Читать книгу The Davey Dialogues - An Exploration of the Scientific Foundations of Human Culture - John C. Madden - Страница 18

Rough winds do shake the darling buds of May,

And summer's lease hath all too short a date.

WILLIAM SHAKESPEARE, “Sonnet 18”

It was a sunny Thursday morning. My wife, Margaret, was out playing badminton as she did most Tuesday and Thursday mornings in the winter months. So far, I had successfully arranged my meetings with Davey to coincide with her absence. I was not keen to have her questioning my sanity as a result of a sometimes loud conversation in my workroom with an invisible being.

– You seem a little nervous, this morning, teacher.

I had not said a word, but was sitting patiently at my computer, a cup of coffee in hand, reviewing the briefing notes I had prepared. If Davey could not see, but could only hear, how could he know I was feeling a little nervous? Furthermore it was hard to tell from his tone of voice if his addressing me as “teacher” was meant to be humorous and to set my mind at ease, or, to the contrary, as a sarcastic reference to my feeble efforts to explain something he already understood much better than I. Later on I would learn that he rarely if ever tried to embarrass me. It was almost certainly a failed attempt to relax me and get me laughing. Not knowing this yet, I bit my tongue and started in without further comment.

– I vividly recall being told in school that a butterfly only lived for about twenty-four hours. In reality the lifetime of a butterfly varies substantially by species but is more likely to be about ten days.[18] Such a short time span for a life, even if preceded by a few weeks spent as a caterpillar preparing for the metamorphosis, seemed incomprehensible to me at the time. I could not begin to imagine how to pack a lifetime into one, or even ten, days.

If I were to live for a hundred years, that would be about 3600 times longer than the ten-day life of an average butterfly. The human sense of time must clearly be very different from that of a butterfly, assuming it has any sense of time at all. Take another leap by a factor of 3600 beyond a hundred-year lifespan, and you get 360,000 years. Now that is quite a long time. If we look backward in time, it takes us well beyond the appearance of people like us (Homo sapiens), generally reckoned to have occurred about 160,000 years ago.[19] These time frames must be totally beyond the ken of a butterfly and put a severe stress on our own imagination. I look on my great-grandparents, only three generations older than I, as having lived quite a long way back in time. 160,000 years takes us back more than six thousand generations!

The big dinosaurs such as Apatosaurus and Tyrannosaurus rex became extinct about 70 million years ago, or almost 440 times longer ago than the first appearance of Homo sapiens. As you have likely learned already, the first dinosaurs appeared quite late in the history of Earth, only about 230 million years ago. The first microfossil records of life on Earth date to about 3.45 billion years ago and are found in Apex chert (a variety of quartz) at Marble Bar in Western Australia. The fossil colonies are cyanobacteria (sometimes called blue-green algae), which built reefs. There are several other locations on Earth showing microfossils of a similar age.

Taking yet another step back, the ages of Earth and the solar system of which it is a part, are thought to be just over 4.5 billion years, in a universe thought to have started with the Big Bang 13.8 billion years ago. Now there is some speculation about “other universes”. Although the term “universe” was originally meant to include absolutely everything, it seems quite reasonable to speculate that other universes may also have started with a Big Bang at other times, and may exist as entities completely inaccessible to us and probably unobservable by us.

– Of course there are other universes! Do you still think I don’t exist?

– Can you imagine me standing up at a conference of cosmologists and saying that I know there are other universes because I have been talking to a disembodied voice that hails from one?

– As a matter of fact, I can imagine it. Indeed I have been conversing with someone who did just that!

– And . . .?

– You are right. He was not believed to be a credible witness.

– I assume I need say no more.

I said this rather too tartly, perhaps because I was guiltily aware that I had not answered his question. I had not yet fully settled in my mind whether or not Davey really existed, so I hastily picked up the thread of what I wanted to say.

– The philosophies and belief systems of my forebears are strongly biased by their understanding of time as well as by their understanding (or lack of understanding) of the world around them. For example, it is much easier to believe that humankind is extra special, and generally above the rules that apply to other mammals and to other life forms if you believe that the universe was created only about six thousand years ago (i.e. long after the evolution of Homo sapiens), than if you believe that our universe is about 14 billion years old. In the absence of any strong evidence for one position or the other, one must expect that humans would be naturally biased to believe that they were special.

