Starship Asterisk*

by **Chris Peterson** » Fri Nov 02, 2012 1:59 pm

ErnieM wrote:Oooops. I mean concentric circles. From Wikipedia: "Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another. Concentric objects generally have different radii, as concentric objects with the same radius are equal."

Then there is no change in the angle of objects as seen from an observer at the common center.

by **ErnieM** » Fri Nov 02, 2012 1:19 pm

Chris wrote:

I'm having difficulty figuring out what you're doing here (what are "concurrent circles?)

Oooops. I mean concentric circles. From Wikipedia: "Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another. Concentric objects generally have different radii, as concentric objects with the same radius are equal."

by **Chris Peterson** » Sun Oct 28, 2012 3:43 pm

ErnieM wrote:two concurrent circles with r1 and r2 radi (r1 is 1/2 inch shorter than r2), you are standing at the shared center (c). r2 - r1 represents the space expansion from the center. draw a radius of the large circle (your line of site), mark two dots (d1 and d2) on the inner circle 1/4 inch equidistant from your line of site intersection. do the same on the outer circle (d3 and d4). mark two more dots (d5 and d6) on the outer circle 1/2 inch equidistant from you line of site. connect all the dots to the center (c). Are the angles identical? I see not.

I'm having difficulty figuring out what you're doing here (what are "concurrent circles?)

In any case, this doesn't seem to have anything to do with the expansion of the Universe, since the only possible geometry in that case places us (the observer) at the exact center of an expanding sphere, and every other point in the Universe is seen as a projection on the surface of that sphere. The angle between any two points never changes with time.

by **rstevenson** » Sun Oct 28, 2012 2:42 pm

Hi Ernie. I hope you don't mind me butting in here.

Your geometrical construction works as you described it, but it does not properly represent the expansion of space. Try this instead...

Draw a circle in the sky, encompassing a portion of your view of the universe at that point in time. Pick two points on the circle, p1 and p2, being the locations of a couple of galaxies perhaps. Draw radii to them from the origin 0, which is where you are in the universe. Now wait several billion years while space expands.

Draw a second circle, centered on the origin (you're at the centre of your observable universe so you haven't moved) and touching the same two galaxies. It may have faded over time, so you may need to redraw the first circle at its original radius just as a reminder of how big it was. Extend the radii that you drew before to p1 and p2 until they intersect the second circle at p3 and p4. You'll find that p3 and p4 are where the galaxies are now. Or do it the other way 'round. Find your two galaxies and draw radii from them to the origin. You'll find each new radius lies along the old radius exactly.

Note 1: real galaxies may well have some proper motion which would cause them to appear slightly offset from our idealized situation. For example, the Milky Way and Andromeda are gradually getting closer to each other. But that proper motion has nothing to do with the expansion of space.

Note 2: this is, of course, vastly simplified. As Chris has pointed out we can only see "now" and must infer the rest. But geometrically speaking the above analogy is reasonable.

Rob

by **ErnieM** » Sun Oct 28, 2012 12:18 pm

Crish wrote:

No they aren't. The angles are identical. There's absolutely no way of telling that any expansion occurred by looking at the angular position of the dots. The only way to detect expansion is to measure the change in distance... something that we can't do in the case of the Universe, although we can infer distance and expansion velocity from the redshift.

two concurrent circles with r1 and r2 radi (r1 is 1/2 inch shorter than r2), you are standing at the shared center (c). r2 - r1 represents the space expansion from the center. draw a radius of the large circle (your line of site), mark two dots (d1 and d2) on the inner circle 1/4 inch equidistant from your line of site intersection. do the same on the outer circle (d3 and d4). mark two more dots (d5 and d6) on the outer circle 1/2 inch equidistant from you line of site. connect all the dots to the center (c). Are the angles identical? I see not.

by **Chris Peterson** » Fri Oct 26, 2012 4:02 pm

ErnieM wrote:Ok, let us look at it your way. You are stationary at the center of your big balloon with two dots on the inside surface. Observation 1 is taken at 10 feet radius. Factoring the balloons elasticity out, as the balloon expands, observation 2 is taken at radius plus two inches (same distance as the separation between the dots). The line of site angles at observation 2 and subsequent observations is greater than that of observation 1.

