Cosmox Blogs

Jul 04, 2022

Time Travel To Past

In life there are so many things we wish we could change but certain circumstances stopped us from doing it. We all have made mistakes in life and we just wish we could fix them, we just wish we could go back in time and fix those mistakes, we wish we could have taken a different decision back then so we wouldn’t have to regret it. I’m pretty sure you would have thought about this once in your life and we all have. That we could just travel back in time and change whatever we want to. 

So let’s see in what ways you can;

Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime or specific types of motion in space might allow time travel into the past and future if these geometries or motions were possible.  In technical papers, physicists discuss the possibility of closed time like curves, which are world lines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetime which contain closed time like curves, such as Gödel spacetime, but the physical plausibility of these solutions is uncertain.

General Relativity

Time travel to the past is theoretically possible in certain general relativity spacetime geometries that permit traveling faster than the speed of light, such as cosmic strings, traversable wormholes, and Alcubierre drives. The theory of general relativity does suggest a scientific basis for the possibility of backward time travel in certain unusual scenarios, although arguments from semi classical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed. These semi classical arguments led Stephen Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel, but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.

Wormholes

Wormholes are closed time like curves in the spacetime fabric which would allow us to travel to the past. A traversable wormhole would be a good option for traveling to the past because it would be stable enough to travel through it. Some scientists believe that black holes might be wormholes which can allow us to travel through time. They say that because some supermassive black holes might have such strong gravitational force that it would create a closed time like curve in the spacetime fabric.

Paradoxes

Unlike traveling to the future which has got a bunch of ways, traveling to the past has got a bunch of paradoxes. What are paradoxes you might ask, well a paradox means an event or situation which has got no conclusion to it, it’s because when we consider traveling to the past it goes against logic and causality? You will understand this as you further, read it.

Grandfather's Paradox -

Now this paradox is as catchy as it sounds. Imagine you invent a time machine, go to the past and kill your grandfather, now if your grandfather is dead your father is not born, and therefore you are also not born, if you are not born then how can you go to the past and kill your grandfather. This of course violates causality which says an effect can’t happen before a cause, you can’t born with your grandfather bring dead.

Some scientists give a theory to add a solution to this paradox, this theory says that when you kill your grandfather you create an alternate timeline that doesn’t affect your timeline, and therefore there will be no change in your timeline. In other words, killing your grandfather will create a different universe where things will go on in a different way as a result of your grandfather being dead.

Predestination Paradox -

Imagine your friend is coming to meet you but unfortunately, he dies in a car accident, you get traumatized by this and you decide to make a time machine and save your friend, after years of hard work you finally make a time machine and travel to the past, at that time when your friend was on the way to meet you. You find a car there and go to save him but accidentally you hit a car and the person in that car dies and the person who dies in that car was actually your friend. So you were the cause of your friend’s death. In other words, your attempt to save him caused his death. So this paradox says that your future affects your past. This concept was also shown in the movie predestination.

Bootstrap Paradox -

Imagine you are sitting in your room and decide to go to the kitchen to drink some water, as you open your door you see there is a book at your doorstep and you pick it up, and when you open that book and see it carefully you realize it has all the mathematical equations and physics to make a time machine, after years you finally invent a time machine and travel to the past, at the time when you were a kid and you keep that same book at your past self’s doorstep due to some reasons and come back to your present, now the question is if you got that book when you were a kid from your future self and you create a time machine and keep that same book at your past self’s doorstep where did that book actually come from because you only gave it to your past self by which you received it when you were a kid. This concept was also used in the Netflix series Dark.

Polchinski's Paradox -

In this scenario, the ball is fired into a wormhole at an angle such that, if it continues along that path, it will exit the wormhole in the past at just the right angle to collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place. Now if the bullet doesn’t enter the wormhole then how it will prevent itself from entering the wormhole, now this is a bit similar to the grandfather paradox but it points out a question at the spacetime geometries which allows time travel to the past, now as it violates causality some scientists say that spacetime geometries will not allow time travel to the past, rather it would lead us to parallel universes and higher dimensions.

Conclusion

So far time travel to the past has been a subject of debate among most physicists, and some of them even consider this impossible, but let’s see what the future brings us as a result of generations of research on time travel and its possibility. Right now we can only focus on the present and try to rectify the mistakes we have done and give our best.