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Have researches managed to “reverse time” and if so, what does that mean for physics?

Why does the low entropy at the big bang require an explanation? (cosmological arrow of time)Time Reversal Invariance in Quantum MechanicsSecond law of thermodynamics and the arrow of time: why isn't time considered fundamental?Time-reversed twin paradoxWhat does it mean to say that “remembering the future and not the past?”Does conservation of information mean that the direction of causality is arbitrary?Demystifying time-reversal symmetry in physicsreverse entropy, reverse causality and physical lawsWhat goes wrong, theoretically, when we reverse time?Are Mirrored Universes With Opposing Directions of Time Theoretically possible?

3

1

$begingroup$

According to press releases, researchers have reversed time in a quantum computer and violated the second law of thermodynamics. What does that mean for physics? Will it allow time travel?

Further information:

• "Arrow of time and its reversal on the IBM quantum computer" (2019-03-13)




• "Physicists reverse time using quantum computer" (2019-03-13)

quantum-mechanics thermodynamics quantum-entanglement time-reversal-symmetry arrow-of-time

share|cite|improve this question

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

$endgroup$

add a comment | 

3

1

$begingroup$

According to press releases, researchers have reversed time in a quantum computer and violated the second law of thermodynamics. What does that mean for physics? Will it allow time travel?

Further information:

• "Arrow of time and its reversal on the IBM quantum computer" (2019-03-13)




• "Physicists reverse time using quantum computer" (2019-03-13)

quantum-mechanics thermodynamics quantum-entanglement time-reversal-symmetry arrow-of-time

share|cite|improve this question

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

$endgroup$

add a comment | 

$begingroup$

According to press releases, researchers have reversed time in a quantum computer and violated the second law of thermodynamics. What does that mean for physics? Will it allow time travel?

Further information:

• "Arrow of time and its reversal on the IBM quantum computer" (2019-03-13)




• "Physicists reverse time using quantum computer" (2019-03-13)

quantum-mechanics thermodynamics quantum-entanglement time-reversal-symmetry arrow-of-time

share|cite|improve this question

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

$endgroup$

share|cite|improve this question

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

share|cite|improve this question

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

edited 27 mins ago

knzhou

44.9k11122217

edited 27 mins ago

knzhou

44.9k11122217

asked 2 hours ago

Omar Einstein Omar Einstein

13115

asked 2 hours ago

Omar Einstein Omar Einstein

13115

2 Answers
2

active

oldest

votes

10

$begingroup$

They did not reverse time, they reversed the "arrow of time", meaning that time continued forward but entropy decreased a little, for a moment. Small temporary violations of the second law happens spontaneously all the time on a microscopic scale, wherever the thermal energy comes together in just the right way to be absorbed into an atom or molecule. It is the same thing as "wind assembles fragments back into unbroken object" except that the macroscopic version is so unlikely as to never actually happen.

In this case a quantum computer performed an entropy-decreasing operation. Basically they simulated one of those unlikely entropy-decreasing fluctuations, and because quantum computers utilize coherent quantum states, the simulation itself involved a decrease in entropy. But it was not a fluctuation in the quantum computer, the quantum computer was steered by careful control along the reverse path.

This method will not be used to raise the dead, unspill cups of coffee, take back stupid actions, or any of the other practical applications of reversing the arrow of time, because it can only be applied to quantum systems that were completely under external observation and control from the beginning.

share|cite|improve this answer

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

$endgroup$

add a comment | 

0

$begingroup$

It just means they can make a couple of quits go back to the state they were originally in, and they can do this in a determinable way. In that very small universe all the EM forces, and EM forces essentially determine time (like we have a gazillion or infinite number of EM forces in our universe that determine time), went to a state they had previously been in, this would be impossible in our bigger universe. No it's not time travel, its just physicists controlling a very small universe.

share|cite|improve this answer

answered 2 hours ago

PhysicsDavePhysicsDave

95647

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add a comment | 

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10

$begingroup$

They did not reverse time, they reversed the "arrow of time", meaning that time continued forward but entropy decreased a little, for a moment. Small temporary violations of the second law happens spontaneously all the time on a microscopic scale, wherever the thermal energy comes together in just the right way to be absorbed into an atom or molecule. It is the same thing as "wind assembles fragments back into unbroken object" except that the macroscopic version is so unlikely as to never actually happen.

