Is time travel realistic?

Amos Ori, a physicist of the Technion Israel Institute of Technology in Haifa, came up with a new time machine design that is more practical than previous. This one doesn't require exotic conditions and materials but uses normal matter and vacuum.

Ken D. Olum of Tufts University in Medford, Mass., is skeptical that Ori's concept could succeed. Until now, scientists have called for using prodigious amounts of an exotic entity known as negative energy, which theorists expect to exist only in minuscule quantities, for time machines. In 1992, Stephen W. Hawking of Cambridge University in England proved a theorem that rules out time machines built without negative energy, Olum notes. Ori counters that Hawking's analysis involves certain conditions that don't apply to his concept.

Read more about the theory over here.