How can we see a galaxy 13.4 billion light years away

[davethawley]

Ok, with a very big telescope I suppose is a good answer but....

2 assumptions
1) As we look at a galaxy we are looking back into time and across a distance.
2) The universe started out as a singularity

Now we can apparently look at a galaxy 13.4 billion light years away. This is how far it is away but also how old we are looking back - i.e. 13.4 billion years into the past.
The universe is about 14 billion years old
Since the light as taken 13.4 billion years to reach us it was 13.4 billion light years away 13.4 billion years ago

13.4 billion years ago is about 600 million years after the big bang
therefore the galaxy must have moved 13.4 billion light years in 600 million years - which is impossible.

I realise there must be a mistake in my understanding but I can't see it. Any ideas anyone

[Old_Geezer]

The space between constellations is being created giving the appearance of the constellations rushing away from us. Space does not have a speed of light limit to it's expansion as it is being created, not moving anywhere. I suspect this may be what is messing up your calculations. Light can find space being created in front of it at a rate similar to the speed it is travelling, so its journey takes a much longer time from our point of view.

[Frank97]

Assuming the the galaxy formed at the start of the universe then the galaxy as we are seeing it is 600 million years old, it took 13.4 billion years for the light from it to reach us so it is actually 14 billion years old now, I think.

[R1Geezer]

you are looking at where the galaxy was then and how it was then. It has probably. Al the stars would have long since died and created second/third generatin stars, the galaxy is somwhere else completey and entirely different.

[jomifl]

Dave has a good point, this is an issue that has puzzled me for some time. If the distant galaxy is moving at a constant speed it must be twice as far away as it appears to be so it must have moved at over twice the speed of light to get here then slowed down so that we can now see it. It doesn't make sense and explanations like space is being created don't quite explain it. We seem to be ignoring something important which has relevance to the assumption of continued expansion of the universe.

[R1Geezer]

There was an early phase of "inflation" shortly after the BB. Well that's what Cosmologists use to make the numbers work at least! All of this is theoretical and many holes exist. It's just the current state of thinking on the subject.

[wildwood]

In relation to Earth, that galaxy has not necessarily moved the same direction as us. It could be moving (as we see it) in any angle to Earth so has probably not moved 600 LY since the 'Bang'. Surely the universe id expanding outwards in all direction!?

Now I've got a sore head and need to lie down.

[jomifl]

R1..Am I to understand that the phase of 'inflation' that occurred 'immediately after the BB' took place when the present 'laws' of physics did not apply therby allowing stuff to travel faster than light (which didn't yet exist) and space to be any size,or not?

[Old_Geezer]

Difficult to get one's head around. My take on it at the moment is as follows:

Assuming our knowledge is correct then the universe is 14B years old.
But the universe will be more than 14B LY in radius since space is being created expanding it faster than that.

We can see another galaxy 13.4B LY away (even though we know that it will have moved further away since the light we see started its journey).

However the calculation 14 - 13.4 = 0.6 is not a useful one in this context because 13.4B LY (distance) will have been achieved in fewer than 13.4B years (time) due to the space creation between us and it.

[carlton23]

couldn`t agree more, ahem!!1

[Old_Geezer]

"In relation to Earth, that galaxy has not necessarily moved the same direction as us."

The motion is all relative, so you may take any reference point you wish. Where you sit at the moment, will be just fine.

There will be what for want of a better term I would call "genuine motion", as witnessed by the fact that not all galaxies are heading away from us: for example Andromeda seems to be heading our way. But as I understand it, most of the motion we see is down to this space creation causing inflation; so yes, generally speaking they are all heading away from us (or from any other point for that matter). I believe that, off at weird angles are not sufficiently significant / affective to be worth considering.

[R1Geezer]

yes jomifl that's how I understand it, that's the theory anyway, I'm a bit sceptical of this!

[Old_Geezer]

"therby allowing stuff to travel faster than light"

As I understand it that limit is set and inviolate. The thing about expansion is that it has much to do with creation rather than movement. Objects may appear to be moving apart faster than light, but it's really that space is being created between them; the objects need not "move" at all. Unless I misunderstood the scientific mags I read when time allows :-) Which is always possible.

[jomifl]

We are only discussing a galaxy that we can see, if that galaxy can get where it is without violating physical laws then there is no reason why the universe can't be very much bigger than we could imagine.
My explanation of all this is that space is staying the same size but matter is shrinking.

[JonnyBoy12]

It is a very big galaxy, I suppose!

[mibn2cweus]

We see the galaxy where it was then, not from where we were then but from where we are now.

[starone]

OMG I wish I never looked at this. My mind is boggling and my understanding is worse than ever. Come to think of it - it was non-existent to start with. Think I'll just lie down with a cold wet flannel over my forehead.

[modeller]

Since reading this thread I am struck by the original question of ' seeing a Galaxy '.
We may see the light or detect the radiation but seeing implies recognising the object.
I may be able to see the light of a candle a mile away but I can't see the candle.

As for the size of the universe if that means all the space then how can it be expanding into something that isn't there.

[mibn2cweus]

A galaxy is implied by the characteristics of the light emitted, red shifted as would be expected for a galaxy at that distance and from that time.

The universe makes its own space by virtue of expansion. There are no known dimensions outside of the universe into which it can expand. The dimensions of the universe exist by virtue of the universe, they are part and parcel of the universe itself.