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My Dad Explains the Science of "Source Code."

Photo of Eric Kohn By Eric Kohn | Eric Kohn April 4, 2011 at 4:12AM

Ever since I caught "Source Code" at an early screening last month, I haven't been able to get its time-spinning, reality-defying concepts out of my head. The movie works quite well no matter how hard of you try to understand it, but since it deals with an imaginary technology that could--if it actually existed--prevent all kinds of disasters from taking place, it's hard not to wonder what it would take to bring its underlying concept to fruition. Partly inspired by these detailed attempts to decode the movie's ending, as well as a video produced by Wired about the science behind the movie, I turned to the one person whose opinion about these things I usually trust more than any other: My dad.
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Ever since I caught "Source Code" at an early screening last month, I haven't been able to get its time-spinning, reality-defying concepts out of my head. The movie works quite well no matter how hard of you try to understand it, but since it deals with an imaginary technology that could--if it actually existed--prevent all kinds of disasters from taking place, it's hard not to wonder what it would take to bring its underlying concept to fruition. Partly inspired by these detailed attempts to decode the movie's ending, as well as a video produced by Wired about the science behind the movie, I turned to the one person whose opinion about these things I usually trust more than any other: My dad.

A physicist who identifies himself these days as a "cyber-control scientist," my dad (whose bio you can read here) loves to dig into the feasibility of pop culture narratives. (You should've heard him dish on "Inception." He loved it.)

After the jump, the old man offers his two cents on why the science of "Source Code," sadly, comes up short. Probably.

Before seeing the movie, he watched the following video:

Knowing nothing about "Source Code" except what the video told him, here's what he wrote me:

The animation, which includes CLASSIC quantum equations like the Schroedinger equations, postulates unproved and highly controversial principles of string theory. (String theory claims that the state of the universe lives in a high dimensional space which is decomposable into many 4-dimensional space-time subspaces in which partial information of the overall state is stored.)

It is true that at the quantum level time is reversible, but this does not mean that "particles travel backwards in time." What it means is that there is a FINITE nonzero probability that any particle can be anywhere in each of the 4-dimensional space-time subspaces.

Decoherence is an important new interpretation of a quantum mechanism of DISORDER called ENTANGLEMENT, which incidentally works against the ideas of decomposition above. ENTANGLEMENT is an essential mechanism in the quantum behavior of particles.

The physical theory that would better support the ideas in the animation is the theory of quantum physics known as SUPER SELECTION. This theory explains some of the behavior of the universe by postulating a set of super selection RULES.  These rules are constraints on the dynamics of particles and their interactions. The rules introduce order (i.e., partial coherence) on the dynamic states of particles and fields (BOSONS and FERMIONS) by PREVENTING entanglement among the different space-time subspaces.

So, if a super selection rule exists that prevents entanglement between 4d space-time subspaces, and if string theory proves to be a good model of the behavior of the universe, and if this model is compatible with general relativity, the animation may be the beginning of something big! 

More later after we see the film.

So he went to see the movie with my mom. Here's a trailer:


Read the synopsis here, if you have either already seen the movie or don't mind the spoilers.

Here's what he wrote me afterward:

First of all, I enjoyed it.

I was trying to correlate the plot with the "physics." One of the huge physical errors is the violation of the second law of thermodynamics: "The internal entropy of a system" --in this case the train system-- "increases monotonically in time."

Once the first 8 minute reality happened, in the second 8 minute episode, the system should have had far more disorder (because its entropy increases monotonically over time). If the system has to be reversible, an enormous amount of ordering energy would have to be provided to revert to the initial state of the episode in a different reality. 

By the way, that video does not mention the second law of thermodynamics!

One of the glaring mistakes is that as time progresses, the universe gets more disordered. So after the first explosion, all the molecules scattered all over the place. Imagine the amount of energy that would have had to be added to the system for the second trip. And Jeffrey Wright's character doesn't even talk about the second law! Even inside the source code, the second law of thermal dynamics can't be violated. It's a fundamental principal of physics. The most order the universe ever had was when it was a single dot. After the Big Bang, from that point on, everything has been getting more disordered.

When these people died in an explosion, all their atoms--the mass--did not disappear. It just transformed into a more disordered state. It's true that time is reversible, but entropy is not. They created a disorder and they have to bring back the order in an alternative universe. I can conceive of that. But you can't violate the second law of thermodynamics.

When you blow up all these bodies on the train, you create an enormous disorder. It has to be valid in all of the realities. So the source would have to provide infinite energy to reassemble it back to the initial state.

A more realistic thing would have been "tunneling." You can tunnel from one reality to another just before the big explosion. Since the disorder has not happened yet, you can bring it back to its initial state.

Still, there are a lot of interesting ideas here. Modern physics was written with string theory, a mathematical theory that has not been proven physically. Newton's ideas were seen as alchemy before he formalized them. So maybe the idea that there are multiple realities will be proven to be valid. Reality has to be in three dimensions and time, but string theory says the universe has a much higher dimension, so it's possible that there are higher realities of the universe that you can project into other spaces.

At some point in the movie, they altered reality, and I can live with that. It's difficult to understand, even with modern physics, how that can happen. But I cannot accept the rejection of the second law of thermodynamics.

I had to explain all this to your mother, along with two other people who were at the theater and overheard us talking.


This article is related to: Pop Culture, New Releases