallel to the returning B traveler, and of the same age, traveling at the same velocity. This 3rd IS inertial (he didn't encounter any acceleration, he didn't made any U-turn). By definition, the age of traveler C will be the same of B at arrival time. IOW there must be a flaw in Janus explanation, more specifically in the return travel, I think. A logic flaw that I cannot spot, maybe an addition instead of a subtraction, something like that.

When I read Swansont's post, I conclude that time accumulates while length contraction not. What do you read? And I am trying to put people into thinking, not only parroting what they have been told.

In the example, the ticking rate for the outbound travel is 1/3. The ticking rate for the return travel is 3. So mathematically, everything is fine. I understand perfectly, I have no objections. It means that as observed from point A (the departure point) the traveling clock ticks late when going away and ticks faster when coming back at the exactly reverse rate. Which means, if you replace the clock with a traveler, he will be observed from A as aging slowly when going away, and aging fast when going back, at the exact reverse rate so that everything ends perfectly fine. Symmetry is maintained. That makes sense, I agree & applause. The maths are correct, Michel has no problem. Why then do you believe that the returning traveler will have a different age than his twin brother at rest at point A? That's my problem. Time dilates & length contracts.

Time. My quest is about time, not relativity. Maybe. Maybe you can help & explain me what about time? Symmetry prevails.

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My search is almost exactly 20 years old. My questions are genuine I can assure you. During this quest I have read numerous books (ranging from popular science like Hawking's "Brief history of Time" to physics course books - of the 80's the only ones at my disposal - and none of Sci-fi). I have realized that the higher the level of the author (Nobel Prize like I. Prigogine) the more awaken about the unanswered questions, and lower the level ( not to mention anyone) less acceptance for questioning. At those ancient times I had no access to Internet. I cannot recall when I joined some physics forum where I naively thought that scientists were discussing the open questions. But I encountered chaos. The Forum suddenly disappeared ( I lost years of posts) and I joined this one that appeared somehow more serious. Since then, not any one question has been answered. Worse, my single question (what is time?) has expanded logarithmically as for each answer more questions arise. Generally I still remain surprised with the facility answers are given when it is obvious (to me) that something goes wrong. Like answers I get at this right moment (concerning lets' say ONE reality, the fact that relativistics effects are "real" and the huge difference between time - accumulating- and length - not accumulating- while at the same time it is argued that "you essentially rotate some portion of the space part into the time part", which says to me that Time & Space are essentially the same. But if you see no contradictions, no problem, no question, that must be me.

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?

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. 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.

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

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. 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.

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. 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 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.

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?

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

I assure you I am not deliberately twisting everybody's replies, so I am afraid the other option may be valid. I don't understand the bold part: clock 2 rushes towards him from 36 light minutes away Because at departure time, when clock 3 & 1 are together, clock 2 lies 1LH away. So I suppose that clock 3 sees clock 2 rushing at him at tremendous velocity.

But the traveler "lived" the travel for 45 minutes. Or, as Halc explains, since he considers himself stationary, he sees clock 2 rushing to him from 1 LH away in 36 minutes (I don't understand why it is less than SOL), and sees clock 1 go away from him & reach 1 LH in ...minutes. If you transfer it grossly instead of minutes to years, it means that at 0.8 c you don't need 10 years to reach a star 10LY away. The astronaut will live the experience in ... years (6 years?). The concept of the incoming clock "chasing its own image" is quite disturbing.

So, from your example I can conclude that: 1. the 3rd clock traveled 1 LightHour in 45 minutes, but that was not faster than SOL 2. as seen from A, the same clock popped in 15 minutes from 1 LH away, but that is not considered faster than SOL.

So it depends on direction after all.