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As long he is moving away from earth, yes, he sees earth clocks go slow, but as soon as he stops at the bar, his clock and earth clocks go in the same pace. But, yes, the earth clocks seem to be one hour behind. That is the delay due to the distance. Right. At least a first step... Yes, and I want your interpretation of why muons reach the surface.

The delay is in what any observer in the bar sees happening on earth. So the traveler and the person living there see exactly the same: what happens on earth one hour ago. That is your delay. On his outbound trip the traveler notices an increasing delay. This increase stops when he stops traveling. If you are moving you see your starting point moving away. But the moment you stop, this moving away stops immediately. Otherwise you get the contradiction that Bufofrog and Janus pointed you to. Even Zapatos understands that! And when do I get your explanation that we can see muons reaching the surface of the earth? What does it look like for an observer on earth, and what does it look like from the FOR of the muon? I assume you cannot answer it, if I don't get an answer.

Galilean relativity yes., but not Relativity (because of SOL). What? Of course the out- and inbound trips take the same time in Galilean and Einsteinian relativity. Same speed, same distance, and therefore same time. The 'only' discrepancy is between both relativity principles. Take the example of flying to a star that has a fixed position seen from the earth, i.e. the star and the earth are in the same reference frame. In Galilean relativity: Traveler's view: travels the distance to the star with its speed and back with the same speed. His speed he can correctly derive from the distance traveled and the time on its own clock. But of course on the outbound trip, he sees a clock on earth running slow. But he knows this is just because the increasing delay. On the inbound trip, he sees exactly the opposite, the earth's clock is running fast. When he ends his journey back on earth his clock, and the earth's clock show the same time again. Earth's view: more or less the same as the view from the traveler. On the outbound trip the traveler's clock seems to run slow, on the inbound fast, and at the end of the trip the clocks show the same time again. Both agree on: the distance traveled and on the time it took. In Einsteinian relativity: Traveler's view: the distance between the star and earth has become smaller, however the speed is the same. So the traveler sees he arrives at the star faster, because the distance is smaller. Returning with the same speed (but opposite direction!, i.e. the traveler changed his reference frame), of course the distance will be shortened by the same amount as the outbound trip. Looking at the clock on earth on his outbound trip he sees it slowed down because on one side the delay, but on the other side the time dilation. Flying back he still sees the time dilation, but also the effect of nearing the earth's clock. So depending on the speed, he sees the earth's clock, ticking faster, but not as fast as in Galilean relativity. Earth's view: the trip takes just as long on earth's clock as in Galilean relativity, but from the earth the traveler's clock is running slow to time dilation. So from the earth, using the clock of the traveler, the trip takes the same time, but not according earth's own clock. On the inbound trip the same happens. So the traveler's clock runs slower than in Galilean relativity. For short: the traveler did fly a shorter distance than seen from earth, therefore he has not grown older as fast as the earth. for the earth the clock of the traveler ran slow, therefore the traveler has not grown older as fast as the earth. So they both agree about reality. Just as the example of the muons: they reach the earth's surface. @michel123456: When do you explain to us why muons can arrive the earth's surface, even if, using Galilean relativity, they live too short to reach the earth's surface? You never seem to answer any of the challenging questions we ask, or show us where our arguments are wrong. You only show us where the results of our arguments conflict with your picture of reality.

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.

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

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. Special relativity is the reconciliation! 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. 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. 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. 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. No, it is your stubbornness.

Where did Pascal got the time to write such things down? According to most other philosophers, philosophy only exists in cultures where people have spare time. E.g. the Greeks had slaves, which gave their masters time to reflect on nature, society and themselves. People who have no time could be: full in the struggle of life: all their time is used to get food, shelter, and stay safe for any danger totally unaware that their world could be different as it is, i.e. accept the culture or society in which they live as a 'naturally given' and conform to to it without reflecting (My disclaimer could be extended from science to more or less all of life ("There is no such thing as philosophy-free science; there is only science whose philosophical baggage is taken on board without examination.")). Ideologically shaped societal dogmas are seen as 'natural', or 'obviously the best principles to live by'.

