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Is Universe really expanding?gaurav.baral1
According to our great scientist of 20th century, universe is ever expanding.For anything to expand there need to be some space.That means universe in itself is not everything.There is some more space left for the space to expand.This indicates that there is either nothing outside universe or there is megauniverse .Which of the two are most likely to be true?
Indi
This premise is not correct: "For anything to expand there need to be some space." An expanding universe doesn't necessarily need to expand "from the outside" (if there were any such thing). Or to put it another way, if the universe is a big bubble, it doesn't need to actually get any bigger on the outside once it's (appearing) to get bigger on the inside. There is no reason to assume that there is anything outside of the universe. Of course, there's no way to prove that there's not, or that there is. JJGY
The theory of replicated energy would mean that the sheer mass of the universe would result in at least some form of mass outside of it, even if it is a theoretical "bubble"
akshar
Sokken
Maybe a little unpolite but here is something from a website explaining about expantion. The source is in the bottom
"The familiar sound of a train whistle as it recedes into the distance is a consequence of the Doppler Effect. As the train moves away from the listener, the crests of the sound waves are stretched out or shifted, resulting in a lower pitch. The faster the train recedes, the more stretched out the waves become. The same holds true for any wave-emitting object--whether they be sound waves, light waves, or radio waves. Conversely, the wavelength of objects that are moving toward us are shorter than those emitted by an object at rest. Atoms emit or absorb light in characteristic wavelengths: hydrogen, helium, and all the other atomic elements have their own spectrum signatures. In the early part of this century, Vesto Slipher was studying the spectra of light emitted from nearby galaxies. He noticed that the light coming from many galaxies was shifted toward the red, or longer wavelength, end of the spectrum. The simplest interpretation of this "redshift" was that the galaxies were moving away from us. Hubble, who had been the first to establish that the universe included many other galaxies outside of our own, noticed something else: the galaxies were receding from us at a velocity proportional to their distance. The more distant the galaxy, the greater its redshift, and therefore the higher the velocity, a relation known as Hubble's Law. The velocity v could be determined by multiplying the distance R by H, the Hubble constant, given by the slope of the line in the above graph, in units of kilometers per second per million light years. The Hubble constant describes the universe's rate of expansion. The apparent linearity of Hubble's Law implies that the universe is uniformly expanding. What does that actually mean? For one thing, it means that no matter which galaxy we happen to be in, virtually all of the other galaxies are moving away from us (the exceptions are at the local level: gravitational attraction pulls neighboring galaxies, such as Andromeda and the Milky Way, closer together). In other words, it's not as though we here on earth are at the center of the universe and everything else is receding from us. The universe has no "edge" as such." Source: http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html unknownc1c
I deffinatly like this topic, unfortunatly i don't think i have a scientific mind, i only like to read about theories like this.
Bikerman
Can you elaborate on this theory - I don't know of it. Is it known by a different name perhaps? Is it a theory in particle physics? Chris chastise
I wish I could thoroughly participate in this. But I also, am not capable of having an answer with some scientific back up. But of coarse, I still do have my own opinions. I think if what you say were true, I'd believe that there is a mega universe.
cong06
Could you expand on that? Explain it better? It's not that I disagree or agree, I'm just curious if you have any reasoning behind it. mattyj
Ooh i like reading physics/cosmology discussions, even if my puny Chemistry based mind doesnt fully understand everything
Interesting reading! Indi
Well, assume two observers - one "inside" the universe and one "outside". The one "inside" notes that the universe is expanding - meaning the farthest points observable are moving away from each other. What does the one "outside" the universe see? The assumption was that he also sees the universe gettting "bigger"... but what does "bigger" mean? It means the space between the two farthest "ends" of the universe is increasing... but "space" (as in distance or length, not outer space) exists only within the universe, it is a property of the universe, just like time, matter and energy. Why would someone "outside" the universe see any sign of space or time on the outside at all? If "size" is a function of "length", and "length" is dimension or property that exists within the universe, why would it have any meaning outside? Or to put it another way, to an "outside" observer, the universe may appear to be a single point for all we know. There's no reason to assume that just because we observe it as 24 Gpc wide, it must appear to be that way to someone outside, because that measurement is a measurement of a property that exists only within the universe - the property of space/length/size. Try imagining this: to an "outside" observer, the universe is the size of a beach ball - and that size remains constant. Within the beach ball is everything we know of as the universe. And everything within the beach ball, as observed from the outside, is shrinking - that is, every object is getting smaller, but staying at its absolute position. To us on the inside, we don't realize we're shrinking because we have nothing to compare it to to realize this. However, when two galaxies that were 100 light years in diameter with 100 light years between their edges both shrink by half without changing their absolute location as measured from their center, each now becomes 50 light years in diameter and they are now 200 light years apart at the edges... but because we think they're both still 100 light years in diameter, we use that assumption to deduce that the distance between them is 400 light years. Thus, we conclude that the universe is expanding. (See below for picture.) 
