Imagine exiting your future and entering your past or the other way round. Albert Einstein’s time dilation theory allows this. It says time moves slowly for objects as they near the speed of light. In physics, time is just another dimension like length, width and height.
Mathematically, you can go backwards or forwards only in these three spatial dimensions, but not in time. This discouraged generations of scientists from taking time travel seriously.
But Einstein said space and time are tangled together in a sort of four-dimensional fabric. When something with mass sits on this “space-time continuum”, it warps, making the object move on a curved path in space. This effect, called ‘gravity’, makes time flow like a ‘river’ that meanders around stars and galaxies, speeding up and slowing down as it passes around massive bodies. In the latest issue of Nature Physics, Gerald Gwinner of the University of Manitoba describes how he speeded up lithium atoms to 6 per cent the speed of light and found their frequency dropped dramatically. This indication that time had slowed down for the atoms confirms the time dilation theory.
A popular time travel theory involves ‘wormholes’ — hypothetical tunnels connecting two regions of space-time. Matter can enter a wormhole at one end and emerge from the other into a ‘parallel universe’. But we need a ‘theory of everything’, which solves all of Einstein’s space-time equations, to validate this. To evolve such a grand theory, scientists are now trying to add quantum theory (where an object exists simultaneously in different states) to gravity.
String theory describes matter in a minimum of 10 dimensions. ‘Cosmic strings’ are narrow energy tubes from the infant cosmos that stretch across the expanding universe. They contain huge amounts of mass. When two such strings approach parallel to each other, space-time warps, making time travel possible. The trouble is, no one’s been able to unravel the string theory fully. So stepping into the future with every moment is the only time travel we can do now.