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Exotic Physics Phenomenon Involving Time Reversal Observed for First Time
- deleted 7y ago[deleted]
- leereeves 7y agoarXiv link: https://arxiv.org/abs/1906.03369 https://arxiv.org/abs/1906.03369
- qeternity 7y agoNoob here: this doesn’t actually mean that time was reversed, rather that this phenomenon was effectively created in reverse order no?
- gboone 7y agoTime-reversal symmetry means reversing the order of the inputs results in appearance the same output regardless of input order. The attempt was to break the symmetry in order to provide evidence the intended input sequencing was achieved. "Time Reversal" would be better written as "Time-reversal" in title.
- empath75 7y agoI’m not a physicist, but in general, Abelian means that operations in an algebra commute, while Non Abelian means that they don’t, which is to say that Abelian means that a+b=b+a To give a non mathematical example of a non-Abelian algebra, think of a Rubik’s cube where moves are the ‘numbers’ and composition of moves is the operation. If you turn the right face clock wise and then turn the top face counter clockwise, that does not produce the same state as turning the top face counter clockwise and the turning the right face clockwise (try it out if you have one handy). Solving the cube in general requires exploiting this property by using what are called commutators, which are performing a move and then another move and then reversing the second move and reversing the first move. If it were Abelian, then that would leave you in the place where you started — which is to say you reversed time — but the state will actually have changed where the first and second move manipulated the same pieces — which makes it non Abelian and breaks ‘time symmetry’ So in this case, think of some physical operation that changes the state of the object somehow as being the same as a Rubik’s cube move, and assuming the operations have an inverse, that performing a commutator where you do one operation and then another and then invert the second and then the first, that leaves you in a new state, which would not be the case if it were time invariant.
- MCompeau 7y agoThis is a very eloquent explanation, thank you.
- deleted 7y ago[deleted]
- solinent 7y agoGreat explanation, small nitpick: in mathematics, if you leave a person's name uncapitalized it's actually a sign of respect. So we usually use the uncapitalized abelian to refer to groups which commute. edit: This is done consistently, and I think abelian is one of the few examples. I've never seen it capitalized before, which is why I made this post.
- leereeves 7y agoI agree that "abelian" is often uncapitalized, but if that's a sign of respect, why is Gaussian (Gaussian elimination, Gaussian distribution, Gaussian process, etc) almost always capitalized? Or Hilbert space, Poisson distribution, Bernoulli trial, Cartesian coordinates, Euclidean distance? It seems to me that Abelian goes uncapitalized because few people know about Niels Henrik Abel, and it should properly be capitalized.
- solinent 7y agoMy professor explained that when it gets used to the extent where people stop capitalizing it it's seen as a sign of respect. You won't see it capitalized anywhere really. At the very least even with the knowledge that it refers to Abel they will still leave it in noun case. Maybe it's just a post-rationalization of the phenomenon you're describing.
- magicalhippo 7y agoFound this interesting MathOverflow question with some interesting possible answers. Not sure if it clears it up much, but the difference between English and French capitalization rules seems to me like it might have something to do with some of it. https://mathoverflow.net/questions/44946/why-is-abelian-infrequently-capitalized https://mathoverflow.net/questions/44946/why-is-abelian-infr...
- leereeves 7y agoRight, this doesn't mean that time was reversed, it means a phenomenon was created that would be different if time were reversed (unlike most physical phenomena, which work the same both ways).
- ngcc_hk 7y agoThanks.
- comboy 7y agoNot sure if it's the first time, we still seem to have a lot to learn about how time and causality works: https://www.youtube.com/watch?v=8ORLN_KwAgs https://www.youtube.com/watch?v=8ORLN_KwAgs
- bpaddock 7y agoThere are lot of examples, studies and experiment on retro causality in the field of Parapsychology. So this is not at all 'the first'. "Time-reversed human experience: Experimental evidence and implications" by Dean Radin is one that happens to be laying on my desk right now. A new book by by Theresa Cheung and Julia Mossbridge, "The Premonition Code" gets into some of the science. Ms. Mossbridge has published several papers and a few YouTube Videos about 'Time'. The field of Parapsychology generally gets dismissed to easily. The top people know they will get criticized, so they tend to design their experiments and statistics to standards higher than most if not all fields of study. If Parapsychologist presented the data that was given as 'Proof' of the Higgs boson, as shown by a small statistical bump in the data, they would have gotten their ass handed to them had they presented the same data has proof of any of their experiments. Optical Phase Conjugation is also interesting in that it involves apparent negative time. Let you do things like a see through frosted glass. True Hacker material...
- gameswithgo 7y agois the james randi prize still available? that frosted glass trick would be an easy million dollars
- lpellis 7y agoUnfortunately not, ended a few years ago and the money was repurposed I assume for other ventures. I guess its hard to keep that price going, you need skilled people (like Randi) that knows the usual tricks.
