07 May 2009


I've often encountered the claim that "there is no time" or "time is an illusion." Taken at face value, I could find no sensible meaning in those statements. I think I finally figured out what at least some of these claims mean, and it was sparked by an offhand comment from Pelletti, about "change." When they deny time, they're not denying that things change, but they hold that separate from time. However, something is required for things to change, and it makes no sense to me to call that anything other than time. That's where my confusion came in. What they're denying is the view of time as a genuine fourth dimension. That may not be clear either, so I'll try to clarify.

Think about a reel of film. Each frame represents one moment of the film. If we stacked these frames on top of each other, we'd get a representation of the film plus its time element as a dimension. Now, we've got three spatial dimensions (that we perceive, at least), and it's harder to picture stacking "cubes" to add in time as a fourth dimension, but the idea is the same. What this implies is, just like the film, there is a physical record of changes through time, and that record exists regardless of what the current "present moment" is. There's a stack of previous frames "behind" us that, if we knew how, we could access and sort through. This, I think, is what scientists who deny time are actually denying.

Instead, they see what I would call time (and they might call change) as something more like ripples in a pond. The ripples rise and fade away and rise and fade away, but leave no permanent record of their presence. There is only a dynamic process, and not anything like a physical dimension of time. Now, even if this view is correct (and I currently don't feel I'm in a position to have a useful opinion on that), it would still be useful to treat time as a dimension. We know the rates with which certain things change, and within the same inertial frame of reference, we can use those to establish the "time coordinates" in that frame. At 0 seconds, a drop of water falls into the puddle. At 1 second, a series of concentric ripples can be seen across the pool. Etc. Just as if we recorded the scene with a camera, we could treat the waves and the relative time at which they occur as a four-dimensional object.

From an everyday standpoint, there doesn't seem to be a way to tell whether time is an actual dimension or merely a process of change. What I wonder, though, is whether treating it as only a process of change is consistent in various relativistic and quantum applications. I remember in A Brief History of Time, Hawking espoused the idea that in a black hole, an outside observer would see time stop as an unfortunate victim plunged towards the event horizon, but that the unfortunate individual would not see that at all; things would continue to change for him but in a time dimension perpendicular to the outside one. I'm not seeing a way to reconcile that with the "dynamic change" model of time. If from the outside we see all change stop, but on the inside change is still occurring, we have a physical presence for one of the prior moments of the falling individual, so that moment continues to exist for us, even as the person within the event horizon moves past it in his time. Maybe there's a way to reconcile dynamic change with this, or maybe Hawking was wrong, or... who knows.

From a purely philosophical standpoint, I variously find the "dynamic change" model liberating and depressing, depending on my mood. It's not a model I care for at all when I'm feeling a bit depressed, as it would mean that all of the people/places/things from my past have actually and completely ceased to exist, rather than continuing to exist in a time that I no longer have access to. However, in a better mood, it's liberating to think that each moment is completely new and fresh with no physical past weighing it down. Neither viewpoint is a useful argument for or against the position, but I find it amusing how completely opposite my own reactions are.

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