Philosophy, Film, Politics, Etc.

Friday, July 29, 2011

Science Phiction #1: the time-lag argument and presentism

Not sure how far I'll go with this, but here's the first entry in my "Science Phiction" series. The point is to identify popular writing which mangles, misidentifies, or otherwise wrongly appropriates philosophical ideas or themes in the name of science. If I were going to award points, I'd award generously for writers who get both the science and the philosophy wrong. However, to qualify for entry, you only have to get the philosophy wrong.

First up: Astrophysicist Adam Frank gets the time-lag argument terribly wrong: Where is Now? The Paradox of the Present

Here's an excerpt:

When you look at the mountain peak 30 kilometers away you see it not as it exists now but as it existed a 1/10,000 of a second ago. The light fixture three meters above your head is seen not as it exists now but as it was a hundred millionth of a second ago. Gazing into your partner's eyes, you see her (or him) not for who they are but for who they were 10-10 of a second in the past. Yes, these numbers are small. Their implication, however, is vast.
We live, each of us, trapped in our own now.
The simple conclusions described above derive, in their way, from relativity theory and they seem to spell the death knell for a philosophical stance called Presentism. According to Presentism only the present moment has ontological validity. In other words: only the present truly exists; only the present is real.

Frank's argument is that everything we perceive has come to us from different parts of space and time. Our perceived "now" is therefore "at the mercy of many overlapping pasts."

This is illogical. If all of our perceptual experience comprises information from different pasts reaching us at the same time, as Frank suggests, then the now is not at the mercy of those pasts. The now is rather the point at which information from those pasts converges. So there is no reason to reject presentism, as Frank does. (Presentism, Frank explains, is the philosophical view that only the present exists.)

To Frank's credit, there is a coherent philosophical argument in the vicinity. It's called the time-lag argument, and it was first proposed by Bertrand Russell in the first half of the 20th century. However, it is not an argument against presentism, but rather against direct (or "naive") realism. The logical conclusion of the argument is that the content of perceptual experience is not the world as it is, but the world as it was.

Frank also errs in supposing that his argument (or the related time-lag argument) relies on relativity theory. He is presumably referring to Einstein's theory of Special Relativity, which relies on the experimentally observed fact that light travels at the same speed relative to every observer regardless of their inertial frame. This fact, however, and the consequences Einstein draws from it, are not required for the sort of argument Frank is trying to make.

In line with the time-lag argument, Frank stipulates that light travels at a finite speed--though I don't see why the time-lag argument needs such a stipulation anyway. All the argument requires is that the information we receive as input (such as the touch of silk against our fingers) takes time to reach our perceptual processors. Of course, it's a well-established fact that light travels at a finite speed, and I don't suppose that is something we should ignore. The time-lag argument should take the speed of light into account, but it is not necessary for the argument as such.

There is much to be learned from the time-lag argument and the many objections which have been made against it. One objection is that the argument relies on a dubious ontological distinction between the perceiving self and the world. Many philosophers reject the idea of a distinct, inner observer which passively receives information from the senses. The very idea of sense-data, which Russell favored, has been widely criticized for decades. Maybe we shouldn't think of the content of perceptual experience as arriving at our minds through our senses. The content of experience might not be so easy to identify, if we are justified in postulating it in the first place.

Another criticism of the time-lag argument is that it ignores what we know about quantum physics: on the one hand, there may, theoretically, be particles (e.g., tachyons) which travel faster than the speed of light; on the other hand, some interpretations of quantum mechanics have it that information can travel instantaneously. On very small scales, causality might actually occur backwards in time. The very notion of temporal direction might only make sense with relatively large scales. These points do not force us to reject the time-lag argument, but they do make it less persuasive.

The question remains: Does contemporary science support or conflict with presentism? On the one hand, special relativity says that there is no privileged observer, no unique inertial frame, which defines the "now" of the universe. On that view, it makes little sense to say that the present is all that exists, since there is no particular present for the universe as a whole. On the other hand, relativity theory also regards time as a variable. Many physicists imagine a block universe, where all events at all times exist "side by side," so to speak. Our perception of time is therefore something of an illusion. This suggests that the present is not all that exists. Yet, we might prefer to say that everything exists in the present, but we are physiologically limited in our ability to regard the present in all its complex glory. The bottom line: There's plenty of room for debate.