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Dark matter: What we know and why you should care

A look at the underground facility in South Dakota where the best research on dark matter is being done. (Courtesy of C.H. Faham)

First of all, what is dark matter?

We don’t know. It must have mass, and it must not emit light or any form of electromagnetic radiation. Otherwise, it would be visible to us. As Meg Urry, the head of the Yale Center for Astronomy and Astrophysics, recently told CNN, “So far, no one has ever seen dark matter directly. You can’t see it, touch it, smell it, throw a net over it, or tag it in the ways particle physicists deal with ordinary particles.”

Astronomers say that as 25 percent of the universe is made of invisible substance.

If we can’t see it, how do we know dark matter exists?

Mostly due to observations of dark matter’s gravitational effects on distant galaxies. There has to be some sort of mass that is creating these gravitational effects. In order for galaxies to behave as they do, there must be significantly more mass that is responsible for these effects. Otherwise, these galaxies would fly apart from each other.

Here’s where research on dark matter is taking place in South Dakota. (Photo courtesy of LUX)

Why is the search for dark matter taking off now?

We finally have the instruments and sensors in place to detect the presence of dark matter. There’s buzz about the new Large Underground Xenon (LUX) facility at the Sanford Underground Research Facility in South Dakota — located nearly a mile underground in an abandoned gold mine — which is the focal point of the world’s search. We seem close to the first recorded detection of dark matter, we just need slightly more sensitive detectors.

Wait, why are we looking for dark matter one mile underground instead of in the sky?

By looking deep underground in an abandoned gold mine, scientists are able to mitigate the background radiation effects of other subatomic particles whizzing around. As the scientists behind LUX point out, “The trick to dark matter detection is… to design a detector sensitive enough to register the tiny bump of a dark matter particle into an ordinary nucleus, but also discriminating enough to avoid confusing any other interaction with that of a dark matter particle.” You can’t do that above ground, where things like gamma rays get in the way. But just to be safe, we are looking for dark matter in the sky as well. Check out what they’re doing aboard the International Space Station.

The LUX detector is shown in its final installation stages. (Photo courtesy of C.H. Faham)

By any chance, does the Higgs boson have anything to do with dark matter?

In a way, yes. Both the Higgs boson and dark matter are about searching for the interactions of particles at the subatomic level and the quest to understand the fundamental structure of the universe. For any of our theories in modern physics to make sense – such as how different forces in the universe like gravity behave — we have to understand  how these particles interact with each other.

What’s been done lately with dark matter?

The most recent experiment to date was the Large Underground Xenon (LUX) dark matter experiment at the Sanford Underground Research Facility in South Dakota that featured giant tanks of super-chilled liquid xenon about one mile below ground.

How did that work out?

The LUX experiment hasn’t found anything yet. But even that was significant news. Particle theorists even applauded “the quality of the nothingness the experiment has revealed.” In other words, in the strange world of particle physics, the fact that they found absolutely nothing was viewed as a resounding success. It meant they could eliminate another candidate in the elusive search for dark matter.

What’s the best candidate so far for dark matter?

One candidate is a class of particles named WIMPs, for “weakly interacting massive particles.” Researchers theorize that when these WIMPs hit the nucleus of a xenon atom head-on, the impact will cause a flash of light that can be detected by sensors. So, maybe they’re not so wimpy after all.

Sounds pretty easy. We just wait until we detect a few flashes of light deep underground?

Not so fast. As Yale’s Meg Urry points out, “The chances of this happening are exceedingly small — about 1 in 10 trillion. It’s like trying to see someone’s nose twitch in a stadium full of crazy football fans.”

Gotcha. But assuming we do detect that twitching nose, what do we do when we find this dark matter?

Well, we might be talking about handing out a Nobel Prize in physics. After all, two of the guys who led the epic quest for the Higgs boson received a Nobel Prize this October.

The water tank where LUX is housed. (Photo courtesy of C.H. Faham)

How could I learn more?

There’s a “Dark Universe” show at the Hayden Planetarium in New York that will blow your mind.

The show is less than 30 minutes, but you’ll walk away questioning your own insignificant role in the universe. How is possible that the trillions of stars and billions of galaxies only account for 5 percent of the known universe? How is it possible, that 13.8 billion years after the Big Bang, the  rate that the universe is expanding is actually accelerating? Is it possible that there are parallel universes that we simply can’t see?

How can I explain dark matter to my friends without sounding like a physics nerd?

Dark matter sounds mysterious and just a little bit spooky. But dark matter — if theoretical physicists are correct — may turn out to be just like radio waves, infrared light, X-rays and gamma rays. We can’t observe them with our eyes, but we are able to harness them every day with cool new innovations. Everything from WiFi networks and cellular networks to microwave ovens and car radios works because of stuff we can’t see around us.

So what’s next after dark matter?

Dark energy. If dark matter accounts for 25 percent of the known universe, then according to Neil deGrasse Tyson in the “Dark Universe” show, dark energy accounts for another 70 percent of the known universe. Dark energy might be the key to explaining why the universe appears to be expanding rather than contracting.

What’s the connection between dark matter and dark energy?

Remember Einstein’s famous equationE = mc2? Energy and mass are flip sides of the same coin. Once we’ve figured out dark matter, we should be well on our way to understanding dark energy. Unless there’s something else out there we haven’t considered.

Dominic Basulto is a futurist and blogger based in New York City.



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