The accelerating expanding universe

I expect that your question (or five) will be considered to be "doing your homework for you".
I would suggest reading articles from the interwebs and then try to narrow down your focus to less broad questions.Remember: Google is your friend.

In a couple of your recent posts I think you mean "though" when you type "tough".--Percy

Hi break and welcome.I had asked a similar question and was referred to Steven Weinberg's "The First 3 Minutes". It is a little dated but gives a good picture of things. Try this link http://www.iot.org.br/...-the-first-three-minutes-ingles.pdfI am not sure that it will answer your questions but it may shed some light. It does say some things that seem contradictory to the current explanations of the expansion of the universe like;"The galaxies are not rushing apart because of some
mysterious force that is pushing them apart, just as the rising
stone in our analogy is not being repelled by the earth.
Rather, the galaxies are moving apart because they were
thrown apart by some sort of explosion in the past."I am assuming that it appears to be a contradiction because of something that I am not understanding or it is outdated.I will say, in sympathy, that it is a complicated subject and requires alot of study.

Broadly speaking yes. I am asking for some insight. I am not being confrontational or argumentative and I apologize if my post came across as such. I have tried to google for the answer but with no success. The pages I came up with describe the difference between co-moving and apparent frames and the technicalities behind an expanding space (ants on a balloon etc) but they do not explain how we know that such a thing is happening. Or in other words, what were the observations that led us to the conclusion that space itself is expanding as opposed to everything just speeding away from everything else.

I didn't feel any "bad vibes". Unfortunately, my knowledge of cosmology is sadly lacking, so hopefully others can guide you to good sources of information (as Dogmafood has).

That was a very healthy discussion,with some good and effective points,I really appreciate this thread,thanks for all the information. Edited by AdminSlev, : removed signature. do not reply to this message

I am sorry - I was very busy around Christrmas and by the time I had checked back with EvC your question had been buried. Good questions.Obsevation strongly suggests that objects at cosmological distances (say >20Mlyrs) are moving away from us, with velocity proportional to distance.The first conclusion could quite reasonably be that the reality is exactly as it appears - these cosmological objects are indeed simply moving away from us. This leads to the problem that we then appear to be located at the centre of the Universe. Why should we be located in such a special location within the Universe?Now, this would make complete sense within the paradigms of certain religions. However, it doesn't really stand up to scrutiny. The centre of this "exploding" Universe is not *us*, not the Earth, not the Sun, not even the Milky Way galaxy in whose outer reaches we reside. The "centre" is located somewhere within our Local Group of galaxies, of the order of 5MLyrs away from us, in the middle of empty inter-galactic space. That doesn't sound like the religiously inspired anthropocentric view espoused...So, the alternative is that we are nowhere special in the Universe, and our observations of a receding Universe are universal: this is what you would see at any other point in the Universe. This leads us to the ideas of isotropy and homogeneity: the Universe looks the same in all directions and looks the same from all points in the Universe. The assumption that this is true is called the Cosmological Principle.It is obviously false on sub-cosmological scales: the Solar System, Milky Way, and Local Group all fail to show isotropy and homogeneity. But as we go further out into the scale of SuperClusters we start to see the Universe becoming more regular. And as we reach the limits of our observation, we see the Cosmological Microwave Background Radiation (CMBR) revealing isotropy to an extreme level.Assuming the Cosmological Principle is true, that would imply that everything on cosmological scales is moving away from everything else. It also implies that there can be no "edge" to the Universe. The only obvious way we can arrange this is if the Universe is infinite. But now, every location in the Universe regards itself the centre of this expansion, with itself unmoving. To rationalise this, we regard the space itself as expanding, and the cosmological objects as unmoving. With this step, we can then further imagine a finite Universe that wraps itself up into a (hyper)sphere, where the expansion is caused by the expansion of the sphere.So, this is the conclusion we reach from observation. What about from theory? In 1915, Einstein published his General Theory of Relativity. This taught us about space-time, showing how it is much more than just the empty space within which "real" objects reside: it is an entity itself with very real properties and it can curve, warp, expand and contract. I'm sure you are aware of how well tested GR is - in fact, it is one of the two most well-verified scientific theories ever discovered! (in terms of the accuracy of its predictions confirmed by obseravtion)When we use GR to calculate the properties of space-time when we are looking at a smooth distribution of matter which is both isotropic and homogeneous, we find there are essentially two answers: space-time is infinite, and is either expanding or contracting; or space-time is finite and wrapped into a (hyper)sphere, and is either expanding or contracting. In all these cases, the matter is not moving, but the space istelf is expanding (or contracting).So we have arrived at the same answer, both by arguing the case from observation, and by considering the theoretical calculations. Hopefully this is sufficeint to convince you that it is indeed the space that is expanding.What does it mean for "space" to expand? Well, that is another question...Edited by cavediver, : tidying up

So let's refresh your TWO possible answers:-Space-time is infinite and expanding.
or
-Space-time is infinite and contracting
or
-Space-time is finite and expanding.
or
-Space-time is finite and contracting.
or
-It is none of the above.Oh, and its false on some scales...Well, there you go.Now I see why you feel you are ready to move on to economic theory!