I have thus found it helpful to learn about the gradual development of our understanding of time, not just because the history is interesting but also because it helps us to understand the origins of some of our belief systems.

For by far the greatest part of the history of Homo sapiens, the boundaries of time measurement have been set by oral or written records, passed down to succeeding generations. Many, if not most, of our great philosophers and religious leaders lived and died long before we had the benefit of understanding the history of other species as recorded in the fossil beds (an understanding that roughly dates from the remarkable work of William Smith in the early 1800s in England), and without the detailed knowledge of the ages of rocks and some cherished human artifacts. It is only during my lifetime, with the discovery of radioactive dating techniques, and even more recently the finding that some changes in genes over time can be used to measure the passage of time, that humankind has been able to learn and to wonder at the vastness of time from a human perspective. Of course the findings of Charles Darwin and William Smith in the nineteenth century certainly provided strong indications that Earth might be a lot more than six thousand years old, but precise measurement of the age of most artifacts was simply not possible. Had the prophets of yore had that knowledge, and had they shared the insights available to people of my generation on the workings of the human brain, and of the power and complexities of evolutionary theory, their writings would surely have been very different. To begin with, they would have been much less likely to place man at the centre of the universe with a prestigious role as the most-beloved species watched over by an omniscient and omnipotent god.

I have fallen heir to one of several family bibles passed down from clergyman ancestors. Like many old bibles, on the first page of Genesis, there is the annotation “Before Christ 4004” beside the opening text, which reads, “In the beginning God created the heaven and the earth”. Behind this annotation lies a fascinating historical footnote.

Figure 5.1 – Archbishop James Ussher, after a portrait by Sir Peter Lely, circa 1654.

Archbishop James Ussher (or Usher, as his name is sometimes spelled) was born in Ireland in 1581, and died in England in 1656. He had been a professor and subsequently vice-chancellor of the then newly established Trinity College in Dublin before becoming primate (or head) of the (Anglican) Church of Ireland in 1625. These were adventurous (that is to say dangerous) times for a cleric in England and Ireland as there were ugly conflicts between supporters of the Church of England, Calvinists and Roman Catholics. Ussher, who leaned toward Calvinism, was heavily embroiled in the conflicts and published several tracts in defence of the Irish wing of the Church (which was Calvinist). As a result, the King viewed him with disaffection. Today, his best-known work, published late in life, is Annales Veteris et Novi Testamenti (Annals of the Old and New Testament). In this work, he sets out a time scale for biblical events, starting with the creation of Earth in 4004 BC (October 23 at high noon to be precise). Stephen Jay Gould has written a rather nice article on Ussher that appears in his book, Eight Little Piggies: Reflections in Natural History.[20] In it he scolds a number of writers of geology textbooks who pillory Ussher for being so narrow-minded as to use the bible (though it turns out he also relied on other historical sources) to come up with such a ridiculously low number for the age of the universe.

Gould points out that Ussher was actually a rather broad-minded man who used any sources available to him to help in his task. Gould claims that Ussher’s estimate was simply considered to be the best of many competing estimates of the age of the universe in his day (and long after), primarily because he was prepared to examine all available sources. To be sure he made use of the copious data in the Old Testament about who begat whom and how old they were when the birth occurred, but this data still left some significant gaps. To close in on some of these gaps, Ussher referred to the works of secular historians, took account of the historical possibility that Christ was actually born in 4 BC (that is, before the death of Herod), and accounted for changes resulting from the adoption of the Gregorian calendar. Gould has written that Ussher’s figure for the age of Earth was actually a good deal higher than almost all other contemporary estimates, but this contention is open to serious doubt.

In As You Like It, Shakespeare has Rosalind observe to Orlando that “[t]he poor world is almost 6000 years old”. It is thought that the play was first performed in about 1600. Shakespeare died in 1616. Ussher was only nineteen in 1600 and didn’t die until 1656. His estimate of the age of Earth was completed in 1654. It is just possible that Shakespeare learned of Ussher’s estimate for the age of Earth some time after his play’s first performance, and added the line in for a contemporary audience for whom Ussher’s estimate was new, though as yet unpublished, news, but it seems a little unlikely. The facts as told in Wikipedia under the heading “Young Earth Creationism” strongly suggest that there were many estimates for a young Earth made between 1000 and 1700 AD. About fifty different estimates are listed in the article. These, in the main, were in the range 6000–3000 BC. Isaac Newton and Martin Luther, for example, weighed in with estimates of 4000 BC and 3961 BC respectively. Recall that Ussher was a senior prelate in the Church at the time that that wonderful literary masterpiece, the King James translation of the Bible, was being produced. It is hardly surprising that Ussher’s estimate was the one used by the translators. Nor is it surprising that he should, as a result, be the target of opprobrium from a variety of scientists now in possession of much more accurate information about the age of the Earth. Shakespeare’s reference to the planet’s age doubtless came from one or more of the many similar estimates current at the time.

