Re:What is 'Space' expanding into?
by joejohnson on Tuesday March 06, 2012 @12:09PM
(#3671853)
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.
Re:What is 'Space' expanding into?
by cmhamill on Tuesday March 06, 2012 @12:20PM
(#3671913)
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.
Re:What is 'Space' expanding into?
by joejohnson on Tuesday March 06, 2012 @12:24PM
(#3671930)
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.
Re:What is 'Space' expanding into?
by rthomas6 on Tuesday March 06, 2012 @12:48PM
(#3672024)
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.
Re:What is 'Space' expanding into?
by mmatants on Tuesday March 06, 2012 @02:49PM
(#3672520)
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.
Re:What is 'Space' expanding into?
by snarkyturtle on Tuesday March 06, 2012 @12:52PM
(#3672036)
I would say /r/politics would be good if it weren't on the frontpage. reddit is fine the way it is, since the frontpage acts as a filter for the masses. A userbase as large as reddit gravitates back towards the norm content-wise as its numbers increase, and the frontpage reddit's moderators couldn't enforce the rules nearly as well as askscience (they were on the frontpage but asked to be taken down due to moderator consensus.) So to anyone who wants to explore reddit, which most people don't, they'd unsubscribe from the frontpage reddits and dig deep. THEN you get the tight communities with common interests that reddit was in the first place.
EDIT: That being said /r/pics recently put a rules system up that works tremendously well. It used to be meme-filled but now generally has great content (except for the MS paint trend popping up as of lately.)
Re:What is 'Space' expanding into?
by vacri on Tuesday March 06, 2012 @04:07PM
(#3672884)
What the hell is 'super lame' with gaming? Lots of people do it, why wouldn't they want to talk about it?
I also find it odd that you're complaining about lack of thoughtful content but are happy to use terms like 'super lame'. Would you use it in your preferred politics thread: 'Too many of Obama's policies are super lame'? Sounds exactly like what you're complaining about.
Re:What is 'Space' expanding into?
by ramidarigaz on Tuesday March 06, 2012 @12:23PM
(#3671929)
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.
Re:What is 'Space' expanding into?
by dmvaldman on Tuesday March 06, 2012 @01:07PM
(#3672088)
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.
Re:What is 'Space' expanding into?
by dmvaldman on Tuesday March 06, 2012 @02:34PM
(#3672442)
That's an interesting idea. My answer would be that even though every volume of space would be contracting if you reversed the clock, each of these volumes don't form their own singularities, instead the near-singularities coalesce at the point of the big bang.
Re:What is 'Space' expanding into?
by joejohnson on Tuesday March 06, 2012 @12:26PM
(#3671942)
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...
Re:What is 'Space' expanding into?
by dmvaldman on Tuesday March 06, 2012 @01:11PM
(#3672111)
All evidence currently points to the universe being infinite, and with trivial topology. So no, you will not return. This can turn out to be incorrect in the future however.
The more interesting question is that if the universe is infinite, what does it mean to "expand" and "contract." Specifically, if the universe was originally localized to a small space in the time of the Big Bang, that space was actually also infinite! When you shrink infinity you still get infinity. The only difference is our rulers are way bigger. Everything will causally affect everything else in far less time (nothing is far away).
Re:What is 'Space' expanding into?
by wbhart on Tuesday March 06, 2012 @06:34PM
(#3673446)
I am no physicist, but I still feel as though this is an immensely misleading subject.
The idea of an infinite universe conjures up images an infinite number of worlds out there, infinitely many of which must be similar to our own. And somehow, all that infinite matter/energy must have been compressed infinitely densely at the beginning.
But isn't it the case that we have only measured the flatness of space to within about half of one percent. If so, it seems much more likely that the universe is locally very flat but still finite, though very large, due to initial inflation (the event, not the process). So the universe might be 10^100 light years across, but still finite, yet definitely flat to well within half of one percent.
But let's suppose that the universe is infinite (since we have not, and may never rule it out). What does this actually mean? Does it mean an infinite number of galaxies out there somewhere at this moment in time? Somehow I doubt it.
What does it even mean for a galaxy to be out there at some point at this time? Do we mean time relative to the local reference frame of that galaxy (stationary in that frame), say with respect to the big bang or time relative to our own reference frame, which we agree is moving rapidly with respect to the other?
Even distance measurements vary between the two frames of reference.
So my guess is that to even have a concept of what this all means, we need to be expert at understanding space-time manifolds, which we are famously hopeless at.
Another obvious point: it isn't possible for an observer to travel off in one direction and return to the same point, even if the universe is curved (as I suspect it is). The reason is simply that you couldn't make that journey. There are points in the universe which lie out of causal contact with us, which means that there is no means of getting there, even theoretically. We can't even observe those points, let alone go there and see them. So we can never make the full journey in one direction and return from the other. Doing so would imply travelling beyond our cosmic horizon.
Re:What is 'Space' expanding into?
by bane on Tuesday March 06, 2012 @03:33PM
(#3672728)
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.
Re:What is 'Space' expanding into?
by sliverstorm on Tuesday March 06, 2012 @05:47PM
(#3673301)
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.
