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EvC Forum ⇒ Science Forums ⇒ Big Bang and Cosmology ⇒

The accelerating expanding universe

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Author Topic:   The accelerating expanding universe
onifre
Member (Idle past 2977 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008

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Message 6 of 149 (550196)
03-13-2010 1:10 PM 		Reply to: Message 1 by Hoof Hearted
03-13-2010 4:40 AM

then that galaxy would be travelling away from us at the speed of light within only 700 million years.
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One thing to consider is that the galaxy itself is not moving, it is the space between the galaxies that is expanding.
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The further away a galaxy is from where ever you measure it from, the faster it will appear to be accelerating because spacetime is highly curved at cosmological scales. In an observational sense, it could appear to be exceeding the speed of light, meaning that one galaxy can't be observed from the other galaxy. But that doesn't mean it's violating the speed of light in a physical sense.
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- Oni
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onifre
Member (Idle past 2977 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008

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Message 11 of 149 (550462)
03-15-2010 5:25 PM 		Reply to: Message 8 by Taq
03-15-2010 3:15 PM

Hubble constant
Would this mean that Hubble's constant is not constant? That is, is Hubble's Constant higher for more distant galaxies than it is for closer galaxies (assuming they are not gravitationally bound)?
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Cavediver can correct this if I'm wrong but, Hubble's constant is exactly how Phage described it: it's directly proportional to the distance.
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See: source
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quote:
The law is often expressed by the equation v = H(o)D, with H(o) the constant of proportionality (the Hubble constant) between the distance D to a galaxy and its velocity v. The SI unit of H(o) is s-1 but it is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy one Megaparsec away.
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- Oni
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onifre
Member (Idle past 2977 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008

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Message 13 of 149 (550472)
03-15-2010 6:22 PM 		Reply to: Message 12 by Phage0070
03-15-2010 5:32 PM

Even though Hubble's constant is constant.
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If this helps, currently I believe the estimated value of the constant is: 71 (+/- 7) km/s/Mpc. Which is roughly about 13-14 miles per second per million light-years.
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- Oni
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