time mirrors
May 17, 2023 10:11 AM Subscribe
Time mirrors: "Light can reflect off mirrors, and sounds off surfaces. However, scientists have long theorized about time reflections, where a signal passing through a time “interface” would act like it was traveling backward in time. Now a new study for the first time demonstrates time reflections with light waves. "
!tnempoleved looc yllaer a ekil sdnuos sihT
posted by grumpybear69 at 11:00 AM on May 17, 2023 [5 favorites]
posted by grumpybear69 at 11:00 AM on May 17, 2023 [5 favorites]
photonic time crystals?
metamaterials?
invisibility cloaks?
temporal slab?
When an ieee article is indistinguishable from scp we're in weird times indeed.
posted by gwint at 11:04 AM on May 17, 2023 [6 favorites]
metamaterials?
invisibility cloaks?
temporal slab?
When an ieee article is indistinguishable from scp we're in weird times indeed.
posted by gwint at 11:04 AM on May 17, 2023 [6 favorites]
Whoa whoa wait what hang on I ... gosh, I fleetingly grasped some of the meanings of some of these sentences but my understanding did not survive the hit that came from each subsequent sentence. What?????? Can MeFi's resident physics people please explain this as if I am a 5 yr old physics nerd?
Most alluring to me is this idea of "reflecting" time by drastically+suddenly changing the properties of the medium that bears a beam of light, and how that is analogous to reflecting light waves by drastically and suddenly changing the direction of a beam. Is it merely analogous to a reflection of light or is this genuinely, literally, mathematically etc. just another form of reflection? Like is there a first-principles way to define/describe the concept of "reflection" that includes both medium and wave's capacity for sudden shifts, and implications for time and normal waves alike? I would love to understand what properties of the medium are being shifted in this time reflection. How is a medium a "boundary" for time? What's bouncing off of what?
Does this mean there's some other thing that's a "boundary" for space? Have we figured out a way to create reflections of space, or is that moot because space isn't a wave like light and sound and (apparently) time are?
Oh shit can we reflect gravity??? I am very excited and I have no answers please help.
posted by MiraK at 11:49 AM on May 17, 2023 [8 favorites]
Most alluring to me is this idea of "reflecting" time by drastically+suddenly changing the properties of the medium that bears a beam of light, and how that is analogous to reflecting light waves by drastically and suddenly changing the direction of a beam. Is it merely analogous to a reflection of light or is this genuinely, literally, mathematically etc. just another form of reflection? Like is there a first-principles way to define/describe the concept of "reflection" that includes both medium and wave's capacity for sudden shifts, and implications for time and normal waves alike? I would love to understand what properties of the medium are being shifted in this time reflection. How is a medium a "boundary" for time? What's bouncing off of what?
Does this mean there's some other thing that's a "boundary" for space? Have we figured out a way to create reflections of space, or is that moot because space isn't a wave like light and sound and (apparently) time are?
Oh shit can we reflect gravity??? I am very excited and I have no answers please help.
posted by MiraK at 11:49 AM on May 17, 2023 [8 favorites]
I don't pretend to understand the physics, but it would be interesting as a sci-fi macguffin, a device that could take a light-encrypted message and use a time mirror to get back to something unencrypted.
posted by They sucked his brains out! at 11:58 AM on May 17, 2023 [1 favorite]
posted by They sucked his brains out! at 11:58 AM on May 17, 2023 [1 favorite]
Wasn't this the plot to TENET? Assuming that movie had a comprehensible plot, that is...
posted by Saxon Kane at 12:01 PM on May 17, 2023
posted by Saxon Kane at 12:01 PM on May 17, 2023
Kinda like Bob Shaw's Slow Glass.
This post brought to you by idly thinking of this short story during my commute, and the words time mirror popped into my head and I thought, hm I should google that.
posted by dhruva at 12:02 PM on May 17, 2023 [13 favorites]
This post brought to you by idly thinking of this short story during my commute, and the words time mirror popped into my head and I thought, hm I should google that.
posted by dhruva at 12:02 PM on May 17, 2023 [13 favorites]
"To stop the light, the physicists used a glass-like crystal that contains a low concentration of ions -- electrically charged atoms -- of the element praseodymium. The experimental setup also includes two laser beams. One is part of the deceleration unit, while the other is to be stopped."
posted by clavdivs at 12:04 PM on May 17, 2023 [1 favorite]
posted by clavdivs at 12:04 PM on May 17, 2023 [1 favorite]
This research paper: We can reflect time from a mirror.
