Hubble and Red Shift

Jerry

Hi, I'm sorta stuck on this thought: when Hubble discovered that the further out one looked the faster the galaxies are receding and concluded that the universe is expanding at an increasing rate, I wonder about the fact that he was also looking into the distant past...........
Wouldn’t one expect to see faster expansion in the past as this is what the Big Bang was all about? Doesn't this imply that actually the opposite is happening in the present (i.e. that the rate of expansion is slowing down)?

Marc

Jerry,

Yes you're right, one would expect that rate of expansion would be slowing down, but as with so many things in modern physics the intuitive answer is not always correct. There is no general consensus as to whether the rate of expansion of the universe is accelerating or not but recent observations point in that direction. How could this be happening? Well scientists have a few theories as to why this could be happening. Perhaps new fundamental forces are at work that we just don't understand yet and which only become apparent on massive scales? The postulated presence of "dark energy" and "quintessence" seem to shed some light on the area.
Check out: http://www.astronomytoday.com/cosmology/quintessence.html for more info.

Jerry

Thanks Marc, I'll check that out.

Jerry

Marc, thanks for the link, it's very interesting. I guess my question was not so much whether the universe is expanding or shrinking, but the fact that the argument for either case seems to be based on observing increasing amounts of red shift the further away one looks - as this extract from the link shows:

Turns out that the most distant Type 1a supernovae are moving away much faster then closer ones, suggesting that the universe's expansion is actually accelerating, not decelerating

If the most distant observed objects are say 13 billion light years away, then we see what recessional velocity they had 13 billion years ago, not what velocity they have now. So......how can it be concluded from those types of observations what the expansion rate of the universe is at the present time?

Marc

Well Jerry, not only do astronomers look at Galaxies 13 billion light years away they also look at galaxies in our Local Group and just beyond which aren't nearly so far away: anything up to 100 million light years (I think), which is a relatively small time ago on the Universe's scale. These are the measurements that are used in predicting how the universe is behaving now.

Hubble and Red Shift

Forum Options

Register