Physics, Astronomy & Cosmology / Re: Can a test of reciprocal time dilation be constructed from this?« on: 10/07/2019 23:39:01 »
If that's all it does, it seems to only measure my speed component in the direction the gun is pointed, a fraction of my actual speed if I'm not driving directly towards or away from the gun.Which is why it is very difficult to defend a charge of speeding against a Doppler radar gun - it can't indicate a higher speed than the target.
Alice could count the rate of rotation of her wheel (I've reduced them to unicycles to save engineering) which is of course how surface vehicles measure speed. Now suppose Bob's vehicle emits a light pulse for each rotation of the wheel. As they approach, Bob appears to be going faster than his measured speed, and as they recede, slower.
Suppose we fit an elastic cylinder to Bob's wheel. As it spins, it stretches, by centrifugal force. At constant speed, its diameter is constant. So Alice can estimate Bob's speed by the diameter of the cylinder, either by looking or
by asking Bob to look and radio her, with no need for a time base. She could have an identical cylinder on her wheel, and using her own clock, can calibrate the speedometer. I can't think of a relativistic reason why Bob's cylinder should appear to contract perpendicularly to the velocity vector, so she now has two different values for their relative velocity.
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