We all know that everywhere inside this universe, time flows naturally forward. That’s true in the general case but not everything in this universe can be placed under such a general case.
Lets take the case of one of the most exotic cosmic objects, black holes. A black hole is usually formed from the death of a supergiant star. When a star expires it’s lifetime, it explodes in a marvelous burst of glowing gas and dust called a supernova. During this process if the mass of the dying star was less than 3 solar masses it would become a neutron star but if it is greater than that it would turn into this cosmic monster called a black hole.
It sucks in everything that comes into its vicinity, even light cannot escape out of a black hole. In the 1950s Einstein explained black holes as places with extreme curvature of the fabric of space-time. It was a theoretical possibility according to relativity that we could make time run backward by making space-time to curve beyond a certain limit. However, it was not accepted by many scientists, even Einstein did not make any significant comments on this.
Nevertheless, relativity says that time is not absolute, which means that there is nothing like an universal clock as Newton suspected. Time can run at different speeds in different frames of reference.
So the question is that does time run backwards? Can we go back to the past or is it gone forever? These are rather hard questions to answer. As of now we don’t have any evidence of objects going to the past or returning from there. There are many theoretical possibility but all of them come with huge uncertainties which makes them nothing more than mere dubious speculations.
However, relativity puts forward another phenomenon, time dilation. This is a process that occurs when the relative time difference between two frames of reference increases significantly. As time runs at different speeds in different reference frames, the faster you move relative an external observer the slower your clocks will become relative to his. But for you everything that moves with you (for an astronaut, everything inside the space craft) will be running at normal speed because the functions of you brain would also get slowed down just like your clocks.
This process is more clearly explained by the twin paradox. In it we consider two identical twins, one stays at Earth and the other travels through space near the speed of light. They meet after a few years and the twin who stayed at Earth would be much older than the traveling twin.
This is because the faster you move the slower time passes when observed from outside. So when you get back to the observers (here the stationary twin) frame of reference, more time would have passed for him because your time was moving slower relative to him.
Notice that this process never takes you (or the observer) back in time, it just chances the speed in which times moves for you (or the observer). So in all cases time always runs forward, the only change that happens is in its speed.
Nevertheless, the question whether time runs backward or not is still unknown but that won’t be for so long. Soon our curious minds will tackle it too.
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