Читать книгу The Infinite Monkey Cage – How to Build a Universe - Robin Ince, Robin Ince - Страница 10

DEATH, WHERE IS THY PUDDING?

‘In many ways, Schrödinger’s Strawberry changed my life. Or death. Or whichever – it’s so hard to tell these days. All I know is the episode which featured that singular fruit gave me and my career a new lease of life. Or death. Oh god…’

Katy Brand, comedian

In the history of human thought, there are a few philosophical questions that become eternal.

Can we ever truly experience reality?

Why is there something rather than nothing?

When is a strawberry dead?

For some reason, neither Plato nor Nietzsche took time to consider the strawberry. Nietzsche’s madman ran into the town square declaring that God was dead, but made no mention of the strawberry – and what of the plum, peach and gooseberry?

It took Professor Cox to contemplate the strawberry.

In a rare moment when he was distracted from thinking about subatomic particles and Hawking radiation, Brian’s brain accidentally allowed a thought about strawberries on a level above muon and lepton.

Could it be that his jam was in a superposition?

Schrödinger’s Compote?

And if there is Schrödinger’s strawberry compote, does that also mean we should be investigating Planck’s raspberries and Heisenberg’s goji berries?

Should market gardeners be looking at their fruit at a quantum rather than molecular level?

We were discussing levitating frogs. Andre Geim is a rarity in the scientific world, being a winner of both the Nobel and Ignoble Prizes. His Nobel Prize in Physics was awarded for discovering a method to isolate a single layer of graphite atoms and thus create graphene, the thinnest and strongest material in the world. His frog levitation took place a decade before. Geim levitated frogs to demonstrate diamagnetism. Biologist and maggot expert Matthew Cobb explained the experiment. He told us it wasn’t really about the frog, though don’t tell that to the frog, they are very egotistical, especially the Poison Dart frog, which does not take criticism well. The experiment was about quantum mechanical effects; Geim also used water and ‘dead strawberries’.

Brian’s Vulcan ears pricked up like those of a German Shepherd. He was perplexed. ‘What qualifies a strawberry as being dead?’

It is here that the potential melancholy of jelly and the funereal possibilities of the trifle began.

What pathologist has the correct qualifications to declare a strawberry dead?

Animals are much easier than fruit to pronounce dead. The clues seem simpler: no heartbeat, no breathing, no eating, no movement. Even that may not offer certainty though.

Rana sylvatica is a species of wood frog (two frog mentions already, this should keep the frogs on side) that has ‘extreme freeze tolerance’. Species with this attribute can survive when two-thirds of their body water is frozen. Rana sylvatica also stops breathing and has no heartbeat for days at a time.

Life is notoriously hard to define. Every time you think you’ve come to a neat definition, some philosopher or other will pipe up, ‘ah, but isn’t that also the property of fire?’ Then, when you redefine, they’ll say, ‘ah, but isn’t that the property of crystals?’ Eventually, rather than define life, you want to take one.

Death must be easier to define.

Questions of life and death, whether on the scale of amoeba, strawberries or physicists demonstrates the complexity of living things and the difficulty of defining what it is to be alive.

For the physicist, the question becomes ‘how do you write the wave function of strawberry?’

According to the work of the French, Nobel Prize-winning physicist Louis De Broglie, it will have a wave length.

The definition of a dead strawberry became slippery. In the simplest terms, Professor Nick Lane stated that if it’s not continually harnessing energy to maintain being alive, it’s dead. The ability to harness energy seems to offer one of the most rewarding views of defining what is alive.

Professor Nick Lane: We need an enormous amount of energy to live… if you put a plastic bag over your head you’ll be dead in a minute and a half.

Brian: No, but I put strawberries in bags all the time and carry them back from the supermarket.

Robin: Can I just say he doesn’t come back from the supermarket with strawberries, he has a man that works for him who comes back with the strawberries from the supermarket…

Series 8, Episode 1 (24 June 2013)

So how do you murder a strawberry?

