*Originally posted by 2inquisitive *

**JamesR, I know this probably sounds stupid, but are there any models, or is it even possible, that the universe is like a huge, round**

ball? What I am trying to ask, is it possible that when we look back

10 billion lys for instance, we are looking in a great circle, instead

of in straight line of sight? Like all light is curved by the mass of the

universe, so the object we are looking at may actually be behind

us, for instance, instead of straight ahead. I know this is more of

a philosophical question, but wondered if there was physical model

along those lines.

this is not a philisophical question, this is in fact an experimentally measurable question. and a good question to ask, furthermore.

yes, there is such a model. the standard Big Bang model allows for this possibility. in fact, there are basically only 2 parameter in the big bang model, one of which is the curvature. if this curvature is 0, then the universe is flat. if the curvature is positive, then the universe is like a huge 3 dimensional ball, just like you described, and if this curvature is negative, then the universe is hyperbolic.

just this year, very accurate results were released from the WMAP experiment, which put tight constraints on the value of this curvature. up to the best experimental accuracy we can muster today, the universe is flat. not a big ball.

does this mean that we know that the universe is not a big ball? no. to know for sure, we would have to measure the value of this curvature to be 0 with infinite accuracy. so all we know is that if the universe is a big ball, then it is very very very big.

note that the equations that govern the geometry of the cosmos tell us that flatness is an unstable state for the universe. therefore if there is even the slightest deviation from flatness, then the universe should not stay flat. since the universe is rather old by now, this makes it hard to explain the observed flatness. inflation, which is an extension to the big bang model, which basically says that in the very early universe, it grew exponentially for some period, was devised to solve this flatness problem, as well as a host of other problems. with inflation, the really fast exponential growth smoothed out the universe and flattened it so that its curvature would be 0 to one part in some big number like 10^60 or something, i forget.