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View Full Version : My geometrical reasoning for infinite universes (and questions)

m74z00219
2008-Nov-21, 10:05 PM
Hi everyone at BAUT. I'm new here; I joined up because this seemed like a good place to post some of the cosmology questions and notions I have.

I have come up with a geometrical notion that offers another way to think of a certain level of multiverse. Wormholes are requisite for this thought experiment.

Construction:
1. Imagine a hubble volume that represents our observable universe.
2. Imagine a wormhole that stretches from the center of the hubble volume to another locations WITHIN the hubble volume.
3. I would argue that this (1) necessarily connects one to a younger place in our universe and (2) puts the traveler at the center of another observable universe embedded in the original (albeit, a younger one who's horizon is tangent to center of the universe he traveled from.

Question: Does this make any physical sense??

What I thought of next was the logical inverse of the above statements. In the manner of using a wormhole, it may be possible to travel to the center of other observable universes that encompass ours.

Construction:
1. Take a wormhole from the center of our observable universe to the center of another that who's center lies beyond the horizon of our observable universe.
Consequences: this universe should not only encompass ours such that they have tangent horizons, but it should indeed be older.

Questions: Does this imply the potential for a multiverse that is infinite in age?

These are theories of mine, but I'm happy to share them with the community here. I'm also eager to here what everyone thinks.

thanks!

speedfreek
2008-Nov-22, 04:26 PM
Hi there and welcome to BAUT! :)

I think the idea of a wormhole is that it connects different parts of the universe allowing one to travel to those parts a lot quicker than would be possible at the speed of light. So you would essentially be connecting the two places as they are now, rather than connecting to a "younger" place, although I can see what you mean. But if you popped through the wormhole to a star a million light-years away and saw it go supernova, we would not see that supernova back here for a million years.

Also, I think, having seen your reply to another thread, that your notion of what the observable universe is might be causing you a few problems with this scenario as the term "observable universe" is often interpreted in different ways.

It is true that the Hubble volume can be considered to represent our visible universe in terms of the proper distance to the place where the light was emitted. The most distant galaxies we have seen are the ones at the edge of the Hubble volume as it was 9.1 billion years ago, and those galaxies were a proper distance of around 5.7 billion light-years away at that time. We have seen nothing with a larger proper distance than around 5.7 billion light-years away when its light was emitted so that can be considered to be the edge of our "visible" universe.

The Hubble radius recedes from us over time and is now estimated to be around 14 billion light-years away. The light has just started its journey towards us from any galaxies that are currently 14 billion light-years years away, but that light will not reach here for a very long time.

But the observable universe is much larger than that. Right now, we detect photons that were emitted as the Cosmic Microwave Background Radiation, 13.7 billion years ago. When it was emitted, the CMBR filled the universe and it still does so today, much cooled and stretched into microwaves by the expansion of the universe. The CMBR photons that we currently detect were emitted at a proper distance of only a few tens of millions of light-years away but those co-moving coordinates have since receded to around 46 billion light-years away due to the expansion of the universe.

If we were to move our point of view (via a wormhole if you like) to a galaxy that is currently at the edge of our Hubble volume, a co-moving distance of only 14 billion light-years away, and looked towards the Milky-Way, you would see the light coming in from whatever was here 9.1 billion years ago. You would be seeing the Milky-Way when it was young, as it was when it was only 5.7 billion light-years away, when the universe was much smaller than it is today.

The edge of our observable universe - the surface of last scattering or particle horizon - is 46 billion light-years away right now and we might assume that galaxies formed there just as ours formed here. A galaxy there would have an observable universe that overlapped our own - in this case the centre of each observable universe is at the edge of the other. If we move our viewpoint to a galaxy that formed at the edge of our observable universe, currently 46 billion light-years away, and look towards the Milky-Way, the only photons that were ever emitted here that are currently reaching that distant galaxy are the photons that were emitted with the CMBR.

If the whole universe is larger than our observable portion of it then there may be galaxies with a co-moving distance of 50 billion light-years away. They would be just outside of our observable universe, outside of our particle horizon, and if the rate of expansion is accelerating then no photon ever emitted here will ever reach there or vice versa, but the observable "bubbles" of space around us overlap and they can see regions of space that we can see. We see galaxies between us with a co-moving distance of over 25 billion light-years and so would they.

A galaxy that were currently more than 92 billion light-years away from here would have an observable universe that does not intersect ours at all and so we would both be looking at completely different parts of the same universe. Neither of us would be able to see any region of the universe that the other can, but we would both still be part of the same universe.

