Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Tuesday, October 20, 2020

The swing of a pendulum

 Physicists have a serious problem.

Back in the mid-1970s, astrophysicist Vera Rubin made an interesting discovery.  She had initially been interested in quasars, but moved away from that because the subject was "too controversial" -- and landed herself in the midst of one of the biggest scientific controversies to hit the field since the discovery of the quantum nature of reality back in the 1920s and 1930s.

She was looking at the rotation rates of galaxies, and found something curious; based on what was known about gravitational interactions between massive objects, the outer fringes of every galaxy she studied were moving at the "wrong" velocity.  The outermost stars were moving far faster than the model predicted, suggesting there was some unseen mass increasing the gravitational field and whirling the edges of the galaxy around faster than the visible matter could have.

And it wasn't by a small margin, either.  Rubin's calculations suggested that there was five times the unseen stuff as there was all of the visible matter in the galaxy put together.  This was way too much to be accounted for by something like diffuse dust clouds or other agglomerations of non-luminous, but completely ordinary, matter.  Rubin nicknamed the invisible stuff dark matter, more or less as a placeholder name until the physicists could figure out what the stuff was, something most researchers figured would be accomplished in short order.

Almost fifty years later, we still are hardly any further along.  Better measurements have confirmed that there is way more dark matter than ordinary matter; Rubin's estimate was spot-on, and current data indicates that 27% of the universe's total mass is dark matter, as compared to only 5% ordinary matter.  (The other 68% is an even more mysterious thing called dark energy, about which the astrophysicists are even more completely, um, in the dark.)

Every attempt to figure out the nature of dark matter -- or even to detect it by anything else but its gravitational effects on the galactic scale -- has resulted in failure.  The leading candidate, called weakly interacting massive particles (WIMPs), has been the subject of repeated detection attempts, and every single one of them has generated "null results."

Which is science-speak for "bupkis."

At some point, you have to wonder if the scientists are going to give the whole thing up as a bad job.  The problem is, if that happens you have 95% of the universe made of stuff we can't account for, which isn't a state of affairs anyone is happy with.

So a team at the National Institute of Standards and Technology is giving dark matter one more chance to show itself, using the only way in which we're certain it interacts with ordinary matter -- gravity.

The trouble is, gravity is a really weak force.  It's only a big player in our lives because we live on a massive chunk of rock, big enough to have a significant gravitational field.  Of the four fundamental forces -- gravity, electromagnetism, and the weak and strong nuclear forces -- gravity is weaker than the next in line (electromagnetism) by a factor of 10 to the 36th power.

So gravity is 1,000,000,000,000,000,000,000,000,000,000,000,000 times weaker than the electromagnetic force that holds molecules together, generates static electricity, and toasts your bread in the morning.

How on earth could you detect something that small, when even a trace of a stray electrical field could overwhelm it by many orders of magnitude?  The NIST scientists think they have the answer: an array of over a billion tiny, incredibly sensitive pendulums, each only a millimeter long, shielded and then cooled to near absolute zero to minimize interference from other forces.

[Image licensed under the Creative Commons Ben Ostrowsky, Foucault's Pendulum, CC BY 2.0]

There are four possibilities of what could happen to the array:

  • Nothing.  Then we're back to the drawing board.
  • Motion of one or two pendulums only.  This is probably due to interaction with an ordinary matter particle, which would hit a pendulum and stick, causing it to swing but leaving the ones around it unaffected.
  • Chaotic or random movement in a number of the pendulums.  This "noise" would most likely be caused by a fluctuation in an electric field -- i.e. the array wasn't well enough shielded.
  • A coordinated "ripple" passing through the detector, setting more or less a straight line of the pendulums swinging.  This, the researchers say, would be the signal of a dark matter particle zooming through the array, and its gravitational ripple streaking across in a specific direction.

Of course, even if the best possible outcome -- option #4 -- occurs, it still doesn't tell us what dark matter is.  After all, Vera Rubin's research in the 1970s showed that it interacts gravitationally with ordinary matter (i.e., we already knew that).  But at least we'll have a demonstration that it exists, that we're not looking at something like the nineteenth century's luminiferous aether, the mysterious substance that supposedly was the medium through which light waves propagated, and was shown not to exist by the Michelson-Morley interferometer experiment (and the nature of light propagation ultimately explained by Einstein and others, decades later).

So I'll be eagerly awaiting the outcome.  Right now, the array is still in development, so it will be a while before we can expect results.  But if it generates positive results, it'll be the first conclusive demonstration that we're talking about something detectable right here on Earth, not just by its effects on distant galaxies.

Of course, that still leaves us with the other 68% unknown stuff to explain.


Have any scientifically-minded friends who like to cook?  Or maybe, you've wondered why some recipes are so flexible, and others have to be followed to the letter?

Do I have the book for you.

In Science and Cooking: Physics Meets Food, from Homemade to Haute Cuisine, by Michael Brenner, Pia Sörensen, and David Weitz, you find out why recipes work the way they do -- and not only how altering them (such as using oil versus margarine versus butter in cookies) will affect the outcome, but what's going on that makes it happen that way.

Along the way, you get to read interviews with today's top chefs, and to find out some of their favorite recipes for you to try out in your own kitchen.  Full-color (and mouth-watering) illustrations are an added filigree, but the text by itself makes this book a must-have for anyone who enjoys cooking -- and wants to learn more about why it works the way it does.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

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