#1
Feb604, 06:47 PM

P: n/a

I am relatively new to relativity (pardon the pun)and have found this a fascinating forum. I am trying to come to grips in my little mind about a place in the universe that is truely at rest with respect to everything else in the universe. Is there such a place? How can one go about finding it (mathematically of course). I suggest that this place would be the initial point of the Big Bang?




#2
Feb604, 08:25 PM

Mentor
P: 22,010

Nope  no such place. And no, the "initial point of the big bang" was everywhere.



#3
Feb704, 03:27 PM

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Please note that the observed beginning of the big bang expansion is on the outermost part of the observable universe. (This, of course, requires magic.)




#4
Feb704, 05:14 PM

P: 1,560

Looking for the Ether !! 



#5
Feb1004, 10:42 PM

P: 1,444

If you consider any point where the cosmic background radiation is isotropic that would be as close as you could get to a null as far as is known  the absolutist regards such a point as the cosmic rest frame. It is of course, not just one point  it is every point where you have adjusted your velocity so as to make the CBR equal in all directions  assuming also you are sufficiently removed from the affects of mass. In SR, all inertial frames are regarded as equal, so there is no significance to adjusting your velocity so as to make the observed CBR appear isotropic. There is the ongoing debate as to whether experiments like MMx and KTx that supported the tenants of SR would have any different outcome if performed at some distance from the earth i.e., does the conditioning of space by matter create a local isotroptic frame?




#6
Mar404, 11:16 AM

P: 358

Like no center of the universe means no ether.
Yeah sure! Right! 



#7
Mar404, 12:29 PM

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As Russ indicated, there is no absolute reference frame and there is no single point in 3D space where the Big Bang occurred. There is no center or edge to 3D space. Yogi makes an interesting point about the cosmic background radiation (leftover heat from the Big Bang) being a possible absolute reference frame, but it's not the kind you're looking for.
As Nudnik suggests, the finite speed of light means that the further away we look, the further back in time we see. So, looking 13 billion light years away means we're seeing how the universe was soon after the Big Bang. A telescope has yet to be invented that can see the Big Bang itself. This sight is available in all directions since, as Russ said, the Big Bang happened everywhere in the universe and not at a central point in space. In short, defining your position, velocity, etc. needs to be expressed relative to something else in the universe. 



#8
Mar504, 05:19 PM

P: 284

I continously hear that the BB did not have an initial point. Can somebody explain how this came to be known?




#9
Mar504, 10:26 PM

P: 1,444

Deevieant  go back to the surface of a sphere  assume you live in a two dimensional universe which is the surface of a sphere  where is the center of the surface? Its a meaningless question  the 3 dimensional universe can be similarly portrayed as a surface  you have a Hubble sphere central to your particular location  I have one also  you are at the center of your Huubble sphere  I am at the center of mine  these may be the same spheres just as the two dimensional creatures view the two sphere surface from different locations and both are able to see the whole surface, you and I view the Hubble surface from different points. This surface each of us considers as geocentric to our own location is where the domaine of the BB  one pointon the surface is not any more central than any other  if you wind the cosmic clock backwards, the three dimensional Hubble surface shrinks to smaller size  but there cannot be a center to a three dimension surface per se just as there cannot be a center to the surface of a two sphere.



#10
Mar504, 11:39 PM

P: n/a





#11
Mar604, 12:33 AM

Mentor
P: 22,010





#12
Mar604, 12:53 AM

P: 176





#13
Mar604, 01:02 AM

P: 1,444

Every observer in our three dimensional universe will judge his position to be central to the Hubble sphere defined by his own location  the two dimensional bug at the North Pole of his 2d universe will look up and see his world as comprising the xy plane and say: "We live in a flat plane that is expanding with time" The bug does not see the curvature  he simply interprets the universe as isotropic and as having the same rate of expansion in every direction  i.e., a Hubble circle  the greater the distance, the bigger his Hubble circle appears  until he sees the great circle that would of the equator  and as he looks back further, the smaller his universe appears until he finally sees a point  the south pole  he sees it in every direction he looks, and concludes his telescope(s) have allowed him to see the big bang origin. But Bug #2 at the South pole will see our #1 bug as being so far away and so remote in time as to be the point of the beginning. Which is right  neither  David  the problem you are stuck on is that the Hubble sphere is not a simple three dimensional sphere with a center that everyone agrees upon  it is a three dimensional plane that appears the same in every direction no matter where you are. We as 3d entities are unaware of the curvature of our own universe, but we are able to survey it and determine its apparent geometry  you can think of the universe as embedded in a higher dimensional hyperspherical space if it helps you analogize to the two sphere curvature, but it is not necessary and probably incorrect  its better to relate the curvature to an intrinsic geometric characteristic without any extrinsic significance. As in our previous discussions  this is the beauty of the RW metric.



#14
Mar604, 01:35 AM

P: n/a

A bug at the north pole will look up and say, “Hey! I live on the surface of a sphere, and that sphere is moving through threedimensional space.” 


#15
Mar604, 01:37 AM

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#16
Mar604, 02:04 AM

P: 176





#17
Mar604, 07:32 AM

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PF Gold
P: 4,005




#18
Mar604, 08:51 AM

P: n/a

Are you talking about the old idea of the socalled “curvature” of universal “space”? If so, that idea was rejected by Einstein in a paper he wrote in 1932, in which he said: ”In a recent note in the Göttinger Nachrichten, Dr. O. Heckmann has pointed out that the nonstatic solutions of the field equations of the general theory of relativity with constant density do not necessarily imply a positive curvature of threedimensional space, but that this curvature may also be negative or zero. There is no direct observational evidence for the curvature, the only directly observed data being the mean density and the expansion, which latter proves that the actual universe corresponds to the nonstatical case. It is therefore clear that from the direct data of observation we can derive neither the sign nor the value of the curvature, and the question arises whether it is possible to represent the observed facts without introducing a curvature at all. Although, therefore, the density corresponding to the assumption of zero curvature and to the coefficient of expansion may perhaps be on the high side, it certainly is of the correct order of magnitude, and we must conclude that at the present time it is possible to represent the facts without assuming a curvature of threedimensional space. The curvature is, however, essentially determinable, and an increase in the precision of the data derived from observations will enable us in the future to fix its sign and to determine its value.” As published in: “On the Relation between the Expansion and the Mean Density of the Universe” Albert Einstein and Wilhelm de Sitter, Proceedings of the National Academy of Sciences 18, 213214, 1932. We are inside a 3D universe, plus time. There is no “surface” of our universe. We are somewhere inside it looking out in all directions. 


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