Starship Asterisk*

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I don't get it: How can that fuzzy blue thing be farther away than the other galaxies clearly visible in the image? And in terms of the shape and size of the universe, aren't we in the same position as those geocentrists prior to Copernicus: we can only observe the universe from here:??

http://apod.nasa.gov/apod/ap091028.html

Mosbycuz3tr wrote:I don't get it: How can that fuzzy blue thing be farther away than the other galaxies clearly visible in the image?

That fuzzy blue thing, JKCS041, is a not just a galaxy, it's a cluster of galaxies. Some of the individual galaxies in the cluster can be seen as faint white dots within the confine of that fuzzy blue thing. Additional information can be found here and here.

Mosbycuz3tr wrote:And in terms of the shape and size of the universe, aren't we in the same position as those geocentrists prior to Copernicus: we can only observe the universe from here:??

I'm not sure what your asking here. Our observable universe hasn't changed since those times. We can still only see what we can see. But our ability to push the limits of what we can see is getting better all the time. Even so, the information we are receiving from our furthest satellites (Voyager) is still here in the universal sense or even the galactic sense.

BTW: this is the Asterisk*, not phpBB. phpBB is just the software used to create this forum.

Mosbycuz3tr wrote:And in terms of the shape and size of the universe, aren't we in the same position as those geocentrists prior to Copernicus: we can only observe the universe from here:??

How else can any observer see anything except from his own here?

We now know that we truly are at the center of the Universe (or more precisely, every observer is at the center of his own observable universe). So we have become the ultimate geocentrists! Of course, that term is usually reserved for the pre-Copernican viewpoint which concerned only the structure of our solar system, and the use of frames of reference that made little sense.

What if . . . you could travel faster than light and head straight for that cluster. What would you see before your eyes as you got nearer and nearer? Would you see the galaxies evolve, move around, collide etc etc until you arrived among them in their local time to see how they are in person so to speak?

What about the opposite? I always wondered if the end of the universe has already happened, and we just haven't seen it yet! What are your thoughts on that?

As I understand it, (from my little reading)… nowadays, astronomers can see the entire universe and it is mostly flat. We are at the center. We have a most excellent vantage point into the cosmos. It is like traveling back in time… not only seeing age old cosmic states as we look farther out, but age old beliefs are paralleled in the flat/center thing. Funny how we seem to travel in circles.

The end is not near, but the end is inevitable. It’s a good time to be alive.

JuanAustin wrote:What if . . . you could travel faster than light and head straight for that cluster. What would you see before your eyes as you got nearer and nearer? Would you see the galaxies evolve, move around, collide etc etc until you arrived among them in their local time to see how they are in person so to speak?

What about the opposite? I always wondered if the end of the universe has already happened, and we just haven't seen it yet! What are your thoughts on that?

Yes i think its what you would see and since you are moving faster then light speed away from our own cluster of galaxies, you will see our own cluster of galaxies de-evolve toward the past. Kind of?

And we cant see in the future yet. Will we someday i dont know for sure but i think not.

emc wrote:As I understand it, (from my little reading)… nowadays, astronomers can see the entire universe and it is mostly flat. We are at the center.

We can see most of the observable Universe, which is probably only a tiny fraction of the entire Universe. We are at the center of the observable Universe, and the rest is forever outside our ability to observe.

Well, my idea of building a scale model of the Universe is just out the window. My house "ain't big enough ". Pass the ice coldone.

JuanAustin wrote:What if . . . you could travel faster than light and head straight for that cluster. What would you see before your eyes as you got nearer and nearer? Would you see the galaxies evolve, move around, collide etc etc until you arrived among them in their local time to see how they are in person so to speak?

It's not really a valid "what if", because you can't go faster than light. You might as well ask what the Universe would be like if the rules of nature were different.

Why specify traveling faster than light? You can do the same experiment without breaking any rules, and you'll still see the same thing you suggest.

i just wanted to get there fast

In the back of my mind was another what if, maybe you can comment on as well.

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

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.

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

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.

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.

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

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

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.

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.

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?

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.

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?

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.

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).

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?

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.