Consequences/applications of "negative time evidence" article in the news, like time-loop computers breaking most of current ciphers?

[Swank]

CPT symmetry says that if there is something, then its CPT analog is also possible - if there is causation forward in time, there needs to exist also backward.
So we are not talking about breaking any law, but accepting CPT symmetry of physics ( CPT symmetry - Wikipedia ).

It needs symmetric formulations: the least action principle, Feynman ensembles ... which need eternalism/Einstein's block universe philosophy of time: Eternalism (philosophy of time) - Wikipedia - in which we travel through some already found 4D solution.

Time-loops are possible, but they have to be self-consistent: Novikov self-consistency principle - Wikipedia
Time-loop computer would prepare situation that physics making time-loop self-consistent, would solve the given problem like cipher breaking ... all of them are already solved in the 4D solution we travel through.

Yeah, but it needs an element that we don't know if it actually exists or we can access. And that's always the problem speculation like this, vacuum energy, etc. The fact that you can observe the underlying principles of the universe is not the same as being able to manipulate them.


I did post about the fiction aspects of this technology. Did you read that?

 

[Jarek]

Feedback loops, where a function of the current output is used as a factor in the input, are common in control technologies

Such loop: "return input if correct, input+1 otherwise" could be indeed enclosed in space as feedback loop - with clock testing succeeding inputs until reaching solution of NP problem (among huge: exponential number of inputs).
Without clock it would be kind of electron hydrodynamics - that's a big question if it could be faster, I thought about it and am skeptical.

However, being able to close such loop in time: by sending output back to input, e.g. dozens of nanoseconds with Steinberg setting, physics through e.g. the least action principle should make it self-consistent, solving the given problem ...
... e.g. breaking a cipher: searching for a cryptographic key which leads to lowered entropy when used to decode the message.

You also didn't answer my question, which I may not have made clear. I wasn't even making any point about whether this breakthrough was proven or not, but that the observations are not synchronous with the effect. In order to act upon the observation of the effect there must be a time lag which is likely to be longer than the time between the response and impulse themselves. It matters not how many thousands of times the delay is repeated to create a much longer delay, because the observational delay will also be increased on each occasion too.

For time-loop computer dozens of nanoseconds might be sufficient - to calculate this "return input if correct, input+1 otherwise" in dedicated ASIC chip.
In Steinberg setting you would need to send each bit separately - the output bits control if there is impulse or not, the nanoseconds earlier medium response is sent to chip input.
Drawing it in space-time there is literally a loop, e.g. action optimization should make it self-consistent, this way solving the given problem.

As to a story where information travels backwards - that's kind of the death of consequence. And what is a story other than consequence? The First Fifteen Lives of Harry August demonstrates how a network of negative time information loops would allow information to travel back in major blocks. But that's with people, not devices that don't insert choice.

I haven't read this book, but I think the most physical (eternalism, Novikov self-consistency principle - Wikipedia ) SF of this type I know is 12 Monkey - persons jumping through spacetime, but finally everything turns as it was.
However, the only allowed by current physics effect to transport a person through spacetime seems wormhole (?)
For information alone it seems much easier, especially that CPT symmetry is at heart of physics - saying e.g. that if there exists causality forward in time, there exists also backward.

 

[Venusian Broon]

You also didn't answer my question, which I may not have made clear. I wasn't even making any point about whether this breakthrough was proven or not,

This isn't a breakthrough. We've known and physically shown "Superluminal" group velocities in materials with light since the 1980s.

Having read the paper, they don't talk about anything causality breaking because they know, of course, that's not what is happening. They actually state near the end: "While it is widely known that the group delay can take on negative values, associated with the peak of the transmitted portion of a pulse appearing at times which may indicate superluminal or negative group velocities..."

Also have a look at the Wikipedia article on Group Velocity:

Group velocity - Wikipedia

en.wikipedia.org

The final paragraphs of the Wikipedia articles discusses superluminal group velocities, it has a number of other links to papers that other experimenters have done. And, yes, "...there is no possibility that signals could be carried faster than the speed of light in vacuum..." as the article states. At least with all experiments done so far. (Maybe we can break causality with some other set up, who knows? . Probably need negative mass and some unobtanium...)

What were they actually trying to do? They are interested in what is happening with this negative group velocity effect on the very smallest scales and the atomic excitations caused by the photons. I think they were firing photons tuned to specific electron gaps in Rubidium to provoke the strongest light-matter interaction and see how that relates to the effect.

