And could you tell by redshifts?
131776
It could be possible but there is something called the cosmological principle that are a set of assumptions about the universe that prevents us from determining that.  Basically we need to assume, among other things, that the laws of physics, as they apply here, work the same in other parts of the universe.  Without this assumption we couldn't make any statements about the universe since it would be pure speculation.
226185
How is that you know?
110734
According to current estimates, roughly 400,000 years.  This is what we can tell from the data from WMAP, which was launched to measure the microwave background radiation.  It is this radiation that is the leftover glow from when light decoupled from matter, which is the point at which the universe would have "turned black".
180560
Very good.  You are close to the truth.\n\nSpace alternately expands and contracts over a two billion year cycle.\n\nWe are now nearing the end of the expansionary phase.  So all the scientists on primitive planets hypothesize a big bang and talk about red shift.\n\nIn the following phase, scientists on other primitive planets will hypotehsize a fiery, incandescent end in the middle of everything and talk a lot about blue shifts.\n\nThe reasons for this have to do with the benefits of dynamic equilibrium.  Static would not work.  Apparently God already knows about this, but so do some physicists.\n\nSoem Dutch guy named DeSitter was also close, I have heard.
254509
ummm,how will you know?
324591
There is no actual proof as such although the evidence to support the theory is pretty convincing. The first piece of evidence is that the universe is observed to be expanding. Galaxies are observed to be receding from us. This is determined by the shift in their light to the red end of the visible spectrum. It's an effect you can hear with sound; as a vehicle approaches you blowing its horn you will hear the pitch of the sound change from high to low as it then travels away from you. It's called the Doppler effect. It aslo happens with light, only light changes colour from blue (coming towards you) to red (going away from you). The lightwaves are compressed and stretched just like sound.\n\nSince galaxies are moving away from us they must have been concentrated at one point in the distant past. That the singularity of the Big Bang.\n\nThe other piece of evidence is the background radiation of heat left over from the Big Bang. This was predicted to exist by proponents of the Big Bang, and was discovered accidentally in 1963. It's the leftovers of the tremendous heat generated by the explosion, and is 2.93 degrees above absolute zero.
12349
actually they do not care at all if you believe it or not, they are just highly intelligent people who are using rational evidence to make theories.  i will share with you the most compelling piece of evidence which proves beyond any doubt that the universe is expanding.  and if the universe is expanding... well, it had to start somewhere right? it's just a logical conclusion formulated and agreed upon by very intelligent people, and they didnt just pull it out of their butts.\n\nso here is how we know the universe is expanding: the doppler effect. This is an effect observed with waves, most observably with sound and light waves. Basically, it says that waves moving toward you have a shorter wavelength, and waves moving away from you have a longer wavelength. \n(  (  (  (x)))) -->\nKind of like that, the waves are closer together at the front, kind of like they are being bunched up, they are staying closer to the object(x) since it is moving and getting closer to them. This is the Doppler effect. With sound waves, this effect means that coming toward you, sound waves have a shorter wavelength(notice that the distance between each wave is shorter) and a higher frequency(notice that more waves would pass a given point per second since they're closer together) the formula is v=fw where v is velocity, f is frequency and w is wavelength; as you can see, since v is constant(the speed of light) f and w are inversely proportional so when one goes up, the other goes down. This higher frequency results in a higher pitch of the sound. This has been easily observed with sound.  this means that the waves coming from an object moving away from you has a lower frequency.\n\nWhen dealing with light, these differences in wavelentgh and frequency actually leads to a change in color, because the different colors just correspond to different wavelengths of light.(speeds must be very high to observe these changes) When an object is moving toward us, the wavelength is shorter and the frequency is higher, so we observe a "blue shift" because blue has the highest frequency, and when an object is moving farther away, the frequency is lower and wavelenth is longer, so we observe a "red shift," since red has the highest frequency(lowest wavelength, it looks longer, see the 'diagram' i tried to represent above...) \n\nWell, we currently observe a red shift in other stars using strong telescopes, meaning that everything in any direction is getting farther and farther away from us and therefore, the universe is expanding.\n\ni hope i gave you some insight into some of the observations that are made before such a theory is created.  science has much evidence, which is why it is supported by so many intelligent people. scientists are very skeptical and will not believe anything unless proper evidence is presented to them, and even then will not really believe it, just admit that it may have happened that way. like the big bang theory, we didn't say "this is what happened, deal with it", we say "hey, it seems from the evidence that this is a possibility and makes a lot of sense... but it's still just a theory."
320815
The spectrum indicates the chemical composition of each star. As the chemical composition changes, the spectrum changes. However, because of the huge mass of stars, these changes are so slow they are not being "observed" by human astronomers. The relative velocity between each star and us is responsible for a shift of the whole spectrum. If a star is "approaching us", the spectrum is shifted towards the blue part of the spectrum. If the star "moves away" the spectrum is redshift.
