The book "The engines of life: how bacteria made our world inhabited"

Published on April 26, 2016

The book "The engines of life: how bacteria made our world inhabited"

    Hello! We have an interesting novelty:

    imageEverything in our world depends on bacteria. For a long time - almost 4 billion years - the Earth was at their disposal. It was these microscopic engines of life that changed the chemical composition of our planet and made the world fit for plants, animals and people.

    Where did these amazing microorganisms come from? How are they arranged and what secrets hide? Why is life impossible without them? And why are bacteria social organisms?

    Famous American oceanographer Paul Falcovski, a member of the American Geophysical Union, the American Academy of Arts and Sciences, tells how and why bacteria survived all the cataclysms and adapted to the changing environment, and also shows the reader that our entire existence became possible only due to their evolution, and they are our true ancestors and the real engines of life on Earth.

    Here we will publish the chapter "Unnoticed microorganisms"

    A few years ago I received the opportunity to work on a research vessel on the Black Sea, off the northern coast of Turkey. The Black Sea is a striking and unique body of water: there is no oxygen below the approximately 150-meter mark. The task of my work was to study photosynthetic bacteria in the upper 150-meter layer.

    Photosynthetic bacteria use the energy of sunlight to build new cells. In any part of the oceans there are microscopic photosynthetic organisms - phytoplankton, which produce oxygen. They are the forerunners of higher plants, but they appeared on Earth much earlier. After a few days of swimming, the tool that my research team used to recognize phytoplankton (a special type of fluorometer that we developed many years ago) recorded strange signals that none of us had ever seen before. The signal came from a fairly large depth - just from that part of the water column, where there is no oxygen and the light is very low. In the course of further work, I realized that the organisms emitting this strange fluorescent signal, live in a very thin layer of water - perhaps no more than a meter thick. These were photosynthetic bacteria, but unlike the phytoplankton living in the upper part of the water column, they could not produce oxygen. These bacteria were representatives of the oldest group of organisms that emerged in the process of evolution long before phytoplankton. They were relict representatives of the time when oxygen has not yet appeared on our planet.

    Work on the Black Sea had a profound influence on my ideas about the evolution of life on Earth. Taking samples from deeper and deeper layers of the water column, I mentally reversed in time, discovering microorganisms that once inhabited all the oceans, and now limited to only a very small part of their former habitat. The organisms that emitted that strange fluorescent signal turned out to be photosynthetic green sulfur bacteria - obligate anaerobes. With the help of solar energy, they break down hydrogen sulfide (H2S) and use the generated hydrogen to produce organic compounds. These organisms can live in very low light levels, but do not tolerate even the very small presence of oxygen.

    Over the next few weeks, cruising the Black Sea to collect samples in different parts of it, we observed flocks of dolphins and fish in the upper layers of the water, but below the approximately 100-meter mark there were no multi-cellular organisms. Animal life cannot exist for a long time without oxygen, and here, at a depth, it disappeared. Bacteria transformed the Black Sea ecosystem: in the upper 100-meter layer they produced oxygen, but in the deeper layers, on the contrary, they absorbed it. Thus, they made the Black Sea basin their unique ecological niche.


    Fig. 1. Theoretical graph of the distribution of oxygen and hydrogen sulfide (gas with the smell of rotten eggs) in the upper 300-meter layer of the Black Sea. In the oceans, this body of water is unique. In most oceanic and marine basins, oxygen can be traced all the way to the bottom. Here, just below the mark, where only 1% of sunlight coming to the surface penetrates, there is a very thin layer of photosynthetic bacteria, which with the help of solar energy split hydrogen sulfide, using it for their growth. The metabolism of these organisms is extremely ancient; It probably originated more than three billion years ago, when the oxygen concentration on the Earth’s surface was still extremely low.

