Q&A: Cosmology

Q:
Instead of saying "..when the universe was half its' size", wouldn't it be more accurate to say "..at a time in the very distant past.." or some such? Do we really know anything of the universe's size or age? We really only know something of that portion of the universe which our instruments can see, or detect and nothing of what is beyond their reach. From all appearances there is every reason to believe that it goes on and on. The so-called "Big Bang" is only a theory, far from proven. So, why not be more accurate and leave room for other, equally astute theories, such as a plasma field created universe?

A:
Statements such as "we see an object when the universe was half its present size" are dependent only on a measurement of the red shift of the object (equal to 1 in this case), and the assumption that the red shift is due to the expansion of the universe. This assumption is on very solid ground, much more so than the Big Bang cosmology, the current theory with the most going for it, that seeks to explain the expansion and other observations, such as the microwave background radiation. Statements about the age are more dependent on the model universe and are on shakier ground.