Whether boiling or freezing it, you are preventing the seed from ever germinating, curtailing the potential of the strawberry and yet increasing its potential too. Who wants to be a live and unknown strawberry when you could be a celebrated dead one smeared on a scone in Torquay? For a strawberry, a frog or a human, that is the key to life over death: do you still have potential? This page is in memory of all the strawberries that have died for us. Your death was delicious.

Brian replies…

Strawberries are inaccurately named, counter-intuitive things. The strawberry is not a berry: the red fruit is part of the stem of the plant from which the flower organs grow. The things we call the seeds – the little pits on the fruit – are not seeds, they are the plant’s ovaries, and the seeds reside inside. So is a strawberry dead or alive?

In the original episode of The Infinite Monkey Cage where I first posed the strawberry death question, Professor Matthew Cobb, from the University of Manchester, answered, ‘As soon as you pick a strawberry, it’s dying. As it decays it increases its sugar content, and that is what makes it sweet, but essentially it is dying.’ This is correct for the berry as a whole, which is a part of the plant and will decay if it isn’t attached. The strawberry no longer has access to the supply of ordered energy from the Sun that a plant uses to maintain its structure through photosynthesis, and the Second Law of Thermodynamics does the rest.

The Second Law of Thermodynamics is arguably the only law of nature that we currently possess that is actually a law, which is to say physicists believe that it is absolutely right. Quantum Theory and General Relativity may one day be refined or even replaced, but the Second Law of Thermodynamics will surely still stand. It states that, over time, an isolated system will become more disordered. In simple terms: Things Can Only Get Worse.

If a teacup falls to the ground, it smashes into pieces, and we never see the pieces spontaneously reassemble into a teacup, even though there is nothing in the laws that govern the motion of the constituent molecules that prevents it. The reason is that there are many more ways of arranging the molecules such that they form a pile of bits on the floor than the very specific arrangement that makes a teacup. A teacup is an unlikely arrangement of molecules, given that all arrangements are equally likely.

Living things certainly seem to run counter to this law. A strawberry is one of the most complex things we know of in the Universe, and it is at first sight hard to see how this can be squared with the Second Law. This has become known as Schrödinger’s Paradox. The resolution to the paradox is relatively straightforward. The strawberry is not an isolated system: when the strawberry is attached to a living plant, it is part of a system that includes the heat of the Sun and the coldness of space. The Sun is a source of high-energy photons cascading down onto the leaves. The plant absorbs these photons and uses their energy to convert carbon dioxide and water into sugar and oxygen through photosynthesis. Sugar is more complex than carbon dioxide and water; the atoms have been rearranged into a more ordered structure, just like a teacup. This is not all that happens, however. The plant radiates heat out into its surroundings, which is in turn radiated into the coldness of space. Heat is also a stream of photons, but they are lower energy and more numerous than those in the incoming sunlight. Heat is a highly disordered form of energy, and when all the sums are done, it turns out that this more than compensates for the increase in order during the formation of sugars and the other intricate structures of the strawberry. We might say that the strawberry increases the amount of disorder in the Universe quicker by the very fact of its existence, thus hastening the demise of all of creation. It borrowed order from the Sun, but increased the disorder of the rest of the Universe as a result.

The moment that the strawberry’s metabolism grinds to a halt, it can no longer function as a little machine sitting between the cascade of ordered energy from the Sun and the coldness of space, and the Second Law reasserts its grip. This is death.

The seeds inside the ovaries attached to the fruit are a different matter, however. They are alive if they are capable of germinating. Seeds can stay dormant for very long periods of time; many decades in some instances, and there are different types of dormancy in the plant kingdom. The strawberry seed exhibits physical dormancy, which means that the seeds’ outer casing, being impermeable to water, prevents the embryo within germinating – germination is defined as the sprouting of the seedling from the seed. When the strawberry is eaten by an animal, the seeds pass through the digestive tract and the outer casing is damaged such that it becomes permeable to water. This begins the germination process. In other species, the outer casing can be damaged by fluctuating temperatures, freezing and thawing, drying, or even fire. The evolutionary advantage of delayed germination is clear; there is a selective advantage to delaying germination until the onset of the rainy season in the tropics, for example. Awaiting dispersal via consumption by an animal can also be seen to offer a selective advantage. Precisely how physical dormancy evolved, however, is a matter of ongoing research.

