I heard the word virtual used to describe the camera, and couldn't figure out if they were, for sure, talking about taking pictures of a single photon in real life -- ergo not simulated. I suspect I misunderstood something.
I'm skeptical because.. how would you see a photon? Unless photons themselves give off light as they travel, but that would mean photons emit photons...
Photons do not emit photons. In fact, photons don't interact with each other at all. But if you send a very short pulse of light (visualized as the thin spherical shell in the video) at an object, the photons in that pulse will hit the object at different times depending on how far away the scattering surface is from the source of the light. After they reflect from the surface, these photons will also take different amounts of time to travel to the camera (your eye). If you can measure the time the photons enter the camera very accurately, you'll see different parts of the scene light up at different times.
This would be very close to watching the light pulse travel across the scene...except for that second effect: that the parts of the scene are different distances from the camera.
>In fact, photons don't interact with each other at all.
They can. It's a non-classical concequence of Quantum Electrodynamics. If you are interested in the cross-sections, check out Berestetskii et al., 1982.
> I heard the word virtual used to describe the camera, and couldn't figure out if they were, for sure, talking about taking pictures of a single photon in real life -- ergo not simulated.
I think they were using the word "virtual" to describe the array of camera sensors as one camera. It sounds like basically they had an array of sensors all snapping as fast as they could, but offset in time from each other by some amount, to achieve the effect of having 1 frame for every N fractions of a second. They also had to break down the scene into long strips and repeatedly use the sensors take the same picture on each strip and re-combine the strips later.
> I'm skeptical because.. how would you see a photon? Unless photons themselves give off light as they travel, but that would mean photons emit photons...
What you were seeing in the video were the photons entering the camera after having bounced off of the scene. It's kind of misleading that they're making it sound like you're seeing the photons as they're hitting the object in real time, When in fact, the photons had already hit the object and are bouncing back into the camera. But the resolution with which they're detecting the incoming photons conveys the "shape" of the waves bouncing and propagating off/around objects. That's my take on it at least.
>It's kind of misleading that they're making it sound like you're seeing the photons
It was misleading in the way the commentator said we can now watch the photons as they travel through space.
Space is full of photons from stars and galaxies. We only ever see the source of their current direction, which is why space is black, but we see the the bodies within it.
The camera records a single scan line from a bunch of different pulses to capture the length of time they need for that scanline. Then they rotate the mirror and capture the next scan line. After that, they reconstruct the video in software. It relies on the regularity of the laser pulse to be accurate. They aren't capturing a real movie, but an aggregate description of how light moves across a scene.
Regarding the "seeing a photon," it's just an analogy.
An analogy they repeat three times. And its just plain false every time. In fact, I'm not sure at all what the analogy is supposed to help us understand. We're not seeing a photon as it moves through space; so why say we are? We're seeing light reflected off of an object; what makes this different from any other camera that does the same thing? Its faster? Then say something to help me understand how that changes things.
We're seeing the way a pulse of photons move through space. So you can see how long it takes for a photon to diffuse through a plastic bottle. You can't see that with other cameras.
It may be the laser being refracted by the air, just like commercial green lasers are refracted by fog. I actually think is the only explanation.(And neutrinos, because seriously, neutrinos rock).
Also, I can see some interesting uses to this camera, beyond light studying...
> It may be the laser being refracted by the air, just like commercial green lasers are refracted by fog. I actually think is the only explanation.
It is. Seeing is interacting with photons, so you can't 'see' a photon that didn't just hit your camera. The process is similar to how I heard we can see speed of light in space, as light from exploding star propagates through a nebula and reflects back to us. I can't find a reference for that though, I heard it as a story from a physics professor.
> And neutrinos, because seriously, neutrinos rock
I'm skeptical because.. how would you see a photon? Unless photons themselves give off light as they travel, but that would mean photons emit photons...