No they aren't. The angles are identical. There's absolutely no way of telling that any expansion occurred by looking at the angular position of the dots. The only way to detect expansion is to measure the change in distance... something that we can't do in the case of the Universe, although we can infer distance and expansion velocity from the redshift.

by **ErnieM** » Fri Oct 26, 2012 9:35 am

Chris wrote:

ErnieM wrote:
No arguments when it comes to angular movement. Allow me to illustrate. Observation 1. Using a partially inflated balloon placed ten feet from me, I marked two dots one half inch apart. I inflated the balloon until the distance between the dots are two inches apart (a 2d representation of space expansion). Then I move the balloon one inch away, now I have a 3d illustration of space expansion. This is observation 2. The line of site angles at observation 2 and subsequent observations is greater than that of observation 1. This illustration does not involve any angular motion.
I fail to see any connection between this analogy and the Universe. We are not viewing a balloon from the outside. We are at the center of the balloon. There is nothing to suggest that different parts of the Universe are independently expanding around local centers.

There's no reason to think that gravity was any stronger in the early Universe than it is now. Of course, there have been many galactic collisions and mergers, many of which we do see.

Ok, let us look at it your way. You are stationary at the center of your big balloon with two dots on the inside surface. Observation 1 is taken at 10 feet radius. Factoring the balloons elasticity out, as the balloon expands, observation 2 is taken at radius plus two inches (same distance as the separation between the dots). The line of site angles at observation 2 and subsequent observations is greater than that of observation 1.

Chris worte:

ErnieM wrote:The young galaxies are closer to each other before space between them expanded.
Yes, but that doesn't mean gravity is stronger. It just means those galaxies feel stronger forces from gravity. Perhaps that's what you meant? There's no evidence that the Universal Gravitational Constant has changed with time.

You are absolutely right. I am referring to the (inverse-square law) law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance, r, between them, not the Universal Gravitational Constant. F=G(m1*m2)/r²

by **Chris Peterson** » Wed Oct 24, 2012 3:38 pm

ErnieM wrote:No arguments when it comes to angular movement. Allow me to illustrate. Observation 1. Using a partially inflated balloon placed ten feet from me, I marked two dots one half inch apart. I inflated the balloon until the distance between the dots are two inches apart (a 2d representation of space expansion). Then I move the balloon one inch away, now I have a 3d illustration of space expansion. This is observation 2. The line of site angles at observation 2 and subsequent observations is greater than that of observation 1. This illustration does not involve any angular motion.

I fail to see any connection between this analogy and the Universe. We are not viewing a balloon from the outside. We are at the center of the balloon. There is nothing to suggest that different parts of the Universe are independently expanding around local centers.

There's no reason to think that gravity was any stronger in the early Universe than it is now. Of course, there have been many galactic collisions and mergers, many of which we do see.
The young galaxies are closer to each other before space between them expanded.

Yes, but that doesn't mean gravity is stronger. It just means those galaxies feel stronger forces from gravity. Perhaps that's what you meant? There's no evidence that the Universal Gravitational Constant has changed with time.

by **ErnieM** » Wed Oct 24, 2012 3:29 pm

Chris wrote:

You can wait until the end of time, and you'll never see the slightest angular movement between galaxies due to the expansion of space, because there is none. Put differently, the coordinates of galaxies on the sky are absolutely fixed in terms of cosmological expansion.

