A fun talk on teleportation

5 February, 1995

I gave a talk to the Science Fiction Club of Rehovot on the 31st of January about quantum teleportation and other crazy stuff. I have been asked to try to write out the first part of my talk where I considered what "teleportation" means and how difficult it might really be. I don't claim this to be definitive on the matter, just my thoughts about it. My own research interests really lie with fundamental quantum phenomena and outside that field I'm as likely to stumble as another.

To start let's ask just what we might mean by the term "teleportation." After all, if someone comes up to you saying "look I've finally done it! I've discovered how to teleport ..." we'd like to be able to decide whether we were even speaking the same language. Fine, so I've seen Star Trek ® so I figure I can take a stab at defining it:

Teleportation is some kind of instantaneous "disembodied" transport.

Now wait a second, I can't buy that! Einstein's theory of relativity - and many decades of experimental evidence back him to the hilt - say that the fastest speed is the speed of light. If we take this as part of normative science then we are going to have to change our definition immediately to:

Teleportation is some kind of "disembodied" transport.

(At least for the moment.)

Well that's a little better, but I have been rather vague by what I mean by disembodied. Perhaps I should let the figure below be our best guide to what that might mean:

I guess if I think about this definition for a little while I start realizing that we already have lots of examples of teleportation around us every day:

telephone: transports sound waves as electricity.
fax: transports an image.
World Wide Web: ...

Well, do these count as teleportation? They are really copying processes. They leave the sound, image, what-have-you behind and send the copy shooting across space in some disembodied way. Hmmmm, should we buy this? They don't leave a copy behind in our favorite TV program. Well, maybe that's just what they do. They have some machine which measures the positions and velocities and types of atoms throughout the entire person and then send that information (say by radio waves) to the place where the body is reconstructed by another machine. Well, on TV they also learned how to recreate the person from the information apparently without a machine to receive it. (One thing at a time, please!)

What about the original? Well, maybe the machine which measures all those atoms has to slice the person apart to do that. I guess that would be like a photocopy machine with a flash lamp which was set too hot (vaporizing the original). This wouldn't be an absolute requirement. As soon as someone worked out how to build a more gentle copying process they could leave the original behind. Would they want to? Would the soul be copied? Would the copy still have to pay taxes if the original were still around? I guess I can't answer every pressing question.

Of course if we could ever learn how to do this we might find new fields of research like "experimental religion." Who knows?

Just how much information are we talking about anyway? Well the visible human project by the American National Institute of Health requires about 10 Gigabytes (that's about 10^11 = 100,000,000,000 "bits," or yes/no answers, this is about ten CD ROMs) to give the full three dimensional details of a human down to one millimeter resolution in each direction. If we forget about recognizing atoms and measuring their velocities and just scale that to a resolution of one-atomic length in each direction that's about 10^32 bits (a one followed by thirty two zeros). This is so much information that even with the best optical fibers conceivable it would take over one hundred million centuries to transmit all that information! It would be easier to walk! If we packed all that information into CD ROMs it would fit into a cube almost 1000 kilometers on a side! Enough said?

Hey, but you're all clamering out there "what about the uncertainty principle, can you really measure things that accurately?" Well quantum theory tells us that the precision with which we can measure position and velocity of any particle are limited by a very simple formula:

                             uncertainty in velocity
  uncertainty in position x -------------------------
                                 speed of light

                         one millionth of the radius of a Hydrogen atom
                    >   ------------------------------------------------
                            the particle mass / the mass of Hydrogen

If we want to measure each atom to within a typical atomic size this means that the velocities will be uncertain by about 300 meters per second (if the particle weighs as much as a Hydrogen atom say).

This sounds fast, but it's not so bad. The ordinary jiggling of our atoms due to us being at room temperature is bigger than this by a factor of three or more. In other words, the uncertainty principle doesn't appear to be too restrictive in terms of how well we can measure those atoms.

Of course, that's not all. What about the "quantum state" of those atoms? Does it matter what energy levels they are all in? Do the chemical reactions need to have this information to work once we reassemble the atoms to make a person? Well, my best guess is no! As is the best guess of several other scientists I've asked too. But that's hardly a definitive answer. I guess what tends to convince me that the detailed quantum state is not important to get right when you want to copy a person and make a new one from the partial information is that people routinely go to hospitals for NMR (nuclear magnetic resonance) and ESR (electron spin resonance) scans to see inside them. These procedures mix up the quantum states of at least some large number of atoms and nuclei of the people being scanned, yet it doesn't seem to disturb their appetites (that makes them still human in my book). Thus here again the quantum nature of our atoms and molecules doesn't appear to rule out the copying method for teleportation.

The shear amount of information involved though is still mind boggling! Perhaps we should start with something smaller ...

Samuel L. Braunstein, schmuel@tangelo.phys.unm.edu

Feed-back encouraged.

Alıntı: http://www.research.ibm.com/quantuminfo/teleportation/braunstein.html

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