# Thread: Inflation: Is our "horizon" the same as our "bubble universe"?

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## Inflation: Is our "horizon" the same as our "bubble universe"?

If inflation caused the universe to be larger than our horizon, as this first picture shows, is the "us" bubble in the second image representing the same horizion? Why are the other bubbles always outside or horizon or universe, shouldn't our universe (and others) expand so eventually our horizons cross?

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It's not as simple as soaps bubbles floating through the air.

What if the bubbles themselves repel? Wouldn't the collections of bubbles expand much like galaxies in a universe? Now we're back at square one.

3. Welcome to BAUT Forum, fxer.

Originally Posted by fxer
[IMG]http://img72.imageshack.us/img72/8016/inflationbp3.gif[/IMG]

[IMG]http://img72.imageshack.us/img72/7665/bubbleuniversesvq5.gif[/IMG]
Images are from University of Oregon, Astronomy 123, Symmetry Breaking & Inflation, along with other content, context, and explanations.

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yep i've been there, put the images on a different host so as not to image leech from that school's server. I've read their explanations but i'm still not exactly clear on the horizon thing.

Since we can only see ~13.7 billion light years in any direction, I assume that is our horizon. But inflation caused the universe to be larger than our horizon if I understand correctly. So isn't there a chance an alien is outside our horizon but as the universe ages and our horizon grows larger, that alien will now be in our horizon and visible to us?

That is what I doing get about the bubble universe thing, if our horizon is getting bigger as time passes, why wouldn't we eventually see into those other "bubbles"?

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Originally Posted by fxer
That is what I doing get about the bubble universe thing, if our horizon is getting bigger as time passes, why wouldn't we eventually see into those other "bubbles"?
As you pointed out, the universe is expanding as well. Even as time passes and more light reaches us, the universe is also expanding.
Last edited by Neverfly; 2008-Apr-30 at 03:46 PM.

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In the diagrams, the "present" is shown as a rectangle implying that the coefficient of cosmological expansion is a true constant. I thought observers have determined that the rate of expansion is variable and increasing. Aren't isolated bubbles reserved for describing domains that are isolated from us spacewise dimensionally? Is this a good way to address portions of our own domain that are isolated from us only by speed of light/gravity constraints? If critters living on a planet 13.7 light years from us in any arbitrary direction observed their domain today, would it look the same in the direction opposite to that towards us--is isotropy, such as it is, conserved?

7. The bubble is not any actual physical object, it's just a representation of how far we can see. Nothing happens when they collide or overlap, and they can't repel.

You can draw those bubbles arbitrarily at any point in space, so overlapping bubbles already exist. Andromeda is 2.5Mly away from us, so they can see 2.5Mly farther in that direction, and we can see 2.5Mly farther in the direction opposite Andromeda.

Additionally, since the expansion of the universe seems to be accelerating, distant galaxies will actually move outside our bubble over time. If it continues to accelerate indefinitely, well, google 'the big rip', it's a depressing scenario.

8. Originally Posted by fxer
yep i've been there, put the images on a different host so as not to image leech from that school's server.
You should have credited them at least. And the surrounding material likely would help us understand what you are asking.

BAUT Forum does allow in-line links to educational site images, probably on the theory that that's their purpose, and they have the bandwidth to support our curiosity. It's good not to abuse their kindness. See Rules for posting, Number 8. Hotlinking.

(But, I don't think the large images in-line added much to the question, so an indirect link to their location, and allied material, should have sufficed.)

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Originally Posted by fxer
If inflation caused the universe to be larger than our horizon, as this first picture shows, is the "us" bubble in the second image representing the same horizion? Why are the other bubbles always outside or horizon or universe, shouldn't our universe (and others) expand so eventually our horizons cross?
We're at the center of the "US" bubble. If we were to miraculous transport to another galaxy, we'd still be at the center of the observable universe, but the boundary of the "US" bubble would have changed.

I don't believe that are other bubble universes out there. Just one big universe, and wherever you go...

...there you are, smack dab in the center of another "US" bubble.