No arguments when it comes to angular movement. Allow me to illustrate. Observation 1. Using a partially inflated balloon placed ten feet from me, I marked two dots one half inch apart. I inflated the balloon until the distance between the dots are two inches apart (a 2d representation of space expansion). Then I move the balloon one inch away, now I have a 3d illustration of space expansion. This is observation 2. The line of site angles at observation 2 and subsequent observations is greater than that of observation 1. This illustration does not involve any angular motion.

There's no reason to think that gravity was any stronger in the early Universe than it is now. Of course, there have been many galactic collisions and mergers, many of which we do see.

The young galaxies are closer to each other before space between them expanded.

by **Chris Peterson** » Sun Oct 21, 2012 2:36 pm

ErnieM wrote:The universe is expanding in all directions, galaxies are moving away from us and from one another. It is also conceivable that these galaxies (both visible and dark matter components) in close proximity have collided and merged given gravity was at full force at those times. So it takes a long time. There is no need to rush. The quest for knowledge is not a race against time.

You can wait until the end of time, and you'll never see the slightest angular movement between galaxies due to the expansion of space, because there is none. Put differently, the coordinates of galaxies on the sky are absolutely fixed in terms of cosmological expansion.

There's no reason to think that gravity was any stronger in the early Universe than it is now. Of course, there have been many galactic collisions and mergers, many of which we do see.

by **ErnieM** » Sun Oct 21, 2012 12:41 pm

Chris wrote:

There is no "lateral" expansion as you describe. The angular position of an object on the sky does not change with time because of the expansion of the Universe (and in fact, we cannot see ordinary lateral motion between different bodies at cosmological distances because doing so would require observations over thousands or millions of years, not decades).

We measure the rate the Universe is expanding by comparing redshift and distance. Redshift is a primary measurement; distance is often problematic, and depends on multiple proxies, each with various strengths and weaknesses.

The universe is expanding in all directions, galaxies are moving away from us and from one another. It is also conceivable that these galaxies (both visible and dark matter components) in close proximity have collided and merged given gravity was at full force at those times. So it takes a long time. There is no need to rush. The quest for knowledge is not a race against time.

by **Chris Peterson** » Fri Oct 19, 2012 2:10 pm

ErnieM wrote:Color shifting is a "property/characteristic" of light waves as the line of site's distance between the emitting source and the observer changes. As space expands in all directions the distance between the 1BLY galaxies grew. Even at such large distance a periodic observations (say every 10 or more years) of these blank spots can reveal the current lateral positions of the emitting sources. Given these data, we can extrapolate the "space rate of expansion".

There is no "lateral" expansion as you describe. The angular position of an object on the sky does not change with time because of the expansion of the Universe (and in fact, we cannot see ordinary lateral motion between different bodies at cosmological distances because doing so would require observations over thousands or millions of years, not decades).

We measure the rate the Universe is expanding by comparing redshift and distance. Redshift is a primary measurement; distance is often problematic, and depends on multiple proxies, each with various strengths and weaknesses.

by **ErnieM** » Thu Oct 18, 2012 10:44 am

ErnieM wrote:
I vision the galaxies when the universe was only 1BLY old to be closer to each other and now have "moved away?" from each other and in our real time have "moved out" of the Hubble's line of site due to the expansion of space.

Chris wrote:
I'm not sure what you mean by that. Where the galaxies are "now" doesn't matter. All that we can see is where they were when the photons we are now capturing were emitted.

Color shifting is a "property/characteristic" of light waves as the line of site's distance between the emitting source and the observer changes. As space expands in all directions the distance between the 1BLY galaxies grew. Even at such large distance a periodic observations (say every 10 or more years) of these blank spots can reveal the current lateral positions of the emitting sources. Given these data, we can extrapolate the "space rate of expansion".
Back when the universe was young, mega stars' evolution were at very rapid pace with abundant material in greater proximity and gravity was at full force. We may even get lucky to observe one or more super novae explosions of those periods making the extrapolation more accurate. I wonder if the JWST with its higher instruments resolution has this in mind.

by **Chris Peterson** » Wed Oct 17, 2012 1:48 pm

ErnieM wrote:I vision the galaxies when the universe was only 1BLY old to be closer to each other and now have "moved away?" from each other and in our real time have "moved out" of the Hubble's line of site due to the expansion of space.