The science their doing seems legit, but their choice of title is a tad click-baity and seems to have confused quite a few people.

 

[Swank]

I haven't read this book, but I think the most physical (eternalism, Novikov self-consistency principle - Wikipedia ) SF of this type I know is 12 Monkey - persons jumping through spacetime, but finally everything turns as it was.
However, the only allowed by current physics effect to transport a person through spacetime seems wormhole (?)
For information alone it seems much easier, especially that CPT symmetry is at heart of physics - saying e.g. that if there exists causality forward in time, there exists also backward.

So you believe physics points to a closed causality loop?

The Harry August reference was to how a series of time loops could be linked to transmit information back much further than any one loop allows.

 

[Jarek]

@Venusian Broon , in their plots they get change of phase before the impulse - why somebody observing change of phase wouldn't receive information sent later?
In other settings like delayed choice quantum erasure, sending of information is forbidden due to postselection - which is also here, but due to use of impulses resembling single photons, what is not always successful - so what if using impulse resembling a thousand of photons?
Why increasing intensity would not just increase strength of the effect, just getting larger change of phase?

@Swank , physics is CPT symmetric, solved by the least action principle (classical) or Feynman ensembles (quantum) - single 4D solution minimizing action, or their weighted ensemble (especially near this classical least action solution).
Now preparing conditions for loop in such 4D solution, e.g. chip calculating "return input if correct, input+1 otherwise" and sending its output back to input, if all these steps are robust enough, e.g. action optimization should make them correct - what needs finding satisfying input, solving the given problem.
However, all these steps cannot be perfect, especially if there is no solution, action optimization would have to break some weakest link of such loop.

Related approach, also in theory able to solve NP problems, are two-way quantum computers (2WQC, Quantum AI Foundation - 2WQC ): exploiting the fact that if there exists state preparation process in CPT symmetric physics, there is also possible its symmetric analog - state postparation the same way enforcing the final state, e.g. by application of reversed state preparation impulse.

 

[Swank]

@Swank , physics is CPT symmetric, solved by the least action principle (classical) or Feynman ensembles (quantum) - single 4D solution minimizing action, or their weighted ensemble (especially near this classical least action solution).
Now preparing conditions for loop in such 4D solution, e.g. chip calculating "return input if correct, input+1 otherwise" and sending its output back to input, if all these steps are robust enough, e.g. action optimization should make them correct - what needs finding satisfying input, solving the given problem.
However, all these steps cannot be perfect, especially if there is no solution, action optimization would have to break some weakest link of such loop.

If you want to discuss science fiction, you'll have to use at least a little bit of plain language like a science fiction writer would.

 

[Jarek]

I am a scientist wanting to discuss consequences of technologies having current classification in Science Fiction, but with quickly growing evidence that they are incoming - like famous experimentalist just showing system response before impulse.

 

[Robert Zwilling]

The title one picks for anything has to attract attention or a lot of people won't even look at it. For reasonable articles there is a fine line between click bait and attention grabber. An earlier article about a compact reactor with the title "First-ever compact nuclear reactor runs for 8 years without water" seems to imply that a compact reactor has already run for 8 years without water. That gets attention and is totally not true.

The negative time event could be very interesting if it turned out that the nuclear structure was an extremely elastic three dimensional matrix. The matrix elements are either occuppied or not with various elementary particles, which pop in and out of existence. The space an atom is contained in could extend outside the space we think it is in, out past the electron shell. It has been shown that introducing a short small wobble in an outer electron spin also produced the same wobble in the nucleus spin. This could show that there is some kind of unseen linkage in the nuclear structure.

The time distortion has to do with the apparent timing of absorbing photons and then re-emitting them. It appears that the light is re-emitted before it is absorbed. The photons we are looking at could be place holders that show where energy was, on some kind of time delay as to what was happening in real time. The resulting light show could look to be out of phase or reflections of what was happening in real time. Which could mean our understanding of how the sub atomic and elementary particles interact is based on illusions instead of reality. Being able to communicate or influence the nucleus by touching the outer electron shells in specific ways could be a real starting point for practicing real magic.

 

[Jarek]

The time distortion has to do with the apparent timing of absorbing photons and then re-emitting them.

