'Interstellar': A Physicist Explains That Crazy Ending

If you think the ending of Interstellar was confusing, try understanding the science — or lack thereof — behind it.

Christopher Nolan’s sci-fi epic, which had a strong opening weekend, touted the accuracy of the basic physics behind its story. Renowned theoretical physicist Kip Thorne consulted closely with the director and his screenwriter brother Jonathan Nolan, advising them on how they might use wormholes, black holes, and other spacetime phenomena to send astronauts (played by Matthew McConaughey and Anne Hathaway) to far ends of the galaxy.

Related: ‘Interstellar’: Meet the Physicist Behind the Science of Christopher Nolan’s Space Epic

The end of the film, however, veers away from proven science into the realm of the very speculative. McConaughey’s character, Cooper, ends up in a massive black hole, which holds a gigantic bookshelf that allows him to communicate, via Morse Code, with a past version of his daughter, Murph. It’s pretty wild, and a bit mind boggling for us non-scientists, so Yahoo Movies got in touch with Thorne’s colleague at Caltech, Dr. Sean Carroll, to discuss the science behind the end of the film.

How much of the film was based on valid, solid science — and what went beyond the science we have today?
The ideas of time dilation and visiting the vicinity of the black hole, and how that would sort of send you into the future, and the actual appearance of the black hole and of the wormhole — this was all very respectable, good science. The wormhole itself, the idea that there is a wormhole connecting our galaxy to another galaxy, is more speculative. It’s plausible, it’s something that is not ruled out by strong evidence that we have right now.

And then the stuff at the end, where they actually go inside a black hole and use some tesseract to visit and influence the past, and then somehow come out of the black hole once again was, I think, pretty far beyond anything we’d consider plausible science right now. But there’s enough we don’t know for sure that you can always say, Well, who knows?

Related: 9 Modern Space Movies That Will Help Prepare You for ‘Interstellar’

Is there any science that could make the stuff at the end possible?
I think that it was mostly magic. But I think that there were a few phrases thrown out, if I caught them correctly, that were supposed to indicate that this was not a naturally occurring phenomenon — that this was some set-up by a much more advanced species that lives in a higher dimensional spacetime, and has learned a lot about how to mess with the laws of nature.

Remember, in the movie there was a brief discussion about how someone could really live in more dimensions, that they would see time as a place they could just visit, and go back and forth. I take it that what we’re supposed to imagine is that’s what happened. It’s not simply that Matthew McConaughey fell into a black hole. But that we’re being manipulated a little bit by a species that knows a lot more than we do, so they can do things that we just don’t know how to accomplish.

Was there any science in the bookshelf?
I think that’s just completely speculative. Clearly, if he was going to see anything at all, the only place that that book shelf and that tesseract comes from is his own imagination and that’s not something you and I would see falling through a black hole. I think that needs to be an artificially constructed thing. I think the big buy in the whole set-up is that not only are there some laws of physics that we don’t understand, which is certainly true, but that there is some hyper-advance species other than human beings that have learned to manipulate them and are helping our hero out a little bit here.

So he’s in the black hole, sending Morse code to his daughter. Then he disappears and they find him again. How would one get out of a black hole, even speculatively?
I think I do have an idea, but I don’t think it was very elaborated in the actual movie. So you need to have some behind-the-scenes information. Remember they were occasionally referring to extra-dimensions and bulk? That actually plays a hugely important role here that they never talked about explicitly. The idea here is that our world has three dimensions of space, and one dimension of time. So there’s four dimensions overall, and maybe our world is like the edge of some world that is one higher dimension.

So there could be a world that has four dimensions of space and one dimension of time, and we’re at the boundary of it. And this five-dimensional universe is what is called by physicists the “bulk spacetime.” And if that’s true, which it may or may not be, then there’s not only wormholes, but there’s another kind of shortcut outside of our ordinary spacetime. I think the idea would be — and again this is speculative — but not absolutely impossible. If you’re stuck in our four-dimensional space time, you can’t get out of a black hole, or the event horizon. But you can sort of sneak out into the extra dimension and then back, if that’s what you have the ability to do.

But I take it that our hero, Cooper, was basically rescued after being treated by some higher dimensional being with the ability to influence the past through the tesseract. That he was also rescued by them by being pulled out of our ordinary four-dimensional universe into a fifth dimension, and then placed back somehow.

Anne Hathaway gives a speech about love being scientific. What did you think about that as a scientist?
I think that was too bad. No scientist would actually say that. It’s not false, but it’s not what a scientist would say, because scientists have great respect for the meaning of the words that they use. And if you want to say that love is a force, there is a definition of the word “force” under which that’s true, but it’s not any definition that any physicist would use. So it’s a little bit of a poetic license that most scientists would indulge in.