what is the "Hubble Constant"?
361467
For most of the second half of the 20th century the value of H0 was estimated to be between 50 and 90 (km/s)/Mpc. The value of the Hubble constant was the topic of a long and rather bitter controversy between Gérard de Vaucouleurs who claimed the value was 100 and Allan Sandage who claimed the value was 50. In 1996, a debate moderated by John Bahcall between Gustav Tammann and Sidney van den Bergh was held in similar fashion to the earlier Shapley-Curtis debate over these two competing values. The Hubble Key Project (led by Dr. Wendy L. Freedman, Carnegie Observatories) significantly improved the determination of the value and in May 2001 published its final estimate of 72±8 (km/s)/Mpc. In 2003 the satellite WMAP further improved that determination to 71±4 (km/s)/Mpc, using a completely independent method, based in the measurement of anisotropies in the cosmic microwave background radiation.\n\nA value for q was measured from standard candle observations of Type Ia supernovae was determined in 1998 to be negative which implied, to the surprise of many astronomers, the universe is accelerating (see the article on dark energy).
814715
no. \nthe stress-energy tensor tells us how the energy is spread, and moves, across spacetime.\nthe gravitational constant is a parameter that determines to what degree 1 kg of mass (for instance) will "warp" the spacetime. \n\nso, you can't derive it from the einstein equation.\n\nin fact, relativists usually set the gravitational constant to = 1, so that they don't have to deal with it. although it's essential when you're trying to determine exactly what your physical predictions will be, it's not really an active element of einstein's theory. it just kind of sits there.
578190
I think you are confusing homogenous with constant. The fact that the universe consists of packs of matter separated by tremendous amounts of empty space makes it exactly inhomogeneous! However, because of conservation of energy, there is a constant interrelationship to the universe.
859100
It was Einstein!. General relativity predicted a model of the universe that could either collapse due to gravity or expand indefinitely. Einstein wanted a static universe,so he introduced a term (the cosmological constant) corresponding to 'negative' gravity or the energy density of the vacuum which causes empty space to accelerate all by itself! If you shove it on the right side of the equation that is..\nThen along came Hubble and burst his bubble..\nFound that the universe was expanding (Big Bang), so obviously the cosmological constant was not required!\nLatest measurements down at the edge indicate accelerating expansion though, so we may have to bring back the CC after all
696569
The Big Bang  is by far and away the most accepted theory as to the origins of the Universe. I would say that 90% of all cosmologists and astronomers subscribe to it.\n  This much we know as FACT: in 1964 two guys working for Bell Labs, named Penzias and Wilson, accidently detected white noise in outer space. This static was later found to be background residue leftover from the Big Bang. FACT: All galaxies are moving away from us; this is known by the color of "shift" they emit, due to the Doppler effect. a red shift indicates something is receding. The further out they are, the faster they move. This is known as the Hubble Constant.\n  So: we know there was a huge explosion that has caused everything to scatter, and we can determine age from gas spectography from stars, using burned out ones as a guidline. Therefore: Big Bang, about 15 billion years ago. There is no other theory out there that meets with even a fraction of the approval this does.
212965
The short answer is: about 72 km/sec/Mpc. \n\nkm=kilometers, sec=second, Mpc=megaparsec \n1 parsec=~3.26 light years, mega=million\n\n72 km/sec/Mpc is actually a measure of the Hubble constant, which we get from dividing the recessional velocity of an object such as a quasar by the distance the object is from us. Different people have come up with different numbers, ranging from 40-110 km/sec/Mpc, and there are groups working actively on this. In general, you can use 72 km/sec/Mpc for now.
988250
space is not infinite  although to us it is pretty much,  confused  great.  the universe is currently expanding, whether it will always continue to do so is due to critical density and mean density of the universe.     if critical density = (3i x hubbles constant^2)/ 8piG      if critical density is greater than average density then the universe will contineue to expand forever although it wont ever become infinite because the recession of the galaxies is limited by the maximum speed of light, and the fact that the universe had a begining therefore has a limmited size. \nalso  if average denisty is greater than critical density then the universe will be closed (hyperbolic) and the gravitational pull of the galxies will cause the universe expansion to slow and eventually contract. if critical density = average density then universe expansion will slow down universe would be flat, Most cosmologists believe that the universe is open and will continue to expand, which is nice, heres something nice to think about that if the universe is exapanding at the speed of light and the universe has been around for 1/Ho   1/hubblesconstant then the unverse is about 13 biliion years old this is 4.16x10^17 seconds  times the speed of light  3x10^8 ms-1 is  1.248x10^26m  in one direction   if the universe is spherical  which it isnt but lets pretent it is for an easier calculation then the Volume of the Universe is  4/3 pi r^3    is 8.142x10^78m^3   which is quite alot of space. As the amount of volume that real mass takes up is insignificant at these measurement  we can forget about it.   On the other hand light follows the shortest routes as mass distorts space it is likely that this answer is a bit smaller.  Oh and the universe isnt spherical its more like a ball thats been sat on,    So in summary the universe is not infinite but it is pretty much as it is likely to be expanding at the invariant maximum speed of light so your never going to hit the edge, infact there isnt an edge im not sure would happen if you got to the edge before the first radiation from the beggining of the big band reached the edge,   But i dont think youd get there,  well about your car  at the moment if your car takes up 6m^3  then theres enough space in the universe to hold 1.3x10^78  cars   but theres not enough matter in the universe to make that much cars  for that so dont worry too much about it, also in 1 second the universes volume increases by lots  uhhh     ok if the universe was 8.142x10^78m^3   rite this second  and the universe is exactly 13 billion years  old  (which its not) then in one second later the universe would be bigger yeas thats right  bigger by           ok one second is too small to make any effect on the calcullation,  but if it was a billion years older then it would be 1.016x10^79m^3  thats 2.02x10^78m^3 more than it was a billion years earlier which means it expansion is well logarithmic exponential whatever, the next billion year the universe would expand even more in the same time,   soo  thats even more parking spaces, if u look hardenough im sure you wiil find some.    No wonder i dont have a girlfreind.
