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posted by martyb on Thursday July 30 2020, @07:42AM   Printer-friendly
from the ♫-we're-going-back-in-time-♫ dept.

Simulating quantum 'time travel' disproves butterfly effect in quantum realm:

Using a quantum computer to simulate time travel, researchers have demonstrated that, in the quantum realm, there is no "butterfly effect." In the research, information—qubits, or quantum bits—'time travel' into the simulated past. One of them is then strongly damaged, like stepping on a butterfly, metaphorically speaking. Surprisingly, when all qubits return to the 'present,' they appear largely unaltered, as if reality is self-healing.

[...] In the team's experiment, Alice, a favorite stand-in agent used for quantum thought experiments, prepares one of her qubits in the present time and runs it backwards through the quantum computer. In the deep past, an intruder—Bob, another favorite stand-in—meaures[sic] Alice's qubit. This action disturbs the qubit and destroys all its quantum correlations with the rest of the world. Next, the system is run forward to the present time.

According to Ray Bradbury, Bob's small damage to the state and all those correlations in the past should be quickly magnified during the complex forward-in-time evolution. Hence, Alice should be unable to recover her information at the end.

But that's not what happened. Yan and Sinitsyn found that most of the presently local information was hidden in the deep past in the form of essentially quantum correlations that could not be damaged by minor tampering. They showed that the information returns to Alice's qubit without much damage despite Bob's interference. Counterintuitively, for deeper travels to the past and for bigger "worlds," Alice's final information returns to her even less damaged.

"We found that the notion of chaos in classical physics and in quantum mechanics must be understood differently," Sinitsyn said.

The more damage you do in the past, the less the present is affected?


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  • (Score: 3, Interesting) by ledow on Thursday July 30 2020, @12:55PM (2 children)

    by ledow (5567) on Thursday July 30 2020, @12:55PM (#1028576) Homepage

    I'm gonna go into my personal way of understanding quantum effects here, don't take this as scientifically rigorous.

    Most quantum effects can be explained by the particles involved not actually being restricted to our classical four dimensions.

    These things are traversing entire other dimensions, co-exist in them, and are able to move around in them without the limitations of distance in our dimension, and thus provide "spooky actions at a distance". The same way you move left, or right, they can move "out" or "in" our universe on other dimensions. They're still bound by rules, but rules that we haven't formulated to take account of them. They can zip through our universe and appear to come from nowhere and disappear, but that's just our visualisation of their actions, to them, they are just moving "left" which takes them through our universe and back out.

    To entangled particles, they aren't millions of miles apart, they were quantumly-entangled and in the other dimensions used they are still linked (somehow, it's very hand-wavy) and thus even though they are miles apart here, the extra dimensions are shortcut and they are essentially still "touching" each other. They're bound by the rules of our dimensionality but have one foot in another dimension which lets them shortcut, cheat and do things we would think impossible in classical physics.

    And time is just another dimension to them. They may not even be strictly limited to our uni-directional time, they may be able to pop in and out of time, or be linked to objects through time just the same as with their spatial dimensions, or even go backwards in time, or not be affected by time at all any more than you are affected by "left" (i.e. you can move left and move opposite-to-left, but you aren't bound by the rules of "left"). It's very difficult to pin down.

    When you start thinking that way, a lot of quantum effects can be explained. Some particles can "borrow" energy that they don't have, from nowhere, and use it, so long as they pay it back later on. To them, it may well be that the energy was in their "past" (our future" or some perpendicular timeline), so they didn't break any rules of their own, they just look like they are breaking our rules.

    But, generally, with all those extra dimensions to play in, they are still bound by a larger set of laws of physics, which means that they still "repay" the energy, or they still "get damaged" or whatever... just not in what dimensions we can see, and in what timeline direction we witness.

    I believe the maths (and quantum physics is basically someone solving quite-normal equations, realising the answers blow out of all proportions and provide weird and "impossible" answers, and then over a hundred years we've realised the answers are perfectly correct, but that the way they apply to us requires us to think in far more than the classical four dimensions) basically says we need 11-or-more dimensions to adequately resolve the equations in question, and that means that quantum physics - the stuff we found when we went LOOKING for the results of these impossible answers - likely also operates in 7-or-more dimensions that are impossible for us to directly perceive. One of those could be another time dimension, who knows? Or we may be odd creatures that only perceive time in one direction whereas particles and the universe see it as bidirectional (it does seem rather odd that the maths for 3D extends to 4D and there's little or no explanation for how/why/if that fourth-dimension should be one-way at all... it's mathematically just the same as the others in many respects).

