The theory of universe in physics was tending to steady state theory until Hawking burst out with a bang, and it has been the big bang teory for quite a while now. Explained here in terms simple enough for non physicists, it is certainly a worth read unless you are a budding physicist - then, it is a must.
Someone recently asked if this was out of date since it has been over a couple of decades since publication. It is hard to imagine that - after all Newton is still relevant and so is pythagoras theorem for that matter, in spite of all the wider wision of reality.
And it might happen after all that the steady state wins with a modification - one suspects that the hasty victory granted to big bang had something to do with a subconscious level comfort that arises out of a subtle conformity worth the prevailing culture, and while big bang gave creation in not a week it was at once instantaneous and slow over billions of years, so the scientist spirit did not feel obedient to church in embracing the big bang theory either - still, even if the big bang comes to be modified, extended, whatever, with a wider vision that might come as it often does in science and generally in knowledge, nevertheless this book is not going to be irrelevant, and it will be a good read even then.
As of now, as far as we know, it is not out date. Perhaps more is known, but the big bang prevails so far.