人类能在水下生活吗？

There are people living in almost every corner of our crowded planet. From the tops of mountains to deep underground, we've always been able to find habitable places to make a home. But with space at a premium, we've started to look even deeper for somewhere to live.

Throughout history, people have been fascinated by the idea of living underwater. More recently, the effects of human activity on the land have led some to look to the oceans for natural resources. Oceanographers and architects have looked at designing vessels, labs and underwater habitats to enable people to live and work in a submerged world. But, while dreams of an aquatic city have remained a fantasy, how close are we to making our home on the seabed a reality?

The pioneer of undersea living was Ian Koblick, sometimes described as an 'aquanaut'. He claimed technology already existed to create underwater colonies supporting up to a hundred people. He even opened La Chalupa, once the largest and most advanced underwater habitat and research facility in the world. 

A more recent and ambitious design for an underwater city is Ocean Spiral. Designed by the Japanese Shimizu Corporation, it's a huge transparent globe attached to the seabed. It's got a tower running through it to the surface, providing space for homes, offices and even an amusement park for five thousand residents. Masaki Takeuchi from the company told the BBC: "Our idea is to connect the sea surface and the deep sea vertically, and that way we believe that we can utilise the capability of the deep sea."

Of course, there are engineering challenges in constructing an oceanic metropolis. And living underwater would have major effects on the human body, especially as there is an increase in atmospheric pressure which could lead to the bends. So, maybe it's too soon to be packing our bags and setting up a new life three thousand metres under the sea!