See? Even if distance had meaning outside of the universe, it doesn't need to be true that the universe is actually expanding for it to appear like it's expanding to us. Coclus
I think it is, though... It/s a wierd image but I guess the human head can't handle it...
Tumbleweed
What fixes the distance for there to be a fixed distance ?........what is immune from the shrinkage ? , if the two objects observed are made from items contained in the distance between them (D) what makes D immune to what effects the two objects I cant wrap my head around the idea that the atoms, ( I think theres a few every cubic centimeter ),light particles and all the other things contained in the vacuum of space between galaxys wouldnt shrink also, keeping fixed distances observably fixed Bikerman
One way to try and imagine it is with a simple analogy.
Imagine stringing a tape measure out to a distant galaxy. You expect it to snap because of expansion but you find it doesn't. What you find is that when you reel it back in that the tape has 'stretched'. Now this only happens in very deep space because gravity otherwise cancels out the expansive force....even in our local system of galaxies the expansion effect is negligible. Indi
Whoa whoa whoa, slow down there. i wasn't presenting an actual scientific theory - or even a real-life pseudoscience one. It was just a thought experiment to demonstrate how it could be possible for (apparent) expansion within a system to not manifest an actual expansion of the system from the outside. Don't try to "wrap" your head around it by actually attempting to apply it to real observations. Can it be done? Sure. i can answer every one of your questions and objections... but i'd be doing it by making crap up that just obscures the point of the illustration - and helps no one in the long run because it won't be anything approaching real science, it will just be (unsurprisingly enough) made-up crap. Hell the entire illustration was just a bunch of making crap up. i don't really intend for you to model the universe as a beach ball. The point of the illustration was to show that you can have a universe that is a fixed size on the outside, but expanding on the inside. Do you really need the imaginary model to be improved to better agree with quantum mechanics in order to believe the point it is intended to make... that what looks like expansion to us need not necessarily actually be actual expansion? dac_nip
yeah, red shift and doppler effect somewhat explains this. its purely theoretical as of this point though.
 Tumbleweed
Well that was my point ... the diagram does not show what you intended , made up crap or not, to me it shows the exact opposite of what was intended , If your really offering to make up more crap to improve your made up crap then feel free....but dont do so on my account* *Unless you need the points  Bikerman
Not really....the theory is based on a lot of observational and experimental results and testing. The problem is, as Indi says, the theory is not at all trivial, Red shift, for example, comes in 3 varieties...standard Doppler Red Shift - no problem with that one, then there is Einsteinian Red-Shift (also called Relativistic or Gravitational Red shift) caused by relativistic effects of time dilation. Then there is Cosmological red-shift which is the one attributed to expansion. The point is that the math works precisely. More than that, the RedShift surveys that have been done provide other corroboration by, for example, predicting the upper limit for the mass of the Neutrino. Most importantly the data all seems to agree with relativity, and the clinching argument at the moment is that there is no alternative theory that is even close to explaining the data in other ways. The only one I have come across if the 'lazy light' hypothesis which was jumped on by the Creationists because it appeared to offer them a way around the age of the universe. That theory (that c is not constant and has changed over time) has been thoroughly refuted. http://physicsweb.org/articles/world/17/5/7 http://bikerman.info/resources/cosmology/darkmatter-paper.pdf Bikerman
I'll have a stab at this for you. Let's start with the basics - Hubble's law z=H*r/c (z is redshift; H is the 'Hubble constant'; r is the distance to the galaxy; and c is, as always speed of light in vacuum). It was in 1929 that Hubble published a claim that the radial velocities of galaxies are proportional to their distance. The redshift of a galaxy is a measure of its radial velocity. Hubble's first set of data showed that if you plot a graph for galaxies, of redshift against distance, the data points on this graph all sit in an approximate straight line. This graph represents the data that was used to derive what is now known as the Hubble constant. The problem was that this predicts an age of the universe at around 2 biollion years which, even then, was known to be dodgy. Later it was found that Hubble made a mistake by confusing two different types of light source - Cepheid variable stars. When the mistake was corrected the Hubble constant came out at around 14 billion yrs which is still roughtly the accepted figure.* 
Another key factor in the picture is the blackbody CMB (Cosmic Microwave Background). This shows that the Universe has 'evolved' from a dense, 'isothermal' state (even temperature) and the temp of the CMB versus redshift shows a uniform cooling. This can only be explained by expansion. Recent work has shown that the expansion of the Universe does not seem to have a special point as a "center", but appears universal and independent of any fixed central point. Here's a current model of the large scale structure of the Universe - it's pretty if nothing else 
This is in keeping with the cosmological principle that demands the universe looks the same way from all direction. Likewise recent CMB studies show that the universe is not as 'clumpy' as thought and that, too confirms previous theory - that the universe should be pretty 'homogeneous' (even) and isotropic (independant of direction). Finally gamma ray bursts and supernovae have been observed to be uniformly scattered across the sky (isotropic again), which is more supporting evidence. 
