There are places, in and around our great cities, where the natural World has all but disappeared.

You can make out streets and sidewalks, autos, parking garages, advertising billboards, monuments of glass and steel, but not a tree or a blade of grass or any animal, besides, of course, the Humans.

There are lots of Humans.

Only when you look straight up through the skyscraper canyons can you make out a star, or a patch of blue, reminders of what was there long before Humans came to be.

It is not hard, going to work every day in such a place, to be impressed with ourselves. How we have transformed the Earth for our benefit and convenience!

But a few hundred miles up or down there are no Humans. Our impact on the universe is nil.

In the last ten thousand years – an instant in our long history – we have abandoned the nomadic life. We have domesticated the plants and animals. Why chase the food when you can make it come to you?

For all its material advantages, the sedentary life has left us edgy, unfulfilled. Even after 400 generations in villages and cities, we have not forgotten.

There are now people on every continent and the remotest islands, from pole to pole, from Mount Everest to the Dead Sea, on the ocean bottoms and even, occasionally, in residence 200 miles up.

Humans, like the gods of old, living in the sky.

These days there seems to be nowhere left to explore. Victims of their very success, the explorers now pretty much stay home.

Maybe it is a little early. Maybe the time is not quite yet. But those other Worlds – promising untold opportunities – beckon.

Just now, there are a great many matters that are pressing in on us, that compete for the money it takes to send people to other worlds. Should we solve those problems first?

Or are they a reason for going? Our planet and our solar system are surrounded by a new World ocean: the depths of space. It is no more impassable than the last.