Farthest galaxies ever seen

[Zarathustra]

This article got me thinking about an issue I've never heard anyone else ask or explain.
www.foxnews.com/story/0,2933,288827,00.html

If it took 13.2 billion years for the light from these galaxies to reach us, that means that they started emitting that light at a time when the universe itself was only .5 billion years old--4% of its present age. Obviously, the universe was much, much smaller at that time. So the distance between our location and that galaxy was much, much less than 13.2 billion light years. Given the fact that nothing moves faster than the speed of light (including, I assume, the expansion of the universe itself), then why did it take so long for the light to reach us? At 4% of its present age, was the universe really so big that light from one point would take 13.2 billions years to reach another point--even taking into account the expansion? I suppose the answer would have to be yes, since we can see that light now. But what is the limit? The universe started out as a singularity. All matter and space compressed to one point. A few seconds after this, the universe was a lot bigger, but surely still small enough that light could easily travel from one "end" to the other faster than the expansion itself. At what point in the expansion of the universe did it get big enough that the light from one point would take so long to travel from one end to the other that it is just now getting to us? The farther we look out into space, the more we see objects that were closerto us when they first started emitting that light because the universe itself was much smaller. Paradoxically. I know that sounds crazy, but the farther we look, the older the objects are. Thus they were younger objects in terms of the age of the universe, and represent a much smaller stage.

Let's imagine that we could see objects that were around at the very beginning (or very close to it). If the universe were less than a light year across at that time, sure, it would take more than a year to reach us, because it's expanding, but it certainly wouldn't take billions of years to cross such a relatively small space. So at some point in the past we'd cross some boundary at which the light was so old that it would have already passed us by and we wouldn't be able to see it, because it was emitted from a point much, much closer to us.

So why doesn't this skew our measurements of either age or distance of very old objects?

Ah, crap, I feel like I'm still not asking the question correctly. Anybody else every think along these lines?

[Phantasm]

I think maybe that the technology used to view the light from these universes has only been around for a short period of time, relatively.

Also, the actual act of searching for these places is a relatively new phenomenon too.

We've only been on this planet for the blink of an eye compared to the age of the universe.

I know what you're saying, that the light should have reached us before now anyway, given the speed of light, and the speed of expansion of the Universe, but that's the only explanation I can come up with.


My head hurts now

[Loredoctor]

The universe started out as a singularity. All matter and space compressed to one point. A few seconds after this, the universe was a lot bigger, but surely still small enough that light could easily travel from one "end" to the other faster than the expansion itself.

Because for a while, the universe was opaque. That is, the energy level of the gases prevented light from moving across the universe.

At what point in the expansion of the universe did it get big enough that the light from one point would take so long to travel from one end to the other that it is just now getting to us?

It's not that it is just now getting to us. Our telescopes and software are powerful/sensitive enough to see that far. But the light had to travel an enormous distance amd has been redshifted due to space's expansion. So literally, we are looking into the past.

The farther we look out into space, the more we see objects that were closerto us when they first started emitting that light because the universe itself was much smaller. Paradoxically. I know that sounds crazy, but the farther we look, the older the objects are. Thus they were younger objects in terms of the age of the universe, and represent a much smaller stage.

Well, not really strange. Just that light takes a while to reach us while space expands. Thus, the further we look the greater the speed of recession and the more the light is redshifted and 'older'.

Let's imagine that we could see objects that were around at the very beginning (or very close to it). If the universe were less than a light year across at that time, sure, it would take more than a year to reach us, because it's expanding, but it certainly wouldn't take billions of years to cross such a relatively small space.

Again, opacity.

So at some point in the past we'd cross some boundary at which the light was so old that it would have already passed us by and we wouldn't be able to see it, because it was emitted from a point much, much closer to us.

By why would the source stop emitting? I mean, the light emitted by an object ten billion years ago would have passed us by five billion years ago (if the universe is 15 billion YO). But if that object is still emitting, then what we would is a younger version of the ancient star. If that makes sense.

So why doesn't this skew our measurements of either age or distance of very old objects?

Because astronomers factor in cosmic expansion - the Hubble constant.

Ah, crap, I feel like I'm still not asking the question correctly. Anybody else every think along these lines?

