"...they can't come to us..," Carl Sagan
Q: I believe Einstein's General Relativity Theory mathematically proved that time travel into the past is impossible. Do the recent experiments
showing that light can be slowed, then returned to its normal speed, have any theoretical implications for time travel ?
A: Yes, according to Ronald Mallett, theoretical physicist and professor at the University of Connecticut, recent
experiments slowing light's speed may make time-travel feasible. Mallet thinks he can harness slow-light energy
and turn the future into the past.
Right: [Richard Hallock] Time machine model
You're somewhat mistaken, however, about Einstein proving time travel impossible. Instead, his general theory
of relativity describes how matter warps space-time. It's theoretically possible to distort the space-time we live
in enough to create a time-travel path (called a closed timelike curve). Walking along such a path, you would
find your watch running forward as normal but you would eventually reach the place-time you started.
Mallett thinks time travel is not merely theoretically possible but doable, given the speed-of-light breakthrough. He and a group of scientists at University of
Connecticut are designing the first experiment to test Mallett's ideas. They plan to build a time-travel device.
Matter distorts space and time. Clocks, for example, run slower in Earth's gravitational field than they do in outer space. Get a really massive object, say the
Universe, spinning and you can twist space and time into a ring. So time, instead of marching straight ahead in a line from past to future, curves around. The
future can meet the past and you, following the ring, can return to a particular moment.
The energy requirements totally rule out this approach. Rotate the Universe? Forget it. Mallett knows, though, he doesn't need mass. He can use light.
Light causes space to bend. Last year Mallett published a paper in Physics Letters describing how a circulating laser beam creates a vortex in space within its
circle. The bent laser light actually causes space to whirl around like a twister within the circle.
Mallett deduced that, if he adds a second laser beam shining in the opposite direction and increases its intensity enough, he can warp time into a loop.
Unfortunately, once again the energy required is out of reach.
Then he saw an answer. His equations show the slower the light moves within the laser circle, the more space and time distort. Bingo. He can get the needed
energy from slow-moving light. The whole crazy notion suddenly became maybe, just maybe, feasible.
In February 1999, Lene Hua and a team at Rowland Institute for Science succeeded slowing light to 38 miles per hour-a galloping zebra goes faster. Mallett
plans to use their results in his experiment.
William Stwalley (Mallett's department head),
Mallett, and a team of cold-atom researchers plan
their attack in stages. First they will trap a particle
in a light circle and observe its spin. Then they will
add the second light beam and observe. Mallett
doesn't know what to expect but hopes for some
evidence of time travel. Perhaps the spinning
particle will be joined by another spinning
particle-itself, from the future.
"...maybe backward time travel is possible, but only up to the moment that time travel is invented. We haven't invented it yet, so they can't come to us. They
can come to as far back as whatever it would be, say A.D. 2300, but not further back in time." -Carl Sagan, NOVA interview
(Answered by April Holladay, science correspondent, June 20, 2001)
Further Surfing:
Virtual Vikki's: Time-machine model creation
Science News: Evading quantum barrier to time travel
NOVA: Time Travel
Friesian School: Time travel paradoxes
Science News: Evading quantum barrier to time travel
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