- What does it mean to say that the Universe had a beginning? There are different ways of spelling this out. I shall develop them, consider the logical relations between them, and support one as best capturing our intuitive understanding of this notion. I shall then draw a conclusion about whether Time could (it is logically possible) have a beginning. Finally I shall consider, on my preferred understanding of what it is for the Universe to have a beginning, what physical cosmology can show about whether it did in fact have a beginning. I understand by a Universe, a system of substances temporally connected to each other.
- I understand by a substance a thing with causal powers or liabilities, that is able to act or be acted upon. Substances will thus include both material objects and any other physical objects there may be such as chunks of energy or the fluctuating Vacuum' of quantum field theory, and immaterial objects, if there are any, such as souls and ghosts. I understand by two substances being temporally connected that they exist for periods of time which are either earlier than, overlap with, or are later than each other. I understand by our Universe that system which includes ourselves, and - although my argument is perfectly general - I shall for simplicity of exposition, phrase it in terms of our Universe, and - believing that there cannot be any substances not temporally connected to those of our Universe (i.e. that there can only be one Time) - shall call it ‘The Universe’. If there can be another universe, and so another time, my arguments will apply to them too.
- Given this understanding of the Universe, what is it for the Universe to have had a beginning? There are several ways of attempting to make this notion more precise. These all involve the concepts of instant and period (alias temporal interval) and of a period having a duration (alias temporal length). I need to begin by arguing for four very modest verificationist theses with respect to these concepts.
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