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Quantum Entanglement Drives the Arrow of Time

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Re: Quantum Entanglement Drives the Arrow of Time

#71

Post by 3rd3 »

sheerun wrote: post #69

I love following article: http://www.flownet.com/ron/QM.pdf It basically shows that observation (measurement) and entanglement are the same things. Think about it: particles are not magically going out of superposition as we observe (measure) them. We (our atoms) become entangled with those particles, we become superposition. It's just propagation of entangled state. Why we don't perceive ourselves as in superpositio…

I have a question: What does being in a superposition mean exactly here? I only know the term from classical mechanics, e.g. that an acceleration vector in R^3 can be seen as a superposition of three accelerations along the base vectors (a linear combination).

Re: Quantum Entanglement Drives the Arrow of Time

#72

Post by [deleted] »

mbq wrote: post #64

This is nonsense; entropy and the arrow of time are essentially a many-body effects and require no quantum effects to occur. A simplest way to see it is to make small simulation of a, say, 1000 gas particles with only classical bouncing in a one side of a box partitioned in half with a barrier, obviously with a time-reversible numerical method -- after the removal of the barrier the gas will evenly spread over the bo…

[deleted]

Re: Quantum Entanglement Drives the Arrow of Time

#73

Post by sheerun »

3rd3 wrote: post #71
sheerun wrote: post #69

I love following article: http://www.flownet.com/ron/QM.pdf It basically shows that observation (measurement) and entanglement are the same things. Think about it: particles are not magically going out of superposition as we observe (measure) them. We (our atoms) become entangled with those particles, we become superposition. It's just propagation of entangled state. Why we don't perceive ourselves as in superpositio…

I have a question: What does being in a superposition mean exactly here? I only know the term from classical mechanics, e.g. that an acceleration vector in R^3 can be seen as a superposition of three accelerations along the base vectors (a linear combination).

Superposition in sense of linear combination of quantum states. For example 2-state superposition is qubit.

If you think about systems can be in superposition only relative to one another. For example in double slit experiment light is in superposition relative to us, but not relative to photon from other slit. Or maybe photon in one slit does not exist in timeline of photon from other slit? I don't know :)

Re: Quantum Entanglement Drives the Arrow of Time

#74

Post by Houshalter »

Just a thought that I've been thinking about. Time has a direction because of causation. State1 causes state2 which causes state3 and so on. You get weird paradoxes if you allow causation to work in both directions. The universe would also have to magically align everything perfectly so that everything is consistent.

Another observation is that even with reversible laws of physics that can work in both directions, if you have a single starting state, all other states will causally propagate from it. In a single dimension of time/causation.

Re: Quantum Entanglement Drives the Arrow of Time

#75

Post by jpeterson »

Houshalter wrote: post #74

Just a thought that I've been thinking about. Time has a direction because of causation. State1 causes state2 which causes state3 and so on. You get weird paradoxes if you allow causation to work in both directions. The universe would also have to magically align everything perfectly so that everything is consistent. Another observation is that even with reversible laws of physics that can work in both directions, if…

Causation relies on a particular direction of time, not the other way around.

For example, suppose you have two billiard balls, A and B. In our world, A travels from left to right, strikes B, and then B flies off to the right.

We would say A striking B caused it to fly off.

But an observer moving through time in the opposite direction would be no less justified to claim:

B travelled from right to left, struck A, and caused A to fly off to the left!

Re: Quantum Entanglement Drives the Arrow of Time

#76

Post by loup-vaillant »

arethuza wrote: post #62
loup-vaillant wrote: post #57

Earlier quoted context omitted.

I must say, I'm not sure what he even means by this "zero universe" business. Sure, the classical illusion is bust, but the wave function itself, as far as we know, is real, is it not? While we're at throwing quantum explanation links, here is the Quantum Physics Sequence on Lesswrong: http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ I'd say the math is even simpler there, yet the explanation go deeper. It's…

Doesn't it depend on what it means for a theoretical construct to be "real" or not? Isn't "does it work" a better question?

Don't get confused by simple words such as "real". It means what it obviously mean in everyday life.

For instance, apples are real, and gravity is real. So when you drop an apple, what happens? It falls. Now what really, ultimately happens? It falls.