170485
This is due to the doppler radar effect.  The wavelength of the reflected sound waves from an object travelling toward you is short (blueshift) whereas the wavelength from a receding object is long (redshift)
566837
By the red shifts of the measurement. Or to make a short story long it's the displacement of features in the spectra of astronomical objects, such as galaxies and quasars, towards the longer wavelengths, generally interpreted as a result of the Doppler effect due to their recessional velocities (i.e. how fast they're moving away from something) The expansion of the universe means that all but the nearest galaxies have redshifted spectra (in fact this is what led to the discovery of the expanding universe back in the 1920's). Hubble first described this back in 1925 that the redshift or recession velocity of a galaxy is proportional to the distance in relationship with the viewer. All that means is that by this redshift they were able to approximate the distance of these galaxies, and since they had these distances they could state them in light years (since light years is a distance, not necessarily a time)
5882
Definitely, we've even used Hubble to detect the flag & footprints. Our gov. would never lie about something on that scale. Considering the size of the universe, Its really not that big of an accomplishment to warrant an elaborate network of lies\n\nFor an incredibly in-depth analysis of pictures, facts and commentary please see the source link.
568245
Hi NY NY 2\n\nQuite a hodge podge of answers above.  let me see if I can clear some misconceptions up for you:\n\nFirst, the evidence. About 8 years ago two separate independent groups announced measurements of the brightness of supernova at a redshift z=1.  (Cosmologists use redshift factor "z" to show how far away something is in space-time by designating how far light from the object is redshifted by the time it arrives at earth.  The redshift is due to the expansion of the intervening space.  Redshift z=1 corresponds to a distance where the wavelength of light has been redshifted to double its original wavelength.).  These results indicated that the universal expansion was accelerating.  Since that time the results have been confirmed, and supporting evidence was found in the detailed mapping of the microwave background.\n\nSurprisingly (you might think) it is very easy to modify the equations which describe the universe's evolution to make the expansion accelerate.  The reason for this is that Einstein originally included such a factor in his early equations.\n\nBriefly, the equations for the universe at large scale talk about gravity and pressures.  Gravity tries to collapse the universe together and pressures push it apart (roughly).  When Einstein came up with his model (1915), everyone thought the universe was static (so called "steady state"), ie it didn't change over time.  So he included a cosmological constant to counteract the collapsing action of gravity and keep the universe steady.  This cosmological constant "pushes outwards" to counter gravities inward push.  By 1928 Hubble's catalogue had convinced people the universe was expanding (not steady) and physicists realised the cosmological constant wasn't required.  Einstein called its original inclusion "his biggest blunder".  It seems that call was wrong.  :o)\n\nNow the cosmological constant is coming back.  To describe an expanding universe you stick it back in and change the values for the density of normal mass-energy and the cosmological constant, and voila - an expanding universe.  The question then becomes: what does this constant physically represent?\n\nAt present cosmologists use the term "dark energy" to refer to a number of possible culprits.  From the equations we know the properties of this dark energy very well.  Some physicists link it to action of the quantum vacuum, some label it "quintessence" (the "fifth force").  \n\nIt is *not* (as suggested above) dark matter or antimatter.  Dark matter is invoked to explain galactic dynamics: galaxies tend to rotate in a fashion which suggests they have more mass than we can actually see.  This missing mass is presumed to be dark (which is why we can't see it).  Dark matter would act like ordinary matter in Einstein's equaitons, and so can't produce an accelerated expansion.  Antimatter also behaves gravitationally like ordinary matter and so it can't be responsible for accelerated expansion either.\n\n\nHope this helps!\nThe Chicken
147933
astronomers have stated that the universe starts from a big bang and eventually will start contracting and end in a "big crunch". \nIf you look at the theory of "red shift" means that the further away stars move, the less gravity there is holding the universe together. that means stars and galaxies will be travelling away from eachother at faster speeds. and the faster something moves away from eachother, it reflects a visible light lower down on the spectrum. So astronomers can calculate how fast the universe is expanding via redshift. \nSo whats to say it will end in a big crunch? \ni beleive it will, because like everything, it has to end. we breathe out (universe expanding) we breathe in (universe contracting.)\nofcourse this wont happen within the next 100 or even 100,000 years so there is nothing to worry about.
60291
A great intergalactic convergance?  A great cosmological simultaneity?\n\nIve noticed that I sometimes track people for a while but then diverge later.  Must be common furrows in the twisted convolutions of our collective brains.  Like passing someone slowly on the freeway.
462624
The space between the galaxies is what is expanding.  Imagine raisin bread being baked.  As the bread rises, each raisin moves away from every other raisin.  Another way to visualize this is by drawing dots on a balloon then blowing the balloon up.  As the balloon get's bigger, each dot moves further away from every other dot.  It's the same for galaxies.\n\nNow the expansion of the universe is only detectable at extremely large distances.  Nearby galaxies like M31 can move towards us.  But most galaxies we see are extremely far away, so almost all of them are receding from us.
567588
Actually you could see right through the nebula. Nebulae are extremely thin and much clearer than the air on clearest day on Earth. The only reason we can see them at all is that they are trillions of miles thick. It wouldn't be like the movies at all, where the space ship is hidden in a dense fog, it would be more like space looking clear but the stars appearing somewhat dimmer. So you could just triangulate on a number of known stars outside the nebula to determine your position.
4767
Check this out:  If our technological progress accelerated beyond our ability to understand it, how would we know?