Here are a couple of links that help explain this a lot better than I can. Both are by the same authors and the first is a simplified article based on the second.

Expanding Confusion: Common misconceptions of cosmological horizons and the superluminal expansion of the universe (http://arxiv.org/abs/astro-ph/0310808).

formulaterp
2008-Nov-23, 06:05 PM
1. Imagine a hubble volume that represents our observable universe.
2. Imagine a wormhole that stretches from the center of the hubble volume to another locations WITHIN the hubble volume.
3. I would argue that this (1) necessarily connects one to a younger place in our universe and (2) puts the traveler at the center of another observable universe embedded in the original (albeit, a younger one who's horizon is tangent to center of the universe he traveled from.

Ignoring the whole "center of the universe" issue:

3.1 - Why would it be younger? Alpha Centauri is in that hubble volume. Is that area of the universe older or younger than ours? How could you tell?

3-2 - So if the wormhole took you to AC, your visible universe would only be 4.3 light years in radius?

m74z00219
2008-Nov-24, 10:35 PM
Thanks speedfreak for those articles, the "The Expanding Confusion..." article was very informative.

:confused: let's see if i understood it...in terms of the proper distance, the boundary of the hubble volume does correlate to our limit of observation. However, we can observe light from objects that have comoving distance around 46bly.

When you say this, "If we were to move our point of view (via a wormhole if you like) to a galaxy that is currently at the edge of our Hubble volume, a co-moving distance of only 14 billion light-years away, and looked towards the Milky-Way, you would see the light coming in from whatever was here 9.1 billion years ago. You would be seeing the Milky-Way when it was young, as it was when it was only 5.7 billion light-years away, when the universe was much smaller than it is today."

you're just tracing the light cone back to its intersection with the hubble boundary? The galaxy you arrive at is 5.7 billion years old then, right? I'm confused how you got you would see the milky as was when only 5.7 billion light-years away...?

Ok, so the surface of last scattering has a proper distance of 14.7 billion cy and a comoving distance of 46 bcy...?

Ok, for the galaxy that formed at the edge of the observable universe with a comving distance of 46 bcy could never be observed by us as it would expand out of our observable universe?

When I think about it now...if a wormhole were stretched along with the expansion of the universe, then the mouths would only ever connect to locations in comoving space as they are now (when the astronaut goes through). Does this make more sense? I'm "slightly" confused by that.

One last question, is this article implying that the maximum size of the observable universe is with a radius of about 60bcy? (see figure 1)

to formulaterp. Um, that's not what I meant, but I'm not sure of anything now that speedfreak has enlightened me.

speedfreek
2008-Nov-25, 12:15 AM
let's see if i understood it...in terms of the proper distance, the boundary of the hubble volume does correlate to our limit of observation. However, we can observe light from objects that have comoving distance around 46bly.

Yes, although the CMBR photons that we detect were not emitted from an object as such - they were emitted throughout the universe. The CMBR photons that we detect today were emitted from a region that, if it moves with the expansion of the universe, is now 46 billion light-years away.

Those photons were only a little over 40 million light-years away when they started their journey. The incredibly fast rate of expansion at the time carried them away from here for billions of years until the rate had slowed enough for them to start making progress back towards us through regions that were receding from here at less than the speed of light. They only made progress towards us (from our point of view) once they had crossed into our Hubble sphere as it was 9.1 billion years ago.

The key thing to remember is that light never overtakes light.

When you say this, "If we were to move our point of view (via a wormhole if you like) to a galaxy that is currently at the edge of our Hubble volume, a co-moving distance of only 14 billion light-years away, and looked towards the Milky-Way, you would see the light coming in from whatever was here 9.1 billion years ago. You would be seeing the Milky-Way when it was young, as it was when it was only 5.7 billion light-years away, when the universe was much smaller than it is today."

you're just tracing the light cone back to its intersection with the hubble boundary? The galaxy you arrive at is 5.7 billion years old then, right? I'm confused how you got you would see the milky as was when only 5.7 billion light-years away...?

These different definitions of distance are confusing for sure, and you have misunderstood (due to the way I described it, no doubt!). Consider the edge of the Hubble sphere, where an object (or co-moving coordinate) apparently recedes at c, due to the expansion of the universe. Right now, we are seeing the edge of the Hubble sphere as it was 9.1 billion years ago.

