With a brilliant idea and equations based on Einstein’s relativity theories, Ronald Mallett from the University of Connecticut has devised an experiment to observe a time traveling neutron in a circulating light beam. While his team still needs funding for the project, Mallett calculates that the possibility of time travel using this method could be verified within a decade.
Black holes, wormholes, and cosmic strings – each of these phenomena has been proposed as a method for time travel, but none seem feasible, for (at least) one major reason. Although theoretically they could distort space-time, they all require an unthinkably gigantic amount of mass.
Mallett, a U Conn Physics Professor for 30 years, considered an alternative to these time travel methods based on Einstein’s famous relativity equation: E=mc2.
“Einstein showed that mass and energy are the same thing,” said Mallett, who published his first research on time travel in 2000 in Physics Letters. “The time machine we’ve designed uses light in the form of circulating lasers to warp or loop time instead of using massive objects.”
To determine if time loops exist, Mallett is designing a desktop-sized device that will test his time-warping theory. By arranging mirrors, Mallett can make a circulating light beam which should warp surrounding space. Because some subatomic particles have extremely short lifetimes, Mallett hopes that he will observe these particles to exist for a longer time than expected when placed in the vicinity of the circulating light beam. A longer lifetime means that the particles must have flowed through a time loop into the future.
“Say you have a cup of coffee and a spoon,” Mallett explaines. “The coffee is empty space, and the spoon is the circulating light beam. When you stir the coffee with the spoon, the coffee – or the empty space – gets twisted. Suppose you drop a sugar cube in the coffee. If empty space were twisting, you’d be able to detect it by observing a subatomic particle moving around in the space.”
And according to Einstein, whenever you do something to space, you also affect time. Twisting space causes time to be twisted, meaning you could theoretically walk through time as you walk through space.
"As physicists, our experiments deal with subatomic particles,” said Mallett. “How soon humans will be able to time travel depends largely on the success of these experiments, which will take the better part of a decade. And depending on breakthroughs, technology, and funding, I believe that human time travel could happen this century.”
Step back a minute (sorry, only figuratively). How do we know that time is not merely a human invention, and that manipulating it just doesn’t make sense?
“What is time? That is a very, very difficult question,” said Mallett. “Time is a way of separating events from each other. Even without thinking about time, we can see that things change, seasons change, people change. The fact that the world changes is an intrinsic feature of the physical world, and time is independent of whether or not we have a name for it.
“To physicists, time is what’s measured by clocks. Using this definition, we can manipulate time by changing the rate of clocks, which changes the rate at which events occur. Einstein showed that time is affected by motion, and his theories have been demonstrated experimentally by comparing time on an atomic clock that has traveled around the earth on a jet. It’s slower than a clock on earth.”
Although the jet-flying clock regained its normal pace when it landed, it never caught up with earth clocks – which means that we have a time traveler from the past among us already, even though it thinks it’s in the future.
Some people show concern over time traveling, although Mallett – an advocate of the Parallel Universes theory – assures us that time machines will not present any danger.
“The Grandfather Paradox [where you go back in time and kill your grandfather] is not an issue,” said Mallett. “In a sense, time travel means that you’re traveling both in time and into other universes. If you go back into the past, you’ll go into another universe. As soon as you arrive at the past, you’re making a choice and there’ll be a split. Our universe will not be affected by what you do in your visit to the past"
OBJECTIONS:
In a recent paper by Ken 0lum an
d allen everett, the authors claimed to have found problems with Mallett's analysis. One of their objections is that the spacetime Mallett used in his analysis contains a
singularity even when the power to the laser is off, and is not the spacetime that would be expected to arise naturally if the circulating laser were turned on in previously empty space. Mallett has not offered a published response to Olum and Everett, but in his book
Time Traveler he mentions that he was unable to directly model the optical fibre or
photonic crystal which bends the light's path as it travels through it, so the light circulates around rather than moving in a straight line; as a substitute he chose to include a "line source" (a type of one-dimensional singularity) which would act as a "geometric constraint", bending spacetime in such a way that the light would circulate around on a helix-shaped path in a vacuum. He noted that closed timelike curves are present in a spacetime containing both the line source and the circulating light, while they are not present in a spacetime containing only the line source, so that "the closed loops in time had been produced by the circulating flow of light, and not by the non-moving line source." However, he does not provide any additional argument as to why we should expect to see closed timelike curves in a different spacetime where there is no line source, and where the light is caused to circulate due to passing through a physical substance like a photonic crystal rather than circulating in a vacuum due to the curved spacetime around the line source.
Another objection by Olum and Everett is that even if Mallett's choice of spacetime were correct, the energy required to twist spacetime sufficiently would be huge, and that with lasers of the type in use today the ring would have to be much larger than the observable universe. At one point Mallett agreed that in a vacuum the energy requirements would be impractical, but noted that the energy required goes down as the speed of light goes down, so he argued that if the light is slowed down significantly by passing it through a medium(as in the experiments of Lene hau where light was passed through a
superfluid and slowed to about 17 metres per second) the needed energy would be attainable. However, the physicist J.Richard Gott argues that slowing down light by passing it through a medium cannot be treated as equivalent to lowering the constant
c (the speed of light in a vacuum) in the equations of general relativity, saying:
- One has to distinguish between the speed of light in empty space, which is a constant, and through a medium, which can be less. Light travels more slowly through water than through empty space but this does not mean that you age more slowly while scuba diving or that it is easier to twist space-time underwater.
- The experiments done so far don't lower the speed of light in empty space; they just lower the speed of light in a medium and should not make it easier to twist space-time. Thus, it should not take any less mass-energy to form a black hole or a time machine of a given size in such a medium.
Later, Mallett abandoned the idea of using slowed light to reduce the energy, writing "For a time, I considered the possibility that slowing down light might increase the gravitational frame dragging effect of the ring laser ... Slow light, however, turned out not to be helpful for my research."
Finally, Olum and Everett note a theorem proved by Stephen Hawkin in a 1992 paper on the
Cronology Protection Conjecture(CPC), which demonstrated that according to general relativity it should be impossible to create closed timelike curves in any finite region that satisfies the weak energy condition, meaning that the region contains no
exotic matter with negative energy. Mallett's original solution involved a spacetime containing a line source of infinite length, so it did not violate this theorem despite the absence of exotic matter, but Olum and Everett point out that the theorem "would, however, rule out the creation of CTC's in any finite-sized approximation to this spacetime."
With these objections proff. Ronald Mallett is still working on his theory.I personally dont have any objections with his theory and would certainly like to see any positive cosequences towards the human quest on TIME.