I'm not sure what you mean by that. Where the galaxies are "now" doesn't matter. All that we can see is where they were when the photons we are now capturing were emitted.

by **ErnieM** » Wed Oct 17, 2012 1:37 pm

That makes sense. However, I suspect that this doesn't reflect the known position of any of the objects, but is simply a statistical distribution based on size, color, and the fact that the volume of space in this image is greater for objects seen earlier in the Universe.

I vision the galaxies when the universe was only 1BLY old to be closer to each other and now have "moved away?" from each other and in our real time have "moved out" of the Hubble's line of site due to the expansion of space.

by **Chris Peterson** » Tue Oct 16, 2012 5:15 pm

BMAONE23 wrote:Here is a good visual displaying the relative distances of various objects in the Hubble Extreme Deep Field image

That makes sense. However, I suspect that this doesn't reflect the known position of any of the objects, but is simply a statistical distribution based on size, color, and the fact that the volume of space in this image is greater for objects seen earlier in the Universe.

by **BMAONE23** » Tue Oct 16, 2012 5:06 pm

Chris Peterson wrote:
BMAONE23 wrote:Perhaps what is needed is another copy of the image with a rollover giving the various distances to some of the galaxies like different colored circles for varying distances, this would stop confusion with the misinterpretation of the text implying that all the galaxies in the image are 13GLY away. Anyone up for the task?
Determining the redshift means placing a spectroscopic instrument on different galaxies- something that I doubt has been done for many of those showing in this image. And tracking down the handful that have been measured and finding them in this image sounds like quite a lot of effort.

Here is a good visual displaying the relative distances of various objects in the Hubble Extreme Deep Field image

by **Chris Peterson** » Tue Oct 16, 2012 3:19 pm

ErnieM wrote:The HEDF 2012Oct12 is a "blank" spot towards the Forrmax constellation. Where HDF-S and HDG-N? How do this three "blank" spots triangulate? What would it mean if the farthest red-shifting galaxies in these "blank" spots were relatively of the same age of 13 billion years, equidistant to and moving away from earth in opposite directions? Is this even possible? Could it be that the 14+ billion years to the BB is simply a limitation of current technological capabilities?

A "blank" spot is just a part of the sky chosen that doesn't have any local objects blocking it (stars, dust, or nebulas within the Milky Way, or nearby galaxies outside it). For small fields of view, most of the sky is "blank" in this way.

The most redshifted galaxies we can detect will be about 13 billion years old (i.e. we are seeing them as they were when the Universe was less than 1 billion years old) no matter where we look. It is nothing technical that limits how far we can potentially see- that is a limitation of physics. We can't see any photons emitted by objects moving away from us at greater than c, which is what all objects beyond our observable universe are doing.

We see bodies moving away from us at very high speeds and in opposite parts of the sky. We see them because they are inside our observable universe. These same bodies would not be in each others observable universes, however. Observers at either of those distant spots would be seeing the Milky Way as it was early in the Universe, and not much beyond that.

by **bystander** » Tue Oct 16, 2012 2:37 pm

kimmeyh wrote:What would a version of this picture look like if everything < 12.5 billion years old was removed?

Chris Peterson wrote: I assume you are asking what the image would look like if all the galaxies that formed in the first billion years of the Universe were removed? There would be a lot fewer galaxies in the image. Probably only a few percent are that old.

I think they may be asking "What if everything closer than 12.5 bly was removed?"

by **rstevenson** » Tue Oct 16, 2012 2:09 pm

ErnieM wrote:... What would it mean if the farthest red-shifting galaxies in these "blank" spots were relatively of the same age of 13 billion years, equidistant to and moving away from earth in opposite directions? ... .

