OT - Physics Question on Anti-Matter

[Raapys]

Thanks for the explanation, SJ.

They haven't figured out how the whole 'dark matter' and 'anti-stuff' fits in, have they? And let's say we had a super-fast spaceship and travelled to the edge of the spacetime, do they have any idea what would happen if we tried to move past it?

[Suicide Junkie]

If one of the ants got into a drop of caffeine and started travelling in clear defiance of the speed limits imposed, it would go round and round... there is no edge.

And that's pretty much what we've probably got, in 3D.
As far as it is possible to see, in all directions... you have stuff, more stuff, older stuff, and eventually the microwave background.

Whether it is closed like a balloon shape, or flat or open (saddle-shaped), it is uniform in all directions to the edge of the visible universe. (7.999... cm on the balloon analogy)
So, no evidence for edges.

If it helps, you could think of a closed expanding universe as a game of asteroids... year by year, you keep increasing the resolution of the screen, but it is still a finite size (320x200 way back when, and 1280x1024 nowadays)... there are no edges to fall off of, since the left side is connected to the right side and the top to bottom.
Its not spherical, but rather doughnut shaped, but still finite with no edges, and a decent example.

Also, if your ship can only travel at 1 pixel per second, and you increase the screen rez fast enough, you won't be able to reach objects that happen to be too far away when you start.

[Renegade 13]

Raapys said:
They haven't figured out how the whole 'dark matter' and 'anti-stuff' fits in, have they?

Nope, they basically have no real idea what dark matter is. An interesting side point about antimatter is that "normal" (baryonic) matter and antimatter should have been created in equal quantity at the big-bang. However, we take a look around and we can't detect any antimatter out there, but there's lots of normal matter. They still haven't figured that one out

[capnq]

Renegade 13 said: An interesting side point about antimatter is that "normal" (baryonic) matter and antimatter should have been created in equal quantity at the big-bang. However, we take a look around and we can't detect any antimatter out there, but there's lots of normal matter. They still haven't figured that one out

They do have a theory about that, though. For example, see this lecture; scroll down to the section labeled "Matter versus Anti-Matter".

[douglas]

There's a whole class of infinities described as "countably infinite" that are all equivalent in size and (among other things) have the property that any two such infinities can be combined to make another infinity that is also countably infinite. The number of rooms in the hotel, the number of current occupants, and the number of frat boys are all countably infinite and can therefore be combined without changing anything. If a fraternity with one member for each irrational number showed up, however, the hotel would be in trouble because that particular set is not countably infinite. No matter what scheme you came up with for assigning people to rooms, you would always have an infinite number still waiting.

Note: A set is countably infinite if and only if it is possible to assign each and every member of the set to a corresponding member of another countably infinite set (the set of all integers is declared to have this property by fiat so you have a base to work with) so that each and every member of both sets has a corresponding member in the other. Put another way, if it's possible to come up with a scheme for labelling each and every item with a different whole number without skipping any numbers, then the set is countably infinite.

On a side note, the set of rational numbers is also countably infinite, but I'll leave figuring out a proof for it to everyone else. I know of one and will post it if enough people ask, but for now I'll leave it as a puzzle.