I think you misinterpreted what Cavediver was explaining. The GR equations don't tell us whether space/time is finite or infinite, or whether it's expanding or contracting. They only tell us the types of space/time consistent with these equations. If these equations do describe our universe, then when we look out and see distant galaxies all retreating from us and ask ourselves whether they're retreating because of their own motion or because of the expansion of space, the GR equations tell us that it must be due to the expansion of space.--Percy

NASA science has an astrophysics page that has some very interesting stuff about dark energy and how the expansion of the universe is now believed by some to have been slowing down until about 6 million years ago. These theory's come as a result of observations made by Chandra x-ray observatory.
It can be found at NASA science's astrophysics page, the topic is near the top center and is titled ' Finding That Dark Matter is Accelerating the Expansion of the Universe. Lots of other good stuff to on the topic in some NASA archives. Basic stuff also like Hubble's Law. Maybe it will help somebody like me who just isn't as knowledgeable as they would like to be....enjoy Edited by fearandloathing, : No reason given.

There is a contradiction in what you are saying, Cavedriver. You state, and that stands to reason very well, that that there could be no single, privileged position inside the spatial infinity and that what any observer may see from anywhere should be roughly the same as what any other observer will see from anywhere else in the universe. No place is a special place but every place strongly appears to be the centre with everything else receding away from it and accelerating in proportion to its distance from that arbitrary centre.
Now if you remember the essential unity of space and time- after all any space is exactly the time it takes light to travel and any time is the potential space that could be covered by that light in motion, I do not see how do you manage to conclude that this democratic Cosmological principle of relativity is to be applied only spatially while postulating a kind of absolute monarchy in temporal terms.
If any position in space is nothing special, no co-ordinate in time could enjoy any privileges either. Therefore it would follow that though to yourself it might look like there was a point of beginning in time, to an observer existing at that time, at that point that seems to you to be the central point of the universal beginning 13.7 billion years ago, there would appear another time-line of a similar length. Thus the Cosmological principle correctly understood and formulated must hold true not only for any place in the universe but for any time anywhere just as well and for the very same reason.
Spatial democracy and equality must necessarily have a corresponding temporal one. As it is your hypothesis sounds like a curious mix of Einsteinian space with Newtonian absolute time with a single clock rate valid for the whole universe and for all times in it, I am afraid.

Hmmm, is your name Fred Hoyle, and is it 1948?Or are you just 63 years late??? This is precisely Fred's old argument against the Big bang comsology, and why he desperately tried to get the Steady State cosmology to work. He strongly believed that the Cosmological Principle should be applied to space-time, not just space, as you suggest. However, this is forgetting one essential concept: space and time, no matter how intrinsically linked, are NOT the same. Time appears in the metric of space-time with the opposite sign to space - we say that space-time has (3,1) or (1,3) signature; it is Riemannian or pseudo-Lorentzian, not Lorentzian; it has an indefinte metric, not a definite metric; etc.So, we do not necessarily expect to see the Cosmological Principle apply in the time direction, and this is exactly what we see when we look at solutions to Einstein's field equations of General Relativity, especially those of the Friedmann, Lemaitre, Roberston, Walker kind that give rise to the Big Bang cosmologies.Edited by cavediver, : No reason given.

Well, my age may be irrelevant to the issue. Otherwise your insinuation takes for granted some linear progress in human understanding. It assumes that the people at the present age possess a better grasp of reality on average and that those so unlucky to have existed in former ages were progressively moronic necessarily and in a direct proportion to the knowledge data accumulated over time by the human kind.
Let us dispense with such absolutist assumptions and replace them with something more relative again. Let's say that every age has its fair share of idiocy and genius whatever is the statistical value of average accumulated knowledge.
Also, Cavediver, let us not appeal to any authority of Friedman, Lemaitre, Robertson, Walker and others .
You brought up Hoyle, not me. Hoyle had his own head to use and I have got mine thus my reasoning is my own reasoning only even if it may have similarities to what Hoyle might have said.
To be clear on that in advance I don't think Hoyle had it right on the whole either.You have to clarify what is it you mean exactly when saying that time has an opposite sign to space? If you mean to say that in this metric the relative curved space has an absolute, flat and linear time as its opposite, then that is just rephrasing of what I stated in my initial post and we agree. I see it as curious Newtonian atavism and you hold it as a sign of a definite and linear progression in scientific understanding of the nature of the universe. Here we have to agree to differ unless you enlighten me as to why should we agree.That is indeed so in that metric. Whether the dialectical opposition of time to space observed in reality corresponds to the metric is another question. You hold that it does and my opinion is that it does not but that both time and space are relative even if their relativity is not exactly of the same kind. They both may curve yet the spatial curvature is obvious and is readily seen in any spherical body while temporal needs to be imagined, understood and modelled. That is what the opposition of signs may mean in real terms, methinks and not any opposition of relative to absolute.
Lemaitre to whose metric you appeal was first of all a catholic priest while Catholicism takes the idea of temporal relations not from Einstein but from Genesis so the idea of absolute and linear time was much closer and natural to his heart. Hence, its presence in the metric. Simple, but note, no linear progression of mankind towards enlightenment you insinuate I am lagging so desperately behind .

