And having read this paragraph, I'm more certain than ever that I understood you correctly. Indeed you are wrong, there very much is a choice of frames in which to synchronize the clocks. If they wait until the one astronaut finishes accelerating and then set the clocks to be synchronized from his POV after the acceleration is complete, his clock will end up recording more ticks than the one who supposedly sat still, i.e. the Earthbound twin will have aged less instead. So the choice of frames in which to synchronize and set a common t=0 origin very much makes a difference to your result, and it resolves the issue you're having with "reciprocity". I'm pretty sure both the Michelson-Morley and Fizeau experiments have been done with moving lab frames, and relative velocity is still all that matters. In any case, for argument's sake let's pretend all of these experiments have only been done in a lab frame at rest w.r.t. Earth. Are you telling us the Earth is always in some kind of magic, god-approved preferred rest frame? If that's your contention, how would you explain stellar aberration? Let's see, you don't believe in the work of Fizeau, Einstein, Michelson and Morley, etc., or you decided that even though Relativity correctly predicts and explains their observations, there is a better explanation out there and you're just going to yell and complain to us until it's found. Yet somehow I'm supposed to spend days poring through mountains of restricted-access proprietary SLAC particle data, writing tedious code telling my computer how to analyze the data and make it into a nice pretty little chart for you? And then what will I get for all that effort and copyright violation? Either I'll get some kind of strawman objection of total irrelevance to my analysis, or you'll choose to put my data on hold and claim my analysis is only tentative at best. Doesn't seem like it would be worth the time or effort when I'm not really trying to convince you of anything, and there are people of infinitely greater respect and recognition than myself who have done these sorts of analyses and published their results in peer-reviewed scientific journals. I'm willing to cite some articles containing particle lifetime analyses, for particles of different shapes, sizes, energies, velocities and subatomic composition. All of these different particles have their lifetimes dilated according to the Lorentz transformation, so I don't think it's reasonable to suggest that strapping them to a rocket makes them all slow down in exactly the same way, if acceleration and associated classical effects were the only cause for this change. Ok so while we're playing the illusions game, can I argue that electricity is only an illusion as well? Perhaps there's no such thing as electric force- charged particles know where all their charged buddies/enemies are hanging out and either want to go there or get the hell away from there as fast as possible. You've been shown or referred to tons of empirical data supporting Relativity. Your response has consistently been "this only proves that absolute motion causes time dilation". In other words, you just keep plugging your ears and sticking your tongue out every time one of these experiments is mentioned. Fact 1: All of these experiments not only demonstrate time dilation, they demonstrate time dilation in the exact manner predicted by Relativity Fact 2: The Earth is not in a universally-preferred rest frame, and can't be because it orbits the sun So now it's time to take your fingers out of your ears, listen to the evidence, and explain in detail how you can predict the exact same results with reference to an absolute, universally-preferred rest frame. Any further claims on your part that there's no empirical support for Relativity will simply be met by demands on my part that you give an alternate explanation for this evidence. You find it more rational to believe in a concept you haven't even fully developed yet? You don't even know if your idea would work in practice, you don't know if it would even apply to what nature does in the real world, yet you think it's a more rational approach? I haven't said much about length contraction up to this point, and I missed your scenario, so a repeat or reference to post # would help. Sounds from the looks of it like you may be trying to set up a paradox like the famous "giant truck in tiny garage" paradox. According to the Lorentz contraction, a 30-foot tractor trailer is capable of fitting into a 15-foot garage if it's moving close enough to the speed of light. You might object that from the trucker's point of view, they ought to see the garage contract even smaller than 15 feet (and they will indeed see this), so how can the house owner see the truck park in his garage? The answer is that the house owner sees the front of the truck line up with the front of his garage and the back of the truck with the back of the garage at the same time, thus arguing that the truck is parked. From the trucker's POV, the front of his truck and back of his truck are lined up with the respective ends of the garage at different times. This means that if the homeowner sees the truck fit in his garage, it's guaranteed that a split second later the truck either bursts through the wall or else crunches up like an accordion. Put atomic clocks on two