How much life is enough? This is the question at the heart of this UNLIMITED film, powered by UBS, in which we meet four people who are using the time they have on Earth today to explore the possibility of extending it indefinitely.

We begin at Cambridge University, and a talk with the author and biomedical gerontologist Dr Aubrey de Grey. Long seen as the terrain of fantasists, the concept of “immortality” has gathered some unhelpful connotations over the years. But Dr De Grey’s argument is disarmingly logical: “The actual defeat of ill health is not controversial,” he reasons. “Nobody wants to be sick. Nobody wants anybody else to be sick. And that’s true irrespective of how long ago they were born.”

If Dr De Grey views ageing as a disease, then Dr Max More is a man waiting for the cure. CEO of the Alcor Life Extension Foundation in Phoenix, Arizona, his field is cryonics: the freezing of the legally dead who hope one day to be revived with the help of future technologies.

Buying a ticket to the profound limbo of Dr More’s “containment vessels” is D.J. MacLennan, a thoughtful Scottish writer and cryonicist who has signed up to be a “neuro-patient” when death comes knocking. He’ll have his brain frozen until the secrets of life extension are better known – a quest that Dr Shin Kubota, a Japanese marine biologist, has dedicated himself to.

His hopes reside in the diminutive Turritopsis Dohrnii – a type of jellyfish that seems to have mastered the ability to regenerate itself once it has died. Its return to a polyp state and eventual rebirth is the equivalent of a butterfly dying and becoming a caterpillar.

Dr Kubota yearns for us to harness this genetic trait for ourselves: “This dream of rejuvenation, I think, must be the ultimate dream for mankind.”