"Dark energy" and "Dark matter"...What is it?

[SoHiAllTheTime]

No, i go by: SoHiAllTheTime, SHATT, sohi, Ryan, conservative, christian fundamentalist whacko, ignorant, blind, and....I think thats about it...I dont remember ever going by "Tr6ai0ls4", but if i do in the future i will let you know.

 

[SoHiAllTheTime]

Petersko: Thanks for that link i am almost finished with it...I totally agree with what traisl is saying! I can see why you confused me with him. But i HAVE to say that the only thing you have said is "well you dont understand it because you cant grasp it", dude, that is so weak that it is pathetic. You didnt really expalin much, zorn did, but not you. Either way, none of your explanations give a decent answer to the question. Or maybe i just cant grasp it 8)

 

[Petersko]

I freely admit that zorn is better at describing stuff (and more qualified to do so). I never claimed that I eventually helped him see it - I wasn't able to find a way of describing it that clicked with him. But I did contribute quite a bit to that thread (entropy, heat death, etc).

My point, made repeatedly, was that his failure to grasp the concept was mostly due to trying to picture it in his mind. Until he gave up picturing it, understanding would elude him. You are in the same situation, I think.

One has to abandon the idea that the universe is expanding into something. Can you?

 

[compact]

But you are saying the area "outside" the box does not exist? I cant see how that is possible (not that i am saying i dont believe you, but that i am not understanding)...I am going to check out those links...Is there a term or phrase in science that refers to this paticular subject? Thanks a lot

I'd suggest doing a search for the word "metric". The universe can expand without expanding into something else because the distance scale of the universe can change. Of course, this scale can change by different amounts in different places.

A silly (but, I think, useful) example would be to imagine if you woke up one morning and everything (and I mean everything) you see had doubled in size. Of course, if everything had doubled in size, you wouldn't be able to tell as you wouldn't have anything of "regular" size to compare it to. Of course, this example is flawed because there's no objective way to tell what it even means to be of "regular" size.

However, reality is equipped with an objective way of determining the length scale of space-time: the speed of light is a constant to all observers in any intertial frame.

 

[zorn]

Zorn, it still seems (to me at least) that the uni is "expanding" and that there would have to be something for it to "expand" into. From the exapmle you posted, everything gets further and further apart from each other, so therefore it is getting larger. The box that surrounds the dots would HAVE to get bigger and bigger to be able to keep all of the dots inside of itself.

But you are saying the area "outside" the box does not exist? I cant see how that is possible (not that i am saying i dont believe you, but that i am not understanding)...I am going to check out those links...Is there a term or phrase in science that refers to this paticular subject? Thanks a lot!

Mmmk... there's two possibilities here, very different:

1. The universe could be infinite. Then there's an infinite amount of dots... the box is just like a window, showing one part of the universe, but it goes on exactly like that forever. So then there's no problem, right? -- you see how it can always be infinite but still expand?
   
   In mathy terms, you can imagine there are galaxies at all the points (m*t, n*t) where m and n are integers and t is the time. So at t=1 year or whatever, there are galaxies at (0,0), (0,1), (0,-1), (1,0), (-1, 0), (1,1), (2,-1)... and so on. A grid spaced 1 unit apart extending out to infinity.
   
   Now as time passes the universe expands -- at t=2 the galaxies are all at least 2 units apart. At t=0.1 they're packed close together, only 0.1 units to the nearest one. But the universe is still infinite.... for all times except t=0, the Big Bang. Then all of the galaxies (an infinite number!) are packed in at (0,0) since 0 times anything is still zero.
   
   (Course having an infinite number of galaxies all in point is pretty fucked up. So is the fact that at t=0 the rest of the universe is empty and then at t=0.000000000000001 or whatever it's completely full. That's why we call t=0 a singularity -- most physicists believe that this didn't actually happen, but that our theory (general relativity) doesn't work for very high densities of stuff.)
   
   
2. The universe could be finite, without having an outside. This is what that thread w/trails was about. Then you have something where the universe "wraps around" at some point and you come back to where you started, just like in some games (eg Asteroids.)
   
   In this case there could be an 'outside' to the universe. The 2-d analogy is the surface of a balloon. A balloon surface has no edges to a 2-d creature living on it, but we know it actually does in the third dimension. Similarly our universe could be embedded in a 4-d (or 5-d, 6-d etc) space. You can't visualize more than three dimensions, so it's hard to imagine what this would 'look' like, but the math works out just fine.
   
   However there doesn't have to be an outside IMO. This is more of a philosophical point than science. But the math works out fine: you can define distances, curvature, and so on without introducing an external space! This is basically why I don't believe there has to be an 'outside' for a finite universe.
   
   Intuitively you think that if something finite then it has to have an edge and an outside -- but that's only because we're used to thinking in plain old regular (Euclidean) geometry. There's no reason the universe has to be like that. Questions like "well what would it look like from outside" just don't make any sense, because there is no outside. It's like asking what's north of the North Pole...