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dshima
2011-Mar-28, 02:58 PM
OK...this my big problem,....
the universe started out in the finite past with a minuscule size. All we had at the time was in this minescule size, so from our point of view big bang happened everywhere and spacetime was all there together...
Nonetheless the Universe is expanding...which means it wasn't everywhere to begin with.....
...Worse if everything is accelerating away from everthing else, and by looking at deep space we can see 14 billion years into the past (cos thats how long the light has taken to reach us) how come its so far away....the light of 14 billion years ago should all be together in the same place....


Help

Shaula
2011-Mar-28, 03:07 PM
Something can expand without expanding in to pre-existing space. The usual analogy is a balloon. You have to imagine that there is no third dimension for this to work... If you blow up a balloon then the two dimensional surface expands - but not into pre-existing 2D space. The universe is believed to be a higher dimensional analogue of this.

Note that the age of the universe is nearly 14 billion years - we have never seen anything that old. We have only seen 13 billion year old light - so it is not the light that should have been everywhere. The universe was already large by that point. The light that was everywhere is out there, massively stretched, and called the Cosmic Microwave Background Radiation (CMBR). We can see and measure that and use it to test our models of the very early universe.

dshima
2011-Mar-28, 04:22 PM
Hi Shaula,

I can understand the ballon expansion... When we see a distant star/galaxy it is already 13 billion years down its path...so is everything travelling in a straight line away from us?...(except Andremeda?) I can see a time when we can see 14 billion plus years backwards (The NICMOS images are said to be within 400 million years of big bang) so when that happens will we see all the light in one place? Look something is wrong...logic (what's that got to do with creation) says if the Universe is 14 and a bit Billion years old...then when we look back that far in time we should see the start, where everything is closer together....but the oldest light is incredibly far away in all directions.

antoniseb
2011-Mar-28, 04:55 PM
... so when that happens will we see all the light in one place? ...

The Cosmic Microwave Background was emitted about 380,000 years after the Big Bang. As far as photons go, that is about as far back as we will ever "see". There are some interesting geometrical relationships that are fun to try and conceptualize owing to the fact that the size of the warm and cold regions at that distance, are much smaller than the angle and distance would suggest. I say this to point out that you are asking about a very interesting but perhaps underdiscussed topic for armchair cosmologists.

Hornblower
2011-Mar-28, 04:56 PM
I am sorry, but I cannot visualize what the OP means by old light being far away. Old light which we are seeing now is right here, entering our eyes or, in the case of the microwave background, our radio telescopes. It left whatever emitted it long ago, and has covered the intervening space in the meantime.

When our expanding universe is back-extrapolated to the presumed initial state, any sort of position relative to us becomes indeterminate. That is the predicament we call a singularity.

csmyth3025
2011-Mar-28, 05:07 PM
OK...this my big problem,....
the universe started out in the finite past with a minuscule size. All we had at the time was in this minescule size, so from our point of view big bang happened everywhere and spacetime was all there together...
Nonetheless the Universe is expanding...which means it wasn't everywhere to begin with.....
...Worse if everything is accelerating away from everthing else, and by looking at deep space we can see 14 billion years into the past (cos thats how long the light has taken to reach us) how come its so far away....the light of 14 billion years ago should all be together in the same place....


Help

One way to look at this is that 13.7 billion years ago we (or at least some of the neutrons, electrons and protons from which we're made) were inside a very hot oven. High energy photons were zooming in from all directions around the place where our planet would eventually form.

In very simple terms, that "oven" is now a lot bigger. The temperature of all that original heat (photons) has spread out to fill that volume. This is the reverse of what happens when you compress air. The air goes in at normal pressure and room temperature and comes out at high pressure (smaller volume) and high temperature.

We're still in the "oven" that was the original (very small) primordial universe. The oven's heat (radiation) still surrounds us and is coming from all directions. We call it the Cosmic Microwave Background. The universe has gotten so big by now that the very hot and tiny oven we were in 13.7 billion years ago is now a very big oven with a temperature of about 2.7 degrees above absolute zero.

Chris

dshima
2011-Mar-28, 06:12 PM
Hi, prehaps I am not explaining myself very well....I can understand the balloon/oven expanding universe concept bit....well prehaps not understand but at least see what is meant.

