What is 'Space' expanding into?

http://www.reddit.com/r/askscience/comments/qk58k/what_is_space_expanding_into/

by sun123 • 14 years ago

67 42 14 years ago

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?

zerostar072• 14 years ago

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

thom• 14 years ago

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."

cpeterso• 14 years ago

Wouldn't our rulers be shrinking, so when we measure the distance between two objects, the number of inches greater than before?

joejohnson4• 14 years ago

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• 14 years ago

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.

joejohnson4• 14 years ago

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.

SkyMarshal• 14 years ago

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

It's not that hard, just look for any subreddit that starts with or contains 'true', 'depth', or 'meta', among other keywords. Example:

http://www.reddit.com/r/truereddit

twiceaday2• 14 years ago

But this expansion is happening much slower than the speed of light, so technically we can travel to the edge.

joejohnson4• 14 years ago

Isn't the universe a closed surface? I thought the metaphor was that the universe is like a globe: if you go far enough in one direction, you end up where you started...

dmvaldman3• 14 years ago

This isn't true. The further away a galaxy is, the faster it recedes relative to us, and this can amplify well beyond the speed of light. This means different regions of space have had absolutely no communication with each other, as not even light could travel from one to the other to catch up with how they were receding from each other.

http://en.wikipedia.org/wiki/Faster-than-light#Universal_exp...

ramidarigaz• 14 years ago

The moderators of Askscience have done a fantastic job of keeping the quality of the subreddit very high. They're really strict about what can be posted as a top level comment, and I think the subreddit is much better for it. Memes and funny pictures have their place, but it's nice to have a serious subreddit where people can get their questions answered by people who (in theory) know what they're talking about.

zerostar072• 14 years ago

Makes one wonder why there arent any tech/entrepreneurship subreddits better than HN. If I could take a stab, HN feels closer to funding sources.

ww520• 14 years ago

Reddit is often mistakenly identified by its front page. It should label the front page as the awww-pic-wtf-political-iama-meme subreddit.

Some of the subreddits are quite good, as AskScience.

bane• 14 years ago

Reddit is like the internet. There's places that are full of junk, and then there are a few places with great, insightful information and discussion ... and fortunately the ability for mods to setup their own rules for that community.

sliverstorm• 14 years ago

I've heard the balloon actually used to describe the universe's expansion.

Consider a balloon. The rubber of the balloon is Reality, or Space-Time, or what have you. Draw two dots on the balloon; blow up the balloon. Notice the spots are farther apart.

pavs• 14 years ago

Same question with much much much better answers/discussions:

http://www.reddit.com/r/askscience/comments/eru42/so_if_the_...

jackalope• 14 years ago

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.

giberson3• 14 years ago

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?

natep3• 14 years ago

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.

giberson3• 14 years ago

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?

What is 'Space' expanding into?

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