Originally posted by ALM
but anyway I know there arent any questions here to solve. I just want to know if any of you have an opinion. thanks
ALM
ALM your post suggests you want a sampling of other people's viewpoints.
Nereid, you explain it just fine. Lots wd agree with the image you gave of the balloon.
My first astronomy teacher used the image of raisinbread dough rising. The raisins are galaxies and they are all standing still (not swimming thru the dough) and all the same the raisins (galaxies) keep getting farther and farther apart.
From each raisin's point of view it looks like the others are running away from it---and the farther away the other raisin is the faster it seems to receed.
But none of them are moving. It is only that the distances between them are all constantly increasing.
That was how my beginning astro prof suggested we think of it.
whether the expansion is speeding up or slowing down depends on
a certain differential equation called Friedmann equation and the
average energy density that gets plugged into it---right now it looks to the astronomers as if the expansion of space is speeding up.
but that is more of a technical detail, not to worry about such things at first but instead just get used to the idea of the expansion itself----the fact that distances between stationary non-moving things can increase. And I mean distances not between nearby stars but between remote galaxies (far enough apart that their attraction for each other is negligible). All of these distances increase by a certain percentage each year. the percentage is different year by year, but in a given year each distance increases by the same tiny percentage, or the same "fractional amount" since that sounds more scientific than saying "tiny percentage".
I will tell you what the annual percentage growth or fractional growth amount is.
It is one part in 14 billion.
Or the fraction 1/14,000,000,000.
If there is some galaxy that at this minute is 14 billion LY away from us (by the usual cosmologist's distance measure) then
this tiny fraction of that is simply ONE lightyear. And so I am saying that in one year the distance to that galaxy will increase by one lightyear.
And it is proportional, so if there is some other galaxy that is right now 28 billion LY away, then in one year the distance to it will increase by 2 LY.
That is, next year it will be 28,000,000,002 LY from us.
This is hard enough to assimilate, I think. Nereid might agree too.
there is no harm in continuing to ask questions until you get used to it and the shock is over. there are unintuitive aspects to this
that you may discover by thinking it over. Like, this picture does not necessarily mean that it all started at a point. Space could always have been infinite, and yet expanding. I remember finding that hard to grasp when I first confronted it, so you might possibly find it so as well. It COULD have begun at a point but it might not have.
The raisinbread dough could have begun as an infinite loaf, extending endlessly in all directions and with its raisins very close together. Or it could have begun at one extremely raisiny point of departure. Either way the thought is positively hair-raising.