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Comment by n3rdy | Hacker News Reader

> Then he didn't understand what you were asking. It can easily be faster than the speed of light because no information can be transmitted through this phenomenon.

If its observable then how could information not be transmitted?

I'm the furthest thing from a physicist but if quantum entanglement causes an atoms polarity to change because millions of miles away another atom it is entangled with did the same, that would seem like an excellent way to encode information into bits, supposing you can change the atoms polarity at a whim.

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Because just observing the polarity changes it, so you can never be sure what position it was in originally. So you can affect an object that is light years away from you instantly, but it's useless for transmitting information, because while you know which state it is in, the party on the other end does not,and has no way of finding out without affecting the information and making it useless.

> Because just observing the polarity changes it, so you can never be sure what position it was in originally.

That does put a crimp in my universal router plans, but that's really interesting by itself that just looking at the atom affects its polarity.

Well it does not _really_ change the polarity.

Think about it this way:

You have two cards(A and B) - you and your friend pick one randomly. Until you look at yours, it's both A and B at the same time. It's the same with your friend's card. So you both own cards that are in a "mixed" A/B state. And then, when you and your friend look at them, the state is "decided".

Therefore, you could send your friend and his card on a rocket million years away from Earth, and then look at the card. Then,you can tell with 100% guarantee which card your friend has. Is that information useful? No,not really. You were able to instantaneously find out the state of an object millions of light years away,but you can't use it to communicate.

It's like you and a friend have a deck of cards.

You each take a card from the deck, and then travel a million miles away.

Then, at the crack of noon (synchronized to GST, of course), you both look at your cards.

Your card is the 3 of Clubs.

You travel back to meet your friend, and discover that his card (which he measured at noon, just like you) was the 7 of Diamonds.

You repeat this experiment a gazillion times and are amazed!! No matter how many times you run it, you and your friend never get the same card!!!

It's as if the cards are sending spooky signals to each other.

And after you double check that you and your friend are both looking only at 1200 GST, you realize that this spooky signal travels faster than the speed of light (since the it takes no time to "travel" a million miles).

It's like magic, eh?

Not really. The fact there is one of each card means it's impossible for you and your friend to have the same card. No magical spooky signals are being sent.

(I think the quantum mechanical case is analogous to this contrived example. The difference in real quantum mechanics it that you really don't know what card you have until you look at it. However, that doesn't mean that your card is sending a faster-than-light spooky signal to tell the other card what to be. And you certainly can't use it for signalling or anything useful.)

((Reposted to main thread with some slight edits, in case people find this comment useful or interesting.))

Still implying hidden local variables - i.e. "the card was always the 3 of clubs".

Thusfar that isn't the case - so it does seem to be spooky action at a distance. It's not just an inability to perform a suitable measurement beforehand.

I have a box. Inside the box my cat is alive and dead until I open the box. I open my box. Now my cat is either alive or dead. The cat in the box a billion miles away is instantly !alive or !dead.

But! Cat_A being alive is paired with Cat_B being dead. We know this. When we discover Cat_A being alive and thus Cat_B being dead we're not really finding out anything about Cat_B; we're just finding out something about the Cat_A / Cat_B pairing, and Cat_A is local to us.

(http://everything2.com/title/Quantum+entanglement+and+faster...)

Also, you can't change the polarity at a whim.

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