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Philosopher Sam Baron (Melbourne) discusses. As always, I’m interested to hear what the philosophers of physics make of a bold claim like this.
There are many places in the essay where I would get off the argumentative train, but here’s perhaps the first. I don’t think we need to have a notion of spacetime in place to get a notion of emergence off the ground.
Baron claims that emergence requires “arrangement” and “causal interaction,” both of which presuppose spacetime. But in quantum mechanics, the relevant space of possibilities one is working in is Hilbert space, and a Hilbert space can be perfectly well thought of as being composed of smaller Hilbert spaces — via the mathematical operation of a tensor product, which doesn’t necessarily require a notion of spatiotemporal arrangement. And in many Hilbert spaces, one can define (again using the machinery of quantum theories without necessarily appealing to spacetime) collective degrees of freedom whose dynamics are robust and autonomous, and hence deserve the title ‘emergent’ if anything does.
This happens all the time outside of the realm of quantum gravity. For instance, to make quantum computers error-tolerant, one defines what are called ‘logical qubits’ which are constituted from physical qubits. These physical qubits don’t have to be spatiotemporally distinct (they could, e.g., be energetically distinct, or distinct via angular momentum) and, what is much more important to the argument here: the relation that the logical qubit bears to the physical qubits need not be, and typically isn’t, one of spatiotemporal arrangement: rather, it is one of encoding in a subspace of the larger Hilbert space.
Unsurprisingly, then, the ideas of quantum error-correction have been taken up in quantum gravity as well, and there are proposals for how spacetime might emerge as a kind of quantum error-correcting code from more fundamental degrees of freedom. My aim here isn’t to defend those proposals but merely to point out that it’s false, both outside and within quantum gravity, that emergence must be thought of as something necessarily to do with spatiotemporality.
Let me recommend Eleanor Knox’s essay on IAI a few months ago for what I think is a much more defensible take than Baron’s on how to think about spacetime in the context of quantum gravity.
https://iai.tv/articles/spacetime-is-an-idea-not-a-reality-auid-3281
I think the extremely weird-sounding announced thesis of this piece arises from making a specific decision about how to use the term “spacetime”. Baron (along with some other philosophers) want to tie the term “spacetime” analytically to a very, very specific structure. Basically, he wants to use it to mean what is described in the introduction (not by him) as “Einstein’s picture of spacetime”, and even more explicitly “the account of spacetime given by General Relativity”. So, for example, that spacetime in a continuum, variously curved by the distribution of matter and energy in accordance with the Einstein field Equation (with or without the Cosmological Constant).
Personally, I think this is a bad terminological decision. For example, I have been working on a geometrical account of a discrete spatial and temporal structure of the world. I myself would describe that as a theory according to which spacetime is discrete. But (if I follow) Baron would rather report that as a theory in which spacetime does not exist, because (for him by definition) spacetime must be a continuum. Hence—according to him—if my theory is correct then spacetime does not exist, and according to my use of language if my theory is correct spacetime is discrete and not a continuum.
Of course, if my theory is correct then General Relativity is wrong! But that’s more or less to be expected. I would report that by saying the General Relativity gives an incorrect account of the spacetime, and Baron would report that by saying that spacetime does not exist. I leave it to the reader to judge which way of speaking is less likely to cause confusion.
Does General Relativity “emerge” in my theory? Well, in an obvious sense no. But it is equally obvious that General Relativity has made many spectacularly accurate predictions, so any successor theory better be able to show that it can replicate those predictions (within observational bounds) where they have been verified. In exactly the same way, quantum theory must have a story about why Newtonian Mechanics worked as well as it did, and General Relativity must have a story about why Newtonian Gravitation theory + Newtonian Mechanics worked as well as it did (excellent except for the anomalous advance of the perihelion of Mercury, as far as anyone knew in 1915). Some people would call such arguments “the emergence of Newtonian Mechanics from quantum theory” or “the classical limit of quantum mechanics”, and similarly “the emergence of Newtonian gravity from General Relativity”. You get what they have in mind. As I understand it, Baron would prefer not to talk about “emergence” here, but maybe something like why a false theory still manages to make quite good predictions in some circumstance. Anyway, the latter is what has to be explained, call it what you will.
If one takes Baron’s route, then one ends up saying if General Relativity is superseded that “spacetime does not exist”. If you take my route, you say “Spacetime turned out not to have the structure attributed to it by General Relativity, but this other structure instead”. Personally, I think the latter is less likely to lead to confusion, although it make for less click-baity titles.
[…] Spacetime does not exist – Leiter Reports, accessed May 23, 2026. Source […]
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