Two research papers later: We can save time in a bottle.
posted by ApplAuD at 12:13 PM on May 17, 2023 [2 favorites]
Two research papers later: We can save time in a bottle.
posted by ApplAuD at 12:13 PM on May 17, 2023 [2 favorites]
Can we shine a light on the past?
posted by night_train at 1:50 PM on May 17, 2023
posted by night_train at 1:50 PM on May 17, 2023
I've only read the first paragraph and thought, great, now tech bros are going to fuck up the past.
posted by slogger at 1:52 PM on May 17, 2023 [2 favorites]
posted by slogger at 1:52 PM on May 17, 2023 [2 favorites]
Not sure I know what it means for light to be reversed as a signal.
posted by Don.Kinsayder at 1:52 PM on May 17, 2023 [1 favorite]
posted by Don.Kinsayder at 1:52 PM on May 17, 2023 [1 favorite]
Based on a quick scan of the internets. I think it's like this. Imagine you walk up to a mirror and as you look into it you see yourself walking backwards away from the mirror, as if someone recorded you approaching the mirror and then played the recording back in reverse. Makes my head hurt.
posted by interogative mood at 1:53 PM on May 17, 2023 [1 favorite]
posted by interogative mood at 1:53 PM on May 17, 2023 [1 favorite]
I'm an optical physicist. This result is not nearly as exciting as it sounds (though interesting for optical physicists.) It's nothing to do with sending people back in time or running events backwards or anything like that. It's just about pulses of light. If you arrange for a light pulse to be brighter at first and then get dimmer before going off, you pretty much know how that should interact with a mirror... The reflected pulse will also be brighter, then dimmer, then off. With this kind of time reversal effect you might be able to cause some light pulses to behave differently... The reflection goes dimmer-then-brighter instead of brighter-then-dimmer. Time reversal, you see?
But really it's just a trick of interference of waves... You managed to shift the phase of some parts of the pulse so that they interfere constructively at the end rather than the beginning. (I don't feel that I have time to explain constructive intereference right now for those who are unfamiliar, but here's a Kahn Academy video that seems helpful...)
A few years ago (when I was doing my thesis) people were getting all excited about "fast light" which is light pulses that seem to travel faster than light... But it's the same idea, just shifting phases to make the front of the pulse come out bigger so that the peak seems to arrive sooner... But you can't use it to send messages faster than light, just as you won't be able to use this new thing to send messages backward in time.
It's literally just a trick of the light... But a cool one.
posted by OnceUponATime at 1:59 PM on May 17, 2023 [40 favorites]
But really it's just a trick of interference of waves... You managed to shift the phase of some parts of the pulse so that they interfere constructively at the end rather than the beginning. (I don't feel that I have time to explain constructive intereference right now for those who are unfamiliar, but here's a Kahn Academy video that seems helpful...)
A few years ago (when I was doing my thesis) people were getting all excited about "fast light" which is light pulses that seem to travel faster than light... But it's the same idea, just shifting phases to make the front of the pulse come out bigger so that the peak seems to arrive sooner... But you can't use it to send messages faster than light, just as you won't be able to use this new thing to send messages backward in time.
It's literally just a trick of the light... But a cool one.
posted by OnceUponATime at 1:59 PM on May 17, 2023 [40 favorites]
My first reaction is, like Fathere Inire's mirrors ?
posted by Rash at 2:31 PM on May 17, 2023 [2 favorites]
posted by Rash at 2:31 PM on May 17, 2023 [2 favorites]
I've only read the first paragraph and thought, great, now tech bros are going to fuck up the past.
If done properly they will have already done so.
posted by pwnguin at 2:35 PM on May 17, 2023 [4 favorites]
If done properly they will have already done so.
posted by pwnguin at 2:35 PM on May 17, 2023 [4 favorites]
As a layperson, the way science works is that there will be all these exciting headlines about time travel or whatever and then you read the actual article and it's like, "If we technobabble these particles over here, it's also possible to technobabble those particles over there." And it goes on like that for decades, with nothing really changing while we all drive our Hondas to our crappy unsatisfying jobs and get cancer. And then, every 40 years or so, science is like, "Oh, hey, if you press this button you can talk to your dead grandma in heaven."
