Path: csiph.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Sylvia Else Newsgroups: sci.physics.relativity Subject: Re: Is it possible to MEASURE the speed of light,iN INTERGALACTIC SPACE ? Date: Fri, 15 Jun 2018 11:17:53 +1000 Lines: 35 Message-ID: References: <86d8ec67-1634-446f-b63d-dc873060e795@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: individual.net yKbfzDuwZ+SpoBmkm9fyUw0uBL1r7fj2vL8Kv/CkEWWOjXDPnJ Cancel-Lock: sha1:3Z6+CuBT5EUjbESmEH5I02EAQ90= User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 In-Reply-To: Content-Language: en-US Xref: csiph.com sci.physics.relativity:461296 On 15/06/2018 10:59 AM, Keith Stein wrote: > On 13/06/2018 02:34, Sylvia Else wrote: >> On 13/06/2018 6:03 AM, Keith Stein wrote: >>> I rather think Einstein DEFINED the speed of light to be constant. >>> One problem with that approach is that if the speed of light in >>> intergalactic space is actually slowing down, then you are going >>> to think the universe is expanding, when in fact it isn't. >> >> This is a misstatement. In his special theory of relativity, Einstein >> takes as a postulate that the laws of physics are dependent only on >> relative velocities. One consequence of that is that the speed of >> light in a vacuum must be constant. >> >> But all that means is that the theory would be falsified if it were >> later determined by experiment that the speed of light in a vacuum is >> not constant. No such falsification has occurred > > Sylvia, there never has been, and never will be, an experimental > determination of the speed of light in vacuum. Intergalactic space > is not a vacuum (although it is much closer to it than anything > obtainable on Earth). The intergalactic medium is known to be mostly, > but not entirely, Hydrogen. As the Universe evolves the intergalactic > medium will no doubt evolve with it, so it is entirely feasible that > the speed of light in intergalactic space is slowing down, and my > guess is that it is. (by about 1 part in 14 billion per year) > > keith stein > > > It is not remotely reasonable to suppose that light behaves in a fundamentally different way just because there are a few atoms per cubic metre in the space traversed by the light. Sylvia.