Exotic Physics Phenomenon Involving Time Reversal Observed for First Time | Hacker News Reader

Exotic Physics Phenomenon Involving Time Reversal Observed for First Time

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177 pointslelf73 comments

Maybe it can be observed even earlier as technology develops :)

They actually discovered it next year :-D

Not for long!

Noob here: this doesn’t actually mean that time was reversed, rather that this phenomenon was effectively created in reverse order no?

I’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.

This is a very eloquent explanation, thank you.

Wait, if a Rubik's cube has this property, then why does the title state that the phenomenon was just observed for the first time?

The title says that a phenomenon was observed for the first time, not that this is the first non-Abelian phenomenon we've observed. The article is specifically about a non-Abelian version of the Aharonov-Bohm effect.

Great 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.

I 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.

Found 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-infr...

My 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.

If it is a name it gets capitalized. If it is an adjective derived from the name (abelian, cartesian, euclidean, ...), it depends on the language, the author and the literature around the word.

I can't say that this is true.

Examples of mathematical operators/functions that are always capitalized:

* Laplacian operator

* Gaussian distribution

* Lorentz factor

* Taylor series

* Bohr radius

etc...

No idea, but one difference I noticed with your examples are that the names are adjectives modifying a generic math term, but "abelian" is the whole label. (e.g. "abelian" vs. "Abelian group")

How is it a sign of respect? Are we not respecting Fourier for his transforms? Are we failing to respect Stokes, Green, Riemann, Cauchy, Ramanujan, and Pythagoras? The vast majority of "respected" mathematicians retain capital names on their theorems/equations/conjectures etc.

This seems false.

Right, 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).

Thanks.

Time-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.

I 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.

Brian Greene's 'Fabric of the Cosmos'[1] has some great explanations of space and time and their relationship.

If you are very interested, I highly recommend Carlo Rovelli's 'The Order of Time.'[2]

And 'Your Brain is a Time Machine'[3], though I ultimately found it unsatisfying, goes directly at the apparent contradiction between our sense of the 'flow' of time, and the implications of general relativity. Although it doesn't have an answer, it states the problem clearly, and has a lot of other interesting facts about our perceptions of time.

Rovelli has also given some interesting talks on YouTube.

[1] https://www.amazon.com/Fabric-Cosmos-Space-Texture-Reality/d...

[2] https://www.amazon.com/s?k=carlo+rovelli+order+of+time&crid=...

[3] https://www.amazon.com/Your-Brain-Time-Machine-Neuroscience/...

Nobody becomes famous, or rarely respected, by saying they don't understand.

There are a lot of mysteries, even ones which arise in deceptively ordinary experiences, for example when we try to confront exactly how a gyroscope works(1).

My personal opinion is, to make an analogy, that we don't really know the source code of the universe. Every natural law is not really a law, but just a theory, or a mental model, articulated in maths, describing what we see, nothing more than that. This becomes obvious when you consider something famous like Newtonian gravity's obsolecense by GR. GR is also not the source code, just another really good mental model to describe behavioral patterns of the universe.

AFAIK time is something we really struggle with wrapping our minds around. There are questions which are so difficult I wonder if they're even worth asking -- such as about places where time would not exist, such as in places outside our universe.

1-https://www.americanscientist.org/article/the-forgotten-myst...

Our conception of time is just totally wrong, or at least this is true for 99.9 % of all humans and that is certainly an underestimate. Something like THE time does not exist, we are just all living together in a small bubble in the universe, all of us experiencing more or less the same gravitational field, all of us moving together at more or less the same speed as Earth moves through space, and that is what makes it look like there is THE time. But actually time is more like counting the calories you burn as you walk through the world, it is specific to you and the path you take. There is a great lecture »The Physics and Philosophy of Time« by Carlo Rovelli [1] aimed at the general public that does a good job pointing out how wrong we are.

