[PGR88]

What are the odds of two colliding?

Satellites are not that big, but the area they exist in is inconcievably huge.

[plsvn]

What are the odds of two colliding?

It's happened once so far between a Russian satellite and an Iridium communication satellite.

[bgill]

I’m more worried about one crashing onto my head.

[dr_lew]

Satellites are not that big, but the area they exist in is inconcievably huge.

I don't think that word means what you think it means :-)

They always say that when two galaxies collide, the odds of even one collision between stars is near zero ...

Check:

Consider a slab of stars 10000 lys thick, each star with a diameter of 1000000 km = 10^9 m, and a separation of 10 ly or ~10^17 m.

So for each ly of thickness there's about ( 10^9/10^17)^2 = (10^-6)^2 or 10^-12 chance of a given star traversing this slab hitting a star in the slab. Well, times 10^5 lys gives 10^-7 chance for each star, so with billions of stars making the traverse expect hundreds of collisions! Check fails!

That's inconceivable!