Starship Asterisk*

by **neufer** » Tue Nov 03, 2009 4:41 pm

Chris Peterson wrote:
Star*Hopper wrote:I read somewhere long ago that our observable universe is oval-shaped, or perhaps more accurately egg- (thinking 3 dimensionally).
This being because we, ie our own galaxy (et al) is moving at a pretty darn good clip also....for instance our entire Local Group is hurtling toward the center of the Virgo cluster at roughly one million miles per hour - and without counting our movement within that, with regard to blue- & red-shifting we can "see" a bit farther in the direction we are moving (blue), & the effect becomes apparent.
That argument doesn't make sense to me. The oldest photons we see are from the period of recombination, about 377,000 years after the Big Bang. And if we develop technology to detect gravity waves, we should be able to see right back to the beginning. I don't see how those fixed times- recombination or the BB- could be different distances because of our motion. They would show different redshifts, of course, but that's a different matter.

It is possible that the observable Universe isn't spherical because space itself is distorted, for instance by some huge mass outside the observable Universe, as has been under discussion elsewhere here.

I would assume that the relative motion of earth vis-a-vis the observable universe
means that the observable universe is an oblate spheroid due to Fitzgerald contraction.

by **Chris Peterson** » Tue Nov 03, 2009 2:29 pm

Star*Hopper wrote:I read somewhere long ago that our observable universe is oval-shaped, or perhaps more accurately egg- (thinking 3 dimensionally).
This being because we, ie our own galaxy (et al) is moving at a pretty darn good clip also....for instance our entire Local Group is hurtling toward the center of the Virgo cluster at roughly one million miles per hour - and without counting our movement within that, with regard to blue- & red-shifting we can "see" a bit farther in the direction we are moving (blue), & the effect becomes apparent.

That argument doesn't make sense to me. The oldest photons we see are from the period of recombination, about 377,000 years after the Big Bang. And if we develop technology to detect gravity waves, we should be able to see right back to the beginning. I don't see how those fixed times- recombination or the BB- could be different distances because of our motion. They would show different redshifts, of course, but that's a different matter.

It is possible that the observable Universe isn't spherical because space itself is distorted, for instance by some huge mass outside the observable Universe, as has been under discussion elsewhere here.

Which made/makes me wonder, are there objects that we cannot now see that we once could have, presuming we'd been technologically capable at that point in time - in effect, objects we've lost sight of because of our movement?

Definitely. There was certainly material around us before the inflationary period that was causally connected to us then, and isn't now.

Or, because even as rapid as our movement might be, we're still not moving faster than light - hence any object once seen will "forever" remain seeable, & not disappear out the short 'back' end of our 'egg'? Which summarily lends that new discoveries will lie in the direction of our movement.

But we are moving faster than light- with respect to objects outside our observable volume of the Universe. That's what defines that volume. However, the observable Universe itself is getting larger as time goes on. We can see more, not less.

by **neufer** » Tue Nov 03, 2009 1:42 pm

Star*Hopper wrote:My understanding is somewhat contrary to the 'spherical' viewpoints.
I read somewhere long ago that our observable universe is oval-shaped, or perhaps more accurately egg- (thinking 3 dimensionally).
This being because we, ie our own galaxy (et al) is moving at a pretty darn good clip also....for instance our entire Local Group is hurtling toward the center of the Virgo cluster at roughly one million miles per hour - and without counting our movement within that, with regard to blue- & red-shifting we can "see" a bit farther in the direction we are moving (blue), & the effect becomes apparent.

Which made/makes me wonder, are there objects that we cannot now see that we once could have, presuming we'd been technologically capable at that point in time - in effect, objects we've lost sight of because of our movement? Or, because even as rapid as our movement might be, we're still not moving faster than light - hence any object once seen will "forever" remain seeable, & not disappear out the short 'back' end of our 'egg'? Which summarily lends that new discoveries will lie in the direction of our movement.

Your thoughts?

One observes exactly the same photons whether one is standing still or one is moving.

However, these photons will have higher energy in one direction and lower energy in the other:
http://apod.nasa.gov/apod/ap090906.html

Of course the center of our current observable spherical universe
differs from the center of our previous observable spherical universes
so that the set of all our previous observable spherical universes
might be considered "egg shaped."

by **Star*Hopper** » Tue Nov 03, 2009 12:07 pm

My 2¢.....Chris might be best to answer this - 'course anyone's free to take a crack at it....