Some seeds exhibit a different form of dormancy known as physiological dormancy, in which embryo growth is prevented by inhibiting chemicals. All gymnosperms – of which conifers are the most common group – exhibit physiological dormancy. Unlike physical dormancy, physiological dormancy can be reversible.

The definition of a dead strawberry is therefore a slippery one, and depends on whether you mean the strawberry itself (which is not a berry), or the seeds it contains. In the simplest terms, Professor Nick Lane, from University College London, stated that if the strawberry is not continually harnessing energy to maintain being alive, it’s dead. Seeds can continue to metabolise, albeit extremely slowly, whilst dormant. They are therefore alive, until they stop.

Brian noted that our understanding of the plight of a strawberry might be further complicated by taking quantum theory into account, extending the discussion to Schrödinger’s Strawberry.

R: I’ll tell you what, we’ll put a strawberry in a box and we won’t observe it and it can be both.

Katy: I love the idea of Shrödinger’s Strawberry.

R: The whole of Wimbledon changes.

B: I’m thinking about how you’d write down the wave function of a strawberry.

R: When are you not thinking of a wave function…?

Series 7, Episode 2 (26 November 2012)

Consider a strawberry in a sealed box with a small thermonuclear bomb triggered by the decay of a single radioactive nucleus sufficiently powerful to completely vaporise the strawberry, but not the box. Quantum theory allows us to calculate the probability that at a given time after the box is closed, the radioactive nucleus will have decayed, thus triggering the death of the strawberry.

Until we observe the nucleus (although see below), quantum theory informs us that we are to treat the nucleus as being in a mixture of both ‘decayed’ and ‘not decayed’. Physicists call this mixture a linear superposition. The amount of ‘decayed’ and ‘not decayed’ changes over time in a way that we can calculate using the Schrödinger Equation, but crucially this is all we can do. The nucleus hasn’t decayed or not – it is simply in a linear superposition.

Since the decay of the nucleus determines the fate of the strawberry, we should also say that the strawberry is in a linear superposition of alive and dead before the box is opened, just like the nucleus. In the form of an equation, a physicist would write:

There appear to be two problems with this description. Firstly, we need to be clear what we mean by ‘observe’. What is so special about observation that it reduces the linear superposition to the certainty of one outcome or another? Why does the strawberry’s experience not count as an ‘observation’ of whether the radioactive nucleus has decayed? What if we replaced the strawberry by Robin Ince? Would he remain in a superposition of alive and dead until we opened the box?

Secondly, the idea that a strawberry can only be in some combination of alive and dead in such an experiment and not one or the other doesn’t correspond to our perception of reality; surely the strawberry cannot be simultaneously both alive and dead before we open the box?

There is an interpretation of quantum theory known as the Many Worlds Interpretation that addresses both these issues. It is the simplest interpretation of the theory, and states that the superposition is never broken. All that happens when we open the box is that we enter a superposition with the strawberry and the nucleus. We might say that there are ‘worlds’ in which we see a vaporised strawberry and ‘worlds’ in which we don’t, but this language is really misleading. Reality is a superposition of all possibilities – and the interesting question becomes why our experience is of a reality consisting of only one set of possibilities. The answer is that the two ‘branches’ of reality following our interaction with the strawberry box evolve separately to each other; they do not interfere and nothing in the future of each branch is contingent on things happening in the other branch. In the Many Worlds Interpretation of quantum mechanics, however, both branches are equally real. The terminology that has developed is to refer to these branches as ‘different worlds’, but that’s misleading. There is only one ‘world’, and it is a world in which everything that can happen does happen and everything is in a superposition with everything else. There are parts of reality in which we opened the box and saw a strawberry, and parts of reality in which we opened the box and saw only vapour. The reason we are unaware of the true ensemble of alternative possibilities in practice is because they have no discernible influence on our experience in a particular branch.

