CMBR's motion wrt the Earth
in [Relativity]
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From: PD on 7 Sep 2009 14:15 On Sep 6, 7:53 am, mluttgens <mluttg...(a)orange.fr> wrote: > CMBR's motion wrt the Earth > ------------------------------------------ > > In cosmology, cosmic microwave background (CMB) radiation > (also CMBR, CBR, MBR, and relic radiation) is a form of > electromagnetic radiation filling the universe. > (fromhttp://en.wikipedia.org/wiki/CMBR) > > By measuring the amount of the dipole anisotropy (the bluest > part of the sky is .0033 K hotter than average), we can determine > the magnitude of the earth's motion with respect to the CMB: > the earth is moving at a speed of 370 km/s in the direction > of the constellation Virgo. > (fromhttp://www.phy.duke.edu/~kolena/cmb.htm) > > It (the CMBR) does move with respect to an object. > (from PD <thedraperfam...(a)gmail.com>, Sep 5, 2009) > > Clearly, the Earth moves wrt the CMBR. According to SR, > reciprocally, the CMBR moves wrt the Earth. > Can somebody explain how, physically, an electromagnetic > radiation filling the universe can move relative to the Earth? > > Marcel Luttgens I think you are confused about what relative motion means, Marcel. You have in your head that motion is an absolute statement, as in either something is in motion or it's not. This is not the case. If you have car and a stop sign and a fire hydrant, the car is in motion relative to the stop sign, and the stop sign is in motion relative to the car, and the fire hydrant is not in motion relative to the stop sign, and the stop sign is not in relative to the fire hydrant, and the fire hydrant is in motion relative to the car, and the car is in motion relative to the fire hydrant. I think you have it in your head that if you have two objects A and B and they are in relative motion, then this means that one of them is in motion and the other is not. As in, A is in motion relative to B, but B is not in motion relative to A. When you say that you don't believe the CMBR is in motion relative to the earth, I believe you think this because you somehow believe the CMBR is fixed and stationary in some absolute sense and so can't be in any kind of motion, relative or not. I don't know where you got this idea. PD
From: alien8er on 7 Sep 2009 15:58 On Sep 7, 5:37 am, "Inertial" <relativ...(a)rest.com> wrote: > "alien8er" <alien8...(a)gmail.com> wrote in message > > news:5df8d699-8d16-4727-baf1-e68cde032dc3(a)k13g2000prh.googlegroups.com... > > > > > On Sep 6, 10:53 pm, Sam Wormley <sworml...(a)mchsi.com> wrote: > >> Koobee Wublee wrote: > >> > On Sep 6, 4:59 pm, Tom Roberts wrote: > > >> >> What you are missing is the fact that measurement of "the earth's > >> >> motion > >> >> with respect to the CMBR" is really a measurement of the earth's speed > >> >> relative to THE FRAME IN WHICH THE CMBR DIPOLE MOMENT IS ZERO [#]. > >> >> This > >> >> is not in any sense a "rest frame of the CMBR", because the CMBR is > >> >> myriads of photons NONE of which are at rest in any frame. This is > >> >> purely a statistical property of the collection of all the photons > >> >> comprising the CMBR. > > >> > This is the second time that you have refused to recognize the > >> > absolute frame of reference. > > > How much acceleration must one apply to an object, in which > > direction, and for how long, in order for the object to come to rest > > in your absolute frame of reference? > > Surely that depends on how fast and in what direction the object is moving > wrt the 'absolute frame' at the time. Exactly, which leads inexorably to the followup zinger: how does one determine that velocity? Mark L. Fergerson
From: alien8er on 7 Sep 2009 16:00 On Sep 6, 11:23 pm, "Inertial" <relativ...(a)rest.com> wrote: > "alien8er" <alien8...(a)gmail.com> wrote in message > > news:ad3edebc-f644-4d89-a75d-fb316e53880b(a)2g2000prl.googlegroups.com... > > > > > On Sep 6, 10:46 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: > >> Koobee Wublee wrote: > > >> [...] > > >> > This is the second time that you have refused to recognize the > >> > absolute frame of reference. > > >> ...and yet the hobbyist still can't explain what makes it "absolute". > > > Even a hobbyist (me) can ask pertinent questions like "if an > > absolute frame of reference exists, in which direction must I > > accelerate, for how long, in order to come to rest in that frame?". > > > No absolutist has ever answered that question. They all pretend to > > ignore it. > > Obviously it would depend on your current motion wrt such a frame. You'd > simply need to accelerate in the opposite direction to your motion relative > to the frame long enough to reduce you velocity wrt the frame to zero. > > Its not a particularly interesting question to ask. The followup question is; how does one determine one's velocity WRT that frame? Mark L. Fergerson