[1] https://www.youtube.com/watch?v=-6rWqJhDv7M

Perhaps: the field of physics, in its discussions, allows for local observation and within local observation, the observation of local causal effects. The lack of causal effects in your observable context when a distant event occurs means that the time of the event to your local context is the time of the effects of that arrival (when you actually have evidence of it). One might suggest this is a correlate of the "no" answer to the "if a treefalls in the woods but no one is around to observe it, does it make a sound?" question but... On the more practical side you can consider CPU clocks and time synchronization. One can only synchronize two clocks to agree up to a time span but within that span the relative ordering of events at each is undefined. The physics reason is that only causality establishes order, the cause precedes the consequence and beyond causal entanglements, ordering is undefined.

I'm not a physicist but I've been pondering this sometime...

If the time does not exist, such measure as speed wouldn’t make any sense, would it?

Two cars, both moving forwards, can still move in different directions! So does "forwards" exist? Not as a global direction, but once you have picked an orientation it is a useful label for a distinguished axis.

Time is like that. Pick a velocity, and then time is a distinguished axis in the coordinate system you overlay on spacetime.

Measures of speed can make no sense even when you allow for time :)

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

In the same way speed depends entirely on your frame of reference, so does our perception of time.

But it doesn't make sense. OP is saying that there is no absolute measure of time, it depends on the frame of reference of the observer. Therefore there is also no absolute measure of speed.

Correct. A fly on the seat of your car travels 0 m/s with respect to the car and to you, but travels, say, 30 m/s with respect to the road. Speed (and velocity, for that matter) always needs a reference to be meaningful.

It 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.

Right; 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.

If 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.

The universe doesn't care about your conception of time.

Your conception of time care about the local time coordinate of the universe.

Your brain has a few clocks:

* Some are not very clear, like the time that the Sodium and Potassium needs to separate after a neuron has fired. It can't fire again until it has been recharged, so it is a clock that regulates the fire rate https://en.wikipedia.org/wiki/Na%2B/K%2B-ATPase

* Other clocks are more clear, for example there is a daily clock that counts approximately 24 hours. It has two substances that accumulate slowly and make the other substances get accumulated or get destroyed. It's tricky, but it's stable enough. https://en.wikipedia.org/wiki/Circadian_rhythm

These clock and all the other clocks and reactions of the brain are affected by the changes in the time coordinate, it's the same effect of a mechanical clock or an electronic clock or a water clock, or ...

If you go to a very fast space ship where there is a big time dilation, you will think more slowly, but the wall clock in the spaceship will be also more slowly, and the plants will grow more slowly, and the muons will decay more slowly, and the sound will move more slowly ...

Everything will happen more slowly, so inside the spaceship you will not notice the change. Everything will be normal. You will not experience "bullet-time" (like in the Matrix Movie) or "anti-bullet-time".

Think of it instead as our perception caring about the universe's version of time. It doesn't care about us, but we certainly care about it, existing in it and all. We might be way off, but there's (I would guess) every reason to evolve to be spot on about perceiving real stuff, at least in the part of time that relates to the local notion of causal structure of X evolves into Y on earth.

Time can be thought of as a direction in the 4th dimension, like up and down in 3D (which does not exist on a 2D plane).

In this way it corresponds to the "change" in the universe. Whenever anything changes, it is moving time forward (and not the other way around). Therefore if we measure some rate of change, and give that rate of change a unit, we have ourselves a way of measuring time. For example, measuring the change in angle for shadows during the day, or measuring the changes in vibration in the Cesium atom. This count then becomes our "time".

My sense of it all is that time is simply the procession of cause and effect, the rate of it is affected by space but it's meaningless to consider it happening backwards, and the main reason anyone might be tempted to is just a side effect of treating it as a fourth dimension for the purposes of plugging it into equations.

Is it correct to say time slows down at high speed and in high gravity?

Only to an external observer, right?

