Published online by Cambridge University Press: 28 February 2022
Intuitively the vacuum state of the Universe is the state that would obtain if the spacetime arena were emptied of its contents. The idea is that if we removed all the material particles, such as quarks and electrons, together with all the force-carrying particles such as photons and gluons, so there was no matter or force in the Universe, then we would be left with a featureless space-time, the bare arena of physics, and this would be the vacuum.
There are many reasons why such an idea is problematic. On a strict relationist conception of space-time, the procedure envisaged would leave us, not with empty spacetime, but literally with nothing. Having removed the relata, the spatio-temporal relations would also disappear. This problem does not arise for space-time substantivalists, but general relativity now raises difficulties.
I am grateful to David Malament for prompting me to think about these issues in the first place.