Cosmos: The Immortals

I find this is one of the hardest episodes of Cosmos to summarise because its central theme on Immortality, at both an individual and species-wide level, manages to be strong while still covering a wide variety of topics over the course of the hour.

It begins in the Iraq of 5,000 years ago, where writing was developed in the city of Uruk. Enheduanna, daughter of the emperor, is the oldest recorded individual whose writing has survived to the present. This is the first example of a form of immortality possible for a human - that of their writing living on after they themselves are dead.

The epic story of Gilgamesh gives him a variant of this immortality - which he sought in the story, making it a doubly appropriate example - as the subject of the writing rather than the writer. He lives on through the retelling of his story, the oldest such work we have. From Gilgamesh Tyson moves on to talk about DNA, and how it is carried across generations, and so moves from the immortality of a single person to the idea of living on through genetic descendants.

Tracing back the existence of DNA as far as we can, we are forced to speculate about the ultimate origins of life, and Tyson suggests that DNA could have come to Earth from space before providing some evidence to make this sound more plausible. First, a sequence tying in to the original Cosmos tells the story of how meteorites that landed in Egypt in 1911 were eventually shown to have originated on Mars (this was uncovered by the Viking landings in the 1970s, cue clip of Carl Sagan talking about Viking), thus proving that meteorites can travel from world to world.

The following scenes establish that we know some bacteria can survive in space, and we know that this must have happened in the past. I found this particularly interesting, that it must have happened because in the first half of the Earth's lifespan there were asteroid collisions so large that they would have sterilised the Earth, so the only way that life would not have had to start again from scratch is if some bacteria were launched into space before the strike and then came back down afterwards.

This leads Tyson on to talk about the lifespan of civilisations, starting with a seeming tangent to this topic of how humans first began broadcasting signals into space at lightspeed in 1946, since when we have created a 70 light year sphere around the Earth of radio waves. These would be detectable by aliens within this sphere using radio telescopes, and likewise we ought to detect alien radio transmissions, but we never have.

But there are issues with this - we can only a fraction of the sky for such signals, and aliens may not use radio. But the issue Tyson wants us to consider is that if we are not looking during the time such signals are passing the Earth, we cannot detect them. It is part of the question: how long do civilisations last?

In Enheduanna's time her city was destroyed by war and drought, as climate change affected the early civilisations of Europe and Asia. I love the image that briefly - but very effectively - illustrates this. This leads Tyson on to list some of the ways that a civilisation can die:

A supernova within 30 light years would devastate the solar system. Fortunately there is not one due in the next few hundred million years.

A supervolcano eruption would block out the sun for 5 years, with effects like a nuclear winter (except without the radiation - something that isn't mentioned is that an actual nuclear winter is vastly less likely now than in the time of the first Cosmos series). Present civilisations would be "brought to their knees" (Tyson's phrase) but humanity would survive as it survived the last such eruption back in the Stone Age.

An asteroid strike is something Tyson claims we may soon have the technology to prevent by deflecting their paths away from the Earth.

Diseases, such as those that devastated the native American populations when Europeans arrived.

Pollution. Tyson suggests that our current civilisation is in denial about how this could affect us within the next 100 years, but from that pessimistic note he turns to a more optimistic view of the future, saying human intelligence is our best weapon with which to survive against anything.

He returns to the Cosmic Calendar to consider what the next year - the next 14 billion years - might bring, a possible future for the human race. The sun will become a red giant in about 5 billion years, but red dwarfs are the most plentiful type of star and last for trillions of years, making them a more secure place for a habitable planet than the solar system.

But in the much nearer future Tyson suggests that we need to increase our environmental awareness, eliminate poverty and reverse pollution, before colonising nearby planets and then nearby star systems. By the time we are doing this humans will have "more of our strengths and fewer of our weaknesses", becoming an interstellar species with an origin on Earth in common.

This is a moving and beautiful ending for the programme, full of hope.