Is Spacetime Real?

Terrible article, terrible comments!

> This example actually weakens your argument. Heliocentric ellipses are chosen because they explain our model well and importantly are simpler than epicycles; but we can make epicycles arbitrarily accurate by piling on as many of them as you like.

Epicycles allowed us to map the motions very well but they were incredibly complicated and didn't provide for explanations of how they came into being. Simpler models that provide the same results are considered to be better. Given two models that make the same predictions, it makes more sense to use the simpler one than the more complicated one (Occam's razor). The heliocentric model no doubt had its detractors until it was refined enough to make the same or better predictions, but its simplicity made it much more attractive as an explanation.

> This model is 100% accurate. Every one of these boxes I have seen always behaves this way. Is there a demon sitting in the box?

Typically we apply Occam's razor in this. If we know how we could construct such a device without a demon, a being for which we have no other evidence of its existence, then our simpler and more readily explainable solution is what we generally go with. However, if this box is indeed unopenable, and the light always changes, then it doesn't really matter does it? Neither the demon nor a more conventional explanation makes any difference to how we interact with the box, nor could it ever.

The "reality" of what happens inside the box is not relevant and some would argue not even something that exists in the realm of scientific thought. It's like, say you live in Conway's Game of Life, and ask "what are cells made of?", it is completely unknowable and even if you somehow had the answer it would be meaningless since cells always behave in exactly the same way that is 100% explained by a simple model.

It's nice to think there must be a missing field that brings it all together, knitting space-time into a consistent quantum reality with causality preserved, and neatly explaining things like quantum vacuum energy, superposition, dark matter, and wave-particle duality.

For some reason the idea of photons stretching a hundred million miles long reminded me of the Asimov story 'The Dead Past' showing how a 'time viewer' would in reality be a Total Informational Awareness device.

> This statement doesn't suggest simplicity as a measure of realness and it is unclear why reality would necessarily prefer the simpler thing.

Because it doesn't matter if the results are the same, and simpler things are inherently preferred. Assume that both of these models are 100% correct in their predictions: there is no reason whatsoever to believe that the more complicated one is a "truer" model of reality, nor is there a reason to believe the simpler one is, so we proceed on the notion that the simpler one is because that is more to our liking and the end results are the same.

I guess one of the fundamental impasses here is that I am not convinced, on a philosophical level, that there is any deeper "realness" than can be modeled. If we can't model it, or rather if modelling it serves no purpose, then it may as well not exist.

> As for whether it matters, I think that's rather the point: We don't know if it matters until we find out it does. I don't think we can know if matters until the moment it definitely does.

Right. We must assume reality is what it appears to be until we make observations and tests that prove otherwise, then we construct a new model. We must assume that new model represents reality because we simply have no alternative until we build a better model.

> A 100% accurate full-knowledge model is, by our own models, an impossibility. And even if we had such a model, how would we ever know it?

To a certain extent we can't. No matter how many correct predictions we make there is always the possibility that we will eventually make an observation that defies our model. That's sorta my point. What we call reality is, by necessity, a product of observation, deduction, testing, and modelling. We have to construct our reality from that, and talking about whether or not an accurate model represents some deeper "reality" or not is pointless without an alternative.

If right now we question the "reality" of spacetime, what changes? Can we even build an accurate model of reality as we currently know it without spacetime? Can that model be made simpler than the ones with spacetime? If so, no one has done it yet. Therefore we have no choice but to believe that the universe isn't deceiving us and spacetime actually does exist, because believing the opposite is completely pointless.

I enjoyed reading everybody's comments. I've been in a long conversation with a friend about the Mūlamadhyamakakārikā---a Buddhist text that argues that nothing _inherently exists_, including, presumably, space-time. I don't find all of the arguments in the text convincing, partly because it is based on a number of outdated metaphysical assumptions, but it is very interesting none-the-less.

My discussion with my friend went back and forth, and we eventually decided that most things don't inherently exist, including people, chairs, and atoms. We ended up on the fence as to whether the "wave function of the universe" inherently exists. Anyway, I captured the essence of our conversation in a dialogue that may be of interest to other HNers:

https://goodlifeodyssey.com/nothing-inherently-exists