Suppose neuroscientists could pin down with a high degree of accuracy a particular region of the brain tightly associated with religious experience. Suppose the association between subjective experience and measurable brain activity goes both ways. Each time the region lights up the test subject reports having a religious experience, and every time he reports having a religious experience, the region lights up. (I know; I know. Those of you who actually pray will tell me that this is not really how “religious experience” works, but run with it for a second.)

Let’s take an even scarier step: suppose that these scientists work out a way to stimulate this region of the brain in such a way that they can induce religious experiences. The scientists have a big red button on a console labeled, “TRANSENDENCE.” Whenever they push it, a man with wires running into his shaved scalp becomes a mystic.

I don’t mean to suggest that such a thing has actually been done. Frequently, I find the reports of such discoveries overblown and misinterpreted. Instead, I want to make these suppositions merely for the sake of argument. These suppositions seem to be the best possible case for those who would discredit religious experience on scientific grounds. I can see those materialists now, just rubbing their hands waiting for that inevitable day when this thought experiment becomes a reality and they can finally declare that Science (always with a capital S) has proven what religious experience really is. I want to argue, however, that even on such a day nothing of the kind would have been proven. Even in their best possible case, with 100% two-way correlation and the capacity to manipulate one of the variables reliably, they could not prove that religious experience is merely activity in the brain, that it is illusory, or that there is no God after all.

To see why, consider the parallel case of vision. We are reasonably confident that we know what occurs inside the retina when blue light comes in through the eye. Indeed, we are much better informed about what goes on inside the retina when people see the blue sky than we are about what goes on inside the brain when people experience the presence of God. I suppose it is only a matter of time before someone discovers a way to induce the experience of a blue spot in a precise place in our field of vision by stimulating the appropriate cones. But all this does not make anyone think that, under normal circumstances, people who see blue things are experiencing mere retinal stimulation. Even when we can explain in the finest detail the chemical processes that go on when people see blue things, we still believe that things outside the person are really blue.

Admittedly, there may be a gap between our subjective experience of blue and the objective nature of the world giving rise to these subjective experiences. We don’t subjectively experience waves of a certain frequency. Nevertheless, we think that our subjective experience of blue maps onto something real about the world in ordinary circumstances.

“Ordinary circumstances” is an important caveat. People do sometimes hallucinate, and there are many optical illusions that alter our ordinary perception of color. We do not, however, typically allow these edge cases to disturb our faith in the real, objective color of our University of Kentucky sports apparel. We find out that things are hallucinations or illusions because we are capable of checking on what we see multiple times, from multiple angles, in different lightings etc.

We can leave aside for the moment the position of radical skepticism such as that which we see famously in Descartes’s Meditations. It may or may not be the case that we can draw into question all our sensory experiences. But if we can, then the experience of God’s presence will be on the same footing with our experience of the blue sky and need not present any extra difficulty in this respect.

The case of induced experience does, admittedly, present a special problem. Typically, when we have a tight correlation between two phenomena, we can figure out which causes the other (or whether there may be some underlying third cause) by manipulating one of the variables. We observe, for instance that the position of the volume knob tightly correlates with the volume from the speakers. Manipulating the knob changes the volume, but we cannot reverse the process. Even if we found a way to directly manipulate the volume from the speakers, it wouldn’t change the knob. The ability to manipulate the chemical or electrical activity in a certain region of the brain and reliably observe a certain type of experience does therefore suggest that this activity is somehow causally responsible for the experience, at least partially.

This is not, however, the end of the story. The chemical or electrical activity may be an intermediary cause in a longer causal chain. By artificially manipulating it, we may be doing no more than interrupting a natural causal sequence midway, with the predictable result that we have altered the effects further down the chain. Using this means alone, we are left ignorant of the prior series of causes leading up to this chemical or electrical activity in natural cases.

If we could induce the experience of blue by stimulating part of the retina, we wouldn’t think this proved normal vision illusory. Under normal circumstances, real blue light from the outside causes particular cones to activate. If we were to artificially activate these cones, we are doing no more than interrupting this normal causal chain and manipulating one of its links independent of the normal process. Paradoxically, perhaps, this should increase our confidence in the normal veracity of the retina. By understanding how the mechanism works and how to make it function improperly, we better understand those unusual situations, such as ocular migraines, that cause us to have misleading visual experiences. This increases our ability to sort out the normal from the non-normal cases, and therefore increases our confidence in the normal ones.

By analogy, there may well be a particular region in the brain that functions like a spiritual eye. It activates in a particular way whenever transcendent holiness approaches. We could know exactly what happens chemically and electrically when this region activates and still not know whether it reflects a reality outside the person or not. Indeed, we should prefer the hypothesis that it does reflect reality because the overwhelming majority of our other systems function this way. Again, even if we could induce religious experience, this would not prove that all religious experiences are illusions any more than inducing blue experiences would prove that nothing was really blue.

We run up against a much more fundamental problem at this point. The entrance of a non-physical reality into a physical causal chain may violate the fundamental physical laws of conservation. I’m not sure that it needs to since there are ways of making a causal difference without altering the net mass–energy. But the even deeper problem for the scientistic way of thinking is to conceive of non-physical causality. I suspect this is the real issue. I suspect that such people simply find the very idea of non-physical causality absurd and interpret all the data under the assumption that such a thing is impossible. Of course, this amounts to assuming that the physical universe is a closed causal system then using this assumption to prove that the universe is a closed causal system. Only rarely have I ever been able to talk someone out of this circle.