{"id":1014,"date":"2006-11-01T11:49:01","date_gmt":"2006-11-01T16:49:01","guid":{"rendered":"http:\/\/blogs.discovermagazine.com\/cosmicvariance\/2006\/11\/01\/after-reading-a-childs-guide-to-modern-physics\/"},"modified":"2006-11-01T11:49:01","modified_gmt":"2006-11-01T16:49:01","slug":"after-reading-a-childs-guide-to-modern-physics","status":"publish","type":"post","link":"https:\/\/preposterousuniverse.com\/blog\/2006\/11\/01\/after-reading-a-childs-guide-to-modern-physics\/","title":{"rendered":"After Reading a Child’s Guide to Modern Physics"},"content":{"rendered":"

Abbas at 3 Quarks<\/a> reminds us that next year is W.H. Auden’s centenary (and that Britain is curiously unenthusiastic<\/a> about celebrating the event). The BBC allows you to hear Auden read this poem<\/a> at a 1965 festival; his father was a physicist.<\/p>\n

If all a top physicist knows
\nAbout the Truth be true,
\nThen, for all the so-and-so’s,
\nFutility and grime,
\nOur common world contains,
\nWe have a better time
\nThan the Greater Nebulae do,
\nOr the atoms in our brains.<\/p>\n

Marriage is rarely bliss
\nBut, surely it would be worse
\nAs particles to pelt
\nAt thousands of miles per sec
\nAbout a universe
\nWherein a lover’s kiss
\nWould either not be felt
\nOr break the loved one’s neck.<\/p>\n

Though the face at which I stare
\nWhile shaving it be cruel
\nFor, year after year, it repels
\nAn ageing suitor, it has,
\nThank God, sufficient mass
\nTo be altogether there,
\nNot an indeterminate gruel
\nWhich is partly somewhere else.<\/p>\n

Our eyes prefer to suppose
\nThat a habitable place
\nHas a geocentric view,
\nThat architects enclose
\nA quiet Euclidian space:
\nExploded myths – but who
\nCould feel at home astraddle
\nAn ever expanding saddle?<\/p>\n

This passion of our kind
\nFor the process of finding out
\nIs a fact one can hardly doubt,
\nBut I would rejoice in it more
\nIf I knew more clearly what
\nWe wanted the knowledge for,
\nFelt certain still that the mind
\nIs free to know or not.<\/p>\n

It has chosen once, it seems,
\nAnd whether our concern
\nFor magnitude’s extremes
\nReally become a creature
\nWho comes in a median size,
\nOr politicizing Nature
\nBe altogether wise,
\nIs something we shall learn. <\/p><\/blockquote>\n

Ol’ Wystan is right; we do have a better time<\/a> than most of the universe. It would be no fun to constantly worry that “a lover’s kiss \/ Would either not be felt \/ Or break the loved one’s neck.” And in a sense, it’s surprising (one might almost say unnatural<\/a>) that our local conditions allow for the build-up of the delicate complexity<\/a> necessary to nurture passion and poetry among we creatures of median size.<\/p>\n

In most physical systems, we can get a pretty good idea of the relevant scales of length and time just by using dimensional analysis. If you have some fundamental timescale governing the behavior of a system, you naturally expect most processes characteristic of that system to happen on approximately that timescale, give or take an order of magnitude here or there. But our universe doesn’t work that way at all — there are dramatic balancing acts that stretch the relevant timescales far past their natural values. In the absence of any fine-tunings, the relevant timescale for the universe would be the Planck time<\/a>, 10-44<\/sup> seconds, whereas the actual age of the universe is more like 1018<\/sup> seconds. This is actually two problems in one: why doesn’t the vacuum energy rapidly dominate over the energy density in matter and radiation — the cosmological constant problem<\/a> — and, imagining that we’ve solved that one, why doesn’t spatial curvature dominate over all the energy density — the flatness problem<\/a>. It would be much more “natural,” in other words, to live in either a cold and empty universe, or one that recollapsed in a jiffy.<\/p>\n

But given that the universe does linger around, it’s still a surprise that the matter within it exhibits interesting dynamics on timescales much longer than the Planck time. A human lifespan, for example, is about 109<\/sup> seconds. The human\/Planck hierarchy actually owes its existence to a multi-layered series of hierarchies. First, the characteristic energy scale of particle physics is set by electroweak symmetry breaking<\/a> to be about 1011<\/sup> electron volts, far below the Planck energy at 1027<\/sup> electron volts. (That’s known to particle physicists as “the” hierarchy problem<\/a>.) And then the mass of the electron (me<\/sub><\/em> ~ 5 x 105<\/sup> electron volts) is smaller than it really should be, as it is suppressed with respect to the electroweak scale by a Yukawa coupling of about 10-6<\/sup>. But then the weakness of the electromagnetic interaction, as manifested in the small value of the fine-structure constant α = 1\/137, implies that the Rydberg<\/a> (which sets the scales for atomic physics) is even lower than that:<\/p>\n

Ry ~ α2<\/sup> me<\/sub><\/em> ~ 10 electron volts.<\/p><\/blockquote>\n

This energy corresponds to timescales (by inserting appropriate factors of Planck’s constant and the speed of light) of about 10-18<\/sup> seconds; much longer than the Planck time, but still much shorter than a human lifetime. The cascade of hierarchies continues; molecular binding energies are typically much smaller than a Rydberg, the timescales characteristic of mesocopic collections of slowly-moving molecules are correspondingly longer still, etc.<\/p>\n

Because we don’t yet fully understand the origin of these fantastic hierarchies, we can conclude that God exists. Okay, no we can’t. Really we can conclude that we live in a multiverse in which all of the constants of nature take on different values in different places. Okay, we can’t actually conclude that either. What we can do is keep thinking about it, not jumping to too many conclusions while we try to fill one of those pesky “gaps” in our understanding that people like to insist must be evidence for their personal favorite story of reality.<\/p>\n

But “politicizing Nature,” now that’s just bad. Not altogether wise at all.<\/p>\n","protected":false},"excerpt":{"rendered":"

Abbas at 3 Quarks reminds us that next year is W.H. Auden’s centenary (and that Britain is curiously unenthusiastic about celebrating the event). The BBC allows you to hear Auden read this poem at a 1965 festival; his father was a physicist. If all a top physicist knows About the Truth be true, Then, for […]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,37],"tags":[],"class_list":["post-1014","post","type-post","status-publish","format-standard","hentry","category-science","category-words"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts\/1014","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/comments?post=1014"}],"version-history":[{"count":0,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/posts\/1014\/revisions"}],"wp:attachment":[{"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/media?parent=1014"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/categories?post=1014"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/preposterousuniverse.com\/blog\/wp-json\/wp\/v2\/tags?post=1014"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}