Re: Quantum Entanglement Drives the Arrow of Time

#77

Post by jpeterson »

mbq wrote: post #64

This is nonsense; entropy and the arrow of time are essentially a many-body effects and require no quantum effects to occur. A simplest way to see it is to make small simulation of a, say, 1000 gas particles with only classical bouncing in a one side of a box partitioned in half with a barrier, obviously with a time-reversible numerical method -- after the removal of the barrier the gas will evenly spread over the bo…

I had the same thought.

For any combined system, i.e. a situation where you've combined two systems such as the hot cup of coffee and the cool room, the number of "dispersed" states is far greater than the number of non-dispersed states. So any change of state is far more likely to be in the dispersed direction.

The article didn't make it clear what role entanglement plays in this.

Re: Quantum Entanglement Drives the Arrow of Time

#79

Post by loup-vaillant »

mbq wrote: post #64

This is nonsense; entropy and the arrow of time are essentially a many-body effects and require no quantum effects to occur. A simplest way to see it is to make small simulation of a, say, 1000 gas particles with only classical bouncing in a one side of a box partitioned in half with a barrier, obviously with a time-reversible numerical method -- after the removal of the barrier the gas will evenly spread over the bo…

yet, once the particles are spread, if you somehow reverse their velocities, they will concentrate back to one half.

Yet we can never do that. Why do you think?

The obvious answer in a classical universe is that we simply don't know the velocity and position of each particle, so we can't just reverse them. To pull such a feat, we'd have to be incredibly lucky, as in "winning every lottery for a century" lucky.

With entanglement and de-coherence however, such reversal becomes impossible even in principle: see, when the universe splits through de-coherence, you no longer have access to the other half. Even if you manage to reverse your half of the universe, you need the other half to be reversed too, or they'll never merge back together.

And not just the other half, since de-coherence happens all the time. You need all the Everett branches to be reversed. No. Way. So it does look like a better candidate for the arrow of time.

(Of course, a better candidate still would be collapse interpretation, since that one is not time reversible in the first place. But this interpretation is ridiculous to begin with, so let's ignore it.)

---

Read this to have an idea of how time could work in a timeless universe: http://lesswrong.com/lw/qr/timeless_causality/

Re: Quantum Entanglement Drives the Arrow of Time

#80

Post by Houshalter »

jpeterson wrote: post #75
Houshalter wrote: post #74

Just a thought that I've been thinking about. Time has a direction because of causation. State1 causes state2 which causes state3 and so on. You get weird paradoxes if you allow causation to work in both directions. The universe would also have to magically align everything perfectly so that everything is consistent. Another observation is that even with reversible laws of physics that can work in both directions, if…

Causation relies on a particular direction of time, not the other way around. For example, suppose you have two billiard balls, A and B. In our world, A travels from left to right, strikes B, and then B flies off to the right. We would say A striking B caused it to fly off. But an observer moving through time in the opposite direction would be no less justified to claim: B travelled from right to left, struck A, and…

Yes, reversible laws of physics are possible. State1 can cause state2, and state2 can cause state1.

Here is the question: Do you pick a state for state1 and then figure out what state2 should be from it (that is, cause state2)? Or do you pick a state for state2 and figure out what state1 should be (causing state1)?

If you have a "starting state", it doesn't matter if the time is reversible. All states will be caused by the starting state propagating forward in one direction. This is exactly what we seem to observe in the real universe. The big bang starts the universe and everything appears to be a chain of cause and effect from it. We never observe events that are caused by things in the future. Glasses do not spontaneously assemble themselves out of shards and fly on top of tables. Photons do not just spontaneously fly from all directions in space to form sensible images on Earth.

Now you might say "what if the universe somehow decided on all the states at once". Well that isn't what appears to be true in our universe for one (or you'd have things spontaneously happening in the future and then rippling effects back in time, rather than the other way around.) Second it might not even be possible. In order to do that you'd have to try every possible combination of states and see which ones are valid. Does writing down every possible combination of bits create universes? Even if you apply some rule to them to check if they are "valid" universes?

I think that "real" universes like ours have to have a chain of causation like that.

Here is a better description of this line of thought than mine: http://lesswrong.com/lw/fok/causal_universes/

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