

What is 'Space' expanding into? - sun123
http://www.reddit.com/r/askscience/comments/qk58k/what_is_space_expanding_into/

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joejohnson
It's been a while since I've used Reddit. I was shocked by the insightful
answers and this subreddit's rules (no anecdotes, speculation, memes, jokes,
things which I hate about Reddit, etc.)

Here's one particularly intriguing reply:

[–]xieish 32 points 1 hour ago There isn't any [space outside of the
universe], and this comes from a fundamental misunderstanding of an expanding
universe. The universe isn't blowing up like a balloon - space itself is
getting larger, as everything moves farther and farther away from everything
else. The actual distance between points is increasing, not the size of the
container.

~~~
cmhamill
The subreddit system did, in fact, save Reddit. It's not the a perfect answer
to the Eternal September problem, but it's one of the best I've seen so far.
AskScience is one of the best examples of the bunch, but there are many
others.

It's a shame Reddit's gotten such a bad rap and that it's so hard to find the
quality subreddits.

~~~
joejohnson
They should clean up the front page. Too many of the default subreddits that
appear are super lame. /r/gaming? And all of the image ones? Even the more
"thoughtful" ones, say /r/politics is filled with awful, insipid comments.
They should adopt better rules like /r/askscience has, and let the children
form their own meme subreddits.

~~~
rthomas6
The problem with putting the high quality subreddits on the front page is that
most high quality subreddits can afford to be that way because of a relatively
small and insular community. There is a fear frequently expressed on some of
these subreddits that the quality will drop if they're put on the front page.
Good examples are /r/truereddit and /r/moderatepolitics. Those subreddits have
a comparatively higher signal to noise ratio due in part to their comparative
obscurity.

~~~
mmatants
It's interesting how the obscurity is a self-selection filter for quality
contributors.

Making quality contributions requires _more effort_. Having the front-page
content as a "honeypot" of sorts weeds out those individuals who are primarily
in the "drive-by" mode, anxious to blurt out emotional statements for
immediate gratification.

The interesting thing, too, is that there is a necessary friction to
maintaining high editorial quality. There _must_ be conflict to be able to
enforce "creme de la creme" level of content for consumption. Which is fine,
and not personal. All of us have our thoughtful/contemplative mood and the
rash impatient one. At least on a relative scale.

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pavs
Same question with much much much better answers/discussions:

[http://www.reddit.com/r/askscience/comments/eru42/so_if_the_...](http://www.reddit.com/r/askscience/comments/eru42/so_if_the_universe_is_constantly_expanding_what/)

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MattBearman
This exact question would literally keep me up at night when I was a child.
Now I just avoid thinking about it.

However, this response from the thread apparently sums it up nicely:

Just as on a sphere where latitude needs to be taken into account when
determining distance between two points because as latitude increases (up to
90) the distance between those points increase, in our universe time needs to
be taken into account when measuring the distance between two points because
as time increases (or moves forward) the distance between two points also
increases? As in, "the universe is expanding" is not saying that a balloon is
necessarily expanding, but rather by moving forward in time, the distance
between two points simply increases?

~~~
zerostar07
I think the much simpler explanation , mentioned in the post is that our
rulers are expanding as we move forward in time.

~~~
thom
My brain rushed ahead and read that as "I think the much simpler explanation,
mentioned in the post is that our rulers decreed it must be so, mysterious
galactic overlords that they are."

~~~
ktizo
Warming to this theme, perhaps our rulers are expanding with time. Quick,
someone weigh the king, if this continues we might need to reinforce the
drawbridge.

~~~
prawn
Relevant:
[http://en.wikipedia.org/wiki/Mayor_of_High_Wycombe#Tolling_o...](http://en.wikipedia.org/wiki/Mayor_of_High_Wycombe#Tolling_out_and_Weighing-
in)

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giberson
I'm afraid none of these explanations work for me. All of these analogies have
the same fatal flaw, regardless of what you try to use to describe how
distance between points expands you still have a material in a container. With
a balloon, the container is the air around it. If you inflate a balloon, sure
the two points you've drawn onto the balloon get further apart, but dammit the
VOLUME of the balloon is increasing too. If space is like a balloon, what does
it's "volume" consist of? When it expands (a balloon), it is displacing
something (air), what does space displace as it expands?

