Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: notesfiles - hp 1.2 08/01/83; site hp-pcd.UUCP Path: utzoo!linus!decvax!tektronix!hplabs!hp-pcd!john From: john@hp-pcd.UUCP (john) Newsgroups: net.sf-lovers Subject: Re: a Matter of Gravity... Message-ID: <8200059@hp-pcd.UUCP> Date: Wed, 7-Aug-85 20:57:00 EDT Article-I.D.: hp-pcd.8200059 Posted: Wed Aug 7 20:57:00 1985 Date-Received: Mon, 12-Aug-85 20:58:20 EDT References: <7800038@orstcs.UUCP> Organization: Hewlett-Packard - Corvallis, OR Lines: 28 Nf-ID: #R:orstcs:7800038:hp-pcd:8200059:000:1203 Nf-From: hp-pcd!john Aug 7 16:57:00 1985 <<< < < Somebody mentioned that Gravity acted only on matter. The one catch is, < the equations which make up Einsteinian (?) physics all depend on matter < being interchangeable with energy, where gravity is defined as a form of < energy. < A good example is the planet Vulcan (Yes there really was one). One of the best ways to discover a new planet was to chart the orbits of the known planets and see if you could spot any perturbation in their orbit that might be caused by an unseen neighbor. Several of the outer ones were discovered using this method. Anyway, someone noticed that Mercury had a wobble in its orbit that suggested another planet orbiting between it and the Sun. This "planet" was dubbed Vulcan and astronomers tried unsuccesfully for years to try and find it. It turned out that the wobble was due to the gravitational effect from the "mass equivalent" of the suns gravitational field. The energy in the field was equivalent to a certain amount of mass and if you considered the effect of this mass the mercury was doing what it was supposed to do. A more complete disscussion can be found in Asimov's "The Planet that wasn't". John Eaton !hplabs!hp-pcd!john