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Hi,

Got a small question for you folks.

We know from the Ultra deep field picture from Hubble and the radiation still detectable of the big bang that the universe is about 14 billion years old. The theory also say that universe is still expending.

I was wondering why they say that universe is 14 billions years old from a picture taken 12-13 billions light years away. I mean, that only mean that universe was that size, 12 billions years ago. That do not tell the current size ...

can anybody help me understand why they say universe is that age, and that size.

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The Universe VISUAL size(radius) is about 14 billions lights years because we can see objects within this distance. Also, it is saying us that the universe is 14 billions years old.

But... real size(radius) of Universe is bigger, about 47 billions lights years - because it is expanding. We can not see objects at, let say, 25 billions lights years because light from an object at this distance needs 25 billions years to reach us - more than Universe age.

Edited by FunkyKoval35
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Plus, when we're talking about light from the early universe, what you really need to look at is the Cosmic Microwave Background. This has been around since the Big Bang, and has cooled down to microwave frequencies over the past 14 or so billion years. Observations of the CMB are the basis of the evidence for the Big Bang and also for Inflation.

As Funky says, we can only talk about the Observable Universe. But the evidence for the age of the universe doesn't come from looking out and saying "I can only see 14 billion light years in that direction, so the universe must be that old." The universe has been expanding everywhere, in all directions, since it began, so it could be much bigger than we can see. And just to add a bit more spice, there's no requirement that the Universe's expansion be limited by the speed of light.

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Give it 50 years and this theory will have changed, like it has many times before and will keep doing so :smiley: Until one day when we will get it right.

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Give it 50 years and this theory will have changed, like it has many times before and will keep doing so :smiley: Until one day when we will get it right.

Maybe, but essentially there have been no big changes in the BB since it was first postulated about 80 years ago. It has had various different versions in terms of detail and lots of refinements in terms of measurements but it remains what it always was, a quite simple working backwards in time from the rate of expansion seen in the redshifts today. 

I think it's a mistake to expect science ever to 'get it right.' I don't believe it ever will and I'm far from sure that getting it right is even possible in principle. Science, in the end, makes descriptive models of reality as we perceive it. What we perceive and what 'is' might be miles apart or what we perceive might be all that there is.

I also think it's a mistake to think that the history of science is the history of chucking out yesterday's theory and replacing it with today's. That has happened and will happen again, but the majority of theories undergo refinement and, above all, greater generalization.

Olly

PS, If the BB has an Achilles' heel I'd say that it would be the way it depends on inflation which, after all, began as a 'fix.' But it may be what happened.

Edited by ollypenrice
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Don't get me wrong Olly as the whole topic is incredibly interesting........ :smiley: but it will change as science evolves and so it should.... I was referring more to the big bang theory as I feel we get carried away with some of the numbers.

Look how the Hubble and Kepler findings have added to and changed thinking in just a few short years.

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Of course if the next attempt at an Even Deeper Field finds still more galaxies then the BB really is in for the high jump. That would be fun!!  Cosmology would become the best funded science of them all...

Olly

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  • 4 weeks later...

Guys I have a question for you regarding the age of the Universe, Big-Bang and "time travel".

We all know that when we look at a galaxy @ 60 million light years away, we are practically looking back in time! We are now able to look back in time and observe our Universe when it was only 700-800 million years old (so  we observe a very young/primitive Universe - galaxies being born....etc).

So my question is: Isn't it possible that when we observe objects at 13.2 billion light years away, we could somehow observe our own Milky Way when it was very young ? :D I know it sounds like fantasy and I don't know if the laws of physics allows that but still it's a question that popped my mind last night when I was observing some galaxies!

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No, because our galaxy was never 13.2 billion light years away from us, it is simply "here".

You are not looking back in time you are looking at how an object was at a distance away - a light year is a distance.

You are observing something that was say a distance of 10 billion lights years away when the light left.

Owing to the 1:1 relationship people transpose the 2 terms of distance and time, it is easy to do so, possibly too easy.

You do similar on a car journey - the trip is 3 hours or 150 miles.

Suspect that if a parsec had become more standard it would seperate distance and time more. Your galaxy at say 10 billion light years distance is now about 3 billion parsecs, that is a simple distance and to an extent time is removed.

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  • 3 weeks later...

No, because our galaxy was never 13.2 billion light years away from us, it is simply "here".

You are not looking back in time you are looking at how an object was at a distance away - a light year is a distance.

You are observing something that was say a distance of 10 billion lights years away when the light left.

Owing to the 1:1 relationship people transpose the 2 terms of distance and time, it is easy to do so, possibly too easy.

You do similar on a car journey - the trip is 3 hours or 150 miles.

Suspect that if a parsec had become more standard it would seperate distance and time more. Your galaxy at say 10 billion light years distance is now about 3 billion parsecs, that is a simple distance and to an extent time is removed.

I think that you are looking back in time. If I post a letter to you on Monday sayng I'm feeling fine then I die on Tuesday and you get the letter on Wednesday, am I feeling fine or am I dead? On Wednesday I'm dead. When you read my letter you're looking back in time to Monday.

A light year is indeed a distance but a year is a time.

Olly

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Guys I have a question for you regarding the age of the Universe, Big-Bang and "time travel".

We all know that when we look at a galaxy @ 60 million light years away, we are practically looking back in time! We are now able to look back in time and observe our Universe when it was only 700-800 million years old (so  we observe a very young/primitive Universe - galaxies being born....etc).

So my question is: Isn't it possible that when we observe objects at 13.2 billion light years away, we could somehow observe our own Milky Way when it was very young ? :D I know it sounds like fantasy and I don't know if the laws of physics allows that but still it's a question that popped my mind last night when I was observing some galaxies!

Somebody is probably (not possibly) doing that right now!
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