10. Once you put yourself a certain distance away from us, your bubble wont overlap ours anymore.

We assume the edge of our bubble, our particle horizon, is currently around 46 billion light years away, but the light we are seeing is from that horizon when it was only 40 million light years away, 13.7 billion years ago when the CMBR was emitted.

If the universe was larger than our observable part of it was then, we can imagine their might have been a point in space that was 80 million light years away at that time and is now 92 billion light years away. We assume that galaxies formed throughout, so we can imagine there is now a galaxy at the edge of our bubble, 46 billion light years away, although we have only ever seen light from that area of space as it was 13.7 billion years ago, before galaxies formed.

We might also imagine a theoretical galaxy that is now 92 billion light years away and it would have a bubble of observable universe that touches but does not overlap our own. If we look towards them and they look towards us, we are both looking at the same place in space, the place where our bubbles touch, which is a point that was then 40 million light years away from each of us and is now 46 billion light years away from each of us, where light has taken 13.7 billion years to make the journey in each direction.

Any galaxy that is currently more distant than 92 billion light years away will have a bubble that is totally separate from our own. But these are separate bubbles within the same overall universe, it is just that we cannot see into the others bubble.

Of course, a galaxy at the edge of our observable universe, 46 billion light years away, would have a bubble that intersects our Milky Way galaxy, although they would only see light that was emitted from here when this point in space was a distance of 40 million light years from them, 13.7 billion years ago when the CMBR was emitted, and their bubble would cut through that galaxy that would now be 92 billion light years away from us, but again they would be seeing that region of space as it was when the CMBR was emitted and that region was only 80 million light years away from us.

11. Originally Posted by fxer
(snip)
Since we can only see ~13.7 billion light years in any direction, I assume that is our horizon. But inflation caused the universe to be larger than our horizon if I understand correctly. So isn't there a chance an alien is outside our horizon but as the universe ages and our horizon grows larger, that alien will now be in our horizon and visible to us?

That is what I doing get about the bubble universe thing, if our horizon is getting bigger as time passes, why wouldn't we eventually see into those other "bubbles"?
Any alien outside the Hubble limit would have great difficulty reaching us because space is expanding faster than the speed of light between our two civilizations.

Based on current theory there is a real physical distance beyond which we will not ever see. As time passes there is less and less of the universe of ours that we will see.

12. Originally Posted by Michael Noonan
Based on current theory there is a real physical distance beyond which we will not ever see. As time passes there is less and less of the universe of ours that we will see.
That distance is known as the cosmological light horizon (or cosmological event horizon) and is currently around 16 billion light years away (where it is right now). We will never see any light that is emitted from an event today from a distance farther than that. We will see light that is already on its way towards us from galaxies that are now more distant than that, but we will be seeing them as they were when they were closer than that!

We have currently only seen light that was emitted at proper distances up to 5.7 light years away, although he cosmological light horizon was over double that distance away at that time, but will end up seeing light that was emitted at proper distances up to 16 billion light years away, although by that time we will actually be seeing less of the stuff in the universe than we can now, as everything is accelerating away from us.

But we have more to see yet, as we are seeing that proper distance of 5.7 billion light years away as it was over 9 billion years ago, when the rate of expansion was still decelerating. A galaxy at that distance then, is now 13.7 billion light years away, and therefore has remained within our cosmological light horizon all this time. Galaxies more distant than that were within our light horizon as the deceleration continued and then passed out as the acceleration started, so we will see more and more galaxies at further proper distances for the next few billion years, and then as time goes on, although we still see further in proper distance we find galaxies we have previously seen are now passing forever from view. By the time we can actually see a proper distance of 16 billion light years, that galaxy we see as 5.7 billion light years away, 9 billion years ago, will have long since disappeared over the light horizon.
Last edited by speedfreek; 2008-Apr-30 at 06:47 PM. Reason: typo

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Thanks for all the replies, I think I am getting closer to understanding.

So does the issue of horizons in the first picture have nothing to do with the second picture? Supposedly the bubbles in the second picture can have their own constants etc, which would be a problem if we were just talking about infinite overlapping horizions like could be possible in the first picture.

On the second picture, it is not possible to have an observer outside of the circles right?

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