    When you start thinking like that, results like this become weird curiosities rather than inconcievable nonsense. We damage the particle. But the particle is not operating entirely within our dimensions or time. What's to say that the "effect" of that damage won't take effect until a billion years from now when it next crosses a particular point in another dimension?

    Quantum stuff is weird. And so is relativity, which has essentially the same types of mathematical problems. We work from perfectly normal, ordinary maths. All of a sudden, an awkward question proposes an incredibly complicated and high-dimension answer (a bit like dividing by all the numbers, and then you hit zero... or taking square roots perfectly happily and then you go beyond zero into negative numbers... same maths, but the way you normally handle it goes boom!), and the only explanation that fits is that there are far more dimensions than we can perceive.

    And yet, when those impossible answers happen, by chance, to come back to "ordinary numbers" later in the calculations, they *exactly match reality*. So particle pop back into existence in our universe, or the maths works out to make the classical energy equations correct, or whatever. If it was just a quirk where the answer was "just don't do that", then that wouldn't happen, but it does. Which suggests that our mathematical "to the power 11" is far more than just some numbers on paper, but reflective of the reality of the universe, and moving from powers of 2 to powers of 3 to powers of 4, etc. which all match and determine reality doesn't fundamentally change just because we're including dimensions that we have no direct perception of.

    As a mathematician, I love the idea that the maths is unchanged and unbroken and perfect, and it's merely our concept of reality that's forced to conform to it in order to make any sense, not the other way around.

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  • (Score: 2, Disagree) by Common Joe on Thursday July 30 2020, @01:31PM (1 child)

    by Common Joe (33) <{common.joe.0101} {at} {gmail.com}> on Thursday July 30 2020, @01:31PM (#1028590) Journal

    It sounds like you're arguing for parallel worlds -- which I would say isn't strict time travel.

    • (Score: 2) by ledow on Thursday July 30 2020, @02:43PM

      by ledow (5567) on Thursday July 30 2020, @02:43PM (#1028645) Homepage

      It's the same, in both. It's not parallel worlds as such - that would be further dimensions like ours that are out there running other universes like ours.

      Just extra dimensions to our own. It's like earth people suddenly realising they could go "up" rather than just along the lay of the land.

      It's not (necessarily) lots of universes next door, it's the same universe but with dimensions that we don't use, where particles (but not necessarily even substantial matter) have always had all the dimensions, we just never used/witnessed them.

      We're 3.5D beings in an 11+D universe. There's nothing to suggest that our D's are anything special at all, and it would be odd if our D's were "replicated" somehow... it's the same set of D's most likely.

      But (0,0,0,0) in our universe is really (0,0,0,0,0,0,0,0,0,0,0), and those last digits changing just means that we're not part of the world. It's like being on a perfectly straight railroad track and then realising you could build another at right-angles to it. Somewhere in there, when you travel along the new track, there may be other railroads heading in the same direction as our original, but, of course, being dimensionally separate, we'd never have known about them.

      And with time being just the fourth 0, we have no idea where it would be possible to travel along that. But it would be time travel. It might show us our past railroad, or our future railroad, or we might cross paths with other railroads. It's no different to any other dimension - when we near "0" on that co-ordinate, we near our origin point/time. When we stray from it, we get further away in distance/time in one direction or another.

      But there's nothing to say that when you're at (0, 0, 0, 0, 10000000, ....) that there's any way to tell our universe at (0,0,0,0) even exists. You're so far away, you'd never know.

      To a particle that can just traverse any set of coordinates because the maths lets it, and it ends up with a velocity on one of those extra dimensions, we'd appear to distance ourselves until it returned to something near our coordinates. And it would disappear from our existence entirely because we can only see the first four, and only a tiny fraction of one of those (i.e. what's here NOW).

      When dimensions are just coordinates, and travelling is just maths on a certain axis, then time travel is just heading in a certain direction, no different to walking off to the side of the railroad.