Paradox of bootstrap in time travel: Mystery of cause and effect



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The paradox of bootstrap in time travel, also known as the loop paradox, has puzzled scientists for a long time. Imagine a situation where one day you receive a mysterious package, but there is no note indicating who sent it and why. Curious yet puzzled, you open the package and find a book titled “How to Build a Time Machine.” At first, you might think it’s some kind of joke, but after reading its contents, you begin to believe that the book may be genuinely authentic. You decide to take up the challenge and start gathering all the materials and objects needed to construct a time machine. It takes a lot of time, but after 10 years and several unsuccessful attempts, you finally manage to build a functional time machine.

During these ten years, you never find out where the book came from and why it was sent to you. However, suddenly, a thought occurs to you. You grab the book and jump into the time machine. You travel back in time by 10 years, leaving the book for your younger self to discover. But where does this book actually come from? You can only build a time machine if you discover this book. However, you can only discover this book if you build a time machine. It seems like the book was never created by anyone and is stuck in an infinite causal loop. This is what we call the bootstrap paradox.

The bootstrap paradox applies not only to objects, like the book, but also to information and even individuals. Imagine traveling further back in the past and meeting a young Albert Einstein before he became famous. You would tell him about the theory of relativity that he will later publish, and you would learn about it many years later in school. Who actually came up with the theory? Another example could be traveling to the late 16th century to meet a young William Shakespeare before he was known. However, you fail to find him, and nobody has even heard of him. Fortunately, you brought with you the complete works of Shakespeare and decide to publish them as your own. In other words, you have always been William Shakespeare.

Understanding the Cause and Effect Relationship

The bootstrap paradox contradicts our understanding of cause and effect. In our linear concept of time, event A in the past causes event B in the present, which, in turn, causes event C in the future. Time flows directly from A to C, and the future is always uncertain, depending on our actions in the past and present. In the bootstrap paradox, event C causes event A, which would mean that the future event has already happened. This clearly goes against our linear notion of time, suggesting that the past, present, and future are equally real, but we subjectively experience only the present moment.

This paradox has significant implications for the issue of free will. Does our time traveler have a choice whether to build the time machine, or is it already predetermined that they will build it? Otherwise, where would they have received the book? One possible solution is the idea of traveling between universes in time (multiverse time travel). When the time traveler goes back in the past, they shift to another universe, a duplicate of the one they left, which is identical up to the moment of their arrival. In this new reality, they are free to act without affecting the original universe. This would not be a true causal loop, but it could explain how time travel is possible and how past events can be changed.

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Paradox Chasing Paradox

Another problem associated with the bootstrap paradox is the violation of the second law of thermodynamics. An object trapped in a time loop, like the book, would age and deteriorate over time. Entropy would increase to the point where it could no longer be used to build a time machine. We could speculate that entropy is reversed by time travel, so the book is restored to its original state. However, it is not clear what the true initial state of the object is when there is no clear beginning. Would the same apply to the time traveler, restoring them to the state from ten years ago? This would render time travel to the 16th century impossible.

Of course, all these considerations pertain to hypothetical scenarios. Paradoxes like the grandfather paradox and the bootstrap paradox demonstrate why some scientists, like Stephen Hawking, believe that time travel to the past is impossible. But what do you think? Will we ever be able to travel through time? Here are five scientific sources that can deepen your knowledge of the time travel paradox:

  1. Barceló, C., & Visser, M. (2014). Closed timelike curves and causality violation. International Journal of Modern Physics D,
  2. Lewis, D. (1976). The paradoxes of time travel. American Philosophical Quarterly, 
  3. Nahin, P. J. (2001). Time machines: Time travel in physics, metaphysics, and science fiction. Springer Science & Business Media.
  4. Smeenk, C., & Wüthrich, C. (2011). Time travel and time machines. Stanford Encyclopedia of Philosophy.
  5. Thorne, K. S. (1994). Black holes and time warps: Einstein’s outrageous legacy. W. W. Norton & Company.
Jakub Markiewicz
Jakub Markiewicz
Hi, I am the author of the blog and series of thematic portals since 2013. I have nearly 15 years of experience in working in the media, marketing, public relations and IT. If you are interested in cooperation, you would like me to write about something or test a product - let me know.
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