In such a concept everything exists and stars/universes formed 13 billion years ago emit light and we can 'see' them. We can see the sun, near stars etc. We can also see the distant galaxies. We see the light they emited some time in the past...8 minutes in the case of the sun...13 billion years in the case of a distant galaxy. Now in that 13 billion years its reasonable to assume that they have travelled, (processed...does that only apply to near stars?) across the sky. Infact they should have travelled from a point near to where they started...near where they all started....yet the light we see...which I am told is 13 billion years old is not close to other light and the oldest galaxies, which emit the oldest light are the furthest away.

Something is wrong....very possibly my understanding of what we are told...but in that case can someone please explain it to me.

Just to throw in another twist...I now see that although the universe is only 14 billion years old its actually 78 billion light years in radius, 156 billion in diameter (give or take a few feet). Again I can sort of understand that the difference is accounted for by the expansion of the universe except doesn't that mean that light...all light...is travelling at the speed of light, plus the speed of the expansion...or faster than the speed of light.....

Shaula
2011-Mar-28, 06:32 PM
...so is everything travelling in a straight line away from us?...(except Andremeda?)
Yup - on a macro scale everything is on average receding from us with a velocity equal to its distance multiplied by a constant. The constant isn't quite constant but hey! Near enough.


I can see a time when we can see 14 billion plus years backwards
Read the Wikipedia article (http://en.wikipedia.org/wiki/Observable_universe) and then go from there. Might help.


so when that happens will we see all the light in one place?
No. Light moves. That oldest light filled the early universe, stretched out with it and formed the CMBR as previously mentioned.


Look something is wrong...logic (what's that got to do with creation) says if the Universe is 14 and a bit Billion years old...then when we look back that far in time we should see the start, where everything is closer together....but the oldest light is incredibly far away in all directions.
We can see the oldest light, as close as possible to all the light being in one place. It is here, it is there, it is everywhere. It is the CMBR.

When we talk about seeing back in time it is a lazy way to say that we are seeing light emitted by bodies a long time ago, light that has had to travel to reach us. If we do look back we see a different universe but we can't see right back to the start. For one thing there was a period when the universe was opaque to light due to it being ionised. You need to read up on recombination (http://en.wikipedia.org/wiki/Recombination_%28cosmology%29) too - the intro to this tells you where the earliest light comes from and when. At 500 million years after the Big Bang the universe has evolved a long way - galaxies existed and we see smaller ones merging and all sorts of odd things like that.

speedfreek
2011-Mar-28, 08:31 PM
Perhaps I can help here.

We see the oldest light, the CMB, coming from all directions. If light all travels at the same speed, that means that at any time, the CMB we detect was originally released from a certain distance away, in all directions. We can think of it a set of coordinates that represent where the CMB was emitted, and those coordinates form a sphere around us, with us at the centre.

We think that, at the time the CMB was released throughout the whole universe, the CMB photons we detect today were only around ~40 million light-years away, heading towards us from all directions. The reason that distance is relatively small is because the universe was relatively small at that time. The reason that light didn't reach us long ago is because the universe was expanding so fast at the time it was released - so fast that, from our point of view here, it is as if that light itself was receding from us, due to the distance in between "here" and "there" increasing so fast. It eventually reached us here 13.7 billion years later, partly due to the deceleration of the expansion rate (it would have reached here eventually despite that, unless the expansion started to accelerate).

All the matter in the observable universe was within that 40 million light-year radius when the CMB was released. All the galaxies that we observe, that formed thereafter, formed in places that were originally closer to us than the place where the CMB was released, but all those places are expanding with the universe. Today, we think the place where the CMB we currently detect was originally released from is over 46 billion light-years away, in all directions!

The upshot of all this is that as we look out into the universe, we are looking backwards through time. As we look at light that has been travelling for a very long time, emitted when the universe was young, we are seeing the universe as it was when it was a lot smaller, but we have always been surrounded by it in all directions. The oldest light comes from a time when we were surrounded by a visible universe only 40 million light-years in radius.

If we could see all the way back to the big bang, we would see it happening right here.

WayneFrancis
2011-Mar-29, 01:06 AM
OK...this my big problem,....
the universe started out in the finite past with a minuscule size. All we had at the time was in this minescule size, so from our point of view big bang happened everywhere and spacetime was all there together...
Nonetheless the Universe is expanding...which means it wasn't everywhere to begin with.....
...Worse if everything is accelerating away from everthing else, and by looking at deep space we can see 14 billion years into the past (cos thats how long the light has taken to reach us) how come its so far away....the light of 14 billion years ago should all be together in the same place....