It is important to remember that in Ussher’s lifetime, only about five hundred years ago, many tools now available for dating artifacts and events were unknown. In my generation, many people still either ignore or outright disbelieve the scientific evidence relating to the age of the universe and of Earth. The dissonance between the book of Genesis and what scientists have learned about our genesis is explained by most clerics by asserting that Genesis was always intended as a poem or fable of creation and was never meant to be taken literally. This assertion is a harmless example of historic revisionism, but it is certainly true that these days, most religious people have found a way to believe both the scientific discoveries and the religious texts, even when the two are incompatible. Those who have refused to do so have found themselves faced with some serious contradictions to resolve.

One of the falsehoods I was taught at school was that the oceans were getting gradually more and more saline, as Earth’s rivers continuously carried small concentrations of salt to the sea. We were told that the salt gradually increased in concentration in the ocean, while the water that carried the salt from the land was recycled by a process of evaporation, formation into clouds and then precipitation back onto land as rainfall. It was not until quite late in life that I learned that this interpretation of events is wrong. Our oceans are not getting saltier. As it happens, again according to a perceptive and interesting chapter in Eight Little Piggies, this particular misunderstanding has been around for quite a few centuries. A distinguished British scientist, Edmund Halley (he after whom Halley’s comet is named), tried to use this assumption as a way of estimating the age of Earth. Halley was born in the same year that Ussher died (1656) and is remembered principally for his contributions to astronomy and for his work on magnetic variation. He was Savilian Professor of Geometry at Oxford University, Astronomer Royal, and a distinguished member of the Royal Society.

Halley lamented the fact that measurements of the saltiness of the sea had not been made by the ancient Greeks and Romans so that he could compare the salinity he measured with that of ancient times, and thus derive a number for the rate at which oceanic salinity was increasing. Then, assuming that the rate of salinity increase was constant, and that the ocean started out as fresh water somewhere near the birth of Earth (both assumptions open to dispute), he reasoned that it should be possible to calculate the age of the oceans, and by extension, the approximate age of Earth. Lacking the all-important early measurements, he never made that estimate himself. However, in the late nineteenth century, Irish geologist John Joly did make an estimate using Halley’s method and came up with 100 million years as the age of the oceans, and thus, he assumed, of Earth – still a long way from current estimates of about 4.5 billion years, but also over ten thousand times closer than James Ussher’s attempt.

For reasons that are only fairly well understood, despite significant variations of salinity in the world’s oceans, overall, the salinity of the oceans appears to have reached a stable state. While salt is continually carried to the oceans by rivers, it is also constantly being used up by various life forms and, it is now believed, at least partially stripped from the ocean water inside hot vents. These vents are located on the ocean floor where tectonic plates are drifting slowly apart, permitting ocean water to penetrate deep into the hot ocean floor before being expelled – usually sulphur rich but relatively salt-free – back into the ocean. It has been estimated that all the water in our oceans is flushed through these hot vents on average once every 10 million years.[21]

Gould draws the following insightful lesson from this classic case of drawing incorrect conclusions as a result of faulty assumptions:

The best signs of history are objects so complex and so bound in webs of unpredictable contingency that no state, once lost, can ever arise again in precisely the same way. Life, through evolution, possesses this unrepeatable complexity more decisively than any other phenomenon on our planet. Scientists did not develop a geological time scale – the measuring rod of history – until they realized that fossils provided such a sequence of uniquely non-repeating events.[22]

While there are aspects of Gould’s statement that I don’t quite agree with (which I will discuss later), I was struck by the beauty of the insight. Most of the physical processes we observe have long ago reached some kind of natural equilibrium and so cannot be useful to demark time. The Halley ocean salinity test provides a nice example of this. However, life forms keep changing in unpredictable ways, and the odds of them reverting to a previous form are negligible. As a result, we can confidently associate an era with the existence of particular life forms, preserved as fossils. Perhaps there will be a time when human fossils will be useful to date soil strata from our era, in which case we had better not all opt to be cremated!

