Tuesday, January 4, 2000

In recent years, a tiny band of renegade physicists has pushed Albert Einstein’s equations to their logical absurd, some say extreme. They argue that time travel is possible, that time can flow backward and that it’s possible to change the past by venturing through alternate universes.
“Researchers have proposed numerous ways in which time machines can be built that do not seem to violate any known laws of physics,” said inventor-author Clifford Pickover of IBM, one of a small number of scientists who are brazenly enthusiastic about the possibility of time travel.
The January issue of Scientific American asserts: “Contrary to a popular misconception, Albert Einstein’s theories do not strictly forbid either faster-than-light travel or time travel,” according to an article by researchers Lawrence H. Ford and Thomas A. Roman. “In principle, by harnessing the elusive force of negative energy, one can shorten stellar distances by bending space-time around would-be star trekkers.”
That such once-forbidden topics are being discussed at all shows how much our view of time has changed since the early 1900s, when Einstein began questioning orthodox physics.
“Time has a very different meaning from what it did a century ago. Einstein’s theory of relativity completely changed our concept of time, especially his first paper in 1905 [on] ‘special’ relativity,” said Raymond Chiao, a noted physicist at the University of California-Berkeley.
Curiously, to this day no one is really sure what time is.
Prior to the 20th century, scientists assumed that a beam of light would travel at slightly different speeds according to the direction in which it was pointed through ether, a hypothetical medium then assumed to pervade space. In other words, they believed, light traveled just as a swimmer swimming through a moving stream will travel at different speeds according to whether she is swimming with or against the current.
Einstein argued otherwise in a famous 1905 paper. He proposed that there is no ether and that the beam of light always retains the same speed, while space and time change their dimensions around it.
On this basis, he argued that as an object accelerates, its onboard time slows down. For this reason, astronauts age slightly more slowly than people on the ground. According to this theory, astronauts in future starships would return to Earth many years younger than the people who stayed behind.
Fundamental paradoxes about time are posed by Einstein’s famous dictum that nothing can travel faster than light (186,000 miles per second). Faster-than-light travel would be impossible, he said, partly because it would require the spaceship to travel backward in time, according to his calculations.
Einstein’s speculations inspired others to imagine weird possibilities e.g., alternate universes in which time runs backwards. If we lived in such a cosmos, then humans would start their lives as senile duffers and gradually get younger, ending their days as fetuses; trees would begin as old oaks and end as acorns; etc.
In that regard, Einstein’s speed limit that nothing can move faster than light hasn’t gone unchallenged, thanks partly to work on quantum tunneling.
In the quantum world, a particle can move almost instantly from point A to point B without physically traversing the space between them, sort of like the way Capt. Kirk on “Star Trek” boards a transporter or teleportation device to transfer from the Enterprise to a planetary surface.
Quantum tunneling may sound like magic, yet it is a well-established phenomenon; in fact, it is the basis for electronic devices such as the tunnel diode.
Several years ago, Mr. Chiao and his colleagues at Berkeley wondered, how fast does quantum tunneling happen? That is, how long does it take a particle to disappear at point A and reappear at point B?
Using a sophisticated tabletop gadget, they found that the particle makes the tunneling voyage at a speed 1.7 times the speed of light. Ironically, the thicker the barrier between point A and point B, the faster the particle travels.
That may sound like it violates Einstein’s sacred speed limit, which bans an object from traveling faster than light. For complex technical reasons, Mr. Chiao stresses that their finding doesn’t violate Einstein’s rule and is completely compatible with his relativity theory. More importantly, he says, there’s no way the technique could be used to transmit information say, the text of a book faster than light.
But not everyone agrees.
In Germany, Guenter Nimtz of the University of Cologne is conducting experiments similar to Mr. Chiao’s and interprets the results very differently. He claims to have transmitted a recording of Mozart’s 40th Symphony over a short distance at a speed five times that of light.

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