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Article #16192Re: Why does light bend under gravity?
From: Tom Roberts
Date: Sun, 16 Mar 2008 17:14
Date: Sun, 16 Mar 2008 17:14
42 lines
4355 bytes
4355 bytes
The Speaking Clock wrote: > On 15 Mar, 08:57, Pentcho Valev <pva...@yahoo.com> wrote: >> [... his usual nonsense] > > Would the speed of light be a non wiggly constant at the very edge of > the universe - bending around it? The speed of light is a constant, c, for any LOCAL measurement anywhere in the universe. I guess that includes "non wiggly". It also includes essentially all measurements of light speed here on earth. At least that is what GR predicts, and there are no observations that contradict it. [Ignore Valev when he brings up Pound-Rebka and similar experiments -- they do not measure speed.] But if you want to see light "bending around the universe" then that would certainly require a non-local path, and there's no solid prediction of the result (given the uncertainties in the physical situation you have in mind). It is rather difficult to perform a non-local measurement of the speed of light, but it has been done by sending radar waves across the solar system to reflect back from mars and venus. By measuring the round-trip delay repeatedly over several years, and fitting to the planetary orbits, one can deduce the round-trip speed of light for these paths. That speed varies, depending on how close to the sun the path passes; look up "Shapiro time delay". The results are in excellent agreement with the predictions of GR. Some people claim this is due to the solar atmosphere. They are wrong: by doing this for multiple wavelengths the effect of the solar atmosphere can be identified, and is found to be negligible. Of course it would be highly unlikely that such a different effect could mimic the GR dependence on path. Indeed, measurements using pulsars agree with the GR predictions for paths that never go inside earth's orbit, and we know what the solar atmosphere is out here. Tom Roberts
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X-Google-Thread: 10b271,1ea0cb1d54d3d906 X-Google-Thread: 10f545,2d47498f99950055 X-Google-Thread: f6c41,2d47498f99950055 X-Google-Thread: fa4c1,c0039b44052ddae9 X-Google-Thread: f74ae,c0039b44052ddae9 X-Google-Attributes: gid10b271,gid10f545,gidf6c41,gidfa4c1,gidf74ae,public,usenet X-Google-Language: ENGLISH,ASCII-7-bit Path: arc1-ca.pugleaf.net!g2news1.google.com!news1.google.com!newshub.sdsu.edu!newscon04.news.prodigy.net!prodigy.net!newsdst01.news.prodigy.net!prodigy.com!postmaster.news.prodigy.com!newssvr29.news.prodigy.net.POSTED!32b1cbcb!not-for-mail From: Tom Roberts <tjroberts137@sbcglobal.net> User-Agent: Thunderbird 2.0.0.12 (X11/20080226) MIME-Version: 1.0 Newsgroups: sci.physics,sci.physics.relativity,sci.physics.particle,fr.sci.physique,sci.astro Subject: Re: Why does light bend under gravity? References: <1de25376-cbdf-4a88-9c24-635b73e962f0@e60g2000hsh.googlegroups.com> <82fb1770-1633-4e2b-abd2-02b8f5e4ecee@k2g2000hse.googlegroups.com> <YpBwj.12517$J41.7185@newssvr14.news.prodigy.net> <pan.2008.02.25.17.17.58@canonicalscience.com> <47C31602.1030806@guesswhatuia.no> <k887s35r0tqpss2mmaj14d9v70qblsjt3v@4ax.com> <7ad9324e-a185-4be5-8d37-36608dda682a@s37g2000prg.googlegroups.com> <6oe7s3t3ffk34ik95onbdq5i7ho1man8vh@4ax.com> <5d081222-5b36-4e82-b8d7-8900c2acbbc4@d4g2000prg.googlegroups.com> <L_mBj.16850$Ch6.2540@newssvr11.news.prodigy.net> <4a84042b-1718-45a4-82f9-0e2b9fa12240@x41g2000hsb.googlegroups.com> <toRBj.16222$xq2.10827@newssvr21.news.prodigy.net> <a2ca4f30-9c55-4fa6-a0a1-cc7ad49e36a4@s37g2000prg.googlegroups.com> <e2b37da4-49a5-40da-95d8-c48add78539d@8g2000hse.googlegroups.com> <350f08c0-cbc4-43ca-9ece-629159f22125@h11g2000prf.googlegroups.com> In-Reply-To: <350f08c0-cbc4-43ca-9ece-629159f22125@h11g2000prf.googlegroups.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Lines: 42 Message-ID: <OzcDj.20839$Ej5.5102@newssvr29.news.prodigy.net> NNTP-Posting-Host: 70.131.99.48 X-Complaints-To: abuse@prodigy.net X-Trace: newssvr29.news.prodigy.net 1205687662 ST000 70.131.99.48 (Sun, 16 Mar 2008 13:14:22 EDT) NNTP-Posting-Date: Sun, 16 Mar 2008 13:14:22 EDT Organization: SBC http://yahoo.sbc.com X-UserInfo1: SCSYQNONARTWSQ@YKROL^_PJFPIFBL@MAHU^_BAMEH]TCDYG^WHUQBKZQLYJX\_ITFD_KFVLUN[DOM_A_NSYNWPFWNS[XV\I]PZ@BQ[@CDQDPCL^FKCBIPC@KLGEZEFNMDYMKHRL_YYYGDSSODXYN@[\BK[LVTWI@AXGQCOA_SAH@TPD^\AL\RLGRFWEARBM Date: Sun, 16 Mar 2008 17:14:22 GMT