Gould’s observation about the use of fossils to date the age of rocks refers to research pioneered by British canal builder William Smith in the early 1800s. Smith discovered that many of the layers of rock that he had to dig through to build canals contained fossils and that the fossils tended to be different in each layer. As he toured about England and Wales, digging more and more canals, he found that he could correlate the layers he encountered at different sites by the similarity of their fossil content. In short, he could determine a relative time at which a rock stratum was laid down by the type of fossilized animals it contained, and could thus correlate the relative ages of the various strata he encountered throughout England.

Smith’s personal story is an interesting one and is ably told in a book by Simon Winchester, The Map that Changed the World. Over a period of twenty years, this observant and self-taught son of an English blacksmith compiled a large map of England and Wales depicting the relative age of the strata to be found near the surface. This map was published in 1815 and caused a small sensation. The credit he received for all his work was initially disappointing to say the least. Smith paid a huge penalty for not being a recognized member of the scientific establishment. His work was plagiarized, and he spent time in debtor’s prison before finally, in his later years, enjoying the recognition he deserved.

Smith’s discoveries did much to promote the scientific field of palaeontology – the study of life in the prehistoric past. There is now a large body of knowledge relating to long-extinct life forms. These studies demonstrate conclusively that humankind is very much a newcomer to the parade of life forms over the past few billion years. In common with most other life forms, many of which have disappeared, its future is by no means assured. This was a message that the Western world of Smith’s time was ill-prepared to receive, since it was still fixated on the idea of spontaneous creation as outlined in the Old Testament, and buttressed by Archbishop Ussher’s precise calculation of the time when that creation occurred.

Palaeontology has allowed scientists to determine the relative age of various rock strata, but it was a long time before non-specialists accepted its basic message about the existence of life long before 4004 BC. In part this was because palaeontology did little to help us determine the actual age of a given rock or relic. Our ability to make such identifications came much later (for the most part after the Second World War) with the discovery that radioactive isotopes of some commonly found elements could be used to determine the age of a variety of substances.

– Well, those were some quaint stories you told me. You humans seem to have had a lot of difficulty sorting out the age of things. It is not a problem I had thought about much before listening in on you and others. However, I now suspect it had much greater importance to my vanished friends than I had realized.

But I missed something in what you said. Can you tell me what radioactive isotopes are?

– I’m surprised you don’t know! Some elements have variants (called isotopes) that are not stable and that decay into other elements. [Isotopes are explained in greater detail in Appendix 1.]

– How strange. You mean that the ninety-two natural elements, which I thought were the basic building blocks of your planet, are not always stable?

– That’s right. Furthermore, the rates of decay vary widely from one unstable variant of an element to another. This turns out to be very useful for calculating time lapses. Don’t you have radioactivity in your universe?

– Not that I am aware of. This is quite a surprise for me. I need to learn more.

– And so you shall.

I tried to mask my astonishment that Davey’s universe had no radioactive elements. In fact, while I was prepared to talk about the application of radioactivity to the dating of old artifacts, I had not guessed that radioactivity itself would be a mystery to him. So, I began at the beginning with a quick summary of the discovery of radioactivity in 1896.

– Henri Becquerel was awarded the first-ever Nobel Prize in Physics in 1901 for his discovery of radioactivity. Marie and Pierre Curie and Ernest Rutherford were subsequently awarded Nobel prizes, too, for their follow-on research that yielded a basic understanding of the phenomenon. The world of the early 1900s was just as surprised and mystified as you apparently are today to encounter the phenomenon.

By their very nature, radioactive elements are unstable. They give up energy in the form of radiation and decay into the isotope of another element. That new isotope may also be unstable, in which case it, too, will decay. Ultimately, the last radioactive isotope in the chain will decay into a stable (i.e. non-radioactive) isotope.

The first watch I ever owned had the numbers on the watch face as well as the hour and minute hands painted with a special luminescent paint containing traces of radium. The radioactivity in the radium excited luminescence in the zinc sulphide with which it was mixed. As a young boy, I loved looking at the watch face in the dark, and wondered at this miraculous appearance of light without an obvious power source.

