Michael Hartl

In the 1990s, Hartl attended Harvard University for his undergraduate studies, graduating with a bachelor's degree in physics.{{cite web |title=Michael Hartl |website=LinkedIn |url=https://www.linkedin.com/in/michaeldhartl/ |access-date=2024-07-11}} Hartl obtained his PhD in Physics from the California Institute of Technology (Caltech) in 2003, where he researched black hole dynamics. His dissertation was titled Dynamics of Spinning Compact Binaries in General Relativity.{{cite thesis |title=Dynamics of Spinning Compact Binaries in General Relativity |last=Hartl |first=Michael |publisher=California Institute of Technology |location=Pasadena, California |date=2003 |url=http://thesis.library.caltech.edu/1940/ |degree=PhD |access-date=2024-06-08}}

File:Michael_Hartl_with_Kip_Thorne_and_Stephen_Hawking.jpg and Stephen Hawking in 2012]]

After finishing his PhD, Hartl served as Caltech's editor on a corrected and expanded version of The Feynman Lectures on Physics at the request of Kip Thorne.{{cite book |last1=Feynman |first1=Richard |author-link1=Richard Feynman |last2=Leighton |first2=Robert B. |last3=Sands |first3=Matthew |title=The Feynman Lectures on Physics including Feynman's Tips on Physics: The Definitive and Extended Edition |title-link=The Feynman Lectures on Physics |page=x |isbn=978-0805390452}}{{cite web |last=Thorne |first=Kip |title=Preface to the Definitive Edition |url=https://www.michaelhartl.com/files/Feynman%20Lectures%20on%20Physics%20-%20Definitive%20and%20Extended%20Edition%20Preface%20-%20Kip%20Thorne.pdf |access-date=2024-07-13}} Explaining in the preface why he chose Hartl for the task, Thorne noted that "Hartl understand physics deeply, he is among the most meticulous physicists I have known, and like Feynman he is an outstanding pedagogue." Thorne also noted that Hartl is the only Caltech graduate student to be granted a "lifetime achievement award for excellence in teaching" by Caltech's undergraduates.{{cite web |title=ASCIT Teaching Awards Recipients 1999-2000 |url=http://www.its.caltech.edu/~arcomm/teachawards/awards2000.html#lifetime-achievement-awards |archive-url=https://web.archive.org/web/20021215060838/http://www.its.caltech.edu/~arcomm/teachawards/awards2000.html#lifetime-achievement-awards |url-status=dead |archive-date=2002-12-15 |access-date=2024-08-08}}

As an entrepreneur, Hartl participated in the Y Combinator program in 2008.{{cite web |title=Social Networking Goes Open Source With Insoshi |website=TechCrunch |date=2012-08-13 |url=https://techcrunch.com/2008/04/29/social-networking-goes-open-source-with-insoshi/ |access-date=2024-07-13}} In 2010, he published the first edition of the Ruby on Rails Tutorial book{{ cite web |last=Hartl |first=Michael |title=The Ruby on Rails 3 Tutorial book (including PDF downloads) is out |website=Learn Enough News |date=2010-07-28 |url=https://news.learnenough.com/the-ruby-on-rails-3-tutorial-book-including-pdf-downloads-is-out |access-date=2024-07-13}}{{cite book |last=Hartl |first=Michael |title=Ruby on Rails 3 Tutorial: Learn Rails by Example |date=2010 |isbn=978-0321743121}} and screencasts,{{ cite web |last=Hartl |first=Michael |title=The Ruby on Rails 3 Tutorial screencast series |website=Learn Enough News |date=2010-10-12 |url=https://news.learnenough.com/the-ruby-on-rails-3-tutorial-screencast-series |access-date=2024-07-13}} which teach web development using the Ruby on Rails web application framework. The Ruby on Rails Tutorial quickly became both a critical and commercial success,{{cite web |last=Riley |first=Mike |title=Ruby on Rails Tutorial: Learn by Example Review |date=2010-11-10 |url=https://www.drdobbs.com/tools/ruby-on-rails-tutorial-learn-by-example/229300293 |access-date=2024-07-13 |archive-url=https://archive.today/20201011213534/https://www.drdobbs.com/tools/ruby-on-rails-tutorial-learn-by-example/229300293 |archive-date=2020-10-11}} eventually going through seven editions.{{cite book |last=Hartl |first=Michael |title=Ruby on Rails Tutorial: Learn Web Development with Rails |date=2022 |edition=7th |isbn=978-0-13-804984-3}} In 2011, Hartl received a Ruby Hero Award for his service to the Ruby community, with the citation mentioning both the Ruby on Rails Tutorial and his first book, RailsSpace.{{cite video |title=Ruby Hero Awards |date=2011-05-17 |website=YouTube |url=https://www.youtube.com/watch?v=EqZFMaN6Vx0&t=621s}}{{cite book |last=Hartl |first=Michael |date=2022 |title=RailsSpace: Building a Social Networking Website with Ruby on Rails |isbn=978-0321480798}} In 2013, Wikipedia co-founder Jimmy Wales described the Ruby on Rails Tutorial as his "favorite book."{{cite web |last=Wales |first=Jimmy |date=2013-03-06 |website=Quora |url=https://www.quora.com/Jimmy-Wales-1/What-is-Jimmy-Wales-favorite-book?share=1 |access-date=2024-07-13 |title=What is Jimmy Wales' favorite book?}}

