gam@amdahl.UUCP (G A Moffett) (05/20/85)
If the Universe is expanding from a common point, where is that
point? In particular, in what area of our sky is the direction
of this point?
--
Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gamethan@utastro.UUCP (Ethan Vishniac) (05/21/85)
> If the Universe is expanding from a common point, where is that > point? In particular, in what area of our sky is the direction > of this point? > -- > Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gam The universe is expanding, but the center of expansion is not uniquely defined. The idealized models of the universe (Friedman models) are spherically symmetric around any arbitrary point. "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas
crm@duke.UUCP (Charlie Martin) (05/22/85)
In article <1544@amdahl.UUCP> gam@amdahl.UUCP (G A Moffett) writes: >If the Universe is expanding from a common point, where is that >point? In particular, in what area of our sky is the direction >of this point? >-- >Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gam Someone better qualified than I will probably give a wonderful technical explanation, but in the mean time.... The big bang background radiation (i.e. 3degK microwave flux) appears to be evenly distributed around the sky in all directions; that is, there is no stronger point in any direction. This could be interpreted to mean that *we* are at the centre of the universe (and I'm surprized that no Creationist has picked that one up.) However, it is easier to explain (for me, anyway) that the universe as we see it is a hypersurface which is expanding is some n-space (say 4-space for tradition, although there are arguments for lots of other spaces). Then we could see the space expanding away in all directions evenly because the actual point from which it is expanding is not in our perceived space at all. This is all pretty loose in these words, but it can be seen with a nice analogy: suppose we were Flatlanders on the surface of a sphere in 3-space (these are actually spherelanders, but you know what I mean). If the sphere expands uniformly in 3-space (like a balloon being inflated) then *each* flatlander will see every other point move away from them while they stand still -- and each will perceive no "direction" from which the expansion of the universe is centered. So the direction you are asking about seems to be backwards in time to the Big Event -- or at least off in some direction outside of our space. -- Charlie Martin (...mcnc!duke!crm)
myers@bnl.UUCP (Eric Myers) (05/23/85)
> > If the Universe is expanding from a common point, where is that > > point? In particular, in what area of our sky is the direction > > of this point? > > -- > > Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gam > > The universe is expanding, but the center of expansion is not uniquely > defined. The idealized models of the universe (Friedman models) are > spherically symmetric around any arbitrary point. > > "Don't argue with a fool. Ethan Vishniac > Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan > Department of Astronomy > University of Texas One way to think of it is this: Blow up a balloon. If you lived on the surface you'd see everything moving away from everything else, and you could say that your universe was expanding. But there is no center about which this expansion takes place. [The inside of the balloon doesn't count -- it isn't a part of your universe if you live on the surface of the balloon.] -- Eric Myers, Physics Dept., Brookhaven National Laboratory, Lon Guyland, NY myers@bnl.arpa / myers@bnl.bitnet / philabs!sbcs!bnl!myers
csc@watmath.UUCP (Computer Sci Club) (05/23/85)
I don't know where he is now, but I used to have him as a roommate. :-) ----------------------------------------------------------------------------- Gilles Dignard Space People think factories are University of Waterloo musical instruments. Waterloo, Ontario They sing along with them. Each song lasts from 8 a.m. to 5 p.m. ...watmath!csc No music on weekends. David Byrne -----------------------------------------------------------------------------
cpf@lasspvax.UUCP (Courtenay Footman) (05/23/85)
In article <1544@amdahl.UUCP> gam@amdahl.UUCP (G A Moffett) writes: >If the Universe is expanding from a common point, where is that >point? In particular, in what area of our sky is the direction >of this point? The universe is not expanding from a common point. It is undergoing an isotropic, homogeneous expansion, with no "fixed point". The usual example is this: consider a 2-dimensional creature that lives on the surface of an inflated balloon. Now inflate the balloon some more. All points on the balloon move away from each other, and the creature says that he is living in an expanding universe; however, no point is privileged over any other point. A person at any point says that the This example descibes a closed universe, but the example does not depend whole universe is expanding away from him. This example describes a closed universe, but the example does not depend on that - an open universe works the same way. -- Courtenay Footman arpa: cpf@lnsvax Newman Lab. of Nuclear Studies usenet: cornell!lnsvax!cpf Cornell University
wilde@apollo.uucp (Scott Wilde) (05/24/85)
