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Quantum entanglement, two-sided spacetimes and the thermodynamic arrow of time (arxiv.org)
44 points by ovidiu69 40 days ago | hide | past | web | favorite | 13 comments

Probably a basic question, but if entropy is causally connected to time, why don't different locales have different rates of time based on how rapidly the local environment is moving toward greater entropy.

That is, in deep space almost nothing is happening while here on earth a lot is happening to increase entropy, so why does time go at the same speed in both places?

Well, deep space is still causally connected to the universe around it (through EM and gravitational radiation), which means there is entropy of a sort. Maybe in deep deep space (a hypothetical void beyond our cosmological horizon), with no light at all, you could argue there is no entropy or passing of time. And there'd be no observation you could make that would invalidate that claim.

Even in some hypothetical void, you’d have the quantum vacuum state. So via quantum mechanics you can have particles pop into and out of existence, providing you with a way to gauge the passing of time even in otherwise completely empty spacetime.

> Even in some hypothetical void, you’d have the quantum vacuum state.

One could imagine that beyond some cosmological horizon the rules of physics as we know them break down and there is no zero point energy.

Normally you think of the rules of physics breaking down at a singularity point, say, beyond a black hole's event horizon or at the start of the big bang. If you subscribe to the idea that the big bang event shaped the laws of physics we know, then beyond the horizon of the "expanding" big bang, those laws won't necessarily apply.

I put expanding in quotes because I subscribe to the idea of a holographic universe. I like to think that while the universe may appear to be expanding at an accelerated pace to us, you can also think of our universe as shrinking within a fixed boundary. (Fixed relative to what?)

For example, imagine a 2D holographic plate (our true plane of existence), through which you can view an image of a 3D virtual object (our perceived plane of existance). Now imagine the interference pattern on that plate is dynamic and increases in entropy, defining and arrow of time for the objects in the 3D virtual image. The plate doesn't change size, but the complexity of the interference pattern increases, creating increasingly finer and finer details, such that from the perspective of a virtual object, everything appears to be expanding, but from an outside observer's perspective the holographic image appears to be shrinking as the entropy increases.

I'm no physicist, but I wasn't sure whether the goings on of quantum mechanics (virtual particles) in a vacuum is sufficient for entropy to occur. It seems like a timeless process, with forward and backward interactions equally likely. Of course, if the underlying fields are slowly changing with time, then that would likely be entropic.

Good point. But I think there is a distinction between measuring entropy and the passing of time. From my understanding entropy provides the arrow of time, meaning the non symmetrical past vs future. Whereas time by itself could still be measured as flowing, though whether forward or backward you may not be able to determine.

Obviously if something like a human brain was there to observe things, you'd have the entropy of your neurons to be sure of the direction as well. =D

It doesn’t - Special / General Relativity demonstrates gravitational time dilation.

So you mean our simulation doesn't bother calculating the state of empty areas on which there are few or no other dependent states which depend in a statistically significant way upon that empty state?

Not just gravitational. The stress energy tensor includes an energy term. Hot things warp spacetime too.

Entropy is causal of the arrow of time. In deep space, going forward on time doesn't look that different than going backward in time. Going faster forward in time also doesn't look that different than going slowly forward. The difference is in our perception of time, not in time itself.

Based on initial conditions, the two-sided spacetime behaves differently with respect to the (thermodynamic) arrow of time.

If the initial conditions are of low correlation, the two sides move in opposite time directions, but the structure as a whole follows the thermodynamic arrow of time.

If the initial conditions are of high correlation, the individual entropies of the two sides can increase and decrease, there is not a dominance over time direction, and the overall structure is that of a one-sided spacetime.

So, their argument on the dual structure is:

less correlation = more disconnection between spacetime forming two-sided geometry

more correlation = more connection, forming one-sided geometry

Remember, though, that we are looking at dual views: gravity vs. quantum information theory and depending from which view you are describing, the words used to describe the system would be different. For example, two-sidedness in geometry refers to the gravity view.

Another explanation for how time can be an emergent property of entanglement:


The point here is the universe has two sides; we can only observe one side. On the other side of the universe the time runs backward, from the future to the past. If one, by any chance, would traverse to the other side, will "grow" younger.

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