findings today in Physical Review Letters<\/a>.\u00a0<\/p>\nA path from pollen<\/p>\n
In 1905, Einstein developed a theory to describe a particle\u2019s motion through fluid and how that motion can reveal the fluid\u2019s microscopic structure. His theory was inspired by the botanist Robert Brown. In 1827, Brown observed a surprising phenomenon: Grains of pollen appeared to randomly jiggle and swirl when suspended in seemingly still water. This curious jittering of particles in fluid was later named \u201cBrownian motion.\u201d\u00a0<\/p>\n
Einstein\u2019s 1905 theory showed that Brownian motion was a product of invisible, microscopic forces within the fluid. A particle\u2019s motion is a balance between the drag that the fluid exerts on the particle to slow it down, and the random kicks within the fluid that keep the particle moving. These random kicks, Einstein argued, must come from microscopic forces within the fluid, exerted by none other than the atoms and molecules that make up the fluid. The energy of these microscopic particles can add up to kick and jostle larger particles.\u00a0<\/p>\n
Since he first published his theory, scientists have applied Einstein\u2019s explanation of Brownian motion to characterize a host of fluids, including quark-gluon plasma. Like most other fluids, it was assumed that a particle moving through quark-gluon plasma should experience a similar balance of microscopic kicks as a grain of pollen moving through water.\u00a0<\/p>\n
This balance is represented by a bell-shaped probability distribution, where a particle is most likely to experience medium forces of kicks (the highest point of the bell), and an equally low probability of the most extreme kicks (the tail ends of the bell), as the particle moves through and eventually settles into a fluid.\u00a0<\/p>\n
\u201cEinstein showed that the drag and the random kicks must balance in just the right way for a particle eventually to come to the same temperature as its surroundings,\u201d Du Plessis explains. \u201cFor the types of fluids he was thinking about, he was correct. But for particles that are moving at relativistic velocities, this relationship breaks down.\u00a0And we\u2019ve known for 20 years that something is missing. So\u00a0we have to go beyond the work that Einstein did.\u201d<\/p>\n
Kick speed<\/p>\n
In their new study, Du Plessis and\u00a0Scheihing-Hitschfeld calculated the forces that a heavy quark would likely experience if it flew through a fluid at relativistic speeds, close to the speed of light. They did so by carrying out calculations of the strong nuclear force, which is the fundamental force that pulls together quarks and gluons.\u00a0<\/p>\n
The team started with a scenario of a relativistic heavy quark flying through a gas of weakly interacting quarks and gluons. The weak interactions made this a manageable starting point for their calculations.<\/p>\n
For this starting scenario, they calculated the heavy quark\u2019s strong nuclear force and how much its momentum is likely to change as it moves through the gas of quarks and gluons. This calculation produced a curve, or a probability distribution of the quark\u2019s changes in momentum. The same curve can represent the quark\u2019s probability of being kicked with various force; stronger kicks cause bigger changes to the quark\u2019s momentum.\u00a0<\/p>\n
The curve that the researchers calculated was bell-shaped, similar to what Einstein found with other fluids, only for small kicks. And, unlike Einstein\u2019s bell-shaped curve, what the team found showed a tilt for heavy quarks moving at relativistic speeds. The tails at either end of the curve were uneven, and revealed a surprising imbalance in the kinds of kicks that a heavy quark would experience.<\/p>\n
\u201cThe usual Brownian picture assumes that large kicks become exceedingly rare,\u201d Du Plessis says. \u201cFor heavy quarks, however, these rare kicks are more common than the bell curve predicts, and are not equally likely in opposite directions: A large kick that slows the quark down more than expected from drag is more likely than an equally large kick that leaves it moving faster than expected.\u201d<\/p>\n
The team carried out the same calculation in plasmas made up of different particles. They found that the same tilted curve applies, regardless of the makeup of the plasma. Furthermore, they found that this same structure was already hiding in an earlier calculation in a strongly coupled plasma, despite the differences in the microscopic physics.<\/p>\n
\u201cThis is the first time that this seemingly universal structure was realized and really formalized,\u201d Du Plessis says. \u201cThis gives a concrete path forward for how to better understand the quark-gluon plasma, using heavy quarks.\u201d<\/p>\n
In terms of what this means for the universe\u2019s first fluid, Du Plessis says that primordial quark-gluon plasma is likely \u201cmore strongly interacting than this Brownian motion way of modeling it would suggest. It\u2019s more like a liquid and less like a gas.\u201d\u00a0<\/p>\n
This research was supported, in part, by\u00a0the Office of Nuclear Physics in the U.S. Department of Energy\u2019s Office of Science, the U.S. National Science Foundation, and the Simons Foundation.\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"In the first fraction of a second following the Big Bang, matter existed as a trillion-degree plasma of…\n","protected":false},"author":2,"featured_media":959846,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,31991,327714,327713,327712,1557,820,314,301254,66],"class_list":["post-959845","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-ca","tag-canada","tag-early-universe","tag-heavy-quark","tag-jean-du-plessis","tag-mit-center-for-theoretical-physics-a-leinweber-institute","tag-mit-physics","tag-particle-physics","tag-physics","tag-quark-gluon-plasma","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/959845","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=959845"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/959845\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/959846"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=959845"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=959845"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=959845"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}