Comments on: The Inverse-What Law? http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/ Random samplings from a universe of ideas. Mon, 23 Nov 2009 03:58:50 -0600 http://wordpress.org/?v=2.8.4 hourly 1 By: Tevong http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-70612 Tevong Mon, 06 Apr 2009 08:51:36 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-70612 ask a stupid question... ? ask a stupid question… ?

]]> By: Tevong http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-70068 Tevong Thu, 02 Apr 2009 11:07:56 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-70068 I was wondering: How were the gravitational masses of planets historically measured? If they are inferred from Newton's law of gravity with observations of planetary motion then isn't that a circular argument when it comes to disproving Newton in favour of general relativity using observations of planetary motion (the precession of the perihelion of mercury)? What I mean is if you're choosing M to give best fit between theory and data then how can you use that same data to show that the theory, calculated with said value of M, doesn't fit? If you had an independent way of measuring M then I can understand that, but historically I'm still puzzled as to how masses of planets could be calculated and the mercury problem was so accurately known without this circularity. I was wondering: How were the gravitational masses of planets historically measured? If they are inferred from Newton’s law of gravity with observations of planetary motion then isn’t that a circular argument when it comes to disproving Newton in favour of general relativity using observations of planetary motion (the precession of the perihelion of mercury)?

What I mean is if you’re choosing M to give best fit between theory and data then how can you use that same data to show that the theory, calculated with said value of M, doesn’t fit? If you had an independent way of measuring M then I can understand that, but historically I’m still puzzled as to how masses of planets could be calculated and the mercury problem was so accurately known without this circularity.

]]> By: Brendon Brewer http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-70030 Brendon Brewer Thu, 02 Apr 2009 02:58:41 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-70030 >>Why do we assume that any phyical laws remain valid from day to day?<< Things that change from day to day aren't often called physical laws. That is all. >>Why do we assume that any phyical laws remain valid from day to day?<<

Things that change from day to day aren’t often called physical laws. That is all.

]]> By: Brendon Brewer http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-70028 Brendon Brewer Thu, 02 Apr 2009 02:52:29 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-70028 >>Best sendup of Bayesian nonsense ever.<< Typical of a pope to deny logic. >>Best sendup of Bayesian nonsense ever.<<

Typical of a pope to deny logic.

]]> By: Pope Maledict XVI http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-70021 Pope Maledict XVI Thu, 02 Apr 2009 01:30:13 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-70021 Best sendup of Bayesian nonsense ever. Best sendup of Bayesian nonsense ever.

]]> By: Ben http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69995 Ben Wed, 01 Apr 2009 20:42:23 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69995 Okay, I will explain the joke. Clearly there are better ways to test the power law of gravity, or derive Kepler's laws, than looking at an instantaneous snapshot of the Solar System and making a Bayesian analysis. However, there are many astronomical objects that are not Keplerian (because they aren't point masses) where you might like to derive the power law of the potential. For example, the Milky Way galaxy. Furthermore, for systems on a galactic scale, the timescale is so long that essentially we only observe an instantaneous snapshot; we can't observe a significant fraction of a Milky Way satellite orbit. The techniques derived in the paper may be useful for applying to problems such as estimating the Milky Way's mass from observations of objects orbiting it, as the last sentence of the abstract points out. Okay, I will explain the joke.

Clearly there are better ways to test the power law of gravity, or derive Kepler’s laws, than looking at an instantaneous snapshot of the Solar System and making a Bayesian analysis.

However, there are many astronomical objects that are not Keplerian (because they aren’t point masses) where you might like to derive the power law of the potential. For example, the Milky Way galaxy. Furthermore, for systems on a galactic scale, the timescale is so long that essentially we only observe an instantaneous snapshot; we can’t observe a significant fraction of a Milky Way satellite orbit. The techniques derived in the paper may be useful for applying to problems such as estimating the Milky Way’s mass from observations of objects orbiting it, as the last sentence of the abstract points out.

]]> By: Nathan http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69990 Nathan Wed, 01 Apr 2009 20:16:52 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69990 uncle sam, it's not about whether the method used is correct or not, it's more that it's completely silly to put so much effort into finding the power law of the gravitational interaction using some strange Bayesian analysis. Now that I've completely ruined the joke, I'll supply a funnier one: http://www.youtube.com/watch?v=3agYeT-T9co uncle sam, it’s not about whether the method used is correct or not, it’s more that it’s completely silly to put so much effort into finding the power law of the gravitational interaction using some strange Bayesian analysis.

Now that I’ve completely ruined the joke, I’ll supply a funnier one:
http://www.youtube.com/watch?v=3agYeT-T9co

]]> By: Sili http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69983 Sili Wed, 01 Apr 2009 19:27:56 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69983 <blockquote> If the Solar System is long-lived and non-resonant (that is, if the planets are bound and have evolved independently through many orbital times)</blockquote> But isn't the solar system actually resonant?

If the Solar System is long-lived and non-resonant (that is, if the planets are bound and have evolved independently through many orbital times)

But isn’t the solar system actually resonant?

]]> By: coolstar http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69976 coolstar Wed, 01 Apr 2009 18:10:30 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69976 Not being a an expert in any of the fields these authors claim to be, I still strongly suspect this paper is an elaborate hoax: phrases like "Newton’s result is therefore arguably more impressive than any results we present in this short note." and "The first force-law inference in the Solar System (Newton 1687, and also work by contemporaries, particularly Hooke, who may have priority)", seem to be something of a giveaway...... Still it's clever and funny. Not being a an expert in any of the fields these authors claim to be, I still strongly suspect this paper is an elaborate hoax: phrases like “Newton’s result is therefore
arguably more impressive than any results we present in this short note.” and
“The first force-law inference in
the Solar System (Newton 1687, and also work by contemporaries, particularly Hooke, who
may have priority)”, seem to be something of a giveaway……
Still it’s clever and funny.

]]> By: Aaron http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69971 Aaron Wed, 01 Apr 2009 17:47:02 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69971 Why do we assume that any phyical laws remain valid from day to day? Why do we assume that any phyical laws remain valid from day to day?

]]>