On Fri, Jan 31, 2014 at 8:19 AM, Edgar L. Owen <[email protected]> wrote:
> At all past times, the universe at all distances was expanding at the > same rate that we can observe it expanding only at a SINGLE distance. > But it hasn't always been expanding at the same rate. The universe is 13.8 billion years old and at first the expansion of the universe was decelerating just as you'd expect it to do because of gravity, but then for reasons that are far from clear about 7 billion years ago the universe stopped decelerating and started to accelerate. Why it has done so has been called the biggest mystery in physics. > we actually have absolutely NO IDEA of how fast it is actually expanding > right NOW > According to Einstein observers don't always agree on what "now" means, and the further apart in space they are the more they will disagree. > The problem is that into the distant universe and back into distant time > the sides of our light cones are not straight but CURVED, > At the largest scales we now know that space is flat, or nearly so. Astronomers proved that the universe is flat by looking at the Cosmic Microwave Background Radiation (CMBR), it is the most distant thing ever seen and was formed just 300,000 years after the Big Bang, so if we look at a map of that background radiation the largest structure we could see on it would be 300,000 light years across, spots larger than this wouldn't have had enough time to form because nothing, not even gravity can move faster than light, a larger lump wouldn't even have enough time to know it was a lump. So how large would a object 13.8 billion light years away appear to us if it's size was 300,000 light years across? The answer is one degree of arc, but ONLY if the universe is flat. If it's not flat and parallel lines converge or diverge then the image of the largest structures we can see in the CMBR could appear to be larger or smaller than one degree depending on how the image was distorted, and that would depend on if the universe is positively or negatively curved. But we see no distortion at all, in this way the WMAP satellite proved that the universe is flat, or at least isn't curved much, over a distance of almost 13.8 billion light years if the universe curves at all it is less than one part in 100,000. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
