The second part of this is not correct. No variety of string theory says there are physical dimensions "outside of" the 4d universe. Instead, the additional dimensions are written down the same way as the traditional 4, but are variously either "wrapped up" or have very small scales, and hence appear to not exist. The classic example is of an ant walking on a table - if you are the ant, and the table has lots of crap on it, you immediately notice the third dimension because it's roughly the same size as the table itself, so it's obvious that you're going up and down along with side-to-side. On the other hand, a very flat table might lead the ant to think there are only 2 dimensions. Similarly, in string theory, the extra dimensions aren't somehow "seperate from" the regular universe - they just have different scales or geometry that make them difficult to detect (not impossible - just very difficult sometimes).

Better yet, send astronauts - NASA did an internal survey of the astronaut corps a few years back on exactly this topic, and they found plenty of current astronauts (mostly those without family) that would volunteer for a one-way trip.

Actually, the explanation for this one is pretty simple: it's because the dark matter is dark. The reason why baryonic matter collapses into a (relatively) tiny disk in the center of a much larger dark matter halo is that baryonic matter emits light... and light carries off energy. So baryonic matter quickly loses all the energy it can while still conserving angular momentum, and the result is a disk-like structure (spiral galaxies). Once it collapses into a disk, the density becomes high enough that it can further clump into nebulae and stars and such. Dark matter, on the other hand, is much lower density and hence isn't able to collapse efficiently (i.e. its Jean's Length is much longer, if you want to think in terms of some simple math).

First of all, the fact that it isn't running right now should prove to you that there is a limited amount. I work in a physics department at a research university, and I can tell you the prices for Helium (esp. Helium-3) have absolutely skyrocketed (just like the helium does, as some later posts point out!) - if it were reasonably economical it would have restarted again by now. The problem is that it's a trace byproduct of other refining processes, and most of the easily accessible oil on the US southwest (where the Helium is most abundant) has become much more expensive. Just like oil, the problem isn't that there will actually be none left - just that it'll suddenly become much more expensive and some crucial applications will become economically infeasible, to the detriment of all.

While I agree with this post right before this comment, I think it's important to point that this is the kind of throw-away statement that tends to drive women away from technical areas (esp. computer-related fields). It's one thing to have a random troll toss out some silly sexist crap... most people can just ignore that. But it's quite another for it to come from someone who says something that otherwise is very reasonable.

"Another impact structure in Siberia was created by an asteroid 100 km in size" That would've caused an extinction as bad if not worse than the end-K event (the one that killed the dinosaurs) - I think they mean the *crater* is 100 km in size - presumably they're referring to Popigai crater, which is dated to the Eocene, but the *crater* is 100 km, not the asteroid. 100 km is a *big* asteroid.