Bootstrap paradox explained!
When we study science sometimes there are paradoxes that come our way. They might look exciting but also confusing at the same time. We’ve seen movies like The Matrix, #Predestination, or perhaps The Netflix series #Dark. These make us question our understanding and beliefs. What If the choices we made are not really ours? What if we are in fact in a dream?
Or what if we are just caught in a time loop? Today we are going to talk about such a paradox, the bootstrap paradox. Let's get to the basics first. What is the flow of time? To our current understanding, it is a continuous progress of events from the past that causes events in the present, which will affect events in future. Therefore, time always passes in a straight line, with the future completely dependent upon events of the past and the present.
Now imagine a boy named Albert who is a great patron of physics, like you and me. He has always wanted to meet his idol, Albert Einstein. Now, somehow he builds a time machine along with the greatest minds of the world. One night, he sneaks into the lab and uses the time machine to travel back in time, to meet Albert Einstein. Now on reaching the time of Albert Einstein, he visits Einstein’s neighborhood to ask about him. Where is he, and how he’s doing. Little does he know, he understands that there was no Albert Einstein, ever existed in that residence. Even surprisingly, no one has ever heard of the name Albert Einstein.
At first, he feels a little bit strange, what in the universe is going on.. Fortunately, he remembers something. He carries a notebook containing all of Einstein’s theories and equations. Everything from E = mc2 to relativity. Still being stuck in that world, he then re-writes the book in the name of Albert Einstein, an idol that has been a lifelong inspiration for him. And then, some scientists picked up his writing and got really intrigued by the theories inside. Over a period of time, those theories have been sensational and eventually, they take the world by storm. He becomes famous and now he understands that he is and has always been ‘the’ Albert Einstein.
So how is that possible? Without Einstein, Albert wouldn’t have been able to become a scientist in the first place. But without him there would have been no Albert Einstein ever existed. And this is the meat of this episode. This paradox goes against our understanding of time. An event A in the past causes event B in the present, which causes event C in the future. However in this case, it is event C which has caused event A in the past. Meaning that it does not fit with the linear explanation of time. Traveling back in time would allow for some causal loops involving events, information, or people and objects, for which histories form a closed loop, and seem to arrive or emerge unexpectedly. This is the essential problem of the bootstrap paradox. The notion of objects or information that are “self-existing” in this way, is very often viewed as paradoxical. And it doesn’t stop there. The bootstrap paradox also violates the law of free will.
Do we really have a free choice to build the time machine or has it been ingrained in us in the first place. The most widely spread idea about it is a multiverse travel. Which says.. when a time traveler uses a time machine, they do not go back in time. Instead, they travel towards another multiverse, giving them the will to act freely in the other universe. Another problem that the bootstrap paradox presents is that it violates the second law of thermodynamics. The entropy of the system will either remain constant or increase. So an object used in a time loop will eventually wear down with time. Suppose that the entropy is altered as we go back in time and hence the object is back to its original entropy. However, its entropy does not have a clear state since it doesn't have a clear origin to begin with. And this sort of gives rise to new problems.
Therefore, paradoxes like the bootstrap and the grandfather paradox make many scientists like Brian Cox and Stephen Hawking believe that time travel is impossible. Hawking made this very clear in his books. He believed that there must be a law of nature to prevent time travel to the past. Time travel to the future is achievable and even clocks in space do that. But time travel in the past cannot be possible. It would simply go against the laws of nature. And in our case we discussed the time loop in which if we would be caught, it would violate all the laws of physics.