Re: Distant objects
- From: John Kennaugh <JKNG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 30 Jan 2006 19:20:29 +0000
wrote:
Hey,
I have a question about very distant objects in the universe that I keep reading about on the internet. It's been a while since I read about relativity and such but if I remember correctly light always travel at the speed of light relative any observer. So if we observe something that is 12 billion lightyears away, the light must have taken 12 billion years to reach us. The only way for this to be true is if the object was 12 billion lightyears away from us at the time the light left that object, which means it was 12 billion lightyears away 12 billion years ago. Is this correct? I'm asking this because I read about some very bright early galaxy or similar object that was said to be 12 billion lightyears away. For this to be possible the universe would have to be at least 12 billion years old at the time the light left that object, would it not?
Forget the age of the universe think of the age of the object. Because it is travelling away from us at a speed which is an appreciable proportion of c, time dilation says that it isn't ageing very quickly at all. I think latest estimates make the age of the universe about 14.5 billion years old. If you don't take time dilation into account then even if we were separating from a distant object at c it would take 7.25 billion years to get 7.25 billion light years away from us and if the light set out then it would only reach us now so we could never see anything older than half the age of the universe.
It is claimed that we can see objects only a few million years after the big bang. If objects were travelling away from us at c then according to relativity the object's time would stop so in theory we could see the big bang itself (ignoring inflation and such) except that we couldn't actually see it because at c all light would be Doppler shifted to zero frequency. For an object travelling at nearly c we can see nearly back to the BB because it is ageing only very slowly. That is assuming you believe in BB theory which seems to be in a bit of trouble at the moment, and if you believe in relativity.
The alternative to relativity theory, ballistic theory, actually predicts the exactly the same thing observationally. It says that the speed of light is c relative to the source so if something is travelling at a velocity v which is an appreciable proportion of c then the speed of light relative to us is c-v so it may have left the object only x million years after the Big Bang it has taken 14.5 billion years to catch us up because of the relatively low value of c-v. Again if it were travelling at c then c-v = 0 we would travelling at the same speed as the image and permanently see it as it was at the Big Bang but again we wouldn't see anything because it would again be Doppler shifted to zero.
Of course Ballistic theory does not say that an object couldn't travel away from us at greater than c but we would never see the light from it because it would never catch us but it might account for some of the missing mass in the universe :o).
Assuming it couldn't have traveled away from us faster than the speed of light and we started in the same place at the big bang. That would make the current age of the universe at least 24 billion years, but I have read it's estimated at much less than that..
Where did I go wrong? =)
Hope I have helped.
-- John Kennaugh to email convert the number from hex to decimal .
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