Scientists at the NEC Research Institute in Princeton, N. J., have submitted a paper to Nature for peer review that describes an experiment in which light was accelerated to 300 times its normal speed, so fast that the pulse exited the test chamber before it entered. While this does not mean that Einstein’s General Theory of Relativity, which states that the speed of light (186,000 miles per second) is the fastest speed in the universe, is necessarily invalid, it does mean that important principles of propagation are just now being discovered. Whether or not this research will lead to the ability to signal across time is unknown, but there is no theoretical barrier to this process. However, it has been shown that the so-called ‘grandfather paradox’ would make alteration of the past impossible if it changed the future.
However, other scientists believe that the universe is dependent upon loops in spacetime, and that the future can indeed influence the past–in fact, that this is what gave rise to the universe in the first place. In the April 6, 1998 Physical Review Letters, two Princeton researchers showed that quantum effects do not necessarily prevent the occurence of loops in time. The results of the faster than light experiments now being conducted suggest that detection of such loops may become possible, and with it intervention in the process. In this way, signaling across time may not only be possible, but a reflection of one of the most fundamental realities of the universe.
On August 12, 1995, the New Scientist reported that “the last of the remaining barriers to time-travel has been banished by an international team of physicists.” One of the chief bars to movement through time has been the fact that violating the grandfather paradox would of necessity take more energy than present in the universe. However, physicists demonstrated that another fundamental law, the principle of least action, would make it impossible to do anything to the past that would alter the future. (It is the principle of least action that dictates that nothing in nature will ever expend more energy than that least amount necessary to perform an action. That is to say, when flowing down a mountain, water will always seek the lowest possible route of travel. It will never detour over a stone higher than the lowest stone present.)
All of this means that, while changing the past may indeed be a thorny problem, viewing it might be quite possible, and the physical means to do so may not be far from discovery.
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