Re: Can Spooky Action allow instantaneous communication?

Hi Greg,

You've asked a very interesting, and timely, question! Exactly this has been in the news quite a bit lately so there's a lot of popular information out there on it. Even so, your question is hard to answer with certainty. The reason for this is two-fold. First, I'm by no means an expert on this rather complicated subject; second, this subject itself is still very much "under construction" (just like the myriad of web pages out on the net). And so this presents a bit of a problem in answering this question: I'm uncertain of how much detail to include. So, I'll divide this answer up into two sections. Click here to see the summary; click here to see the gory details.

Blood and Gore (without the blood)

Before I get into the heart of the matter, let me say that my main source for this is J.J. Sakurai's classic Modern Quantum Mechanics (for my money, this is *THE* best book on quantum) and various sites on the Net (bookmarked below). The interesting thing about this is that Sakurai's book is a graduate text (albeit very readable) whereas the links only talk about it at the popular level. I'm guessing that there are probably intermediate books out there that address this but I'm sorry to say that I can't refer you to any of them as I don't personally know of any. However, if you try a search on the net for Bell's Inequality, you should get better results than for just spooky action or teleportation.

Okay, let's get started. The phenomenon you talk about is sometimes referred to as the Einstein-Podolsky-Rosen paradox although Einstein is said to have called it, with his characteristic wit, spooky action at a distance. The reason this has a rather sarcastic tinge to it is that Einstein didn't like the non-local aspects of quantum theory, which are expressed in this paradox. Quantum mechanics is inherently a non-local theory; i.e., one in which an action at one place is transmitted instantaneously to another.

So what is this effect? It is the idea that two quantum particles can become "entangled" and somehow mirror each others' states. Usually this is associated with measuring one aspect of their state (e.g., their spin in the x-direction, which is, say, either up or down). One of the basic tenets of quantum mechanics is that before a particular state of a quantum particle is measured, all possibilities are equally likely. That is, the particle is said to live in all the possible states at the same time. But, when you actually measure a particular state, the wave function collapses to one possibility, that which was measured. As an example, say you have an electron which can have spin pointing up or spin pointing down in the x-direction. Before you measure it, you can't say whether the spin is up or down. The electron's spin state is described as being in a superposition of all the possible states (in this case, up and down).

But, and this is the weird part, when you decide to go ahead and measure the electron's spin in the x-direction, you get either up or down. But not both. It goes from having all possibilities existing at the same time (i.e., spin up and down) to just one actuality (say, spin down). The wave function collapses from all possibilities down to one, that which is measured. Of course, you couldn't predict which state it was going to end up in until you actually measured it.

So what does all this have to do with spooky action and entanglement? When two particles become entangled, it turns out that they mirror each others states. If one is measured to be spin up in the x-direction, it's partner will necessarily be in spin down in the x-direction (when it's measured). But, until you measure one or the other of the pair, you can't say anything about their state. Imagine that you have two electrons that you've managed to entangle somehow. Then you fire them off in different directions, one to your friend Joe, in California, and the other to your friend Jenny, in New York. You can't say anything about their spins because you haven't measured them yet and all states are equally likely. But then Joe, in California, decides to measure his electron's spin in the x-direction and finds that it has spin up. This immediately collapses the wave function of Jenny's electron and, whenever she decides to measure it, she will find that it has spin down in the x-direction. This action (Joe's measurement of his electron influencing Jenny's electron) is kinda spooky because it's instantaneous! Understandably, this makes a lot of physicists, including Einstein, a little uneasy.

How to explain this away? A lot of people have come up with many inventive theories to sort of explain this aspect of quantum mechanics. Some have said that the whole probabilistic foundation of QM needs modification; others invoke Heisenberg's uncertainty principle; and still others have pointed to hidden variables, either local or non-local, that we are unaware of that influence this interaction. And some have decided to forego QM and pursue alternative theories to explain the physics of the small and fast. The most successful have been Bohm (who went back to a formulation of QM that was based on DeBroglie's original concept of pilot waves) and Bell (who decided to show that it wasn't possible for there to be any local hidden variables). Bell came up with, appropriately enough, Bell's Inequality, based on the idea of local hidden variables (which Einstein and crew endorsed). However, it has been shown by various experiments that Bell's Inequality does not hold and so QM is saved once again (at least for a while). But, there are people who believe that Bell's Inequality needs modification and still others who are pursuing the possibility of non-local hidden variables.

