# The Naked Scientists Forum

### Author Topic: Where are we in the Universe?  (Read 8061 times)

#### Airthumbs

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##### Where are we in the Universe?
« on: 11/04/2011 03:45:21 »
So here goes, something that has been nagging me in my sleep recently.

Recently in science news we have been informed that scientists, using Hubble, have been able to look far out into space, don't quote me on this but something like 13 billion light years...... We are informed that this amazing distance is essentially like looking through history, back in time, so to speak 13 billion years!!

Apparently the Universe is about 13.7 billion years old.  This would indicate that the Hubble image was getting pretty close to actually seeing the origin of the universe itself, but, and for me it's a big BUT, what if now Hubble was then directed in the complete opposite orientation to that of the image going back 13 billion years.  Now we have a problem, if Hubble can look in both directions for 13 billion light years then already we have a universe that is more then 26 billion light years in diameter!

Someone will have an answer I am sure but I have another point to raise.  If the universe has expanded faster then the speed of light then to state that one light year is a measurement of time and distance is false?  In actual fact, let me try and get this right, if the universe has expanded faster then the speed of light then the image that Hubble took would be a lot less then 13 billion light years in distance.  Lets say the universe is expanding at 13 times the speed of light, just for simplicity, then the image Hubble took would only really be looking back over an actual distance of 1 billion light years. Or would that be the other way round!?

And then this leads me to my question, where in the universe are we?  Of course I suppose if the Universe has in fact been expanding faster then the speed of light there would be no way to tell where we are within it.  Still it would be nice to know :-)  Any ideas?

#### briligg

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##### Where are we in the Universe?
« Reply #1 on: 11/04/2011 04:54:25 »
Someone else will get to this and give you much better answers, but let me make a beginning. The big bang created the universe - space did not exist before that, it was created by the big bang. Since it created space itself, it didn't occur just in one spot - it happened everywhere. Yes, at the time it was all packed tightly together, then it expanded - but space itself expanded, it didn't expand into space that existed before it. Everywhere you look, you are looking into the earlier history of the universe, but that doesn't tell you how big the universe is. I don't know that anyone has any theory about how big it is - how old it is, is a separate issue.

#### briligg

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##### Where are we in the Universe?
« Reply #2 on: 11/04/2011 05:00:39 »
The Hubble Deep Field image gets mentioned a lot - Hubble looked into a tiny dark patch of our sky for a long time to see what there was in the deepest part of space we can see - and the image came back filled with galaxies. Lots and lots of them. Just like around here. There was no sign at all of some sort of limit.

#### Airthumbs

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##### Where are we in the Universe?
« Reply #3 on: 11/04/2011 05:05:24 »
Thanks for your response brilligg, I don't mean to be argumentative but supposing the universe was created in a big bang, then this origin as you could call it would have had to have come from a single point.  To state that it happened everywhere at once would be like saying the Universe is infinite which it is not.

Also the Deep Field Image that Hubble took does not show galaxies the way they are around here at all, but in fact shows them in a much younger state!

Scientific results of Hubble Deep Field

High rates of star formation during the very early stages of galaxy formation, under a billion years after the Big Bang.[3]
Improved characterization of the distribution of galaxies, their numbers, sizes and luminosities at different epochs, allowing investigation into the evolution of galaxies.[3]
Confirmation that galaxies at high redshifts are smaller and less symmetrical than ones at lower redshifts, showing the rapid evolution of galaxies in the first couple of billion years after the Big Bang.[3]

source: http://en.wikipedia.org/wiki/Hubble_Ultra_Deep_Field

« Last Edit: 11/04/2011 05:18:35 by Airthumbs »

#### briligg

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##### Where are we in the Universe?
« Reply #4 on: 11/04/2011 16:04:11 »
Supposing the universe was created in a big bang, then this origin as you could call it would have had to have come from a single point.  To state that it happened everywhere at once would be like saying the Universe is infinite which it is not.

Yes, it came from a single point. That single point contained not only everything that later became matter and energy, but also everything that became space, too. And time, too, for good measure. Is it really that much more mind-boggling to consider that these things also came from the big bang, since we are already talking about every particle in the universe being squished into one point?

Also the Deep Field Image that Hubble took does not show galaxies the way they are around here at all, but in fact shows them in a much younger state!

Alright, i wasn't clear there. The galaxies in the Deep Field image are just like the ones around here in their younger days. Because they are so far away, we see them when they were very young, but they seem very much like they were on their way to evolving into exactly what we see around us in our galactic neighbourhood. I said that the way i did to try to make the point that there was no discernible difference between the universe out there, and the universe around here, other than that spot looks younger, although it isn't anymore. There was no sign that we were seeing different conditions that might indicate a boundary to the universe nearby.

