The Astrophysics Spectator
The Astrophysics Spectator
On a rainy day in Kalispell, Montana I found myself in a book store. My wife and I had already hiked many miles in Glacier National Park over the previous week, and we were ready for a rest. Browsing in the history department, I began reading a book by Cicero, the Roman politician of Julius Caesar's era. One of the charms of reading ancient philosophy is seeing how arguments hold up under our current understanding of the world. Often these works confound several different issues into a single problem. I can see this in Cicero's writings about uncertainty in our knowledge of the universe. I can also see in his writings links to modern science.
Cicero belongs to a school of philosophy known as the "New Academy," which is a philosophical branch descended from Plato that asserts we cannot "perceive" the universe. In Cicero's peculiar terminology, our mind and our senses give us “presentations” of the world. If an object that exists produces the presentation, then the presentation is true, and Cicero says that we “perceive” the object. If, however, there is no object that produced the presentation, then he says that we do not “perceive” the object. From what he writes, it is clear that an object is also not “perceived&rdquo if there is some doubt as to its existence.
There are four heads of argument intended to prove that there is nothing that can be known, perceived or comprehended, which is the subject of all this debate: the first of these arguments is that there is such a thing as a false presentation; the second, that a false presentation cannot be perceived; the third, that of presentations between which there is no difference it is impossible for some to be able to be perceived and others not; the fourth, that there is no true presentation originating from sensation with which there is not ranged another presentation that precisely corresponds to it and that cannot be perceived.1
In demonstrating the first point, Cicero lumps together three types of example of misleading representations: the action of the mind in dreaming, hallucinating, and imagining; optical effects, such as the refractive bending of light; and the limitations of our senses, especially the limitation of our vision. This is where things get interesting, because while the first point is a common point of discussion among philosophers, all three are in the domain of science, with the second and third the uncertainties that most interest the scientist.
The first type of uncertainty, the inability to prove that what we see is objectively real, is an uncertainty that any scientist is happy to concede so that he can go on with his work. But making this assumption, science then shows precisely how we can be misled by our senses and by our mind, and it clarifies some of the phenomena Cicero cites as false presentations. We understand how the senses work, how the brain works, and why hallucinations occur. Unlike Cicero, we can give an objective account of when our vision of the universe is wrong, which means that the occurrence of false representations is not a random event. We don't worry that a god may give us a waking dream at his own whim. Our understanding of how our senses can fool us is so strong that a whole industry of novels and moves exists that depends on this understanding. Why even invoke the gods to demonstrate our uncertainty when a computer network will do?
But it is the second and third types of error that deserved attention, because these are central to modern science. Cicero notes that our abilities are limited. What we see up close up is not what we see at a distance.
Do you see yonder ship? To us she appears to be at anchor, whereas to those on board her this house appears in motion. Seek for a reason for this appearance, and however much you succeed in finding one— though I doubt if you can—you will not have made out that you have got a true witness but that your witness is for reasons of his own giving false evidence.2
Like our vision, our instruments are limited in what they can see. A telescope on Earth can only resolve to an angle determined by the size of the mirror and the turbulence in the atmosphere. An x-ray detector can only determine a brightness for a source down to the counting statistics of individual x-rays; for example, a constant luminosity source with an average count rate of 100 x-ray photons per second over an hour will give an measured count rate that varies from second to second, with perhaps 90 counts in the first second interval and 105 in the next. In all instruments there are limits to the accuracy of the calibration and of the performance of the electronics. If the gain of an amplifier in a gamma-ray detector is set slightly higher than intended, then the detector will assign an energy to each gamma-ray that is systematically too high. A large part of each observer's research is devoted to understanding and characterizing these errors.
The other uncertainty cited by Cicero, the modification by intervening space of light traveling from a source to the observer, is not generally considered an uncertainty by the scientist, but is in fact part of the phenomena he wants to understand. We understand that an oar appears bent because of the difference in the index of refraction of water relative to air. Today, when we observe galaxies far beyond an intervening galaxy cluster, we see multiple galaxy images because gravity slightly changes the path of light, making the cluster act like a lens. We don't consider the multiple images as false presentations, as images that falsely representing galaxies that do not exits, but rather as part of the physical process of light propagation, one that can be used to measure the properties of the galaxy cluster.
The Plato's scepticism, which Cicero is heir to, is the often unrecognized as the mode of operation for modern science. Like Plato, we scientists never prove that a theory is correct; we only prove that it is invalid. But unlike Cicero, we are not afraid to adopt a theory that appears to be correct. Cicero said that the wise man does not assert a belief, because the wise man does not want to tell falsehoods; because any representation can be false, asserting a belief risks telling a falsehood. We scientists are not Cicero's “wise men,” because we are not afraid of holding views that prove to be false. Our goal is not a true description of the universe; our goal is to have an adequate description of the universe.
Freddie Wilkinson
1. Cicero, Nature of the Gods; Academics, trans. H. Rackham, Loeb Classical Library, vol. 268, (Cambridge, Mass.: Harvard University Press, 2000), 571.
2. Ibid.
