In our own galaxy and beyond, violent collisions fling a never-ending stream of stuff at the earth, and astrophysicists are eager to learn more about the processes that produce this cosmic barrage.

Researchers from around the world have teamed up to build the High-Altitude Water Cherenkov (HAWC) gammy-ray observatory, an array of hundreds of huge water tanks on a mountain in Mexico. HAWC helps astrophysicists spot active cosmic neighborhoods by capturing the shower of particles created when high-energy packets of light smash into the earth's atmosphere.

Jordan Goodman, HAWC's lead investigator, and Dan Fiorino, a postdoctoral researcher at UMD, tell Chris Cesare about the details of the HAWC experiment and how it promises to fill some gaps in our understanding of the universe. To learn more about HAWC, please visit www.hawc-observatory.org. The collaboration is preparing to publish the first results of its search, and you can read about the details in an upcoming source catalog or a paper about high-energy gamma rays from the Crab Nebula.

This episode of Relatively Certain was produced by Chris Cesare, Sean Kelley and Emily Edwards and edited by Chris Cesare and Kate Delossantos, featuring music by Dave Depper, Podington Bear, Kevin MacLeod and Chris Zabriskie. Relatively Certain is a production of the Joint Quantum Institute and the University of Maryland, and you can find it on iTunes, Google Play or Soundcloud. 

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Consider, for a moment, the humble puddle of water. If you dive down to nearly the scale of molecules, it will be hard to tell one spot in the puddle from any other. You can shift your gaze to the left or right, or tilt your head, and the microscopic bustle will be identical—a situation that physicists call highly symmetric.  

That all changes abruptly when the puddle freezes. In contrast to liquid water, ice is a crystal, and it gains a spontaneous rigid structure as the temperature drops. Freezing fastens neighboring water molecules together in a regular pattern, and a simple tilt of the head now creates a kaleidoscopic change.

In 2012, Nobel-prize winning physicist Frank Wilczek, a professor at the Massachusetts Institute of Technology, proposed something that sounds pretty strange. It might be possible, Wilczek argued, to create crystals that are arranged in time instead of space. The suggestion prompted years of false starts and negative results that ruled out some of the most obvious places to look for these newly named time crystals.

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Cosmic rays are not rays at all, but highly energetic particles that zoom through space at nearly the speed of light.  The particles range in size, from subatomic protons to the atomic nuclei of elements such as carbon and boron. Scientists suspect that the particles are bits of subatomic shrapnel produced by supernovae, but could also be signatures of other cataclysmic phenomena.

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When your heart beats, blood courses through your veins in waves of pressure. These pressure waves manifest as your pulse, a regular rhythm unperturbed by the complex internal structure of the body. Scientists call such robust waves solitons, and in many ways they behave more like discrete particles than waves. Soliton theory may aid in the understanding of tsunamis, which—unlike other water waves—can sustain themselves over vast oceanic distances.

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Chaos is all around us, a fact that weather forecasters know all too well.

Their job is notoriously difficult because small changes in air pressure or temperature, which ultimately drive winds and weather systems, can have huge consequences on a global scale. This sensitivity to tiny differences is commonly called the butterfly effect, and it makes weather patterns chaotic and hard to predict.

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