Many years Carl Sagan was a guest on The Tonight Show with Johnny Carson and the two men somehow got into a conversation about the composition of the universe — what it’s made of. Sagan said something to effect of, “Space is mostly empty space. That’s why we call it ‘space.’” Johnny found that observation quite amusing ,and the conversation continued from there.
I always thought that exchange was a great example of hitting somebody over the head with the obvious. How interesting to learn that Carl Sagan’s “obvious” observation may, in fact, not be true:
“No Empty Space in the Universe” –Dark Matter Discovered to Fill Intergalactic Space
New research concludes that instead of “edges,” galaxies have long outskirts of dark matter that extend to nearby galaxies and that the intergalactic space is not empty but filled with dark matter.Researchers at the University of Tokyo’s Institute for the Physics and Mathematics of the Universe (IPMU) and Nagoya University used large-scale computer simulations and recent observational data of gravitational lensing to reveal how dark matter –which makes up about 22 percent of the present-day universe –is distributed around galaxies in a clumpy but organized manner.
Of course, if Sagan had said that the universe was made of galaxies and dark matter (not an idea that got a lot of attention back in those days), I’m sure Johnny would have thought of some comic possibilities there, too.
It’s interesting to think that the vast stretches of intergalactic space might actually have something in them — even if it’s something invisible and about which we seem to have a difficult time making meaningful statements. Check out the exchange on the Wikipedia dark matter discussion page concerning how much of the mass of the universe dark matter makes up versus how much of the matter in the universe it constitutes.
One interesting thing to note: as pointed out by one of the commenters, the Daily Galaxy headline quoted above appears to be an overstatement. There is about a billion light-year stretch of the universe that apparently really is empty space. No matter. No dark matter. Nothing.
So perhaps my headline should be revised to ”It’s Always Something — Except When It Isn’t.”
So what is dark matter? And why is there an unbelievably big hole in the universe that doesn’t have anything in it? Questions such as these keep life interesting. It’s too bad they don’t come up on late-night talk shows any more.