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Quantum Entanglement Drives the Arrow of Time

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Re: Quantum Entanglement Drives the Arrow of Time

#21

Post by throwaway7548 »

I have a question. I just went to a source of physical (quantum) randomness http://www.randomnumbers.info/ and I'm giving you a random number between 0 and 10,000 which I've just generated there. Here it goes: 6296.

Ok. Now that light cone had finally reached you. And you (neurons in your brain to be precise) are thoughtfully entangled with that random event (outcome), now in your past.

Now imagine the following. A few days passes. And you forget that number. A few years passes. Connections between the neurons which were storing this information are now gone. Molecules and atoms which were part of these neurons are gone from your body. There are no entanglements any more which link you to that event. Is that event in your future now? Again?

Re: Quantum Entanglement Drives the Arrow of Time

#22

Post by tim333 »

gfodor wrote: post #12
tim333 wrote: post #8

The reasoning sounds a bit iffy as in: “Finally, we can understand why a cup of coffee equilibrates in a room,” said Tony Short, a quantum physicist at Bristol. “Entanglement builds up between the state of the coffee cup and the state of the room.” I think you can understand coffee cooling quite well without any quantum stuff - the atoms in the coffee are moving faster than those in the room. There will be a tendency…

your claim is that the quantum physicist cited is making the analogy just to sound impressive?

Actually I was thinking more of the quantum consciousness self help folks. The physicist cited may well have something.

Re: Quantum Entanglement Drives the Arrow of Time

#23

Post by carlob »

tedsanders wrote: post #18
cromwellian wrote: post #3

This Google Talk https://www.youtube.com/watch?v=dEaecUuEqfc uses entanglement and quantum information theory in a clear and understandable way to explain 'spooky' quantum phenomena, like the quantum eraser, de-coherence, the aspect experiment, and the measurement problem. Even if you don't know any QM, just basic algebra and calculus, it's really approachable. I used to be a fan of the Many Worlds interpretation, bu…

I'm having a difficult time following his explanation. Here are a few of my stumbling points. Maybe you can help me out. 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? 3) Why does the interpretation rely on the density matrix? I've always thought…

Without reading the paper or watching the video.

> 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1?

The density matrix does not have the same properties of a joint probability distribution, so quantum entropy doesn't really have the same properties of classical entropy. [1]

> 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix?

The log of a matrix is defined as the inverse of the matrix exponential. The matrix exponential can be defined as the usual power series, only using matrices rather than scalars.

What one usually does is: diagonalize the matrix (if possible), take the log of the eigenvalues and rotate again. Obviously taking the log of a matrix is a little trickier than the exponential because if you have negative or complex-valued eigenvalues you have to be a bit more careful.

[1] http://arxiv.org/abs/quant-ph/9610005

Re: Quantum Entanglement Drives the Arrow of Time

#24

Post by DonGateley »

dkarapetyan wrote: post #10
tim333 wrote: post #8

The reasoning sounds a bit iffy as in: “Finally, we can understand why a cup of coffee equilibrates in a room,” said Tony Short, a quantum physicist at Bristol. “Entanglement builds up between the state of the coffee cup and the state of the room.” I think you can understand coffee cooling quite well without any quantum stuff - the atoms in the coffee are moving faster than those in the room. There will be a tendency…

The physical implications of entanglement might be strange but on a mathematical level it's all just vector addition so it's not really that strange.

The strangeness is the fact that they add and that the sum is as physically meaningful as the components. In a nutshell, so to speak.

Re: Quantum Entanglement Drives the Arrow of Time

#25

Post by aaren »

throwaway7548 wrote: post #21

I have a question. I just went to a source of physical (quantum) randomness http://www.randomnumbers.info/ and I'm giving you a random number between 0 and 10,000 which I've just generated there. Here it goes: 6296. Ok. Now that light cone had finally reached you. And you (neurons in your brain to be precise) are thoughtfully entangled with that random event (outcome), now in your past. Now imagine the following. A f…

> There are no entanglements any more which link you to that event.

Not directly, but the information has spread out from your neurons into the surrounding matter ad nauseum. It's just we can't interpret the information anymore.

The event still happened in your past, you just can't see it through your limited human view of reality.

Re: Quantum Entanglement Drives the Arrow of Time

#26

Post by officialjunk »

i recall learning that time "flows" both ways at the quantum scale, but i admit is has been a while since i've attended any lectures. has there been any new discoveries to say otherwise? i think i've read about research of both time reversal violations and time-invariance at the quantum scale.

also, what are peoples' thoughts on time being an emergent property at the macro scale and that down at the quantum level, everything is described by time independent equations, like the Wheeler-DeWitt equation? http://en.wikipedia.org/wiki/Wheeler%E2%80%93DeWitt_equation

Re: Quantum Entanglement Drives the Arrow of Time

#27

Post by andbberger »

salimmadjd wrote: post #16

Seeing this article is rather bittersweet. I came to a similar conclusion in my college years but I never pursuit it further. Taking Quantum Physics in college was a life changing experience and it reshaped how I viewed the world. I was always obsessed by time and one afternoon it became clear. I explained my variation not as a cup of coffee but a handful of dice. Essentially every tick of time is rolling these dice.…

There's good reason you got the most amount of resistance from physics majors. Intuition won't help you with theoretical physics. The only understanding is that achieved through studying the math in depth. Unless you've developed the formalism (in which case you'd be the subject of this article), you haven't reached any conclusions.

Hate to break it to you. There's no such thing as pedagogical theoretical physics- no shortcut to understanding physics.

Re: Quantum Entanglement Drives the Arrow of Time

#28

Post by TeMPOraL »

Is this really new? IANAP, but I clearly remember being taught about the Arrow of Time as a probabilistic/thermodynamical phenomenon even in high school and I also read similar explanations that involved causality and probability theory without refering to quantum entanglement. Is the "quantum" bit even needed there for anything?

Re: Quantum Entanglement Drives the Arrow of Time

#29

Post by tedsanders »

carlob wrote: post #23
tedsanders wrote: post #18

Earlier quoted context omitted.

I'm having a difficult time following his explanation. Here are a few of my stumbling points. Maybe you can help me out. 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do you take a log of a matrix? 3) Why does the interpretation rely on the density matrix? I've always thought…

Without reading the paper or watching the video. > 1) What does it mean that entangled particles are supercorrelated? How can S(A|B) = 2 or -1? The density matrix does not have the same properties of a joint probability distribution, so quantum entropy doesn't really have the same properties of classical entropy. [1] > 2) The formula for Von Neumann entropy is S = -Tr(p log(p)), where p is the density matrix. How do…

Thanks for the link - it's exactly what I needed!

Re: Quantum Entanglement Drives the Arrow of Time

#30

Post by sinesha »

yati wrote: post #9

I've always wanted to study quantum mechanics because of this very "entanglement". Can people please post recommendations on good resources/books on the topic for a person like me having no solid experience with physics(except college level courses)?

The bible is Nielsen and Chuang's Quantum Computation and Quantum Information: http://www.amazon.com/Quantum-Computation-Information-Cambri... See also these resources in Nielsen's blog: http://michaelnielsen.org/blog/writing/
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