9.1 billion years ago, the edge of our Hubble sphere was only 5.7 billion light-years away. 9.1 billion years ago, everything over 5.7 billion light-years away was receding faster than light.

So a galaxy (call it galaxy X) that was 5.7 billion light-years away, 9.1 billion years ago, was receding from here at the speed of light. We can reverse the picture and say that the Milky-way was 5.7 billion light-years away from galaxy X 9.1 billion years ago and the Milky-Way was receding from galaxy X at the speed of light at that time. The view is symmetrical.

Just as we are receiving the light emitted by galaxy X, emitted 9.1 billion years ago when that galaxy was only 5.7 billion light-years away, so we must assume that galaxy X is now receiving the light emitted by the Milky-Way 9.1 billion years ago, when the Milky-Way was only 5.7 billion light-years away from galaxy X! That galaxy is now estimated to be around 14 billion light-years away as it receives that light/as we receive its light.

Ok, so the surface of last scattering has a proper distance of 14.7 billion cy and a comoving distance of 46 bcy...?

Ok, for the galaxy that formed at the edge of the observable universe with a comving distance of 46 bcy could never be observed by us as it would expand out of our observable universe?

Not quite. The edge of the observable universe, the surface of last scattering, the particle horizon etc, has a light-travel time of 13.7 billion years and a co-moving distance (its current proper distance) of 46 billion light years. The proper distance at emission of the CMBR photons we detect today was around 42 million light-years.

That "surface" is an interesting way to think about things as the CMBR photons are coming in from all directions, as if emitted towards us from the inside of a sphere which recedes with the expansion of the universe. As time goes on we should receive photons that were originally emitted slightly further away, emitted from the inside of a slightly larger sphere with an original radius slightly larger than 42 million light-years, if you see what I mean.

Now for that galaxy that is currently just inside our observable universe, with a co-moving distance a little under 46 billion light-years. We will never see that galaxy, but it is in our observable universe as it is in a region of space from which we have received CMBR photons. Photons from that galaxy will never be in our visible universe as they will never pass into our Hubble sphere due to the acceleration of the expansion of the universe.

I suppose it all depends on your definition of the observable universe.

One last question, is this article implying that the maximum size of the observable universe is with a radius of about 60bcy? (see figure 1)

No, for the "conformal time" diagram you have to draw a vertical line through the place where the "now" line and the particle horizon intersect. You will find that line hits the co-moving distance axis right where our light cone hits it - at 46 billion light-years. The "conformal time" diagram will probably mislead you so stick to the top two diagrams for now, they are shown larger on page 11. And may I suggest you should only be reading that paper from the second link if you have completely understood the article in the first link.

Or try this one for starters: Distance Scales of the Universe (http://www.atlasoftheuniverse.com/redshift.html). :)

WayneFrancis
2008-Nov-25, 05:34 AM
thanks speed freak, great articles. Don't know if they will sway my friend that is an expansion denier, but then he's also a 911 conspiracy believer and possible Holocaust denier. He likes to poke holes and claim something isn't right but doesn't care about how the majority of evidence shows that the current models are currently the best fit.

astromark
2008-Nov-25, 06:01 AM
thanks speed freak, great articles. Don't know if they will sway my friend that is an expansion denier, but then he's also a 911 conspiracy believer and possible Holocaust denier. He likes to poke holes and claim something isn't right but doesn't care about how the majority of evidence shows that the current models are currently the best fit.

Around the world are many astronomers and cosmologists. Talking of worm holes as if they were factual is a mistake. hypothetical is the same as imaginary. We know a great deal about our universe and its rate of expansion... all the models are pointing in the same direction. Those people whom know things because... should be avoided.

John Mendenhall
2008-Nov-25, 03:34 PM
Talking of worm holes as if they were factual is a mistake. hypothetical is the same as imaginary. We know a great deal about our universe and its rate of expansion... all the models are pointing in the same direction. Those people whom know things because... should be avoided.

Thank you, Astro.

OP, questions that assume something unlikely, unobserved, and highly speculative, such as wormholes, are basically unanswerable, except with additional speculations. Not quite the idea of Q&A, but . . . it is fun. And it can be educational. For example, the universe as we understand it is spatially unbounded, uniform in all directions, and has no center. Even if we could travel to some distant part of the accessible universe, it will look the same on large scales.

m74z00219
2008-Nov-26, 07:24 AM
Wow, BAUT is awesome. Thank you very much speedfreak for bettering my understanding of expansion and right way to interpret it.