So I've encountered the site "" – a website proposing "alternative" theories to theories in modern physics. Of course, the site claims that both SR and GR are wrong. To show "why" SR is wrong, the author presents two apparent contradictions in SR, as following:           Two accurate identical clocks, A and B, move with uniform motion along a shared straight-line path but with different constant velocities such that the distance between them steadily decreases with time.      [...]      We wish to know which clock runs more slowly.      (Keep in mind A will eventually catch up to B and you don't need to change reference frame by accelerating in order to measure the times side-by-side)   I can obviously see the apparent contradiction – one can claim that A is at rest and B is experiencing time dilation or equally claim that B is at rest and A is experiencing time dilation, giving two different results when the two clocks "meets" – but I have no idea to actually solve it.  When solving this, please use real numbers of your choosing.  The second "paradox" involves a circular particle accelerator with equally spaced electrons. Now, if we'd would speed them up to relativistic speeds, say $\gamma = 2$, how would the tube look like?   (source: )     (source: )     (source: )     (source: )    My own thought on this is that the electrons have a non-inertial motion and thus alternative A must be right (the electrons shrinking but their spacing staying the same). Is this correct a reasoning?
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Suppose we have two twins travelling away from each other, each twin moving at some speed $v$:    Twin $A$ observes twin $B$’s time to be dilated so his clock runs faster than twin $B$’s clock. But twin $B$ observes twin $A$’s time to be dilated so his clock runs faster than twin $A$’s clock. Each twin thinks their clock is running faster. How can this be? Isn’t this a paradox?
23658
Is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then to B it APPEARS that A's clock moving slower, but A sees his own clock moving at normal speed.  Similarly, to A it APPEARS that B's clock is moving slower, but B sees his own clock moving at normal speed.  If the above is true, then both A seeing his own clock moving at normal speed and B seeing his own clock moving at normal speed means that in reality both clocks are moving at normal speed, and neither has slowed down, whereas the other person's clock APPEARING to move slowly is merely an illusion.   Now is this true or false: If A and B have clocks and are traveling at relative velocity to each other, then A sees his own clock move slowly (compared to the speed of the clock when A was at rest with respect to B) and B sees his own clock move slowly, so that in reality both clocks are moving slowly, but they still remain synchronized (since both are slow by the same amount)  If the above statement is not true, then why do muons decay slowly when moving fast? [it could only be possible if the muon saw its own clock as moving slowly. If we saw the muon's clock moving slowly, but the muon saw its own clock moving at the normal rate, then the muon would decay at the normal rate, and not slowly]  Can anyone please explain where I went wrong?
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Greatings!  I'm trying to understand special relativity and have one question bugging me.  In almost every book or video about the subject there is a thought experiment with moving light clock. I hope I need not elaborate on the sutup and the outcome of the experiment.  So the question is this: When a light source on the MOVING light clock emits a photon of light the path of the photon is triangular.   How this can be?   I thought since light speed is constant in every reference frame the movment of the "emmiter" can't affect the movment of the light so light should shoot right up (from the point of stationary observer) and thus move backward and up from the point of moving observer.  So you see my logic is: light speed is invariant => you can't make it move UP &amp; FORWARD only UP. i.e. you can't change it's direction once it's emited in UP direction. Why the hell light moves sideways then?  And I'm puzzeled. There is flaw in the logic but I don't see it.  Thanks for help.
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Can someone help me giving a qualitative answer to this problem in General Relativity:  Imagine you are on earth with two perfectly synchronized clock's. If you hold on in your hand but you throw the other one in the air and catch it after a certain time interval, would they still give the same time?  I think that the one in the air would run faster but I cannot explain why.  Thank you!
