Looking for the Ether !! 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?
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.)
Re: Looking for the Ether !! Suspect that that point, if existant, would be pre-BB...after BB, all is in motion, and remains so, to this day, as we know it...
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?
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.
I continously hear that the BB did not have an initial point. Can somebody explain how this came to be known?
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.
Go outside and look up at the sky. We live inside a three-dimensional universe, that is expanding with time. We do not live on the “surface” of a spherical universe. The only spherical surface we live on is the earth.
Actually, we live in at least a four dimensional universe. Furthermore, there is no reason to believe we don't live on the "surface" of a 4-dimensional hypersphere (or hyper-hyperbola). The FRW metric certainly admits the possibility.
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 x-y 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 R-W metric.
There are no such things as “two-dimensional bugs”. You can learn that if you take a biology course. 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 three-dimensional space.”
Are you talking about the curvature of the surface of the earth? Well, we know the earth is curved. I guess a smart bug could figure it out too. Are you talking about the old idea of the so-called “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 non-static solutions of the field equations of the general theory of relativity with constant density do not necessarily imply a positive curvature of three-dimensional 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 non-statical 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 three-dimensional 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, 213-214, 1932. We are inside a 3-D universe, plus time. There is no “surface” of our universe. We are somewhere inside it looking out in all directions.
data? Observational cosmology has improved somewhat since 1932; for example Spergel et al report estimates of cosmological parameters (with estimated errors etc) determined from the first year of data from WMAP. "We find that the emerging standard model of cosmology, a flat [tex]\Lambda[/tex]-dominated universe seeded by a nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data." That is one description; there are, of course, others. The extent to which observations match the various descriptions - and the descriptions can accurately predict what future observations will find - are active areas of research (and vigorous discussion).
Oh, I didn't realize Einstein had rejected the idea. I guess I should inform the other cosmologists who might be misled by this notion. I'm happy that Einstein considered the possibility. However, the buck does not stop at Einstein when it comes to all things relativistic. I think it's great that you're versed in these historic papers, but it's frustrating to have a conversation in 2004 with someone who constantly cites journal articles exclusively from before 1934. David, there has been literature published on the subject since the day of Einstein. I suggest that you follow up on it. You and protonman seem to be upset that physicists are happy to use the models they currently have without care of whether or not they're exact. Yet, you constantly quote Lorentz and Einstein, as if no one needs to possibly build on their ideas?