Good thread, by the way.

[Zarathustra]

Because for a while, the universe was opaque. That is, the energy level of the gases prevented light from moving across the universe.

Ah, I do seem to remember something about that. How long did it last and how big was the universe at that point?

It's not that it is just now getting to us. Our telescopes and software are powerful/sensitive enough to see that far. But the light had to travel an enormous distance amd has been redshifted due to space's expansion. So literally, we are looking into the past.

I understand that we're just now able to see it, technologically. And, yes, it traveled an enormous distance. In fact, it traveled 13.2 billion light years, which means we're seeing them as they were 13.2 billion years ago. However, the universe has been expanding during all that time. So those galaxies weren't 13.2 billion light years away 13.2 billion years ago. They were much closer.

Just that light takes a while to reach us while space expands. Thus, the further we look the greater the speed of recession and the more the light is redshifted and 'older'.

Yes, but isn't there a limit at which the recession speed would surpass the speed of light (which is impossible)? At that point, wouldn't we cease to see any light?

By why would the source stop emitting? I mean, the light emitted by an object ten billion years ago would have passed us by five billion years ago (if the universe is 15 billion YO). But if that object is still emitting, then what we would is a younger version of the ancient star. If that makes sense.

But light sources stop emitting all the time. In fact, there's no object that has been glowing for 96% of the age of the universe. Our own sun has only been going for 4-5 billion years. Many of the stars we see now could have already gone out. Surely you're not saying that we're still seeing those very distant galaxies because they're still glowing, are you?

[Loredoctor]

But light sources stop emitting all the time. In fact, there's no object that has been glowing for 96% of the age of the universe. Our own sun has only been going for 4-5 billion years. Many of the stars we see now could have already gone out. Surely you're not saying that we're still seeing those very distant galaxies because they're still glowing, are you?

It is true they stop emitting, but some stars are incredibly ancient. I would not be surprised if some are still shining - albeit less - today. But I am not saying that we still are seeing those galaxies because they are still shining. I am saying that it's possible they are still emitting light.

I'll reply to your other points soon.

[Loredoctor]

Because for a while, the universe was opaque. That is, the energy level of the gases prevented light from moving across the universe.

Ah, I do seem to remember something about that. How long did it last and how big was the universe at that point?

It was a million years old.

It's not that it is just now getting to us. Our telescopes and software are powerful/sensitive enough to see that far. But the light had to travel an enormous distance amd has been redshifted due to space's expansion. So literally, we are looking into the past.

I understand that we're just now able to see it, technologically. And, yes, it traveled an enormous distance. In fact, it traveled 13.2 billion light years, which means we're seeing them as they were 13.2 billion years ago. However, the universe has been expanding during all that time. So those galaxies weren't 13.2 billion light years away 13.2 billion years ago. They were much closer.

They were, but because space is expanding, and due to earlier opacity, our view of the universe is obscured. Light is redshifted (wavelengths 'drawn out') so that the light becomes difficult to see, and beyond a certain point, we cant see any of the young universe (opacity). Hence, the dark sky is really just the Doppler-Shifted light (light stretched out by cosmic expansion).

Without meaning to sound condescending, you have to understand that it is not that the galaxies are receding at certain velocities (and it appears that way), it's that space is expanding. So light from galaxy A might take x billion years to reach B, but as space is expanding that light is 'drawn out' - made fainter.

Yes, but isn't there a limit at which the recession speed would surpass the speed of light (which is impossible)? At that point, wouldn't we cease to see any light?

I don't believe the expansion happens faster than the speed of light, though there are theories there have been stages of incredibly fast expansion. But even then, light would still be heading to our view point. Do you want to think about something cool? Factor in the Observer Effect (quantum physics) into that; there are some theories that light 'knew' how to behave billions of years ago when you stepped out of your house and looked into the night sky yesterday.

[Zarathustra]

Loremaster, don't worry about sounding condescending. I'm just glad to have someone to talk to about these issues.

Okay, so the universe was 1 million years old before it became transparent. How big was it at that point? When I do online searches for the timeline of the universe, I can find info on events at time x, but not size at time x. Do you have a good link?

