Time machine theory: a step forward in travelling backwards?

From H.G Wells' classic novel to Bill and Ted’s Excellent Adventure, the popular imagination has long been enthralled by the prospect of time travel. Now researchers at the Israel Institute of Technology, Techion, have released a paper outlining theoretical advances that could one day assist in liberating the notion of a time-machine from the realms of pure science fiction. The research by Prof. Amos Ori of the Technion’s Faculty of Physics centers around a new model of space-time that overcomes some (but not all) of the theoretical stumbling blocks that would prevent the required curvature of space-time needed to facilitate time travel.

The paper entitled “A Class of Time-Machine Solutions with a Compact Vacuum Core” was published recently in the scientific journal Physical Review and in it Prof. Ori posits theoretical model for space-time that could develop into a time machine.

“In order to travel back in time, the spacetime structure must be engineered appropriately,” explains Prof. Ori. “This is what Einstein’s theory of general relativity deals with. It says that spacetime can be flat. That is – it has a trivial, simple structure. But it can also be curved with various configurations. According to the theory of relativity, the essence of gravitational fields is in the curving of spacetime. The theory of relativity also defines how space is curved and how this curvature develops over time.”

Einstein was a genius for good reason, and consequently the idea of space-time is a very difficult concept to get your head around. One analogy that’s often used is to imagine a bowling ball resting on a large trampoline – if the bowling ball is the sun, the sagging trampoline is akin to space-time and a smaller ball will roll around it the way the earth does. Thus gravity is really just a result of the warping of the fabric space-time. This doesn’t really explain how time gets involved in the equation, but suffice to say that the idea of time travel involves bending this fabric back on itself and somehow connecting two different points to make travel between present and past possible. Wormholes are seen as one potential way to achieve this.

Prof. Ori’s model solves some of the problems associated with theoretically achieving this bending of space-time. One such problem is the belief that material with “negative density” (it isn’t even clear whether this actually exists in the quantities required) would be necessary for the creation of a time-machine. Prof. Ori’s theoretical model proposes a vacuum space that contains a region field with standard positive density material and therefore by-passes this problem.

“The machine is spacetime itself,” he explains. “Today, if we were to create a time machine – 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, apparently, cannot return to previous ages because our predecessors did not create this infrastructure for us.”

This final point means that – unless some ancient civilization built a time machine or such a phenomena somehow exists in nature – there is no way to go back in time beyond the point at which the time machine was constructed, even in theory.

Prof. Ori does not pretend that we yet have the technology to control gravitational fields at will and admits that a number of “non-trivial open questions” remain unanswered… and indeed might remain that way for ever.