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How long ago the big bang


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Er, no... the light leaving an object 10bn years ago will take 10bn years to get here... However, the object will have moved further away during those 10bn years so won't actually be where we see it.

I like the way people talk about the big bang as if it were fact. It is only a theory, not a proof ;)

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I am undecided about the big bang theory and if there was a big bang and everything is expanding away from it does that mean the part of the universe expanding on the opposite side of the big bang is now 28 billion light years away ???

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Indeed. It is a very flawed theory. If there was a big bang, then where's the point of origin? Certainly not here, unless we go back to being the centre of the universe again ;)

All we can describe is the limit of our observable universe, the furthest point of which does not represent the point of origin.

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Indeed. It is a very flawed theory. If there was a big bang, then where's the point of origin? Certainly not here, unless we go back to being the centre of the universe again ;)

All we can describe is the limit of our observable universe, the furthest point of which does not represent the point of origin.

IMO, flawed, but the best we have at the moment. The "point of origin" is surely anywhere/everywhere because the Universe was extremely small at the time - we were part of that as is everything else (matter, once it had condensed anyway) in the observable Universe.

Chris

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IMO, flawed, but the best we have at the moment. The "point of origin" is surely anywhere/everywhere because the Universe was extremely small at the time - we were part of that as is everything else (matter, once it had condensed anyway) in the observable Universe. Chris

All the sub-atomic particles and later atoms in my body were present in a pinhead singularity right here at the origin of the Big Bang 13.6 billion years ago and in that intervening time everything has expanded away from me. The same applies to you and everything else in the universe - everything once occupied that singularity :rolleyes:
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The way i look at it is by looking at the ring nebula and the star in the centre is the so called big bang and the ring as the aftermath ....it is spreading out in all directions..the opposite side of the ring to us would be moving away quicker than the sides even though it is all going the same speed.....but until we know where the edges of our universe are , we wont know where the centre is if there is one !

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I am undecided about the big bang theory and if there was a big bang and everything is expanding away from it does that mean the part of the universe expanding on the opposite side of the big bang is now 28 billion light years away ???

Things are not expanding "away" from the location of the big bang as when the bang happened it involved the whole universe, including here. That was 13.7 ish billion years ago, but the observable universe has a radius of 46.7 billion light years, because since then it has expanded quite a bit. Doubling the figure only works in static models of special relativity, but we live an Hubble universe."Opposite side" is also a misnomer - under most models of the bang, it does not matter where you are, as you always see the the light from the beginning after it has travelled for 13.7 billion years. If that wasn't true, then the earth would have to be at the centre of the actual universe, which is very unlikely, rather than the centre of the observable universe, which is pretty certain.

These are difficult concepts! - there are some nice animations here: http://www.phys.ksu.edu/personal/gahs/phys191/horizon.html which help explain it.

N

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Things are not expanding "away" from the location of the big bang as when the bang happened it involved the whole universe, including here. That was 13.7 ish billion years ago, but the observable universe has a radius of 46.7 billion light years, because since then it has expanded quite a bit. Doubling the figure only works in static models of special relativity, but we live an Hubble universe."Opposite side" is also a misnomer - under most models of the bang, it does not matter where you are, as you always see the the light from the beginning after it has travelled for 13.7 billion years. If that wasn't true, then the earth would have to be at the centre of the actual universe, which is very unlikely, rather than the centre of the observable universe, which is pretty certain.

These are difficult concepts! - there are some nice animations here: http://www.phys.ksu....91/horizon.html which help explain it.

N

cheers :smiley:

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Indeed. It is a very flawed theory. If there was a big bang, then where's the point of origin? Certainly not here, unless we go back to being the centre of the universe again ;)

All we can describe is the limit of our observable universe, the furthest point of which does not represent the point of origin.

I disagree. It is reasonable to say it was here provided you allow anyone, anywhere, in the universe to say the same. In the initial, unexpanded, BB, infinitely dense universe there was no difference between 'here,' 'there' or anywhere else. They were the same place. There was no centre, or, if you prefer, everywhere was the centre. This means 'centre' was not a very useful term back then and it still isn't!

The trouble is that every other 3D object in our experience can have a centre so we feel the BB universe should have one. That's just our problem. There is one fundamental difference between the BB universe and any other spatial object and this is what confuses us; all other objects can be seen or conceived of from the outside. The universe cannot. So the words we use for all other other objects and the ways in which we think about all other objects must be abondoned when we wish to think about the BB universe. It just is not like them and if we insist on thinking it must be then we have even less hope than ever of coming to terms with it.

As you say, the BB is a theory. Could you give me an example of a fact from anywhere outside mathematics?

Olly

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