3 ms·

The title is very click batey. It doesn't reverse how light travels in time, it just reverses light in terms of the order of photons, as in "Last in First out"

by tomxor 4y ago

The title is very click batey. It doesn't reverse how light travels in time, it just reverses light in terms of the order of photons, as in "Last in First out" instead of "First in First out". The concept is quite natural to grasp. The article makes it harder to understand than necessary by making it sound like science fiction. The "reflector" is actually a medium that encompass the entire signal being reversed... in the same way that you would need to buffer the entire segment of a signal in memory before reversing it (you can't send what you haven't yet received), you would also need the entire segment of light to be travelling through the medium at the same time in order to reverse it. This is why their experiment involves such long sections of material. It's an interesting and useful phenomenon, effectively being able to instantly change a material's properties to reverse the direction of photons currently passing through it, which probably has good application in signal processing performance (it would be comparable to hardware signal processing using electrical components). But "time" is not reversed; the direction of photon's currently traversing a medium is dynamically reversed, but unlike a reflective surface, a reflective medium could change the direction of multiple photons simultaneously instead of one at a time, which affects the order of that segment..

nobodyandproud 4y ago
So photons would effectively be reflected back in a LIFO manner rather than FIFO? If so, thank you for the translation.
- tomxor 4y ago
  Yes, exactly, I came to the same realisation that was an appropriate label and made an edit to describe it as such. In fact comparing it to FIFO as you have makes even more sense so I've edited it again. Surface reflections are FIFO, because there is no medium, no "storage"; This novel medium based reflection is LIFO, based upon whatever is traversing the medium at the time of the change to the medium. It's not magic, but it's an interesting way to achieve this in pure photonics, without first converting to something more manageable like electronics... it also doesn't require discrete memory like electronics, it's kind of analogue processing but with a buffer? but can only support analogue processing.
  - deleted 4y ago
    [deleted]
retrocryptid 4y ago
I think you misunderstand. What's being described is a Phase Conjugate Mirror (PCM) -- Think of it as a mirror where the angle of incidence equals the angle of reflection, but without being translated into the opposite quadrant. It does not "buffer" signals incident upon it, but reflects it along a path that it took to get to the PCM. So it's the same path through space that you would get if you reversed time from the moment the signal hit the mirror. I'm sure that was clear as mud, here's a wikipedia link: https://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase_conjugation https://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase...
- nielsbot 4y ago
  So the photons re-trace their steps instead of continuing forward. I think the picture of the tiger seen through the distorion of a glass bottle on the linked page explains it pretty well. But I'm a layperson.
  - fnordpiglet 4y ago
    No I don’t think that’s right: When a light wave enters the new time interface and the device changes its optical properties, the signal keeps moving forward in space. However, the signal gets reversed—if it were a spoken word, it would sound as if it were getting played backwards. In contrast, with a conventional reflection, a light or sound wave would travel back at its source but mostly look or sound the same as it did before the reflection. — They continue forward, but they behave in the reverse with respect to time alone.
- tomxor 4y ago
  I did interpret it as effectively reflecting along the same path, I was using "buffer" in a more abstract sense to compare how it would be processed digitally. But I don't doubt I've misunderstood something, my description of photons traversing the medium is probably what sounds physically inaccurate, I'm no expert in photonics and don't really know what a PCM is. As someone who does, are you able to corroborate whether the effect differs abstractly from what I described in terms of reversing the signal, as in a LIFO? Because this was my gripe with the article, the way the concept was explained makes it sounds like something more than it is.
iamerroragent 4y ago
So instead of: light: --123-> :Wall light: <-321-- :Wall it is: light: --123-> :Wall light: <-123-- :Wall ?
- fnordpiglet 4y ago
  No: When a light wave enters the new time interface and the device changes its optical properties, the signal keeps moving forward in space. However, the signal gets reversed—if it were a spoken word, it would sound as if it were getting played backwards. In contrast, with a conventional reflection, a light or sound wave would travel back at its source but mostly look or sound the same as it did before the reflection. — So it’s Light -123-> wall -321-> Where wall isn’t a wall but a time mirror.
  - iamerroragent 4y ago
    Thank you!
fnordpiglet 4y ago
I think it’s right. The mirror takes f(x,y,z,t) and maps it to f(x,y,z-t), thus reversing it in the time dimension but not space. It doesn’t make it go backwards through time, it just reverses lights behavior with respect to time.
NoPicklez 4y ago
> The concept is quite natural to grasp. I'd use that term to explain perhaps understanding seeing an Apple falling from a tree.
fsckboy 4y ago
> very click batey click bait would entice you to click, like baiting a fish. click bate would stop you from clicking, like abating your breathing and therefore holding your bated breath.

