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Why quantum entanglement doesn't allow faster-than-light communication (2016)

forbes.com

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Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#11

Post by elcritch »

mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

> One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side.

> I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about.

The quantum erasure experiment is to my mind the best example of the spooky action at a distance. The outcome of the particle pairs is measured after the entanglement occurs implying not just "spooky action at a distance" but also in time. https://www.youtube.com/watch?v=8ORLN_KwAgs

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#12

Post by vjerancrnjak »

bowsamic wrote: post #7
mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

> I accept that this coin-hypothesis has been disproved by people who actually knows what they're talking about. The classical idea is more like as follows: you have a guy Charles who makes two letters each with a card in that has written on it either number 0 or 1, and gives one letter to Alice and another to Bob. Now, "entanglement" here is that if Charles writes 0 in Alice's letter he writes the number 1 in Bob's,…

Yes, Bell's theorem is such a strong result. 1. locality 2. (local) reality 3. statistical independence

Only 2 can hold at once and there's consensus to have 1. and 3., with that we lose the hidden variables. Instead, having 1. and 2. hold would be so interesting.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#13

Post by causi »

TheDudeMan wrote: post #2

"3 Body Problem" has so many problems! Wake me up when the next "Expanse"-level sci-fi lands.

Yeah, the whole "planet's climate is stable enough for a sapient species to evolve and become hyper-advanced yet so unstable they're going to be wiped out" is so, so stupid.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#14

Post by magicalhippo »

honeyed_coffee wrote: post #9
mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

The spooky part occurs when two parties who share this entangled state know what measurement to perform. If the measurement choice aligns for both parties, their outcomes can be correlated precisely. If the measurement choices are not aligned, the outcomes are also random

> If the measurement choices are not aligned, the outcomes are also random

Just to be a bit pedantic, as it can otherwise lead to some confusion: the measurement outcomes are always random.

If the particles are entangled, then it is the correlations that are not random.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#15

Post by spintin »

isodev wrote: post #10
spintin wrote: post #6

The problem with entanglement is obviously that it does not scale many-to-many, just like Erlang. You need Java to do many-to-many or C with a GC VM.

I've seen a few "can't scale many-to-many" Java/C things in my career... it's all about how you put things together. I don't think Java and C can go faster than light either ;-).

The Java concurrency package is the only way to get your multi-core CPU to share memory atomically without going "Arrays of 64 byte atomic Structures" with C.

And then you are in segmentation fault hell.

Sun had to rewrite the entire JVM in 2003 with a new memory model, later adopted in C++11 (and still the current C++ memory model) which failed for C++ because this model only works well if you have a VM with GC.

C# is just a plain Java copy after Microsoft got sued for J++ in 1998.

All other languages have problems with concurrency and threads that make them unsuitable for anything really.

So again, Java is the ONLY language/VM you can use on the server and on the client you still want a combination of C(++) and Java for performance + ease of use (avoid segmentation fault hell that no person should suffer).

If you saw bad Java code then that is not the fault of Java.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#16

Post by endisneigh »

causi wrote: post #13
TheDudeMan wrote: post #2

"3 Body Problem" has so many problems! Wake me up when the next "Expanse"-level sci-fi lands.

Yeah, the whole "planet's climate is stable enough for a sapient species to evolve and become hyper-advanced yet so unstable they're going to be wiped out" is so, so stupid.

What’s stupid about it?

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#17

Post by sebzim4500 »

mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

Disclaimer: I am not an expert, but I understood this stuff pretty well 5 years ago.

If you have a single particle there is no local experiment that you can do to determine whether that is entangled to a particle somewhere else. You need to use both particles in the experiment in order to prove it one way or the other. Mathematically, this is due to the fact that the density function for one half of an entangled pair is the same as the maximally mixed state for one particle.

See CHSH[1] for an example of an experiment you can do if you have access to both particles and you want to show they are entangled.

[1] https://en.wikipedia.org/wiki/CHSH_inequality

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#18

Post by jemmyw »

bowsamic wrote: post #7
mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

> I accept that this coin-hypothesis has been disproved by people who actually knows what they're talking about. The classical idea is more like as follows: you have a guy Charles who makes two letters each with a card in that has written on it either number 0 or 1, and gives one letter to Alice and another to Bob. Now, "entanglement" here is that if Charles writes 0 in Alice's letter he writes the number 1 in Bob's,…

> Bell's theorem says you either need to give up the idea that there is no "spooky action", or give up determinism

Can you not also say that the determinism includes the observer, aka superdeterminism (which is just determinism because that would surely be global).

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#19

Post by dist-epoch »

mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

> you'd need to be unable to distinguish between a measured/unmeasured particle

This is true. There is no way to tell if a measurement you do happened on an entangled particle or on a "free" one.

You can only tell in retrospect, when you correlate results, which requires classical communication.

Re: Why quantum entanglement doesn't allow faster-than-light communication (2016)

#20

Post by gwill »

vlovic wrote: post #8
mrkeen wrote: post #3

The gap I still have in my understanding: One hypothesis is that there is no spooky action. One particle was 'always' going to resolve one way, likewise with the other. Like inspecting 'heads' on one side of a coin 'forces' 'tails' onto the other side. I accept that this coin-hypothesis has been disproved by people who actually know what they're talking about. But to me, this implies that you should build your spooky…

The answer is Bell's Theorem. Scott Aaronson has some good explanations.

i won't have time to read this until later, but here's a post by him on it: https://scottaaronson.blog/?cat=33
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