In one of the wildest developments in serious science for decades, researchers from all over the world have recently been investigating the possibility of time travel; but they have realized that according to the equations of Albert Einstein's general theory of relativity (the best theory of time and space we have), there is nothing in the laws of physics to prevent time travel. It may be extremely difficult to put into practice; but it is not impossible.
Time has fascinated people throughout our history; we have constantly come up with every increasingly more complex and accurate ways to measure the passing of this thing which we call time. However, I wonder how many people realize that time itself is not exactly the same wherever you are. Astronomer Carl Sagan had it right when he said that time is "resistant to simple definition." Lots of us think we know what time is, but it is hard to define. You cannot literally see or touch time, but you can see its effects. The evidence that we are moving through time is found in everything -- our bodies age, buildings weather and crumble, trees grow. Most of us feel the pressure of time as we are pushed to meet deadlines and make appointments. Our lives are often dictated by what time we need to be somewhere. Ask most people to define time and they are likely to look at their watch or a clock. We see time as the ticking of the hands on these devices. We know that there are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day and 365 days in a year. These are the basic numbers of time that we all learned in grade school.
Albert Einstein was the first to show in his Theory of Relativity that time was not, in fact, a smooth river, constant in its flow, but something that could be affected by motion and by gravity - an effect known as time dilation. Einstein did not consider time and the three spatial dimensions as being separate, but as being linked to form a four-dimensional quantity known as space-time. He defined time as being the fourth dimension of our universe. The other three dimensions are of space, including up down, left-right and backward-forward. Time cannot exist without space, and likewise, space cannot exist without time. This interconnected relationship of time and space is called the space-time continuum, which means that any event that occurs in the universe has to involve both space and time.
According to Einstein's theory of special relativity, time slows as an object approaches the speed of light. This leads many scientists to believe that traveling faster than the speed of light could open up the possibility of time travel to the past as well as to the future. The problem is that the speed of light is believed to be the highest speed at which something can travel, so it is unlikely that we will be able to travel into the past. As an object nears the speed of light, its relativistic mass increases until, at the speed of light, it becomes infinite. Accelerating an infinite mass any faster than that is impossible, or at least it seems to be right now.
It sounds like science fiction, but it is taken so seriously by relativists that some of them have proposed that there must be a law of nature to prevent time travel and thereby prevent paradoxes arising, even though nobody has any idea how such a law would operate. The classic paradox, of course, occurs when a person travels back in time and does something to prevent their own birth -- killing their granny as a baby, in the more gruesome example, or simply making sure their parents never get together, as in Back to the Future. It goes against commonsense, say the skeptics, so there must be a law against it. This is more or less the same argument that was used to prove that space travel is impossible.
According to one interpretation of quantum physics (there are several interpretations, and nobody knows which one, if any, is "right"), every time a quantum object, such as an electron, is faced with a choice, the world divides to allow it to take every possibility on offer. In the simplest example, the electron may be faced with a wall containing two holes, so that it must go through one hole or the other. The Universe splits so that in one version of reality -- one set of relative dimensions -- it goes through the hole on the left, while in the other it goes through the hole on the right. Pushed to its limits, this interpretation says that the Universe is split into infinitely many copies of itself, variations on a basic theme, in which all possible outcomes of all possible "experiments" must happen somewhere in the "multiverse". So there is, for example, a Universe in which the Labor Party has been in power for 15 years, and is now under threat from a resurgent Tory Party led by vibrant young John Major.
How does this resolve the paradoxes? Like this. Suppose someone did go back in time to murder their granny when she was a little girl. On this multiverse picture, they have slid back to a bifurcation point in history. After killing granny, they move forward in time, but up a different branch of the multiverse. In this branch of reality, they were never born; but there is no paradox, because in he universe next door granny is alive and well, so the murderer is born, and goes back in time to commit the foul deed!
Once again, it sounds like science fiction, and once again science fiction writers have indeed been here before. But this idea of parallel universes and alternative histories as a solution to the time travel paradoxes is also now being taken seriously by some (admittedly, not many) researchers. Their research deals with both time, and relative dimensions in space.
No comments:
Post a Comment