Have researches managed to “reverse time” and if so, what does that mean for physics? [on hold]
$begingroup$
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
edited 6 hours ago
knzhou
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
$endgroup$
put on hold as too broad by WillO, Jon Custer, GiorgioP, ZeroTheHero, Chair 4 hours ago
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
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
edited 6 hours ago
knzhou
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
$endgroup$
put on hold as too broad by WillO, Jon Custer, GiorgioP, ZeroTheHero, Chair 4 hours ago
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
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
edited 6 hours ago
knzhou
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
$endgroup$
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
quantum-mechanics thermodynamics quantum-entanglement time-reversal-symmetry arrow-of-time
edited 6 hours ago
knzhou
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
edited 6 hours ago
knzhou
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
edited 6 hours ago
knzhou
44.9k11122217
edited 6 hours ago
knzhou
44.9k11122217
edited 6 hours ago
knzhou
44.9k11122217
44.9k11122217
asked 8 hours ago
Omar Einstein Omar Einstein
13416
asked 8 hours ago
Omar Einstein Omar Einstein
13416
asked 8 hours ago
Omar Einstein Omar Einstein
13416
13416
put on hold as too broad by WillO, Jon Custer, GiorgioP, ZeroTheHero, Chair 4 hours ago
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
put on hold as too broad by WillO, Jon Custer, GiorgioP, ZeroTheHero, Chair 4 hours ago
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
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.
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
$endgroup$
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
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.
answered 8 hours ago
PhysicsDavePhysicsDave
98647
$endgroup$
add a comment |
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
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.
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
$endgroup$
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
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.
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
$endgroup$
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
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.
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
$endgroup$
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.
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
answered 7 hours ago
Mitchell PorterMitchell Porter
7,91011344
7,91011344
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
add a comment |
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I think I disagree with this answer. Where is there any notion of a thermodynamic process in this paper? It looks like deterministic control of a coherent 2-qubit system, in which case entropy isn't even a sensible quantity as far as I can tell.
$endgroup$
– DanielSank
5 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
I may have been misled by the press release, which clearly implies that the "time reversal" involves evolution "from chaos to order". Though what if you consider the von Neumann entropy of the individual qubits?
$endgroup$
– Mitchell Porter
2 hours ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
$begingroup$
Did you read the paper?
$endgroup$
– DanielSank
12 mins ago
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.
answered 8 hours ago
PhysicsDavePhysicsDave
98647
$endgroup$
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.
answered 8 hours ago
PhysicsDavePhysicsDave
98647
$endgroup$
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.
answered 8 hours ago
PhysicsDavePhysicsDave
98647
$endgroup$
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.
answered 8 hours ago
PhysicsDavePhysicsDave
98647
answered 8 hours ago
PhysicsDavePhysicsDave
98647
answered 8 hours ago
PhysicsDavePhysicsDave
98647
answered 8 hours ago
PhysicsDavePhysicsDave
98647
98647
add a comment |
add a comment |
