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A laser pointer at 2B FPS [video]

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Re: A laser pointer at 2B FPS [video]

#11

Post by snitty »

MostlyStable wrote: post #8

As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. Would an upgraded version of this that was actually capable of capturing the progress of a single laser pulse through the smoke be a way of getting…

>As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam.

It is not different phases, but it is a composite! On his second channel he describes the process[0]. Basically, it's a photomultiplier tube (PMT) attached to a precise motion control rig and a 2B sample/second oscilloscope. So he ends up capturing the actual signal from the PMT over that timespan at a resolution of 2B samples/s, and then repeating the experiment for the next pixel over. Then after some DSP and mosaicing, you get the video.

>It seems like if you could measure the pulse's propagation in one direction, and the other (as measured by when it scatters of the smoke at various positions in both directions), this seems like it would get around it?

The point here isn't to measure the speed of light, and my general response when someone asks "can I get around physics with this trick" by answer is no. But I'd be lying if I said I totally understood your question.

[0] https://www.youtube.com/watch?v=-KOFbvW2A-o

Re: A laser pointer at 2B FPS [video]

#12

Post by snitty »

bob1029 wrote: post #9
01HNNWZ0MV43FF wrote: post #5

Earlier quoted context omitted.

Scanning a single pixel over an image? How does that work with an explosion? The laser pointer is reproducible

https://en.wikipedia.org/wiki/Rapatronic_camera

But that bears no relation to what happened in the video.

Re: A laser pointer at 2B FPS [video]

#13

Post by ahofmann »

avidiax wrote: post #10

He did a good job on his setup, but I have to think that adding a spinning mirror would have made everything much faster and easier. He could then capture an entire line quite quickly, and would only need a 1 dimensional janky mirror setup to handle the other axis. And his resolution in the rotating axis is limited only by how quickly he can pulse the laser. Of course, his janky mirror setup could have been 2 off-the…

But I think he does capture an entire line quite quickly. As I understood it, he “scans” a line of pixels in seconds.

Re: A laser pointer at 2B FPS [video]

#14

Post by masfuerte »

bob1029 wrote: post #9
01HNNWZ0MV43FF wrote: post #5

Earlier quoted context omitted.

Scanning a single pixel over an image? How does that work with an explosion? The laser pointer is reproducible

https://en.wikipedia.org/wiki/Rapatronic_camera

The rapatronic camera had an incredibly fast electronic shutter. To record a video they needed one camera per frame. Rather like "bullet time" in the movies. The technique in the youtube video is completely different.

Re: A laser pointer at 2B FPS [video]

#15

Post by fluoridation »

masfuerte wrote: post #14
bob1029 wrote: post #9

Earlier quoted context omitted.

https://en.wikipedia.org/wiki/Rapatronic_camera

The rapatronic camera had an incredibly fast electronic shutter. To record a video they needed one camera per frame. Rather like "bullet time" in the movies. The technique in the youtube video is completely different.

It's not completely different. I'd argue it's the exact opposite. Instead of using a single single-pixel camera to record video of a repeatable event, a sequence of regular film cameras captured photographs of an unrepeatable event.

Re: A laser pointer at 2B FPS [video]

#16

Post by kllrnohj »

avidiax wrote: post #10

He did a good job on his setup, but I have to think that adding a spinning mirror would have made everything much faster and easier. He could then capture an entire line quite quickly, and would only need a 1 dimensional janky mirror setup to handle the other axis. And his resolution in the rotating axis is limited only by how quickly he can pulse the laser. Of course, his janky mirror setup could have been 2 off-the…

I think a spinning mirror would make it a lot harder. He's only moving the mirror after the "animation" finishes. So it's capture video, step by 1 pixel, capture video, step by 1 pixel, capture video, etc... He's replaying the scene ~1 million times, for 1 million unique single pixel 2 billion fps videos.

Re: A laser pointer at 2B FPS [video]

#17

Post by monster_truck »

throw327489 wrote: post #7
dist-epoch wrote: post #4

Techniques like this are/were used to film nuclear explosions (but with a single explosion).

Who detonated 2073600 bombs?

They did the way more expensive version briefly mentioned towards the start of the video, having 12+ cameras with ridiculously fast shutters (as low as 10 nanoseconds) arranged to run in seqeunce.

Re: A laser pointer at 2B FPS [video]

#18

Post by evanb »

MostlyStable wrote: post #8

As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. Would an upgraded version of this that was actually capable of capturing the progress of a single laser pulse through the smoke be a way of getting…

No, you cannot escape the conclusion of the limitations on measuring the one-way speed of light.

While the video doesn't touch on this explicitly, the discussion of the different path lengths around 25:00 in is about the trigonometric effect of the different distances of the beam from the camera. Needing to worry about that is the same grappling with the limitation on the one-way speed.

Re: A laser pointer at 2B FPS [video]

#19

Post by monster_truck »

MostlyStable wrote: post #8

As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. Would an upgraded version of this that was actually capable of capturing the progress of a single laser pulse through the smoke be a way of getting…

Think of it more like "IRL raytracing", where a ray (the beam) is cast and the result for a single pixel from the point of view is captured, and then it is repeated millions of times.

Even if you had a clock and camera for every pixel, the sync is dependent on the path of the signal taken. Even if you sent a signal along every possible route and had a clock for each route for each pixel (a dizzingly large number) it still isn't clear that this would represent a single inertial frame. As I understand it even if you used quantum entanglement for sync, the path of the measurement would still be an issue. I suggest not thinking about this at all, it seems like an effective way to go mad https://arxiv.org/pdf/gr-qc/0202031

E: Do not trust my math under any circumstances but I believe the number of signal paths would be something like 10^873,555? That's a disgustingly large number. This would reveal whether the system is in a single inertial frame (consistency around loops), but it does not automatically imply a single inertial frame. It's easy to forget that the earth, galaxy, etc are also still rotating while this happens.

Re: A laser pointer at 2B FPS [video]

#20

Post by bb88 »

MostlyStable wrote: post #8

As I understand it, this is sort of simulating what it would be like to capture this, by recreating the laser pulse and capturing different phases of it each time, then assembling them; so what is represented in the final composite is not a single pulse of the laser beam. Would an upgraded version of this that was actually capable of capturing the progress of a single laser pulse through the smoke be a way of getting…

The problem (ignoring quantum mechanics) is that the sensors all require an EM field to operate in. So assuming that the speed of light was weighted with a vector in space-time, it would be affected everywhere -- including in the measurement apparatus.

If on the other hand one could detect a photon by sending out a different field, maybe a gravitational wave instead... well it might work, but the gravitational wave might be affected in exactly the same way that the EM field is affected.

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