Tuesday, December 30, 2014

The Science of Interstellar

Last month Christopher Nolan's Interstellar was released, and in this blog we looked at Interstellar and the Fifth Dimension. I've been particularly excited about this film because world-renowned physicist Kip Thorne was a consultant throughout its creation, tasked with making sure that the science represented in the show was not, in fact, pseudo-science. As Professor Thorne says in the book's introduction:

…in the end I have no qualms about defending what Chris did with the science. On the contrary, I'm enthusiastic! He turned into reality… my dream of a blockbuster movie with foundations of real science, and with real science woven throughout its fabric.

There are lots of interesting discussions in this book about the science of black holes, wormholes, relativistic time dilation, and so on. But here's the question that has attracted so many new visitors to the Imagining the Tenth Dimension project: is representing the fifth dimension as I have with my project able to be aligned with the scientific approach supported by Kip Thorne in this movie?  Here's some of his thoughts on the subject from his book:
How can space "bend down"? Inside what does it bend? It bends inside a higher-dimensional hyperspace, called "the bulk", that is not part of our universe! 
...In Interstellar, the characters often refer to five dimensions. Three are the space dimensions of our own universe or brane (east-west, north-south, up-down). The fourth is time, and the fifth is the bulk's extra space dimension.
Does the bulk really exist? Is there truly a fifth dimension, and maybe even more, that humans have never experienced? Very likely yes.
This is important! Professor Thorne is saying (as I have often said) that you can't talk about the fifth dimension without implicitly acknowledging that it is part of a multi-dimensional system. The fifth dimension can't exist in isolation, any more than it's possible in the third dimension to have an object with only a length, with no width or depth. And for those nitpickers who claim "there is no fifth dimension, there are only five dimensions", Professor Thorne is yet another expert comfortable - as I am - with using the phrases interchangeably.

(Spoiler Alert, stop reading here if you don't want to know about the climax of the movie)  

The other idea which I have talked about extensively, and which figures prominently in the plot of Interstellar, is that gravity is the only force which exerts itself across the extra dimensions. But there is one plot point that I wish had been made clearer: this movie's logic collapses into contradiction if the fifth dimension does not include the many potential probabilistic outcomes which exist for our universe, as described in Everett's Many Worlds Interpretation of Quantum Mechanics. Is Everett wrong? Is there really only one single and inevitable world line for our universe? Then free will is an illusion, and of all of Cooper's efforts in the movie to use extra-dimensional gravity to communicate with his daughter are pointless, because he has already achieved his goals before he began. But if free will and multiple outcomes do really exist, then what Cooper is looking at from his fifth dimensional vantage point is a branching set of possibilities, and his goal is to navigate towards the versions where his efforts become effective and the desired outcome is achieved.

This is the contradiction we keep coming back to: if Everett is correct, then the timeless underlying quantum fabric already includes a version of the universe where what any of us are about to do has already happened! And yet we can still make other choices and get to "other versions" where some other choice has been made.  When we get to the end of the movie, or when we get to the end of our lives, we see that only one set of choices was made, but I remain convinced that this inevitability is an illusion.

Professor Thorne describes the climactic scene in which Cooper sees his daughter in a kaleidoscopic vision of cascading rooms:
...the various bedrooms are out of time synch with each other. ...Cooper can move far faster than the flow of time in the bedroom extrusions, so he can easily travel through the tesseract complex to most any bedroom time that he wishes!

A few pages later he talks about a concept I called "the long undulating snake" in the book and animation that got this project rolling, a way of representing the space-time object (or "spime") of a person from their conception to their death. Professor Thorne shows us a diagram of a book as viewed from this same outside-of-space-time vantage point, and refers to the book as having a "world tube": same concept.

 (this image, Figure 30.2 from The Science of Interstellar, is copyright 2014 by Kip Thorne)

In the movie, Cooper uses extra-dimensional gravity to maneuver his daughter's "Many Worlds" to the version where a book mysteriously falls from the bookshelf:
...Cooper slams his fist on the book's world tube over and over again, creating a gravitational force, which travels backward in time ... the book's tube responds by moving. The tube's motion appears to Cooper as an instantaneous response to his pushes. And the motion becomes a wave traveling leftward down the tube (Figure 30.2). When the motion gets strong enough, the book falls out of the bookcase. 
If you, like me, have fond memories of the way the pieces of the puzzle fit together in one of Christopher Nolan's earliest movies, Memento, then you may have felt similarly satisfied as the mysteries presented in the first two thirds of Interstellar are gradually solved by the "reverse causality" Professor Thorne found a way to explain with modern scientific theories. For me, though, I feel it's important to remember that there must still be many other versions of the universe depicted in the movie where Cooper hadn't yet formed his plan, or wasn't able to execute his plan successfully, and so on, causing the disastrous future for our planet depicted in the movie's opening act to continue unabated.

Ultimately, the statistical unlikelihood of any of us being right here and right now must surely represent a miniscule subset of the Many Worlds universes where none of us exist. One of my favorite blog entries from a few years ago where we explored this idea was called Beer and Miracles, check it out.

Enjoy the journey!

Rob Bryanton

Biographical note from the back cover of The Science of Interstellar:
Kip Thorne is the Feynman Professor of Theoretical Physics, Emeritus, at the California Institute of Technology, scientific advisor and executive producer of Interstellar, and the author of four books, including the best-selling Black Holes & Time Warps.

Coming up next: Interstellar and Pendulum Clocks

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