7 ms·

My understanding is that entanglement doesn't actually allow for transfer any information faster than the speed of light but is more like having two coins seale

by fryguy 11y ago

My understanding is that entanglement doesn't actually allow for transfer any information faster than the speed of light but is more like having two coins sealed in a box and given to two parties, that "God" always keeps the same way up until they're opened. You can manipulate them by flipping the coins over, but you don't know what it was originally. You can open your box and see that your coin is heads, and send a conventional message to the other person that says "if your coin is heads, then attack at dawn", but you don't know what the coin is until you open it, so are still reliant on sending the message over means that obey the speed of light in order to transfer the information. Is that an accurate (given that it's an analogy) description of how entanglement works, or does this work disprove that idea and is what was mentioned as Einstein's idea?

lclemente 11y ago
I think the problem with your analogy is that it doesn't include the measurement basis. Consider polarization of a photon: you can either distinguish between horizontal or vertical polarization with a measurement, so your basis looks like a "+". Or you can distinguish between diagonal polarizaitons, so your basis looks like an "X". Now, considering two photons, you don't know which basis Alice or Bob will choose in advance. If you just say "the photon is polarized horizontally", then their outcomes will be random if they measure in the "X" basis. If you include so-called "hidden variables" for all possible measurements, then you're basically at Einstein's idea. (I've simplified some things above, so please don't quote me on it ;)
dools 11y ago
What you've quoted there is a good analogy of an entangled state. In reality there are several differences, and the biggest piece of misinformation is that measurement of one system somehow "collapses a wave function" in the other system which isn't the case. The phenomenon of entanglement is that measurements of certain things are either perfectly correlated or anti-correlated. Eg. Measurement of spin along some axis on electron A will always be -1 when measurement of spin along the same axis of electron B is +1. The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to understand this in terms of classical physics, it's weird. But it's not classical physics. I wrote more about it here: https://news.ycombinator.com/item?id=10133674 https://news.ycombinator.com/item?id=10133674 Also check out the leonard susskind messenger lectures for a quick overview and his stanford continuing ed lectures on youtube for the long version :)
- coldtea 11y ago
  >The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to understand this in terms of classical physics, it's weird. If that was the case (the coin analogy) it would be perfectly understandable by classical physics. In fact it wouldn't even need physics to understand it, just common sense. If that was the case there wouldn't be any EPR paradox etc. The coin analogy is very misleading in this way -- and doesn't convey the problems physicists have had with explaining this phenomenon.
  - dools 11y ago
    No what I'm describing is a way of understanding why entangled states aren't spooky. It's also a direct lift from Leonard Susskind so it's not even me doing it. The point is that the state is prepared in some way X, and the state is such that by knowing something about one thing, you also know something about the other thing. The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand. Same as I can't visualise a 5-sphere but I have mathematical tools to work with one. I can't "picture" the mechanism that allows measurements of quantum states to be anti-correlated, but I can use maths to express that behaviour and make predictions about how the universe behaves.
    - coldtea 11y ago
      >No what I'm describing is a way of understanding why entangled states aren't spooky. I think that if the explanation doesn't also convey the spookiness, it's not right. >The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand. That's just pushing the spookiness under the carpet.
adekok 11y ago
The analogy is more this: Take a coin and split it in two. One side has heads, the other has tails. The key thing is you don't look at the two halves. Now, take one half at random, and send it to a person very far away. Too far away to communicate easily at light speed. Then, have the other guy look at what he has. He will (of course) determine that it has either heads or tails. Which means (of course) that the one you have is the opposite, either tails or heads. Nothing weird yet, right? The quantum weirdness comes in when you start doing variations of the tests to see what state the coin halves are in before you do the final measurement. It turns out that any model you can think of (hidden variables, etc.) has physical consequences. When you look for those physical consequences, you don't see them. What does that mean? In this case, your coin half and the other coin half are in an "indeterminate" state. They both have some properties of "heads" and they both have some properties of "tails". But their state is not determined. It really is an unknown state. And why move one half far away? Because you can do tricks where you both measure the coin halves at the same time, or near the same time. If (somehow) one measurement sent information from one coin to the other... that information has to transfer at light speed. But it doesn't. When one half is measured, the other half instantly becomes the opposite state. So far as anyone can tell, this process is instantaneous. And any "communication" between the two halves has infinite speed. The difficulty here is setting up systems so that they're isolated, and nothing interferes with the test. Then, doing all of the little measurements testing the edge conditions of your theory. In short, everything you think you know is wrong. The coin halves really aren't anything until you look at one of them. Then, both of them instantly become determined as heads/tails.