>If the Universe is expanding from a common point, where is that >point? In particular, in what area of our sky is the direction >of this point? The point is not one in three dimensional space. The best explanation I have heard uses an 2D analogy with a ballon. Pick any set of points you want on an uninflated ballon. As the ballon is blown up, all points will simultaneously move away from all the others. But the center of expansion is the center of the ballon , which is not a point in the 2d "universe" of the balloon surface. This sounds a little childish, but is probably more understandable that some mathematical explanation ( it was for me.). Scott Wilde Apollo Computer, Chelmsford, MA ...!decvax!wanginst!apollo!wilde
chris@leadsv.UUCP (Chris Salander) (05/24/85)
One step towards an answer is to break the problem down. We are part of a cluster of galaxies. The galaxies in each cluster are expanding away from each other and every cluster is expanding away from the others. If our cluster is like those that we can see, then the galaxies in it are moving away in the direction of their flat sides, rather than spinning away on their edges like a buzzsaw. This would mean that a line drawn through the perpendicular axis of a galaxy would tend to point to the center of the galactic cluster. A natural result of this orientation would be that the side (or flat face) of the galaxy that was facing the center of the cluster would also face most or all of the galaxies in the same cluster. Quickly: since Andromeda is our major cluster partner, the side of the Milky Way that we see it on is where the center of our cluster is. The center of our galaxy is in Sagittarius, so find the point in the sky 90 degrees away from Sag., perpendicular to the line of the Milky Way and on the side with Andromeda. That is the center of our galactic cluster. NOW THE UNIVERSAL SOLUTION!!!: We can now apply the same principle to the clusters if we treat the universe as a cluster of clusters. There would be one particular area of the sky (Hercules?) where a tremedous concentration of galacitc clusters has been observed. The would be the direction of the center of the universe. If all the clusters are expanding away from us, most of them will be in the direction of the center! ta da. conditions: 1) it is hard to apply this to spherical galaxies, but they are immature, and therefore no responsible for their actions. 2) that there is a uniform distribution of matter (clusters0 in the universe. - Chris "Space Cadet" Salander
john@x.UUCP (John Woods) (05/24/85)
> In article <1544@amdahl.UUCP> gam@amdahl.UUCP (G A Moffett) writes: > >If the Universe is expanding from a common point, where is that > >point? In particular, in what area of our sky is the direction > >of this point? > > Someone better qualified than I will probably give a wonderful technical > explanation, but in the mean time.... > > The big bang background radiation (i.e. 3degK microwave flux) appears to > be evenly distributed around the sky in all directions; that is, there > is no stronger point in any direction. This could be interpreted to > mean that *we* are at the centre of the universe (and I'm surprized that > no Creationist has picked that one up.) > Well, not quite. It is, in fact, a tad warmer in the rough direction of Saggitarius, which is therefore the center. The difference is extremely small, so it took some time to detect it. -- John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101 ...!decvax!frog!john, ...!mit-eddie!jfw, jfw%mit-ccc@MIT-XX.ARPA "MU" said the Sacred Chao...
gam@amdahl.UUCP (G A Moffett) (05/25/85)
Thanks for all your replies, and also the letters. I understand
the situation now and realize that my question did not make sense.
(Or, as I had suspected all along, *I* am at the center of the universe!
but then, so are you).
--
Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gamnather@utastro.UUCP (Ed Nather) (05/26/85)
> > In article <1544@amdahl.UUCP> gam@amdahl.UUCP (G A Moffett) writes: > > >If the Universe is expanding from a common point, where is that > > >point? In particular, in what area of our sky is the direction > > >of this point? > > > > Someone better qualified than I will probably give a wonderful technical > > explanation, but in the mean time.... > > > > The big bang background radiation (i.e. 3degK microwave flux) appears to > > be evenly distributed around the sky in all directions; that is, there > > is no stronger point in any direction. This could be interpreted to > > mean that *we* are at the centre of the universe (and I'm surprized that > > no Creationist has picked that one up.) > > > Well, not quite. It is, in fact, a tad warmer in the rough direction of > Saggitarius, which is therefore the center. The difference is extremely > small, so it took some time to detect it. > -- > John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101 Hardly. The "tad warmer" is, in fact, more in the direction of the giant cluster of galaxies in Virgo than anywhere else. It indicates gravity still works at vast distances, and we are falling into (or around) that massive collection of matter. The spectacular uniformity of the 3 Kelvins radiation from the "Big Bang" is the best evidence we have that the "center of the Universe" is inaccessible to us, trapped in our measley 4 dimensions as we are. -- Ed Nather Astronony Dept, U of Texas @ Austin {allegra,ihnp4}!{noao,ut-sally}!utastro!nather
crm@duke.UUCP (Charlie Martin) (05/28/85)