- bpaddock 7y agoYou also need to have objective people, unlike Randi. One lady did keep passing all of his tests, all day long, so they keep fiddling with the test to "improve it". Until the lady was completely exhausted and failed the test. Guess which test result they used? After this no one took Randi seriously, so no one with skill bothered.
- 7y ago
- sidcool 7y agoI have always struggled with understanding time in the context of the universe. Why would the universe care for our conception of time? It obviously cares, because time slows down at high speeds and in gravitational dilation. I can't wrap my mind around it.
- Aqueous 7y agoIt doesn't really care. Time dilation is the natural consequence of the universe having laws that are true in every reference frame. 'Relativity' is a misnomer - it's really a statement about the absolute nature of physical laws.
- gwd 7y agoRight; the word "relativity" comes from the concept that the laws of physics should be consistent in all frames of reference. That concept -- i.e., that when you're on a moving train, you toss a ball up and catch it, and it's the same physics as if you're standing still -- people seem to "get" quite intuitively. What's weird about Relativity is that our experience leads us to expect that things like distance, mass, and time will be the same in every frame of reference. Instead, what's apparently the same in every reference frame is "how fast light appears to travel"; and that distance, mass, time actually warp to cause this law to be true.
- criddell 7y agoIf you take an equation from physics (like the mass-energy equivalence) and rearrange it to solve for t, you don't seem to get anything that makes any kind of intuitive sense. Time is very confusing.
- TheSpiceIsLife 7y agoIs it correct to say time slows down at high speed and in high gravity? Only to an external observer, right?
- fennecfoxen 7y agoWell, "slows down" is relative terminology, but that says a little more about the terminology than the physics. The more interesting thing is that "high gravity" is essentially acceleration (and interchangeable with acceleration in most relativity contexts+). This is why the classic "twins on a spaceship" scenario makes the twin on the spaceship the younger one, instead of them being totally interchangeable: the young one is the twin that experiences the acceleration. And you can tell all by yourself that you're undergoing acceleration; you don't need an external reference. (+ if you accelerate forever, you can even make an acceleration event-horizon. light from beyond this horizon will never actually catch up with you, just like a black hole)
- maitredusoi 7y agoat least !!!!
- lngnmn1 7y agoBullshit. Not "observed". Modeled, which means nothing real. Map is not a territory. A models is not What Is.
- saul_goodman 7y ago"To produce the effect, the researchers use photon polarization. Then, they produced two different kinds of time-reversal breaking. They used fiber optics to produce two types of gauge fields that affected the geometric phases of the optical waves, first by sending them through a crystal biased by powerful magnetic fields, and second by modulating them with time-varying electrical signals, both of which break the time-reversal symmetry. They were then able to produce interference patterns that revealed the differences in how the light was affected when sent through the fiber-optic system in opposite directions, clockwise or counterclockwise..." Lordy, I with these folks would speak english, but no, whats really important is saying things in a way only others in your field can comprehend. You can actually comprehend papers written even just 50 years ago because they written to be understood, not to confuse the granting body. TL;DR: they setup a laser interferometer and twiddled the light in different ways through each path, the resulting interference pattern was evidence of the effect claimed. On one path they polarized the light by running it through an LCD (a "crystal biased by powerful magnetic fields"). On the other path I'm less sure what they mean by "time-varying electrical signals", probably just means they were effectively pulsing it on and off. And somehow, by running each path through opposing winds of a fiber optic system they think they are getting results indicating "time reversal". I'll have to take them on their word on that, that's where I know less about the subject matter.
- fourthark 7y agoI prefer accurate reporting that I don't understand, to the usual oversimplified and overhyped nonsense that usually passes as science reporting.
- BurningFrog 7y agoMaybe it can be observed even earlier as technology develops :)
- deleted 7y ago[deleted]
- jjtheblunt 7y agoWould time reversal violate the law of thermodynamics about entropy never decreasing?
- namirez 7y agoProbably not! The 2nd law of thermodynamics is a statistical law describing the interactions of many particles, so it doesn't necessarily apply to microscopic scales. https://www.newscientist.com/article/dn2572-second-law-of-thermodynamics-broken/ https://www.newscientist.com/article/dn2572-second-law-of-th...
- not_a_cop75 7y agoClickbait, but thanks for playing.
- imvetri 7y agoPlaying a video in reverse is time reversal. I'm sorry, I cannot really appreciate anything that plays with time and space. These are metrics to measure. I'm really not sure we can apply any thought process to imagine time reversal. We can only imagine time reversal but that exists only in the mind not outside the head. Another anology I would like to use "I have 100 litre of water, and I found a way to double it, compress it while keeping the mass volume unchanged". That's how anything with space / time reversal / space wrap travelling machine all sounds!. Stop encouraging these kind of flawed theories. Spacetime is a unit, I cannot stand researchers providing theoritical proof that spacetime is flexible etc etc. If I have a graph sheet with me and If I stick one edge to another edge drawing on the graph remains the same!