Is your preference for applying the cosmological principle to both space and time philosophical, or is there some observational evidence that your model explains better than current models?--Percy

My personal approach to cosmology is indeed purely philosophical in nature. My philosophy as applied to cosmology is very simple and is based on the first principles of necessity only.
Or rather a single principle, if you wish, the corresponding equivalent of which in the physical science is known as the first law of thermodynamics from which all the rest of the principles may be derived necessarily.
Mind you, that is an extended take on that law which in this extended shape may have the following implications:
Energy may not be created or destroyed.
Energy, space, time, mass and motion are one and the same and are but aspects of the same unity and are in a single knot, always relative to each other and may not be created, inflated, expanded or destroyed but only transformed into one another through a relative perspective. No separation of energy from time, time from space or space from motion is possible. For energy is the energy needed to be in motion through space measured in time.
To be is to do and to exist is to be in motion.
Motion in the universe may not be created or destroyed, expanded or inflated.
Thus there is a constant ratio of matter to void and their constant parity necessitated by the constant motion.
The other aspect of this law that is overlooked by the erroneous theories is that the size of the universe may not be created, inflated, expanded or destroyed but only changed in a relative perspective.
Light is the bridge from space to time and its velocity is constant for that reason and also because the Speed of light is the speed of time itself and is the speed of universal motion and causality and thus exceeding that speed is impossible since it may imply jumping ahead of time which is absurd. Time travel is impossible because it is time that is travelling in anything and in every direction but nothing travels in time.
Mind is the thinking light and is the bridge from here to now and that is why now is as constant as the speed of light. No jumping out of here and now is possible for the very same reason the velocity of light may not be possibly exceeded.
Light is the visible time and the causality seen and light is the now watching its moving reflection in the mirror.The universe is all that exists and is one and only for anything else that exists may be included in it necessarily already and it is finite and infinite at once and it has no possible outside of itself and therefore it is bounded by nothing. Thus it may not expand or inflate for to expand is something to expand into is needed necessarily and to expand is to gain in volume while as nothing is all that does not exists and all that does not exist takes no place to exist and what takes no place to exist may have zero volume. Thus to expand into nothing means to be gaining zero volume and gaining zero volume may only mean to retain the same volume and size as ever. Also to expand into nothing may only mean to expand into itself which is rather a synonym of to contract or collapse and that is not what is being observed.
Also being in a relative physical motion subject to all the necessary and unchanging physical laws governing motion may apply to all the relative, finite and bounded bodies in the universe. To expand is not to be at rest therefore it is to be in motion and is a relative bodily motion inside a greater volume a lesser volume is expanding into. Universe is not a finite, relative and bounded body but is the body Absolute, therefore it cannot be in a relative motion and none of the physical laws that govern all the relative motions of all the relative bodies contained therein may apply to the universe. The body Absolute or spacetime may instead be at rest and serve as the rest frame to all the relative bodies in motion contained therein.Now this is the law of Alfred Maddestein and it is derived via the pure deductive reasoning. You may consider that all I say is as arrogant and mad as my name suggest but I'll tell you this: any hypothesis whose premises may violate a single letter of the above, sooner or later may be proved wrong and thrown in the trash bin together with the flat earth idea or any other creationist model of the universe. Any theory conforming to the principles above may explain the natural phenomena well and will be retained.
You ask about something based on concrete observations meaning a formal scientific theory. Well...until quite recently I have not read a mathematical model that would not violate some of the above. All the alternative theories offered would fall short of the mark and I have been remaining sceptical of most of their claims. I have been supporting none.
Now that have changed. A couple of months ago I have indeed found a new cosmological model thought out by an independent researcher which strictly follows the first principles of necessity outlined.
Currently it is ignored and it will be ignored for quite a while yet. Still, since it fits the observational data much, much better than the standard Big Bang model, improves on Einstein greatly instead of clashing with the man, is beautiful in its simplicity and shows a good predictive power, that situation may not continue indefintely. No dark matters or forces are resorted to but everything is explained naturally with all the reasoning and all the explanations stemming directly from the first principle of the invariance of the speed of light only. The logic and mathematics are compelling, the paper have been around for quite a while and no refutation is available as yet and that is a clear sign that to refute it may prove too hard a nut to crack.
Until the hypothesis is formally tested against nature and improved upon or a still better model is derived, I am perfectly happy to support it even as an overwhelming minority view.
If before I would sometimes doubt my own good sense and consider that the conjectures of the standard model may somehow be improved upon and made into something to make sense, that is not the case any more.