The problems of overpopulation and the threat of various disasters - from climatic to nuclear and space - are increasingly making us think about alternative spaces for life. Alas, space has not yet been mastered by us to such an extent as to build colonies on other planets. So, only earthly resources remain. Or rather underground...
First of all, if humanity dares to descend underground, it will have to solve a number of issues related to ensuring life in the new conditions. Perhaps people will no longer have access to those energy resources that were on the surface of the planet. Experts believe that the best option would be to take energy from the bowels of the planet - geothermal sources and rocks. It must be borne in mind that those water sources that were before may also become inaccessible. However, underground, as you know, there are natural water reservoirs. True, they will have to be "civilised" somehow - to build treatment facilities and make them convenient for consumers.
Even a huge amount of canned food and other food products that do not spoil for a long time will be enough underground for several years at best. One way or another, you will have to learn how to produce food yourself. For example, take animals with you, from which you can later receive meat and milk. As well as everything you need to grow edible plants - vegetables, fruits, etc.
If sewage accumulates where people live, it will soon affect their health. Some waste can be used as fertilizer, since we decided to go into agriculture. But then we also need a ventilation system. For the rest, most likely, you will have to look for ways to bring it out - for example, throw waste into the sea. In such a situation, it is unlikely that anyone will care about the ecology on the surface. As you know, the sun is the main source of vital vitamin D. True, natural sunlight can be replaced with artificial - for example, LED lamps that emit ultraviolet radiation. Or you can consume foods rich in vitamin D. But even if these problems can be solved (and not yet the fact that it will be possible), the psychological aspect remains. Some people are claustrophobic and simply cannot be in an enclosed space, no matter how comfortable it is.
Those who used to live upstairs may feel depressed about the lack of sunlight and fresh air. In addition, underground inhabitants may experience fear that they will not be able to escape in the event of some kind of cataclysm - fire or flood. They just have nowhere to run. They may also fear that they will die under the rubble if an earthquake occurs.
Researcher from SINTEF (Norway) Gunnar D. Jenssen specializes in underground psychology and space design. In other words, he studies how people perceive underground spaces, how they react to being underground. At one time, he developed projects for four tunnels with the illusion of an expanded space. This was achieved by arranging artificial oases on the routes with imitation of palm trees and blue skies. “You have a feeling of breathing, a feeling that you are outside, despite the fact that you are a thousand meters underground, passing through a mountain,” comments Jenssen. “If you give these people something that allows them to tangibly control the situation, they will come to terms with the fact that they are in it. This is a key point,” the specialist said in an interview with the BBC.