Relativistic Doppler shift
in [Relativity]
|
From: I.N. Galidakis on 27 Jul 2010 09:16 Dono. wrote: > On Jul 25, 2:05 pm, "I.N. Galidakis" <morph...(a)olympus.mons> wrote: >> >> Btw, this expression seems to give a "blue-shift" for a fast-rotating green >> laser (since I find that the 532nm reduces towards the blue to 520nm for my >> case), but I understand that the term "redshift" may be used generically for >> both cases, blue-shift and red-shift. >> > > > "red-shift" is meant to mean "observed frequency < emitted frequency" Yes, sorry, I think I've got them mixed up. If f_o=f_s/gamma, then as f=c/lambda, this gives: lambda_o=lambda_s*gamma, so if I plug in 532 nanometers, I get: lambda_o=533.66nm So this seems like "observed wavelength > emitted wavelength", which is the same as "observed frequency < emitted frequency". Is this a red-shift? I'd expect the rotating laser beam to have given me a blue-shift instead. -- I.
From: Dono. on 27 Jul 2010 09:55 On Jul 27, 6:16 am, "I.N. Galidakis" <morph...(a)olympus.mons> wrote: > Dono. wrote: > > On Jul 25, 2:05 pm, "I.N. Galidakis" <morph...(a)olympus.mons> wrote: > > >> Btw, this expression seems to give a "blue-shift" for a fast-rotating green > >> laser (since I find that the 532nm reduces towards the blue to 520nm for my > >> case), but I understand that the term "redshift" may be used generically for > >> both cases, blue-shift and red-shift. > > > "red-shift" is meant to mean "observed frequency < emitted frequency" > > Yes, sorry, I think I've got them mixed up. > > If f_o=f_s/gamma, then as f=c/lambda, this gives: > > lambda_o=lambda_s*gamma, so if I plug in 532 nanometers, I get: > > lambda_o=533.66nm > > So this seems like "observed wavelength > emitted wavelength", which is the same > as "observed frequency < emitted frequency". > > Is this a red-shift? > Yes.
From: Dono. on 27 Jul 2010 09:58 On Jul 26, 12:11 pm, Tony M <marc...(a)gmail.com> wrote: > I was also thinking about the relativistic Doppler shift lately. > Two observers A and B are heading towards each other at relative speed > c/2. Observer A shoots a laser beam of frequency fA (as measured by A) > towards observer B where it is received at frequency fB (as measured > by B). What fB does B measure? What should fB be from observer As > perspective? Will the two observers agree on the value of fB? > The way I see it: > From As perspective B is heading towards him at c/2 so fA is Doppler > blue-shifted. Bs clock is slower so theres an additional > relativistic blue-shift. B should measure fB = fA x 2 x gamma. > From Bs perspective A is heading towards him at c/2. As clock is > slower so fA first gets a relativistic red-shift then a Doppler blue- > shift. B should measure fB = fA x 2 / gamma. > So A and B would disagree on the value of fB, if Im analyzing the > problem right. fB/fA=fA/fB=sqrt[(1+v/c)/(1-v/c)] In your case v=c/2 so fB/fA=fA/fB=sqrt(3)
From: BURT on 27 Jul 2010 16:16 On Jul 27, 6:55 am, "Dono." <sa...(a)comcast.net> wrote: > On Jul 27, 6:16 am, "I.N. Galidakis" <morph...(a)olympus.mons> wrote: > > > > > > > Dono. wrote: > > > On Jul 25, 2:05 pm, "I.N. Galidakis" <morph...(a)olympus.mons> wrote: > > > >> Btw, this expression seems to give a "blue-shift" for a fast-rotating green > > >> laser (since I find that the 532nm reduces towards the blue to 520nm for my > > >> case), but I understand that the term "redshift" may be used generically for > > >> both cases, blue-shift and red-shift. > > > > "red-shift" is meant to mean "observed frequency < emitted frequency" > > > Yes, sorry, I think I've got them mixed up. > > > If f_o=f_s/gamma, then as f=c/lambda, this gives: > > > lambda_o=lambda_s*gamma, so if I plug in 532 nanometers, I get: > > > lambda_o=533.66nm > > > So this seems like "observed wavelength > emitted wavelength", which is the same > > as "observed frequency < emitted frequency". > > > Is this a red-shift? > > Yes.- Hide quoted text - > > - Show quoted text - Turn flow rate or anti gravity drives up light energy by gamma at absorption from every angle. Mitch Raemsch
From: Tony M on 28 Jul 2010 00:00
On Jul 27, 9:58 am, "Dono." <sa...(a)comcast.net> wrote: > On Jul 26, 12:11 pm, Tony M <marc...(a)gmail.com> wrote: > > > I was also thinking about the relativistic Doppler shift lately. > > Two observers A and B are heading towards each other at relative speed > > c/2. Observer A shoots a laser beam of frequency fA (as measured by A) > > towards observer B where it is received at frequency fB (as measured > > by B). What fB does B measure? What should fB be from observer As > > perspective? Will the two observers agree on the value of fB? > > The way I see it: > > From As perspective B is heading towards him at c/2 so fA is Doppler > > blue-shifted. Bs clock is slower so theres an additional > > relativistic blue-shift. B should measure fB = fA x 2 x gamma. > > From Bs perspective A is heading towards him at c/2. As clock is > > slower so fA first gets a relativistic red-shift then a Doppler blue- > > shift. B should measure fB = fA x 2 / gamma. > > So A and B would disagree on the value of fB, if Im analyzing the > > problem right. > > fB/fA=fA/fB=sqrt[(1+v/c)/(1-v/c)] > > In your case v=c/2 so > > fB/fA=fA/fB=sqrt(3) Dono, Math-wise fB/fA=fA/fB only holds when fA=fB. fB/fA=sqrt(3) means fB>fA fA/fB=sqrt(3) means fA>fB They can't both be true. |