{"id":70,"date":"2017-02-04T11:31:56","date_gmt":"2017-02-04T11:31:56","guid":{"rendered":"https:\/\/petermc.net\/blog\/?p=70"},"modified":"2017-02-04T11:31:56","modified_gmt":"2017-02-04T11:31:56","slug":"pi-is-trancendental","status":"publish","type":"post","link":"https:\/\/petermc.net\/blog\/2017\/02\/04\/pi-is-trancendental\/","title":{"rendered":"Pi is trancendental"},"content":{"rendered":"<p>First the rabbit. The introduction of this function is the part which I don&#8217;t know how to motivate. Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f\" class=\"latex\" \/> be a polynomial and define<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+I%28z%2Cf%29%3D%5Cint_0%5Ez+e%5E%7Bz-t%7Df%28t%29%5C%2Cdt.+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle I(z,f)=&#92;int_0^z e^{z-t}f(t)&#92;,dt. \" class=\"latex\" \/> <\/p>\n<p>Integration by parts gives the recursion<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+I%28z%2Cf%29%3De%5Ez+f%280%29-f%28z%29%2BI%28z%2Cf%27%29+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle I(z,f)=e^z f(0)-f(z)+I(z,f&#039;) \" class=\"latex\" \/> <\/p>\n<p>and therefore we have the formula<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+I%28z%2Cf%29%3De%5Ez%5Csum_%7Bj%5Cgeq+0%7D+f%5E%7B%28j%29%7D%280%29+-+%5Csum_%7Bj%5Cgeq+0%7Df%5E%7B%28j%29%7D%28z%29.+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle I(z,f)=e^z&#92;sum_{j&#92;geq 0} f^{(j)}(0) - &#92;sum_{j&#92;geq 0}f^{(j)}(z). \" class=\"latex\" \/> <\/p>\n<p>Now suppose (for want of a contradition) that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cpi+i+%5Cin+%5Coverline%7B%5Cmathbb%7BQ%7D%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;pi i &#92;in &#92;overline{&#92;mathbb{Q}}\" class=\"latex\" \/>. Let the set of Galois conjugates of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cpi+i&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;pi i\" class=\"latex\" \/> be <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5C%7Ba_1%2C%5Cldots%2Ca_k%5C%7D.&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;{a_1,&#92;ldots,a_k&#92;}.\" class=\"latex\" \/> Then we have <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cprod_%7Bi%3D1%7D%5Ek+%281%2Be%5E%7Ba_i%7D%29%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;prod_{i=1}^k (1+e^{a_i})=0\" class=\"latex\" \/>, expand this as <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Csum_%7BJ%5Csubset%5Bk%5D%7De%5E%7B%5Csum_%7Bj%5Cin+J%7Da_j%7D%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;sum_{J&#92;subset[k]}e^{&#92;sum_{j&#92;in J}a_j}=0\" class=\"latex\" \/> and rewrite as<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+%282%5Ek-d%29%2B%5Csum_%7Bi%3D1%7D%5Ed+e%5E%7B%5Ctheta_i%7D%3D0+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle (2^k-d)+&#92;sum_{i=1}^d e^{&#92;theta_i}=0 \" class=\"latex\" \/> <\/p>\n<p>where the <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Ctheta_i&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;theta_i\" class=\"latex\" \/> are the nonzero exponents.<\/p>\n<p>Now consider<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29%3D%28d-2%5Ek%29%5Csum_%7Bj%5Cgeq+0%7Df%5E%7B%28j%29%7D%280%29-%5Csum_%7Bj%5Cgeq+0%7D%5Csum_%7Bi%3D1%7D%5Edf%5E%7B%28j%29%7D%28%5Ctheta_i%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle &#92;sum_{i=1}^d I(&#92;theta_i,f)=(d-2^k)&#92;sum_{j&#92;geq 0}f^{(j)}(0)-&#92;sum_{j&#92;geq 0}&#92;sum_{i=1}^df^{(j)}(&#92;theta_i)\" class=\"latex\" \/> <\/p>\n<p>Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"N\" class=\"latex\" \/> be an integer such that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=N%5Cpi+i&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"N&#92;pi i\" class=\"latex\" \/> is an algebraic integer. Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/> be a (large) prime and we choose to take<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+f%28x%29%3DN%5E%7Bdp%7Dx%5E%7Bp-1%7D%5Cprod_%7Bi%3D1%7D%5Ed%28x-%5Ctheta_i%29%5Ep%5Cin%5Cmathbb%7BZ%7D%5Bx%5D.