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I've been pondering the precise mechanism of time dilation for the example of a simple pendulum in two different situations:   The observer and ground are at rest in one frame of reference;  the pendulum is moving at high speed with respect to that frame. The observer is at rest in one frame of reference; the pendulum and the ground together move at high speed with respect to that frame.   user8260 has pointed out that in situation 1, in the pendulum's frame $g$ is greater by $\gamma^2$ compared to $g$ in the observer's frame. Thus in the pendulum's frame the period is less than it is in the observer's frame by a factor of $1/\gamma$, just as one would expect from time dilation.  But what about situation 2? Here, compared to the pendulum frame, the observer sees the pendulum with the same length in a stronger gravitational field, yet observes a longer period. Does the inertial mass of the pendulum change differently than its gravitational mass? Also, does the analysis depend on whether the plane of swing is perpendicular or parallel the direction of motion?
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Photons in vacuum have no proper time, and they are not considered as observers and not as reference frame. But what about photons travelling through matter? Their velocity is lower than light speed, thus the proper time formula (multiplication with reciprocal gamma) would yield a proper time, but do we consider that they have a proper time/ that they are observers/ that they may be reference frames?
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If an observer approaches a clock at a significant fraction of the speed of light, would they see the clock's hands moving at a faster or slower than usual rate?  I figure there are two competing effects at play - time dilation and diminishing distance.
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Einstein's Special Relativity theory is based on the assumption that the laws of physics are invariant in all inertial frames, and from there - according to Maxwell's equations - it derives that the speed of light must be the same in all reference frames, thus the need for time dilation etc...  But how is the initial assumption justified? I have always been explained this assumption in an "intuitive" way, as a thought experiment, for example regarding the fact that sitting on a sofa feels no different than sitting in a plane. But I could have made the same thought experiment about the hypothesis that velocities always add together, so one could make light "faster" by shining a beam from the tip of a rocket...
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As of this writing it has been made clear to me that classical physics' Luminiferous aether was a terriblly poor discriptor of space. With the advent of Special Relativity and General Relativity, that aether ceased to be applicable. Today I began reading on the Higgs boson, and the Higgs field. How are those theories different from or similar to the seemingly irrational Luminiferous aether?  P.S. I am a first year student at Bakersfield Community College. If this question seems naive, you now have an explanation.  (EDIT) To me the similarity rests upon their fundamental influences regarding static positions in space. I currently only accept models in which static spacial positions are impossible. Contrastingly relative positions seem quite reasonable. In my humble opinion my naivatisms inhibit me from absorbing and understanding the Higgs boson. If they actually are similar, public protest would probably be more apparant. However, I have put forth my best effort to pose an direct question here.  P.S. The questions Where does space go when it falls? and What happens to time lost when matter accelerates? come much earlier in my studies, and they seem relevant.
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I recently watched  by Veritasium where he talks about the One Way Speed of Light and talks about the limiting case where in one direction the speed of light is $c/2$ while it's instantaneous in the other. He also says this is perfectly fine according to our Physics theories. He also points at Einstein's assumption in his famous 1905 paper where he assumes that the speed of light is same in all directions. This made me ask this question is taking the speed of light same in all directions an axiom of some sort? As I've often read no information can be sent at more than the speed of light but here one-way taking the speed to infinite makes no difference. So are all of our physics theories based on the assumption and what would happen if light turns out to be moving at different speeds in different direction? Will that enable transfer of information faster than the speed of light and is there any way for us knowing that the transfer happens faster than the speed of light? The video takes a Earth Mars case where he says it isn't possible for us to every realize this discrepancy but is there a more general proof which says it isn't possible
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In Feynman's Lectures on Physics , chapter 15, page 6 he writes about 2 identical, synchronized light signal clocks. These are clocks that consist of a rod (meter stick) with a mirror at each end, and the light  goes up and down between the mirrors,  making a ,click each time it goes down. He describes giving one of these clocks  to a man flying out in space, while the other remains stationary. The man in the space ship mounts the clock perpendicular to the motion of the spaceship. Feynman then writes:      "the length of the rod will not change. How do we know that   perpendicular lengths do not change? The men can agree to make marks   on each other's y-meter stick as they pass each other. By symmetry,   the two marks must come a the same y- and y' coordinates, since   otherwise, when they get together to compare results, one mark will be   above or below the other, and so we could tell who was really moving."   what exactly is the "test" with the marking of meter-sticks that Feynman is describing? why would it violate relativity, since it seems the person in the space ship would be looking outside? why would a change in a perpendicular length violate relativity, but not a change in parallel length--couldn't the men also make marks on each other's sticks, in the case of parallel lengths?  Thank you!
