Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 beta 3/9/83; site byucsc.UUCP Path: utzoo!linus!decvax!harpo!utah-cs!beesvax!byucsa!byucsc!trk From: trk@byucsc.UUCP (Tom Kimpton) Newsgroups: net.physics Subject: Doppler shift and relativity Message-ID: <137@byucsc.UUCP> Date: Wed, 1-Aug-84 17:43:04 EDT Article-I.D.: byucsc.137 Posted: Wed Aug 1 17:43:04 1984 Date-Received: Fri, 3-Aug-84 02:04:02 EDT Organization: BYU Compter Science -- Provo UT Lines: 35 I've got a question that popped into my mind the other day, that maybe one of you physics types can answer: Suppose you have a spaceship flying towards you at such a speed that a red light(638nm) shining from it is blue-shifted such that it appears blue(475nm). To figure out the speed that it would have to travel for this doppler shift I used the equation: f' = f(1-v/c)/((1-v**2/c**2)**.5) Which transforms to: v = ((f**2 - f'**2)/(f**2 + f'**2))*c Plugging in appropriate values I obtained ~8.57*10**4 km/s. Let us say that an astronaut on this space ship shines this light towards us for exactly 1 second. During this time his light emits ~4.68*10**14 wave crests ( cycles = f*t ). But because of his speed he has a time contraction which is: t' = t((1 - v**2/c**2)**.5) or t' = .958t or 1.044t' = t. Then during his 1 second of time, 1.044 seconds would have elapsed our time. During this time ~6.57*10**14 wave crests of blue light would have been received. Somehow these two figures 4.68 and 6.57 don't match. What have I done wrong, or where have I misunderstood things? I'd appreciate any help on this. Please reply via Mail to: Tom Kimpton harpo!utah-cs!beesvax!byucsa!byucsc!trk