When I studied this stuff in the ‘60s and ‘70s, cosmologists agreed that the universe was “finite but unbounded” – meaning that it contains a specific and limited amount of mass/energy, equal to 10 followed by 50 zeroes tons, in a curving matrix so that you’d never reach a wall or boundary. It all supposedly began at a Big Bang, now believed to have taken place 13.7 billion years ago. The expanding universe, the ratio of hydrogen to helium and the cosmic microwave background (CMB) and its temperature point decisively to a Big Bang as our origin.
All Big Bang models show the infant Cosmos to have exhibited a number of physical states, like density, that were at infinity. Sadly, a physical parameter of “infinity” is utterly meaningless – not to mention that you can’t get something from nothing. Also there’s the thorny issue of where the nascent “egg” came from. No one knows, and no one can ever know. So the Big Bang is both definite and impossible, and it also explains nothing.
Going the other way, hard evidence since the mid-‘90s – namely the value of the Hubble constant, the ratio of dark matter to baryonic matter, the CMB anisotropy angular power spectrum (don’t ask), the flat topology of space and how the supernova flux compares with red shift, along with other data – tells us that no more than 1.6 percent of the universe will ever be visible to us. At least 98.4 percent of the galaxies are receding faster than light, or else were born too recently for their light ever to reach us in this wildly expanding Cosmos. Actually, if you insert the most likely and accepted values for these data, you get an infinite universe. In that case, all that we can observe is zero percent of the Cosmos.
Zero percent is a pretty small sample of the whole thing. It means that any assumptions we make based on observations are pretty close to valueless. So perhaps the Cosmos is not homogeneous after all. Maybe it has neighborhoods, with disparate properties. If so, we can speak only of conditions in our own life-friendly Zip Code – meaning the observable universe – and haven’t a clue about the larger meta-Cosmos beyond.
None of us can picture an infinite universe – especially one that’s infinite in several different ways. It’s apparently infinite in spatial extent, infinite in content (since all our models assume a homogeneity) and infinite temporally. If there are “multiverses” existing simultaneously with ours – which is an increasingly popular notion – well, they’re infinite too.
The bottom line is that astronomy is now firmly divided between the known and potentially knowable, like what makes the Sun shine and what we might find on Mars, and the utterly unknown and unknowable. It’s not all up for grabs, like we used to assume. Our brain/logic/thought/math systems now appear incapable of knowing the underlying nature of the universe. This is where the data of the past decade or so are taking us, even if no TV science guys yet seem able to ‘fess up and say so.
Just thought you should know.