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Where is the center of the universe?by thetexan
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#109
Feb712, 08:17 AM

P: 36

On sci channel, Nikodem Poplawski. Google him and check it!!! This feller also thinks the center of our universe, when found, will be a black hole from which our universe was "puked" and, in my own opinion, still is puking"!! Peace Brothers and Sisters!!!!!



#110
Mar1612, 11:30 AM

P: 23

You really can't tell. If everything was energy, then you could just trace the straight line back to the source, but due to matter which has gravity, then light becomes curved and all jumbled up till you really can't find the center or origin



#111
Mar1612, 11:50 AM

P: 15,319




#113
Mar1612, 06:57 PM

P: 23

Fair enough, I stand corrected!



#114
Mar2612, 09:07 PM

P: 36




#115
Mar2712, 04:30 AM

P: 29

maybe there is no middle.
could it be at any point anywhere. we have in our mind that the first action of reaction must mean the middle but in my mind there is no middle in anything 


#116
Mar2712, 07:06 AM

Mentor
P: 11,891




#117
Apr812, 06:29 AM

P: 10

I have read most of the discussion up to date and believe that the question of the whereabouts of the centre of the universe is in danger of joining such topics as religion, politics and global warming by manmade carbon dioxide emissions, in that we are unlikely to get to the bottom of the question. The answer might be found at the end of the scientific process, which requires observation and theory: that is observations are made and a theory formed to explain them. Further observations are made and as long as the observations support the theory, we may have more confidence in the theory, but if observations contradict the theory we should be ready to discard or at least modify the theory.
A relevant observation to the question is the Hubble result, namely, that the further away a galaxy is, the faster it is moving from us. A theory (or analogy), which will also help, is the balloon model of the universe (used also by Stephen Hawking in explaining his Big bang theory). Debris (or galaxies) originating from the Big Bang is contained in the skin of the balloon model. The skin moves away from the point of Big Bang (or centre of the universe) at a speed (estimated with the Hubble constant), which we can denote as V. Now, a galaxy, which is diametrically opposite our observational point in terms of our approximately spherical balloon model will also be moving at V from the point of Big Bang, but in the opposite direction, with resultant parting velocity of 2V. Other galaxies on the skin will be closer and the parting velocities will be less than 2V because they will be made up of the observer's velocity plus a component of the observed galaxy's velocity. To make this clearer consider the special case of a plane through the centre of the balloon universe, and intersecting the observer's point and the diametrically opposite observed galaxy. The plane will also intersect other galaxies around the skin. On this plane the parting velocities (Pv) between the observer and the observed will be given by: Pv = V(1+ cosθ) (1) where θ is the angle between the diameter of the balloon universe, (a diameter which intersects the observer) and the line of inclination (or declination) of the observed galaxy. From (1) it is seen that the parting velocities of all the galaxies will vary from 0 to 2V as theta varies from pi/2 to  pi/2. To locate the direction of the universe's centre is now a simple task: just find the direction of the most redshifted galaxy i.e. the one with the maximal Pv and this line will intersect the centre of the universe. The distance of the centre of the universe along this line, apart from being approximately half way, could be estimated using age of the universe times the estimate for V. This outline of where the centre of the universe is uses existing robust theories and observations with a little thinking. 


#118
Apr812, 07:08 AM

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P: 6,353

Bill Crean, your post is nonsense. That the universe has no center is observational fact, not theology and you misunderstand the baloon analogy.



#119
Apr812, 09:28 AM

P: 15,319

From Earth? You will find Earth is the centre of the universe. From Andromeda? You will find Andromeda is the centre of the universe. From M247? You will find M247 is the centre of the universe. The observations will be the same no matter where you are. Each point of observations will reveal a spherical observable universe equidistant in all directions, with highest red shift at its farthest points. How does your explanation work now? 


#120
Apr812, 09:33 AM

P: 72

And this is where you lose most of us astrophysical midgits, right there. It's possible to observe??? that there is no center but it is impossible to contemplate the possiblility that there is a center but we just cant find it........YET. Bill has, what seems to me, to be a good analogy. Why is it not possible.
If there was an expansion as it is usually described, it had to expand from somewhere, to somewhere. Either we should at least try to find the center of the expansion as a matter of curriosity or quit using the word 'expansion' to describe whatever it was that happened. But that might step on a few theories, dog gone it. tex 


#121
Apr812, 10:17 AM

P: 15,319

I refer you back to the expanding balloon analogy. A hundred ants on it surface all see the other ants receding from it with their recession proportional tot heir distance. Which one can claim to be at the centre of the surface of the balloon? 


#122
Apr812, 10:47 AM

Astronomy
Sci Advisor
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P: 23,235

Just to emphasize what Dave said here.
The balloon analogy is a 2D analog. In that toy universe, all existence is concentrated on the 2D surface and the point which WE see the balloon expanding outwards from does not exist in that universe. None of the 2D critters slithering around in that 2D (with no thickness) universe would be able to point a finger in the direction of the centerofexpansion. They can only point in 2D level directions in their world. Lightrays in their world travel along greatcircle routes in their 2D world, always staying in the balloon surface. A light beam is never observed to take a "shortcut" (go out of existence, or into some "higher dimension" and come back into existence somewhere else). The 2D denizens of that 2D universe have no visible evidence that their world is immersed in a 3D one. That is how WE see it, but that is not how it is for them. It sometimes helps if you watch the brief animation of an expanding 2D universe with galaxies and little colored packets of light traveling between them. I put the link to it in my signature at the end of the post. This animation helps some people get the concept. 