Well, "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)

In the "twins on a spaceship" scenario the interchangeability breaks down because there are not two but three relativistic frames - the stationary one; the frame moving away from Earth very fast, and the frame moving towards the Earth very fast. It's not really the acceleration per se, but the combination of these two different frames (of course, switching between them requires changing velocity and thus acceleration) that result in that twin being younger.

arXiv link: https://arxiv.org/abs/1906.03369

Playing 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!

Clickbait, but thanks for playing.

Would time reversal violate the law of thermodynamics about entropy never decreasing?

Probably 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-th...

"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.

I prefer accurate reporting that I don't understand, to the usual oversimplified and overhyped nonsense that usually passes as science reporting.

Not 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

at least !!!!

There 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...

"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."

Heh.

https://slate.com/health-and-science/2017/06/daryl-bem-prove...

https://slatestarcodex.com/2014/04/28/the-control-group-is-o...

"That is, in let’s say a drug testing experiment, you give some people the drug and they recover. That doesn’t tell you much until you give some other people a placebo drug you know doesn’t work – but which they themselves believe in – and see how many of them recover."

There is actually a science of studying Placebos. It is not as simple as most think. For example the strong the drug in many trials, the stronger the Placebo effect is. Things like the total number of trials of the drug become relative. Spatial Separation does not necessary imply Independence.

Yes, but what's your control for the placebo study?

To prove the placebo effect exists, you need to have a group that thinks it's getting a placebo, but actually gets nothing...

To be clear, I'm not just making a joke, I think the ideas people have about the placebo effect are deeply incoherent and harmful.

Ummm... sure? I mean, cool, sounds like an interesting subject.

But... that is not at all what the linked essay is about? There's one paragraph in a 4.5k word essay explaining what a control group is that mentions the concept of a placebo because that's a concept related to control groups that the reader might be familiar with.

Here's the same author treating the subject of placebos more seriously: https://slatestarcodex.com/2018/01/31/powerless-placebos/

is the james randi prize still available? that frosted glass trick would be an easy million dollars

Unfortunately 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.

You 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.

Do you have a link for that? That's very much different from how I understand the tests were undertaken, so I'd be very interested in reading about it.

Not familiar with that story, but here's a scientist's response to one of Randi's rebuttals.

https://www.sheldrake.org/reactions/james-randi-a-conjurer-a...

Randi's the worst kind of enemy science can have, someone who violates every principle of scientific inquiry for the sake of his own dogma, while claiming to care about the integrity of science.

You're claiming that a professional magician is a bad scientist? He's an entertainer and not a trained scientist.

Here's a statement from Randi about the dog ESP:

“I over-stated my case for doubting the reality of dog ESP based on the small amount of data I obtained,” he wrote. “It was rash and improper of me to do so. I apologise sincerely.”[1]

Sounds like he's willing to revisit his initial claims. Has there been further evidence of dog esp that you're aware of?

[1] https://www.telegraph.co.uk/culture/film/film-news/11270453/...

>"I apologize sincerely"

As sincerely as when he said he'd replicated the experiment no doubt. And if he isn't capable of reproducing an experiment, what the frack was the prize supposedly for? I don't think he'd be capable of sincerity if he tried.

As for your other question, I saw a response Sheldrake posted about someone else's rebuttal stating that if the rebuttal's raw data were analysed the way his data was, it would have led to the same conclusion. That the attempt at replication looked at the first time the dog went to the window, rather than the average time it spent at the window. Don't have a link right now though.

Dog ESP is a pretty niche experiment though, I just brought it up because it's one of the more egregious lies Randi was caught in. If you're interested in psi data, there are much larger datasets with experiments into ganzfeld and skin conductivity precognition.

This came up in a group discussion of parapsychologists that I hang out with form time to time. Some of the top people in the world. I expect you could find it covered in the Journal of Parapsychology as a place to start looking.

