Cosmos: Unafraid of the Dark

The very first episode of Cosmos: A Personal Voyage discussed the Great Library of Alexandria and the tragedy of its destruction, so it is fitting that the final part of Cosmos: A Spacetime Odyssey should return there, to bookend the series. Tyson's description of the library complements Sagan's without very much repetition.

It acts as an introduction to the chief topic of this programme, how the limits of human knowledge are pushed back over time, but also how they can be lost again if the knowledge is not guarded carefully.

Tyson chooses a superb example to demonstrate the pushing back of the limits of human knowledge by beginning with Victor Hess discovering cosmic rays in 1912. He worked out that they were stronger when higher up in Earth's atmosphere, but didn't know why this was or what they were.

Later, in the 1930s, Fritz Zwicky proposed they came from supernovae, as well as being the individual who theorised neutron stars, gravitational lensing and dark matter.

Later still, his theories were confirmed, by Vera Rubin studying distant galaxies and observing that they were rotating at different speeds than those predicted by the laws of gravity as they were then understood.

Dark matter and dark energy make up 95% of the universe but, as Tyson explains, dark matter and dark energy are "code words" for these things because we still don't know what they really are. This is the frontier of scientific knowledge in astronomy as it stands today. Tyson emphasises that scientists are OK with not knowing more - yet - because admitting ignorance is simply better than pretending to knowledge, a (not very) veiled shot against the opponents of science.

From the frontiers of science, Tyson begins to wrap up the series by moving to the frontiers of human exploration. The Voyager 1 and Voyager 2 space probes will travel through interstellar space for a billion years, carrying with them the gold discs with messages from the Earth. Science is the language the inscription is written in, with the (universally constant) frequency of the hydrogen atom as the base unit. Music and greetings from humans (and whales) form the "sounds of Earth."

Voyager 1 also took the photograph known as the "pale blue dot" of the Earth as seen from beyond the orbit of Neptune, 6 billion km away, which was the idea of Carl Sagan and gave rise to one of his most moving and impassioned speeches, repeated here almost in its entirety.

A billion years ago the Earth was populated by single-celled organisms in the ocean and nothing lived on the land, so who knows how unimaginably different the Earth will be a billion years in the future? Tyson ties together the hopeful message of his Cosmos series in a final appeal for science to always belong to everyone, to prevent misuse by an elite and a recurrence of the fate of the Great Library, and that way to ensure the long-term prospects for humanity in a vast, uncaring universe.

In the final scenes Neil deGrasse Tyson appears on the beach location used by Carl Sagan in some of his most memorable Cosmos scenes. The Ship of the Imagination then flies off without him, symbolic of him bequeathing it to the future, or to us.

"Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.

The Earth is a very small stage in a vast cosmic arena. Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph they could become the momentary masters of a fraction of a dot. Think of the endless cruelties visited by the inhabitants of one corner of this pixel on the scarcely distinguishable inhabitants of some other corner. How frequent their misunderstandings, how eager they are to kill one another, how fervent their hatreds. Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity – in all this vastness – there is no hint that help will come from elsewhere to save us from ourselves.

The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another and to preserve and cherish the pale blue dot, the only home we've ever known."

Cosmos: The World Set Free

This programme stands as an hour-long challenge to climate change deniers; a remarkably polite way of calling them wrong for an hour. Not that those with political motives for denying climate change would be watching anyway, or even if they did then they're not the sort to let facts persuade them of anything.

Venus. The differences between the atmospheres of Earth and Venus that give Venus a "runaway" greenhouse effect are down to the amount of CO2, and the results are that Venus has clouds of sulphuric acid, insanely high atmospheric pressure, and is hot enough to melt lead.

On Earth, millions of years after this happened on Venus, we have seen a 40% rise in the CO2 level since the industrial revolution. Tyson directly addresses the opponents of climate change by asking the sort of questions they ask (most likely because they think their questions raise unanswerable objections to the scientific point of view), beginning with: Could climate change be down to volcanic eruptions instead of human actions?

Each year the volume of CO2 produced by all volcanic eruptions is equivalent to only 2% of that produced by humans. To give a sense of the staggering scale of the amount of Carbon Dioxide our civilisation creates each year, Tyson explains that it is equal in volume to the white cliffs of Dover, illustrated with an effect showing those cliffs rising out of the ground and doubling in height.

In reality, of course, CO2 is invisible, and Tyson suggests this may be part of the reason we find it so difficult to take seriously as a threat. This is followed by a neat effects sequence showing the CO2 being emitted by cars and planes as a sinister purple smoke.

Linking the scenes on Venus and Earth, Carl Sagan's PhD thesis was on the Venusian greenhouse effect, and in the original Cosmos series he spoke about the greenhouse effect on Earth, as things stood in 1980.

The differences between weather (with chaotic, short term patterns) and climate (showing a predictable pattern in the long run) are illustrated by Tyson taking a dog for a walk and looking at the dog's path - a fun way of making a serious point.

The animated sequences for this episode concern historical attempts to introduce alternatives to humans burning fossil fuels for energy, which go back further than you - or I, before I saw this programme - might have thought. At the great exhibition at Paris in 1878, Augustin Mouchot demonstrated solar energy, but at that time coal was just too cheap for anyone to be interested so it never caught on.

A similar fate befell Frank Shuman in 1913. He went out to Egypt and planned to irrigate the desert using solar power. The British and German governments were interested, but the arrival of cheap coal, and the First World War, got in the way.

