COSI Blog
18
April
2013

The Electroscope, Dark Matter, and Mystery

A photo of Steve Whitt.

We have a new toy in the Electric Workshop at COSI. It's called an electroscope.

On the 1898 side of Progress, you might happen upon our Electric Workshop Show (check your daily schedule for show times). The Electric Workshop is one of COSI's hidden gems, a live demonstration all about the history (and future) of electricity. You can become an electric generator, make real lightning with our Wimshurst machine, and discover the mysterious power of a new kind of energy called radio waves.

Now we've added an antique electroscope to help reveal one of science's great discoveries: the entire universe is electrical. With the electroscope we discover the effect of separating electric charge.

But there's a further story to be told. The electroscope lies at the heart of another mystery of science – one that, believe it or not, we still haven't solved even in 2013.
Most electroscopes, like the one in Progress, use a metal leaf to sense electric charge. When the leaf gains an electric charge, it stands up. When it loses that charge, the leaf falls again. Very soon after the invention of the electroscope, scientists realized that every electroscope, no matter where it was placed or how it was protected, slowly lost its electric charge.

No one could say what mysterious force was causing the electroscope's leaves to fall. Whatever it was, it was incredibly powerful, able to pass through seawater, lead walls, or any other protection anyone put in its path.
Some thought the culprit must be invisible radiation from the ground. In 1912 a scientist named Victor Hess decided to test this idea by taking an improved electroscope for a ride in a high-altitude balloon. When Hess performed the experiment, he found that the rate of discharge didn't go down, as expected. Instead, the rate went up!

Hess had discovered "cosmic rays," invisible radiation coming not from Earth, but from the deepest reaches of outer space. These rays (really incredibly fast particles) are everywhere, passing through our bodies every moment of every day. Here on the surface, some of the rays are absorbed by the atmosphere, but high in the sky (and in deep space) the cosmic rays are stronger still.

For a hundred years now, scientists have studied cosmic rays, exploring the various astronomical events – supernovas, black holes, colliding stars – that might produce these super-fast particles. Now results from an experiment called the Alpha Magnetic Spectrometer (AMS) are suggesting a new, even more mysterious, source for cosmic rays.

The AMS is attached to the International Space Station, allowing it to capture cosmic rays without the interference of Earth's atmosphere. The scientists studying the results of the AMS experiment are looking for evidence that some cosmic rays are produced by – ready for this? – dark matter.

We know that dark matter exists. We also know that it makes up around 80% of all the matter in the universe. But we have no idea what it is. It's pretty amazing, here in the 21st century we still don't know what makes up most of the universe. Maybe more amazing, though, is how the deepest mysteries often begin with the simplest experiments.

Wouldn't it be incredible if the solution to the secret of dark matter begins with the slowly falling leaves of a simple electroscope, just like the one you might encounter on the streets of 1898 Progress?

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