Science In Real Life

I decided to write this essay on time. So not only is it not late, it explains, elucidates, and otherwise explicates the nature of time itself. Time is a constant presence in our lives, and yet very little is understood about both its fundamental character and how our brains process it. Get your thinking caps on, because tonight we’re about to brush up against some of mankind’s biggest unanswered questions, and they don’t care much for your personal space.

First, I want to draw a distinction between how we measure time and the “flow” of time itself. The first clocks were, of course, the sun and the moon. People noticed that from our perspective on Earth, the sun and moon move in regular cycles. That right there is the key to measuring time – we can divide the continuous streaming of experience into intervals the length of whatever repeating cycle we choose. We can use the sun, or Old Faithful, or your mother’s guilt trips, or maybe just nine billion oscillations of a cesium atom. The point I must emphasize here is that the units of time we derive from these cycles are arbitrary divisions that people impose on time, not the other way around.

So what’s left? Physicists describe time as a dimension, just like space has dimensions. First, a little aside about the word “dimension”. In bad science fiction you’ll often hear things like “an alien from another dimension” or what have you, referring to a concept closer in nature to a parallel Universe, some other world not immediately accessible from our own. This is not how scientists use the word. Ask an engineer to describe the dimensions of a rectangular box, and you’ll get three numbers: length, width, and height. This is exactly how physicists use the word. A dimension is a number you need to use to describe the physical extent of an object, how big it is from one end to the other. So I would say our box over there has not three dimensions, but four. In addition to length, width, and height, it has duration. At some time it was created, at a later time it will be destroyed. The interval between them is the box’s duration.

We can also describe dimensions in terms of the possible ways an object can move. Wave your hand around. You can move it left-right, up-down, and forward-back. Any spatial motion you can conceive can be described as a combination of those three motions. Now, don’t move your hand. Oops, you just moved it – in time. Your hand traveled from one moment to the next like an illegal immigrant crossing the border: you can’t stop it. As far as we can tell, that’s it. There are no other ways for something to move in our Universe. (Advanced note: some of you may have heard that string theory postulates additional dimensions. So where are they? The string theorists suggest they may be “curled up” so small we haven’t noticed them. The usual analogy is an ant on a garden hose. Close up you can see the ant has two dimensions, along the hose or around it. Zoom out and you can only see the ant moving lengthwise. The dimension of “around the hose” is curled up too small to see. There is as yet no evidence that this is actually the case in our Universe.)

Okay, so far it seems time is just like space. But there is one crucial distinction: direction. One thing leads to another, time elapses, seconds and minutes and hours tick onward, days and months and years go by, centuries and ages and eons slip away, and before you know it you’ve finally finished reading this sentence. We can go to a point in space, leave it, and come back. We cannot return to a moment in time. Once it passes, it’s gone, deader than disco and just as impossible to resuscitate. Intimately linked with this restriction is the phenomenon of causality.

Causality is at the heart of the scientific confusion about time, and this is where the subject gets really heavy. The every day notion and the classical physics notion are one and the same: an effect is always preceded by its cause. The theories of special and general relativity strengthen this notion by creating a well-defined past and future region for each event (Advanced note: the light cone). And then it all goes to hell when we bring in quantum mechanics. Using quantum mechanics is like living with a controlling spouse: everything works perfectly, but she’s uncomfortable to be around and impossible to understand.

You see, right now the only way physics has of “explaining” the directionality of time comes from the second law of thermodynamics, which says: entropy increases over time. “Great!” you say, “Time is defined as the increase in entropy, which we all know is always happening.” There’s only one problem. The second law is a statistical law, which means it only talks about aggregated trends. On the small scale, there’s always a chance entropy will suddenly decrease. The smaller you go, the more likely this is to happen (you can see why quantum mechanics exemplifies the problem). Does this mean time suddenly reverses? Well, no one knows. If you put a gun to my head and forced me to answer, I’d probably blubber incoherently. If you took the gun away and asked nicely, I’d say my gut instinct is no, time does not reverse. But since spontaneous entropy reversals like that only really happen on the quantum scale, we don’t know for sure.

Physicists in the field of quantum gravity, such as myself, are working to get around this problem by creating a theory that incorporates causality into the very nature of the spacetime continuum that forms the dynamic canvas to the cosmic landscape of our Universe. I’ll let you know when we’ve got something.