Many scientists believe that around 75,000 years ago, humanity almost went extinct. The eruption of a supervolcano in Lake TobaA large natural lake on the island of Sumatra in Indonesia, formed within the caldera of a massive supervolcano that takes the same name. caused a global volcanic winterA reduction in global temperatures caused by volcanic ash blocking the Sun. of up to 10 years and reduced the global human population to as little as 3,000.

Humanity survived and flourished. But in the last 70 years, it has once again found itself on the brink of extinction, thanks to the threat of nuclear war, then climate breakdown. Either one could bring an abrupt end to the 300,000-year human story.

Now physicist Brian CoxAn English physicist at the University of Manchester best known for his work presenting popular BBC documentaries. He was also a member of the band D:Ream. warns that something more is at stake than the future of the species. He argues that given the very specific conditions that have to exist for a planet to support life, the chances that life was ever going to develop in the galaxy were very slim. And it was even less likely that a form of life would develop intelligence complex enough to produce its own sense of meaning.

He suggests that there must be very few advanced civilisations per galaxy: indeed, we might be the only one in ours. Any other life is likely just unthinking "slime". And that means if our civilisation comes to an end, it will eliminate "meaning in a galaxy forever".

Which raises the question: what exactly does meaning mean?

Throughout most of human history, and for around 93% of people around the world today, the answer lies in the divine. According to some faiths, meaning is not a human attribute at all: God has a plan for humanity, and the meaning of life is to follow it. Others teach that the meaning of life is to escape the material world and enter a blissful, enlightened afterlife.

But philosophers have also wrestled with the idea of what meaning there can be without God. One influential group of thinkers, the subjectivistsPeople who believe that meaning has no existence outside the human mind, i.e. that it is an entirely subjective phenomenon., have argued that there is no one meaning of life: it is up to each individual to define their own meaning.

Existentialists like Jean-Paul SartreA French philosopher who is perhaps the most famous name associated with existentialism. He was married to Simone de Beauvoir. and Simone de BeauvoirA French feminist philosopher best known for her book The Second Sex. argued that humans are "condemned to be free". That means we have sole responsibility for making our own decisions and choosing our paths. They thought that we cannot give up the task of creating meaning in our lives to anyone else, be it a God or another person.

For subjectivists, meaning does not just die with humanity: it dies with each individual human.

Another group, the objectivists, disagree. They argue that this cannot explain why some activities, like living a moral life or creating beautiful art, are more meaningful than others, like brushing one's teeth.

As such, there must be some things that are meaningful independently of the human mind, although since only humans are capable of these activities, the extinction of humanity would still bring about the end of meaning.

But some think the whole debate is flawed. They argue that "meaning" is just a word, one that has no inherent meaning of its own. For them, the survival of humanity has no bearing at all on meaning, because meaning never existed: life on Earth is nothing more than slime itself.

Yes, say some. Given the fragility of life, the rarity of human-like intelligence, and the short timespan in which advanced civilisations exist, there is almost certainly no other sentient life in the galaxy. So there can be no meaning without human beings either creating it or being its object.

Not at all, say others. Assuming "meaning" actually exists at all, it seems that it must have some kind of existence outside human beings. It would be strange to say that nothing that happened before human beings evolved was "meaningful", so it must be that things that come after us can have meaning.