(Any two points which are moving away from the origin, each along straight lines and with speed proportional to distance from the origin, will be moving away from each other with a speed proportional to their distance apart.) OK..enough of the evidence, let's consider your questions. 1) Why does everything not expand or shrink? The points that Indi made are valid and I'm not wishing to appear as though I am saying otherwise. I'll just consider it from another angle. Firstly expansion is a weak weak force. In systems like ours which are 'gravity bound' then it is swamped out by gravity itself. That goes even for the tiny gravitational attraction between the local group of galaxies - Andromeda etc. 2) Virtual particle/pairs that pop in and out of existence are the 'zero point' energy of space and it is possible that they are actually responsible for the expansion. Whatever the expansive force is, it can be considered as a negative gravity type effect - we could say it was a negative pressure whereas gravity is a positive one. The effect of energy in empty space is one possible explanation of why a vacuum would expand - a simple mode explains the concept: 
There are other possibilities and the matter is still open to debate (the mechanism, rather than the existence of expansion, which most people know agree is solid)... *Because expansive force can (and we think does) change with time, we can write the expansive force as a differential equation 
Now, if the parameter is 0 (no expansion) then it follows that H = 1/t, where t is the time to the Big Bang. To get an age for the universe all we have to do is the integral : 
(where a(t) is the scale factor and Big Bang is put at t=0).)]. The Hubble age comes to 13968 million years for H=70 km/s/Mpc, or 13772 million years for H=71 km/s/Mpc. http://www.physics.fsu.edu/courses/fall98/ast1002/Cosmology/ http://www.superstringtheory.fanspace.com/guest_book.html http://news.bbc.co.uk/1/hi/sci/tech/2940333.stm http://en.wikipedia.org/wiki/Lambda-CDM_model Tumbleweed
Is that my question ? .... you have given a very informative post ( current scientific thinking on the matter ) but I dont think it comes even close to a stab at the question I asked .....which was about shrinking parts of the universe to create expansion ( or the impression of) in other parts of the universe, given Indi's thought experiment is deserving of some imagination what are your thoughts, even imaginary ones on such a universe toughtrio
If it just seems to be expanding to us, as in like it shrinks, but we remain same, and we tend to think that it expands. So that means that the universe actually just seems to expand, but the space inside our universe, relative to us doesnot.
I mean to say that the outer space length, or 4d as shown in the diagram, increases but the inner length remains same relative to us. I am doing AS level and can't analyse this situation perfectly, but can understand what is conveyed by the Doppler Effect. I then tend to think that this is all crap, as how would something tend to shrink from the inside, but remain same relative to the objects INSIDE. This theory makes me think alot when in the 'toilet' (actually thats the place where I use my mind the most). Amazing how God has made this world full of surprises and has made us capable of finding them as the world progresses. But if you think deeply, God must have given us a source of knowledge that gives us hints to find all those surprises. And we Muslims believe, that that source is the HOLY QUR'AN. Sorry if I deviated from the topic a bit, but I can really prove anyone what God had revieled to us with the help of Qur'an, some 1500 years ago. And all these things include the basic things such as the quantity of land and water on earth and other astonishing facts stated plainly, what we need is some intelligent minds to interpret it. For more information, just PM me and I will list all the wonders of QURAN. Sorry again if anyone feels that I have deviated from science to religion, but I think there should be bridge that links these two aspects of the world. Warm Regards, Bikerman
Ahh...OK... maybe I answered it indirectly or indistinctly... The basic point is that expansion occurs only in deep space where gravitational attraction is negligible. Any concentration of matter exerts a gravitational attraction which is orders of magnitude greater than the expansive force and therefore swamps it. This means that expansion does not occur in, for example, our own galaxy, but only in deep intergalactic space. There is no need, therefore, for parts of the universe to shrink in order to explain expansion. Related topics
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