    Having spent almost a month at sea, I finally returned to the port of Istanbul, where I began to admire Turkish carpets. Mount Ararat in northeastern Turkey is famous for its woven carpets, which depict the story of Noah's Ark. Kilims made in this region are richly decorated tapestries with a woven pattern in the form of pairs of giraffes, lions, monkeys, elephants, zebras and all sorts of other animals familiar to us. Watching the merchants unwrap their goods, and sipping from the infinitely sweet tea they offered, I began to reflect on how the history of the ark influenced the formation of our distorted view of life on Earth. On the one hand, this is a story of destruction and resurrection. On the other - it tells about how God instructed people to look after nature. Neither is

    The word “evolution” literally means “deployment,” but as I watched the merchant unfold his delightful carpets in front of me, I realized that the biblical story about the ark does not give us the key to understanding how life evolved. Was all life on Earth preserved by Noah? Is it possible that some organisms were not taken into the ark? Although the ark’s history is deeply rooted in Western culture, it cannot be a source of information about the origin of life. To approach the understanding of the origin of life, we need another perspective, based on science, and especially on those sections that concern the evolution of microorganisms.

    Science to a large extent is the art of finding patterns in nature. This requires patient observation, but we inevitably fall under the influence of our senses. Man is a visual animal, and our perception of the world is based mainly on what we see. And what we see is determined by what tools we have at hand. The history of science is closely connected with the history of the invention of new tools, allowing to see things from a different perspective, but paradoxically, the invention of new tools depends on what we see. If we do not see any thing, we, as a rule, let it out of our attention. In the same way, microorganisms remained out of sight for a long time, especially as regards their role in the history of evolution.

    The first few chapters of the modern history of the evolution of life on Earth were written mainly in the XIX century by scientists who studied the fossil remains of animals and plants — remains that they could easily see. The natural patterns observed by them did not take into account the microorganic life for two simple reasons: the rocks did not contain visible fossil remains of microorganisms, and when observing living organisms it was impossible to easily distinguish the patterns of microbiotic evolution. Tools for the detection of fossil microorganisms almost did not exist; and in any case, even if they were, the role of these organisms in shaping the evolution of the Earth could not be evaluated until other, more advanced tools became available in the following decades. Patterns of evolution, observed for animals and plants, were historically derived from the shape and size of their remains, as well as the location of these remains in geological time. For microorganisms, this approach is far from being so effective.

    In general, the fact that we did not notice microorganisms, both literally and figuratively, distorted our understanding of evolution for more than a century, and the inclusion of microorganisms in our picture of evolution is not yet fully completed. Science is not just the art of finding patterns in nature (which is difficult enough in itself). It requires the ability to find patterns that are not visible to the naked eye.

    However, first of all, let us briefly consider the history of evolution, as it was seen in the XIX century. It was then that many of our current scientific concepts about life on Earth were formed. These ideas were largely based on what could be understood in biblical stories about the creation of the world, including the story of the flood and how Noah took care of God's creatures - stories similar to those that were woven on Turkish carpets.

    In the early 1830s, the noble scholar Roderick Impey Murchison and the charismatic Cambridge professor Adam Sedgwick reported finding fossilized animal remains deep in the land of Wales. The fossils have been known for several centuries, but their significance was not completely clear. Many people understood that these were the prints of organisms that died a long time ago, but how long ago no one could say; it remained unclear how these prints were preserved.

    Sedgwick was one of the leading English fossil experts, and one of the students attending his lectures was Charles Darwin. In the summer of 1831, Darwin, who was barely twenty-two at the time, went with Sedgwick on an excursion to North Wales to see the fossils with his own eyes. This trip turned Darwin's life forever. He not only helped Sedgwik to look for the remains of animals among the stones - he also studied the basic principles of geology, and these observation abilities more than once served him well throughout his later life.

    Fossils similar to those found by Sedgwick and Murchison in England and Wales were also found in other parts of Europe, as a result of which the classification system based on a series of similar fossils began to spread. Often, the appearance of fossil animals reminded us of the inhabitants of the ocean — mollusks, crustaceans, or fish; the appearance of others, however, was incredibly bizarre - they were not like any inhabitants of modern oceans. Regarding the value of these fossils, heated discussions were in full swing, but in any case, these discoveries unambiguously suggested a series of successive changes in the appearance of animals in the strata formed by these ancient marine sediments — from the lower layers to the layers above. At that time, the idea that rocks,

    The discovery of fossil animals in the rock mass could hardly be called news. Probably the most famous of the first descriptions of fossil remains was made by the Danish scientist Niels Stensen (Nicolas Steno) in 1669. He found among the rocks in Italy objects that looked very much like shark's teeth, and wondered how the fossilized remains that once belonged to organisms could be preserved so well. Stensen, however, took into account how fossils were located in the midst of rocks. The deposits lay in layers, and it occurred to the scientist that the more ancient layers should lie below the younger ones. This concept, later called the principle of superposition, is one of the basic laws of sedimentology. It greatly influenced the interpretation of the Sedgwick fossils more than a hundred years later. Stensen himself eventually abandoned science and turned into the bosom of the Church, deciding to devote his life to God. His early work on the fossil record was almost completely forgotten, and he continued to believe that life on Earth originated as described in the Book of Genesis.