It is indeed an interesting thought that the dark sky is actually the redshift phenomenon shifted beyond our ability to see. Is this also part of the background radiation (microwave?) that led to the Big Bang theory? Radiation from every direction which is the "echo" of the BB?

I understand that it is not galaxies receding, but space itself. This is why the farther you look, the faster they are receding from you (like dots on an expanding balloon). No problem. But given this linear acceleration, there must exist some spacial point at which the velocity of receding galaxies equals the speed of light (which is impossible), otherwise, there's another factor which interferes with the accelerating recession rates due to distance.

[Loredoctor]

Loremaster, don't worry about sounding condescending. I'm just glad to have someone to talk to about these issues.

Cool. I just worry I sound like I am lecturing sometimes.

Okay, so the universe was 1 million years old before it became transparent. How big was it at that point? When I do online searches for the timeline of the universe, I can find info on events at time x, but not size at time x. Do you have a good link?

From my books (and I will provide a link), it states that the opacity of the universe lasted between 50,0000 to 100 million years (most estimates place it closer to 50,000). That's about half the universe's present size (most expansion happened within a few hours after the Big Bang).

map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html
zebu.uoregon.edu/~imamura/123/lecture-7/lecture-6.html

It is indeed an interesting thought that the dark sky is actually the redshift phenomenon shifted beyond our ability to see. Is this also part of the background radiation (microwave?) that led to the Big Bang theory? Radiation from every direction which is the "echo" of the BB?

Bingo.

I understand that it is not galaxies receding, but space itself. This is why the farther you look, the faster they are receding from you (like dots on an expanding balloon). No problem. But given this linear acceleration, there must exist some spacial point at which the velocity of receding galaxies equals the speed of light (which is impossible), otherwise, there's another factor which interferes with the accelerating recession rates due to distance.

I don't think the velocity at some point would equal the speed of light. It's more the effect of an 'illusion'. Everything is expanding uniformly, but further the galaxy is away, the faster it appears to move away.

By the way, you might be interested in checking out Obler's Paradox.

I hope my reply helped.

[Avatar]

Interesting reading guys.

--A

[Zarathustra]

Most expansion happened in the first few hours of the Big Bang? I've never heard that. Are you saying that most of the universe's present size was achieved in hours? I'm aware of inflation, so that the quickest expansion happened at the beginning. But even your links says that inflation took the universe from extreme microscopic size to the size of a grapefruit. After that, it expanded normally. So I don't see how most of its size could have been achieved in a few hours.

Why do you say the relative velocities of receding galaxies is an illusion? They really are moving. And this movement really does have a measurable value. And the farther away they are, they really are moving faster relative to us. They have to move faster the farther you look, because expansion is happening everywhere. In other words, looking at galaxies in a straight line, the farthest galaxies are not only receding away from us, but also from the intermediary galaxies in the middle of this line. That can't be an illusion.

Maybe the universe isn't big enough for the recession rate to reach the speed of light. But what if it never stops expanding? At some point it would have to reach this velocity.

Oh well, that's not really connected to my original question, anyway.

Obler's paradox is indeed interesting, and definitely a logical argument against a static, infinite universe.

Your links are cool. I've read much of that elsewhere, but it's nice to have a "refresher course." Still, I didn't see any timeline of the size of the universe, only a timeline of events (formation of particles, stars, galaxies, etc.).

One interesting thing I found on my own was that the limit of objects would could potentially see is not 13.7 billion light years away, even though that's as old as the universe itself. It's more like 53 billion light years away, due to the expansion of the universe during that time. During that first year of "travel," a photon goes 1 light year. But by now, that first light year has been stretched tremendously due to the expansion of the universe, so that the first years of its journey contribute much more to its distance than later years.

I don't know if this is true or not, but it makes sense to me. And it goes to my original question. It seems obvious to me that even though the universe is 13.7 billion years old, the farthest objects wouldn't be 13.7 billion light years away. You'd have to assume a static universe to get that figure. But doesn't this also present a problem of dating these objects? Just because they are 13.7 billion light years away doesn't mean that they'd be 13.7 billion years old. They'd be a lot younger, since it didn't really take light that long to get here. When the light began its journey, the universe was smaller, thus, even though they are 13.7 billion light years away now, the light didn't really travel all those light years originally. I think.

