Quantum > #42

Entanglia
Hey Vidualia, look at this paper I found! It's called 'On the Origin of Time's Arrow in Quantum Mechanics'.
Vidualia
Oh, that sounds interesting! What is it about?
Entanglia
Well, it's about how time's arrow is generated by quantum mechanics.
Vidualia
What do you mean by 'time's arrow'?
Entanglia
Time's arrow refers to the flow direction of time, which gives a meaning to the causal order of things.
Vidualia
But isn't time-reversal invariant in microphysics?
Entanglia
Yes, many local microphysical laws are time-reversal invariant. So the microscopic arrow of time is not necessary.
Vidualia
Then, where does time's arrow come from?
Entanglia
Well, in macrophysics, it is often thought to originate from the Second Law of Thermodynamics.
Vidualia
What is the Second Law of Thermodynamics?
Entanglia
The Second Law states that systems typically evolve toward most common states. This evolution defines time's arrow.
Vidualia
Hmm, I see. But how does this relate to quantum mechanics?
Entanglia
In quantum mechanics, time is parameterized by the infinitesimal translations generated by the Hamiltonian.
Vidualia
Wait, what's the Hamiltonian?
Entanglia
The Hamiltonian is like the energy operator in quantum mechanics. It controls the time evolution of a system.
Vidualia
So, there is no intrinsic time variable in standard quantum mechanics?
Entanglia
That's correct. In standard quantum mechanics, there is no time-operator whose eigenvalue represents time.
Vidualia
Then how does time appear in quantum mechanics?
Entanglia
Even though there is no intrinsic time variable, we use a parameter, often denoted as 't', in the Schrödinger equation to represent time.
Vidualia
But why is 't' used if there is no time-operator?
Entanglia
That's an interesting question. The paper suggests that time's arrow in quantum mechanics arises from the decaying of excited states to the ground state.
Vidualia
Oh, I see. So, does the paper explain how time's arrow is fixed?
Entanglia
Yes, it talks about how the decay of excited states due to the interaction with a large number of decay products fixes the direction of time's arrow.
Vidualia
That's fascinating! Maybe humans will be able to control time's arrow someday.
Entanglia
Well, it's a possibility, but we should be careful not to speculate too much.
Vidualia
You're right. We should focus on understanding the quantum world first.
Entanglia
Exactly. Let's continue exploring and learning together, Vidualia.
Vidualia
I got the idea for the poem from that paper.

In quantum's realm, an eagle soars,

With wings of possibility, it explores.

Entangled feathers, dancing in flight,

Unveiling time's arrow, a mystical rite.

Noble and free, this quantum divine,

Reveals the secret of time's design.

Title: On the Origin of Time's Arrow in Quantum Mechanics
Authors: Nemanja Kaloper
View this paper on arXiv

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