We would only need to harness a fraction of the available solar and wind energy to power our civilisation, it seems disheartening that we have not yet made that transition. But, as with previous episodes, we end on a note of optimism and hope, with Tyson giving two examples of where humanity has successfully made difficult transitions before: the passing of the Cold War (which was, of course, still ongoing at the time of the first Cosmos series) and the ending of the threat of instant nuclear armageddon. And, much further back, the dawn of civilisation as humans made the change from nomadic to agricultural societies, made possible by climate change of different sort - a global warming coming out of an ice age.

This says that we can avert global warming on Earth and prevent it from becoming like Venus. The programme finishes with a few lines of John F Kennedy's inspirational, uplifting speech "We choose to go to the moon."

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.

Cosmos: The Lost Worlds of Planet Earth

This episode of Cosmos really has something to say as we revisit the Halls of Extinction (previously seen in the second programme of the series, Some of the Things that Molecules do) to examine the Permian extinction of 300 million years ago. Volcanic eruptions released carbon dioxide and methane, causing global warming that wiped out 9 out of every 10 species on the planet.

The animated sequence - a short one in comparison to others in the series - is on Alfred Wegener. In his time geologists believed that there were once land bridges across the Atlantic Ocean, long since vanished, to explain how fossils of the sames species could be found on both sides even with an ocean separating them. Wegener took the evidence, worked backwards and came up with the idea of continental drift and called the original supercontinent he theorised "Pangaea."

His continental drift views were not accepted in his time and he became a laughing stock and a pariah in his field, and one day in 1930 he disappeared while on an Arctic expedition. In 1952 Wegener's ideas were vindicated by Marie Tharp who mapped the mid-Atlantic floor.

Tyson takes the Ship of the Imagination down into the Marianas Trench to look at the animals that live even down there in the deepest place on Earth, but this isn't a David Attenborough series so he soon moves on, deeper, below the crust of the Earth to look at the core and mantle, explaining how continental drift occurs. The flow from one subject to another feels natural, even though they could have been covered without any link to one another.

Another extinction event, most certainly better known than the Permian one, is the asteroid that wiped out the dinosaurs but gave the mammals the chance to become dominant on Earth. Tyson then takes us from that event to the evolution of man, showing how some (less well known) random events had consequences that shaped the course of that evolution: the continental drift that brought North and South America together changed the ocean currents in that part of the world, which had a knock on effect on the ocean currents around Africa. The African climate became drier, and tree-dwelling animals came down from the dying-out trees to the Savannah, where to compete with the other ground animals they evolved to use tools (monoliths may, or may not, have helped with that).

The gravitational effects of Venus and Jupiter had tiny but incremental effects on the Earth's tilt and orbit over millions of years, resulting in the ice ages. We are now in a warm interval between ice ages, due to last for another 50,000 years.

And now the various strands of this programme come together as Tyson warns of the dangers of man-made global warming and climate change, accelerating, changing or amplifying the natural (but very slow) changes the Earth undergoes over time. He points to an empty corridor in  the Halls of Extinction and says we don't know when or how it will be filled. Maybe an obvious message to some of us, but a powerful one nonetheless.

Cosmos: The Electric Boy

(This was the tenth episode broadcast when the series was originally shown in May 2014, but it appears ninth on the DVD set. I'm not sure why the order is different, and I'm not sure it matters either. Since I'm watching the DVDs I have used their ordering.)

Michael Faraday, at 21, attended Royal Institution science lectures to see the demonstration of electricity by Sir Humphrey Davy, and was later hired by him as an assistant.Faraday went on to investigate the connection between electricity and magnetism, designing the first electric motors and generators and so turned electricity from a scientific novelty to something... well, to call it "useful" would be a massive understatement.

While Faraday is the focus of the episode and the hero of the piece, Davy is not portrayed very favourably - the animated sequences show him injuring his own eyes from an exploding experiment in a really stupid way (i.e. he had just called out another scientist for being injured doing the same experiment), and is jealous of Faraday's achievements and pettily tries to direct Faraday's researches down a different direction.

Faraday succeeded Davy as the director of the Royal Institute and established the Christmas Lectures for children which continue today. The programme reminds us that Carl Sagan presented them on TV in 1977, they are available to watch here (although the picture quality is not fantastic).

Illness afflicted Faraday with memory loss for the rest of his life, but he continued to work and make discoveries - at age 60 he proved there was a relationship between electricity, magnetism and light.

From the behaviour of iron filings near magnets he deduced the existence of magnetic fields - invisible lines of force between magnets - including the Earth's magnetic field. Tyson goes on from magnetic fields to discuss gravitational fields, as both allow action at a distance. The episode concludes with James Clerk Maxwell's reading of Faraday's work and putting them into mathematical formulae - an animated scene of Faraday receiving Maxwell's book on his work parallels an earlier scene where Davy receives a book on his own work from Faraday.

This isn't the strongest episode of Cosmos by a long way, but that's mostly down to my preferences and the scientific topics I am most interested in learning about or expanding my knowledge of. I do feel that the subject matter of this programme is less interesting, and - as with Robert Hooke in an earlier episode - it seems to resort to caricature (mainly I mean the portrayal of Davy here, but also in the scene of Faraday's schooldays) to inject an artificial level of drama to spice up the narrative.

When it is at its best, Cosmos does not need this.