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Faradave » July 9th, 2018, 11:51 am wrote:Right. Doppler shifts will be in addition to and typically more pronounced, than effects attributable to length contraction.
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bangstrom wrote:Things like relativistic length contraction are irrelevant as an explanation for electromagnetism.
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Feynman wrote:Because they are moving, they will behave like two currents and will have a magnetic field associated with them (like the currents in the wires of Fig. 1–8). An observer who was riding along with the two charges, however, would see both charges as stationary, and would say that there is no magnetic field.
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Faradave wrote:These are the same objections raised by many beginners in Relativity.
Faradave wrote:Length contraction is indeed difficult to verify directly, as we are not yet able to accelerate measurably large objects to significant fractions of lightspeed.
DJJ wrote:Even time dilation for eg. If a train moves relative to you, the train frame concludes that you are moving and your clocks are slowing down. You say, no, my clocks are fine.
So how do you measure time dilation? By knowing who is really moving. In which case, it's not really relativity, it's one of many earlier aether frame theories. Then you can measure time dilation. If you use SR, no clock slows down, because they are all mutually at rest.
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Faradave » July 11th, 2018, 11:10 am wrote: Feynman is wonderful but if not your cup of tea, there is abundant other literature.
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Faradave » July 11th, 2018, 11:10 am wrote:Time dilation is another matter, exhaustively verified with great accuracy and complete agreement with Relativity.
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Faradave » July 11th, 2018, 10:10 am wrote:
Time dilation is another matter, exhaustively verified with great accuracy and complete agreement with Relativity. (Muon experiments are the prototype.) Time dilation implies length contraction from velocities, which necessarily incorporate contracted path lengths.
"their half-life, which itself is modified by the relativistic corrections of two quantities: a) the mean lifetime of muons and b) the length between the upper and lower atmosphere (at Earth's surface). This allows for a direct application of length contraction upon the atmosphere at rest in inertial frame S, and time dilation upon the muons at rest in S′."
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DJ_Juggernaut wrote:you won't be able to measure length contraction, directly. Because you have to put your detector on the moving body. When you do, it's not moving relative to the body. Hence you can't detect length contraction, directly. You can only indirectly infer it.
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Faradave » July 11th, 2018, 1:17 pm wrote:But this seemingly simple presentation requires an understanding of (or at least agreement with) the relativity of simultaneity.
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Faradave » July 11th, 2018, 4:29 pm wrote:Allowing adequate sensitivity, it would find the object length contracted in the direction of motion. That does not mean the light was emitted simultaneously in the frame of the moving object (quite the contrary).
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Faradave » July 11th, 2018, 4:29 pm wrote:Agree or not, the point is that your objection is not new.
Faradave wrote:Many (some quite intelligent) folks who originally agreed with you, now agree with Relativity. Very few (if any) go the other way.
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DJ_Juggernaut wrote:A camera can't detect contraction.
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Faradave wrote:No one is asking it to. It just has to measure length
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DJ_Juggernaut wrote:[moving]object... is contracted. Take a picture again, due to relativity of simultaneity, its emissions occur sequentially, thus artificially broadening its emissions.
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Faradave » July 12th, 2018, 11:38 am wrote:By "broadening", I take it that you mean the distance between the events of their emissions.
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Faradave » July 12th, 2018, 3:44 pm wrote:The camera will only catch light it views as simultaneous in its rest frame.
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DJ_Juggernaut » July 12th, 2018, 4:13 am wrote:Of course, I'm keeping the scenario very simple here. Relativistic beaming not taken into account. And you shouldn't bring that in, given we are only interested in knowing an object's length.
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DJ_Juggernaut wrote:I think the camera not being able to see a length contraction...
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Wiki wrote:It was shown by several authors such as Roger Penrose and James Terrell that moving objects generally do not appear length contracted on a photograph. For instance, for a small angular diameter, a moving sphere remains circular and is rotated.
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Faradave » July 13th, 2018, 10:18 pm wrote:Thus, in principle, length contraction is detectable by a camera.
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Faradave » July 13th, 2018, 10:18 pm wrote:That's not to concede any point on the reality of length contraction. I would assume the same of your contrary position.
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