In response to the Great Dead Strawberry Debate, Monkey Cage regular Professor Nick Lane sent us this contribution:

Strawberries really are in a superposition of states, although unlike Brian I’m not thinking about quantum states: parts are alive and parts are dead. We tend to think of death as a digital process: we are either alive or dead. But even when a person dies, many of their constituent cells are still alive. These will die in time, because they don’t get the services they need to remain alive. Our cells need a lot of services because they have a lot to do – we are high-energy beings, so when the energy flow ceases, we die fast. Strawberries are not: their cells don’t have all that much to do, so they can persist much longer before being pronounced dead. The seeds themselves, nicely shrink-wrapped in their own personal ovaries, can persist for years because they’ve been practically switched off altogether. They’re dried out carefully – turned to glass! – without losing their nanoscopic structure. That means their metabolism – the process of living – can be kick-started again when they germinate. The Second Law itself is put on hold, for a while, because the shrink-wrapped state seriously restricts the number of alternative states that they are free to access. I hate to say it, but the chemistry trumps physics, if only for a while. As long as the seeds don’t lose their structure they can switch on again and grow when water is restored. So the most valuable parts of the strawberry are still alive and the rest is just a doomed vehicle at the service of the next generation. Aren’t we all?

A Further Frog Footnote

Zoologist Lucy Cooke, whose fruit work includes playing a dancing raspberry in the TV series The Smell of Reeves and Mortimer, was fascinated by poison frogs from an early age; in particular, the Golden Poison Frog. Appearing on a Monkey Cage about toxins, venom and poison, she told us of her quest to see one. Its poison, an alkaloid poison, is so powerful it will kill you in three minutes, and for the last minute, you’ll be in such a state of petrification you will look, to all purposes, to be quite dead already. You only need to touch it and your fate is sealed. While making a TV documentary, she finally came face to face with one. Heavily gloved and visored, she held one in her hand. The rush from her childhood desires being fulfilled, a tear came to her eye. As the frog departed her hand, she put her hand to her eye to wipe away the tear.

NOOO!’ yelled the crew and she realised that she was millimetres away from joining those who have died for the love of a frog.

Now Lucy lives her life wondering if it is better to live to old age or die young and be memorialised as a zoologist who died due to the overwhelming and potential toxicity of the natural world.

Nick Lane: Without death there wouldn’t be evolution at all. All the magnificent things in this world are as a result of death, and without it they wouldn’t be here. From a non-religious point of view, it’s glorious because of death.

Professor Sue Black: And if death is such a great thing, why are we so scared of it? I think it’s a wonderful thing. It’s the last adventure. No one knows what’s coming. Bring it on!

Series 8, Episode 1 (24 June 2013)

AN INTERLUDE

Darwin’s worm

‘The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!’ wrote Charles Darwin in a letter to Asa Gray.¹ He went on to write that this was countered by Asa’s story of the black pigs of the Everglades that had evolved to be able to eat a plant root that made the hooves of all other coloured pigs drop off. It seems that Darwin considered the peacock to be weighed down by excessive evolutionary cost compared to the seeming pragmatism of the black pigs.

Charles Darwin had a mind to envy but a physical constitution that few would aspire to. He was hampered by ill health throughout much of his life after his voyage on the Beagle. Having spent five years travelling across the world, Darwin lived out the rest of his life in England, mainly in his house in Kent where he mulled over what he had seen and started to understand what it meant, breaking up the day by boiling pigeons to the bone and taking walks around his thinking path. Geneticist and snail expert Steve Jones, a regular guest on Monkey Cage, when asked which of Darwin’s books could be avoided by the casual reader said, ‘Don’t read his books about barnacles, he became overly obsessed.’

