Friday, April 28, 2017


Kelley and I were talking about space last night, partly because the Cassini probe completed a dive between Saturn and its rings, and partly because Jace has been been learning about planets. We watched this excellent video, which starts out comparing the sizes of various planets and stars, then zooms out to compare the scale of galaxies and more.

Such mind-boggling vastness can make one feel very small, so naturally we tried to counter that by thinking of the tiniest things in the universe. Here is the chart we came up with. Unfortunately, I got some things wrong, so please refer instead to the revised chart below it.

Here we have the revision with text labels and more accurate spacing. The axis is a log scale, so each step of 3 brings you to something a thousand times bigger or smaller.

A few of our observations:

  • It takes approximately the same step in size (~9 orders of magnitude=a billion* times bigger in diameter) to get from an electron to an atom, from an atom to us, and from us to the sun.
  • Two more of those steps take you from sun to observable universe, but the galaxy is well past the first of those. (This was the main error in my napkin version--the galaxy is approximately one billion solar systems across, not one billion suns.) Note: That is linear distance; our galaxy contains 100 billion stars. 
  • Two big steps in the other direction take you from an electron down to the Planck length (below which "distance" ceases to mean anything).
  • Once you contemplate the vastness of something a billion-billion-billion** times bigger than you, it is not helpful to say "Well, yes, but that's just the observable universe. The whole thing could not only be far vaster, it could truly be infinite."
For a great illustration of the bigger-than-us half of the chart, check out this xkcd image. If you want to look at an interactive zoomable chart with a lot more objects than mine, this is a good one.

*I use the American billion here. If you are feeling European today, feel free to translate to milliard.
**Octillion for Americans, or quadrilliard for the traditionalists.

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