+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle f(x)=N^{dp}x^{p-1}&#92;prod_{i=1}^d(x-&#92;theta_i)^p&#92;in&#92;mathbb{Z}[x]. \" class=\"latex\" \/> <\/p>\n<p>There are absolute constants <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"A\" class=\"latex\" \/> and <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=B&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"B\" class=\"latex\" \/> (independent of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/>) such that<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+%7C%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29%7C%5Cleq+A+B%5Ep&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle |&#92;sum_{i=1}^d I(&#92;theta_i,f)|&#92;leq A B^p\" class=\"latex\" \/> <\/p>\n<p>(look at the integral definition of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=I%28z%2Cf%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"I(z,f)\" class=\"latex\" \/> and apply the naive estimate).<\/p>\n<p>Now consider <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;sum_{i=1}^d I(&#92;theta_i,f)\" class=\"latex\" \/>. It is a Galois-invariant algebraic integer, hence an integer. We have<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29%3D%28d-2%5Ek%29f%5E%7B%28p-1%29%7D%280%29%2B%5Ctext%7Bhigher+order+terms%7D.+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle &#92;sum_{i=1}^d I(&#92;theta_i,f)=(d-2^k)f^{(p-1)}(0)+&#92;text{higher order terms}. \" class=\"latex\" \/> <\/p>\n<p>Here higher order means at least <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/> derivatives appearing. Each of these higher order terms is divisible by <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p%21&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p!\" class=\"latex\" \/>, hence by <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/>. Since <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/> is prime, for large enough <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/>, <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;sum_{i=1}^d I(&#92;theta_i,f)\" class=\"latex\" \/> is not divisible by <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/>, hence nonzero.<\/p>\n<p>Now every term is divisible by <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28p-1%29%21&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(p-1)!\" class=\"latex\" \/>, so we get the lower bound<\/p>\n<p align=\"center\"> <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdisplaystyle+%7C%5Csum_%7Bi%3D1%7D%5Ed+I%28%5Ctheta_i%2Cf%29%7C%5Cgeq+%28p-1%29%21&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;displaystyle |&#92;sum_{i=1}^d I(&#92;theta_i,f)|&#92;geq (p-1)!\" class=\"latex\" \/> <\/p>\n<p>As there are infinitely many primes, we can send choose <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=p&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"p\" class=\"latex\" \/> large enough to get a contradiction, QED.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>First the rabbit. The introduction of this function is the part which I don&#8217;t know how to motivate. Let be a polynomial and define Integration by parts gives the recursion and therefore we have the formula Now suppose (for want &hellip; <a href=\"https:\/\/petermc.net\/blog\/2017\/02\/04\/pi-is-trancendental\/\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[6],"tags":[],"class_list":["post-70","post","type-post","status-publish","format-standard","hentry","category-maths"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":false,"jetpack_shortlink":"https:\/\/wp.me\/p7V6a7-18","_links":{"self":[{"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/posts\/70","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/comments?post=70"}],"version-history":[{"count":10,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/posts\/70\/revisions"}],"predecessor-version":[{"id":84,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/posts\/70\/revisions\/84"}],"wp:attachment":[{"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/media?parent=70"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/categories?post=70"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/petermc.net\/blog\/wp-json\/wp\/v2\/tags?post=70"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}