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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?
(Score: 4, Insightful) by BsAtHome on Thursday July 30 2020, @07:57AM (9 children)
The result then begs the question whether or not the universe is deterministic.
Is the outcome predetermined if changes made to the initial state do not propagate? That would also mean that the world of quantum probabilities may collapse into a (or the same) deterministic system regardless the initial state. Funny then, that we can't determine anything at the quantum level when its result at the macro level apparently does not change.
(Score: 3, Informative) by leon_the_cat on Thursday July 30 2020, @08:37AM
https://www.technologyreview.com/2019/03/12/136684/a-quantum-experiment-suggests-theres-no-such-thing-as-objective-reality/ [technologyreview.com]
(Score: 5, Informative) by aristarchus on Thursday July 30 2020, @08:51AM (5 children)
NO!!!!! It does not "beg the question"! In that case, it would just be arguing in a circle! Like, "the universe is deterministic because everything in it is necessary consequence of a cause". That is question begging. Or, "things happen for no reason, because there is no reason for things to happen". THAT is begging the question. Now just RAISING the question (my ancient Greek Hecate god, how many times do we have to go over this!) of whether the universe if deterministic or totally random and nonsensical to the point where no rational being could even
begraise the question of whether it was, . . . well, we have answered that, then, haven't we? Unless those rational beings cannot even grasp the meaning of "begs the question". Then we are all truly fucked.I like to cite Grammar Girl, since she gets it wrong: https://www.quickanddirtytips.com/education/grammar/begs-the-question [quickanddirtytips.com]
And, of course, the Grammarist: https://grammarist.com/rhetoric/begging-the-question-fallacy/ [grammarist.com]
Of course, for the handy business cards: http://begthequestion.info/ [begthequestion.info]
Now write it one hundred times! Ex Romani Domus Petitio Principii Excoriatorum.
(Score: 5, Funny) by leon_the_cat on Thursday July 30 2020, @09:03AM (1 child)
lol u need some catnip.
(Score: 0) by Anonymous Coward on Thursday July 30 2020, @07:04PM
What he really needs is a mirror
(Score: 0) by Anonymous Coward on Friday July 31 2020, @07:02AM (1 child)
It's an idiomatic phrase. The individual words in the phrase don't matter, just the use of the phrase as a whole, and "begs the question" to mean "raises the question" is far more common to the point where people bringing up the issue of something assuming the conclusion is true will just outright say the words "assumes the conclusion".
In fact, the fucking name in that latter sense is still idiomatic, because it's a terrible, terrible translation of the Latin phrase (which was also altered a bit from the Greek it derived from).
(Score: 2) by aristarchus on Friday July 31 2020, @10:16AM
You are begging the question. Or looking for a beating. It is a technical usage, and the common usage is based on an illiterate similarity. The Greek is nothing like the Latin, it is τὸ ἐξ ἀρχῆς. So your entire objection is something of a damp squid. It is rough to be stupid and wrong like this, but at least it is better than being stupid and right, because it gives you plausible deniability.
(Score: 2) by corey on Friday July 31 2020, @11:15AM
Bloody hell, he got a +5 and I don't have any idea what he said!
(Score: 4, Interesting) by Non Sequor on Thursday July 30 2020, @02:13PM (1 child)
Any system is deterministic if you mutliplex the hell out of it so that all possible initial conditions are paired off with possible outcomes in a many to many relationship. Nondeterminism comes from picking a specific thread.
This is a consequence of the linearity of quantum mechanics. It's easiest to follow for the discrete time model using matrix mechanics. (You can approximate the continuous time, general system case from discrete time systems of qubits.) You have a system state (as a linear combination of pure states) at time zero and you have a evolution operator U that represents performing some interaction (e.g. applying a magnetic field) on the system for a time increment. U acts on pure states (e.g. electron with known spin) in the same linear way as it acts on mixed states (e.g. electron with known superposition of up and down states or experimental ensemble of random up and down states). Each state gets mapped to one or more outcomes, proportional to the probability amplitude for that state (think of it as the fraction of the system that is in that state). Linear.
Your operator U is unitary, meaning that it preserves the fact that the probability amplitudes for all of the pure states that make up the superposition sum to 1. Being unitary means that U is invertible and that in fact its inverse is its conjugate transpose. If you have solved for a matrix that represents a forward time increment for a system, it is trivial to calculate the matrix for undoing the interaction you've performed. If you are simulating that matrix in a quantum computer, you can just as easily simulate the reverse direction with the same number of qubits. This is a peculiarity of quantum mechanics: there is nothing particularly special about the way processes run forward in time. On paper, time reversal is generally equally plausible. With quantum field theory, time reversal does impose the condition that all charges need to be flipped and the position coordinates need to be mirrored for both directions to obey the laws of physics, but these are not really radical distinctions between forward time and reverse time.
So move time one direction, disturb the system, move time the other direction, the influence of the disturbance is linear. This is at odds with the classical result where most non-trivial systems exhibit exponential sensitivity to disturbances in initial conditions (chaos). This kind of feels like a variation on Lochsmidt's paradox: you can't derive the second law of thermodynamics from time-symmetric dynamics. On the other hand, gravity, which has resisted description as a quantum phenomenon has a distinct time-asymmetry: the charges for gravity are all positive and the time reversal does not obey the same law of gravity as the forward time version. There's not a complete picture of how to reconcile all of this.
Write your congressman. Tell him he sucks.
(Score: 2) by corey on Friday July 31 2020, @11:17AM
Yeah this is another one, +4 and I got two sentences in. Maybe people are modding because it sounds informative?