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, 13 Feb 2012 22:30:13 +0000 hourly 1 http://wordpress.org/?v=3.2.1 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?

]]> By: Theo http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69960 Theo Wed, 01 Apr 2009 16:14:14 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69960 Not having read the paper, the answer to your last question, "what makes the authors so convinced that their instantaneous kinematic snapshot is valid tomorrow?" is "We're assuming that today's snapshot is typical". Indeed, it would be very unlikely for it to fail to be. Not having read the paper, the answer to your last question, “what makes the authors so convinced that their instantaneous kinematic snapshot is valid tomorrow?” is “We’re assuming that today’s snapshot is typical”. Indeed, it would be very unlikely for it to fail to be.

]]> By: Thomas http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69957 Thomas Wed, 01 Apr 2009 15:56:30 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69957 apthorp, you can measure velocities by redshift. Useless for the solar system, but if you want to derive properties of galaxies this approach may be useful. Waiting for Earth to complete a significant fraction of its orbit is one thing, waiting for the sun to do the same around the galaxy, well, you'd need a lot of patience. apthorp, you can measure velocities by redshift. Useless for the solar system, but if you want to derive properties of galaxies this approach may be useful. Waiting for Earth to complete a significant fraction of its orbit is one thing, waiting for the sun to do the same around the galaxy, well, you’d need a lot of patience.

]]> By: uncle sam http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69950 uncle sam Wed, 01 Apr 2009 14:50:14 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69950 Well - I suppose it's not a coincidence about April "1.0", but the general point is still valid "in principle" as I stated: other power laws create instability, check up on it. The planets likely would be thrown out of the solar system or wander around enough that they wouldn't likely keep a nice Titus-Bode style arrangement (note: a "snapshot" does show the current distances, and if you make the assumption those distances are most likely "typical" ...) Why then these authors would make fun of that, I don't know. Maybe they follow the questionable temptation to make fun of what sounds cutesy (the way many conservatives like to make fun of liberal ideas that sound "squishy" or wealking-sympathetic.) Just remember one thing: the fact that someone presents a point in jest doesn't prove it is inherently invalid anyway, it just shows their attitudes. "Ad hominem" works in all directions. BTW, didn't Newton say the solar system should be unstable anyway (from planets pulling on each other) even with inverse square? Well "there it is" so what happened with all that? Well – I suppose it’s not a coincidence about April “1.0″, but the general point is still valid “in principle” as I stated: other power laws create instability, check up on it. The planets likely would be thrown out of the solar system or wander around enough that they wouldn’t likely keep a nice Titus-Bode style arrangement (note: a “snapshot” does show the current distances, and if you make the assumption those distances are most likely “typical” …)

Why then these authors would make fun of that, I don’t know. Maybe they follow the questionable temptation to make fun of what sounds cutesy (the way many conservatives like to make fun of liberal ideas that sound “squishy” or wealking-sympathetic.) Just remember one thing: the fact that someone presents a point in jest doesn’t prove it is inherently invalid anyway, it just shows their attitudes. “Ad hominem” works in all directions.

BTW, didn’t Newton say the solar system should be unstable anyway (from planets pulling on each other) even with inverse square? Well “there it is” so what happened with all that?

]]> By: greg http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69946 greg Wed, 01 Apr 2009 14:15:18 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69946 uncle sam - it obviously has <i>something</i> to do with april 1 as the kinematic snapshot in use is from that date ;-) uncle sam – it obviously has something to do with april 1 as the kinematic snapshot in use is from that date ;-)

]]> By: uncle sam http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69944 uncle sam Wed, 01 Apr 2009 13:52:44 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69944 The authors' point is fully valid in principle, and familiar to those who have studied comparitive dimensionality (like, what kinds of orbits with two or four spatial dimensions "D" and hence power laws g = GMr^(1-D). If the solar system looks about what it does right now and has been in existence for a long time, any other power law (within some range) other than 1/r^2 leads to instability. No, you don't need the velocities to know that the planets couldn't be arranged as they are now under a different power law. The only thing I could puzzle over is the degree of precision in the expected exponent. You can get this general point from reading Barrow and Tipler's classic, <i>The Anthropic Cosmological Principle.</i> Indeed, that point is part of the AD argument that life couldn't have developed under other laws of gravity. BTW, so I don't think it does or should have anything to do with April 1. The authors’ point is fully valid in principle, and familiar to those who have studied comparitive dimensionality (like, what kinds of orbits with two or four spatial dimensions “D” and hence power laws g = GMr^(1-D). If the solar system looks about what it does right now and has been in existence for a long time, any other power law (within some range) other than 1/r^2 leads to instability. No, you don’t need the velocities to know that the planets couldn’t be arranged as they are now under a different power law. The only thing I could puzzle over is the degree of precision in the expected exponent.

You can get this general point from reading Barrow and Tipler’s classic, The Anthropic Cosmological Principle. Indeed, that point is part of the AD argument that life couldn’t have developed under other laws of gravity.

BTW, so I don’t think it does or should have anything to do with April 1.

]]> By: apthorp http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69942 apthorp Wed, 01 Apr 2009 13:42:34 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69942 umm, if you only look for an instant, how do you measure the velocity? Guess that is a variation on the "valid tomorrow?" question. Perhaps the suggestion that it only works on 4/1 is the kindest answer. umm, if you only look for an instant, how do you measure the velocity? Guess that is a variation on the “valid tomorrow?” question. Perhaps the suggestion that it only works on 4/1 is the kindest answer.

]]> By: daniel http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69887 daniel Wed, 01 Apr 2009 04:27:04 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69887 As long as it's blogs that are untrustworthy, and not bloggers. As long as it’s blogs that are untrustworthy, and not bloggers.

]]> By: Sean http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69885 Sean Wed, 01 Apr 2009 04:20:31 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69885 Blogs are notoriously untrustworthy. Blogs are notoriously untrustworthy.

]]> By: CoffeeCupContrails http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69884 CoffeeCupContrails Wed, 01 Apr 2009 04:18:37 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69884 oh... velocities. ok. oh… velocities. ok.

]]> By: daniel http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/comment-page-1/#comment-69883 daniel Wed, 01 Apr 2009 04:06:30 +0000 http://blogs.discovermagazine.com/cosmicvariance/2009/03/31/the-inverse-what-law/#comment-69883 Sean/joye, I was trying to figure out how they were doing it with just positions. My head was starting to hurt. Much better. Sean/joye, I was trying to figure out how they were doing it with just positions. My head was starting to hurt. Much better.

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