5 hours ago

Created a post • 120 points @theafhWhat is the prevailing theory to explain quantum entanglement? Must there be another dimension we cannot access or measure that is not subject to the laws of relativity? (I understand the laws of relativity break down at the quantum level but please ELI5)

ReplyIf you "measure" the bits per character in the base 45 alphanumeric encoding used in QR code, you'd get 5.5 bits per character as 11 bits is used for two characters.

How is it possible to have information less than a bit, a partial bit? What is that ".5" part? Isn't a bit indivisible?

Only in the context of a character doublet is all information expressed. To know the "half bit" part, you cannot "look" at just one character, you have to look at the total. The information is shared between the two characters. Measuring the bits-per-character is only useful when considering the whole system. The "partial bits" is information smeared across the system. Changing the middle bit may change one, or both, characters.

Here's a 11 bit example, where the middle bit is changed and it changes both characters: (11101001010 vs 11101101010, or '/L' vs '%8' encoded)

https://convert.zamicol.com/?in=11101001010&inAlpha=01&outAl...

https://convert.zamicol.com/?in=11101101010&inAlpha=01&outAl...

vs changing the last bit only changes the last character: (Using the preceding example, 11101101010 vs 11101101011, or '%8' vs '%9' encoded)

https://convert.zamicol.com/?in=11101101011&inAlpha=01&outAl...

The same principle applies to information theory and cryptography. Security can be measured in "partial bits" because it's measured across something larger.

ReplyOr Superdeterminism is true: https://en.wikipedia.org/wiki/Superdeterminism

ReplyMWI allows you to have entanglement without “spooky action at a distance”. However, it requires exponential blowup in representational complexity of the universe, which also feels aesthetically displeasing.

ReplyDoes the article do justice to the hidden variables hypothesis?

In case of the hidden variables, the spin is a (3-dimensional?) value that is identified by the measurement result. In case of quantum theory we have have a probability distribution. How is that probability distribution different from a hidden variables, except that it's not a straight number but a function instead?

Speaking as a programmer, is the difference between hidden variables and quantum mechanics that the former postulate a real-valued property whereas the latter speak of something like a monad?

ReplyI'll never understand entanglement. Every explanation makes me wonder why it can't be used to instantaneously send a message. I never fully understand the explanations why it can't be used to do so. I don't understand how you can be sure about the state of the other particle, what if someone already measured it and then did something to it?

Reply"This is the first of a set of papers that look at actual Einstein-Podolksy-Rosen (EPR) experiments from the point of view of a scientifically and statistically literate person who is not a specialist in quantum theory."

https://arxiv.org/abs/quant-ph/9611037

...I wonder if anyone has ever followed up on Caroline Thompson's work after she passed away.

https://arxiv.org/abs/quant-ph/0210150

Reply> really permits instantaneous connections between far-apart location

The phrasing in this article is tricky, as it wasn't FTL communication that was proven; just that there are correlations between things that *would require* FTL communication, were they classical processes. This is an important point: https://xkcd.com/1591/

There's no spooky action at a distance. It's just systems running in parallel. Let's imagine we have an entangled qubit system that consists of a superposition of the states (0,1) and (1,0), i.e. either part A is in state 0 and part B in state 1 or vice versa. When we perform a measurement on the first part of the system and obtain 1, it simply means that we have "branched" into the (1,0) state of the system. This is irreversible because of decoherence caused by the measurement. There is no information exchange or any type of exchange between the two parts of the system going on, we simply branch into a part of the probability space defined for the system. The question whether the other branches still exist then leads to either the "classical" interpretation of quantum mechanics or the "many worlds" interpretation. The latter seems to be favored today as we know that there's nothing special about the measurement process that causes the collapse of a wave function (it's a quantum process in itself), but in the end there's not really a way to test this so it's really more of a philosophical question.

Articles about "spooky action at a distance" should really mention this, as we have a much better understanding of the measurement process in quantum mechanics.

ReplyNote that there is a very important property of entangled particles that is hardly ever mentioned in this kind of exposition, which IMHO casts a lot of light on what is really going on, and that is that entangled particles do not self-interfere the way non-entangled particles do. For more details see:

https://flownet.com/ron/QM.pdf

ReplyI've been posting this explaination for more than 10 years now:

http://www.felderbooks.com/papers/bell.html

I think I prefer Felder's explaination more than Quanta's. It's omitting some details (eg. the angles) but is better at explaining the difficulties of Bell's Inequality--why it seems like spooky action at a distance and why it cannot be used for communication.

ReplyIf we were in a simulation, would the speed of light be the processing speed of the universe as each area re-renders, and spooky action at a distance be two variables pointed to the same memory location, populated with a lazy-loaded value, with copy-on-write semantics?

edit: seems like it is lazy loaded, so revised my summary.

Replysite design / logo © 2021 Box Piper