Science: New Model Eliminates Barriers to Time Travel

Noted time-travel theorist Amos Ori has developed a theoretical model of a time machine that could enable future generations to travel into the past. In his paper published in the July issue of "Physical Review," he provides practical solutions to a number of criteria long seen by other experts as obstacles to the realization of time travel.

A Technion-Israel Institute of Technology physicist has developed a theoretical model of a time machine that could enable future generations to travel into the past. In his paper published in the July issue of Physical Review, noted time-travel theorist Professor Amos Ori provides practical solutions to a number of criteria long seen by other experts as obstacles to the realization of time travel.

Ori's theory is actually a set of mathematical equations describing hypothetical conditions that, if established, could lead to the formation of a time machine, technically known as "closed time-like curves."

Previous theories addressing time travel are well grounded in Einstein's General Relativity theory. Renowned physicist Stephen Hawking has called time travel "an important subject for research," but has also proposed some of the strongest challenges to the concept. General Relativity states, among other things, that the gravitational pull of large objects such as planets can actually bend time and space. Time travel research is based on bending space-time so far that the time lines actually bend back on themselves to form a loop.

"We know that bending does happen all the time, but we want the bending to be strong enough and to take a special form where the lines of time make closed loops," says Ori. "We are trying to find out if it is possible to manipulate space-time to develop in such a way."

While the possibility of time travel has never been eliminated, scientists have identified a number of physical challenges, including the perceived need for some form of exotic matter with negative density. Such matter is predicted by quantum field theory to exist, though only in quantities too small for the construction of a time machine.

In a 2004 paper, Ori outlined a set of conditions that would allow for the creation of a time loop without the need for exotic matter. That theory called for the time loop to form as a donut-shaped vacuum, inside which time would curve back on itself, so that a person traveling around the loop might be able to go further back in time with each lap. A sphere containing non-exotic, but unidentified matter, would in turn envelop the loop.

Ori's latest work eliminates the need for that unidentified matter. His new calculations show that the envelope can in fact be filled with dust, a simple modeling of which is used regularly in theoretical physics, while still allowing for the evolution of a time machine.

Ori also addresses the possibility of the initial conditions forming a point of infinite gravitational field that no one could pass (instead of a time travel loop). His current paper outlines a more robust system that would prevent such an occurrence. "The internal core is now mathematically protected," says Ori, "and it is easy to show that no irregularity could penetrate it." The paper also more thoroughly defines the required spherical envelope.

Ori says serious questions remain about the overall stability of a time machine. His own calculations - done in collaboration with Technion Ph.D. student Dana Levanony - and those of other physicists, suggest that the evolution of a time machine would be dependent on a very narrow range of initial conditions that might be difficult - or even impossible - to achieve. He is also working to show ways such a configuration could be achieved.

"If the proper initial conditions were achieved, the time machine would evolve on its own without any further intervention," says Ori, of the Technion Faculty of Physics. "It can be likened to shooting a ship with a cannon. Once the cannon is aimed properly and fired, the cannonball hits the ship on its own, driven solely by the laws of physics."

"The machine is space time itself," he explains. "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time. We, however, could not return to previous ages because our predecessors did not create this infrastructure for us."

The Technion-Israel Institute of Technology is Israel's leading science and technology university. Home to the country's winners of the Nobel Prize in science, it commands a worldwide reputation for its pioneering work in nanotechnology, computer science, biotechnology, water-resource management, materials engineering, aerospace and medicine. The majority of the founders and managers of Israel's high-tech companies are alumni. Based in New York City, the American Technion Society is the leading American organization supporting higher education in Israel, with 17 offices around the country.

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