space probes and send them flying around, far enough away from the Earth and sun so that gravitational time dilation won't play a role and SR can be applied. That would be a nice, simple, direct and definitive test in my book. There should also be several different clocks used and, if possible, operating on different physical mechanisms, so one can conclude it unreasonable to think acceleration affects all these clocks and mechanisms in exactly the same way. They could also try different schemes and reference frames for synching the clocks when they start the experiment, to further confirm what I said at the top of this post. Only in the same sense that electromagnetism is also just a theory. You're talking about GPS here, right? Not going to pretend I'm an expert on GPS, but from what I've read, you can't handle it in SR alone because you have to account for gravitational time dilation as well (gravitational time dilation has been proven for decades, BTW). Otherwise, GR says you can use any coordinate system whatsoever for your calculations, as long as you always apply the correct tensor rules for transforming between coordinates. The key is that not all coordinate systems were created equal, some are far more convenient than others depending on the physical situation. In any case, SR can't be used here because gravity plays a significant role, both on Earth and as the cause for a GPS satellite's circular/elliptical orbit. Whose definition of realism are we going by here? I always thought realism involved believing in what your experiments are telling you instead of passing them all off as illusions. Good, your honesty here is appreciated. Our challenge to you and like-minded people is to come up with an alternative explanation that makes accurate quantitative predictions. Physicists don't refer to absolute motion because it's never been needed. Once you have the relative velocities, that's all you need to calculate the resulting effects. In light of what I said above about how the results depend on the frame in which you define time "t=0", there has never been a need for a physicist to stop and question whether or not the Earth is at absolute rest. If they did have a reason to consider absolute rest, someone would have already found the universe's divinely-ordained rest frame and we'd know how it's moving with respect to us. But no, even in GPS calculations, if you redid the calculations with Earth moving a constant 1000 kilometres per second through space, you'd still get the same result for how clocks on Earth must compare at the end. No mathematical fudging required. I'm happy to let those who desire an alternative seek it for themselves. When I first learned about Relativity I was also looking for a viable alternative, and I made very similar arguments about reciprocity and the supposed paradoxes that ought to arise in this case. Then over time as I learned more, I realized I didn't understand Relativity as well as I had thought, and discovered how much math and experimentation underpinned its foundation (it blew me away, was much more detailed and complicated than I had initially thought). I gave it a shot, and my conclusion at the end is that Relativity is practically inevitable unless we throw away everything we've discovered going back almost all the way to Newton, maybe beyond. So yeah, it really seems like your objections to Relativity are personal rather than factual, and that's fine, you just have to accept that we have different views on what's "logical" and "rational" when it comes to describing the way things work. I consider Einstein's work logical and rational because it's mathematically self-consistent, and doesn't disagree with anything we've observed in the lab and in daily life, while on the other hand it's certainly very famous for anticipating a huge range of effects before they were actually first observed. To me, Newton's picture of the world with all these mysterious invisible forces and whatnot seems a more irrational view of the world, and while relativity and QM don't have a full explanation of why the universe works the way it does, they certainly do narrow the mystery down. So if you can come up with a working alternative, only then could I seriously consider whether your viewpoint is truly more rational. Given all the previous failed attempts at finding an alternative to Relativity, often from some of the greatest mathematical minds in history, it doesn't look like a very promising line of work. Well, my only appeal to what SR says is in response to when you make (what I see as) false claims about it. I never said that because SR says something, that automatically makes it so in reality. I only refer to what would happen according to the theory, to clear up misconceptions as they arise. I never called you a crank or a crackpot, because those names don't apply to you. You haven't come out making extraordinary claims, demanding that all of science stand upside down on its head and bow to you. The accurate word for you would be stubborn- you're clinging to an older way of thinking, and from our POV you're causing yourself to miss out on a lot of progress that newer ways thinking have allowed. But it's your call, I'm always open to the idea Relativity could be fundamentally disproved if the data necessary to disprove it was obtained some day.