I think we will be a space-faring civilization by year 3000. By 100,000 AD, Earth is probrably going to still be inhabitated, but I think it will be kinda of a natural preservation of our original planet, with some great metropolises still in earth. If we turn into one big federation, earth won't probrably be even the capital world, the capital will probrably be in some planet we pretty much terraformed it to be paradise. If, in the future, we fragmentate in many groups, many groups and nations will colonize other planets and solar systems, dividing our part of the galaxy in many space-faring nations. We would be so many, and growing, thanks to new planets, new arable lands and new farming techniques. Maybe we would't even need food by that time, but direct nourishment from stars.
Due to genetic engineering, nanomachines and cybernetic enhancement, we won't probrably be the same species from today. It would't surprise me if there were multiple species that branched off homo sapiens, either though genetics, cybernetics or nanomachines. We will either modify ourselves to be super-soldiers, super-brainiacs, sex masters, unkillable survivalist or just to adapt to diferent planets. Some modifications will be simple and discrete. Others will be drastic, causing mutants with diferent appearances from normal humans. This will either be common or it will produce lots of prejudice, causing death, wars and hate. We will divide people in many groups: Asides from national and ethnic prejudice, we'll probrably call the others things like "Borgs, Muties, Transhuman Freaks, Nanos, Zero-Grav Babies, Heavy-Grav strongmen, Virtual Reality Addicts, Earth Scumbags, Martian Freaks, Centauri madmen, Hybrids", etecetera...
It would't surprise me if by 100.000 we either already had contact with aliens long ago or we found them around 100.000 AD. It would probrably bring humans and derivated races together, but it would possibly mean eletric death for one of the sides of the find. It would't surprise me if we either found a species of pacifist that would subsequently be murdered by us, or a race of bloodthirsty gore killers that would make Attilla the Hun call them "Barbarians."