Back to the Future
צילום: מתוך הסרט
Back to the future
Time travel has always been the exclusive domain of science-fiction novels and popular movies. But a Technion professor now believes that fantasy and reality may converge in the future
Imagine taking a trip in a time machine back to the Beatles’ first concert. Or maybe you’d prefer to jump ahead a few years in order to see what the future has in store.
Sounds like the plot of a typical science-fiction novel? Actually, Technion Israel Institute of Technology researchers say that they’ve developed a theoretical model of a time machine. In a paper published Saturday in the Physical Review journal, the scientists claim that future generations would be able to use the model to travel back in time.
British author and historian HG Wells was likely the first to conceive of such a machine, in his 1895 classic book “The Time Machine”. Later, Albert Einstein’s Theory of Relativity established the scientific principles necessary to examine the physical significance as well as the feasibility of time travel.
Simply put, the Theory of Relativity explains why the speed of light does not change in a vacuum. The relative motion between the observer measuring the speed of light and the light source does not affect this measurement (approximately 186,282.397 miles per second).
The fact that the speed of light is constant leads to other interesting corollaries. For instance, neither time nor space is absolute; rather, they are both dependent on the observer’s motion. This means that motion can impact the beat of time. Therefore, a clock in motion will appear to be moving slower than a clock at rest.
Manipulating the space-time structure
“In order to travel back in time, the space-time structure has to be manipulated appropriately,” explicates Professor Amos Ori of the Technion’s Physics Department. “This is what the General Theory of Relativity is about.
“According to it, space-time can be flat. That is, it has a trivial structure – simple and without complexity – but it also can be curved, with different configurations. According to the Theory of Relativity, gravitational fields are basically warps in space-time. The Theory of Relativity also defines how space is curved and how this warping develops over time.”
The question is: can these principles be used to build a time machine? In other words, can space-time be warped in such a way to allow people to travel back in time? After all, researchers note, time travel requires a significant and specific warping of the space-time structure.
In effect, traveling backwards in time involves closing a loop in time’s structure: the time traveler returns to a moment that has been experienced before. When space-time is flat, loops cannot be closed, and therefore, backward time travel is not viable. Thus, in order for such closed loops to exist, space-time must be curved in a particular manner.
Ori’s research focuses on the laws of gravity. Do they permit space-time to develop with the required curves? In the past, scientists have speculated that this is impossible, but Ori has now developed a theoretical model which indicates that space-time can, in fact, be warped as needed.
Matter with positive density
The new model resolves some of time travel’s more daunting challenges. For instance, scientists believed that time machines called for matter with negative density. However, such matter doesn’t appear to exist in large enough quantities.
But Ori’s model takes a completely different approach and therefore requires matter with positive density, which is far less exotic. “The machine is space-time itself,” he declares. “If we were to now create a time machine - an area with a distortion like this in space which allows time lines to close on themselves – it’s possible that future generations would be able to come back and visit our era.
“Apparently, we will not be able to return to previous eras, because our predecessors did not create this infrastructure for us."
Ori stresses that although his theoretical model indicates that gravitational fields can be manipulated as needed, we still don’t have the necessary technology to do so.
“The model which we developed at the Technion is indeed a significant step,” he emphasizes. “But we are still faced with several unresolved problems which are far from simple. Conceivably, some of these problems won’t be resolved in the future either. It remains to be seen.”
For instance, Ori says, there’s a problem of instability. The very existence of a time machine may lead to disruptions in space-time. If these disruptions grow strong enough, space-time would become increasingly distorted, and the time machine would be nullified.
Professor Ori, a pioneer in this field, hopes that future research will help clarify these and other concerns.