In article <514@x.UUCP> john@x.UUCP (John Woods) writes: >> >Well, not quite. It is, in fact, a tad warmer in the rough direction of >Saggitarius, which is therefore the center. The difference is extremely >small, so it took some time to detect it. Well, Saggitarius is the direction of the centre of the Milky Way galaxy; I`m just a poor innocent philosopher, but that seems like quite a coincidence to me (i.e. that we just happen to be at the point in our orbit around galactic downtown at which the centre and the Universe's own central point are in the same direction. On the other hand, that it is a big coincidence doesn't mean it can`t be a coincidence. But doesn't the universe having an observable centre screw up some cosmological stuff that works well otherwise? Could someone who is up-to-date expand on this a little? Is it coincidence? -- Charlie Martin (...mcnc!duke!crm)
ethan@utastro.UUCP (Ethan Vishniac) (05/31/85)
> In article <514@x.UUCP> john@x.UUCP (John Woods) writes: > >> > >Well, not quite. It is, in fact, a tad warmer in the rough direction of > >Saggitarius, which is therefore the center. The difference is extremely > >small, so it took some time to detect it. > > Well, Saggitarius is the direction of the centre of the Milky Way > galaxy; I`m just a poor innocent philosopher, but that seems like quite > a coincidence to me (i.e. that we just happen to be at the point in our > orbit around galactic downtown at which the centre and the Universe's > own central point are in the same direction. > > On the other hand, that it is a big coincidence doesn't mean it can`t be > a coincidence. But doesn't the universe having an observable centre > screw up some cosmological stuff that works well otherwise? > > Charlie Martin OK folks. Allow me summarize the current state of affairs. The blackbody background of the universe, which is detectable in the microwave region, is isotropic to a high degree of accuracy. The only exception to this is a weak dipole moment (of order 10^-3). All higher order anisotropies are down from this by *at least* an order of magnitude. This dipole moment has a straightforward interpretation. It is exactly what one would expect if the observer (that's us) were moving at a few hundred kilometers a second with respect to the microwave background. The direction of motion of the sun is toward RA 11.4, dec 5 degrees. The velocity is about 400 km/sec. The galactic center is at RA 12.8, dec 27.5 degrees. In other words, they are not in the same direction. The motion of the sun is presumed to have the following components motion with respect to the local standard of rest [ This is approximately our motion with respect to the motion of stars at the same distance from the galactic center and orbiting in perfect circles.] rotation of the galaxy motion of our galaxy within the local group motion of the local group within the Virgo Supercluster motion of the supercluster due to nearby superclusters If we correct for the motion of the sun relative to the local group of galaxies we find a residual motion of about 550 km/sec toward galactic coordinates longitude = 265 degrees, b=35 degrees. Although our motion within the local supercluster is not entirely certain there is evidence that our average motion with respect to galaxies at a distance of 50 Mpc h^-1 is the same as that observed in the microwave background. In other words, the frame of reference in which the galaxies are, on the average, motionless is the same as the one in which the microwave background is isotropic. This is taken as evidence that the universe is homogeneous and isotropic, which is to say that it has no center. Of course, this is science. I have been privately assured that the center of the universe is well known to be in Texas somewhere. "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas -- "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas
ethan@utastro.UUCP (Ethan Vishniac) (05/31/85)
In my last article I said: > The direction of motion of the sun is toward RA 11.4, dec 5 degrees. The > velocity is about 400 km/sec. The galactic center is at RA 12.8, dec 27.5 > degrees. In other words, they are not in the same direction. The motion > of the sun is presumed to have the following components I blew it. Those are the coordinates for the North Galactic Pole. The coordinates of the galactic center are RA 17 hr 42.4 m and dec=-28 degrees 55m. Sorry for the confusion. I read the wrong numbers out of Mihalas and Binney. Thanks to Harold Corwin for pointing out my error. -- "Don't argue with a fool. Ethan Vishniac Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan Department of Astronomy University of Texas
u555027396ea@ucdavis.UUCP (Farin Reborn) (06/04/85)
> If the Universe is expanding from a common point, where is that > point? In particular, in what area of our sky is the direction > of this point? > -- > Gordon A. Moffett ...!{ihnp4,cbosgd,sun}!amdahl!gam *On the subject of expanding universe, most responses only addressed spatial expansion. We live in a four dimensional reality, with time being the fourth dimension. Is there also an expansion along the time axis? In other words, does time run slower today than yesterday? If so, can galactic redshifts be equally well interpreted as: 1. Atoms were smaller yesteryear, hence electron energy levels were different, spectral lines "redder" than today. 2. Time ran faster yesteryear, hence a photon emittted then would be interpreted today to be "oscillating" slower (i.e. lower frequency) hence redshifted. Jon Waggoner & Dr. Bill, UCD Astronomy Club ** REPLACE THIS LINE WITH YOUR MESSAGE ***