    In my opinion, the logical conclusion that the remains preserved in rocks are located in a certain correspondence with the time scale was an amazing insight, but it was not so easy to substantiate, because at that time basic geological data were not yet available. To a large extent, the task of identifying patterns in the fossil remains awaited the great mind of Charles Lyell, one of Darwin’s intellectual mentors and close friends. Lyell, a Scottish lawyer who became a naturalist, is often referred to as the discoverer of a new scientific field, which he called geology. Like Stensen, Lyell realized that there is a logical sequence in the occurrence of fossil remains; however, unlike Stensen, he took up the interpretation of geological processes, such as erosion, volcanism and earthquakes, with their help to explain this sequence observed by him. In fact, it was his interpretation of the location of fossil remains in the rock that later led Darwin to reflect on how organisms change over time. The lifelong friendship between Lyell and Darwin was a legendary example of scientific collaboration.

    On December 27, 1831, Darwin’s famous voyage began on the Royal Beagle Expeditionary Vessel - a ninety-foot ten-brigade brigade with a crew of seventy-four on board. Darwin was given an extremely cramped mess in his bedroom, where he was allowed to keep very few books. He slept in a hammock in a 9 foot by 11 foot room with a ceiling at a height of 5 feet — it was dark and uncomfortable there, and he also had to share the room with others. Among other things Darwin took with him was the first volume of the first edition of Lyell’s new book Principles of Geology, published in 1830, as well as his personal copy of the King James Bible. On ships where I have to work, I have the opportunity to take a hot shower every day, and, although sometimes I have to live in a cramped cabin with other people, most of the research courts have a library. Given the conditions on the Beagle, it may not be particularly surprising that Darwin, referring to seasickness, sought to go ashore and on foot covered considerable distances to meet the Beagle at the next port of destination.

    Lyell took on the difficult task of explaining to the interested public how the remains of the same living organisms could be found in the Alps in Central Europe, in the hills of Scotland, and also throughout the British Isles. First of all, it was necessary to explain how and when these remains were formed.

    Over the centuries, several hypotheses have been put forward on this subject. One of them, which appeared in the Middle Ages, stated that God created stones similar to animals familiar to us in order to test the faith of his flock. No matter how absurd it may sound, such an idea still has many adherents, especially in some areas of the United States. The second idea was that in ancient times there was a volcanic eruption, which carried animals from the oceans to land, where they died, as a result of which their skeletons were imprinted in stone. The third hypothesis stated that these animals died after the Great Flood, when the sea level dropped. And indeed, the idea of ​​a diluvial (that is, deluge) origin of organic remains occurred to Sedgwik himself. There were several other hypotheses

    Lyell put forward a revolutionary idea: the remains of marine animals were found in rocks on land because many years ago these rocks themselves were under water. Over time, there was their rise, and they were on land. This assumption, tested in many different ways, turned out to be really true, although the processes that resulted in such a move became possible only more than a hundred years after Lyell’s death. One of the main problems that Lyell faced was the determination of the age of the Earth. How long has it been “many years ago”?

    The age of the Earth was meticulously calculated by James Asher, Archbishop of Armaghsky, in his book Annales Veteris Testamenti, published in 1654. Practically every educated British citizen of the time believed that it gave the most accurate definition of the time of creation of the world. Based on the literal interpretation of the Bible, Asher determined that the Earth was formed on Sunday evening, preceding October 23, 4004 BC. er according to the Julian calendar, that is, about 6000 years ago.

    As a lawyer, Lyell became adept at leading the discussions, so he was amused by how some illogical and sometimes irrational ideas were used to explain the existence of fossil animals and the change in their appearance. Understanding the power of argumentative dispute, he wrote: “... the system of scholastic disputes, encouraged in medieval universities, unfortunately created a habit of unlimited debate in people, so they often preferred to defend absurd and extravagant positions, because it required greater skill; the result and the purpose of such intellectual battles was only victory, but not the truth. ” However, even the most gifted attorney cannot win an argument against the written word of God.