Help

I'm going to focus on this one statement


...which means it wasn't everywhere to begin with.....

Yes it was. There are 2 ways that we can look at the universe
1) The that universe is infinite in size.
or
2) That the universe is finite in size but unbounded.

Both have a similar answer. The "Expanding" isn't into a pre-existent space. It is just just an expansion of that space.

By definition the word "Universe" means all that there is. If the universe is getting larger in volume then you can say it is expanding. The issue here is not to think of it as growing in some space that it may eventually fill up or that is even there. It is just expanding. That is it. It might not sit well with you because you can't visualise it but hey that's ok. It isn't something we are exposed to evolutionary wise so its a concept that won't come natural to people. Just like quantum mechanics is very foreign to our common sense view of the world.

The universe is what it is. Sometimes we use words and analogies to try to describe the universe or some trait of it but remember that will always fall short. Just as if you try to describe a person you'll fail at some level of detail.

Now...

....the light of 14 billion years ago should all be together in the same place....

The exact opposite is actually the case. The light from ~14 billion years ago is EVERYWHERE and it never stays in one place, it just keeps travelling. The photons that pass through us are only a VERY small portion of all the photons that where created in the early universe. The amount is equivalent to the area you take up on the surface of a sphere that is roughly 14 billion light years in diameter.

WayneFrancis
2011-Mar-29, 01:12 AM
Hi, prehaps I am not explaining myself very well....I can understand the balloon/oven expanding universe concept bit....well prehaps not understand but at least see what is meant.

In such a concept everything exists and stars/universes formed 13 billion years ago emit light and we can 'see' them. We can see the sun, near stars etc. We can also see the distant galaxies. We see the light they emited some time in the past...8 minutes in the case of the sun...13 billion years in the case of a distant galaxy. Now in that 13 billion years its reasonable to assume that they have travelled, (processed...does that only apply to near stars?) across the sky. Infact they should have travelled from a point near to where they started...near where they all started....yet the light we see...which I am told is 13 billion years old is not close to other light and the oldest galaxies, which emit the oldest light are the furthest away.

Something is wrong....very possibly my understanding of what we are told...but in that case can someone please explain it to me.

Just to throw in another twist...I now see that although the universe is only 14 billion years old its actually 78 billion light years in radius, 156 billion in diameter (give or take a few feet). Again I can sort of understand that the difference is accounted for by the expansion of the universe except doesn't that mean that light...all light...is travelling at the speed of light, plus the speed of the expansion...or faster than the speed of light.....

One key thing to know is that the VISIBLE universe is that big. The actual universe is much much larger ... it is just that we can't see it yet. comoving distance is not an easy concept to grasp especially when you're not comfortable with the properties of light. Perhaps someone has a good link to a video of the expansion of space?

WayneFrancis
2011-Mar-29, 01:15 AM
Perhaps I can help here.....

Well put

dshima
2011-Mar-29, 09:22 AM
Thanks everyone....your insights and answers go a long way to answering my original question.......I still think the question is only partially answered and I suspect that when we have more sensitive instruments we will find 'light' further away than can be explained by current thinking.......I need to read a lot more and expand my knowledge so that I can answer the same question.......but from a different perspective.

Amber Robot
2011-Mar-29, 09:05 PM
I suspect that when we have more sensitive instruments we will find 'light' further away than can be explained by current thinking.

I think we will be hard pressed to find light from farther away than the surface of last scattering.

WayneFrancis
2011-Mar-30, 12:32 AM
Thanks everyone....your insights and answers go a long way to answering my original question.......I still think the question is only partially answered and I suspect that when we have more sensitive instruments we will find 'light' further away than can be explained by current thinking.......I need to read a lot more and expand my knowledge so that I can answer the same question.......but from a different perspective.

It is impossible to see light from further away then the CMBR because the CMBR is the first light that was free to travel uninhibited through the universe. In the future we will see light that is older and further away then now but that is only because there will have been more time passed since the CMBR was produced. I'll predict that that light will have a longer frequency then the CMBR now...we might not be able to measure that difference for a long time tho.

What "different perspective" are you alluding to?