Slashdot Mirror
The Universe is Pretty Big
Psiolent writes "According to a recent article on Space.com, the universe is pretty big (156 billion light years across, to be more precise). Some recent research examining 'primordial radiation imprinted on the cosmos' has led to this conclusion, as well as a few others. This finding is particularly interesting considering the universe is only 13.7 billion years old (which would mean the universe has been expanding faster than light travels), but the article does a good job addressing this seeming paradox."
Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the drug store, but that's just peanuts to space.
Douglas AdamsThere's another good reason to pick Earth as the center; if the universe is 13.7 billion years old then there is no way that anything - light, gravity, particles, aliens - from farther than 13.7 billion light years has reached us. We are at the centre of a 13.7 billion light year sphere containing everything which we can possibly observe.
Not only does this not rule out the possibility of light which hasn't reached us yet, it is defined by it. This observable universe, which some have called "the cosmos", expands by 1 light year every year, as light further out has time to reach us. The entire universe could well be much larger than this; we can only theorize.
By the way, the observable universe is very symmetrical in every direction, so we can consider ourselves to be at the centre even in a literal geometric sense of the word.
Of course it would be easier to post "ten to the power of twenty three" if slashdot supported <sup> tags.
In addition to this, the observable universe has no visible boundaries which could be deemed symmetrical, as what we observe is not so much the universe itself but the contents thereof. Since the contents aren't spread symmetrically or in any particular order for that matter, any observed boundaries can't be symmetrical.
If you can't see where it ends, does that mean it ends where you no longer see it?
click-clack, front and back. I'm not moving this car otherwise.
My guess is that objects do expand, but since even the biggest objects are infinitesimally small compared to the massive distances between them, we are not going to be talking about objects expanding in the same way we talk about space expanding, since the detectable expansion of objects is likely to be fairly negligible.
:)
I'm not a scientist either, so I'm just making a complete stab-in-the-dark guess, and I'm very happy to be corrected by anyone with a more researched answer.
SofaMan -- Occasionally Battling Evil With His Mighty Powers Of Indolence.
Actually, causality isn't violated unless an object is moving FTL in respect to a "fixed" reference point. If two objects are moving at LT light speed away from the "fixed" point. they may be moving FTL in respect to each other. In fact it sorta has to work that way. Just like two cars moving at 60 mph(each) away from a fixed point in opposite directions have a separation speed of 120mph does not mean that one is standing still and the other is moving 120mph. You gotta define the fixed point first.
Food not Bombs is a nice platitude but it breaks down when you notice that the Bombees are usually well fed
Actually the whole point of the article is that light which has traveled 13.7 billion years to reach us came from objects that are now at least 78 billion light years away, due to expansion. They aren't saying that the universe is exactly that radius in every direction from earth, they are saying it's AT LEAST that radius. Earth is the only frame of reference that makes sense (for now) since the universe looks fairly uniform in every direction. This article isn't about ruling out a universe bigger than the sphere centered on earth that we can observe, the article is about setting a minimum size for the universe. It clearly says 'at least 156 billion light-years'. If the words 'at least' go over your head, you need to take some reading comprehension lessions.
This is actually a really great question. Don't let the flurry of responses fool you, the answer to something like this is not so easy or cut-and-dry.
The truth is, no one is completely sure. The replies you've gotten aren't too far off from nice, accepted answers that you might get from a physicist, but it's one of those things where no one really knows.
First, consider the statement "space is expanding". Sounds simple enough, but lets start with the simple: What is space? I mean, what is it that's expanding when space expands? Mostly, our understanding of space usually breaks down, eventually, into putting wooden sticks we call "meter sticks" next to objects, or putting them in-between objects.
Beyond that, some fun questions:
What is gravity?
What is magnatism?
What are the other forces (weak, strong, they seem to be trying to come up with new ones all the time)?
Are those all the forces?
By what means do those forces exert themselves on matter?
What, exactly, is the relationship between gravity and matter?
So, though it's possible to answer your question in a statement to the effect of, "General relativity says electro-magnetism and gravity act on the particle and makes it work like that," but don't think that answers your question. It ends up being like when someone says, "Why do objects, when unhindered, move towards each other? Gravity!" They've effectively given a name to "the force which makes objects move towards each other", but haven't really explained why.
I'm not being clear either, but I can tell you what's tricky about it. When people talk about general relativity allowing for space to be expanding, it really is something like a reverse-gravity (gravity being when space bends in). Matter seems to produce gravity, or, according to the fancy of an occasional clever thinker, matter is produced by spikes in the gravity field. In any event, it's not clear what either space-time or matter would be without the other, and "gravity" and "space-time expansion" are names for measurements of the interaction between them. Whatever- matter and this "expansive" force are mixed up in weird games. They are linked. Good question.