My understanding is somewhat contrary to the 'spherical' viewpoints.
I read somewhere long ago that our observable universe is oval-shaped, or perhaps more accurately egg- (thinking 3 dimensionally).
This being because we, ie our own galaxy (et al) is moving at a pretty darn good clip also....for instance our entire Local Group is hurtling toward the center of the Virgo cluster at roughly one million miles per hour - and without counting our movement within that, with regard to blue- & red-shifting we can "see" a bit farther in the direction we are moving (blue), & the effect becomes apparent.

Which made/makes me wonder, are there objects that we cannot now see that we once could have, presuming we'd been technologically capable at that point in time - in effect, objects we've lost sight of because of our movement? Or, because even as rapid as our movement might be, we're still not moving faster than light - hence any object once seen will "forever" remain seeable, & not disappear out the short 'back' end of our 'egg'? Which summarily lends that new discoveries will lie in the direction of our movement.

Your thoughts?
~S*H

by **JuanAustin** » Mon Nov 02, 2009 10:46 pm

so, back to one of my questions, if i've been following corectly..., if i go 9 billion ly in any direction, then when i get there kepp going 9 billion ly in another direction, and so forth and so forth and so forth say 9 billion times more, then how can we possibly make a statement that dark matter is unaccounted for? Seems like an infinite number so how can anybody be close to being right?

by **Chris Peterson** » Thu Oct 29, 2009 9:33 pm

mark swain wrote:quantum fluctuation, makes another set of rules for you chris. read up .. http://en.wikipedia.org/wiki/Quantum_fluctuation

Nothing new there; this theory has been around for a long time. And I wouldn't say it makes another set of rules, it's just one part of the rules. It has nothing to do with the large scale structure of the Universe or the geometry of the Universe. It's a fundamental part of quantum mechanics and the nature of the vacuum. Interesting, but not topical in this discussion.

by **The Code** » Thu Oct 29, 2009 9:22 pm

Chris Peterson wrote:It's not a question of rules. "Rules" as used here means the laws of nature, and by definition they can't be broken. The Universe either is or is not infinite. Current knowledge isn't sufficient to determine the answer to that. Someday, maybe.

quantum fluctuation, makes another set of rules for you chris. read up .. http://en.wikipedia.org/wiki/Quantum_fluctuation

great read.

by **Chris Peterson** » Thu Oct 29, 2009 9:10 pm

mark swain wrote:If the rules can be broken, the universe will be infinite. if not universes.

It's not a question of rules. "Rules" as used here means the laws of nature, and by definition they can't be broken. The Universe either is or is not infinite. Current knowledge isn't sufficient to determine the answer to that. Someday, maybe.

by **The Code** » Thu Oct 29, 2009 8:13 pm

Chris Peterson wrote:It is entirely likely that the Universe is not infinite. Most cosmologists would probably bet against it being so.

If the rules can be broken, the universe will be infinite. if not universes.

by **Chris Peterson** » Thu Oct 29, 2009 7:57 pm

dlw wrote:When I was a little boy I looked up at the stars and wondered what all was up there and how far it went. That's why I've been an avid APOD follower for many years. I was (and still am) puzzled by the notion that the super-universe is infinite - literally without edge and not curved so that going far enough would bring you back to where you started.

It is entirely likely that the Universe is not infinite. Most cosmologists would probably bet against it being so. But the details of inflation, and the exact geometry of the Universe make it impossible to know for certain its true extents.

The notion that there is a 13.7 BLY "sphere of observability" from any point in the universe reinforces the concept of an infinite universe.

It shouldn't. It should only suggest the possibility that the Universe itself is larger than the part we can see from here. That certainly doesn't imply it is infinite.

Perhaps then the conceptual mistake is thinking of the "big bang" as occuring at a single infinitely small point. Perhaps a better way to think of it as occuring at a single point in "time" (for some definition of time) but physically everywhere (for some definition of those things).

Really, a single point in spacetime. Thus, a point that is outside the three-dimensional spatial universe we observe.

But then what "meaning" does the 91 BLY have? The notion of "observable universe" versus "sphere of observability" is confusing. I understand the latter but not the former if indeed there is a 13.7 BLY SoO from any point in the OU. What's beyond the OU or is there a 91 BLY OU around every point as well?

I'd say both your terms are the same thing. There is a large universe, presumably many times larger than 91 billion ly. From any point in this universe you have an observable sphere with a diameter of 91 billion ly, a diameter dictated by the speed of light and the expansion rate of space. Beyond any observable universe is just more space, the same as anywhere. Don't get confused by the fact that what we see at the edge of the observable Universe is very young; we're just seeing photons that took a long time to get here. What is really out there "now" isn't younger than what is here. Everything in the Universe is the same age, 13.7 billion years old. It's not like you could travel outwards billions of light years and see your surroundings get younger.