For health reasons, the use of radium-powered luminescent paints was banned in most countries in the two decades starting in 1960. The deleterious health effects were first noted in the women who painted the watch face dials, many of whom licked their paintbrushes to give them a sharp point and subsequently developed cancerous growths on their tongues. Today’s luminescent paints are either powered by tritium, an isotope of hydrogen, which decays much faster and more safely than radium, or they are pumped by external radiation sources, such as ultra-violet light. The luminescent face on my watch today has only a very feeble glow as compared to that of my first watch!

Although clocks and watches with radium paint dials have now virtually disappeared, there is another kind of radioactive clock that has revolutionized our measurement of historical time.

As already mentioned, fossils provide a marvellous record of the comparative ages of different sedimentary rock strata. Using the simple assumption that a layer of sedimentary rock that is on top of another layer is therefore more recent in origin, it is possible to establish the relative ages of different fossils by correlating layers of similar fossils that appear around the world. As Gould so nicely pointed out, the very complexity of the evolutionary process means that the same animal has, for practical purposes, no chance of evolving twice in the same form. This makes comparison of fossils to other fossils found elsewhere in the world an excellent way of determining the comparative age of a rock or a fossil. The process is aided by the finding that in the early days of Earth’s history there was only one, large, contiguous landmass, making it much easier for one animal to appear in many divergent places.

However Gould went too far when he wrote: “The best signs of history are objects so complex and so bound in webs of unpredictable contingency that no state, once lost, can ever arise again in precisely the same way.”[23] For while the fossil record – the pre-eminent exemplar of this phenomenon – is very good at giving us relative time, it is of very little use in telling us exactly how old a given fossil might be. For that, we need a clock with a regular beat that leaves a record of how long it has been ticking away since the clock was “started”.

Radioactive dating (or radiometry) provides just such a facility. Used in combination with the fossil records, it has enabled us to gain a spectacular insight into events that took place long before the arrival of humankind on Earth, providing some humbling news about our place in the world’s history.

There were two main streams of radiometry development. Geologists were most interested in dating the age of rocks (whose ages are typically millions [and occasionally billions] of years old) and started work soon after the discovery of radioactivity in 1895. They tended to work with isotopes with long periods of radioactive decay, measured in millions or billions of years. Their estimates were rather inaccurate until after the Second World War, when much better instruments for measuring radioactivity were developed.

The second main stream of research focussed on isotopes whose radioactivity decayed much faster. These substances decay too quickly to be useful for measuring time scales as long as billions of years but very useful, for measuring much shorter time frames. Radioactive carbon-14 is the best known of the elements used for shorter-term dating, but it is not the only useful isotope applied to this task.

The undoubted pioneer in developing radioactive carbon–dating techniques was Willard Frank Libby (1908–80), an American chemist. According to Libby, carbon-14 and tritium dating had their origins in studies of the effects of cosmic rays on Earth’s atmosphere.[24] In 1939, just before the Second World War, Libby developed an instrument that permitted him to detect very low concentrations of carbon-14 and tritium – respectively radioactive isotopes of carbon and hydrogen. This instrument allowed him to discover that interactions of cosmic rays with the upper atmosphere led to the generation of about two neutrons every second over each square centimetre of Earth’s atmosphere. The neutrons thus created are trapped by nitrogen atoms, which then decay, for the most part into radioactive carbon-14 plus stable hydrogen. One per cent follow an alternative decay route that leads to the production of the most common (and stable) isotope of carbon (carbon-12) and an unstable isotope of hydrogen (i.e. tritium).

The atmospherically generated carbon 14 becomes mixed with stable carbon-12 and oxygen, and is incorporated into carbon dioxide in the air, where it is taken up by plants and, later in the food chain, by animals. The net result is that in living plants and animals, there are about 14 counts (or disintegrations of carbon-14) per minute per gram of carbon present.

But radioactive elements are elements in transition to becoming other elements, sometimes stable forms of other elements, sometimes yet more unstable isotopes. In the case of carbon-14, the radioactive element is on its way to becoming nitrogen once again, but it takes its time to decay. In fact, given a container full of carbon-14, it will take 5730 years (±40 years) for half of it to decay. Another half of the remaining carbon-14 will decay in the next 5730 years, and so on. Hence, 5730 years is defined as the half-life of carbon-14. (Incidentally, the term “half-life” was first coined by Sir Ernest Rutherford while a professor at McGill University.)

