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Einstein's theory of general relativity revolutionized our understanding of space and time. He proposed that space and time are not separate entities, but rather are interwoven into a single fabric called spacetime. This spacetime is curved by the presence of mass and energy, and this curvature is what we experience as gravity. He thought of space as being like a trampoline. If you place a heavy ball on a trampoline, it will cause the trampoline to curve. This curvature will then cause other objects placed on the trampoline to be attracted to the ball. The same principle applies to spacetime. The presence of mass and energy curves spacetime, and this curvature is what causes objects to be attracted to one another. The more mass and energy an object has, the more it curves spacetime.
Does the inability to utilize time dilation for backward time travel imply that the past is eternally unreachable? Maybe not. Einstein postulated the possibility of accessing the past through an Einstein-Rosen bridge, which is a form of a wormhole. Wormholes are theoretical regions of space-time that exhibit a curvature enabling the connection of distant points in space. According to Einstein's equations, it was hypothesized that this spatial bridge could potentially connect two moments in time if it possessed sufficient stability. However, presently, even an Einstein-Rosen bridge cannot facilitate travel to the past or future due to its inherent instability, rendering it short-lived.
In the movie Interstellar, the crew of the Endurance land on a planet near a supermassive black hole called Gargantua. The intense gravitational field of Gargantua causes time to slow down on the planet so that one hour on the planet is equal to seven years on Earth. This means that when the crew returns to Earth, they find that many years have passed, while they have only aged a few years. When Cooper (Matthew McConaughey) returns to Earth, he finds that his daughter, Murph (Jessica Chastain), is now an old woman. This is because Murph has aged seven years for every hour that Cooper has spent on the planet.
Although the idea of journeying back in time to witness dinosaurs or engage with Albert Einstein and demonstrate the concept of time travel is intriguing, it might be more prudent to leave the past undisturbed. Venturing into the past opens up the potential for unintended changes that could have detrimental effects on the future. Consider the movie "Back to the Future," where Marty McFly travels to the past and accidentally alters his parents' encounter, jeopardizing his own existence. However, if he had ceased to exist, how would he have been able to travel back in time initially?
A more common form of this is the Grandfather Paradox: If you travel back in time and kill your grandfather, your father won’t be born and neither would be you. If you weren’t born how did you travel back in time to kill your grandfather in the first place?
Despite the intriguing nature of these recent discoveries, they seem to provide stronger evidence supporting the notion that while time dilation enables us to catch glimpses of the future, traveling to the past will forever remain beyond our reach. As expressed by the late Stephen Hawking in his book "Black Holes and Baby Universes, “The best evidence we have that time travel [into the past] is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”
Even if you could travel to the past would you take the risk of changing it, because you will have to wait to see the consequences and tweak it here and there again and again to achieve the utopian future or present? Or for that matter of fact, if you somehow know the future like Louise gets to know the future through aliens and their language in the movie Arrival (2016), will you bother to change it?
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