Is there a good reference on this subject that a layman might understand?

As already noted, the Wikipedia articles on cosmology, the Universe, the age of the Universe, and the observable Universe are all good starting points.

by **bystander** » Thu Oct 29, 2009 7:16 pm

dlw wrote:Is there a good reference on this subject that a layman might understand?

Try starting with the Wikipedia article Observable Universe. It's fairly easy to read, with a lot of good references.

by **dlw** » Thu Oct 29, 2009 6:54 pm

Chris Peterson wrote:91 billion ly is the diameter of the observable Universe, so nothing in the Universe can see that far. The farthest you can see is the radius of the observable Universe, about 46 billion ly. A creature looking at us from that distance would see the same thing we see looking at it: a region of space as it looked about 13 billion years ago. And each of us would have different, but overlapping observable universes. That is, we would see parts of the Universe it couldn't, and it would see parts that we can't.

Chris Peterson wrote:From any point in the Universe you see a sphere around you that decreases in age as you look outwards, with the limit of visibility at 13.7 billion years. There is no edge of the Universe, only an edge to each observer's visible universe. Your creature at the edge of our observable universe would see us at the edge of his, and looking the other direction he would see a part of the Universe that we can't observe, because it is out of our own light cone (light from there hasn't had enough time since the beginning of the Universe to reach us).

Thanks for your patience with this discussion. I find it quite interesting and enlightening.

When I was a little boy I looked up at the stars and wondered what all was up there and how far it went. That's why I've been an avid APOD follower for many years. I was (and still am) puzzled by the notion that the super-universe is infinite - literally without edge and not curved so that going far enough would bring you back to where you started.

The notion that there is a 13.7 BLY "sphere of observability" from any point in the universe reinforces the concept of an infinite universe. Perhaps then the conceptual mistake is thinking of the "big bang" as occuring at a single infinitely small point. Perhaps a better way to think of it as occuring at a single point in "time" (for some definition of time) but physically everywhere (for some definition of those things).

But then what "meaning" does the 91 BLY have? The notion of "observable universe" versus "sphere of observability" is confusing. I understand the latter but not the former if indeed there is a 13.7 BLY SoO from any point in the OU. What's beyond the OU or is there a 91 BLY OU around every point as well?

Is there a good reference on this subject that a layman might understand?

by **Chris Peterson** » Thu Oct 29, 2009 2:15 pm

dlw wrote:OK, so the model that comes to mind is an elastic string with beads on it. They start out all together but as I pull the string they move apart at a rate that is the same relative to the adjacent bead. So if the matter created at the big bang began to disperse (expand) relative to each other, it is possible that the bead at one would be moving away from the bead at the other end at greater than "the speed of light" even though the speed relative to an adjacent bead was less than that. I know the physics isn't quite like that but it's the conceptual model I'm looking for. If it's relevant, what -is- the rate of expansion in terms of the elastic string and beads model?

That's a reasonable analogy to use. The current rate of expansion is given by the Hubble "constant", 70.8 km/sec/Mpc; I use "constant" loosely because the rate probably isn't constant with time.

dlw wrote:
Chris Peterson wrote:91 billion ly is the diameter of the observable Universe, so nothing in the Universe can see that far. The farthest you can see is the radius of the observable Universe, about 46 billion ly. A creature looking at us from that distance would see the same thing we see looking at it: a region of space as it looked about 13 billion years ago. And each of us would have different, but overlapping observable universes. That is, we would see parts of the Universe it couldn't, and it would see parts that we can't.
Right - but I was asking about looking in the opposite direction. A creature on a planet within a few BLY of "the edge of the universe" would observe things in our direction up to 13+ billion years ago but in the opposite direction there would be nothing more than a few billion years old - right?

From any point in the Universe you see a sphere around you that decreases in age as you look outwards, with the limit of visibility at 13.7 billion years. There is no edge of the Universe, only an edge to each observer's visible universe. Your creature at the edge of our observable universe would see us at the edge of his, and looking the other direction he would see a part of the Universe that we can't observe, because it is out of our own light cone (light from there hasn't had enough time since the beginning of the Universe to reach us).

by **Mosbycuz3tr** » Thu Oct 29, 2009 11:20 am

Thanks to Chris Peterson and all for the discussions. So, I realize I should have put "geocentrist" in quotes, and that the more proper term might now be something like "univercentrist". In sum all I have to say is WOW!!!: it's great having some idea of how big God's universe is.

by **dlw** » Thu Oct 29, 2009 6:19 am

Chris Peterson wrote:"Nothing can travel faster than the speed of light" is really an oversimplification. The actual rule has to do with causality: the distance in time and space that two events can be separated and still affect one another. There is nothing that says the Universe itself can't expand at a rate that could be said to be "faster than light".

