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"2 video cameras that are synchronised in their start. 0t"That's where the problems start.But, if we can assume that local gravity is small enough that it has little effect and that the cameras are synchronised while next to each other then moved apart sufficiently slowly that relativistic effects are small and that you bring the cmaeras together again slowly to compare the recordings. then yes.You can use that setup to measure the speed of light.However, one way of "synchronising" the videos would be to wait for a lightning strike and say that, since it clearly was only 1 event it must happen at the same time for both cameras.Then you get into problems.
The synchronisation is a lot easier than you think, the cameras can already be recording in situate position before we synchronise them, the only synchronisation needed on the videos is the timelines, 1 reset button tarring both recorders to 0 to synchronise recordings.
Quote from: Thebox on 09/07/2017 15:18:35The synchronisation is a lot easier than you think, the cameras can already be recording in situate position before we synchronise them, the only synchronisation needed on the videos is the timelines, 1 reset button tarring both recorders to 0 to synchronise recordings.No they can't.Simultaneity is only defined locally. You have to take account of how long it takes for the signal saying you pressed the "zero button" to get to the two videos.Since you seem to be trying to set up a thread about relativity, I think you might start by learning about it
Quote from: Bored chemist on 09/07/2017 15:52:32Quote from: Thebox on 09/07/2017 15:18:35The synchronisation is a lot easier than you think, the cameras can already be recording in situate position before we synchronise them, the only synchronisation needed on the videos is the timelines, 1 reset button tarring both recorders to 0 to synchronise recordings.No they can't.Simultaneity is only defined locally. You have to take account of how long it takes for the signal saying you pressed the "zero button" to get to the two videos.Since you seem to be trying to set up a thread about relativity, I think you might start by learning about itThis is a thread about measuring the speed of light if not testing simultaneity.
Quote from: Thebox on 09/07/2017 17:18:25Quote from: Bored chemist on 09/07/2017 15:52:32Quote from: Thebox on 09/07/2017 15:18:35The synchronisation is a lot easier than you think, the cameras can already be recording in situate position before we synchronise them, the only synchronisation needed on the videos is the timelines, 1 reset button tarring both recorders to 0 to synchronise recordings.No they can't.Simultaneity is only defined locally. You have to take account of how long it takes for the signal saying you pressed the "zero button" to get to the two videos.Since you seem to be trying to set up a thread about relativity, I think you might start by learning about itThis is a thread about measuring the speed of light if not testing simultaneity. They are strongly related.
Einstein synchronization (or Poincaré–Einstein synchronization) is a convention for synchronizing clocks
Most attempts to negate the conventionality of this synchronization are considered refuted
But, if we can assume that local gravity is small enough that it has little effect and that the cameras are synchronized while next to each other then moved apart sufficiently slowly that relativistic effects are small and that you bring the cameras together again slowly to compare the recordings. then yes.
What is this experiment trying to show?It's NOT showing that you can measure the one-way speed of light independent of two spatially separated clocks.
But from who's perspective is the relativistic effect small?
For the sake of discussion, mine.I'm sat round near one of the cameras. and both cameras are on the ground. All of us are stationary wrt one another.I took a while, and I delivered the cameras to their locations three million meters apart by bicycle. They certainly never exceeded 30 m/s i.e. C/10,000,000 .Most of the time they were travelling at about a millionth of CAnd I found a "flat" bit of the Earth to use as my baseline. There were no hills on my journey.So the relativistic effects on the clocks due to their changes in velocity and altitude (thus gravity) were small.If you are not content that they are small enough we can, in principle, repeat the experiment with cameras delivered by snails or even continental drift."To an observer's moving at 90% the speed of light past one clock"OK, so we won't ask him, we will ask me.I set off a flash bulb near one of the cameras. and the cameras capture that flash.Then I go and collect the cameras and I develop the films.They are slightly odd cameras (since this is just a thought experiment). They use old fashioned film and they run at a million frames per second.I count the frames in each film until I reach the frame with the flash in it (never-mind how long a real flash takes- this is a thought experiment).There are lots of frames but the important thing is the difference in frame number.I find that the camera near the flash records it on frame number n and the one far away records it on frame number n+m.So it takes m millionths of a second for the flash to travel 3 million metres from the first camera to the second camera.Now, I know from other experiments - Fizeau and so on, that the speed of light is about 300 million metres per second.So I expect it to take about a hundredth of a second to make the journey.Each frame takes a microsecond, so I should find that m is about 10,000What value of m do you expect to find?
OK, so we won't ask him, we will ask me.
I have thought some more, if we had the two cameras recording the one location live and two corresponding monitors of each camera, we should be able to observe a flash of lightning on one screen before the second screen . .....Then if some how we can measure the time difference in screens, we should be able to calculate a speed.
In doing science by thought experiments it's not exactly rare to start with the simplest possible case as a foundation.That's pretty much the case I have considered.You don't seem to have included an answer to my question.What value do you expect me to get for m?
They could easily predict what you'd see in your reference frame when using their synchronization.
After that we can consider the more complicated cases like spacemen who believe in unicorns if that's what we want to, but simply not answering a question isn't helpful
Incidentally, it's not so much that I assume that slow transport doesn't dilate time.It's that I know that people who know more about t than I do assumed that fast transport dilated time more.Are you saying that teh people who did this experimenthttps://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experimentshould have used a rowing boat, rather than a jet plane?
Incidentally, I'd like to introduce a slight refinement to the thought experiment.Imagine that , in the field of view of each camera is a clock counting (local) microseconds.That will number the frames for me and stop me needing to count them.With that amendment we can talk about what time things are recorded as happening from the point of view of each camera.
There has never been any way around this. You're assuming clocks are running at the same rate, the clocks are synchronized, and the one-way speed of light is the same in both directions.
Yes, I know I'm making those assumptions (and some others).Under what circumstances are they invalid?
If you could do it then you may have something but that's a rather big if. People have been saying they've measured the one-way speed of light independent of a clock synchronization convention for over 100 years but they never have. Amusingly, they attempt to measure this value to defend Einstein's Relativity unnecessarily because it was Einstein who showed that you couldn't.
To test the present speed of light one way we can simply use a strobe set to flash once per second. We can then have a detector (radiometer) a set distance away to detect the light.
Quote from: Bored chemist on 16/07/2017 22:07:52Yes, I know I'm making those assumptions (and some others).Under what circumstances are they invalid?Where did I say they were invalid?