# Why are there galaxies everywhere we look?

## Main Question or Discussion Point

Apologies in advance: This is my first post; this might be a stupid question; I am not a scientist (just an over-educated carpenter with an interest in science). In any case, here is my question:

If the universe started from a single point in space in a "big bang" why is it that the Hubble sees the most ancient (and therefore youngest) galaxies in all directions? Wouldn't they be clustered?

PeterDonis
Mentor
If the universe started from a single point in space in a "big bang"
It didn't. To the extent that the question "where did the Big Bang happen?" even has an answer, the answer is "everywhere". The universe is not expanding into a pre-existing space; it's more correct to think of space itself as expanding (though that view has issues as well).

Oh gosh...I hate "issues". So I assume there really isn't an answer to my question?

Bandersnatch
The answer is "yes they would cluster". That they don't is a good indication that the universe did not actually start as an explosion from a single point in space.
It's just a misconception about what the theory says.

PeterDonis
Mentor
So I assume there really isn't an answer to my question?
Sure there is. The answer is that the universe does not work the way your question assumes that it works. If the universe were indeed expanding from a single point into a pre-existing space, then you would expect to see a cluster of ancient galaxies all in one direction, and no ancient galaxies in other directions. But we don't see that, so the model of the universe as expanding from a single point into a pre-existing space doesn't work; it's falsified by observation. Fortunately, the Big Bang theory does not use that model; it uses a different model, which I briefly described in my previous post.

So that means the galaxies are not moving away from each other? Space itself is just getting "larger"?

Bandersnatch
They are. They're moving away because space is "getting larger" (distances grow).

Getting confused. Distances grow, but isn't the space then moving, not the objects themselves? Maybe it depends on how you define "moving".
I'm appreciating you folks taking the time to answer me. I rarely find anyone to ask these questions of.

Also what the heck is "Latex Preview"? Sounds kind of kinky.

Bandersnatch
When you hear about the expanding space, it's pretty much the same thing as saying that "distances grow". Your observation that the objects themselves don't move is spot on - they stay where they have always been (barring local "proper" motion). That's why, for example, there is nothing contrary to the postulates of Relativity in saying that some distant galaxy or other is receeding at velocities exceeding the speed of light.

(latex is a forum code used for writing equations. E.g., F=ma using latex looks like so $F=ma$. There's a guide in the "info/how-to" menu.

PeterDonis
Mentor
Distances grow, but isn't the space then moving, not the objects themselves?
The word "moving" is relative; it doesn't have a unique physical definition. The physical fact is that distances grow (actually, even that can be a matter of interpretation--see below.) Whether you want to view that as the objects moving apart, or as the objects staying "in the same place" but space expanding, is a matter of interpretation, not physics. (As bandersnatch noted, though, if you interpret it as objects moving apart, they can move apart faster than light, so the usual rules of special relativity don't apply to this kind of "motion". This is why many people favor the "expanding space" view.)

The above is why I said that the view of space as expanding has "issues"; you have to be careful to distinguish the physical facts and observations from the models and interpretations we use to analyze them. That can be difficult to do precisely; for example, take the "fact" I mentioned above, that distances grow. Actually, these "distances" themselves are frame-dependent; the "distances" that cosmologists are referring to are distances in the FRW coordinate chart, the standard chart used in cosmology to model the universe. Choosing other coordinates would give other "distances". Also, none of these coordinate distances are directly observed; there are various observations that can be used to give distance measures, but they give different answers and the answers don't necessarily match up with any of the coordinate distances. Picking out the actual observations that tell us that the universe is expanding in an invariant (i.e., not frame-dependent) sense requires considerable care.

For a good overview of this subject and more detail about the issues I've mentioned, I suggest reading Ned Wright's cosmology tutorial:

http://www.astro.ucla.edu/~wright/cosmo_01.htm

The second part, in particular, talks about the various distance measures I mentioned.