Re:What is 'Space' expanding into?
by MattBearman on Tuesday March 06, 2012 @12:05PM
(#3671837)
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?
Re:What is 'Space' expanding into?
by thom on Tuesday March 06, 2012 @03:51PM
(#3672808)
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."
Re:What is 'Space' expanding into?
by ktizo on Tuesday March 06, 2012 @05:33PM
(#3673254)
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.
Re:What is 'Space' expanding into?
by giberson on Tuesday March 06, 2012 @06:30PM
(#3673430)
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?
Re:What is 'Space' expanding into?
by natep on Tuesday March 06, 2012 @06:41PM
(#3673468)
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.
Re:What is 'Space' expanding into?
by giberson on Tuesday March 06, 2012 @06:48PM
(#3673488)
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?
Re:What is 'Space' expanding into?
by natep on Wednesday March 07, 2012 @12:41PM
(#3676286)
(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]
Re:What is 'Space' expanding into?
by giberson on Wednesday March 07, 2012 @02:52PM
(#3676829)
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.
Re:What is 'Space' expanding into?
by smeg on Tuesday March 06, 2012 @07:14PM
(#3673592)
The problem is you are applying linear Earth-scale concepts of space to the whole Universe.
In reality space (or space-time) is curved - as you approach the "edge" of the universe you actually are traversing a loop around a 4-dimensional hyper-sphere.
The common analogy of an ant on the surface of a balloon is quite effective. As the balloon expands, the distance between points on the surface of the balloon certainly grow and they become further apart. The ant can measure this, see this, but for the life of him, no matter how far he walks, he cant find the "edge of the universe".
Of course it is hard to visualise this analogy when projected into our 4-dimensional universe, but it's the best we've got.
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.
It's a shame Reddit's gotten such a bad rap and that it's so hard to find the quality subreddits.
No. That's what mass popularity is ALWAYS like.
What they need to do is create a better way to find sub-reddits you are interested in but which are not popular.
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.
EDIT: That being said /r/pics recently put a rules system up that works tremendously well. It used to be meme-filled but now generally has great content (except for the MS paint trend popping up as of lately.)
I also find it odd that you're complaining about lack of thoughtful content but are happy to use terms like 'super lame'. Would you use it in your preferred politics thread: 'Too many of Obama's policies are super lame'? Sounds exactly like what you're complaining about.
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
http://en.wikipedia.org/wiki/Faster-than-light#Universal_exp...
Doesn't this imply that there is a reverse event horizon around every point in space? That we are on the inside of an inside-out black hole?
Wow! Thanks for the new perspective! Very original and intriguing.
The more interesting question is that if the universe is infinite, what does it mean to "expand" and "contract." Specifically, if the universe was originally localized to a small space in the time of the Big Bang, that space was actually also infinite! When you shrink infinity you still get infinity. The only difference is our rulers are way bigger. Everything will causally affect everything else in far less time (nothing is far away).
The idea of an infinite universe conjures up images an infinite number of worlds out there, infinitely many of which must be similar to our own. And somehow, all that infinite matter/energy must have been compressed infinitely densely at the beginning.
But isn't it the case that we have only measured the flatness of space to within about half of one percent. If so, it seems much more likely that the universe is locally very flat but still finite, though very large, due to initial inflation (the event, not the process). So the universe might be 10^100 light years across, but still finite, yet definitely flat to well within half of one percent.
But let's suppose that the universe is infinite (since we have not, and may never rule it out). What does this actually mean? Does it mean an infinite number of galaxies out there somewhere at this moment in time? Somehow I doubt it.
What does it even mean for a galaxy to be out there at some point at this time? Do we mean time relative to the local reference frame of that galaxy (stationary in that frame), say with respect to the big bang or time relative to our own reference frame, which we agree is moving rapidly with respect to the other?
Even distance measurements vary between the two frames of reference.
So my guess is that to even have a concept of what this all means, we need to be expert at understanding space-time manifolds, which we are famously hopeless at.
Another obvious point: it isn't possible for an observer to travel off in one direction and return to the same point, even if the universe is curved (as I suspect it is). The reason is simply that you couldn't make that journey. There are points in the universe which lie out of causal contact with us, which means that there is no means of getting there, even theoretically. We can't even observe those points, let alone go there and see them. So we can never make the full journey in one direction and return from the other. Doing so would imply travelling beyond our cosmic horizon.
Some of the subreddits are quite good, as AskScience.
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.
http://www.reddit.com/r/askscience/comments/eru42/so_if_the_...
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?
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.
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?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.
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 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...
[2] http://www.youtube.com/watch?v=0fKBhvDjuy0
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.
In reality space (or space-time) is curved - as you approach the "edge" of the universe you actually are traversing a loop around a 4-dimensional hyper-sphere.
The common analogy of an ant on the surface of a balloon is quite effective. As the balloon expands, the distance between points on the surface of the balloon certainly grow and they become further apart. The ant can measure this, see this, but for the life of him, no matter how far he walks, he cant find the "edge of the universe".
Of course it is hard to visualise this analogy when projected into our 4-dimensional universe, but it's the best we've got.
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.