I heard that this was a mindbender film so I embargoed myself out of reading anything about it. That means no reviews, no forum posts talking about it, nothing. That’s probably why I enjoyed the film as much as I did, given that:
- It has a terrible title which tells you nothing whatsoever about the subject of the film and, more importantly, is a misnomer given that the term “source code” in computer programming does not mean anything even vaguely resembling what they refer to in the film.
- The science involved is claptrap of the lowest order. How do you explain how a dead man’s mind can contain all the information in the universe? It’s quantum mechanics. Parabolic calculus. Just brilliant.
So this is just your usual Hollywood thriller written with absolutely no understanding of science or mathematics, using jargon to handwave away logical impossibillities and bearing a title that makes you think it must be a documentary about the history of Linux or something. Yet I still enjoyed it quite a bit. For one thing, I have fond memories of Groundhog Day and in some ways Source Code is the thriller version of it, right down to the maudlin message of learning to appreciate life and the people around you.
But the main thing is that this is simply a very well-crafted film. Unlike, say, M. Night Shyamalan, director Duncan Jones is astute enough not to hang the entire film on a single twist. The characters come out and clearly explain exactly what is going on at just the right point in the film when the audience is beginning to piece everything together anyway, rather than trying to withhold the truth in effort to preserve mystery way past its breaking point. I also enjoyed all the mistakes Col. Porter made in trying to work out who the bomber is. Yes, he’s super-smooth at the very end but it took many, many tries to get there, not unlike reloading a savegame, come to think of it.
Still, the main reason why I’m writing this post is that while the Many Worlds interpretation of quantum mechanics is how most people interpret what happens in this film, it strikes me that a much better explanation is Greg Egan’s Dust Theory as laid out in his short story Dust and his novel Permutation City. Now, fellow fans of Egan’s stories will be familiar with his underlying premise that intelligence and consciousness can be expressed as computation. Permutation City takes this further, laying out how an entire universe can be seen as basically one huge computer program.
In principle, any computer program needs to be run on hardware. Let’s call this the substrate. But Egan shows through a series of thought experiments how the program has a measure of freedom from its substrate. Say, I’m running a program simulating an entire universe, complete with intelligent and conscious inhabitants. Then, I suspend the program only to resume it later. To this universe and its inhabitants, the pause is irrelevant and undetectable. Even the program is stopped for a thousand years in the real world and resumed later, it makes not a whit of difference to the simulated universe. Another is that the location and nature of the substrate is irrelevant. For example, I could run the program in Kuala Lumpur on one computer one moment, then run it on a completely different computer in Shanghai the next moment, and there would be no difference to the simulated universe either.
If you’re still with me so far, you should see that all of the above still depends on saving the state of the program from moment to moment and transporting it to a new computer or a new location to be run. But why would even that be necessary? After all, each discrete state in the simulated universe directly corresponds to a discrete state in the memory and processors of the program itself. And what describes the state of the memory and processors is simply the specific arrangement of molecules and atoms that make up that computer. Since we’ve established that time, location and specific identity of the substrate doesn’t matter, it’s not much of a stretch of the imagination to picture how a computer sometime in the indeterminate future and somewhere in the universe could arrive at the next state of the simulated universe purely by coincidence even if the operators of said computer knew nothing whatsoever about our simulated universe.
Egan actually goes much further than this. He claims that pseudo-random interactions of all kinds, such as dust swirling in the air, hence the dust in Dust Theory, performs computations as well. He also claims that the directionality of time is irrelevant. For example, if the physical state of a system in the real world first describes state B of our simulated universe and then later some other system describes state A, inside the simulated universe, the inhabitants would still experience state A and then state B in the correct order. All this means that once you start a program running, so long as it is internally cohesive, it will continue running on its own, as if by magic, without seeming to require any hardware.
How does all this connect with Source Code the film? Well, in Permutation City, one visionary realizes all of the above. He hatches a scheme to collect copies of software people, creates a brand new universe for them to inhabit so they won’t get bored, and collects enough money from them to rent computer hardware to run all that but only enough for a few moments. Due to Dust Theory, he is confident that the simulation will continue running on its own even though he has no proof and no way of accessing the simulation once the computers are shut down. And I think this is exactly what happens in Source Code. Every fork of the universe created from the teacher Sean Fentress’ memories run for a short time within whatever amalgamation of Col. Stevens’ and Fentress’ brains the scientists come up with. But since the simulated universe is cohesive, it just goes on running on its own.
Well, that was a long digression but I hope it was at least interesting food for thought. If every version of reality does continue, there are some weird implications however. For example, think of the poor version of Christina Warren who must somehow make sense of Fentress seemingly freaking out for no reason and suddenly getting killed on the railway tracks. Plus as another QT3 poster observed, even though Col. Stevens managed to get himself killed in his original universe, a copy of him still exists in the forked universe. The implication is that this copy will be activated and used in a future crisis, but that will then create yet another forked universe with two copies of Stevens inhabiting other people’s bodies and a comatose Stevens in the fridge. Eventually, this should result in a forked universe in which every person is Col. Stevens! Now that’s a real mindbender.