The clue is non-intuitive process indeed allowing to literally enforce atoms to re-emit: Stimulated emission - Wikipedia
The same laser can cause both absorption by target, and its stimulated emission - for example in STED microscopy - Wikipedia or Rabi cycle - Wikipedia

So we have two scenarios being analogs in CPT symmetry:
CPT(laser causes excitation) = CPT(laser) causes deexcitation
it is predicted by CPT symmetry and indeed both are applied e.g. in STED microscopes ... but if they are CPT analogs, then they have opposite delay sign - effect of one is later, so for the second should be earlier ... for example as observed for impulse source in the discussed "negative time evidence" in the news.

However, textbook view on stimulated emission has opposite photon direction - I have searched literature for experimental tests of this assumption (against CPT), but haven't found any - so it seems just guessed and repeated without reflections ...
... and it just needs experimental test - what is relatively simple, here proposed with many arguments, to be performed within weeks: https://arxiv.org/pdf/2409.15399 ... and if confirmed that CPT symmetry is right, leading e.g. to time-loop computers in a few months ...

 

[Tremendinah Rectiferus X]

 

[Jarek]

The most dangerous would be single players secretly developing and applying such technology e.g. to break current ciphers ...
If possible, and there are lots of arguments that it is relatively easy (if only not stubbornly assume its impossibility), such technology needs to be spread and developed all over the world ... e.g. allowing for crime, war prevention - usually based on actions secret before, what might be no longer possible for such widespread technology.

 

[Dave]

Do you foresee a world without any secrets? - a world where nothing can be kept secret and everyone can know everything? Now there is a SF story idea! What a frightening place. People would be scared witless if they knew what was being kept secret from them!

It couldn't happen though. It isn't only blockchain cyphers that protect information and there are still old fashioned physical methods.

 

[Jarek]

... but instead of incarceration before crime, potential criminal would know being caught, through e.g. the least action principle leading to 4D solution without this crime - to avoid inconsistent time loops ...

 

[Vladd67]

Do you foresee a world without any secrets? - a world where nothing can be kept secret and everyone can know everything? Now there is a SF story idea! What a frightening place. People would be scared witless if they knew what was being kept secret from them!

It couldn't happen though. It isn't only blockchain cyphers that protect information and there are still old fashioned physical methods.

Asimov wrote a short story involving a device for looking at the past which covered the loss of privacy and the death of secrets. The Dead past I believe it was called.

 

[Jarek]

I am afraid we are already approaching world without secrets - through electronics, AI ...
Being able to build time-loops, physics would optimize avoiding inconsistencies, would speed up this process, also approach of technological singularity ... also actively preventing arbitrage, gambling, crime, wars ... would lead to evaluations closer to real values, enforcing to focus on common goals instead of acting against other players - collaborations, more harmonic world ...

I have mixed feelings about such consequences, but, if possible, we don't have much choice, and it could be quite close ...

 

[Swank]

I am a scientist wanting to discuss consequences of technologies having current classification in Science Fiction, but with quickly growing evidence that they are incoming - like famous experimentalist just showing system response before impulse.

If you want to discuss science, find some scientists. If you want to discuss how a theory could be applied to story writing, you'll have to speak in the language of science fiction because almost no SF writers are theoretical physicists and converse in that technical jargon you are insisting on.

SF does not predict the future and it certainly doesn't provide guideposts that inspire future technology.

 

[Venusian Broon]

@Venusian Broon , in their plots they get change of phase before the impulse - why somebody observing change of phase wouldn't receive information sent later?

So this is a question about where does the 'information' on a pulse reside. It is very tempting to think that the peak of a photon pulse is where this resides, but information on the arrival of the photon is obtainable before the peak arrives.

Thus I think the mistake here is to assume the above and also to think that the peak of the output wave is related to the peak of the input wave. Other experiments on such systems looking at this find that they are not linked. The peak of the output wave is a result of a response to an earlier input (See M. W. Mitchell and R. Y. Chiao, B Causality and negative group delays in a simple bandpass amplifier, [ Amer. J. Phys., vol. 66,no. 1, pp. 14–19, 1998. for example.)

In the original case you refer to a photon is actually going through a medium. Because of EM/Matter interactions it's leading edge is being amplified, and its 'backend' is being dampened or distorted, therefore changing the shape of pulse and altering the phase of the peak.

What is not happening is that they are picking up a output signal before an input signal is even sent in.

