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Just can't make sense of it. If we can look in one direction, and see an object 10 billion light years away, and look in the opposite direction and see an object 10 billion light years away, that would suggest a universe that was at the very least, 20 billion light years wide, 10 billion years ago. The universe has continued to expand in the mean time, and those two objects are even more distant from each other now.


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Neglected to type the implied question. If the universe is 15 billion years old, the two objects only had 5 billion years to get separated by 20 billion lightyear's distance, which means they were separated at a rate much greater than the speed of light. (twice the speed?). Isn't this impossible?

And if we would discover an object 11billion lightyears away, and look in the opposite direction with the same technology and discover a similar object 11billion light years away, that would put those two objects, each at an age of 4 billion years, with a separation of 22 billion lightyears. Hypothetical 12 billion lightyear distant objects, 3 billion years old separated by 24 billion lightyears, 2billion year olds by 26 billion lightyears, 1byearolds by 28bly, and so on, till we find the earliest things we can see, at the GREATEST distance of separation. Doesn't this imply that the universe was BIGGER when it was younger? Where am I going wrong?

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We really need Martin to answer this question.

 

But what I can tell you is that the objects are not moving at relativistic speeds in a traditional sense as the space itself is expanding, the space between objects is getting bigger. Even if the two galaxies were at rest with each other ignoring expansion then the space would be expanding at such a rate as to make them move apart at a speed greater than the speed of light.

 

This has other consequences as well, as the photons sent out from each of the galaxies is moving along space that is expanding, they have to travel much further than the original instantaneous distance would appear to have been, they are also frequency shifted

 

There is also the problem that you are reference frame mixing. Three objects

 

a----------------------------------------b----------------------------------------c

 

b measures the distance to a to b and c 13billion light years.

 

Object a will measure the distance different due to relativistic transformations, but even if you ignore this, the universe has only existed for a little over 13 billion years so the light from object c has yet to have time to reach it. It has no possible way of knowing that object c exists, this is why the night sky is black and not very very very bright indeed.

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Klaynos,

 

Thanks for the response. I think I have not, before, but do now, understand the role of expansion in imagining what is and has gone on in the universe. It has to be happening at a really rapid pace, though, to explain everything. Let me do some reading on expansion.

 

Regards, TAR


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Did a little reading. At 13km/s/Mpc, I suppose those far away objects that we are finding are receeding at what my rudimentary math, would put at about 1/2 the speed of light. But what sticks in my craw still is the fact that long ago, those objects were much closer to our location in space. Logic would suggest that object a can not be seen by object c because the expanse of space, now, is wider than light can travel in the time it has had to travel anywhere since the beginning of the universe. But, if we are talking about the objects a and c, that we are measuring, now, 13 billion years after the start of the universe, at 10 billion light years distance from us respectively, we are really talking about the image of a and c, when they were 3 billion years old. Now, if it took the light from 3 billion year old c, 10 billion years to arrive at our (b) location, it is going to take more that 10 million years more, to cover the distance from b to a across an already daunting and expanding distance. So I have no problem accepting that the light from 3 billion year old c, will never reach a's location in expanding space. However, this does not suggest that the light from location a never has, and never will, reach location c. The light from a 1 billion year old "location a" left "location a" when a-b-c where much closer together, and has had 12 billion years to make the trek to location c. Although I have not done the calculus, my intuition suggests that the light from 1 billion year old location a has already had the time to reach location c. How old location c was, is or will be, when the light from 1 billion year old location a reaches it, even if it is in the form of "background radiation", rather than an identifiable object, is not as important as DOES it. If it does, then I would guess that every location in space has a view of every other location in space, even if the view is of the location at a very very young age.

 

Regards, TAR

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if something expanda then it requires space outside. does it mean there is space outside universe also? atleast it must be when it was a point. for a point must be somewhere in space & expand to somewhere in space to occupy a volume.

 

No during the big bang there was no such thing as space, as space was confined to a singularity. So when the big bang occurred space it self was expanding. I know it has already been used but the best analogy is to imagine all of space as a balloon that is being inflated which means space is expanding. At the beginning of the big bang it was as if the balloon was crumpled up into a real small balloon representing that all of space was compressed into a singularity.

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But when they were closer together the universe was younger, so there was even less time for the light to travel... the expansion does not just effect the light being sent out 'now' but the light that has yet to arrive as well...

 

This isn't really my area of physics, Martin is the guy we really need here!

