When scientists collide nuclei at the Large Hadron Collider, they produce tiny droplets of trillions-of-degrees-hot liquid with pressures 10 million trillion trillion times Earth’s atmospheric pressure. This “stuff”—which filled the microseconds-old universe—should be called hot quark soup. By recreating this primordial fluid in “Little Bangs,” we have learned that it is the most liquid liquid in the universe, making it the first complex matter to form as well as the source of all protons and neutrons. After a look at how we have learned this, Prof. Rajagopal will focus on the road ahead, particularly on new probes being developed, to answer questions like: How can we see the inner workings of hot quark soup and understand how it emerges from quarks and gluons? How does the droplet of hot quark soup ripple after it has been probed? Cold quark soup, at pressures almost as high, can be found at the centers of the heaviest neutron stars where the inward pressure of the surrounding star prevents it from exploding. Cold quark soup is expected to be the quark analog of a superconductor, a prediction that may be within reach of coming astrophysical observations. Further, Prof. Rajagopal will explore recent work pointing to the surprising possibility that ordinary protons remember the pressure of the hot quark soup from which they were born during the Big Bang.
