Daily Archives: February 21, 2012

It’s Always Something

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.

Perpetual Motion?

Starts out sounding pretty exciting…

Time crystals could behave almost like perpetual motion machines

As every young science student knows, moving objects have kinetic energy. But just how much energy does something need to move? In a new study, a pair of physicists has shown that it’s theoretically possible for a system in its lowest energy state, or ground state, to exhibit periodic motion. This periodically moving system can be thought of as the temporal equivalent of a crystal, which is defined by its spatial periodicity. What’s even more intriguing about these “time crystals” is that, by exhibiting motion at their state of lowest energy, they break a fundamental symmetry called time translation symmetry and become “perilously close” to looking like perpetual motion machines.

Sadly, we’ll have to file this either under “nothing to see here” or “not much to see here.”

First off, we don’t know that any of these systems existing in their lowest energy state and yet demonstrating periodic motion actually exist. It seems they could exist. And (this is potentially the most interesting part) we might be able to create them.

Secondly, even if we found one or created it, it would have to be a completely closed system. No energy going in, but none coming out, either — meaning our perputaul motion machine would not be able to do any work or produce any energy. It would just be a very interesting system.