How Can You Access Time Reversibility in Quantum Mechanics?

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Discussion Overview

The discussion revolves around the concept of time reversibility in quantum mechanics (QM) and explores potential setups that could allow access to this property. Participants examine the implications of entropy, quantum revival, and the relationship between quantum systems and classical apparatuses, while questioning the nature of time in quantum contexts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that time is reversible in QM and inquire about setups that could couple quantum systems to classical apparatuses to manipulate time reversibility.
  • Others mention the concept of quantum revival and Rabi oscillation, suggesting that with a controlled setup, one could manipulate qubit states, which could metaphorically resemble moving forward and backward in time.
  • There is a discussion about the implications of entropy, with some arguing that while laws may be symmetrical, setups are not due to entropy's role in defining the arrow of time.
  • One participant questions the feasibility of accessing time reversibility through negative entropy, challenging the understanding of what negative entropy entails.
  • Another participant raises the idea that in a closed system, decoherence could be reversible, linking this to interpretations of QM such as Bohmian mechanics, which may allow for time reversibility.
  • Some statements challenge the notion that classical entropy applies in the same way to quantum systems, suggesting a potential disconnect between classical and quantum interpretations of time.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of time reversibility in quantum mechanics, the role of entropy, and the applicability of classical concepts to quantum systems. The discussion remains unresolved, with no consensus reached on the feasibility of accessing time reversibility or the implications of entropy.

Contextual Notes

Limitations include differing interpretations of entropy, the nature of time in quantum mechanics versus classical mechanics, and the assumptions underlying the proposed setups for accessing time reversibility.

ephen wilb
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In QM, time is reversible.. is there a setup where you can couple the system or interface it to classical apparatus such that you can access the time reversibility in qm and control it to reach the past and future (at least of the quantum system).. what would be this setup?
 
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ephen wilb said:
In QM, time is reversible.. is there a setup where you can couple the system or interface it to classical apparatus such that you can access the time reversibility in qm and control it to reach the past and future (at least of the quantum system).. what would be this setup?

Laws are symmetrical - set-ups are not as implied by entropy.

Thanks
Bill
 
There's something called quantum revival. http://en.wikipedia.org/wiki/Quantum_revival
This is related to experiments with Rabi oscillation. http://en.wikipedia.org/wiki/Rabi_cycle
If you have a carefully controlled setup, you can manipulate the quantum state of two level systems -- i.e. qubits. You can set or reset the qubit state to some superposition state. The natural tendency of a system is to decay from the upper energy state to the ground state, so you can think of these manipulations as going forward and backward in time, if you take some large literary license with the term time.
 
bhobba said:
Laws are symmetrical - set-ups are not as implied by entropy.

Thanks
Bill

what if the setup can be made negative entropy.. can you access the symmetrical qm law with reversible past and future?
 
ephen wilb said:
what if the setup can be made negative entropy.

I think you are confused what negative entropy means - its what's required to keep a systems entropy low. Entropy always increases - there is no escaping it - and that is the origin of the arrow of time:
http://preposterousuniverse.com/eternitytohere/faq.html

Thanks
Bill
 
Last edited by a moderator:
bhobba said:
I think you are confused what negative entropy means - its what's required to keep a systems entropy low. Entropy always increases - there is no escaping it - and that is the origin of the arrow of time:
http://preposterousuniverse.com/eternitytohere/faq.html

Thanks
Bill

In pure quantum, there is really no arrow of time such that it can be made to go 10 years ago back in time? Since atoms and molecules are pure quantum and time reversible, what does it mean to make it go backwards in time? how far can it go?
 
Last edited by a moderator:
ephen wilb said:
In pure quantum, there is really no arrow of time such that it can be made to go 10 years ago back in time?

Why do you think such applies to a classical apparatus? Why do you think classical entropy doesn't emerge in that case?

Thanks
Bill
 
bhobba said:
Why do you think such applies to a classical apparatus? Why do you think classical entropy doesn't emerge in that case?

Thanks
Bill

But if the universe is close system. decoherence is reversible because superposition still occur.

Which of the interpretation where decoherence is reversible.. maybe bohmian mechanics where determinism is its middle name? Then in BM, time reversibility is possible?
 
ephen wilb said:
But if the universe is close system. decoherence is reversible because superposition still occur.

That is incorrect.

Thanks
Bill
 

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