OK, so the model that comes to mind is an elastic string with beads on it. They start out all together but as I pull the string they move apart at a rate that is the same relative to the adjacent bead. So if the matter created at the big bang began to disperse (expand) relative to each other, it is possible that the bead at one would be moving away from the bead at the other end at greater than "the speed of light" even though the speed relative to an adjacent bead was less than that. I know the physics isn't quite like that but it's the conceptual model I'm looking for. If it's relevant, what -is- the rate of expansion in terms of the elastic string and beads model?

dlw wrote:Also, if there really -is- a dimension like 91 BLY for the "observable universe", what would a creature on a planet 90 BLY from us observe if it looked away from the direction of Earth?

Chris Peterson wrote:91 billion ly is the diameter of the observable Universe, so nothing in the Universe can see that far. The farthest you can see is the radius of the observable Universe, about 46 billion ly. A creature looking at us from that distance would see the same thing we see looking at it: a region of space as it looked about 13 billion years ago. And each of us would have different, but overlapping observable universes. That is, we would see parts of the Universe it couldn't, and it would see parts that we can't.

Right - but I was asking about looking in the opposite direction. A creature on a planet within a few BLY of "the edge of the universe" would observe things in our direction up to 13+ billion years ago but in the opposite direction there would be nothing more than a few billion years old - right?

by **Chris Peterson** » Thu Oct 29, 2009 1:36 am

dlw wrote:I don't understand this. If nothing can travel faster than the speed of light, then something traveling away from the big bang could have gone only 13.7 BLY since the bang. Or are you saying the frame of reference has expanded too so it's meaningless to talk about "distance", only time?

"Nothing can travel faster than the speed of light" is really an oversimplification. The actual rule has to do with causality: the distance in time and space that two events can be separated and still affect one another. There is nothing that says the Universe itself can't expand at a rate that could be said to be "faster than light".

Also, if there really -is- a dimension like 91 BLY for the "observable universe", what would a creature on a planet 90 BLY from us observe if it looked away from the direction of Earth?

91 billion ly is the diameter of the observable Universe, so nothing in the Universe can see that far. The farthest you can see is the radius of the observable Universe, about 46 billion ly. A creature looking at us from that distance would see the same thing we see looking at it: a region of space as it looked about 13 billion years ago. And each of us would have different, but overlapping observable universes. That is, we would see parts of the Universe it couldn't, and it would see parts that we can't.

by **dlw** » Thu Oct 29, 2009 12:55 am

Chris Peterson wrote: No, the observable Universe is much larger: about 91 billion ly across. That's because it's been expanding for the entire 13.7 billion years of its existence.

I don't understand this. If nothing can travel faster than the speed of light, then something traveling away from the big bang could have gone only 13.7 BLY since the bang. Or are you saying the frame of reference has expanded too so it's meaningless to talk about "distance", only time?

Also, if there really -is- a dimension like 91 BLY for the "observable universe", what would a creature on a planet 90 BLY from us observe if it looked away from the direction of Earth?

by **Chris Peterson** » Wed Oct 28, 2009 10:49 pm

orin stepanek wrote:The age of the universe is thought to be about 13.7 billion yrs. so if were at the center of the observable universe that would make the observable universe about 27.4 billion light years across.

No, the observable Universe is much larger: about 91 billion ly across. That's because it's been expanding for the entire 13.7 billion years of its existence.

If we are not near the center of the universe than it may be even larger; or am I missing something. So when did the big bang happen? If it was 13.7 billion years ago than maybe we are at the center of the universe.

We are, pretty much by definition, at the center of the observable Universe. The Universe as a whole is probably much bigger, maybe even infinite. Assuming the usual sort of geometries assumed for the Universe, we are at its center as well, assuming by "center" you mean a three-dimensional coordinate. It can become more complex in higher dimensions, or odd geometries.

by **Chris Peterson** » Wed Oct 28, 2009 10:42 pm

jpbyrd wrote:I have always wondered why these terrifically distant objects aren't really much farther away at the present. If this cluster is 9 billion LY away, what has it been doing in the 9 billion years since the light left? Assuming (not a good assumption, likely) that it's been receding at a similar pace for all that time, shouldn't it be 18 billion LY away by now? What does this kind of thinking do to estimates of the age of the universe?