468084
Greetings,\n\nKinda outta my league, but perhaps the link I posted can be of some use to you.\n\nDiscover had an article last year about a couple of inflation cosmology theorists who believed the speed of light, while constant now, was not constant in the very early universe, it was in fact slower.  Not sure about all that, but thought you might want to go digging for the article.\n\n-matt
1075536
No. There is no center of the expansion. Every place in the universe would see redshifts acting exactly the same way we see them. So if you were in a galaxy 4 billion light years from us and looked around,  the other galaxies would be moving away from you at a rate that is proportional to their distance from you. This happens no matter where you are in the universe.\n\nRemember that motion is relative. In other words, we don't say that some galaxy is moving at 400 km/sec. We say it is moving at 400 km/sec *with respect to us*. But if you look at relative motion with respect to any other galaxy, the expansion looks the same.\n\nOne problem with the term 'Big Bang' is that it encourages people to think of the universe expanding like the debris from a bomb. That is *not* how it is. There really is no center of expansion!\nNeat huh?
470012
A couple of years ago there was a study that said that the speed of light is not a constant. I need to look it up and see if I can find it. Now I'm wondering what the reason was behind that claim.\n\nYep, I found it:\nhttp://www.newscientist.com/article.ns?id=dn6092
155835
The problem is to tabulate the total mass of the Universe, a realy BIG problem.  There may be a lot of undetected dark matter in the universe that would shift calculations of the Gravitational Constant that will determine the fate of the Universe.  It is like trying to count the mushrooms in a totally blacked out cellar while blindfolded, or even much harder.  Progress is being made as the limits of the Universe are being explored by every means possible, especially by use of the human brain.
534809
Think about the angular size that anything we left on the moon would have when viewed from earth. The Hubble telescope is in near earth orbit, so it wouldn't make a difference that it is in space. So let's see.\n\nI don't have the exact figures for the LEM on the moon, but let's say it was 30ft across. The moon is 238 thousand miles away, so the LEM would have an angular diameter of .005 seconds of arc. The angular resolution of the Hubble is .05 arc seconds. This means that the LEM would have to be about 10 times its actual size to be detctable by Hubble.
216581
The cosmological constant attempts to quantify the repulsive force of negative vacuum pressure that explains the accelerated expansion of the universe that is unaccounted for by the amount of matter in the universe.\n\nIf you are religious, you could use the fact that in our universe this number could be called "miraculously" close to 1 as evidence for a creator. But then again, if it wasn't close to 1, we probably would not exist to wonder at how miraculous it is that its value is the universal equivalent of balancing a penny on a thin knife blade.
13401
It's true that the speed of light is constant no matter what speed at which you or the source is moving.  This is a fundamental postulate of relativity, and there is no explination.  It's just accepted because our experiments indicate that it is true.  You used the formula "lights speed + X = actual speed"  this type of velocity addition is called "Galilean".  It turns out that speeds don't actually add that way.  Far out.\n\nWhere is the rest of the energy? Good question.  The frequency of the light you observe from the sun DOES depend on how fast you and it are moving.  The energy of each photon is given by E = hf, where f is the frequency of light.
1450
Go to the website below...\n\nhttp://hubblesite.org/
138427
"Hubble" is named after an astronomer from the 20's, Edwin Hubble.  He discovered the fact that the universe is expanding, by measuring the red shifts of distant galaxies.  The Hobble Space Telescope was developed by NASA, and is currently managed by STSI (Space Telescope Science Institute) in Baltimore.
1112611
The universe expanded from an extremely hot and dense state approximately 13.7 billion years ago.  Scientists base this theory on the universe's background radiation and redshift of distant galaxies.  In 1929, Edwin Hubble (yes, the guy they named Hubble Telescope after) discovered that galaxies were moving in every direction at speeds directly proportional to their distance from Earth.  Two theories actually grew out of this.  One was the Big Bang theory, from a term for this theory used by Fred Hoyle during a BBC broadcast.  According the other theory, new matter was being created as the galaxies moved apart.  However, observational data came to favor the Big Bang theory, and it won out.