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I’ve mentioned Shrinking Future Time (SFT) before, and according to the Internet Encyclopedia of Philosophy, it isn’t one of the three theories on the ontological differences (or lack thereof) between the past, present, and future. As the name suggests, the theory is just turning Growing Past Time (GPT) on its head: the present and future are real, but the past is not.

My goal here is just to start setting up a motivation for further inquiry. Why think SFT is even plausible? Thus I’ll mostly be appealing to some intuitions to try to draw out the possibility.

Presentism has the appeal of, well, right now is all we can seem to access right now. The past is gone and the future isn’t here yet. Dinosaurs don’t exist, and neither do teleporters. GPT adds the past, while still acknowledging the present is special. The past did happen, after all, so saying dinosaurs aren’t real seems kinda silly. But the future is still left undetermined. The present is special as it’s the edge of the block. Eternalism is different from these two both in the reality of the future as well as the present not being objectively special. Subjectively, sure, I’m now, but I’m also here, and we don’t think here is more special than there besides that we’re here. So likewise tomorrow and yesterday are no different than now; I just happen to be now.

SFT clearly shares some elements of each of these, and comparing to space continues to be intuitively useful. In space, there are some places that are, and some places that are not. If we embrace presentism, a place can be and then not be. Or not be and then be. (If we embrace eternalism, it can be only at certain times.) Twenty years ago, if I asked you to go to Blockbuster and pick up a tape, I’d be making a coherent request because Blockbuster was indeed a place. If I ask now, I’m asking nonsense because there is no such place.

Regardless of whether it’s 2017 or 1997, here is always a place, assuming anywhere is, and Narnia is not. (It’s at least not real.) Now one may object already with the Blockbuster example by saying that all that’s changed is the name and maybe some local geography, but the absolute location in space is still there. There’s a patch of ground there that was there twenty years ago and whether the building on top is a Blockbuster or a Burger King doesn’t make an ontological difference here. So consider instead first Narnia. It’s not a real place, so a request to fetch something from Narnia is an impossibility at best. If the universe (i.e. the totality of all space) itself is changing size, then absolute locations (if there are such things) may exist and then not or not and then do.

What Blockbuster helps illustrate is an idea of accessibility. Blockbuster being there basically means it is in some sense accessible. Of course, we also want to say Neptune is a place, but as it stands, nobody can get there from here. However, there’s no deep (meta)physical restriction in the way like there is with places that just don’t exist, only a lack of technology. Presumably the ontology of time and space is not reliant on human technology. (Well, I think it probably is, but not in a way that seems to affect the plausibility of SFT.)

Let’s return to time. Like I can get from here to there, I can get from now to later. The restriction on the “there” is just that the place has to be real. If we continue the analogue, then the restriction on getting to another time is that the other time has to be real. The inverse also applies: if I can’t get somewhere, it’s because it’s not real (again, using this broad definition of “can”), and likewise if I can’t get to some time, it’s because it’s not real. Thus we have the accessible, thus real, present and future and the inaccessible, thus unreal, past. Thus, SFT.

An obvious presentist objection is that we can’t actually get to the future because we’re always in the present. Of course, by that reasoning we can never get there because we’re always here. What we have in motion through time would thus be akin to moving through space but obliterating every location as soon as you leave it. This seems to not be the case for space, but it looks like it could fit for time.

In sum:

• The present obviously exists.
• The future must exist for us to be able to get there.
• The past not existing explains why we cannot go back.