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

[ErnieM]

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.

[Chris Peterson]

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.

[ErnieM]

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.

[Chris Peterson]

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.

[ErnieM]

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.

[Chris Peterson]

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.

[ErnieM]

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

[Chris Peterson]

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.

[ErnieM]

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.

[rstevenson]

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

[Chris Peterson]

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.

[ErnieM]

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."

[Chris Peterson]

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.