This cluster has a redshift of 1.9, which means we are looking at something as it appeared 10.2 billion years ago. That does not mean it is 10.2 billion ly away. As you note, it has been moving away that entire time, and its actual distance (called the comoving distance in cosmology) is now 16.6 billion ly.

The physical radius of the observable Universe is 45.6 billion ly; that is, objects that emitted light at the very beginning, 13.7 billion years ago (which are the most distant things we could possibly see) are now 45.6 billion ly away from us, at the edge of the observable Universe.

by **jpbyrd** » Wed Oct 28, 2009 10:32 pm

OK. Try this on for size. No pun intended. Makes much more sense to me now (if this stuff ever makes "sense").

http://www.space.com/scienceastronomy/m ... 40524.html

by **orin stepanek** » Wed Oct 28, 2009 9:00 pm

http://www.universetoday.com/2008/03/28 ... verse-yet/
The age of the universe is thought to be about 13.7 billion yrs. so if were at the center of the observable universe that would make the observable universe about 27.4 billion light years across.
If we are not near the center of the universe than it may be even larger; or am I missing something. So when did the big bang happen? If it was 13.7 billion years ago than maybe we are at the center of the universe.

Orin

by **dlw** » Wed Oct 28, 2009 8:59 pm

I have always wondered why these terrifically distant objects aren't really much farther away at the present. If this cluster is 9 billion LY away, what has it been doing in the 9 billion years since the light left? Assuming (not a good assumption, likely) that it's been receding at a similar pace for all that time, shouldn't it be 18 billion LY away by now? What does this kind of thinking do to estimates of the age of the universe?
Thanks.

The original statement in the APOD was "it takes the age of the universe for light to cross the universe" and that is exactly correct. That primordial galaxy was 9 billion light years away when the energy we now see left it. It has long since moved on and may even have evolved to something else. Yes it's farther away - that's what expansion is all about.

And apparently the "pace" of expansion has not been uniform. Last I heard it is now accelerating. I suppose that means that red shift alone is not sufficient to estimate distance; you might need to estimate how it got to that velocity starting at the big bang.

by **jpbyrd** » Wed Oct 28, 2009 8:28 pm

I have always wondered why these terrifically distant objects aren't really much farther away at the present. If this cluster is 9 billion LY away, what has it been doing in the 9 billion years since the light left? Assuming (not a good assumption, likely) that it's been receding at a similar pace for all that time, shouldn't it be 18 billion LY away by now? What does this kind of thinking do to estimates of the age of the universe?
Thanks.

by **The Code** » Wed Oct 28, 2009 7:35 pm

JuanAustin wrote:what if our membrane touched the adjacent one, and the fabric of space was annihilated and there was another big bang.

This Was a question i was going to get to. Current rate of accelerated expansion due to another big bang.

mark

by **Chris Peterson** » Wed Oct 28, 2009 6:20 pm

JuanAustin wrote:what if our membrane touched the adjacent one, and the fabric of space was anihalated and there was another big bang.
if it happened in the area where this cluster is at that distance, would the cataclysm tak that long for us to experience it or would it be instant everywhere?

The idea of branes is so extremely speculative, that virtually everything about them remains in the realm of guessing. I doubt anybody could answer your question. I do think, however, that you are imagining these brane-universes as 3D structures, when in fact they would almost certainly exist in higher dimensions. So when two of them touch, what does that mean? It probably doesn't translate to some particular 3D location in our universe being affected; it could as easily be a time, or even something that can't be expressed non-mathematically.

How can we possibly get a good picture of our surroundings if it's always having to backward or forwards in time.

We rely on the reasonable (and apparently true) assumption that the laws of physics are the same everywhere and everywhen (except possibly for the first fraction of a second). So while we can't see what everyplace in the observable Universe is like right now, we can see how it evolved an therefore understand its fundamental, if not literal, structure.

Seems like we're so dependent on light properties and physics, is dark matter also in a nascent stage in this cluster area?
how can anybody account for amounts of matter when everything everywhere is either now or in the past??

We're dependent on light because its what we have the best technology for measuring. But that allows us to indirectly see many other things as well. At the time seen in this APOD, neither matter nor dark matter were in a "nascent stage". Both had the same properties they have today, and had for billions of years.

Starship Asterisk*

JKCS041: Farthest Galaxy Cluster Yet Measured (2009 Oct 28)

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