Stable carbon in rocks, which has generally been in place for time periods of the order of at least millions of years, will not show any detectable radioactivity since any carbon-14 present when the rock was formed will long since have decayed to undetectable amounts. However, remnants of organic material that date from times up to about fifty thousand years ago (i.e. about nine half-lives of carbon-14 decay) will still have detectable radioactivity. Life forms only take in carbon for as long as they are alive. Once the life forms die, carbon dioxide uptake from the atmosphere ceases, and the existing radioactive carbon decays at a fixed rate, hence providing a signature identifying its age.

One of the best-known applications of carbon dating that I am aware of was finding the age of the Shroud of Turin, which purportedly was used to cover the body of Jesus when he was taken down from the cross. Carbon-14 dating carried out in 1988 established that the shroud came from cloth woven between 1250 and 1400 AD, long after the death of Jesus. It needs to be said that this estimate has not been accepted by all experts on the grounds that the small samples of the shroud used to determine its age may not be representative of the age of the whole shroud. The carbon-14 dating technique is now in wide use by archaeologists and anthropologists. It will likely continue to be a workhorse for artifact dating for many years to come.

While carbon-14 is only useful for dating material up to about fifty thousand years old, experts are now using many different radioactive elements to measure time frames ranging from a few years up to the age of the universe, i.e. 13.8 billion years.

I have already mentioned that the age of our solar system is about 4.6 billion years, without explaining how this number was derived. In practice, the age of the solar system is derived from radiometric dating applied to many meteorites, as well as to rock samples from the moon. Because the Earth is in a state of continuous change, it has to this date not been possible to find many rock samples older than about 3.5 billion years. However in 2001 a small fragment of the mineral zircon found in Australia was age dated at 4.4 billion years. The oldest large samples of bedrock have been found on the eastern shores of Hudson Bay in northern Canada. Some samples of that rock are as much as 4.28 billion years old.

Amongst other key dates established through radiometry are the disappearance of dinosaurs at the end of the Jurassic age 70 million years ago, and the first appearance of life on Earth about 3.45 billion years ago.

So, you can see that radioactive dating, when used in combination with the fossil records, has enabled us to gain a spectacular insight into events that took place long before the arrival of mankind on Earth, providing some startling news about our place in the world’s history. Some humans find such a diminution of human centrality in the history of the Earth hard to reconcile with their religious beliefs. As a result these scientific findings quite frequently come under attack.

Davey broke in almost immediately. He was agitated and incredulous.

– But surely that is extraordinary! Why wouldn’t everyone want to know as much as possible about their own origins?

– Actually, it is exactly what you should expect. Remember that we are the only animals in our planetary system with any curiosity at all about our origins. Our curiosity is almost certainly primarily motivated by an innate drive to seek knowledge that will enhance our pleasure and our odds of survival.

But what if that knowledge diminishes our pleasure, upsets our most hallowed beliefs, or threatens our economic or physical security? In such circumstances, our innate curiosity can evidently be easily vanquished by a strong urge to deny “inconvenient truth”. Human history is full of examples of such denial.

– In that case, it is a wonder that humanity has survived so long. Surely it must be doomed if it doesn’t change! It is one thing for a few astronomers to be imprisoned or killed because the authorities cannot adapt to the idea that Earth orbits the sun and not vice versa, but quite another to deny, for example, the real history of your species.

– You may be right. I wonder if your own long-lost friends in your universe have any useful lessons for us in that regard.

– We’ll come to that in due course. In the meantime I must tell you that your words have been of great interest to me. I had not imagined a world where it is possible to date the origins of objects going back billions of years.

– And I cannot imagine a world where one has no idea how far back one’s past extends. Did your superhumans really have no idea how they evolved? Did they not study history?

– Yes and no. I mean, I think so.

– What is that supposed to mean exactly?

Now I was really paying attention. I sensed the possibility of a chance to get a glimpse of life in Davey’s universe that heretofore he had deliberately kept hidden. Davey spoke.

– Well, as I told you, we went through a horrendous period. First there was a huge amount of information lost beyond the possibility of recovery – a situation we had thought to be impossible, since we went to great lengths to preserve important information in many places. This disaster was very sad and very costly. But the truly horrendous result was that it led to the death of all superhumans. Not a single one survived. It was an unimaginable catastrophe!

I was stunned. The more so as I was just learning to detect Davey’s emotions as he spoke, and I could feel how very deeply saddened he was. Then suspicious thoughts seeped into my mind.