Thanks for the lead to the Wright tutorial. Will read to get more informed before I continue my queries. And thanks for explaining "latex". That was a relief!

marcus
Gold Member
Dearly Missed
Hah! This post is already obsolete. Bandersnatch and Peter already clarified things. I wrote this before I saw their continued conversation. slow this morning. I'll post this anyway.
...If the universe started from a single point in space in a "big bang" why is it that the Hubble sees the most ancient (and therefore youngest) galaxies in all directions? Wouldn't they be clustered?
It didn't. ... it's more correct to think of space itself as expanding...
Oh gosh...I hate "issues". So I assume there really isn't an answer to my question?
Hi Rayven, I'm not sure what Peter means about "issues". Pared down to essentials, he gave you a good answer to your question. You asked "If A, then why B?" He pointed out that A is not true. That resolves the question.
It is not true that the universe started from a single point in space. There is no point in space where you can point your finger and say "the universe started over there".
that is a misconception fostered by mass media---TV programs on Discovery Channel that show pictures of spectacular explosions and talk about "from a singularity" as if the word singularity meant "a single point in space."

The Scientific American had a good article called Misconceptions about the Big Bang. I keep a link in my signature. It is the "Charley" link because it is by Charley Lineweaver a world class cosmologist who knows how to write clear simple English and use pictures. Maybe you should read it and ask a new question.

Beginner questions in cosmology very often stem from trouble with the words. (and misconceptions fostered by mass media). I hesitate to say anything because I think Lineweaver says everything better, but I'll take a chance and hope it doesn't add to the confusion :)
I try not to say "space expands" because that triggers the question what is space, and "into what" does it expand?
Instead I say something like this:

The universe has a beautiful and natural idea of being at rest with respect to the most ancient light we can see, light coming to us from all directions from the most ancient matter we can see---dazzling hot gas before it cooled enough to condense into dust clouds and galaxies of stars. A galaxy is at rest if the ancient light is approximately the same temperature in all directions. Then it is stationary relative to the ancient matter from the earliest days when the gas cooled enough to become transparent. If it were moving there would be a doppler hot spot ahead and a doppler cool spot behind.

Hubble expansion law says that distances between stationary objects are increasing at a certain percentage rate.

This has been checked a lot. The rate at present (as best we can measure) is about 1/144 or 1/145 of one percent per million years. Every million years, large-scale distances increase by that small fraction of a percent.

The 1915 General Relativity equation which is our best law of how geometry works, so far, allows large-scale distances to change in ways that are not intuitive to us. That is what "spacetime curvature" is about. You have to accept that two galaxies can each be at rest relative to the ancient light and yet the distance between them can be undergoing a percentage growth.

And the GR equation also (using a simplified version derived from it by a guy called Alex Friedmann) tells us how the percentage rate must evolve over time.

It says that the percentage rate of distance growth was much greater back when the universe was much denser. Naturally since distances have been increasing it has been getting less dense. So way back when, it was more dense. The math says distance growth was more rapid then.

I'm trying, as a kind of conversational experiment, to talk without using familiar material analogies , like "bang". And without talking about "space" as if it were some kind of metaphorical material. As far as I know, there is no fabric or material. There are, however, distances, and angles, we can measure them, they change according to some formulas. :) I think you said you were a carpenter :w You know something about lengths, areas, angles----geometry in other words. GR says geometry is dynamic, ie. it changes and interacts with matter. In cosmology we get a taste of that, in a very direct way.

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If the universe were indeed expanding from a single point into a pre-existing space, then you would expect to see a cluster of ancient galaxies all in one direction, and no ancient galaxies in other directions.
I would expect to see nothing. This scenario results in a giant black hole.

PeterDonis
Mentor
This scenario results in a giant black hole.
After enough time has passed, yes. But "enough time" could be very long if the initial outward velocities of all the pieces of matter were very fast.

phinds
Gold Member
Rayven, I recommend the link in my signature. It is a good one-page intro to the part of cosmology that you are asking about, written with a lot of help from the folks on this forum.

The links to articles you folks offered me were extremely helpful. I found the Scientific American article via Marcus to be the most concise and layman friendly. I am thinking far more clearly about this topic at this point. I do wonder how there can be so much misconception being put out there not just by the media but by some of the scientists/astronomers themselves. I sure was caught up in it. So much for watching Cosmos....

marcus