I might be misunderstanding the concept of the term "radius". Ever since I can remember radius was distance from the ourter edge directrly to the center. How can a strait line have curvature?
I think I understand why they say the universe is flat. But then its only flat from our perspective, right? If there was a being so large, looking at the universe from the "outside", for that being our universe could be a perfect sphere and have a very definite and positive curvature.
"From us. And every other point in the universe. Think of the balloon blowing up and all the points on the surface stretching away from each other."
OK. I understand that. But I'm still not entirely clear about Hubble's law.
"Any two points which are moving away from the origin, each along straight lines and with speed proportional to distance from the origin, will be moving away from each other with a speed proportional to their distance apart."
So it just says that with time the universe is expandinig at a faster rate, and all the objects within the universe get further away from each other at a faster rate and so on. I guess it explains that there is no center for that purpose.
"However, the best way to calculate the recessional velocity and its associated expansion rate of spacetime is by considering the conformal time associated with the photon traveling from the distant galaxy.That is Hubble's law."
I guess that the term "distance" mislead me into wondering "where from" and "to what". In my mind, "conformal time" seems to explain it better. I think I'm starting to understand.
"No, there is not. The balloon is the rubber surface, not the space inside. Same with the universe. It is the surface that matters, except that the surface is 3d. This is child's play to a mathematician as one of the first things they learn is that a sphere is a 2d object, not 3d. It is the surface that matters. There is no inside. The sphere can be defined without any reference to a 3d embedding space. The inside does not exist! There is no spoon..."
OK, gotcha.
But, if we take a balloon and measure its circumference, or diameter, we could find its center, or really the center of the sphere of air that the balloon surounds. So could there be an imaginary center of the universe, or space within the universe?
P.S: Those graphs don't make any sense to me.
I don't even know what they are of.
This message has been edited by Ragged, 11-15-2005 03:45 PM
"I may disagree with what you have to say, but I shall, to the death, defend your right to say it" ~ Voltaire