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Ursprungligen postat av amo-bake
Du har missförstått mig, jag frågar inte om galaxens egenrörelse kring det lokala masscentrumet.
Om jag skall omformulera mig så frågar jag om hur snabbt galaxen expanderar i förhållande till en absolut stillastående observatör.
Varför skulle inte universum inte ha en mittpunkt ifall man tror på bigbang? Allt sprängdes ju från en solid massa, och då bör ju massan expandera åt alla håll med samma hastighet.
Det finns ingen plats i universum där en absolut stillastående observatör kan stå. Om du tror att universum har en mittpunkt enligt big bang så har du inte riktigt förstått hur Big Bang skiljer sig från en normal explosion. Galaxens expansion i förhållande till en absolut stillastående observatör går inte att avgöra eftersom det blir helt beroende på vart denna observatör står.
Jag citerar en lärobok i kosmologi beträffande universums centrum:
"In a conventional explosion material expands out from a central point. A short moment after the explosion starts the centre will be the hottest point. Later there will be a spherical shell of material expanding away from the centre until gravity brings it back down to Earth. The Big Bang as far as we understand it was not an explosion like that at all. It was an explosion of space, not an explosion in space. According to the standard models there was no space and time before the big bang. There was not even a "before" to speak of. So, the Big Bang was very different from any explosion we are accustomed to and it does not need to have a central point.
If the big bang were an ordinary explosion in an already existing space we would be able to look out and see the expanding edge of the explosion with empty space beyond. Instead we see back towards the big bang itself and detect a faint background glow from the hot primordial gases of the early universe. This Cosmic Microwave Background Radiation (CMBR) is uniform in all directions. This tells us that it is not matter which is expanding outwards from a point but rather, it is space itself which expands evenly.
It is important to stress that other observations support the view that there is no centre to the universe, at least in so far as observations can reach. The fact that the universe is expanding uniformly would not rule out the possibility that there is some denser, hotter place that might be called the centre, but careful studies of the distribution and motion of galaxies confirm that it is homogeneous on the largest scales we can see, with no sign of a special point to call the centre."
