McNutcase wrote:What's the current consensus on the age of the universe, its size, and whether it's open or closed?
Age is the easiest to answer. Consensus is pretty strong on that point, giving a value of about 13.8 billion years with uncertainties on the order of a few tens of millions of years. This result gets arrived at independently from a number of different methods, so it's probably pretty sound.
As a side note, you may have heard at various times the "scandal" that when astrophysicists try to calculate the age of the oldest stars, they get an answer older than the age of the universe. Of course no astrophysicist believes that the universe formed with old stars in it, so this has always been taken to mean that either cosmological or stellar models (or both) needed correction. So it's not viewed in astrophysics as a scandal, but instead business as usual in an evolving field of study. It just sounds
more embarrassing than some other discrepancies that science has had to deal with.
Anyway, the good news is that, while stellar models seem to still be giving higher numbers, the two numbers now have overlapping uncertainty ranges (oldest stars calculated as about 14.5 billion years with an uncertainty of about .8 billion years). Obviously, the ideal would be to get the models refined to the point where the numbers are consistent and
have smaller uncertainties, so even the best estimate of the stellar ages was less than the age of the universe. Regardless, overlapping uncertainties is a win.
Size depends on whether you are talking about the visible universe or the whole universe.
The size of the visible universe is the distance to the source of the cosmic microwave background (CMBR to its close friends and family). The CMBR comes from the time when the universe had cooled enough that electrons and nuclei were able to combine into atoms. At that point, the opacity of the universe dropped abruptly. The photons in the CMBR have been travelling unimpeded ever since. Cosmologists put the distance to the "surface of last scattering" at 46 billion light years.
That distance may sound goofy on the surface, given that the universe is supposed to be 13.8 billion years old. A light year is the distance light travels in one year, so it would seem at first blush that the universe should be 13.8 billion light years in radius. The extra distance is due to the expansion of the universe. The space in between where the light came from and here got bigger in the intervening time.
Rather bizarrely, the actual size of the universe could be somewhat smaller than that.
This is under the assumption that the universe is curved to such a great extent that a straight line path curves back on itself (or comes close). The linked paper is academic and technical but has islands of lucidity in it.
Basically, the authors used the observations of the CMBR, considered the possibility that you might be able to look through the same part of space in two directions due to this curvature, and then figured how tightly the universe could be curved before it would introduce discrepancies (basically that it would become more obvious than it is that you're looking at the same thing in two different directions.) I really love this result.
All that said, I believe that the majority of cosmologists believe that the universe is, if not infinite, large compared to the visible universe. This ties into the last point. Whether the universe is open or closed is essentially the same question as to whether the universe is infinite or finite. A closed universe is, in the jargon of the biz, finite but unbounded. It curves back on itself. This is the type of universe that will eventually stop expanding and collapse back down. An open universe is infinite and will expand forever.
Theoretical cosmologists tend to favor a universe that is "flat" i.e. right on the borderline between being open and closed. It will expand forever, but the expansion rate will approach zero as time goes by. The big reason for preferring this is that we have reason to believe that if the universe isn't flat, it has to be extremely close. A small deviation from flatness in the closed direction should have been enough for the universe to have collapsed long ago. A small deviation in the open direction would have caused it to expand so quickly that no structure (i.e. things like galaxies, stars, planets, little things like that) should have been able to form. If the universe isn't precisely flat (with an accompanying good physical reason for being so), then it begins to look like we were just extremely lucky. Scientists hate answers like that.
It's all still something of an open question, however. There's good observational evidence that, at least right now, the expansion of the universe is accelerating. The name that you may have heard for the cause of this expansion is "Dark Energy," but that's really at this point still a case of "let's give the thing we're ignorant about a name." So a flat cosmology is still attractive, but that means that eventually the Dark Energy can't continue to make expansion accelerate. The closed universe may at first glance seem to be out of the running, but if dark energy can lose enough steam for the universe to be flat, it raises the possibility that it could even lose steam a little bit faster.
Basically, the only thing I think people are sure of is that physical cosmology will remain an exciting field of study for the foreseeable future.