YSM Issue 90.4

More documents

Recommendations

Info

WHAT IS HOT, DENSE, & spins like crazy? art by Emma Wilson by Sophia Sánchez-Maes It all started with a big bang...but then what? Our universe is 13.8 billion years old— the most remarkable detail about this fact is what it implies about its beginning. Space itself is continuously expanding, and winding back the clock shows it getting smaller and smaller, eventually shrinking down to a single point from whence it all came: life, the universe, and time itself. Squeezing the contents of the entire universe into a single point may seem unimaginably difficult, but compress matter enough, and that inward pressure is enough to break molecular bonds into atoms. Compress further and atoms themselves break into their components: protons, neutrons, and electrons. Next, the stress would break even the bonds that tie those subatomic particles together, releasing even smaller particles called quarks and gluons—two of the 13 elementary particles that constitute the most basic building blocks of matter. As carriers of the strong force, gluons are the glue that acts to bind quarks together into protons and neutrons. The strong force governs interactions between all particles with a color charge, like quarks and gluons, and is also responsible for binding together the atomic nucleus. In order to overcome intermolecular and interatomic forces and explore the properties of this primordial cosmic soup, scientists must replicate the conditions of the early universe just milliseconds after the Big Bang, which involved blistering temperatures and tightly packed matter. This August, the STAR collaboration, a group of scientists aiming to deduce the properties of the quark gluon plasma and the physics that underlay them, published their measurement of the vorticity of the quark-gluon plasma in Nature: a experiment which elucidates the unexpected fluid properties of this matter that dominated early in the universe, and is an important step to bettering our theory of the strong force. IMAGE COURTESY OF BROOKHAVEN NATIONAL LABORATORY ►The tracks in this image depict the particles produced by the collision of gold ions at RHIC, as captured by the STAR detector’s Time Projection Chamber. Exploring the universe, before it was cool Researchers like Yale’s Helen Caines don’t need to journey through time to discover properties of early universe. They have only to cross the Long Island Sound to Brookhaven National Laboratory, where the Relativistic Heavy Ion Collider is cooking up the same conditions. At Brookhaven, STAR researchers focus narrow beams of gold ions (atoms which have lost their outer electrons) at one another, each traveling close to the speed of light. Such incredible speeds also give the ions incredible energy, so any headon collision between gold ions is able to dissolve the 79 protons and 118 neutrons in each gold ion into quarks and gluons, forming, for a brief instant, the quark gluon plasma, a soup of quarks and gluons which exists at extreme temperatures and densities. The Relativistic Heavy Ion Collider, along with CERN’s Large Hadron Collider in Geneva are the only facilities in the world with machines powerful enough to produce quark gluon plasma. Having proven that the produced plasma is indeed comparable to that of the primordial cosmos, scientists in the STAR collaboration moved on to also show that this material is full of unexpected surprises. For example, researchers anticipated that such a hot, energetic state of matter would behave like some sort of super gas, without the strong collectivity properties that characterize liquids, unlike gasses, which diffuse evenly. In actuality, the quark gluon plasma (QGP) behaves like a liquid, since its constituents interact more strongly than those of a gas. “We know that the gluons themselves interact, and the quarks interact via gluons, so it makes sense if they can interact very strongly with each other,” Caines said. In this series of experiments, scientists are aiming to determine the properties of the quark gluon plasma’s fluid properties. Not only is the QGP a liquid, but it has the lowest viscosity of any liquid ever encountered, meaning that unlike viscous substances like honey, it has nearly no resistance to flow. This unique property has prompted scientists to call it nearly “perfect.” Since this medium formed under such extreme temperatures and pressures, it’s 12 Yale Scientific Magazine October 2017 www.yalescientific.org
