Every Thursday I go out to lunch with my father-in-law and a couple of other older gentlemen. Yesterday, one of these guys, who we will call Bill (because that's his name), posed two questions that I'm finding difficult to answer... perhaps you could help...
Before posing this question, let's take a step back. When I first heard about the "Big Bang" theory of the universe, including the fact that all of the galaxies are "flying" away from each other (and that the further away they are, the faster they are receding from us), I visualized the galaxies as ink dots on the surface of a balloon that was in the process of being inflated.
Later, I heard a better analogy, which was to imagine the universe (by which I mean "our universe" or "the universe we inhabit") as a piece of bread dough with raisins mixed throughout. When you put the dough in the oven it starts to expand, its volume increases in three dimensions, and the raisins all move away from each other. (This is actually a pretty good way to visualize things, because the further apart the raisins are the faster they will move because there's more expanding dough between them.)
But we digress. As Bill noted to me, if there was a Big Bang and all of the galaxies are racing away from a common point of origin, then shouldn't we be able to trace things back and say: "Here are the X-Y-Z galactic co-ordinates of the place where the Big Bang took place."
Bill says he's searched the Internet, but has found no mention of this location. And, when I come to think about it, I've never seen anything about this either. Have you?
As an aside... in the middle of Kansas (in the East-West direction), and half an inch from the top (on my map) there's a town called Lebanon. A couple of miles north of Lebanon is the geographical center of the conterminous United States. I once went there and stood for a while pondering the granite block marking the spot.
Wouldn't it be strange if, one day (and assuming the discovery of a faster-than-light space drive), mankind visited this X-Y-Z galactic location and found some sort of beacon erected by another race saying the equivalent of: "You are here!"
This poser is a tad harder to answer. Every time one reads an article or sees a television program on the universe, we are informed that (a) all of the galaxies are receding from each other and (b) the universe is expanding.
Well, Bill asked me if we were sure that the universe hadn't already reached its maximum extent some time ago; maybe, he suggested, the universe was now in the process of contraction heading toward the "Big Crunch". I of course replied: "But all of the galaxies are flying away from each other," to which he responded by drawing the following diagram on the table cloth (it was a paper one):
Of course we know that the galaxies are scattered randomly in three-dimensional space, but for the purposes of this discussion let's assume that they are arranged on the surfaces of three concentric spheres.
Under Bill's theory, the galaxies on the surface of the innermost sphere are now moving toward the center the fastest with a speed of "+++" ("three whatsits-per-second"). The galaxies on the surface of the outermost sphere are heading toward the center the slowest with a speed of only "+" ("one whatsit-per-second"). Meanwhile, the galaxies on the surface of the middle sphere (this is where Bill suggests our galaxy is to be found) are currently moving toward the center with a speed of "++" ("two whatsits-per-second").
On this basis, Bill says that since our speed is "++", the galaxies closer to the center with a speed of "+++" will appear to be moving away from us with a speed of "+". Similarly, the galaxies further away from the center will a speed of only "+" will also appear to be receding from us with a speed of "+".
Bill bases this latter point on the fact that you can't tell from the red shift effect whether other galaxies are moving away from us or whether our galaxy is moving away from them. Consider the classic audio analogy where you are standing still and a police car with its siren blaring passes you by. As it approaches the siren sounds like "woop-woop-woop"; as it recedes is sounds like "waah-waah-waah" (or whatever ... you get my drift).
But suppose the police car was stationary and you were the one in motion (on a rocket-powered skateboard, for example). If your eyes were shut (and something prevented you from feeling the wind, etc.) you wouldn't be able to tell under which scenario you were involved (unless you stepped off the skateboard while it was in motion, of course).
Truth to tell, I found Bill's second question to be a bit of a poser ... for a while ... and then I realized how one could demonstrate that the universe is indeed still expanding. But I don't want to spoil this for anyone else... what do you think?
Questions? Comments? Feel free to email me – Clive "Max" Maxfield – at firstname.lastname@example.org). And, of course, if you haven't already done so, don't forget to Sign Up for our weekly Programmable Logic DesignLine Newsletter.