[Loredoctor]

Most expansion happened in the first few hours of the Big Bang? I've never heard that. Are you saying that most of the universe's present size was achieved in hours? I'm aware of inflation, so that the quickest expansion happened at the beginning. But even your links says that inflation took the universe from extreme microscopic size to the size of a grapefruit. After that, it expanded normally. So I don't see how most of its size could have been achieved in a few hours.

I'm not saying most of its size was achieved in a few hours, but many theories suggest that expansion was extremely fast and has slowed down.

Why do you say the relative velocities of receding galaxies is an illusion? They really are moving. And this movement really does have a measurable value.

Sorry, I wasn't being clear. What I mean is that space is expanding not that the galaxies are flying off (even though they are from our perspective). Second, the fact that the further away they are the faster they move is really due to perspective:

en.wikipedia.org/wiki/Image:Raisinbread.gif

The analogy of the raisins in dough as the bread expands might be helpful if you think of the raisins as galaxies and dough as space. The further the raisin is from our raisin, the more space it has to travel - the more it is redshifted - and thus the faster it appears to be moving.

[Zarathustra]

I'm not saying most of its size was achieved in a few hours, but many theories suggest that expansion was extremely fast and has slowed down.

Yes, inflation.

What I mean is that space is expanding not that the galaxies are flying off (even though they are from our perspective). Second, the fact that the further away they are the faster they move is really due to perspective.

The analogy of the raisins in dough as the bread expands might be helpful if you think of the raisins as galaxies and dough as space. The further the raisin is from our raisin, the more space it has to travel - the more it is redshifted - and thus the faster it appears to be moving.

But distant galaxies don't merely appear to be moving faster, they really do move faster from us. All motion is relative; saying that it's a matter of perspective doesn't mean that it's not real. Raisins in expanding bread really are moving away from each other, and their relative velocities are real.

Another way to put it: no matter where you stand on the earth, it still takes 24 hours to make a complete rotation. But you're going much faster at the equator, because you're traveling a greater distance in this rotation. So your velocity is "just a matter of perspective," depending on where you stand. But this doesn't mean that the velocity differences aren't real.

Redshift itself is an effect of velocity. If they weren't really going faster, then they wouldn't have such a big redshift. Now granted, part of that redshift is due to our own motion. We're moving away from those galaxies, too. So it's really a measure of the combined velocities. But that's the way all velocity is calculated. If two cars pass each other on the freeway going opposite directions, they are receding away from each other at a velocity which is the sum of their individual speeds. Now with galaxies, it's a little more complicated because even galaxies moving in the same direction are moving away from each other, because the space between them is expanding. But the effect is the same. Just because the situation would look different if we were following one of those cars in our own car doesn't mean that the original two aren't receding from each other at a real rate.

[Loredoctor]

But distant galaxies don't merely appear to be moving faster, they really do move faster from us. All motion is relative; saying that it's a matter of perspective doesn't mean that it's not real. Raisins in expanding bread really are moving away from each other, and their relative velocities are real.

The galaxies are not moving with respect to the universe. It's space that's expanding. The galaxies have no velocity. I agree that the galaxies appear to movie due to relative positions. However, any redshifting of light is entirely due to space not that the galaxy has velocity with respect to the universe.

My point, perhaps I was unclear before, is that if a distant galaxy appears to be receding faster from you than a nearby galaxy, it doesn't meant that that distant galaxy really has that velocity.

Me thinks we're debating from the same side.

[Zarathustra]

Hmm, I'm going to have to respectfully disagree. Nothing moves with respect to the universe. That's the whole point of Einstein's insight. There is no absolute reference frame. Any kind of movement is only movement relative to body x or body y. To say that anything "really has that velocity" is meaningless. If there was only one body in the whole universe, you couldn't say that it has any movement at all, even if it were "really" moving. Actually, there's no sense that it would be "really" moving, so I can't even say that much. In addition, I couldn't say that it is sitting still, either.

