Time

For more than a century, it has been commonplace for physicists and philosophers to assert that our ordinary understanding of time is wrong. As Einstein put it,

the distinction between past, present, and future is only a stubbornly persistent illusion.

For most of our physical laws, time is a dimension little different from the three dimensions of space. In principle, our fundamental laws work the same way forward and backward in time, implying that time could reverse itself and that the future is every bit as real and fixed as the past.

But this has never been universally accepted by physicists or anyone else. There are certain stubborn things in our experience that seem to refute any notion that time could run backwards. We remember the past but not the future. Eggs are easily scrambled but are never unscrambled. For a scientist the great example of one-way change is biological evolution, which never reverses itself and seems to declare that life at least has a one-way passage through time.

Of course people in the "time is an illusion school" recognized these problems and some thinkers devoted great effort to explaining away the apparent one-way nature of historical time. Einstein, according to his friend Carnap, was preoccupied by the problem of "now":

He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics.

Now physicist Lee Smolin has written a book arguing that time is real and fundamental:

I used to believe in the essential unreality of time. Indeed, I went into physics because as an adolescent I yearned to exchange the time-bound, human world, which I saw as ugly and inhospitable, for a world of pure, timeless truth…. I no longer believe that time is unreal. In fact I have swung to the opposite view: Not only is time real, but nothing we know or experience gets closer to the heart of nature than the reality of time.

Following up on Einstein's conundrum, he asserts that the now of our experience is somehow at the heart of what it means for things to exist:

Everything we experience, every thought, impression, action, intention, is part of a moment. The world is presented to us as a series of moments. We have no choice about this. No choice about which moment we inhabit now, no choice about whether to go forward or back in time. No choice to jump ahead. No choice about the rate of flow of the moments. In this way, time is completely unlike space. One might object by saying that all events also take place in a particular location. But we have a choice about where we move in space. This is not a small distinction; it shapes the whole of our experience.

As an archaeologist I deal every day with processes that move only in one direction: decay, disintegration, cultural change. To me there is nothing more certain that the absolute irreversibility of time. The past, present and future are, I am sure, different from each other in fundamental ways. I can dig up the past, but nobody can dig up the future. If our physics cannot account for this, that is a problem with our physics, not our own experience.

Lee Smolin agrees, and he, who understands these things, has found ways to make this insight fit within the mathematical framework of general relativity. He writes

The world remains, always, a bundle of processes evolving in time. Logic and mathematics capture aspects of nature, but never the whole of nature. There are aspects of the real universe that may never be representable in mathematics. One of them is that in the real world it is always some particular moment.

Glad to have him on my side.