    Lyell had no idea what the laws of evolution could be, much less how geological time could be measured. He decided that the theory of Jean-Baptiste Lamarck that the characteristics acquired by animals throughout life and then somehow passed on to future generations is no worse than any other, and in any case more reasonable than most others. In fact, Lamarck's research on animal species (he was the leading global authority on animals that do not have a ridge, that is, invertebrates), led him to speculate that organisms can be built along the time axis - from the simplest to the most complex. This Lamarck put forward the idea that organisms in some way change over time, that is, evolve.

    The idea that the fossil remains of animals are distributed in the layers of rocks along the time axis, led Darwin to reflect on life on Earth on such a time scale that he could hardly conceive and could hardly appreciate. If the oldest remains are at a depth of many meters below the others, how long could it take to lay such strata on top?

    Darwin was extremely puzzled by the earliest deposits discovered by Murchison and Sedgwick. He knew that below the layers of rocks containing animal remains, there are layers in which there are no remains, but he could not understand why. It seemed as though the chronicle of organic life was appearing from nowhere; the evolution of organisms looked relatively fast. But how fast? And why for no reason at all in the sediments suddenly fish remains appear, while in the lower layers you can only find organisms similar to invertebrates? And if you look deeper: why are there no remains of living organisms at all? It all looked like the geological equivalent of an unfolding Turkish carpet depicting the history of the ark, but there were no animals on half or most of the carpet. Darwin had to clarify these questions first for himself and then for his colleagues. To find answers to them, he needed to date rocks, and for that he needed a watch.

    On September 7, 1859, for the first time, the bell of Big Ben rang on the clock tower of the parliament building. These chimes, distinguished by their meticulous finishes and extraordinary precision, became the symbol of English technical genius and craftsmanship at the dawn of the industrial revolution. Two months after this historic event — November 24, to be precise, John Murray III, the venerable London publisher of Albemarle Street, published a new book by Charles Darwin, “The Origin of Species by Natural Selection, or the Preservation of Favorable Races in the Struggle for Life ".

    In the ninth chapter, The Origin of Species (later abbreviated title of the book), Darwin attempts to calculate the time it takes an extinct animal to change, or evolve, to the state of modern forms. This task was not straightforward. Lyell and his predecessor, Scottish physician James Hutton assumed that the age of the Earth is infinitely great. Darwin could not have known whether this hypothesis was true, but he undoubtedly believed that the earth was over 6000 years old. In order to get a more realistic dating, he developed a rather interesting, one might even say quite innovative approach to the measurement of geological time.

    Darwin’s clock was based on a geological phenomenon — the rate of weathering of sedimentary rocks, namely, that species, which contained organic remains. For observations, Darwin chose Veld - a well-studied coast of Kent, breaking off into the sea by a cliff consisting of Cretaceous and sandstone sediments. Darwin calculated that this formation weathered at a rate of approximately one inch per century, and taking into account the size of the cliff at that time, he determined that “Veld should have taken 306,662,400 years to denudate, or a round count of three hundred million years.”

    Darwin did not take into account the time required for the formation of the cliff itself, but it was an insignificant detail. Moreover, he did not consider the rocks lying below the Veld, the presence of which only made the cliff more ancient, and possibly infinitely ancient, Lyell The Darwinian estimate of the age of the cliff, of course, was a bold inference and, in the absence of other restrictions, was undoubtedly based on a rational, physically testable concept. The conclusion was obvious: The earth is incredibly old - much, much older than Asher’s calculations, and much older than most people at the time could have imagined. And if the time of life on Earth remained undefined (it is not defined to this day), the fact that there were rocks without organic remains under the overlying layers,

    Nevertheless, millions of years are not the age specified in the Bible, and it certainly did not correspond to what was then taught in schools. Of course, Darwin understood that his assessment would be met with skepticism, but he could not even guess what that would mean. In addition to the fact that Darwin came into conflict with the biblical authority of the calculations made by the Archbishop of Armagha in the 17th century, the age of Earth proposed by him was attacked by his fellow scientist, Einstein of those days, physicist William Thomson, who later became Lord Kelvin. Thomson set out to correct the dating, based on the basic principles of physics.