Hartl later co-founded the online education company Learn Enough to expand on the Ruby on Rails Tutorial, adding tutorials on other computer technologies and including online courses.{{ cite web |title=Learn Enough to Be Dangerous |website=Learn Enough News |date=2015-09-18 |url=https://www.learnenough.com/about |access-date=2024-07-13}}{{ cite web |last=Hartl |first=Michael |title=Learn Enough Command Line Draft |website=Learn Enough News |date=2015-09-18 |url=https://news.learnenough.com/learn-enough-command-line-draft |access-date=2024-07-13}}{{cite web |title=The Learn Enough Courses |website=Learn Enough |url=https://www.learnenough.com/courses |access-date=2024-07-13}} In partnership with Pearson Education, Hartl authored or co-authored five books published under the brand Learn Enough to Be Dangerous.{{cite book |last=Hartl |first=Michael |date=2022 |title=Learn Enough Developer Tools to Be Dangerous: Command Line, Text Editor, and Git Version Control Essentials |isbn=978-0-13-784345-9}}{{cite book |last=Hartl |first=Michael |date=2022 |title=Learn Enough JavaScript to Be Dangerous: Write Programs, Publish Packages, and Develop Interactive Websites with JavaScript |isbn=978-0-13-784374-9}}{{cite book |last=Hartl |first=Michael |date=2022 |title=Learn Enough Ruby to Be Dangerous: Write Programs, Publish Gems, and Develop Sinatra Web Apps with Ruby |isbn=978-0-13-784413-5}}{{cite book |last1=Donahoe |first1=Lee |last2=Hartl |first2=Michael |date=2022 |title=Learn Enough HTML, CSS and Layout to Be Dangerous: An Introduction to Modern Website Creation and Templating Systems |isbn=978-0-13-784310-7}}{{cite book |last=Hartl |first=Michael |date=2023 |title=Learn Enough Python to Be Dangerous: Software Development, Flask Web Apps, and Beginning Data Science with Python |isbn=978-0-13-805095-5}} Learn Enough was acquired by a tech private equity group in 2022.{{ cite web |last=Hartl |first=Michael |title=Learn Enough and the Rails Tutorial have been acquired |website=Learn Enough News |date=2015-09-18 |url=https://news.learnenough.com/big-news-about-learn-enough |access-date=2024-07-13}}

File:Michael_Hartl_talks_about_tau_at_BIL.jpg at the BIL Conference in 2015]]