particle physics FOCUS distance, it gets increasingly strong, like a spring that wishes to retract. Eventually, so much energy is expended in pulling apart this particle that another particle antiparticle pair is pulled from the vacuum to preserve net colorlessness. This means that it’s impossible to detect free quarks. This might be puzzling, since quarks in the QGP aren’t bound in mesons or nucleons, but zooming in anywhere in this soup, conditions are “locally” colorless. Since scientists can’t detect the quarks individually, the STAR collaboration scientists instead detect the particles created from the QGP as it cools, whose motion is inherited from this fluid that formed them. It’s not “just a phase” not surprising that the medium breaks other records. These record-setting properties include a low viscosity, a high temperature, and a now legendary vorticity, or swirling properties. These measurements not only help us understand this unexpected liquid phase, but also assist in our understanding of quantum chromodynamics (QCD), a theory which governs the interactions of the colored charged particles (quarks and gluons) which make up the QGP. The force is strong with this one Quarks are never observed in alone, but are always bundled in pairs or groups of three by gluons, which carry the strong force. There are six types of quark, with up and down quarks combining in groups of three to create protons and neutrons – the heaviest components of atoms. The theory governing their interactions is called quantum chromodynamics (QCD). Quarks come in three states called ‘colors.’ The strong force, which governs the behavior of quarks, is incredibly unusual. Gravity, the force with which we’re most familiar, only attracts objects toward each www.yalescientific.org IMAGE COURTESY OF WIKIPEDIA` ►The color charge acts such all matter must be locally white, binding quarks into combinations that preserve this colorlessness and preventing the sustained existence of free quarks. other. Electromagnetism has positive and negative (anti-positive) charges – but like gravity, their effect fades with the inverse square of the distance. Quarks and gluons have color-charge, which has nothing to do with color but for convenient metaphor. There are three colors (red, green, and blue) and three anti-colors (anti-red, anti-green, anti-blue) Any stable state must be colorless – which can only be achieved by mixing all the colors, like in protons and neutrons (made up of three quarks) – or by combining a color and anti-color, like in particles called mesons (which consist of a quark and an anti-quark). Furthermore, mass and charge are fundamental properties of particles, whereas color charge can change via gluon interactions. It is the strong force, and the color charge that mediates it, that is responsible for the interactions between quarks and gluons. By understanding the behavior of the QGP, scientists are probing these fundamental forces and properties. Try pulling a meson apart and you’ll see that the strong force operates differently in another important way: with increasing The QGP is a fluid, and is defined by superlatives. At four trillion degrees Celsius, tens of thousands of degrees hotter than a supernova, it’s the hottest thing we know in the universe. It also has the lowest viscosity, or resistance to flow, of any known fluid. Now, the STAR collaboration has also made the first measurement of its vorticity, or rotation. When gold ions collide head-on, their constituent particles combine to create the QGP; but typically the collision between ions is more glancing. In that case, region of contact, like the center of a Venn diagram, will combine to become QGP, while the outside regions will continue speeding away from each other. These glancing collisions give the resulting soup a net angular momentum, setting the QGP spinning. Scientists in the STAR collaboration aimed to detect this spin by detecting the particles generated by the plasma as it cools. October 2017 IMAGE COURTESY OF WIKIPEDIA ►The quark gluon plasma kicked off the start of the radiation era of the universe’s history from 10e-12 to 10e-6 seconds after the big bang, right after cosmic inflation. Yale Scientific Magazine 13
Page 1 and 2: OCTOBER 2017 VOL. 90 NO. 4 | $6.99
Page 3 and 4: Yale Scientific Magazine VOL. 90 IS
Page 5 and 6: F R O M T H E E D I T O R Reaching
Page 7 and 8: in brief NEWS The Twists and Turns
Page 9 and 10: neuroscience NEWS NOW YOU HEAR ME,
Page 11: public health NEWS NOT SO SWEET Met
Page 15 and 16: THE SEARCH Mathematical model expla
Page 17 and 18: cell biology FOCUS ematical model w
Page 19 and 20: neuroscience FOCUS they were studyi
Page 21 and 22: molecular biology FOCUS However, if
Page 23 and 24: organic chemistry FOCUS key player
Page 25 and 26: genetics FEATURE NATURE AND NURTURE
Page 27 and 28: geology and geophysics FEATURE ΜIC
Page 29 and 30: low-density gas circling the galaxy
Page 31 and 32: molecular biology FEATURE a profess
Page 33 and 34: designed with attachments that bind
Page 35 and 36: INN VATI N STATION Decluttering our
Page 37 and 38: ALUMNI PROFILE SANDY CHANG (YC ‘8
Page 39: cartoon FEATURE BEFORE/AFTER ►BY

YSM Issue 90.4

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?