by fryguy 11y ago

lclemente 11y ago

I think the problem with your analogy is that it doesn't include the measurement basis. Consider polarization of a photon: you can either distinguish between horizontal or vertical polarization with a measurement, so your basis looks like a "+". Or you can distinguish between diagonal polarizaitons, so your basis looks like an "X". Now, considering two photons, you don't know which basis Alice or Bob will choose in advance. If you just say "the photon is polarized horizontally", then their outcomes will be random if they measure in the "X" basis. If you include so-called "hidden variables" for all possible measurements, then you're basically at Einstein's idea. (I've simplified some things above, so please don't quote me on it ;)

dools 11y ago

What you've quoted there is a good analogy of an entangled state. In reality there are several differences, and the biggest piece of misinformation is that measurement of one system somehow "collapses a wave function" in the other system which isn't the case. The phenomenon of entanglement is that measurements of certain things are either perfectly correlated or anti-correlated. Eg. Measurement of spin along some axis on electron A will always be -1 when measurement of spin along the same axis of electron B is +1. The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to understand this in terms of classical physics, it's weird. But it's not classical physics. I wrote more about it here: https://news.ycombinator.com/item?id=10133674 https://news.ycombinator.com/item?id=10133674 Also check out the leonard susskind messenger lectures for a quick overview and his stanford continuing ed lectures on youtube for the long version :)

coldtea 11y ago
>The similarity to 2 coins is: if i have a 1972 coin and a 1973 coin, and give one to you randomly, then you go a million light years away and look at your coin and find you have the 1973 coin, you will know I have the 1972 coin. Although this is only a simplified analogy of entanglement the important point is that the state was prepared before we separated, and no information has been communicated. When you try to understand this in terms of classical physics, it's weird. If that was the case (the coin analogy) it would be perfectly understandable by classical physics. In fact it wouldn't even need physics to understand it, just common sense. If that was the case there wouldn't be any EPR paradox etc. The coin analogy is very misleading in this way -- and doesn't convey the problems physicists have had with explaining this phenomenon.
- dools 11y ago
  No what I'm describing is a way of understanding why entangled states aren't spooky. It's also a direct lift from Leonard Susskind so it's not even me doing it. The point is that the state is prepared in some way X, and the state is such that by knowing something about one thing, you also know something about the other thing. The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand. Same as I can't visualise a 5-sphere but I have mathematical tools to work with one. I can't "picture" the mechanism that allows measurements of quantum states to be anti-correlated, but I can use maths to express that behaviour and make predictions about how the universe behaves.
  - coldtea 11y ago
    >No what I'm describing is a way of understanding why entangled states aren't spooky. I think that if the explanation doesn't also convey the spookiness, it's not right. >The actual mechanism by which this occurs is only "spooky" if you try and interpret it classically. But if you just accept that "hey, it's quantum mechanics" then it's very easy to understand. That's just pushing the spookiness under the carpet.

adekok 11y ago

The analogy is more this: Take a coin and split it in two. One side has heads, the other has tails. The key thing is you don't look at the two halves. Now, take one half at random, and send it to a person very far away. Too far away to communicate easily at light speed. Then, have the other guy look at what he has. He will (of course) determine that it has either heads or tails. Which means (of course) that the one you have is the opposite, either tails or heads. Nothing weird yet, right? The quantum weirdness comes in when you start doing variations of the tests to see what state the coin halves are in before you do the final measurement. It turns out that any model you can think of (hidden variables, etc.) has physical consequences. When you look for those physical consequences, you don't see them. What does that mean? In this case, your coin half and the other coin half are in an "indeterminate" state. They both have some properties of "heads" and they both have some properties of "tails". But their state is not determined. It really is an unknown state. And why move one half far away? Because you can do tricks where you both measure the coin halves at the same time, or near the same time. If (somehow) one measurement sent information from one coin to the other... that information has to transfer at light speed. But it doesn't. When one half is measured, the other half instantly becomes the opposite state. So far as anyone can tell, this process is instantaneous. And any "communication" between the two halves has infinite speed. The difficulty here is setting up systems so that they're isolated, and nothing interferes with the test. Then, doing all of the little measurements testing the edge conditions of your theory. In short, everything you think you know is wrong. The coin halves really aren't anything until you look at one of them. Then, both of them instantly become determined as heads/tails.