Astronomer Neil deGrasse Tyson caused some significant consternation last week among historians and archaeologists by tweeting that “We are prisoners of the present, in perpetual transition from an inaccessible past to an unknowable future”. Reactions from archaeologists and historians were swift and critical. I take this as an opportunity for reflection on questions that we, as practitioners, don’t ask ourselves often enough.

Early in the thread, Darrell Rohl writes “Every historian on the planet just looked down, rubbed their eyes, and sighed deeply”. Elon Musk memes were pressed into service. Paleoecologist Jacqueline Gill summed up much of the feeling with “If the past was inaccessible, I wouldn’t have a job”. For some reason, futurists were not quite as upset, or at the very least, not quite as vocal.

Yet, no one can deny that we don’t actually know very much about the past, and that our perception of the future is cloudy at best. The sin of deGrasse Tyson’s flawed aphorism, is that it both underestimates our access to the past and future, and overestimates our grasp of the present.

The past

The past is removed from us. It is, literally, not present. Whether at the scale of our individual lives, or at the scale of our species, or of life on earth, we actually know very little about the past, and we know almost nothing for certain.

One thing we do know, is that the past constrains the future. What passed before organizes, but doesn’t necessarily determine, what comes next. This means our knowledge of the past is constrained by the present. We can predict back, to some extent, based on what we can see now. The present only allows a limited set of possibilities for what happened before. What we observe around us now, including artefacts found, stories told, sediments laid down, conjugations used, fossils preserved, genes disseminated, etc, must, in some way, be a product of the past.

How the present was generated from the past is uncertain, but not unknowable, since there are a limited number of kinds of transformations that can lead from one to the other. There is a systematic and at least partially knowable relationship between past and present.

That is what archaeologists, historians, and geologists work with, among others. We propose and rule out transformations that could have made the present out of the past. The present can constrain our knowledge of the past to some extent, without ever nailing it down completely.

The alternative is that the world is a dream. Perhaps it is, but for now, I will continue to work as if it isn’t. Suffering in the world seems real, and it often seems to result from the way the past produces the present. I will continue to assume that the suffering of others is not just part of my dream, but is real.

A big part of the reason I study the past is that I think knowing it more fully can help us make things better now. This might be part of the reason for the outrage palpable in reaction to deGrasse Tyson’s tweet. We don’t study the past for nothing. We study it for something. Saying the past is inaccessible is the same as saying that we study it for nothing.

The future

The future is much like the past, with one screaming difference: The past has already happened. Of the myriad possibilities that could have generated the present out of the past, only one was actually realized. We’ve traveled one road, and we’re at the edge of a thick fog. We can look back some distance with some confidence. We can tell from where, in general, we must have come, although we can’t quite be sure very precisely how we got here. We can often tell how we didn’t get here, and that is the bulk of our knowledge of the past.

We can’t see ahead, but based on the way that lies behind, we can prepare in very general ways for what could lay ahead. Just as the past constrains the present, the present constrains the future, but many different possibilities are ahead of us. Whereas we have evidence in the present of which possibilities were realized in the past, and which weren’t, we can only reflect on which future possibilities can eventually be realized, which are likely, and which are impossible.

I was going to write that we can only speculate about the future, but that would be too strong a term. The present is weaker foundation from which to think about the future than about the past, but it is still a foundation, and that is not nothing. The future is less accessible than the past, but it is not completely unknowable. People often make fun of futurists, and they are almost invariably wrong in detail, but theirs is no more useless an art than the historian’s.

The present

I kept the present for last. Here I must again mention scale. The present of the human species is a broader stretch of time than the present of any one of us, and the present of planet is larger than both. I find it surprising that deGrasse Tyson, as an astronomer, didn’t include that qualifier.

The processes that organize the geological past of the earth unfold at different rates than the physical and social processes that constrain the future of a human family. The present can cover wildly different periods of time.

Having said that, I don’t think we have quite as much access to the present, or quite as good a grasp of it as we often think, or as deGrasse Tyson seems to assume. Just as our knowledge of past and future fade as we move away from the present, so our knowledge of the present, however defined, fades as we move away from our current spatial and informational location.

The speed at which information travels through networks, like the speed of light in astronomy, constrains the bubble that we can call our present. It may be, in fact, that we don’t have a much better grasp of the present than we do of the past or the future. Just as the past constrains the present, and the present constrains the future, what we know of the present constrains the present outside of our information bubble.

There are many possibilities for what lies beyond our grasp of the present, but just as the past has already happened, the present is currently happening. So it is just possible that we can more confidently infer the present than the future, but all things considered, I am not convinced we actually know much more about the present than we know about the past.

If I had to rewrite deGrasse Tyson’s tweet, I would say that we are in the present, uncertain about exactly how we got here, and less certain about where we will be next.

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