From a 2022 review by a philosopher, of a 2021 book I haven't read by a physicist, quoting from a 1998 book I haven't read by a physicist:
What’s Eating the Universe is undoubtedly a very interesting book. Davies presents a concise summary of the latest state of research in cosmology and elementary particle physics, and shows us the links between exact science and many significant philosophical problems.
Physicists can explain the evolution of the universe as far back as the first split second. It’s one of the greatest scientific achievements. So far, it has not been possible to combine quantum mechanics with general relativity and formulate a “theory of everything” (TOE, or quantum gravity). However, in A Brief History of Time, Stephen Hawking has written that “if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason - for then we would know the mind of God”. Davies would probably agree with that view.
P.s. Hawkings said in 2014 “What I meant by ‘we would know the mind of God’ is, we would know everything that God would know, if there were a God, which there isn’t. I’m an atheist.”
P.p.s. Paul Davies had a controversy where he apparently compared scientists belief in immutable laws to religious faith, but seems to have complained he wasn't directly equating them.
P.p.p.s. I didn't intend this question to be about religion or faith Vs science at all. I find it strange that Hawkings was misleading in his popular book (saying God. Also saying 'we and the universe exist' as if separate), and then I think misleading in his later statement in the opposite way (because if we don't know why there's a universe, how do we know there wasn't a mental creator of it, given that we have evidence that minds which can create things can evolve within a universe).
P.p.p.p.s to qualify as a physical 'theory of everything', should it also explain phenomenal consciousness? (why and where qualia), and might that help know why there's a universe?