So the galaxies do really have this velocity relative to us. Of course, if we were on a different galaxy, we'd measure different velocities for those very same galaxies. But that's the way it is when measuring any velocity. If I'm sitting on the side of the road, cars are moving 65 mph relative to me. But if I'm in one of those cars, then they aren't moving that fast relative to me. What's their "real" velocity? It's tempting to say that it's the velocity relative to the road. But the road is moving, too. Depending on where it is on the earth, it could be moving 20,000 mph. So that car could be going 20,065 mph. But not only is the earth spinning, it's going around the sun, etc., etc. The car has no "real" velocity, in the sense that there's only one answer. It's always a relative motion.

However, even though there are many different reference frames from which to take a measurement, relativity tells us that no matter which reference frame you choose, it could never be measured at more than c (speed of light). It doesn't matter if you think of it as real or apparent motion--it can't even appear to move faster than light. So my problem is that I've thought of a reference from from which objects would appear to move faster than light, and I can't think of any rationale to get me out of this line of thinking. All that counts is measurement events. No body's velocity can be measured at greater than c. Yet, the bigger the universe gets, the distant galaxies would surpass this limit.

I suppose we could just say that we'd stop seeing them at that point. Then there would be nothing to measure. But that still means that the universe itself would have to be expanding faster than light, even if we couldn't measure it. I'm stumped.

[Loredoctor]

Hmm, I'm going to have to respectfully disagree. Nothing moves with respect to the universe. That's the whole point of Einstein's insight. There is no absolute reference frame. Any kind of movement is only movement relative to body x or body y. To say that anything "really has that velocity" is meaningless.

Malik, I realise that. I've been following astrophysics all of my life, so I am very well aquainted with relativity. I actually quoted the previous statement above directly from a text book. I think you might misunderstand me, or that the textbook wasn't clear. What the statement means is that the galaxies do not have velocity with respect to space. The car analogy you used earlier is useful, although a bit misleading. You could also look at cosmic expanion another way (although this one lacks a third dimension):

Ant on a balloon model

The ant on a balloon model is a two-dimensional analog for three-dimensional metric expansion. An ant is imagined to be constrained to move on the surface of a huge balloon which to the ant's understanding is the total extent of space. At an early stage of the balloon-universe, the ant measures distances between separate points on the balloon which serves as a standard by which the scale factor can be measured. The balloon is inflated some more, and then the distance between the same points is measured and determined to be larger by a proportional factor. The surface of the balloon still appears flat, and yet all the points have appeared to recede from the ant, indeed every point on the surface of the balloon is proportionally farther from the ant than earlier in the life of the balloon universe. This explains how an expanding universe can result in all points receding from each other simultaneously. No points are seen to get closer together.

But this is why I said we are debating from the same side. All I am saying is that it is space that is expanding and thus causing redshift and the appearance that the more distance the galaxy is from us, the faster is appears to be moving. But it is not that galaxies are flying away from each other since the big bang, since that doesn't make sense. If the galaxies are receding from each other due to their own velocity, where are they receding to?

[Loredoctor]

No body's velocity can be measured at greater than c. Yet, the bigger the universe gets, the distant galaxies would surpass this limit.

I suppose we could just say that we'd stop seeing them at that point. Then there would be nothing to measure. But that still means that the universe itself would have to be expanding faster than light, even if we couldn't measure it. I'm stumped.

All it would mean is that light becomes infinitely redshifted. Further, I doubt we could see far enough for the relative velocities to exceed C, as the opacity of the early universe might prevent that.

I've just been reading some more and found out some interesting theories.

Apparently, when the universe was very young there was massive inflation of space/time. Accordingly, spacetime can expand faster than the speed of light (even Einstein's calculations allow for that). So there is a point where the light from galaxies will become infinitely redshifted. But with respect to the eigenpoints of spacetime, or space itself, the galaxies do not travel at more than the speed of light. From our observer position their light will 'stretch out' and vanish. (Louis Bernstein - The Big Bang and Beyond).

[Hyperception]

Some terms to consider in your discussion...

Light horizon or light cone
Neutrino Decoupling
Photon Decoupling
Standard candles and cepheid variables

[Loredoctor]

Standard candles and cepheid variables

I didnt think that they needed to be mentioned, as they are integral to Hubble's theory and observations.

By the way, where the hell can I find Hubble's book on observations?