{"id":44384,"date":"2017-09-26T17:17:59","date_gmt":"2017-09-26T23:17:59","guid":{"rendered":"http:\/\/admin.patheos.com\/blogs\/danpeterson\/?p=44384"},"modified":"2017-09-26T17:22:08","modified_gmt":"2017-09-26T23:22:08","slug":"consider-gravity","status":"publish","type":"post","link":"https:\/\/www.patheos.com\/blogs\/danpeterson\/2017\/09\/consider-gravity.html","title":{"rendered":"“Consider gravity.”"},"content":{"rendered":"\n<\/head>

\u00a0<\/p>\n

\"2<\/a>
Two types of spiral galaxies: \u00a0An artist\u2019s representation \u00a0(Wikimedia Commons public domain)<\/figcaption><\/figure>\n

\u00a0<\/p>\n

A bit more\u00a0from Geraint F. Lewis and Luke A. Barnes,\u00a0A Fortunate Universe: Life in a Finely Tuned Cosmos<\/em>\u00a0(Cambridge: Cambridge University Press, 2016):<\/p>\n

\u00a0<\/p>\n

\u201cConsider gravity. \u00a0Newton described gravity with his famous \u2018inverse square\u2019 law: \u00a0any two masses attract each other, with a force that decreases with the square of the distance. \u00a0Einstein\u2019s General Theory of Relativity is a more accurate and more difficult improvement on Newton\u2019s theory. \u00a0In both theories, a quantity known as Newton\u2019s gravitational constant appears, which is usually given the symbol of G<\/em> and has a value of \u00a06.67 x 10-11<\/sup> m3<\/sup> kg-1<\/sup> s-2<\/sup>.<\/span><\/p>\n

\u201cIf the value of G<\/em> were different, what would happen? \u00a0We need to be a bit careful here. \u00a0Suppose we\u2019ve transported you to another universe and asked you to measure G<\/em>. \u00a0You\u2019ll need to calibrate your instruments to measure metres, seconds and kilograms. \u00a0But wait . . . that platinum-iridium lump is back in our Universe! \u00a0Thankfully, changing G<\/em> doesn\u2019t affect the elements, so we can (in principle!) make what we need. \u00a0With some caesium 133, you can calibrate your clocks to measure seconds. \u00a0Measuring the speed of light gives the metre: \u00a0the distance light travels in 1\/299, 792, 458 of a second. \u00a0We can then construct a replica platinum-iridium lump to give us the kilogram. \u00a0You can then measure G<\/em>.<\/span><\/p>\n

\u201cNothing in Newton\u2019s or Einstein\u2019s theory tells us the value of G<\/em>. \u00a0We have to ask nature, measuring from experiment.<\/span><\/p>\n

\u201cIn Newton\u2019s theory, if G<\/em> were twice as large, the gravitational force between masses would be twice as large. \u00a0In Einstein\u2019s deeper understanding of gravity, G<\/em> measures how strongly mass and energy distort the geometry of spacetime. \u00a0Changing the value of G<\/em> affects just about everything in astrophysics, from the expansion of the Universe and the formation of galaxies to the size and stability of stars and planets.<\/span><\/p>\n

\u201cSimilar constants appear in all of the force laws, where they are called coupling constants<\/em>. \u00a0The only way we have of knowing the value of these constants is to measure them from nature.\u201d \u00a0(pages 30-32)<\/span><\/p>\n

\u00a0<\/p>\n

Let me repeat two of those sentences: \u00a0(1)\u00a0\u201cNothing in Newton\u2019s or Einstein\u2019s theory tells us the value of\u00a0G<\/em>. \u00a0We have to ask nature, measuring from experiment.\u201d \u00a0(2) \u201cThe only way we have of knowing the value of these constants is to measure them from nature.\u201d<\/p>\n

\u00a0<\/p>\n

In other words, important as these constants are to the emergence of the Universe and of life within it, there is (so far as we now know) nothing inevitable about them. \u00a0Neither Newton\u2019s theory nor Einstein\u2019s theory predicts their specific values. \u00a0That is \u2014 once again, so far as we know \u2014 they\u2019re both contingent. \u00a0They could have been otherwise. \u00a0And, in many cases, had they\u00a0been even slightly different than they actually are, neither we nor the planets, stars, and galaxies would be here.<\/p>\n

\u00a0<\/p>\n

\u00a0<\/p>\n<\/body><\/html>\n","protected":false},"excerpt":{"rendered":"

\u00a0 \u00a0 A bit more\u00a0from Geraint F. Lewis and Luke A. Barnes,\u00a0A Fortunate Universe: Life in a Finely Tuned Cosmos\u00a0(Cambridge: Cambridge University Press, 2016): \u00a0 \u201cConsider gravity. \u00a0Newton described gravity with his famous \u2018inverse square\u2019 law: \u00a0any two masses attract each other, with a force that decreases with the square of the distance. \u00a0Einstein\u2019s General […]<\/p>\n","protected":false},"author":1019,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-44384","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"\n"Consider gravity."<\/title>\n<meta name=\"description\" content=\"    A bit more\u00a0from Geraint F. Lewis and Luke A. 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