– I don’t suppose you or your colleagues were involved in any way in what you imply was an event of mass destruction?

Davey’s response surprised me.

– How could you ask that? I told you I loved the superhumans more strongly than you on Earth can begin to imagine.

I immediately wondered how he could possibly know that his love for his friends was stronger than any love we experience, but I dared not ask. I remained silent, eyes downcast.

Davey was quiet for some time, as well. Eventually he appeared to rouse himself.

– Let’s meet again at the same time next week.

I hesitated.

– Before you go, I wonder if a table of key dates would help you to get a feel for the critical time frames of the development of our universe, of life on our planet and of our civilization?

– Yes, but you will have to read out the columns and rows to me. You have no idea how frustrating it is to listen in on all those academic conferences where the participants apparently project something called a “PowerPoint” and then mumble out a few incoherent sentences to elaborate on what I cannot see in the first place.

And by the way, your references to useful books are very irritating to me. As you know, I cannot read them.

– But you can always talk to the authors if they are alive. Bill Bryson, for example. Why don’t you go and talk to him? He is obviously intelligent, and he has a good sense of humour.

For the first time, I heard something resembling a hollowed out sigh fill the room.

– I suppose it is hard for you to understand, but I did start to listen in on Bryson shortly after he published his book about “nearly everything”. I don’t even want to think about how many interviews on radio and television he had. His voice was coming at me from all directions, but most of the time the questions he was answering were unhelpful and were posed by people who had not read his book. So, finally I dropped in on him much as I did with you. He was in bed at the time, and he was furious with me. He told me to get lost, go back to where I came from by way of a place called Hell, and never to haunt him again. He seemed not to have much of a sense of humour after all – though you will appreciate that it is difficult to appreciate a sense of humour when there are no shared instincts or culture involved. I believe that most humour arises from a conflict between instinctual behaviour and behaviour dictated by cultural imperatives.

– Sorry it didn’t work out. I hope you weren’t bored by my discussions of time and space. I am convinced that our evolving understanding of those two important concepts has been key to the development of religion and philosophy over the ages. An essentially static universe with Earth at the centre leads to very different conclusions about our place in nature from what we know today about our universe. Similarly, a world that is only six thousand years old necessarily lends a completely different hue to history than a universe which is over 13 billion years old, with intelligent humanity around to appreciate it only for the last 160,000 years or so.

– I appreciate your point, but what about mass, force and energy. Aren’t they key concepts, too? Time and space have a certain aesthetic appeal, but without living mass, such as you, what meaning can they possibly have?

– Of course, you are right – and that is a really tough problem for we humans to get our collective minds around. In our next session I will give you a whirlwind tour of the subject, but don’t expect that you will come away completely satisfied. Despite some early attempts by such brilliant scientists as Isaac Newton and Albert Einstein, both of whom provided theories that explained beautifully the world as it was known in their time, our expanded view of our universe, illuminated by a vast new store of astronomical data and buttressed by complex particle physics experiments, has shown us that their theories are inadequate to completely describe our universe as we now observe it. To make the data fit our theories, we have to “invent” (most scientists would say “postulate”) great quantities of dark (i.e. unobservable) matter and energy, without any firm idea of their origin. Dark matter and dark energy stand as the two greatest beacons of human ignorance in our time.

– Perhaps, but just think how bored you would all be if you knew everything!

After I had carefully read out the contents of Tables 5.1 and 5.2 reproduced below, we finished our dialogues on time and space, with the promise of a dialogue on matter and energy planned for the following week.

After listening to me read the tables, Davey’s only comment was to say how fortunate it was that he did not visit our universe one or two hundred years ago, or he would have learned nothing of interest!

