Dark Matter

Scanning for Dark Matter With a Dark Matter Radio

Scientists know — okay, are fairly certain — that only five percent of the universe is made up of stuff we can identify. The rest is "dark." Our measurements and calculations tell us something is there, but we just can't detect it. Twenty-seven percent of the universe is supposed to be made up of what's called dark matter, and researchers are doing everything they can to try and detect even a single particle of the stuff. In 2017, a team of researchers announced they were trying something different: instead of looking for particles, they're going to look for waves.

Let's Make Waves

One of the most fundamental concepts in quantum mechanics is wave-particle duality, which says that at the very, very smallest level, particles also exist as waves. Light is a prime example of this. Light exists in massless particles called photons, but it also exists in waves, the length of which determines whether they make up visible light, UV light, microwave radiation, or radio waves, to name a few.

If there's a dark-matter particle, it exists as a wave, too. "If dark matter particles were very light, we might have a better chance of detecting them as waves rather than particles," Peter Graham, a theoretical physicist at the Kavli Institute for Particle Astrophysics and Cosmology of Stanford University and the Department of Energy's SLAC National Accelerator Laboratory, in an interview with Symmetry Magazine.

You're Listening to EMC2, the Universe's Best Hits

If we're ever going to find dark matter, researchers think we'll do it in one of two ways. The first way is by detecting what are called hidden photons, which are a hypothetical type of light particle that might mediate the interactions between dark-matter particles. The second way is by detecting axions, which are another type of hypothetical particle that scientists think could be the main constituent of dark matter itself. There are already projects underway looking for axion particles of various masses, but none looking for their waves. As for using hidden photons to find dark matter — something these researchers hope to do — Stanford graduate student Saptarshi Chaudhuri tells Symmetry that their project "will be completely unexplored territory."

A regular radio works by using an antenna to intercept radio waves and turn them into sound. As you tune the dial, the radio adjusts an electric circuit to make the electricity oscillate at a particular frequency. If you hit upon the frequency that matches the radio wave's frequency, boom — a broadcast you can hear clear as day.

The dark matter radio does the same thing. Scientists can adjust the electric circuit in the device to a particular frequency, and if that frequency matches the frequency of a dark matter wave, the circuit resonates. That winning frequency tells the scientists the mass of the dark matter particle. The same way you'd search the radio bands on a road trip in the middle of nowhere, the researchers plan to do a full sweep of available frequencies. They'll search for particles in a mass range of trillionths to millionths of an electronvolt. The device only needs to be shielded from broadcast radiation, not cosmic rays, which means it doesn't have to be buried deep underground like other dark-matter detectors.

If we're lucky, the dark matter radio just might tune in on a breakthrough discovery.

What We (Don't) Know About Dark Matter

Written by Ashley Hamer December 7, 2017

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