Now we're right back at the "fundamental misunderstanding of the space
expansion theorem" again...

So what about if I pose the same question in a different thought experiment.

Go back to the origin, the big bang. Everything is in this super condensed
super hot state (from wikipedia). Lets say you are this tiny rebellious
particle and you decide you've had enough, you're not gonna wait around for
this "inflation" event to occur that every one is all excited and talking
about. You take off, at an infinite speed away from wherever you currently
are.

    
    
        PBBU                   TRP
        (#)                     .
    

So, if the Pre-Big Bang Universe is on the left, and the Theoretical
Rebellious Particle is on the right, what is TRP in NOW?

~~~
natep
Every one of these analogies are flawed in some way because they are just
that, analogies, and the authors of them acknowledge that. You are meant to
look at only the aspects of the situation that are analogous, and ignore the
parts where the analogy breaks down, because no one is trying to claim that is
actually how the universe works.

To answer your question, your TRP cannot have ever existed, even in theory.
There is no 'outside the universe' for the TRP to have gone, even at the time
of the big bang.

You seem to think that the big bang happened at a specific point, which is not
true. The 'big bang' happened at every point, and never really 'bang'ed at
all. Things are not moving away from each other so much as the distance
between things is getting larger, which has a similar effect.

~~~
giberson
Expanding on "There is no 'outside the universe'".

Is the universe infinite in dimension?

Is there such a path that a particle could take at infinite speed for an
infinite time such that the distance between itself and a particle that had
stayed in the same position is always increasing?

Is there infinite matter in the universe?

If no, is there a point at which this traveling particle will have left the
"vicinity" of all matter, to never meet another particle again?

~~~
natep
(Edit: I'm responding to each question in its own paragraph)

What do you mean, 'infinite in dimension'? The universe has only 4 dimensions,
3 spatial, 1 in time.

Your question barely makes sense to me. Why do you need to invoke infinite
speeds and times? If 2 particles stay in the same place, and do not interact
with each other (gravitationally, electromagnetically, etc) then the distance
between those 2 particles would increase over time, due to the expansion of
the universe.

Yes, there is an infinite amount of matter in the universe [1]

Maybe. If you pick a random direction and travel really fast for a really long
time, the chances of you running into any other matter is extremely remote.
[2]

[1]
[http://www.reddit.com/r/askscience/comments/ewt9y/good_analo...](http://www.reddit.com/r/askscience/comments/ewt9y/good_analogy_for_the_ends_of_the_universe/c1bn55h)

[2] <http://www.youtube.com/watch?v=0fKBhvDjuy0>

~~~
giberson

         What do you mean, 'infinite in dimension'? The universe has only 4 dimensions, 3 spatial, 1 in time.
    

I'm was not asking how many dimensions the universe has. I was asking if the
universe is infinitely tall, infinitely wide and infinitely long.

    
    
         Why do you need to invoke infinite speeds and times? 
    

Simply for matters of scale. I was trying to avoid considerations like "it's
so big, it would take so long ...".

    
    
         If 2 particles stay in the same place [...]
    

Actually, it's one particle that moves, and other is stationary, thus
providing two points of reference for determining a displacement. Specifically
the intention was to indicate a path through space such that you always are
moving further from where you started and will never arrive back at your
starting point (as opposed to the spherical theory of space such that you can
only go half way around the sphere until you start getting closer to the point
at which you started.

    
    
          If you pick a random direction and travel really fast for a really long time, the chances of you running into any other matter is extremely remote. 
    

I didn't mean physically collide with other matter, I simply meant to pass by
it in the "vicinity". Similar to how traveling along a highway you pass by or
through towns, you don't physically collide with them though. If matter in the
universe was finite, then regardless of how sparse that matter is, there's an
imaginary bounding box you could draw around all matter in the universe. A
particle moving really fast for a long time would eventually end up outside of
that bounding box. At which point its distance not just from the stationary
particle at it's original, but all particles of matter would forever be
increasing. However, if matter is in fact infinite, then such a scenario can
not occur.

Luckily, despite my questions barely making any sense, you've managed to
provide in your reference [1] a comment that answers exactly my questions so
thank you for that.

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jackalope
To infinity _... and beyond!_

Sorry, I couldn't resist. However, this synopsis is consistent with some of
the comments in that thread and may be as good a tl;dr as any other.