In this case a quantum computer performed an entropy-decreasing operation. Basically they simulated one of those unlikely entropy-decreasing fluctuations, and because quantum computers utilize coherent quantum states, the simulation itself involved a decrease in entropy. But it was not a fluctuation in the quantum computer, the quantum computer was steered by careful control along the reverse path.

This method will not be used to raise the dead, unspill cups of coffee, take back stupid actions, or any of the other practical applications of reversing the arrow of time, because it can only be applied to quantum systems that were completely under external observation and control from the beginning.

share|cite|improve this answer

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

$endgroup$

add a comment | 

10

$begingroup$

They did not reverse time, they reversed the "arrow of time", meaning that time continued forward but entropy decreased a little, for a moment. Small temporary violations of the second law happens spontaneously all the time on a microscopic scale, wherever the thermal energy comes together in just the right way to be absorbed into an atom or molecule. It is the same thing as "wind assembles fragments back into unbroken object" except that the macroscopic version is so unlikely as to never actually happen.

In this case a quantum computer performed an entropy-decreasing operation. Basically they simulated one of those unlikely entropy-decreasing fluctuations, and because quantum computers utilize coherent quantum states, the simulation itself involved a decrease in entropy. But it was not a fluctuation in the quantum computer, the quantum computer was steered by careful control along the reverse path.

This method will not be used to raise the dead, unspill cups of coffee, take back stupid actions, or any of the other practical applications of reversing the arrow of time, because it can only be applied to quantum systems that were completely under external observation and control from the beginning.

share|cite|improve this answer

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

$endgroup$

add a comment | 

$begingroup$

They did not reverse time, they reversed the "arrow of time", meaning that time continued forward but entropy decreased a little, for a moment. Small temporary violations of the second law happens spontaneously all the time on a microscopic scale, wherever the thermal energy comes together in just the right way to be absorbed into an atom or molecule. It is the same thing as "wind assembles fragments back into unbroken object" except that the macroscopic version is so unlikely as to never actually happen.

In this case a quantum computer performed an entropy-decreasing operation. Basically they simulated one of those unlikely entropy-decreasing fluctuations, and because quantum computers utilize coherent quantum states, the simulation itself involved a decrease in entropy. But it was not a fluctuation in the quantum computer, the quantum computer was steered by careful control along the reverse path.

This method will not be used to raise the dead, unspill cups of coffee, take back stupid actions, or any of the other practical applications of reversing the arrow of time, because it can only be applied to quantum systems that were completely under external observation and control from the beginning.

share|cite|improve this answer

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

$endgroup$

share|cite|improve this answer

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

answered 1 hour ago

Mitchell PorterMitchell Porter

7,82011343

0

$begingroup$

It just means they can make a couple of quits go back to the state they were originally in, and they can do this in a determinable way. In that very small universe all the EM forces, and EM forces essentially determine time (like we have a gazillion or infinite number of EM forces in our universe that determine time), went to a state they had previously been in, this would be impossible in our bigger universe. No it's not time travel, its just physicists controlling a very small universe.

share|cite|improve this answer

answered 2 hours ago

PhysicsDavePhysicsDave

95647

$endgroup$

add a comment | 

0

$begingroup$

It just means they can make a couple of quits go back to the state they were originally in, and they can do this in a determinable way. In that very small universe all the EM forces, and EM forces essentially determine time (like we have a gazillion or infinite number of EM forces in our universe that determine time), went to a state they had previously been in, this would be impossible in our bigger universe. No it's not time travel, its just physicists controlling a very small universe.

share|cite|improve this answer

answered 2 hours ago

PhysicsDavePhysicsDave

95647

$endgroup$

add a comment | 

$begingroup$

It just means they can make a couple of quits go back to the state they were originally in, and they can do this in a determinable way. In that very small universe all the EM forces, and EM forces essentially determine time (like we have a gazillion or infinite number of EM forces in our universe that determine time), went to a state they had previously been in, this would be impossible in our bigger universe. No it's not time travel, its just physicists controlling a very small universe.

share|cite|improve this answer

answered 2 hours ago

PhysicsDavePhysicsDave

95647

$endgroup$

share|cite|improve this answer

answered 2 hours ago

PhysicsDavePhysicsDave

95647

answered 2 hours ago

PhysicsDavePhysicsDave

95647

answered 2 hours ago

PhysicsDavePhysicsDave

95647