(AI is the new dead grandma.)
posted by Ursula Hitler at 2:36 PM on May 17, 2023 [23 favorites]
(AI is the new dead grandma.)
posted by Ursula Hitler at 2:36 PM on May 17, 2023 [23 favorites]
You know, I come to Metafilter for comments like those of OnceUponATime and those of Ursula Hilter. :-)
posted by Don.Kinsayder at 2:50 PM on May 17, 2023 [15 favorites]
posted by Don.Kinsayder at 2:50 PM on May 17, 2023 [15 favorites]
I've only read the first paragraph and thought, great, now tech bros are going to fuck up the past.
If done properly they will have already done so.
Upon further reflection, I’m beginning to think they did.
posted by slogger at 3:05 PM on May 17, 2023 [2 favorites]
If done properly they will have already done so.
Upon further reflection, I’m beginning to think they did.
posted by slogger at 3:05 PM on May 17, 2023 [2 favorites]
No, the reflection looks that way, but as explained above it’s just a trick of the light.
posted by nickmark at 4:07 PM on May 17, 2023 [2 favorites]
posted by nickmark at 4:07 PM on May 17, 2023 [2 favorites]
I've only read the first paragraph and thought, great, now tech bros are going to fuck up the past.
Presumably this already willhasis happeninged*.
*"One of the major problems encountered in time travel is not that of becoming your own father or mother ... The major problem is simply one of grammar, and the main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveler's Handbook of 1001 Tense Formations."
posted by pompomtom at 7:16 PM on May 17, 2023 [6 favorites]
Presumably this already willhasis happeninged*.
*"One of the major problems encountered in time travel is not that of becoming your own father or mother ... The major problem is simply one of grammar, and the main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveler's Handbook of 1001 Tense Formations."
posted by pompomtom at 7:16 PM on May 17, 2023 [6 favorites]
Another optical/atomic physicist here commenting because this sort of stuff really gets my goat (don't even get me started on "invisibility cloaks"). As OnceUponATime said, it is a neat optical effect that may have some useful applications, but it is disingenuous on the part of the authors (or the writers of the popular science article) to pretend that what we scientifically describe as time reversal is in any way similar to what the general public will think about when they hear about a time mirror.
We describe something as time reversal when the evolution of a system after some event is mathematically equivalent to the initial evolution, if time were reversed. e.g., in a photon echo, a pulse of light is absorbed by a material, and you can manipulate that material (with more light pulses, electric or magnetic fields,etc) to spit that pulse back out again (the echo) - mathematically the atoms re-radiating the light is the time reversal of the atoms absorbing the light in the first place.
What's new in this paper is that they are using a metamaterial (made of "artificial" atoms) to manipulate light in ways we typically have only previously been able to do with real atomic materials (metamaterials are also more practical for some applications than atoms, which I won't go into). Atoms can be used to manipulate light in all sorts of ways - you can store and recall light, you can shift its frequency, its spatial direction, time reverse it, make "time crystals" etc. The stopped light paper clavdivs referenced (itself just a redo of an earlier experiment which was done by some of my colleagues) is a very similar effect in the same type of atomic medium.
The actual underlying physics has been around for over 50 years but is constantly getting rebranded to make it sound cool.
posted by neatsocks at 9:29 PM on May 17, 2023 [5 favorites]
We describe something as time reversal when the evolution of a system after some event is mathematically equivalent to the initial evolution, if time were reversed. e.g., in a photon echo, a pulse of light is absorbed by a material, and you can manipulate that material (with more light pulses, electric or magnetic fields,etc) to spit that pulse back out again (the echo) - mathematically the atoms re-radiating the light is the time reversal of the atoms absorbing the light in the first place.
What's new in this paper is that they are using a metamaterial (made of "artificial" atoms) to manipulate light in ways we typically have only previously been able to do with real atomic materials (metamaterials are also more practical for some applications than atoms, which I won't go into). Atoms can be used to manipulate light in all sorts of ways - you can store and recall light, you can shift its frequency, its spatial direction, time reverse it, make "time crystals" etc. The stopped light paper clavdivs referenced (itself just a redo of an earlier experiment which was done by some of my colleagues) is a very similar effect in the same type of atomic medium.