by tomxor 4y ago

nobodyandproud 4y ago

So photons would effectively be reflected back in a LIFO manner rather than FIFO? If so, thank you for the translation.

tomxor 4y ago
Yes, exactly, I came to the same realisation that was an appropriate label and made an edit to describe it as such. In fact comparing it to FIFO as you have makes even more sense so I've edited it again. Surface reflections are FIFO, because there is no medium, no "storage"; This novel medium based reflection is LIFO, based upon whatever is traversing the medium at the time of the change to the medium. It's not magic, but it's an interesting way to achieve this in pure photonics, without first converting to something more manageable like electronics... it also doesn't require discrete memory like electronics, it's kind of analogue processing but with a buffer? but can only support analogue processing.
- deleted 4y ago
  [deleted]

retrocryptid 4y ago

I think you misunderstand. What's being described is a Phase Conjugate Mirror (PCM) -- Think of it as a mirror where the angle of incidence equals the angle of reflection, but without being translated into the opposite quadrant. It does not "buffer" signals incident upon it, but reflects it along a path that it took to get to the PCM. So it's the same path through space that you would get if you reversed time from the moment the signal hit the mirror. I'm sure that was clear as mud, here's a wikipedia link: https://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase_conjugation https://en.wikipedia.org/wiki/Nonlinear_optics#Optical_phase...

nielsbot 4y ago
So the photons re-trace their steps instead of continuing forward. I think the picture of the tiger seen through the distorion of a glass bottle on the linked page explains it pretty well. But I'm a layperson.
- fnordpiglet 4y ago
  No I don’t think that’s right: When a light wave enters the new time interface and the device changes its optical properties, the signal keeps moving forward in space. However, the signal gets reversed—if it were a spoken word, it would sound as if it were getting played backwards. In contrast, with a conventional reflection, a light or sound wave would travel back at its source but mostly look or sound the same as it did before the reflection. — They continue forward, but they behave in the reverse with respect to time alone.
tomxor 4y ago
I did interpret it as effectively reflecting along the same path, I was using "buffer" in a more abstract sense to compare how it would be processed digitally. But I don't doubt I've misunderstood something, my description of photons traversing the medium is probably what sounds physically inaccurate, I'm no expert in photonics and don't really know what a PCM is. As someone who does, are you able to corroborate whether the effect differs abstractly from what I described in terms of reversing the signal, as in a LIFO? Because this was my gripe with the article, the way the concept was explained makes it sounds like something more than it is.

iamerroragent 4y ago

So instead of: light: --123-> :Wall light: <-321-- :Wall it is: light: --123-> :Wall light: <-123-- :Wall ?

fnordpiglet 4y ago
No: When a light wave enters the new time interface and the device changes its optical properties, the signal keeps moving forward in space. However, the signal gets reversed—if it were a spoken word, it would sound as if it were getting played backwards. In contrast, with a conventional reflection, a light or sound wave would travel back at its source but mostly look or sound the same as it did before the reflection. — So it’s Light -123-> wall -321-> Where wall isn’t a wall but a time mirror.
- iamerroragent 4y ago
  Thank you!

fnordpiglet 4y ago

I think it’s right. The mirror takes f(x,y,z,t) and maps it to f(x,y,z-t), thus reversing it in the time dimension but not space. It doesn’t make it go backwards through time, it just reverses lights behavior with respect to time.

NoPicklez 4y ago

> The concept is quite natural to grasp. I'd use that term to explain perhaps understanding seeing an Apple falling from a tree.

fsckboy 4y ago

> very click batey click bait would entice you to click, like baiting a fish. click bate would stop you from clicking, like abating your breathing and therefore holding your bated breath.