Stephen Hawking famously said that we don't know what breathes fire to the equations of Physics, have philosophers tried to identify what that might be and what are the things they found called? I am curious about what philosophers have found or imagined relating to this mystery.
Hawking is talking about the fact even if we discovered the equations of a complete and final unified theory of fundamental physics, there would still be the question of why a universe described by those equations exists at all. So, I don't think there would be any philosophical term other than "existence" or "being" here (the philosophical study of what exists, or why anything exists, is called 'ontology'). Here's some context for his comment, from ch. 12 of A Brief History of Time:
Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?
Hawking wanted to know the thoughts God had when he created the physical world. His thoughts about the laws to which govern this world and the Nature of this world. What is it exactly that conforms to these laws? Can it be desribed by the equations themselves or do these equations need fire to be breathed in them? Its this what he addressed. What do the equations describe exactly? Where the stuff comes from is another question which can't be answered with the help of physics. Or you must support the view that the physical world is eternal in which case the question makse no sense.
The question of fire can also be asked in an eternal universe without the question where the equations themselves come from. The equations can be considered a part of a larger structure bjut then the question is merely shifted. From where comes the all comprising super (mathematical) structure?. The universe has to "obey" some equations because liife would be impossible without such a structure of equations. Chaos would rule. The question of origin is a a difficult one. When you have stated the origin you can always ask where the origin comes from. So I think Hawking meant to ask what the Nature of the fire is that the equations describe. There are physical reasons why the universe is eternal. The physical Nature of the things desribed can maybe be known in a future physical theory. But about the internal Nature of this stuff is to know God. Maybe we can experience it somehow because of the simple fact that we are made grom this stuff. On the inside we can feel this stuff. We can feel, see color, think, hear music, love, etc. But now I'm running off off the mind.