It is easy to see how the image you posted can be misleading. It shows the Hubble telescope looking into deep space to look backwards in time, but the layers it shows don't actually exist. The photons Hubble detected were here, not there. They were 13 billion year old photons, which landed on Hubble's detector. (It seems a shame to destroy something so old that has traveled so far, doesn't it? But to be detected, they had to be absorbed.) The galaxies Hubble looked at are now just as old as the ones around here (and some will have smashed together to form bigger ones, or been torn by gravity into smaller ones, and so on). The radiation that looks like an outer wall to the universe in the picture exists all over the universe, everything in the universe is floating in it. It is called the Cosmic Microwave Background, reading the Wikipedia article on that will explain how that radiation was used to determine that the universe is expanding. The right sidebar in that article has links to all the other major subjects of physical cosmology.

If there is a 'boundary' to the universe that we can detect from here, it is the event horizon of the universe from our point in it. That would be the distance at which everything further away is moving away from us at faster than the speed of light, meaning photons from objects beyond that distance can never reach us. We would only see a silky smooth blackness, in every direction, beyond that distance. We may in the future build a super-telescope that can see that keenly, and it may show us that blackness. But that wouldn't be to say there aren't things beyond that distance, nor would it help us to determine the size of the universe.
(p.s. - things moving faster than light is allowed under general relativity in this situation.)
« Last Edit: 11/04/2011 16:32:19 by briligg »

#### Pikaia

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##### Where are we in the Universe?
« Reply #5 on: 11/04/2011 16:17:33 »
To state that it happened everywhere at once would be like saying the Universe is infinite which it is not.

The universe does seem to be infinite, and always has been. To say that it is finite is to say that it has a boundary, which makes no sense, or else some weird geometry, which is not supported by observation.

#### JP

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##### Where are we in the Universe?
« Reply #6 on: 11/04/2011 16:58:46 »
Recently in science news we have been informed that scientists, using Hubble, have been able to look far out into space, don't quote me on this but something like 13 billion light years...... We are informed that this amazing distance is essentially like looking through history, back in time, so to speak 13 billion years!!

I think briligg and Pikaia have answered the question as well as I could, but just to nitpick a tiny bit, the visible universe is ~14 billion parsecs in radius.  The universe is  roughly 13.7 billion years old, but since it's been expanding, the light arriving at the Hubble from that time actually corresponds to things much, much further away (14 billion parsecs is roughly 40 billion light years.)  This is possible because if you imagine the light as a wave traveling from a distant star to the earth, the front of the wave always moves through the space around it at the speed of light, even if the tail is being pulled further away from us.  In other words, the wave is free to stretch, and pulling the tail back doesn't slow the tip of the wave down.  Because of this, the head of the light reaching us has never moved faster than the speed of light, and yet the entire light wave appears to be longer than 13.7 billion light years.

#### briligg

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##### Where are we in the Universe?
« Reply #7 on: 11/04/2011 18:18:36 »
Props from JP - yay!
There are some aspects of this i wonder about, as i have now divulged everything i know (and i strongly suspect i am basically parroting a very similar explanation i think i heard some years ago, which i think was even a gripe from a cosmologist over a diagram very similar to the one Airthumbs posted).

I take it we can't say how large the universe is because although we know when the big bang happened, and we know how fast the universe is expanding, and has expanded in the past, we don't know how much stuff was in the big bang in the first place. This Wikipedia article seems to be the best one for explaining cosmic inflation in general:
http://en.wikipedia.org/wiki/Metric_expansion_of_space#Understanding_the_expansion_of_Universe
At one point that article says:
Quote
the question "why is the universe expanding?" is now answered by understanding the details of the inflation decay process which occurred in the first 10−32 seconds of the existence of our universe. It is suggested that in this time the metric itself changed exponentially, causing space to change from smaller than an atom to around 100 million light years across.
Does that refer to the observable universe inflating to 100 million light years across, or the whole universe? Because wouldn't we be able to plug in the expansion rates to get a size for the whole universe, if we knew its size at any time?

Here's a gem from that article talking about how space has no edge:
Quote
Finite space theory does not suppose space has an edge, but rather that space wraps around on itself. If it were possible to travel the entire length of space without going faster than light, one would simply end up back in the same place, not unlike going all the way around the surface of a balloon (or a planet like the Earth).