    Thomson argued that the age of the Earth can be calculated with sufficient accuracy, assuming that the planet was initially a molten mass and subsequently cooled down. Taking into account these changes in temperature as it deepens into the Earth's crust, as well as the results of its own experiments to determine the thermal conductivity of rocks, he derived an equation showing how quickly the Earth could cool to its present state. In 1862, Thomson announced that the Earth was about one hundred million years old, although he recognized that this figure was very uncertain and that it could be between twenty and four hundred million years old. Over time, he became increasingly uncompromising, arguing that the age of the Earth should be closer to twenty million years. This time frame he calculated seemed too short to accommodate the evolution of life, as Darwin saw it. Thomson became one of the most brutal critics of Darwin's innovative ideas on evolution - not because he did not believe in evolution as such, but rather because, as a physicist, he did not trust the calculations of the age of the Earth based on such unreliable geological indicators as the rate of weathering. . Ultimately, Thomson’s objections forced geologists to develop more advanced models for determining the age of the Earth, but this took almost another century.

    If Darwin was even remotely right, then the development of life on Earth took a very, very long time - much more than anyone had imagined. However, how did this development take place? In a sketch on the thirty-sixth page of his notebook “B” dated 1837, Darwin portrayed the family tree of life, in which he expressed the radical idea that organisms are interconnected by common ancestors and that this relationship can be traced due to similar features in their appearance. This fundamental concept was identical to the views of Lamarck, which he had developed more than fifty years before; however, Darwin had a different idea of ​​how this process took place.

    Changes in the forms of living organisms were almost imperceptible, and also, judging by the thickness of the layers separating the organic remains in the geological section, apparently, occurred very slowly. In addition, in order for this assumption to be valid, some organisms appearing in earlier sections of the section would have to become extinct in order to be replaced by new species, otherwise the Earth would be overflowing with an increasing number of animal and plant species. In other words, after the organism died out, it could no longer appear in the later layers of the geological section.

    Darwin understood that this outstanding, revolutionary idea would provoke criticism — and it did. The fossil remains clearly belonged to the once existing animals and plants, but human bones were not found anywhere in the rocks. Darwin was clearly aware of the meaning of the “missing” human link - like animals found in the geological annals, we also had to arise as a result of some process that allowed some organisms to develop into others for some indefinite but rather long time.

    The concept of genes and the basic principles of physical inheritance of traits at that time were completely unknown to either Darwin or anyone else. (Gregor Mendel will publish his work on the inheritance of traits only more than six years after the publication of the first edition of The Origin of Species - in 1866.) In fact, despite the confusion in most biology works, Darwin, most likely, without special difficulties adopted the basic concept of Lamarck, which was that organisms can inherit signs due to the environment. The main contribution of Darwin himself was the idea that in all forms there are natural deviations that can be inherited. This rule was constantly used by breeders of dogs and pigeons; However, Darwin suggested that in nature, the selection of signs occurs under the influence of the environment,

    Fig. 2. Reproduction of Darwin’s sketch in notebook “B” (between 1837 and 1838). The basic idea is that the living species are descended from extinct, but are also associated with other preserved species, forming the genealogical tree of life. This sketch became the core of the theory of the origin of species with consistent changes leading to natural selection — the main Darwinian evolutionary process. (Published with permission from the University of Cambridge, with gratitude to Peter and Rosemary Grant. 2008, Charles Darwin Notebook Committee.)

    Selection or improves the body's ability to reproduce, or not. If it improves, then in this case, the signs that are most suitable for a particular habitat are passed on to subsequent generations. The concept of the origin of species with deviations, followed by subsequent selection, occupies six chapters of the “Origin of Species”. It was one of the most outstanding scientific ideas ever advanced; until today, it remains the core, the unifying principle of biology.

    The book "The Origin of Species" was provided with a single illustration, placed at the end, which depicted the hypothetical origin of taxa. This drawing was a free processing of the sketch from the notebook “B”. Oddly enough, the illustration showed not a single source for all taxa, but many sources giving rise to new species. The concept of origin, in the sense of the beginning of all life, was on Darwin’s mind, but was not openly discussed in the book.

