Glad I could help.
Thanks Marley and Lob. I was just asking.
Marley clarified nicely above, re: “flat”.
I must admit I have a hard time myself imagining how the universe could have a finite age, or, at least, there is a finite amount of time between now and the Big Bang, and it still could be infinite in size, flat or hyperbolic.
It is thought that the universe expanded wickedly fast in size an exceedingly tiny fraction of a second after the Big Bang, during the “inflationary” epoch (which also lasted a miniscule amount of time). During this time the universe as we know it increased from the size of a proton to about the size of a grapefruit, according to some models. Space was stretched and bits of matter were pulled away from each other at well above the speed of light before this “inflationary field’s” strength was dissipated enough that the expansion of the universe more resembled what we see in the current epoch (though there is some evidence the expansion of the universe is accelerating again).
How one gets from this “grapefruit”-sized thing to infinite and flat I can’t imagine. I’m not sure if it’s possible to imagine it. Having said that, I do know that nobody really has enough confidence in any of our theories about cosmic evolution to say they know for sure what was going on right after the Big Bang (much less before it).
When in doubt, look to experiment. Experiment (extrememly precise measurements of CMB anisotropy) says: Maybe it’s flat and infinite, maybe not; it depends on how you look at it.
Now must be a fun and frustrating time to be a cosmologist.
Turtles. Turtles all the way down, dammit!
Tris