Well, its expanding, but in all directions at once. On a macro scale, the CG is probably constant.
The large structure seems to be "clumpy" and there is considerable local motion around galactic clusters and superclusters, but I believe the overall mass distribution is fairly homogeneous on the largest scales (gigaparsecs). The only common "motion" detected so far is the expansion.
Do you have a specific reason for saying the CG is moving?
Does anyone know where the center of the universe is? Does it even have a "center" as we know it, or is it's center some kind of extra-dimensional thing?
Well personally I agree with you. but most do not believe in the universe = all that is all that is not idea. IE everything (since it causes "god" issues with some people)
to be safe I use it like most people do when in doubt.
but you know what I mean. :-) IE their may be a reference point being C itself to tell if you are moving or stationary regardless of what is around you.
There is no "center" of the universe. Before the "big bang" there was no universe so it essentially happened everywhere at the same time.
One method that works for stars that contain radioactive isotopes is to compare the ratio of the isotope to it's "daughter elements" as it decays. That will tell you how many half-life periods have elapsed and simple arithmetic will tell you the age.
I seem to recall that there is another method that uses the star's luminosity and distance, but I'm not sure how it works.
Mario Perdue NAR #22012 Sr. L2 for email drop the planet
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"X-ray-Delta-One, this is Mission Control, two-one-five-six, transmission concluded."
I was in an airport shuttle somewhere - San Jose maybe - and some lady said 'Cleveland'. I asked if she knew of 'Man-too-uh'. She said it's 'Man- away'. If I ever make it up there, I'll bring stickers to put on the signs at the city lmits. "Welcome to Man-away" :)
Doug
Q: What is "Where Do We Go From Here?" ?
A: What Johnny Cash says after singing _I've Been Everywhere_
Okay, sure, the matter "inside" is moving all over the place. I was speaking like the Universe were a jar of gas; the molecules of gas are moving, but the jar itself (the Universe) is not.
She's right! I was corrected pretty promptly when we first moved here, but of course I also pronounced Conneaut (NE most Ohio city) "Ka-know", when, duh, it's actually "Con-nee-ought".
Mantua has this giant, almost billboard size sign at the city limit covered with all the little placards celebrating all the championship wins of the various school athletic teams... back to, oh, 1965 or so..
Pretty amazing for a town that's only one square mile, one traffic light, one gas station, and two bars... I'm amazed the woman you talked to even *knew* where it is! Honestly, 'round here we like to keep our location a secret. Unbeknownest to most, every couple of years or so, we actually pick the whole village up and move it to a different location... Keeps things nice, and quiet.
Everytime I read the thread title, I start to hear Alan Parsons...
One guesstimate uses the assumed ratio of hydrogen to helium in the early Universe (essentially, all hydrogen and very little helium). As a star fuses hydrogen into helium in it's core, the ratio changes over time and you can extrapolate an age based upon the current ratio. The luminosity of the star tells us how fast the fusion reactions are proceeding. Since a closer star will appear more luminous than a similar one farther away, you need to know the distance to a star to determine its absolute luminosity (fusion rate).
One of the experiments envisioned for the Hubble telescope was the detection of the "afterglow" from the Big Bang (a light pulse which happened when the early Universe expanded enough to become transparent. The current residue of that pulse is the cosmic microwave background radiation). This glow should be seen beyond the farthest galaxies as it, presumably, happened before the galaxies formed. It would appear, I guess, as a constant background glow "behind" the images of the most distant galaxies.
Very deep Hubble exposures seemed to indicate the afterglow, but after careful analysis it was found that the apparent glow was just a myriad number of galactic images merging into each other; Hubble didn't have the resolving power to "see" past the edge of galaxy formation. So far, the deeper into space (hence, the past) we look, the more galaxies we find and it is a challenge to the theorists to explain that. Looking past this "confusion" limit is one goal of the astronomical instrument community.
I only mention this as it may relate to your question. If we knew the distance to the "edge" in every direction, a "center" might be computed. As it is, we have no idea where we are in the Universe. The Universe and it's expansion look the same as far as we can "see" in every direction, as it would from any point within an expanding Universe.
I purposely avoided your main point because I have no easy way to talk about relativistic mass increases. A search of the Net didn't turn up much help, either. It is a debated issue even now how/when to include relativistic mass in discussion or mathematical analysis. Even Einstein admitted the difficulty. See the comment at the end of this article:
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Consider this; no matter how fast you are going, a block of lead in your spacecraft is moving at zero relative speed. You will never see an inertia change in that block by any experiment, if you are moving at a constant velocity. It will take the exact same force to accelerate it across a table whether you are stationary with respect to some object outside your reference frame, or are moving at a high fraction of c relative to that external object.
In the rest frame, mass does not change. Your spaceship is in the rest frame. Accelerating your spacecraft requires moving from Special to General Relativity and I am not comfortable giving an opinion on GR so I can't comment on your idea of increasingly difficult accelerations to determine absolute reference frames.
To be honest, however, there ARE reference frame issues with SR. The biggest issue is with the cosmic background radiation; it permeates all (visible) space in the Universe. It is, in fact, a necessary result of modern Big Bang theory and the CBR may be symmetrical within space-time, giving an absolute velocity reference. Objects moving with respect to the CBR should see a (Doppler) blueshift in the direction of travel and a redshift in the opposite direction. Luckily(?), variations in the intensity and wavelength of the CBR can be attributed to several factors (mass clumping, intervening dust, assymetric Big Bang, gravitational redshifts, etc) and a determination of Earth's absolute velocity relative to the CBR has not been made. Yet. Many people are working on it and satellites (MAP, COBE) have been launched in an effort to measure the CBR with suffient accuracy and precision to make the determination. A perplexing problem for SR, nonetheless.
So far, we've never seen SR (or GR) to experimentally fail. Many predictions have been verified. An important test of GR is coming up in the next year. A satellite called Gravity Probe B is being launched to determine if space-time can be "dragged" around by a rotating mass, ie, the Earth. This is a fundamental test of GR and a failure of the experiment to detect frame dragging could actually cast GR into doubt:
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