Wednesday, 5 October 2016

TIME TRAVEL

TIME TRAVEL



Time travel's been one of man's wildest fantasies for centuries. It's long been a popular trend in movies and fiction, inspiring everything from Charles Dickens' A Christmas Carol to H.G. Wells' The Time Machine to the Charlton Heston shrine that is The Planet of the Apes. And with the opening of Interstellar today—n0t to spoil anything—we're about to fantasize about it even more.

The most fantastic thing? It's probably possible.

What's almost impossible

Let's start with the bad news. We probably can't travel back in time and watch the Egyptians build the pyramids. In the last century scientists came up with a number of theories that suggested it is indeed plausible to take a leap into the future; going back in time, unfortunately, is much more complicated. But it's not necessarily impossible.

Albert Einstein laid the groundwork for much of the theoretical science that governs most time travel research today. Of course, scientists like Galileo and Poincaré that came before him helped, but Einstein's theories of special and general relativity dramatically changed our understanding of time and space. And it's because of these well-tested theories that we believe time travel is possible.

One option for would be a wormhole, also known as an Einstein-Rosen bridge. Along with physicist Nathan Rosen, Einstein suggested the existence of wormholes in 1935, and although we've yet to discover one, many scientists have contributed their own theories about how wormholes might work. Stephen Hawking and Kip Thorne are probably the most well known. Thorne, a theoretical physicist at CalTech, even helped Christopher Nolan with the science behind Interstellar.



So let's just assume that wormholes do exist. In the late 1980s, Thorne said that a wormhole could be made into a time machine. According to Einstein's theory of general relativity, a wormhole could act like a bridge though space-time by connecting two distant points with a shortcut. Certain types of wormholes, it's theorized, could allow for time travel in either direction, if we could accelerate one mouth of the wormhole to near-light speed and then reverse it back to its original position. Meanwhile, the other mouth would remain stationary. The result would be that the moving mouth would age less slowly than the stationary mouth thanks to the effect of time dilation—more on this in a second.

But there are several major caveats of traveling back in time with this method. Chief among them is the simple fact that we'd need a method for creating wormholes, and once created, the wormhole would only allow us to travel as far back as the point in time when it was created. So we'll definitely never be spectators to Great Pyramids' construction.

The other really serious caveat is that we'd need a way to move one of the mouths of the wormhole nearly the speed of light. In their seminal 1988 paper on wormholes, Thorne and his colleagues assumed that "advanced beings [would] produce this motion by pulling on the right mouth gravitationally or electronically." We can't do that right now, however.

What we can do is travel into the future—but only by a little bit.

What's almost certainly possible

In recent years, we've seen some aspects of Einstein's fanciful theories proven true. The latest and perhaps most exciting theory is the aforementioned effect called time dilation. Though we've based technology on the theory for decades, an experiment finally proved this year that time dilation is absolutely a real phenomenon. It's also a phenomenon that could allow us to travel into the future.

Time dilation basically refers to the idea that time passes more slowly for a moving clock than it does for a stationary clock. The force of gravity also affects the difference in elapsed time. The greater the gravity and the greater the velocity, the greater the difference in time. Black holes, like the one depicted in Interstellar, for instance,would produce a massive amount of time dilation, due to t

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