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Einstein's two postulates of special relativity are as follows,     1. The principle of relativity: The laws of physics are the same in all inertial   systems. There is no way to detect absolute motion, and no preferred   inertial system exists.      2. The constancy of the speed of light: Observers in all inertial systems mea-   sure the same value for the speed of light in a vacuum.   Now for an exercise in my book, I am requested the following:     'Explain why Einstein argued that the constancy of the   speed of light (postulate 2) actually follows from the   principle of relativity (postulate 1).'   I have been trying to figure this out for a very long time now with no luck. I thought of identifying a physical law that if not the same in two different inertial systems leads to a contradiction, but I can't think of anything. Could you push me in the right direction?
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I am doing some research about &quot;time travelling&quot; by shrinking humans to the quantum level. It's something based on the delayed choice quantum experiment, so that we can go back to the past and travel to another parallel universe or to another universe in another timeline. So I just want to make sure if smaller mass changes the way the smaller object experiences time. But do note that I am only 16 so I do wish that it can be simple haha so that I don't end up being more confused.
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I have been studying causality (specifically why there is no such thing as a simultaneous instant of time across all observers) recently and I keep hearing references to the Andromeda paradox. Can anyone tell me what it is and how it is resolved?  I've tried reading what  says about it, but I could really use someone's explanation.  Edit Ok, after reading the related question, now I'd like to know does this imply there is some sort of privileged reference frame, in which there exists absolute velocity and absolute time? I ask because the answer for the other question seemed to indicate that the actions seem to be at different points of simultaneity but that in fact the person not moving is getting it right. But this seems strange to me because if we accelerated our galaxy to a different speed, we would still perceive our stationary observer as being right even though they'd see something different than before the acceleration.  So who is right? In what frame can we be sure that our present is Andromeda's present?
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I understand the  as "The physics in a freely-falling small laboratory is that of special relativity (SR)." But I'm not quite sure why this is equivalent to "One cannot tell whether a laboratory on Earth is not actually in a rocket accelerating at 1 g".
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Is it possible to have an alternative theory which is consistent with experiments supporting GR, but which doesn't mandate a speed limit on causality?  In other words, I understand there is experimental evidence for gravitational/relativistic time dilation, spacetime curvature, etc. but is there any inherent reason why these effects cannot be explained without the max speed requirement?  QM clearly shows that "communication" can happen instantaneously but, supposedly, causality cannot break the speed limit.  I also know the speed of light is derived from other principles, but is there anything that says that speed has to be a max limit of any kind?  I want to emphasize that the QM "communication" doesn't imply causation or information exchange, merely the establishment of the entangled attribute.  Bell's inequality tells us that the attributes were not predetermined and were only established upon measuring one of the particles.
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It is said that we can verify time dilation by flying a very accurate clock on a fast jet or spaceship and prove that it registers less time than the clocks on earth. However, the clocks on earth would be moving relative to the clock on the spaceship, and since time always dilates and never goes faster regardless of the direction of relative motion,  the clocks on earth should register less time than the clock on the spaceship.  Is this true? Whenever there is a fast-moving object such as a rocket do all clocks on earth really become slow?  If the rocket with the clock landed after moving at relativistic speed, would its clock and the earth's clock again show the same time since during its travel both appeared slow to each other?  Or is all this just an illusion, ie. the clocks just appear to be slow to each other but in actually run at normal speed, and neither is behind when the rocket actually lands?