<\/p>\n
If you thought that a kid\u2019s room, a Norwegian Nobel Laureate and a laser pointer had nothing in common, two UA physicists are about to enlighten you. <\/p>\n
It\u2019s hard to believe, but after having unraveled many of the laws that make the universe tick, physicists still haven\u2019t reached an agreement on whether something as seemingly simple as \u201chot\u201d or \u201ccold\u201d can be measured in a system under certain circumstances.<\/p>\n
\u201cImagine you threw an iceberg into the sun and right before it\u2019s melted and gone, you wanted to know, \u2018How hot is that iceberg at that moment?\u2019 Would that be a meaningful question to ask?\u201d says Charles Stafford, a professor in the Department of Physics in the UA\u2019s College of Science. \u201cAccording to traditional physics, it wouldn\u2019t be.\u201d<\/p>\n
Put simply, traditional knowledge holds that properties such as temperature or voltage can only be measured as long as a system is in equilibrium. (Hint: an iceberg plunging into the sun is not.)<\/p>\n
\u201cTemperature and voltage are two basic variables developed in the 19th century,\u201d Stafford says, \u201cso it may come as a shock that such basic notions have until now lacked a mathematically rigorous definition except for the case of equilibrium, an idealized case that does not actually occur in nature, except perhaps for the \u2018heat death\u2019 predicted to mark the end of the universe.\u201d<\/p>\n
Together with doctoral student Abhay Shastry, the first author of the study, Stafford used mathematical modeling to explore this conundrum. They published their results recently in the journal Physical Review B<\/em>. Their manuscript shows that these two quantities are so closely linked that it is impossible to know one without knowing the other. <\/p>\n \u201cWe have shown that actually any state of a system whatsoever, even far from equilibrium, can be characterized by a temperature,\u201d Stafford says.<\/p>\n This where the kid\u2019s room comes into play. (We\u2019ll get to the Nobel Laureates and laser pointers in a little bit.)<\/p>\n Everything in the universe \u2014 from quarks to galaxies \u2014 has an inherent tendency to achieve equilibrium with its surroundings and head toward the greatest possible degree of disorder. In reality, this phenomenon, called entropy and described in the Second Law of Thermodynamics, is a bit more complicated, but let\u2019s not worry about that for now. After all, we know this intuitively: Plop an ice cube into a drink and leave it alone for a while; soon, the water molecules in the ice cube have left their highly ordered crystal structure and settled into a cozy equilibrium, happily mingling with their disorderly, watery brethren. Same goes for the stuff in the kid\u2019s room: Leave things alone for a while without tidying up \u2014 you get the idea. <\/p>\n That iceberg that\u2019s about to vaporize when we tossed it into the sun earlier illustrates a system that is very, very far from equilibrium, but let\u2019s look at a more everyday example: an ordinary laser pointer. When you push the button to activate that red dot of light your cat is so crazy about, an inferno breaks loose inside the little device. <\/p>\n \u201cWhen they\u2019re lasing, the electrons inside the device get hotter than a temperature we call \u2018plus infinity,’\u201d Shastry says. \u201cIf you heated up a pot of water, no matter how hot, even if you vaporized it at a million degrees, it would still not be as hot as the electrons in the laser.\u201d<\/p>\n Now, it\u2019s important to point out that we\u2019re talking about quantum phenomena here \u2014 in this case the electron temperature, which has nothing to do with the temperature of the laser light and is the reason your laser pointer doesn\u2019t vaporize instantly in your hand upon activation. <\/p>\n Nevertheless, if you could somehow how touch the electrons in your laser, it would feel very, very hot, Shastry explains. <\/p>\n The point, according to the two physicists, is that when a laser is lasing, it is very far from equilibrium, much more so than, say, weather phenomena. Unlike the weather, which is driven largely by thermal differences, systems such as semiconductors and electronic devices are driven electrically, which can push their components \u2014 in this case, electrons \u2014 much farther from equilibrium than heat. <\/p>\n Under the current view, physicists would say that measuring the temperature in such a device that\u2019s far from equilibrium can\u2019t be done. Stafford\u2019s and Shastry\u2019s results say, yes, it can be done, but that conjures another question: Why would one want to? <\/p>\n \u201cCurrent microelectronics technology is limited by the fact that the devices dissipate a lot of heat, and they\u2019re getting smaller and smaller,\u201d Stafford says. \u201cAs they get smaller, they dissipate more heat, so this is creating a big problem for advancing the technology. <\/p>\n \u201cBecause we show that it\u2019s possible to define temperatures and voltages even at the subatomic scale, and define it rigorously, one could hope to make devices that are integrated in such a way that one could have local cooling of just one spot on the device where that one transistor sits that is getting really hot, instead of cooling the entire chip. Currently, there is no way to do something like that.\u201d<\/p>\n Stafford and Shastry are currently exploring a possible collaboration with Pramod Reddy, a colleague at the University of Michigan whose lab has set the record in creating a thermometer capable of probing temperature across a few atoms, to subject their findings to experimental study. <\/p>\n Another example to which the work might apply is nuclear magnetic resonance, a technology routinely used in medical imaging. <\/p>\n \u201cSomeone who has experienced that might not have realized the atomic nuclei in their body were put into a state of absolute negative temperature, which is hotter than anything in the universe, but that is the case,\u201d Stafford says. <\/p>\n \u201cOur theory is very general. It applies to lots of things, from quark-gluon plasmas generated in particle accelerators to laser pointers to neutron stars,\u201d Shastry says. \u201cThey all follow the exact same formalism.\u201d<\/p>\n As a side product of this research, Shastry and Stafford provide the first proof of a version of the Second Law of Thermodynamics formulated in 1931 by Norwegian chemist Lars Onsager, which applies in particular to thermoelectric processes, a feat that had eluded the physics community for 85 years. <\/p>\n \u201cThe Second Law of Thermodynamics is the most general of not just the laws of physics, but all the laws of nature,\u201d Stafford says. \u201cAnd there are many practitioners in this field of quantum physics who are proposing that the second law doesn\u2019t apply to systems that are in a state that\u2019s far from equilibrium, but we show that it does.\u201d<\/p>\n As it turns out, everything has to respect the second law. Including a kid\u2019s room.<\/p>\n ###<\/p>\n Research paper: <\/strong><\/p>\n Temperature and voltage measurement in quantum systems far from equilibrium, by Abhay Shastry and Charles A. Stafford; Phys. Rev. B<\/em> 94, 155433 \u2013 Published 19 October 2016; https:\/\/journals.aps.org\/prb\/abstract\/10.1103\/PhysRevB.94.155433<\/p>\n","protected":false},"excerpt":{"rendered":" If you thought that a kid\u2019s room, a Norwegian Nobel Laureate and a laser pointer had nothing in common, two UA physicists are about to enlighten you. It\u2019s hard to believe, but after having unraveled many of the laws that make the universe tick, physicists still haven\u2019t reached an agreement on whether something as seemingly […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-60546","post","type-post","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/posts\/60546","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/comments?post=60546"}],"version-history":[{"count":0,"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/posts\/60546\/revisions"}],"wp:attachment":[{"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/media?parent=60546"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/categories?post=60546"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/healthmedicinet.com\/news\/wp-json\/wp\/v2\/tags?post=60546"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}