Pie in the Sky
Most recent answer: 10/22/2007
- Mike (age 39)
Grayson County College, Sherman, Texas
Mike- That’s a good start in trying to think about the Big Bang, but there are a few mistakes in how you analyze the pie picture, and the standard physics picture is somewhat different in fundamental ways.
Let’s start with your pie picture. Let’s take it a step toward being a picture of the standard BB by saying that everybody leaves the from the same starting point with different velocities, not at different times. Then some of your conclusions about the relative velocity of our neighbors to us are right but others are off a little. In this picture where everybody picks up a fixed velocity at the start and those velocities don’t change everybody’s current displacement from us is just the time since the bang times their velocity difference from us. What we see from our point of view is just that velocity difference. So that leads to an even simpler effect than the one you describe, but very much along the lines of what you were after: The current velocity relative to us is a universal constant times the displacement from us.
That’s called the Hubble law. It’s approximately true, and was the first major piece of evidence for the Big Bang.
There are some obvious small corrections to take into account all the small-scale motions in more ore less random directions. There are more important, deep corrections to take into account that the geometry of our universe is given by General Relativity, not Euclid. In addition, there are a collection of fascinating corrections due to understood and not understood physical effects.
However, the general first-glance picture of the Hubble effect is well captured by your pie picture, so long as you analyze it carefully.
Mike W.
Have a look at a nice article on the Big Bang, which is still fortunately available online (at least for the moment) at https://hubblesite.org/contents/articles/the-big-bang.
Tom
(published on 10/22/2007)