As you can tell, this is a very complicated field. The reason I went into all this detail was because of the information aspect of your question. You asked if it was possible to transmit a morse code through this phenomenon and the answer seems to be yes and no (welcome to quantum mechanics!). In a recent experiment, researchers did something similar to sending off an entangled pair of photons (instead of electrons) to Joe and Jenny. But, instead of having Joe measure his electron's state, they fired another photon (call it Steve's photon, all the way from Texas) at Joe's photon (in California), entangled these two, and then measured the states of these two newly entangled photons. The act of measuring them destroyed both Joe and Steve's photons. And the measurement showed that Joe's photon had the opposite polarity (state) of Steve's photon. But, since Joe's photon was also entangled with Jenny's photon, Jenny's photon had the opposite state of Joe's photon... and hence the same state as Steve's photon. This has been referred to as teleportation in the media but, as you can see, it's quite different from Capt. Kirk being beamed up by Scotty.

So how does all this relate to your morse code idea? It shows that in order to transmit any information, you have to know what happened at the other end. For example, if Jenny is sitting in New York, measuring the state of an endless stream of electrons, all she sees is a random distribution of spins (up, up, up, down, up, down, down, etc.) but she has no way of correlating this to what Joe wants to convey in California. For example, following your idea of only using certain electrons to convey the information, she has no way of knowing that Joe didn't want to use the first three electrons transmitted as part of their agreed upon code. Another aspect of this is that there is no way to really predict or control ahead of time the state information. The entanglement is dependent on a quantum superposition of states and as soon as you know one of the states, the other is instantly set, thus destroying the superposition of states. Thus, even if Joe tells Jenny to only look at every 3rd particle's state, he still can't control what state it will be in and the sequence ends up being random once again. So you couldn't really send a morse code because that would imply knowing the sequence of ups and downs before you observe them.

However, this is an area of active research and many people are trying to make quantum computers that calculate using this quantum superposition of states instead of the ones and zeros that conventional computers use. Still others are working on using this "quantum teleportation" to make the next generation of encryption (where such cryptographic methods can be used to make "totally secure" transactions). These "super-codes" work by having one party (the bank) having a transmitter and the other parties (Joe and Jenny again) each having a receiver. The bank sends out a (random) sequence of particles; both Joe and Jenny measure the spins of their respective particles, thus getting a random sequence. Joe uses this random sequence to carry out a series of mathematical operations to encipher the message. Jenny uses the reverse sequence to decipher the message. Each letter ends up having it's own unique key and the message "pad" is used only once and destroyed. Thus, although it doesn't seem likely to be able to transmit a morse code using this phenomenon, it is possible to utilize it in other ways. There are many theoretical aspects of this that need to be worked out and many researchers are actively studying the theory in addition to the technological applications of this.

Just the Facts

So, in summary, it probably isn't possible to send any information, including a morse code, via this phenomenon. At least, this is the most popular way of resolving this paradox with relativity (since, according to relativity, information can't be transmitted faster than the speed of light). Another reason for this is that there's no way for us to force a particle into a particular state without collapsing it's wave function... for example, we can choose to measure it's spin in the z direction but we can't say if it'll be up or down. We only find out after we measure it. And in order to communciate this state information, we would have to send it, via presumably sub-luminal means, to the receiving station, thus saving relativity. Also, the information has to be carried by the particles themselves, which travel at luminal or sub-luminal speeds. Although this seems to rescue relativity, it is something very hard to explain away with complete confidence and, as mentioned before, there are quite a few conflicting theories out there. However, despite the theoretical dilemmnas raised by this, people are actively exploring the practical applications of "spooky action" to everything from totally secure "quantum codes" to a new generation of quantum computers.

Bookmarks -- hot off the presses!

http://www.laurin .com/Content/Jan97/techAlice.html
http://dustbunny.physics.indiana.edu/~dzierba/HonorsF97/Week1/NYTJ uly22.html
http://www.washingtonpost.com/wp-srv/WPlate/1997-12/11/180l- 121197-idx.html
http://www.newscie ntist.com/ns/970628/nlight.html
http: //www.sciencefriday.com/pages/1997/Aug/hour1a_080197.html

I hope that helped. If you have any questions, please don't hesitate to drop me a line and I'll be more than happy to go into it in greater detail. Good luck and good hunting!

Best regards,

Rick.