That's exactly what we see. The universe looks the same to us in all directions. But that does not mean we just happen to be in the center of the universe. It means we are in the center of our observable universe. The universe itself is larger than the part of it that we can see. (There is some disagreement about how much larger.)

Rob

by **ErnieM** » Tue Oct 16, 2012 1:58 pm

Bystander write:

ErnieM wrote:
Is this the only sweet spot Hubble is able to see galaxies as young as 13 billions years ago? Are we looking towards the direction of a long (13 billion years) elongated tapering tube of a Picard horn shaped universe? The farther we are able to see, space are more compact and dense hence the red-shifted young galaxies are much closer to each other.

This is just one relatively "blank" spot in the sky where they chose to aim the Hubble. We could choose any other "blank" spot and get much the same results, just different galaxies. The HDF-S and HDF-N are two early results of the same type of images.

The HEDF 2012Oct12 is a "blank" spot towards the Forrmax constellation. Where HDF-S and HDG-N? How do this three "blank" spots triangulate? What would it mean if the farthest red-shifting galaxies in these "blank" spots were relatively of the same age of 13 billion years, equidistant to and moving away from earth in opposite directions? Is this even possible? Could it be that the 14+ billion years to the BB is simply a limitation of current technological capabilities?

by **Chris Peterson** » Tue Oct 16, 2012 1:09 pm

kimmeyh wrote:What would a version of this picture look like if everything < 12.5 billion years old was removed?

I assume you are asking what the image would look like if all the galaxies that formed in the first billion years of the Universe were removed? There would be a lot fewer galaxies in the image. Probably only a few percent are that old.

by **BDanielMayfield** » Tue Oct 16, 2012 12:30 pm

kimmeyh wrote:What would a version of this picture look like if everything < 12.5 billion years old was removed?

Good question kimmeyh. I would imagine that the larger and brighter galaxies would be filtered out, but the great majority of the faint fuzzies would still be there, and those make up the large majority of the 5500 count.

Bruce

by **kimmeyh** » Tue Oct 16, 2012 12:55 am

What would a version of this picture look like if everything < 12.5 billion years old was removed?

by **BDanielMayfield** » Mon Oct 15, 2012 5:34 pm

starchaser wrote:

This image compares the angular size of the XDF field to the angular size of the full Moon. The XDF is a very small fraction of sky area, but it provides a "core sample" of the heavens by penetrating deep into space over a sightline of over 13 billion light-years. Several thousand galaxies are contained within this small field of view. At an angular diameter of one-half degree, the Moon spans an area of sky only one-half the width of a finger held at arm's length.
Source: http://hubblesite.org/newscenter/archiv ... 7/image/c/

Truly amazing, and gets things into perspective about the vastness of our Universe!

Very true starchaser. Thanks for providing the moon for comparison here. There have been many interesting comments about colors and such, but to me the fantastic thing about this apod is the shear number of galaxies packed into such a tiny area of sky. What does this imply about the total number of galaxies inside our temporal event horizon? Pondering this led me to the following:

I believe there are about 41,255 square degrees in the entire celestial sphere. Since there are 60^2 arc minutes per degree^2, there are about 148,518,000 arcmin^2 across the entire sky. So then at 4.6 arcmin^2 this XDF represents 1/32,286,522nds of the whole sky. If this 5500 galaxies per 4.6 acrmin^2 is a fair sampling of the universe at this distance then we can extrapolate the existence of around 1.776x10^11 galaxies, NOT COUNTING all galaxies closer than the distances sampled by the XDF! Therefore the often quoted estimate of 100 billion (1x10^11) would appear to be too low. 300 billion would seem more accurate, but my pure guess is that 1 trillion galaxies may also be on the low side. I wonder how many more the JWST might be able to reel in.

Is my mathmatical thinking on this accurate?

Bruce

Starship Asterisk*

APOD: The Hubble Extreme Deep Field (2012 Oct 14)

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