There are many people doing experiments with independent replication. Both experiments that succeed and fail. We learn from both. Sadly people would rather dismiss such things as impossible dogma rather than learn new things on the leading edge of science.

Sadly, with that we can't know if it's actually something that occurred, an anecdote, or something conceived of to explain a failure or bias.

What does one do to qualify as one of the "top parapsychologists"? And how do you determine which bits are "the leading edge of science" and which are just bunk?

This did not happen.

Before dismissing something, might want to check the physics:

[Concetto R. Giuliano, 1981]

Concetto R. Giuliano, "Applications of optical phase conjugation," Physics Today, vol. 34, no. 4, pp. 27-35, Apr. 1981.

Abstract: Light waves that are, in effect, time-reversed images of their original can serve to restore severely aberrated waves to their original state.

It's also important to understand the physics.

This is just a mirror that keeps the shape of the wave intact, but moving the other way (but still forward in time).

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

https://www.jstor.org/stable/24975872?seq=1#page_scan_tab_co...

I expect you might find these obscure papers of interest:

* Yoseph Imry and Richard A. Webb, "Quantum Interference and the Aharonov-Bohm Effect," Scientific American, vol. 260, no. 4, Apr. 1989.

Abstract: Can electrons be influenced by a nearby magnet so well shielded that its force field cannot be detected? The counter intuitive answer is yes:an energy emanation from the magnet known as the potential does indeed affect the electrons' wave function. This quantum-mechanical effect is being brought to bear on the development of new microelectronic devices.

* Capt. Robert M. Collins (TQTR), "Soviet Research On The A-Vector Potential and Scalar Waves (U)," Unknown.

Abstract: Active in the areas of the Aharonov-Bohm effect as applied to the A-vector potential and scalar fields as applied to solving force related problems.

* Capt. Robert M. Collins (TQTR), "Soviet Research On Unified Field Theories, False Vacuum States, and Antigravity (U)," Unknown.

Abstract: Theoretical progress in dealing with unified field theories...new concepts in weapons, transportation, propulsion.

* Dr. Jack Dea, "Fundamental Fields and Phase Information," vol. 4, no. 3 Unknown.

Add to those the list of patents by Raymond C. Gelinas assigned to Honeywell from the 1980's and what today is being called Extended Electrodynamics as well:

L.M. Hively & G.C Giakos, “Toward a more complete electromagnetic theory”, Int. J. Signals & Imaging Syst. Engr., 5, 3-10(2012).

L.M.Hively, “Methods and Apparatus for Generating and/or Utilizing Scalar-Longitudinal Waves”, US Patent #9,306,527, (Apr. 6,2016).

L.M.Hively & O.Keller, “Electrodynamics in curved space-time: Free space longitudinal wave propagation”, Phys. Essays, 32 (3), Sept 2019.

Can't really get more up to date than a paper published this month. Sad that people will still be quick to down vote things without knowing what is going on in the world today. :-(

The Aharonov-Bohm Effect is indeed interesting, but how is it, or are any of those, related to parapsychology?

It was your jstor link that sent me down the A-B path. I apologize if I miss understood your intention.

I apologize if I misunderstood yours.

If we've changed topics to physics, I agree it's very interesting. The more we learn the stranger the universe seems.

The original subject here was a about reversal of time.

I mixed the two subjects of Parapsychology and Optical Phase Conjugation under that heading. They have nothing to do with each other (as far as we know at the moment).

It's not about reversal of time so much as time-reversal symmetry in a physical system (putting a -t in place of a t).

In the case of Optical Phase Conjugation that is correct. Which is why I said "apparent" in my original post. Physics allow for -t in many places.

However in the case of psi it is about time, that is effect happens before the cause.

"... PAA [predictive anticipatory activity, an other term for Presentiment], the predictive physiological anticipation of a truly randomly selected and thus unpredictable future event, has been under investigation for more than three decades, and a recent conservative meta-analysis suggests that the phenomenon is real. ..."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3971164/

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