Yes.(1) (1) IIRC this effect is not taken into consideration in the twins paradox. Of course it is! I think if you google a little, you will find descriptions what A and B observe. That what they see is a combination of time dilation and delay because of the increasing distance. You are just saying something without being informed. However, only the time dilation is really responsible for the different age of the twins. No, of course not. You argument is based on non-physical assumptions. Assuming SOL is not invariant, without giving a premise what is the case then, you cannot know. I see 2 possibilities: light behaves as material objects, i.e. its velocity depends on the movement of the source only. If B moves away faster than SOL, you see nothing anymore because the light is also receding from you or there is a fixed medium, like sound in the air, in which case you continuously see B's clock ticking slower than A's clock. Now the frequency of the ticks depends on the velocities of A and B in relation to the medium. However, nothing of this gives you the time dilation of SR, which you should see now: if B moves to A, in 'your universe', you get a time contraction.

And now turn the direction. B travels back to A. Now the B's clock ticks faster than A's, from A's viewpoint. So what?

@20ny: You are confusing 'time' with 'measurement scales of time'. Time zones have nothing to do with relativity theory.

But aren't you taking general relativity for granted here? My point is only that even if we would live in a Newtonian universe, it would be dynamic because of gravity. Even if the universe would be infinite. If we would start with a 'magically created' homogeneous distribution of static mass, the universe would 'collapse', i.e in a Newtonian framework, all masses would be moving to each other. The only other option would be that all masses would have gotten an initial velocity large enough to move away from each other. Now this would look like a kind of explosion in space (not of space) I think many lay people still imagine the big bang like that.

@michel123456: I am still waiting how you see the situation in the opposite direction: A seeing the clock of B at a lighthour distance, and the B traveling to A. Can you explain the example of muons reaching the earth's surface, even if they would not be able to reach it, according their velocity (near light speed) and their half life. So take A to be an observer on the earth's surface, and B the location high in the atmosphere where the muons are created. For simplicity of argument, you can assume that the muons on their path send regular light signals to earth (of course they don't, but it would not change anything in your example).

@michel123456: Now turn your example the other way round: Two clocks, 1 lighthour distance, A and B, not moving relative to each other At A it is ten o'clock. A looks at the clock of B and also sees ten o'clock. Does that mean that the clocks are in sync? And then, B travels back to A. Now, at ten o'clock according to A's own clock, B's clock shows 11:00h. So time expanded? And instead of a delay we have an 'advancement'?

Hmmm. I thought that a 'Newtonian universe' would also be unstable, i.e. it must also expand or collapse. No doubt it would be a different kind of universe, but at least it would expand (or collapse).

You cannot explain the time dilation of the muon with just delay. Time dilation and delay are not the same. So you cannot deduce time dilation by a delay. If you think you can, please show me with my example of the muon.

Hmm, you are already too long in relativity. People like you and Janus know relativity so well, that it has become intuitive for you. 'Intuition' is not a given, it is something to develop, it comes with experience. So to answer the question if relativity is intuitive, I think you should go back to the first time you heard about it. I remember my first 2 encounters: me reading a children-level book about astronomy, in which was an example of time dilation, a rocket flying to the Andromeda galaxy and back again. I think an important factor in accepting this was that when I told my father, he confirmed that he knew that (and that it was not understandable how that is possible). The second encounter I found really astonishing: that of the invariance of the speed of light. Now I am also pretty used to it, and I understand the absolute basics of special relativity. But still... You, @Markus Hanke take one of the postulates that nearly everybody would agree upon. Everybody who has been travelling in a train or even an airplane, knows that everything works exactly the same as on the surface of the earth. It is only in combination with the fact that the speed of light is invariant, and not infinite, that we get at the non-intuitive results of special relativity, like time dilation and the equivalence of mass and energy. Personally, I feel that a dynamic solution, based on the æther, is much more intuitive. It compares with the experience of air. I you walk slowly, you do not notice it, but as you go faster, you feel the effects, and see them. Airplanes are just not fast enough to feel the æther pressure... This is ridiculous. First you should know better, there are more than enough explanations of the basics of special relativity, and the invariance of the speed of light is essential in all explanations. Second, this invariance is a fact. So try the following: Take a muon: we know its half-life from laboratory experiments. Now we know that muons are produced by cosmic rays in the upper atmosphere. However given their half-lives, next to none should ever reach the earth's surface. But they do. This is explained by the time dilation we observe for the muons. Now take your explanation. Just assume the muon has a wristwatch that we can see. Now explain why its time seems slower for us, than for the muon itself.