This still leaves you with books about orchids, emotions, coral reefs and occasional baboon behaviour interludes, as well as, of course, On the Origin of Species. Darwin studied every part of the animal world, including his own children: ‘I repeatedly observed my own infants, from under the age of one week to that of two or three months, and found that when a screaming fit came on gradually, the first sign was the contraction of the corrugators, which produced a slight frown, quickly followed by the contraction of other muscles around the eyes.’ Darwin was most definitely an attentive father, but he may have let his children cry for a little while longer for the purposes of research. By reading Darwin you will find out that blue-eyed cats are deaf, bald dogs invariably have bad teeth and that it is quite pointless to try to train yourself to stop flinching when a Puff Adder attempts to strike (he experimented with this in the safety of the reptile house at London Zoo).

We are now so used to seeing the world and its enormous variety of species on television that it is easy to forget how exotic and strange much of our planet seemed before mass communication. When Darwin was on the Beagle he was experiencing things that had barely been imagined by other humans. On 28 February 1832, he wrote of his day in the rainforest:

‘The delight one experiences in such times bewilders the mind, if the eye attempts to follow the flight of a gaudy butter-fly, it is arrested by some strange tree or fruit; if watching an insect one forgets it in the stranger flower it is crawling over, if turning to admire the splendour of the scenery, the individual character of the foreground fixes the attention. The mind is a chaos of delight, out of which a world of future and more quiet pleasure will arise.’

We may not have ready access to a rainforest, but it is important to remember that however mundane your environment may seem to be, the life you see in it and the lives of the creatures that exist inside it are remarkable examples of a planet that has more ways of assembling atoms into different forms than any other we know of. Stare out of your train window at the hills and think of all the life before you, some visible – trees and grasses, a possible cow, rabbit or alpaca – many others invisible. You don’t need a rainforest for a chaos of delight.

Though many of Darwin’s books explored the exotic, as well as pigeons, his final book was on earthworms, The Formation of Vegetable Mould Through the Action of Worms with Observations on their Habits. Some may consider that this doesn’t sound like one of his speedier page-turners, and they would be wrong. This is the Monkey Cage’s favourite book about earthworms and we have read three (this is the only one that is non-fiction, though, the others are Superworm by Julia Donaldson and Tim Curran’s novel Worm, about killer worms escaping the sewer and wreaking havoc). We love it for the delight of seeing an elderly man whose curiosity about living things has not dimmed with age.

It contains some of my favourite experiments, each one conceived to understand the earthworm a little more. Darwin saw that, like so many living things, this simple creature performed vital functions. Darwin’s experiments included breathing on worms after chewing on a variety of different things – from tobacco to perfumed cotton wool – to examine their sense of smell, and putting hot pokers near them to see how sensitive to heat they were. It is his experiments on earthworm hearing that I enjoy most, though. He begins with a metal whistle ‘which was repeatedly sounded near them’. Seeing no result, some scientists may have stopped there, but not Darwin. Next up, he brought out the bassoon, which they also took no notice of. ‘They were indifferent to shouts’ and ‘when placed on a table close to the keys of a piano, which was played as loudly as possible’ there was similarly no reaction. This series of experiments may well have been how they invented jazz. They were reactive to vibrations; this was discovered by placing them on the piano ‘and the note C in bass clef was struck’, which caused the earthworm to retreat. Darwin then tried the note G, ‘above the line in treble clef’, and had a similar result.

Darwin’s summary of the worm contains his usual mix of beauty and wonder at living things:

‘When we behold a wide, turf-covered expanse, we should remember that its smoothness, on which so much of its beauty depends, is mainly due to all the inequalities having been slowly levelled by worms. It is a marvellous reflection that the whole of the superficial mould over any such expanse has passed, and will again pass, every few years through the bodies of worms. The plough is one of the most ancient and most valuable of Man’s inventions; but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world…’

Now gather up your bassoons and prepare to experiment, your garden awaits.

¹ A renowned American botanist (1820–88).