The actual underlying physics has been around for over 50 years but is constantly getting rebranded to make it sound cool.
posted by neatsocks at 9:29 PM on May 17, 2023 [5 favorites]
Time flies like the excrement pits of 16th century London.
posted by Ten Cold Hot Dogs at 1:39 AM on May 19, 2023 [1 favorite]
posted by Ten Cold Hot Dogs at 1:39 AM on May 19, 2023 [1 favorite]
We describe something as time reversal when the evolution of a system after some event is mathematically equivalent to the initial evolution, if time were reversed.
But why would you call it that? Don't blame some journalist for hyperventilating when they overhear physicists talking about having achieved "time reversal".
posted by straight at 10:00 AM on May 19, 2023
But why would you call it that? Don't blame some journalist for hyperventilating when they overhear physicists talking about having achieved "time reversal".
posted by straight at 10:00 AM on May 19, 2023
The biggest problem with time travel is that so many people go back in time to kill Hitler that it changes the Earths center of mass enough to affect its axis of rotation and killing everyone.
posted by interogative mood at 3:44 PM on May 23, 2023
posted by interogative mood at 3:44 PM on May 23, 2023
But why would you call it that? Don't blame some journalist for hyperventilating when they overhear physicists talking about having achieved "time reversal".
If you run a film clip backwards, you're showing a time-reversed version of the clip. What else would you call it?
Same with pulses of light or collisions between particles -- the "time reversed" version of the pulse or the collision is the one which looks exactly like the original version except that everything happens in reverse order. There are good reasons [1] in physics to talk about time-reversed versions of events!
It's only confusing when taken out of context!
[1] For instance, does the time reversed version of a specific event also obey the relevant laws of physics? If so, then the laws governing that event are "time-symmetric." Billiard ball collisions are like this... The backwards in time version is just as physically possible as the forwards version. But if instead of billiard balls you have oppositely charged particles attracting each other, the time-reversed version would look like they were repelling, so the time reversed version in that case DOESN'T follow the laws of physics. But if you flip the signs on both charges and also look at the mirror image of the film (as you're running it in reverse) then that DOES follow the laws of physics, so that's charge/parity/time symmetry. If we can find out what kinds of symmetries physical laws obey, we can better understand why those laws are true, and what other laws we may not have yet discovered.... Emmy Noether showed that every symmetry is associated with a conservation law. If you assume that the laws governing a specific event are time-symmetric, then you can prove that energy is conserved in that event. Pretty profound and yet also still just regular physics about billiard balls and static electricity, not time travel.
posted by OnceUponATime at 9:40 AM on May 24, 2023
If you run a film clip backwards, you're showing a time-reversed version of the clip. What else would you call it?
Same with pulses of light or collisions between particles -- the "time reversed" version of the pulse or the collision is the one which looks exactly like the original version except that everything happens in reverse order. There are good reasons [1] in physics to talk about time-reversed versions of events!
It's only confusing when taken out of context!
[1] For instance, does the time reversed version of a specific event also obey the relevant laws of physics? If so, then the laws governing that event are "time-symmetric." Billiard ball collisions are like this... The backwards in time version is just as physically possible as the forwards version. But if instead of billiard balls you have oppositely charged particles attracting each other, the time-reversed version would look like they were repelling, so the time reversed version in that case DOESN'T follow the laws of physics. But if you flip the signs on both charges and also look at the mirror image of the film (as you're running it in reverse) then that DOES follow the laws of physics, so that's charge/parity/time symmetry. If we can find out what kinds of symmetries physical laws obey, we can better understand why those laws are true, and what other laws we may not have yet discovered.... Emmy Noether showed that every symmetry is associated with a conservation law. If you assume that the laws governing a specific event are time-symmetric, then you can prove that energy is conserved in that event. Pretty profound and yet also still just regular physics about billiard balls and static electricity, not time travel.
posted by OnceUponATime at 9:40 AM on May 24, 2023
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posted by Paul Slade at 10:54 AM on May 17, 2023 [7 favorites]