PLEASE explain entanglement...

And when Einstein called it “spooky action at a distance”, was he saying he didn’t believe it happened, or that he was freaked out by it, or didn’t understand it?

I want to hear from a physics person, cuz this stuff sounds wacky.

A very quick and general layman’s (IE: from a layman!) explanation:

Entanglement refers to the ability of one of a pair of particles to influence the behavior of the other particle in the pair over distances which ordinarily woulkd be too great for information to travel between the two particle by ordinary means.

In other words, if you have one half of an entangled pair of quarks sitting on the desk in front of you, and the other quark is a zillion miles away on someone’s kitchen counter, and you give the quark in front of you a poke… the other quark will immediately react as well (even though there is no time for the information about the poke to be transmitted to the other quark.).

I think…:slight_smile:

Scroll down to Number 21 for visual representation.

Before you get all excited about a faster-than-light communication device however realize that this method cannot eb used to transmit information.

Personally I don’t see why not as I could envision a series of entangled particles and we agree ahead of time to a code so if particle 1 spins one way and particle two changes to another way (and 3 and 4 and so on) that we couldn’t communicate. At least simple Yes and No stuff.

Say you travel 5 light years out to get a better view of a star we expect to go supernova (you’re 5 years closer to the soon to explode star). We entangle the particles before you leave and everyday I check my set of particles. If I see the particles change in a coded series that would mean that you had just witnessed the supernova. It would take the rest of the earth 5 more years to figure that out though.

I must be missing something because I recall discussions on this very thing around here before and our more science minded Dopers were pretty clear and united on the no FTL communication thing using this.


You can’t transmit information because you have no way of controlling which way your particles (or what have you) are going to go. Setting up a code in advance doesn’t help you, since the sequence of results is essentially random. I can’t alter my particles to let you know one way or the other what I’ve observed about the nova.

Scientists have long objected to ‘action at a distance’ since it implies that anything at any time could be changed without warning, and makes the laws of physics meaningless (or at least resting on an uneasy basis).

The phrase should not be confused with gravity or electromagnetism, which we might call ‘action over a distance’ in contrast. The idea of action at a distance is that, for example, I could move my arm here and knock over your computer in exactly the same way as if it were here in front of me, or that the sun would shine as brightly in the Andromeda Galaxy as it does on Earth.

I thought it was possible to change a particle’s spin. Is doing so actually impossible or just beyond our current technical means?

Sorry…meant to mention this in my last post.

I’m reasonably certain that gravity, electromagnetism and so on propogate at light speed. I think gravity was a bit of a question mark since it was hard to test but IIRC some recent tests did suggest a propogation speed for gravity and it is what scientists expected anyway.

So, if you could somehow magically make our sun blink out of existence the earth would continue its orbit for another 8 minutes or so before hurling off into deep space.