Personally what I think this all means is that if you are just waiting for a photon to register, looking at some output from such a device, you'd probably not be able to register the difference immediately between a photon that has received this change of phase and a photon that did not. To do so you'd need to make multiple measurements of multiple photons to plot out the actual shape of both sets of photons, which defeats any temporal gains.

I suppose you could argue, "why don't I increase the sensitivity of my photon meter so that I can pick up the shifted leading edge of my negative time photon?" But then you'll likely also be picking up much more noise and therefore would be have many more false positives and therefore not have a true signal.

In other settings like delayed choice quantum erasure, sending of information is forbidden due to postselection - which is also here, but due to use of impulses resembling single photons, what is not always successful - so what if using impulse resembling a thousand of photons?
Why increasing intensity would not just increase strength of the effect, just getting larger change of phase?

Yes I believe you can change the phase change depending on your experimental set up. They stated that they expected an imparted phase shift of between 10-20 micro rads (That's about 1e-3 degrees for those who are scratching their heads over the term rad!). Anyway there would be a maximum phase shift you can possibly get, namely 180 degrees That would shift the peak of the photon by half it's wavelength (I think this is around about 780nm for the transition for Rubidium, but I may be wrong - anyway, not much!) Any more and you will start to return your photon back to its original state, and obviously the output signal would just look identical to the input signal if you shifted everything 360 degrees.

I fully admit that I don't know what is experimentally possible for phase changes from negative refractive indices. All the literature I see seems to suggest it's pretty small, as given above.

I believe that this phase change is not dependent on the intensity of the signal (and even if it was, if you pumped in a higher intensity and that increased the phase change, because the phase change is cyclical, you can only get a maximum when the set up coincides with the maximum change of 180 degrees as stated.)

----

In this experiment, because they were probing what was happening to the transition times of Rubidium atoms and they were utilising something called the Kerr interaction to provide the necessary antistrophic effect from the Rubidium, they fired in a continuous stream of photon pulses each about 600 ns apart and because of the background noise they stated that it took them about 10 hours to collect enough date for 'a single set of parameters'. i.e. the Kerr interaction scatter was very weak. My guess is if you increased the signal intensity in this particular experimental set up would swamp the signal you were trying to measure. (?)

Furthermore with regards to the experiment, from their abstract they state: "Our results, over a range of pulse durations and optical depths, are consistent with the recent theoretical prediction that the mean atomic vexcitation time caused by a transmitted photon (as measured via the time integral of the observed phase shift) equals the group delay experienced by the light."

This is quite interesting because thinking of this whole process in a classical wave-like manner is not particularly fascinating - you are just changing the phase of an incoming wave and distorting it a little - but it raises the question on the quantum level, what is happening to the atom in it's excited state when the system is experiencing a negative group delay?

 

[Jarek]

@Swank , Who are you gonna call ... before technology changes status from Science Fiction to reality?
Scientists are too careful for such discussions ... I could only think of futurologists, SF people (?)
I talk with scientists about the test ( https://arxiv.org/pdf/2409.15399 ), but if CPT symmetry remains valid (lots of arguments), then e.g. time-loop computers breaking ciphers seem weeks away, and humanity is not prepared ... even worse if it is already secretly used ...

@Venusian Broon , thanks, I will take a look at the articles ... but this is just a first official setting of this kind, very different from studied like delayed choice quantum erasure - there will be next, simplified, practical ...

I believe, as e.g. in STED microscopy laser causes both excitation and deexcitation of target, this is also true for impulse source of this "negative time evidence" experiment.
And these two causalities swap places if applying CPT symmetry - what means they have opposite sign of delay, leading to ~time symmetric response as they observe ... if so, e.g. below STED-like setting is sufficient - do you maybe have any counterarguments?

 

[Christine Wheelwright]

Do you foresee a world without any secrets? - a world where nothing can be kept secret and everyone can know everything? Now there is a SF story idea! What a frightening place. People would be scared witless if they knew what was being kept secret from them!

It couldn't happen though. It isn't only blockchain cyphers that protect information and there are still old fashioned physical methods.

Isn't this the philosophy of Julian Assange and Wikileaks? "Privacy for the weak, transparency for the powerful."

 

[Dave]

I have no idea what they stand for, sorry. And I guess we should stay away from real world examples as it will quickly become a discussion of current affairs. I do know that the problem today isn't too little information being available, but rather sorting out what is real from the manufactured (or truth from falsehoods, or in other words, pure lies.)