In 2010, Hartl published The Tau Manifesto, in which he proposed using the Greek letter tau to represent the circle constant {{math|1=τ = C/r = 2π}},{{cite web |title=The Tau Manifesto |author-first=Michael |author-last=Hartl |date=2010-03-14 |url=https://hexnet.org/files/documents/tau-manifesto.pdf |access-date=2019-08-05 |url-status=live |archive-url=https://web.archive.org/web/20190718051848/http://www.math.utah.edu/~palais/pi.pdf |archive-date=2019-07-18}} the first time tau was publicly proposed for this purpose. The Tau Manifesto proved popular,{{cite web |last=Landau |first=Elizabeth |title=The Tao of Tau |website=Scientific American |date=2017-06-27 |url=https://www.scientificamerican.com/blog/observations/the-tao-of-tau/ |access-date=2024-07-11}} and a revised edition was published in 2019,{{cite web |title=The Tau Manifesto |author-first=Michael |author-last=Hartl |date=2019-03-14 |orig-date=2010-03-14 |url=http://tauday.com/tau-manifesto |access-date=2013-09-14 |url-status=live |archive-url=https://web.archive.org/web/20190628230418/https://tauday.com/tau-manifesto |archive-date=2019-06-28}} followed by a print edition in 2021.{{cite web |last=Hartl |first=Michael |title=State of the Tau 2021 Print edition |website=tauday.com |date=2021-06-28 |url=https://tauday.com/state-of-the-tau#print-edition |access-date=2024-07-15}}{{cite web |last=Hartl |first=Michael |title=The Tau Manifesto: No, really, pi is wrong |website=Amazon.com |url=https://www.amazon.com/Tau-Manifesto-No-really-wrong/dp/B096CXMQ3W/ |access-date=2024-07-15}} As of 2022, The Tau Manifesto had been translated into seven different languages.{{cite web |last=Hartl |first=Michael |title="State of the Tau 2022" |url=https://tauday.com/state-of-the-tau#state-of-the-tau-2022 |date=2022-06-28 |access-date=2024-08-19}}

With the initial publication of The Tau Manifesto in 2010, Hartl founded Tau Day as a mathematical celebration and to promote adoption of the new constant. Observed annually on June 28, or 6/28 (in analogy with the celebration of Pi Day on 3/14), Tau Day has become a widely celebrated mathematical holiday.{{cite tweet |user=MIT |number=1144622756044185600 | access-date=2024-07-11 |title=Three cheers for double Pi! #TauDay http://mitsha.re/i9TP50uP4Id
Image: Chelsea Turner/MIT}}{{cite web |website=Simons Laufer Mathematical Sciences Institute |date=2024-06-20 |url=https://www2.slmath.org/tau-day-2024 |access-date=2024-07-11 |title=Tau Day 2024}} Hartl's constant has also seen significant adoption, including support for tau in the official Google calculator{{cite web |website=google.com |url=https://www.google.com/search?q=tau*1 |access-date=2024-07-11 |title=tau*1}} and inclusion in programming languages such as Microsoft.NET,{{cite web |website=github.com |url=https://github.com/dotnet/runtime/pull/37517 |access-date=2024-07-11 |title= Add Math.Tau, MathF.Tau #37517 }} Java,{{cite web |website=oracle.com |url=https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/lang/Math.html#TAU |title=TAU |department=Math (Java SE 20 & JDK 20) |access-date=2024-07-11}} Rust,{{cite web |website=doc.rust-lang.org|url=https://doc.rust-lang.org/beta/std/f64/consts/constant.TAU.html |title=TAU in std::f64::consts |access-date=2025-03-21}} and Python.{{cite web |website=python.org |url=https://bugs.python.org/issue12345 |title= Add math.tau |access-date=2024-07-11}}{{cite web |website=python.org |url=https://docs.python.org/3/library/math.html#math.tau |title= math.tau |department=Python 3.12.4 documentation |access-date=2024-07-11}} Notable supporters of tau and Tau Day include MIT,{{cite web |last=McGann |first=Matt |title=Pi Day, Tau Time |url=https://mitadmissions.org/blogs/entry/pi-day-tau-time/ |date=2012-03-12 |access-date=2024-08-19}}{{cite web |last=A. |first=Paolo |title=in honor of tau |url=https://mitadmissions.org/blogs/entry/in-honor-of-tau/ |date=2021-02-20 |access-date=2024-08-19}} SLMath, Vi Hart,{{cite video |last=Hart |first=Vi |title=Pi Is (still) Wrong.

