Today in church we were going through Romans 9, a passage which is often a major source of controversy among Protestants regarding salvation. Our pastor pointed out the irony of the fact that Romans is meant to bring unity into the church, and yet we let ourselves get separated by this fact.
In the course of the sermon, my mind naturally kept going back to a principle of physics, so I decided I should go ahead and share that. I'll get back to the whole predestination thing in a bit, after we discuss the physics part.
One of the strangest concepts to me as a young engineer studying physics was that of paired forces. I had always heard the saying, "Any action creates an equal and opposite reaction." This makes perfect cause-and-effect sense to us, of course: I hit the cue ball, the cue ball hits the 8-ball, the 8-ball caroms off at an equal and opposite angle, having been impacted by the vector (magnitude and direction) of the cue ball's kinetic energy. So there is a clear cause-and-effect: it is easy to tell which is the 'action' and which is the 'reaction'.
But not all forces act in this way. Sometimes you get what is called a "paired force"--that is, two forces which are inseparably connected. For example, take the effect of gravity on a stationary object. Right now, you are probably sitting in a chair. If a physicist were to draw out that scenario, he would draw a downward gravitational force (F=ma, or your mass times the gravitational acceleration). Likewise there would be an equal-and-opposite Normal force pointing upward.
You see, as you sit, you undergo a paired force: gravity and your mass exerts a force on the chair, which simultaneously exerts an equal-and-opposite force on you. These forces cancel out, allowing you to stay seated. If your force was stronger than the Normal force, then you would fall through the chair; if the Normal force was stronger, you would leave the atmosphere. Your static position is determined by two equal forces.
Now, the question becomes - does one force cause the other? This is the part that once confused me. It seemed to me that the downward gravity force caused the equal-and-opposite Normal force. This, however, is not the case. They both exist exactly simultaneously. There is not a single nanosecond of time where only one of the forces exist and the other one reacts; instead, both come into existence at the same time.
For another example, consider paired electrons. Two electrons are said to be 'paired' if changing the spin of one also changes the state of the other. Now what has been shown--much to the surprise of physicists--is that you can separate two paired electrons and change one of their spins...and the other changes instantaneously. It reacts faster than the speed of light could have carried information to it. Somehow, the two states exist in perfect harmony, without either one causing the other.
So...what does this have to do with Romans 9?
Well, many people get really hung up on the "chicken or egg" question of salvation. The Bible says that we choose God because He chose us, and that He chooses whom He will. This implies that God predestines our salvation. The Bible also says that God does not will that any reject Him, and shows time and again those who choose to accept or choose to reject. This implies that God does not predestine us. So which is it? Do we choose Him only because He chooses us? Does He choose us only because we chose Him? Which came first and caused the other?
Think back to my physics example. Paired forces exist simultaneously - one does not cause or pre-date the other. One is not the cause and the other the effect. I see the same principle in the Scriptures regarding God's calling us. We choose God and He chooses us--both instances must exist. One doesn't cause the other, they are intimately woven together in the same mysterious way that paired electrons are made. We cannot possibly choose God if He does not choose us, but neither does God have to force us beyond our will. The two decisions are paired, and linked.
Hopefully that helps clear it up. If not, ignore this. If you (for some strange, bizarre reason) actually think this is useful, then you might enjoy some of my other thoughts on physics as a method of understanding theology: Schrodinger's Christian and Flashforward, Quantum Mechanics, and Christianity.