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So what are you trying to say by bringing that into this discussion? If the coin is stationary and some observers see it as elliptical either because they're looking at it from an angle that makes it look elliptical or because they're moving past it at a high speed that makes it appear length-contracted, those observers are not seeing the true shape of the coin.

Movement of the sun and the galaxy will lead to changes in contraction at any point on the Earth's surface as the Earth rotates unless it's at the poles, but the sun isn't guaranteed to have moved unless we wait millions of years. We only have to wait a few weeks or months to guarantee that the Earth has moved though, which is why it's the Earth's orbit round the sun that's most important as it guarantees that the rate at which clocks at sea level cannot be ticking at the same rate as each other other than on average over a full rotation of the Earth.If a planet could rotate at such a speed that a point on its surface moved at 0.866c relative to the centre and if that planet could remain spherical, it would take twice as much cable to stretch round the equator than to make a loop round over the poles. If in addition to that the planet is moving along at 0.866c on the same plane as the equator, on one side of the planet the equatorial cable will be uncontracted while on the opposite side it will be contracted three and a half times as much as the average contraction on the loop (and the surface of the Earth will have the same contraction acting on it in the same places). A clock sitting at any point on the equatorial loop will likewise vary in its ticking rate, sometimes ticking twice as often as the average and at other times ticking three and a half times slower than average. But if you analyse it from the frame of reference in which the planet is stationary, you won't detect any of that variation at all.

All views are equally valid by observed position. You try to diss relativity by using a strict interpretation of valid.

Ok you either do not know the limits of relativity or you are stuck on 0.887. Since one direction of spin would allow ~1.7c lets look at the relativistic limit of spin and speed. At 0.5c speed through space and rotation of 0.5c the one direction would be c and the other direction at rest. So the forward spin the light would be relative to the spin and not move to an observer that could not observe anyway. The electron cycle using a physical clock likewise could not cycle. So no time would be recorded. In the opposite direction relative light is at rest and is moving relative 2c. c in one direction and c in the opposite direction relative is 2c. c being constant in any direction. So you have ticking in the opposite direction. Ok the physical object has zero length forward and a physical length backwards. I am not to keen on physical contraction. Explain your position on this.

And yet, for an observer on the planet, no warping is measured at all (other than the length contraction caused by rotation which leads to the circumference round the equator being measured as twice as long as the circumference passing through the poles even though they measure that the planet is spherical in shape).

I understand why the distance at the equator would be contracted, but I don't understand why it would be observable. If we would use a rope to measure the two distances for instance, it would contract when we would measure the equator, and stretch when we would measure the distance between the poles, so there would be no way to observe the difference.

Let's say there cable from NY to SF and you are sitting on the moon. There is a mirror on the SF side to return light. There is an event in NY an observer is able to view that moves to SF and the observer is able to watch the photon progress With his measuring stick on the moon. He measures the distance with his measuring stick. Taking the same position of termination and returned event the observer measures the returning light. His measurement is longer on the return trip. The cable did not change but the distance light traveled in each direction did.

The time light takes to make the roundtrip is observable, it has lead to the time dilation effect, but contraction is not. Things really live longer when they move, and they should contract too in their direction of motion, but that contraction is supposedly unobservable from any viewpoint.

On the Earth if you move East to West timing increases and so does reactions such as your cell rate of decline. You age faster in that direction because you are slowing down. If you go West to East reactions slow because you are moving faster. Definitely imperceptible.

It would be observable if the earth was rotating at .866c though, and contraction should still be unobservable.

If you start with a non-rotating disc and then spin it such that the edge is moving round at 0.866c, that edge will contract to half its rest length, so the disc will split and leave lots of gaps in it - the same amount of gap as there is remaining edge.

Quote from: DavidIf you start with a non-rotating disc and then spin it such that the edge is moving round at 0.866c, that edge will contract to half its rest length, so the disc will split and leave lots of gaps in it - the same amount of gap as there is remaining edge.It means that contraction is observable even if we are rotating with the disc. Relativists use to say that contraction is not physical, so I thought it was unobservable. What do they say when you present that mind experiment?

If you go to my ref-frame camera program ( http://www.magicschoolbook.com/science/ref-frame-camera.htm ) and load the fourth set of example objects (you have to type "d" into the dialog box after clicking the first button), you'll see a blue ring with eight red or yellow boxes round its edge, though only the corners of the boxes are shown.

David You are using circular logic all based on your model of contraction strictly based on clocks ticking at the same rate in any orientation. Yours is only one model that cannot be verified except through math. Math does not prove a theory is correct. Math only proves a theory is not correct. The ladder paradox is based on simultaneity of relativity showing the signal to get to the doors affect the synchronicity of the doors being closed at the same time. While it's useful to show simultaneity of relativity it does not prove contraction. The design of contraction eliminates a testable measurement. Your model passes the hurdle of math but math does not prove your model.

You are using circular logic all based on your model of contraction strictly based on clocks ticking at the same rate in any orientation. Yours is only one model that cannot be verified except through math. Math does not prove a theory is correct. Math only proves a theory is not correct.

The ladder paradox is based on simultaneity of relativity showing the signal to get to the doors affect the synchronicity of the doors being closed at the same time. While it's useful to show simultaneity of relativity it does not prove contraction. The design of contraction eliminates a testable measurement. Your model passes the hurdle of math but math does not prove your model.

I already had a glance at this simulation but I didn't understand it and it didn't seem to work properly. I load object D, I change the reference frame number, and nothing changes.

You said that the boxes were all moving at .866c with regard to the boxes at rest in the middle, so I understand that we can chose another reference frame than this one, which means that we can consider that one of the moving box is at rest, but why should we consider that it moves at other speeds than those two ones? And why can't we get a change when we change the reference frame without changing the speed?

The coin has a diameter of 1 unit length. The coin has the diameter oriented along x, the direction of motion. A and B each have an identical coin. B passes A at speed v. A measures the B-coin x diameter as 1/γ. B measures the A-coin x diameter as 1/γ. Are their measurements correct? Yes. One may be length contracted via em field deformation, and the other via time dilation for the observer. It may even be a combination of both. Since perception is reality confined to the mind of the observer, both are real or true, and based on laws of universal behavior. Perception does not alter the object being observed. SR is also a theory of perception, which is why it's so observer dependent.

It may be that some of the functionality doesn't work on more recent browsers, but I have no way to test that. Do the letter keys S and D function in the way I described or is that broken too?

The initial frame shows all objects with their actual speeds and the actual length contractions acting on them. When you change to a different frame, you see the "God view" for the new frame instead (which shows a distorted version of reality, but which also looks just as real and which for observers co-moving with it behaves exactly as if it is the absolute frame). You can set it to display an infinite number of different frames, and each box can be made to appear to have any speed you like by selecting a frame that is moving at that speed relative to it. Changing the frame is done by typing in the speed of the new frame relative to the absolute frame, so you can't change frame without changing that speed, but the view continues to track the blue disc no matter which frame you select.

S and D keys do function. I think it's me that doesn't.

When we give a speed to a frame, it can move in any direction, not only in the one it has with regard to the blue boxes when they are considered at rest. If we give a speed to the right to a frame for instance, all the system should be considered to move to the right while the red boxes are still considered moving at a tangent to the blue ones.

In this case, I think that the simulation would be a lot easier to understand if the whole system would already be traveling to the right on the screen before we hit the S key. That's what you simulation of the MMx does.