Western Washington University Professor of Philosophy Ryan Wasserman recently had his book, “Paradoxes of Time Travel,” published in paperback by Oxford University Press.
The book, which was originally published online in 2018, uses physics and philosophy to examine the plethora of questions associated with time travel and the paradoxes associated with the concept.
A time paradox is a contradiction created by time travel. According to Wasserman, there are four broad categories of paradoxes: temporal paradoxes; casual paradoxes; paradoxes of freedom; and paradoxes of identity, such as a time traveler visiting their younger self.
One specific paradox Wasserman discusses in his book, the grandfather paradox, is an example of a paradox of freedom.
“In the classic version of the grandfather paradox, we're to imagine a time traveler who goes back in time and meets an infant version of his paternal grandfather. On the one hand, it seems as if the time traveler should be able to kill his infant grandfather, since he would have both the means and the opportunity to do so,” he said. “On the other hand, it seems as if the time traveler would not be able to commit the crime since, in that case, his father would not be born and the time traveler would not be born -- so he would not be there to kill his grandfather in the first place. This kind of case raises all sorts of interesting questions about the nature of ability, freedom, and fatalism.”
According to Wasserman, this brings up the same kinds of problems as paradoxes of identity.
“If you traveled back to the days of your youth, then you would end up being in two different places at the same time and would presumably have different properties as well -- different beliefs, different physical features, and so on. But this would violate a basic principle of logic -- namely, that nothing can differ from itself,” he said.
As a philosophy professor, Wasserman is asking if time travel is compatible with the laws of logic. His book applies this line of logic to pop culture icons, such when he used the “Harry Potter” franchise to illustrate another time-travel quandary called the bootstrap paradox.
“The bootstrap paradox involves someone (or something) playing a role in its own creation,” Wasserman said.
Wasserman broke down the paradox in J.K. Rowling’s book this way: At one point in the story, Harry is attacked by a pack of deadly dementors and only escapes because a mysterious stranger shows up and casts a powerful patronus charm. Later, Harry travels back in time with Hermione and sees his younger self being attacked. When no one else shows up, Harry realizes that he was the mysterious savior from before, and this knowledge gives him the confidence he needs to perform the difficult spell.
“In this case, the casting of the spell saves Harry's life, which allows him to travel back in time, which enables him to cast the spell. So, the spell ends up being a cause of its own existence. This is supposed to be analogous to the proverbial case of ‘picking yourself up by your own bootstraps,’ something that seems obviously incoherent,” he said.
Wasserman got into philosophy as an undergraduate student at Western, then went on to Rutgers for his doctorate and returned to campus in 2005 to teach. He said that his interest in science fiction and the philosophy of time made his work with time travel and paradoxes a natural train of thought.
“I had been teaching a short unit on time travel for many years at Western and every time I taught the topic a new question or puzzle came up,” Wasserman said. He decided to expand the unit into an entire class, the notes of which ended up serving as the basis of his book.
“The main goal of the book is to defend the possibility of time travel and to show that this has important implications for issues like time, freedom, causation, and identity,” Wasserman said. “But it's also just a fun topic to think about, so I hope that students will read the book and get excited about studying more philosophy.”
For more information about “Paradoxes of Time Travel,” contact Wasserman at firstname.lastname@example.org.