Most of us think that reality has a foundational level, perhaps in the form of ultimate particles. But Ross Cameron argues that this view is misguided and that the nature of reality might be turtles all the way down.

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Imagine you’re on the ground floor of an office building. You could go up the stairs, to an above-ground floor. Or you could go down the stairs, to the basement, and stand among the foundations of the building. Some buildings have a sub-basement, so you can go down even further than the basement. Some even have multiple sub-basements: perhaps you have to go down three floors from the ground floor to reach the true foundations. You can easily imagine more and more extensive sub-basements: ten levels below ground, a hundred, a billion! We outstrip the bounds of architectural plausibility, but not the bounds of coherence. For any finite number, n, it’s at least conceivable to have n basement levels below the ground floor.

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But we can imagine still more elaborate possibilities. Imagine a building where you can keep descending, without ever reaching a bottom level. Where for every level of sub-basement you reach, there is yet another beneath it. No matter how far you descend, you will never reach the foundations of this building, for there are no foundations: every floor rests upon a lower floor. Perhaps even wilder still, imagine a building where you descend from the ground floor to the upper basement, and from here you descend to the lower basement, from which you descend to the second floor, from which you descend to the ground floor. In this building you keep going down and end up back where you started (likewise if you keep going up). And this isn’t because there is a teleporter in the lower basement that makes you think you’re going down but in fact it teleports you up – it’s the even stranger thought that immediately below the upper basement is the very same level of the building that is above the floor that is above the ground floor.

Both of these imagined buildings involve a type of infinite regress. The first building has infinitely many floors, and so you can descend and descend ad infinitum without ever reaching the end and without ever setting foot in the same floor twice. The second building has finitely many floors but they go in a circle, so you can descend and descend ad infinitum, finding yourself back where you started despite never retracing your steps. Neither building has a foundation: in each case, every floor rests upon another floor.

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The claim that reality must have an ultimate level is often supported by little more than an appeal to intuition or incredulous bafflement at the alternative.

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