From: Inertial on 7 Sep 2009 19:32 "mluttgens" <mluttgens(a)orange.fr> wrote in message news:523b7307-93cc-44c3-940e-8bd1f368776e(a)h13g2000yqk.googlegroups.com... > On 7 sep, 14:22, "Inertial" <relativ...(a)rest.com> wrote: >> "mluttgens" <mluttg...(a)orange.fr> wrote in message >> >> news:6e6cbfbb-70bb-4fa6-99c3-45f00c351fa7(a)w36g2000yqm.googlegroups.com... >> >> >> >> >> >> > On 7 sep, 01:59, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: >> >> mluttgens wrote: >> >> > Can somebody explain how, physically, an electromagnetic >> >> > radiation filling the universe can move relative to the Earth? >> >> >> Your descriptions are insufficiently precise. There is no such thing >> >> as >> >> "The CMBR" -- the cosmic microwave background radiation is comprised >> >> of >> >> myriads of photons moving in all directions. This is not a "thing" in >> >> any normal sense, it is a vast collection of photons. >> >> >> [For the purposes of this thread I'll ignore the quantum >> >> aspects of photons.] >> >> >> What you are missing is the fact that measurement of "the earth's >> >> motion >> >> with respect to the CMBR" is really a measurement of the earth's speed >> >> relative to THE FRAME IN WHICH THE CMBR DIPOLE MOMENT IS ZERO [#]. >> >> This >> >> is not in any sense a "rest frame of the CMBR", because the CMBR is >> >> myriads of photons NONE of which are at rest in any frame. This is >> >> purely a statistical property of the collection of all the photons >> >> comprising the CMBR. >> >> >> [#] Careful authors phrase it this way, not in the careless >> >> way you did. I have been phrasing it as "the CMBR dipole=0 >> >> frame" in this newsgroup for many years. >> >> >> It is rather remarkable that there is such radiation apparently >> >> filling >> >> the universe (it has been observed interacting with distant stars and >> >> galaxies). This is quite strong evidence in support of the big bang >> >> cosmologies, and the synthesis known as the standard model of >> >> cosmology. >> >> There remain details still unknown, and some downright puzzles (dark >> >> matter, dark energy, ...). >> >> >> Tom Roberts >> >> > Thank you. >> >> I would have assumed it was taken from the context of talking about >> frames, >> and absolute frames in particular, that 'the CMBR' was referring to what >> is >> sometimes called the CMBR rest frame (as described above by Tom). >> >> > Do you consider that claiming (like Paul Draper and others) >> > that the CMBR moves wrt an object, makes sense? >> >> It makes as much sense as an object moving wrt the CMBR. > > No, read what Tom Roberts said: I did .. read what I said > "The measurement of "the earth's motion with respect to the CMBR" > is really a measurement of the earth's speed relative to THE FRAME > IN WHICH THE CMBR DIPOLE MOMENT IS ZERO." That's right > He didn't say that the Earth has no motion wrt the CMBR, Neither did I > he only > gave his interpretation of such motion. No .. he gave a more specific terminology for what we had simply been calling 'the CMBR' in this thread as a frame of reference .. he said that what one should technically be saying it "the frame where the CMBR dipole moment is zero". but that's pretty words, so i think its ok to continue using 'the CMBR' as a shorthand, as long as we all know what we mean.
From: Inertial on 7 Sep 2009 19:34
"alien8er" <alien8752(a)gmail.com> wrote in message news:1b0a5cee-720b-4dcb-b860-9b4abd6e2515(a)l35g2000pra.googlegroups.com... > On Sep 7, 5:37 am, "Inertial" <relativ...(a)rest.com> wrote: >> "alien8er" <alien8...(a)gmail.com> wrote in message >> >> news:5df8d699-8d16-4727-baf1-e68cde032dc3(a)k13g2000prh.googlegroups.com... >> >> >> >> > On Sep 6, 10:53 pm, Sam Wormley <sworml...(a)mchsi.com> wrote: >> >> Koobee Wublee wrote: >> >> > On Sep 6, 4:59 pm, Tom Roberts wrote: >> >> >> >> What you are missing is the fact that measurement of "the earth's >> >> >> motion >> >> >> with respect to the CMBR" is really a measurement of the earth's >> >> >> speed >> >> >> relative to THE FRAME IN WHICH THE CMBR DIPOLE MOMENT IS ZERO [#]. >> >> >> This >> >> >> is not in any sense a "rest frame of the CMBR", because the CMBR is >> >> >> myriads of photons NONE of which are at rest in any frame. This is >> >> >> purely a statistical property of the collection of all the photons >> >> >> comprising the CMBR. >> >> >> > This is the second time that you have refused to recognize the >> >> > absolute frame of reference. >> >> > How much acceleration must one apply to an object, in which >> > direction, and for how long, in order for the object to come to rest >> > in your absolute frame of reference? >> >> Surely that depends on how fast and in what direction the object is >> moving >> wrt the 'absolute frame' at the time. > > Exactly, which leads inexorably to the followup zinger: how does one > determine that velocity? First you have to find the frame. Those that hold the CNBR reference frame is 'the absolute' frame, and our motion relative to that is known and measureable. |