    More than ten years later, after the appearance of the Origin of Species, in a letter to Joseph Hooker, dated 1871, Darwin reflected on how life could have originated: “... if ... we assume that in one of the small warm water reservoirs ammonia and phosphoric acid salts under the influence of light, heat, electricity, and so on, protein compound appeared, ready for further more complex transformations, now it would be immediately absorbed or destroyed. However, before living beings appeared, this could not happen. ”

    Eighty years after this remark was made, the young chemist Stanley Miller and his scientific adviser, Nobel laureate Harold Yuri really managed to create amino acids (building “building blocks” of proteins) in the laboratory of the University of Chicago. They used gaseous ammonia, methane, hydrogen, as well as water and an electric discharge that simulated a lightning strike. This experiment, the results of which were published in 1953, gave reason to hope that an understanding of how life began on Earth is just around the corner. Nevertheless, between the creation of the chemical components of living organisms and the creation of these organisms themselves lies a whole gulf. Even in the simplest organisms, chemical constituents are like microscopic mechanisms that trigger metabolic processes and allow cells to divide.

    The simplest living organisms are bacteria - organisms, the existence of which Darwin undoubtedly knew; however, he was not sure how to incorporate them into his theory. In fact, Darwin had a microscope on the Beagle (in addition to the Bible and books on natural history, he also took two pistols with him, a dozen of shirts, two books for which he was going to learn Spanish, and a wallet with money). However, due to the fact that microorganisms did not leave traces in the geological record clearly visible with the naked eye, Darwin could not have known that the strata lying below the layers with distinguishable organic remains belong not to the period in the history of the Earth, preceding the birth of life, but simply a time when there were no animals and plants. Even if he could detect fossil bacteria, he would almost certainly not be able to grasp their connection with plants or animals. Darwin, like almost any scientist of the XIX century, would have been surprised to the depth of his soul if he knew that all plants and animals were descended from bacteria and this happened during the period, the duration of which in the XIX century was absolutely impossible to imagine - much more than three hundred million years old. In fact, the microorganisms in the Bible does not explicitly say anything - unless indirectly, at the mention of such diseases as the plague. There is no doubt that Noah did not intend to take them with him to the ark, and you will not see their images on woven Turkish carpets with the history of the Great Flood. that all plants and animals descended from bacteria and this happened during a period whose duration in the XIX century it was absolutely impossible to imagine - much more than three hundred million years. In fact, the microorganisms in the Bible does not explicitly say anything - unless indirectly, at the mention of such diseases as the plague. There is no doubt that Noah did not intend to take them with him to the ark, and you will not see their images on woven Turkish carpets with the history of the Great Flood. that all plants and animals descended from bacteria and this happened during a period whose duration in the XIX century it was absolutely impossible to imagine - much more than three hundred million years. In fact, the microorganisms in the Bible does not explicitly say anything - unless indirectly, at the mention of such diseases as the plague. There is no doubt that Noah did not intend to take them with him to the ark, and you will not see their images on woven Turkish carpets with the history of the Great Flood.

    Despite the fact that we have made great progress in the 150 years that have passed since the publication of The Origin of Species, scientists are still unable to determine whether life originated in a small warm pond, deep-water hydrothermal source, or anywhere else. What could have made her a start? How did it develop? How did bacteria evolve to plants and animals? How did it happen that these organisms went unnoticed for so long in our search for the origins and development of life on Earth?

    These questions are not so easy to answer, and many aspects are still far from complete understanding, but thanks to the tools developed over the last century, we were able to learn a lot. If Darwin had been able to visit an oceanographic research vessel in the Black Sea in the 19th century, he probably would have noticed that animals do not dwell in the water below the one hundred meter layer, and would conclude that there is no life in the deep layers. However, if he were a microbiologist, our understanding of the origin of species could be completely different. Although bacteria in the 19th century were already well known, it took another century before they took their place in our ideas about the evolution of life on Earth. We overlooked them due to bias in our observations.

    So let's get acquainted with these inconspicuous microorganisms and see what a huge role they played in ensuring that this planet could function. Without bacteria, we would not be here.

    More information about the book is available on the publisher's website.

    For readers of this blog, a 25% discount on the entire catalog on the coupon - Life Engines.
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    Fear of physics. Spherical horse in a vacuum and paradox. Nine great mysteries of physics
    Eternity. In search of a definitive theory of time,
    Love and Mathematics. The heart of the hidden reality
    The history of everything. 14 billion years of cosmic evolution