Time is the intangible, mysterious fourth dimension. From H.G. Wells to Harry Potter, the very notion of being able to journey through time is chilling. If we could go back in time, we’d be able to live our sweetest childhood memories, take a tour through history, or change our most painful mistakes on the most fantastical scale. We could very well repeat history or undo it; we could be reborn or never come into existence; or, we might forever trap ourselves in a dimension of no time, of still surreal floating frozen clocks. The possibilities are endless.

Unlike its sister sci-fi concept of invisibility, time-travel is still embedded in theory between the walls of fantasy simply because the idea of turning time engenders various complicated paradoxes. If a mysterious old man were to tell you the secret to build a time machine in the first place, and as an old man, you go back in time to tell the younger version of yourself that very secret, then the idea behind the time machine has no one certain origin. Or, if you were to go back in time and kill your parents before you were born, you couldn’t then possibly be alive to do the heinous deed. Maybe, like Marty McFly, you’ll end up back in the future, with enough adventures for three movies.

Both Newton and Einstein had dismissed the reversibility of time. Newton had described it as a single, uniform, forward-moving concept where a second on Earth is the same as a second anywhere else. Einstein, by his theory of relativity, had detailed it as a non-uniform forward-moving phenomenon varying throughout the universe where a second on Earth is not the same as second elsewhere. The concept of this ring had monumental consequences in the theory of time-travel.

Then come along the legendary mathematicians Kurt Goedel and Roy Kerr to break this perfect and enticing logic. Goedel took Einstein’s very own equations to render the idea of time-travel possible in a universe of rotation fluid. Kerr had taken Einstein’s equations to do the same with the idea of an unusual rotating black hole that collapsed to neutrons that spun around in a ring in an incredibly fast speed effectively creating what would be Alice’s Looking Glass.

Going back in time may defy certain logic, as illustrated in the paradoxes of no past and no parent, but with Kerr’s ring we find that time-travel is possible with the existence of alternate universes. Effectively, you could go back and prevent yourself from being born, but you would be creating an alternate reality.

Have we come close to constructing the Muggle world’s real version of Hermione Granger’s time-turner or H.G. Well’s time machine? Hardly. Even the mathematical logic of Goedel and Kerr does not offer practical energy-feasible and realistically stable solutions for the reversibility of time. Of the myriads of so-called impossibilities residing in the intersection of science and science fiction, even Einstein would agree that the eerie, convoluted, and endlessly paradoxical concept of time travel is best kept to in the realms of fiction and wishful theory.

To learn more about the mind-boggling idea of time-travel, take a look at this article by theoretical physicist Dr. Michio Kaku.