The prospect of immortality has been with humanity for as long as we have understood our own mortality. It has been explored in culture after culture through mysticism, religion and, latterly, medical technology. The prospect of immortality is a uniquely human optimism created in answer to a uniquely human curse – the ability to contemplate our own existence, and its inevitable end.

As our technology improves, the prospect of immortality is beginning to look less and less ludicrous. Perhaps not true immortality any time soon, but the idea that in the mid-to-distant future we might be able to prevent ageing and eradicate most diseases is at least conceivable. But before we allow ourselves to become hopeful, it is important to give serious philosophical thought to the pros and cons of living indefinitely. Are there any convincing objections to the prospect of immortality?

The most common dismissal of the desirability of individual immortality is the point that it would not be worth living only to watch all of our friends and loved ones grow old and die. This is a valid criticism, but not a strong one. After all, the longest-living person in any group is already going to go through this, without any of the added benefits of perpetual youth and with many fewer opportunities to make new friends and find new lovers. Yet we would not give nearly so much credence to the argument that we should not prolong the lives of the elderly so as to save them the pain of watching their friends die.

This objection is, of course, irrelevant if we are discussing immortal societies rather than individuals. Yet the second standard objection to individual immortality is also relevant to whole societies. This is the contention that without the deadline of death we would lack the motivation to do anything with our lives. This too is easily dismissed, I think, by simply looking at our own motivations.

How many things that one does in life are inspired by the idea that they have to be done some time in the next 50 years, because death is waiting at the other end? Very few, one would imagine. Rather, we work and study because we want to create comfortable and happy lives for ourselves. We create things because we feel the need to express ourselves and exercise our talents. We are motivated by the need to be fulfilled and content in the short term, not because we are ticking off a bucket list before death. Even the idea of packing everything in while one is still young is becoming antiquated in the face of increasingly mobile 80-year-olds travelling the world and jumping out of planes.

A stronger criticism is to look at the possible consequences of an immortal society. Barring huge technological improvements we can assume that reproduction would have to be strictly limited, probably to the same level as the accidental death rate, to preserve resources and space. The society we would end up with, then, is one made up of a near-static population of ancients, with perhaps a few children and young people born to a privileged or randomly allocated few. We would essentially be taking our immortality at the expense of the existence of future generations. Is this a moral problem?