A stunning revision of quantum theory has effectively replaced Heisenberg's uncertainty principle with the concept of quantum entanglement. According to German physicist Werner Heisenberg, whose groundbreaking ideas were first published in 1927, both the momentum and position of a particle cannot be known at the same time, because the process of measuring the position changes the particle's momentum.

Previously, only "thought experiments" were available to test the theory, but this has changed. The emerging view has huge implications in areas such as communications, implications so deep they are just beginning to be realized.

The indeterminacy of reality at the quantum (sub-atomic) level has been proved by the famous "two slit" experiment, which indicates that light can be either a wave or a particle depending on whether or not an effort is being made to measure it. Even single particles, sent through the slits over a period of hours, will set up a pattern that proves that they pass through both slits at the same time and interfere with themselves. Quantum theory has therefore said that a particle splits into two "ghosts" of itself, one going through each slit. It wasn't possible to confirm this because measuring the actual position of the particles altered their motion, just as Heisenberg had predicted.

Now it has become clear that the apparent "ghosting" is not due to some mysterious and inaccessible aspect of reality, but to an actual, physical effect that can be understood and perhaps eventually exploited in so-called "quantum machines," notably including devices that would enable instantaneous communication over virtually infinite distance.

Certain kinds of sub-atomic particles such as photons have a characteristic "spin." In 1997, physicist Nicolas Gisin and colleagues at the University of Geneva in Switzerland used particles of light that had been "entangled" -- by linking their spins -- to engage in simple but instantaneous communication over a distance of 7 miles. When the spin of one entangled particle was changed after the two particles had been sent down separate fiber-optic cables, the other particle instantaneously made the same movement.

There is no theoretical limit to the distance over which this could be accomplished, and the small size of individual photons implies that detailed and instant communications could eventually be accomplished.

More recently, Gerhard Rempe and colleagues at the University of Konstanz in Germany have effectively measured the actual motion of the particles in the "two slit" experiment without interfering with them. What was revealed was that the process of measurement still ended the interference pattern, even though it did not transmit enough energy to the particles to change their momentum. What this proves is that the particles are linked in such a way that one moves when the other is pushed. In effect, they act as a single object, even though they exist in different places. "Loss of interference is always due to entanglement," said physicist Yu Shi at the University of Cambridge.

Now the question becomes: Just how deep is this linking and how extensively can it be exploited for real-world gain? For example, is everything linked? If the big bang happened, then there was a time prior that all particles now existing in the universe were packed tightly together. Does the "ghost" of this linkage still haunt the universe, and can it be exploited to extend humankind's vision to the infinite?

If so, it might explain why SETI (the Search for Extraterrestrial Intelligence), now being conducted on radio telescopes around the world, has thus far failed to find any ET signals. An ET race even slightly more advanced than ourselves might already know, as we are on the verge of discovering, that communication based on quantum entanglement is infinitely more effective than mere radio. This would be especially significant to any spacefaring race, including ourselves in the near future, where communication over distances of billions or trillions of miles were desired. If current discoveries can be adapted to practical purposes, instant communication between stars, even galaxies, will be possible.

Thanks to Nature and The New Scientist. Further reading "Origin of quantum mechanical complementarity probed by a 'which-way' experiment in an atom interferometer," S. Durr, T. Nonn, G. Rempe, Nature vol. 395, p. 33. "An End to Uncertainty," Mark Buchanan, The New Scientist 6 March 1999, "Light's spooky connections set distance record," Mark Buchanan, The New Scientist, 28 June 1997.