Site's Spoiler Alert: I’m about to give away details about the latest season of Doctor Who, including the latest episode: “The Angels Take Manhattan.” Consider yourself warned.

Doctor Who is a magnificent British sci-fi show about a time traveler called simply “the Doctor.” In his time machine called the TARDIS he explores all of time and space with companions who he picks up along the way—usually, sexy young females. (Ironically, the Doctor never has any sexual interest in them; they are just there for the male fans.) The latest companions are a ravishing redhead named Amelia (Amy) Pond—oh yeah, and her boyfriend and eventual husband, Rory (the male nurse). Their final adventure with the Doctor, “The Angels Take Manhattan” aired this last Saturday on BBC America—and it ended with their names on a tombstone.

I’m still sad, and a little chocked up.

I want to fight through the tears, however, and talk about it because their adventure and demise raised some interesting philosophical questions.

The villains Amy and Rory faced in their final episodes were The Weeping Angels—a species introduced in what is likely the most famous and well regarded episode of Doctor Who ever: “Blink.” Much like quantum particles that don’t take on a position or location until they are observed, the Angels are alien life forms that turn into stone statues while you are looking at them, but are merely fast moving wisps of energy when you are not. If you see one in the distance, look away for a moment and then look back— you will find that it is right upon you, with a grotesque screaming face. They feed off of “time energy,” and if an Angel touches you while you are not looking, it will harvest your remaining “time energy” by sending you back in time and simply “letting you live to death.” Many a person about to be touched by a weeping angel first discovers his aged self, warning of an impending doom.

In “The Angels Take Manhattan” Rory is touched, and sent back from the present day to April 3rd, 1938—a fact that Amy and the Doctor discover by reading a book about a detective in the 30’s that they surprisingly discover is a chronicle of the adventure they are about to go on. (That’s right, the Doctor found a book in his jacket that describes one of his adventures, before the adventure ever happens—such is par for the course in Doctor Who.) Amy starts to look ahead to see how things will turn out.

Amy: …we’re gonna get [to 1938] somehow. We’re in the rest of the book…Page 43, you’re gonna break something.

The Doctor: I’m What?

Amy (reading from the book): “Why do you have to break mine?” I asked The Doctor. He frowned and said “Because Amy read it in a book and now I have no choice.”

The Doctor: Stop! No! You can’t, you can’t read ahead. You mustn’t, and you can’t do that….

Amy: It can help us find Rory.

The Doctor: And if you read ahead and find that Rory dies? This isn’t any ol’ future Amy—it’s ours. Once we know what’s coming, it’s fixed. I’m going to break something because you told me that I’m going to do it. No choice now.

Amy: Time can be rewritten.

The Doctor: Not once you’ve read it. Once we know it’s coming, it’s written in stone.

Once the adventure is over, they find themselves back in a present day New York City graveyard. As they are about to leave, Rory notices a grave stone with his name on it—and then disappears into the past, touched by a Weeping Angel. Once the Doctor sees Rory’s name, written on the stone, he realizes that Rory can’t be rescued. The Doctor just “read ahead.” Because she knows that she should be with Rory, Amy allows herself to be touched by the angel as well—even though she believes it means that she will never see the Doctor again. And when the Doctor now sees both their names on the tombstone, we know she is right.

Steven Moffit, the show’s head writer, has borrowed quite brilliantly from a well-known philosophical thought experiment, popularized by Philosopher Thomas Davis. Imagine you have discovered in a library a book that says it is about your life. You read its opening chapters to discover that it describes your early years accurately. Noticing that the book has clearly been on the shelf for a while, you wonder whether it has predicted the events of your life subsequent to its publishing date accurately. You look. It has. But what about today? You turn to the appropriate page and it reads, “He discovers this book, the book of his life, and wonders how accurate it is. After discovering that it accurately describes his distant and recent past, he turns to this page, to read these very words, to discover that it accurately describes his present too. He then remembers that he is half-an-hour late to pick up his daughter from her first day of pre-school, so he closes this book, puts it back on the shelf, and rushes away.” Oh no! You forgot! You close the book, put it back on the shelf, and rush away.

After a good scolding from your daughter, your mind returns to the book. What about the rest of it? There were chapters left in the book—but how many? And do they accurately describe your future too? You go back to discover that the last line of the book reads, “He dies in a plane crash at LAX.” You wonder, can you avoid your own death by vowing to never going to LAX? Perhaps, unlike the Doctor thinks, reading something before it happens can let you avoid it. But the book accurately predicted every event of your life between the time it was published and the time that you found it. Why would its descriptions of the future be any different? How could the fact that you found the book and read some of it make them any less accurate? And if they are accurate, and you can’t do any different, how could you possibly have freewill?

This thought experiment calls to mind many philosophical problems. For example, if God knows what you are going to do before you do it, can you do otherwise? And if not, can you really be free? Perhaps, like in Doctor Who, knowing what will happen before it happens is incompatible with freewill.

But what I like most about this thought experiment is that such a book could potentially exist. All such a book would be is a complete collection of all the true statements about your life. And, even though they are not written down anywhere, there is a collection of true statements about your life—and there was even before you were born. The basic laws of logic dictate that every statement has a truth value—whether true or false—even if you don’t know what it is. And there are true statements about your future, even if you don’t know what they are. In a hypothetical library that contained every possible book that could be written, one of those books would be the book of your life.

The disturbing thing is, the mere possibility of such a book may threaten your freewill just as much as if the book were actually written. Regardless of whether you read the last chapters of the book or not, the statements it contains are already true. If it’s already true that you will die in a plane crash at LAX, then it’s already true—regardless of whether you read it or not. And if some fact about the future is already true, it can’t later become false—otherwise, it was never true in the first place. But if it’s already true that you will die in a place crash at LAX, it’s still true regardless of whether or not it’s written down anywhere. So it doesn’t matter whether the book is read, or even if it is written. The mere fact that it could be written—the fact that there are already truths about your future—seems to be incompatible with freewill.

The Doctor is likely deluding himself. He thinks that not reading what the detective novel says about their future means that it’s not written in stone—he can still change it. But the book is already written; the words are already on the page. The Doctor not reading it may make it seem to him like he has a choice—that he can do otherwise. But the truth is, he can’t do anything different than what is already written in the book—whether he has read it or not. And the same may be true for us, for when it comes to the book of our lives, it doesn’t matter whether or not it has even been written. Whatever we will do, it is already true that we will do it—and if it is already true, we can’t do otherwise. Fortunately, like the Doctor, our ignorance about such truths keeps the illusion of freewill intact. Unfortunately, like the Doctor, we are only deluding ourselves.

Ultimately, you can’t fight your fate. You only read the last line; not the last paragraph:

“On his final day, he discovers his non-stop flight to Hawaii has to make an emergency landing at LAX. He goes crazy, declaring to everyone that the plane is going to crash because he read it in a book. He tries to get into the cockpit to force the pilots to land somewhere else, ultimately causing them to lose control of the aircraft. He dies in a plane crash at LAX.”