@Markus Hanke: Is a quantum theory of gravity the only kind of solution for the singularity? E.g. just like when a neutron star is formed by combination of protons and neutrons, wouldn't it be possible that in a black hole all matter is compressed into a very compact form we do not know? In other works, instead of quantum gravity, might we not need an extended form of quantum mechanics?

But they had no children... And to make things complicated, Elsa, Albert's cousin: Relativity theory is simpler than these family relationships...

I hope I cite Mordred correctly: a dimension is a parameter that can change independent of other parameters. So e.g. you can move north, i.e. you change your 'north-south' coordinate, while staying at the same place when you only think about moving in the 'east-west' coordinate. What you also can do is staying where you are in space, and you will move through time only. So we get at 4 dimensions, 3 in space, and one time dimension. So this also means one dimension cannot be 'foundational' for the others. 'Dimensions' are used in all kinds of corners of physics, not just space and time: we have 'phase-space', sometimes useful for describing a collection of particles: for every particle we have its position in space (3 dimensions), their momentum in 3 directions (i.e. another 3 dimensions), and then we have every single particle. So if we study a system of 100 particles, we have a 600-dimensional phase-space', in which all 100 particles are characterised by one point with 600 coordinates. In quantum mechanics, we have Hilbert space, which has nothing to do with our familiar 3+1 dimensions, and even uses complex numbers (i.e. with components of the square root of -1), and can even be infinite-dimensional. No, you are completely misusing the concept of 'dimensions'. So I completely agree with MigL here: If I remember correctly, from the old Superman comics, he sometimes had opponents from 'another dimension'. But I assume that the idea that 'other dimensions' are alternate realities was not invented by the authors of Superman.

And it was only meant as that: a simple description of the quantum vacuum in our universe. Nothing more. That's why I said 'particles pop into and out of existence'.

Because of the uncertainty principle. One of its forms says that in a process energy and time cannot be defined precisely together. But from that follows that an absolute vacuum cannot exist, because you would now the exact energy: 0. So for short times particles can pop into existence, and pop out again. This is what you see in joigus' animation. We know these processes are real, because otherwise we cannot explain the exact spectroscopic lines we see; and then there is the vacuum pressure that can be measured in the Casimir Effect. Then you are not alone. The laws of nature are useful abstractions, i.e. abstract descriptions, of natural processes. The only thing we can say about nature is that obviously there are regularities, otherwise the formulation of any law of nature would be impossible. But how to apply the idea of regularity when we talk about a one-time event, like the big bang? How can we derive, from a situation of nothingness, that there are (will be?) regularities, and even stronger, that they can be described by our present laws of nature?

I am not a physicist, but in A Universe from Nothing, Lawrence Krauss says that "Nothingness" is unstable. The "Nothingness" that joigus talks about is the 'emptiest' we can reach in our universe. Nothingness in our universe is a bit like a water surface: it can be in complete rest when simply looking at it, but zooming in, you will see molecules bouncing in each other, some of them escaping the surface, some others (or the same) caught at the surface. So a "Nothingness" still less then absolute vacuum in our universe would be unstable, and could produce the Big Bang. However, somehow the laws of nature should somehow exist, i.e there must be a road from absolute nothingness to our universe.

Both? I was sitting about 2 meters behind the flag, and zoomed in to the maximum. To be sure that the autofocus would not focus on the flag itself instead of the interference pattern, I focused manually, and exposed 2 stops (That is what they call it in Dutch) less than the lighting meter would normally do. And then on the computer I increased contrast, made it even a bit darker, and cropped to the pattern itself, so yes, it is pretty magnified. With my bare eyes I nearly could not see the colours. It was super, everything, everybody. I especially enjoyed the wine: very light, maybe only 6% alcohol, so I could drink much more than usual without getting tipsy or having a headache the next morning. Yes, that is definitely an advantage of living (and having salary) in Switzerland, nearly everything foreign including holidays, is cheap. Why, at the moment of writing, I realise I soon could buy the USA. I will think about a few improvements I could make then... ⚡

Yes. But I did not stay in Pisa, it was extremely hot, so we were there only one morning. And our stay was at the countryside. No, what is that? 😉 I looked at the official figures of Italy and compared them with Switzerland. Switzerland was worse: (New Infections, per Million inhabitants, against time, i.e. days since the first 0.1/million cases) We left August,4th. Maybe I should have decided to stay in Italy until Switzerland has solved its Corona-crisis?

Here, a mirror...