|date=2011-03-14 |website=YouTube |url=https://www.youtube.com/watch?v=jG7vhMMXagQ}}{{cite video |last=Hart |first=Vi |title=A Song About A Circle Constant

|date=2012-06-28 |website=YouTube |url=https://www.youtube.com/watch?v=FtxmFlMLYRI}} Vitalik Buterin,{{cite tweet |user=VitalikButerin |number=1238971048948830210 | access-date=2024-08-16 |title=I'm boycotting pi day because tau day is better: https://tauday.com}}{{cite tweet |user=VitalikButerin |number=1674017688300011520 | access-date=2024-08-16 |title=Happy tau day!}} and Elon Musk{{cite tweet |user=elonmusk |number=1496066844284928003 | access-date=2024-08-16 |title=tau > pi}} (who named one of his children after the constant{{cite web |last1=Hawkinson |first1=Katie |last2=Dean |first2=Grace |title=New Elon Musk biography says he has 3rd child with Grimes named Techno Mechanicus |website=Business Insider |url=https://www.businessinsider.com/elon-musk-grimes-child-techno-mechanicus-tau-2023-9 |date=2023-09-11 |access-date=2024-08-16}}).

• {{cite journal |last=Hartl |first=Michael D. |title=Lyapunov exponents in constrained and unconstrained ordinary differential equations |journal=Phys. Rev. E |date=2003 |arxiv=physics/0303077 |bibcode=2003physics...3077H }}
• {{cite journal |last=Hartl |first=Michael D. |title=Dynamics of spinning test particles in Kerr spacetime |journal=Physical Review D |volume=67 |issue=2 |date=2003 |page=024005 |issn=0556-2821 |doi=10.1103/PhysRevD.67.024005|arxiv=gr-qc/0210042 |bibcode=2003PhRvD..67b4005H }}
• {{cite journal |last=Hartl |first=Michael D. |title=Survey of spinning test particle orbits in Kerr spacetime |journal=Physical Review D |volume=67 |issue=10 |date=2003 |page=104023 |issn=0556-2821 |doi=10.1103/PhysRevD.67.104023|arxiv=gr-qc/0302103 |bibcode=2003PhRvD..67j4023H }}
• {{cite journal |last1=Hartl |first1=Michael |last2=Buonanno |first2=Alessandra |title=Dynamics of precessing binary black holes using the post-Newtonian approximation |journal=Physical Review D |volume=71 |issue=2 |date=2005 |page=024027 |issn=1550-7998 |doi=10.1103/PhysRevD.71.024027|arxiv=gr-qc/0407091 |bibcode=2005PhRvD..71b4027H }}

• {{cite book |last1=Hartl |first1=Michael |last2=Prochazka |first2=Aurelius |title=RailsSpace: Building a Social Networking Website with Ruby on Rails |publisher=Addison-Wesley Professional Ruby Series |date=2007 |isbn=978-0321480798}}
• {{cite book |last=Hartl |first=Michael |title=Ruby on Rails Tutorial |publisher=Addison-Wesley Professional Ruby Series |publication-place=Boston Columbus New York San Francisco Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montreal Toronto Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo |date=2022 |isbn=978-0-13-804984-3}}
• {{cite book |last=Hartl |first=Michael |title=Learn Enough Developer Tools to Be Dangerous |publisher=Addison-Wesley Professional |date=2022 |isbn=978-0-13-784345-9}}
• {{cite book |last1=Donahoe |first1=Lee |last2=Hartl |first2=Michael |date=2022 |title=Learn Enough HTML, CSS and Layout to Be Dangerous |isbn=978-0-13-784310-7}}
• {{cite book |last=Hartl |first=Michael |title=Learn Enough JavaScript to Be Dangerous |publisher=Addison-Wesley Professional |date=2022 |isbn=978-0-13-784374-9}}
• {{cite book |last=Hartl |first=Michael |title=Learn Enough Ruby to Be Dangerous |publisher=Addison-Wesley Professional |date=2022 |isbn=978-0-13-784413-5}}
• {{cite book |last=Hartl |first=Michael |title=Learn Enough Python to Be Dangerous |publisher=Addison-Wesley Professional |publication-place=Boston |date=2023 |isbn=978-0-13-805095-5}}

{{reflist}}

• {{Official website|https://www.michaelhartl.com/}}

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