#123
Apr812, 12:05 PM

P: 72

I agree that you cannot, UP TO THIS POINT, determine where the center is due to the fact that from where ever you make the observation it seems to be the center of the universe.
Then, all that has been asserted at this point is that...you cannot observe where the center is because all receding objects seem, from that vantage point, to be receding from that observation point. This doesnt prove, in and of itself that there is no center. 1. It may be true that we cant, now, prove where it is. 2. This inability does not, in and of itself, prove there is no center. 3. If the possibility exists that there is a center (a point that closely approximates where the big bang took place, or from where true expansion is radiating) why doesnt anyone make the attempt to try to find a new way to go looking for it, such as what Bill suggested? 4. In fact, there seems to be such an aversion for even contemplating the possibility that there seems to be something else at play here, especially since what we are dealing with here are THEORIES. And I think it is that no one wants to risk his or here peer respect for suggesting such a thing or for making the attempt at locating it. And, one does not want to ask a question they cant stand the answer to...meaning....what would be the ramifications of finding it? tex 


#124
Apr812, 12:11 PM

Sci Advisor
P: 4,805

There is no such unique point of symmetry for our universe. 


#125
Apr812, 12:50 PM

P: 10

I seemed to have stirred up a hornets' nest. On an Easter day as well.
I used the balloon analogy as Stephen Hawking used it. If the universe has no centre then it is infinite, but this disagrees with Stephen Hawking's Big Bang theory. However, I concede that the observable universe is not the universe, in which case my method for locating the centre of the universe would not work. Indeed the diametrical opposite light source, which I was relying on, would not be available, However, I still maintain that one can find the centre of the observable universe by the method stated. I do not think that what I said was at odds with Davec426913's view. Yes, the ants on the surface of the balloon will move away from each other as the balloon expands. Agreed. However, the question posed is "where is the centre of the universe?" Not, where is the centre of the skin of the universe? The balloon has a centre and it is the balloon's centre, which I attempted to locate. "the point at which we see the balloon expanding outwards from does not exist" . Well, I would be obliged to be directed to where this theory was stated and survived peer review. There may be some astronomical observations to support this but I do not know them. I presume the proponents of this theory must believe that a void pervaded the centre of the "balloon" after the material of the Big Bang had passed through. A "void" being literally that. That is, it is not even empty space and in which case the light from my diametrically opposite galaxy will never be able to reach the observer in the Milky Way. 


#126
Apr812, 02:05 PM

Astronomy
Sci Advisor
PF Gold
P: 23,235

I'm trying to communicate to you the view that the overwhelming majority of peer review literature is based on. To understand it you probably need to go here and watch carefully for a while. http://www.astro.ucla.edu/~wright/Balloon2.html (while watching remember to think that in this 2D toy model all existence is concentrated on the 2D surface, it is all space and all points of space are on that surface) If you think about it, what are the possibilities for a 2D spatial universe? Two of the simplest are: an infinite flat sheet of paper (with no thickness) a 2D "skin" wrapped about a nonexistent 3D ball (again no thickness, the balloon universe idea, no inside or outside). there are others but they tend not to be so simple and symmetrical, a 2D creature plopped into some random location on, say, the skin of a donut, might notice some odd optical effects that wouldn't be the same in all directions. So we take the two simplest ideas of 2D space, and pick one, the sphere, and study it. Now then for COSMOLOGY, to do the analogous thing for 3D, we have to imagine either infinite 3D space (analogous to the flat piece of paper) or a 3D skin wrapped around a nonexistent 4D ball. Those are both convenient models of 3D space to work with (mathematically speaking) and people work with both. We can say what the angles of triangles add up to in either case. We can write formulas for how volume depends on radius etc etc. How many galaxies to expect to count within a certain distance? What angular sizes to expect things to have at various distances. etc. It's pretty commonsense, what other possibilities for 3D space do you seriously want to consider? And thinking of space in these two basic ways goes back to the 1920s and the work of Alex Friedmann. He studied several possible expandingdistances models of cosmos based on Einstein's 1915 general theory of geometry. He could have told you about the 3D universe which can be thought of as the skin wrapped around a nonexistent 4D ball, even before the Belgian priest Father LeMaître. Of course many people would credit LeMaître, but he actually thought of it later, in 1927. And space still could be infinite! We have to keep our options open until there is enough evidence to decide which. So people continue to use both models and fit data and calculate with either. In neither simple model case does 3D space contain a point which you can point your finger at or aim a lightbeam at which is the "centerofexpansion". Friedmann's and LeMaître's formulas can be adapted to EITHER the infinite or the wraparound case just by adjusting parameters. Happy Easter by the way! And you didn't stir any hornets nest Everybody is just trying to help you. Sometimes it takes a while. Watch the little 2D animation. http://www.astro.ucla.edu/~wright/Balloon2.html 


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