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Quantum Theory and Abortion Rights

-- Richard Stallman

Christian fundamentalists argue against abortion on the grounds that fetuses have souls. The argument starts with two premises: that people have souls while animals do not, and that the right to life goes with possession of a soul. It proceeds by asserting that the developing fetus must acquire its soul at some instant; and because no point after conception is special enough to be that instant, it must happen at conception. (It takes hours for an egg and a sperm to unite, but they could choose some brief part of the process as the crucial "instant".) Therefore, the argument concludes, the fetus has a soul and the same rights as a grown human.

Those two premises--that souls exist, and that they are the basis for moral or legal rights--are openly acknowledged; one can dispute their validity, but no one denies that the fundamentalists' argument rests on them. However, a later stage in the argument depends on another premise that neither the fundamentalists nor their critics have recognized: an assumption taken from classical non-quantum "common sense" physics. This assumption enters in the step which claims that the fetus must acquire its soul instantaneously.

As the argument goes, the fetus at any given time either has a soul or it doesn't. There is no intermediate state, no way to change gradually from soul-absent to soul-present, so the change must be a sudden and instantaneous discontinuity.

But that is not how things work in the real world, the world of quantum mechanics. It is normal in quantum mechanics for an object to change gradually from state A to state B, even though there are no intermediate states between A and B.

For example, an electron's spin can either point up or down (along whichever axis you choose for the measurement); there is no possible intermediate value it can have. Yet the proper radio wave in the proper conditions can reliably and gradually convert spin-down electrons into the spin-up state, over a predictable length of time. The process can be made as slow as you wish.

What happens to these electrons in the middle of that time interval? They don't have spin values between up and down--intermediate values are impossible. Instead, they are partly in both states at once. A certain fraction of the electron's existence is in the up state, and the rest is in the down state. The fraction in the up state (the "amplitude" of that state) starts at 0% and gradually increases to 100%. The fraction in the down state gradually decreases from 100% to 0% over the same time.

If you measure the spin of an electron in the middle of this transition, you will observe its spin to be either up or down--no other outcome is possible. But the probabilities of the two outcomes gradually change as the electron's existence gradually moves from the down state to the up state. The probability of finding the spin up starts at 0% and gradually increases to 100%. The probability of finding the spin down starts at 100% and gradually decreases to 0%. (The probability is proportional to the square of the magnitude of the amplitude.)

This quantum behavior is counterintuitive, even hard to describe without equations, but--strange as it may seem--this is how everything in the world works. Quantum mechanics is a fundamental and universal principle of nature, confirmed by thousands of experiments. It applies to everything in the world, even large objects such as rocks, people and planets, because it applies to the particles they are made of. The direct effects on objects large enough to see are usually too small to be measured, but there are occasional exceptions.

It is hard to make positive statements about the behavior of souls in the absence of positive evidence that they exist, but they would probably obey quantum mechanics like everything else. It is hard to fit any exception to quantum mechanics into the world of quantum-mechanical entities such as compose a human body; besides, the Bush's Prisoner thought experiment (like the Schroedinger's Cat thought experiment but with a human victim; see below) shows that the very existence of a human being is subject to quantum mechanics, so the states where one would or would not expect a soul can be combined in continuously varying amplitudes.

For the present argument, it is sufficient that there is no proof that souls (supposing they exist) are not governed by quantum mechanics. That knocks a hole in the argument that leads from fundamentalism to disapproval of abortion, because it means that the change from the soul-absent state to the soul-present state need not be instantaneous. It can occur over a period of time, like the electron's transition from spin-down to spin-up. During the transition, there would be at any moment a certain probability that a measurement would find the fetus already has a soul. That probability would start from zero, and presumably end up close to unity.

With this understanding, there is no reason for fundamentalists to conclude the change must occur at a unique special instant. It could happen across a nonzero length of time during some stage of development--perhaps starting at 7 months, when the brain begins to be wired up. Thus, they are no longer led to the position that a single-cell fertilized ovum, with no more brain than an amoeba, possesses a soul while the amoeba does not.

Christians are unlikely to change their belief that people have souls. But with an understanding of quantum mechanics and its application to gestation, Christian fundamentalists have a way to reconcile that belief with support for abortion rights.

Note: In the Bush's Prisoner experiment, a person is anonymously accused of having associated with members of al Qa'ida. Rather than hold a trial to determine the truth of the accusation, Bush imprisons him, then tortures him by putting him in a cell with a device that could execute him at any moment. More precisely, it will kill him if and when a certain atom decays. After some time goes by, the cell's state is an entangled quantum superposition of the state with an undecayed atom, a living prisoner, and (supposing souls exist) a soul, and the state with a decayed atom, a corpse, and no soul. At the start, the amplitude of the first partial state is 1 and the amplitude of the second partial state is 0. After a period of time equal to the atom's half-life, both amplitudes are equal.

Copyright 2011 Richard Stallman Verbatim copying and distribution of this entire article are permitted in any medium without royalty, provided this notice is preserved.