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Klaynos,

 

I am just trying to get a good picture of what did and is happening in the universe (generally speaking.) We will not see what is happening "now" anywhere in the universe until the light of the events get to us. We will have to wait 4.3 years to see what is happening "now" on Alpha Centauri. (But we can see now, exactly what was going on on Alpha Centauri 4.3 years ago.) We can only surmise that the rest of the universe is most likely pretty much like it seems to be around here, with strings of galaxies, clusters of galaxies, and voids. The objects we see 13 billion light years away, most likely tell us what things around here were like those billions of years ago. Those objects are no longer what occupies that location in space, that population III star, or whatever we see(in infrared) has long since become whatever population III stars became, and that location of space is probably inhabited by the children objects, or grandchildren objects of that population III star. "Now" meaning what that location of space is like, 13.7 billion years after the Big Bang.

 

I have wondered several times, in my readings in the last couple days, what people mean, time wise, when they say "the universe consists...". Are they talking about what is around here and figuring that is what the rest of the universe consists of as well, or are they making their measurements and calculations based on what they observe far away (and hence long ago.) If it is the latter, then they should be saying what the universe consisted of.

 

Regards, TAR

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Causally the light hitting us is allowing us to see 'now' there is no universal time.

 

We do actually use the observations of distant objects to study objects that were more likely to form at earlier stages in the universe.

 

There's something called the cosmological principle, might be worth reading about it...

 

http://en.wikipedia.org/wiki/Cosmological_principle

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Klaynos,

 

So still, I have a few questions. One is, when I read a finding, like "the universe is 158 billion light years wide", is that statement assuming a universal "now", and imagining the universe when all objects and locations in space are 13.7 billion years old?

 

Regards, TAR

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I just was thinking what is there next to the black space(universe is growing in a black space)

 

There is nothing next to the black space. The universe is not expanding into anything; the universe is everything.

 

Because there is nothing to compare it to as humans have no experience of "nothing" surrounding "something" it's a difficult concept to grasp.

There is no vacuum of space that contains "nothing" for the universe to expand into because technically a vacuum of nothing is infact something.

 

A good way to perhaps understand is an analogy of a young baby and how limbs and fingers start off small and with time grow - compare an adult with a child and you will see that arms and legs are much longer than a childs and this is because they've expanded and grown over time, the tip of the fingers is much further away from the base of the arms because the space between them has expanded.

 

The problem with this analogy is that people "expand" into the space around them where as space only expands......into nothing.

 

As said before, the best way to understand it is to not imagine "nothing" for it to expand into because "nothing" doesn't exist. The universe is everything.

Edited by Leader Bee
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Because there is nothing to compare it to as humans have no experience of "nothing" surrounding "something" it's a difficult concept to grasp.

 

I'm of the opinion this is fundamentally important to try and grasp, the fact that we can't can't grasp it...

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I have not had time to read the whole thread, but let me tackle a misconception which is evident from the first few posts.

 

The universe was not 'a point' at the moment of creation. It was still infinite. It is simply that the distances between different points in space tends to zero as you go back in time.

 

(Of course, saying it is infinite is a bit unphysical, so I really mean that it is always bigger than our horizon.)

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Anything before the big bang and the point of singularity can not quite franky be explained. Because the mathematics of general relativity break down, and obviously you can not do an experiment, but from what we do know about the big bang and singularity points there are some very credible ideas. For one since space-time started at big bang then its logical to view time at a stand still before the big bang. All the laws of thermodynamics and special relativity do not exist because time as a whole does not exist in essence nothing is moving not even the smallest subatomic particle, but also there never was anything to move to begin with. To conclude imagine the area before the big bang to be an infinite abyss of darkness.

Edited by relativist
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The big bang erased all trace of whatever existed before it. I doubt there was "nothing" before the big bang, but there is no way to prove it. It is hard to imagine what existed then. Something certainly existed before the big bang, the conditions that caused it.

AirBrush,

 

So far I like your answer (to Swaha) the best.

 

Regards, TAR

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Think of it as a balloon, if you press hard enough you can make a balloon into a small ball, if you press with unlimited pressure you can compress it into a point that is invisible. But if you release the pressure your balloon will take back it original shape, an object with a normal size. If you blow up this balloon you can see it expanding ( not exploding, it was not an explosion). There was nothing outside of the universe. No empty space, because the empty space is inside of the balloon. So the universe didn't expand into any space, its birth created the space which expanded.

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