Slowly catching up on science fiction classics, reading Lem's Solaris, I'm struck by how the narrator, Kris, escapes a skeptical quandary. Worried that his sensory experiences might be completely delusional, Kris concocts the following empirical test:
I instructed the satellite to give me the figure of the galactic meridians it was traversing at 22-second intervals while orbiting Solaris, and I specified an answer to five decimal points.Except in detail, Kris's test closely resembles an experiment Alan Moore and I have used in our attempt to empirically establish the existence of the external world (full paper in draft here).
Then I sat and waited for the reply. Ten minutes later, it arrived. I tore off the strip of freshly printed paper and hid it in a drawer, taking care not to look at it.... Then I sat down to work out for myself the answer to the question I had posed. For an hour or more, I integrated the equations....
If the figures obtained from the satellite were simply the product of my deranged mind, they could not possibly coincide with [my hand calculations]. My brain might be unhinged, but it could not conceivably complete with the Station's giant computer and secretly perform calculations requiring several months' work. Therefore if the figures corresponded, it would follow that the Station's computer really existed, that I had really used it, and that I was not delirious (1961/1970, p. 50-51).
Kris is hasty in concluding from this experiment that he must have used an actually existing computer. Kris might, for example, have been victim of a deceiver with great computational powers, who can give him the meridians within ten minutes of his asking. And Kris would have done better, I think, to have looked at the readout before having done his own calculations. By not looking until the end, he leaves open the possibility that he delusively creates the figures supposedly from the satellite only after he has derived the correct answers himself. Assuming he can trust his memory and arithmetical abilities for at least a short duration (and if not, he's really screwed), Kris should look at the satellite's figures first, holding them steady before his mind, while he confirms by hand that the numbers make mathematical sense.
Increasingly, I think the greatest science fiction writers are also philosophers. Exploring the limits of technological possibility inevitably involves confronting the central issues of metaphysics, epistemology, and human value.