#### Airthumbs

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##### Where are we in the Universe?
« Reply #8 on: 11/04/2011 19:25:10 »
Thank you everyone for your answers, I am going to need a little bit more time to absorb them all in there entirety.

I have to say though I have never really felt comfortable that the Universe can be potentially expanding faster then the speed of light and yet at the same time is infinite!

Is it really necessary that for the Big Bang theory to work there had to be nothing before?  I support the theory that our universe is just one of many and if that is the case then how can they all be infinite?  I suppose I could relate to this infinity if it were somewhat like a 3 dimensional Mobius strip!

#### JP

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##### Where are we in the Universe?
« Reply #9 on: 11/04/2011 19:50:28 »
Airthumbs,

One of the ways I understand it is that if the universe is and always was infinite, then it's possible to squeeze it down so that it's infinitely dense, but still infinitely large.  As I understand it, that's what the state might have been like the instant after the big bang.  It's a mind-boggling concept to think about something infinitely big so that you can squeeze it and it's still infinitely big, but it's one of the possibilities for the universe.  When you're trying to describe the whole universe it makes sense that you get some mind-boggling concepts.

As for what happened the instant before the big bang--that question confuses me to even think about.  If time and space were created by the big bang, then does "before" even mean anything?  Certainly it can't in the sense we're used to thinking about things, since time didn't exist!  And when we get to the nearly infinitely dense early universe do concepts like time and space as we know them mean the same things we're used to?  I don't think anyone knows the answer to those questions, though string theorists and those working on similar theories are looking for them.

#### Pikaia

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##### Where are we in the Universe?
« Reply #10 on: 11/04/2011 20:37:46 »
Quote
I have to say though I have never really felt comfortable that the Universe can be potentially expanding faster then the speed of light and yet at the same time is infinite!
I also have trouble with the idea that we can be standing still in our frame, a distant galaxy is also standing still in its own frame, yet the space in between is expanding! How can nothingness expand?

In this sort of situation you simply have to accept what Science tells us, and not try to understand it in everyday terms, because our intuition is inadequate. Some people never learn that lesson.

There are many similar examples in Relativity and Quantum Mechanics, and even Newtonian Physics sometimes violates our intuition (eg gyroscopes).

Quote
Is it really necessary that for the Big Bang theory to work there had to be nothing before?
No it isn't, and I have never understood why people equate the BB with the origin of the Universe.

To quote Scientific American on Looop Quantum Gravity:
"Einstein’s general theory of relativity says that the universe began with the big bang singularity, a moment when all the matter we see was concentrated at a single point of infinite density. But the theory does not capture the fine, quantum structure of spacetime, which limits how tightly matter can be concentrated and how strong gravity can become. To figure out what really happened, physicists need a quantum theory of gravity.
According to one candidate for such a theory, loop quantum gravity, space is subdivided into “atoms” of volume and has a finite capacity to store matter and energy, thereby preventing true singularities from existing.
If so, time may have extended before the bang. The prebang universe may have undergone a catastrophic implosion that reached a point of maximum density and then reversed. In short, a big crunch may have led to a big bounce and then to the big bang."

http://www.scientificamerican.com/article.cfm?id=big-bang-or-big-bounce

I find this idea seductive because it allows the Universe to be infinitely old, just as it extends to infinity in the other direction of time, and also in space, which seems more elegant to me.

#### Ron Hughes

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##### Where are we in the Universe?
« Reply #11 on: 11/04/2011 22:55:06 »
How do we know that space did not exist before the BB?

#### Airthumbs

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##### Where are we in the Universe?
« Reply #12 on: 27/04/2011 01:59:54 »
Could Space exist without time.....?

#### yor_on

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##### Where are we in the Universe?
« Reply #13 on: 27/04/2011 19:51:29 »
Nope, not as I see it. Without an arrow there would be noting 'singular', like a linearly temporally working consciousness (like a human) to observe anything. We build our explanations in, and from, a temporal 'arrow of time'. But on a quantum plane probability seems to step in and do the 'thinking' defining 'reality'. But how such a 'consciousness' functions I wouldn't dare guess, and neither do I know what it sees. SpaceTime seems to be able to be seen in several ways, and we constantly seem to be finding new ones too.

Any measurement we do is done inside that 'arrow' as far as I know. And we know that SpaceTime questions both distance and motion macroscopically, as QM microscopically but from different perspectives. It's such a weird universe :)

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##### Where are we in the Universe?
« Reply #13 on: 27/04/2011 19:51:29 »