Table 5.1 – Some Perspectives on Time
Time	Comment
~13.8 billion years ago	Age of the Universe, that is 13,800,000,000 years ago.
~4.56 billion years ago	Age of our Solar System (including the Sun and the planets).
~3.8 billion years ago	First appearance of life on Earth (see Dialogue 15).
250 million years	Period of rotation of the Sun in our galaxy.
~125 million years ago	First appearance of mammals on Earth.
6-11 million years	Ages of bright stars in Orion’s belt.
~1.8 million years ago	First appearance of primitive man (Homo erectus).
800,000 to 200,000 years ago	Earliest known figurines (Venus of Bereket Ram, Golan Heights, Israel, and Venus of Tan Tan, Morocco).
~160,000 years ago	First appearance of Homo sapiens (cf Dawkins, 2005, pp. 62-66).
~143,000 years ago	First daughter of “Eve” is born. (See Appendix III).
32,000 years ago	Earliest known cave art, Chauvet, France.
10,000 - 60,000 years ago	First migration of humans across the Behring Strait to North and South America.
13,000 years ago	Earliest known pottery (Japan).
~7000 BC	“Dawn of recorded history” (Crete)
~3000 BC	“Dawn of recorded history” (Sumeria)
~3000 BC	“Dawn of recorded history” (China)
~2500 BC	Hinduism founded.
~1000 BC	Judaism founded.
~500 BC	Buddhism and Taoism founded. (Buddha Siddartha Gautama (563-484 BC), Taoism started ~500 BC but not formalized until about 500 years later.)
399 BC	Socrates dies in Athens.
384-322 BC	Aristotle’s lifetime.
0 AD	Jesus Christ is born. (Possibly 4 BC, i.e. before King Herod died.)
~570 AD	Mohammed is born.
1601-1602	Shakespeare’s Hamlet first performed.
1654	Bishop Ussher estimates “Creation” started at noon on October 23, 4004 BC. (see Dialogue 3)
1686	Isaac Newton completes formulation of the theory of Gravity. He started work on the problem in 1666.
1858	Darwin and Wallace publish the Theory of Evolution by Natural Selection. (see Dialogue 8)
1900	Quantum Theory is born (Max Planck).
Feb. 28, 1953	Discovery of the structure and function of DNA. (see Dialogue 11)
2000-2005	Preliminary understanding of the long term memory function in the brain. (see Dialogue 18)

Table 5.2 – Some Perspectives on Distance Measurements
1.616199 x 10-35 m	Planck length – the shortest measurable length. Approximate dimension of the vibrating “strings” in String Theory. Not measurable in practice, the Planck length emerges from theory.
~10-15 m	Diameter of the proton (i.e. hydrogen nucleus), as measured by scattering electrons off the proton.
50 x 10-12 m	i.e. 50 picometres. Diameter of the hydrogen atom.
~10-9 m	i.e. 1 nanometre. Diameter of a carbon nanotube.
~2 x 10-9 m	Diameter of a DNA strand. The largest human chromosome (DNA strand) stretched out is 8.5 cm long, or about 10 million times its diameter.
22 x 10-9 m	i.e. 22 nanometres. Smallest transistor gate in commercial use in 2012. Estimate for the year 2020 is 5 nanometres.
~100 x 10-9 m	Size of typical virus (range from 20-450 nanometres. HIV virus about 90 nanometres).
(380 to 740) x 10-9 m	Wavelength range for visible light. [violet – 380 nm to 435 nm; red – 625 nm to 740 nm]
(1 to 5) x 10-6 m	i.e. 1 to 5 microns. Typical size range for Prokaryotic cell. A typical Eukaryotic cell (e.g. animal or plant cell) is 10 -100 microns. See Dialogue 13.
100 x 10-6 m	i.e. 100 microns. Average diameter of a human hair.
1 m	i.e. 1 metre. About a ten thousandth of a degree of latitude (which is approximately 100 km). The largest living animal, a blue whale, is about 33 m. long.
8,848 m	Height of Mount Everest. The Marianas Trench, the deepest part of our oceans, is 10,911 m deep.
12,756 km	Diameter of Earth at the Equator (7,026 miles). Great Wall of China 6,400 km. Nile and Amazon rivers, 6,600 km.
300,000 km	Approximate distance light travels in one second. A more accurate estimate is 299.792458 km.
(149 to 152) x 106 km	Range of distance from the Sun to Earth. (Sunlight takes about 8 minutes to go the distance.)
9.46 x 1012 km	Distance light travels on one year, i.e. one light year. The Milky Way galactic disk is 100,000 light years across. The Andromeda galaxy is 2.5 million light years away.
2.4 x 1024 km	Lower bound for the size of the universe. It is likely that the universe is very much larger, possibly even infinite.

Sources: The two primary sources of information for this table are:

(1) http://www.falstad.com/scale/, and

(2) http://en.wikipedia.org/wiki/Orders_of_magnitude_(length), as accessed on 29/1/2013.