[Je zou dit boek een journalistieke reis naar de grenzen van het heelal kunnen noemen. Het is jammer dat Potter zo graag met namen en citaten gooit. Dat is helemaal niet nodig om het idee wat hij heeft over te brengen. Integendeel: die leiden maar af. Tegelijkertijd vind ik dat Potter weinig diepgaande filosofische vragen stelt bij alle wetenschappelijke theorieën en feiten die hij naar voren brengt. Het is dus meer een geschiedenis van de (astro)fysica dan een filosofie ervan en dat is jammer.]
"Scientists are pragmatists. If it works, philosophical considerations are superfluous."(10)
[Leuk en zinvol is de indeling hier in steeds groter getallen van 10 meter naar 102 over 1000 biljoen kilometer (1015 meter) over ongeveer één lichtjaar (ongeveer 1016 meter) tot meer dan 10 biljoen lichtjaren (1026 meter). Dat geeft goed weer hoe groot - en als je andere kant uitwerkt zoals in het zesde hoofdstuk: hoe klein - de natuur is.
We weten zo weinig. Hoe kunnen we zelfs maar over het ontstaan van het heelal of over de grens ervan nadenken? Alsof er nog andere heelallen bestaan, alsof 'niets' niet kan of mag. Er is geen grens, dat is verkeerd taalgebruik zouden we kunnen zeggen, er is nooit een grens aan wat we niet kunnen bevatten, niet macro, niet micro.]
"There may be many objects out here, even of considerable size, that we cannot see because they do not reflect enough of the sun’s light to be visible, and are also too distant to be detected gravitationally."(28)
"In the bowl of space that surrounds the sun 16.31 light-years in every direction, 50 stellar systems have been found so far. The list isn’t definitive, and there are doubtless other nearby stars that have not yet been discovered."(31)
"Where now is in the universe is no more apparent than where its centre is."(35)
"Here, then, is our universe: between 30 and 50 billion trillion (between 3×1022 and 5×1022) stars arranged in 80 to 140 billion galaxies. These billions of galaxies are, in turn, arranged in clusters, clusters of clusters called superclusters, and as filaments of superclusters like the Great Wall. A precocious child might write her address as: the earth, the solar system, Orion Arm, the Milky Way, the Local Group, Virgo supercluster. (...) We have arrived at what seems to be the edge of the universe with no clearer understanding of how the universe could have an edge. We cannot rest here."(42)
"We believe the universe is as we describe it because we believe in the means by which we measure and describe, and because we believe that the reality out there is consonant with reality as we have found it to be locally here on earth. We believe in the scientific method. But what is the scientific method and what are we actually doing when we make a measurement?"(43)
"Overwhelmed by time and space we may be, but defining what we mean by time or space turns out to be more problematic."(44)
"Ultimately, science searches for descriptions that can be agreed on across the universe not just around the world. Science is based on the belief that no matter where we might be in the universe, the reality we perceive, whatever we think it is, is the same reality. The ancients did not make this assumption ..."(46)
"This ‘we’ who describe the universe is a strange inclusive group. We earthlings have not yet travelled far from home, nor do we know whether or not we are the only beings in the universe who have embarked on such a description of nature, but science believes that there is a universal perspective."(47)
Dat is natuurlijk een groot probleem. Als we contact zouden hebben met 'aliens' zouden onze maatstaven kunnen afwijken van die van hen met als onderliggend probleem dat hun kijk op de werkelijkheid volstrekt anders zou kunnen zijn dan die van ons.
"When we make measurements, we don’t seem to be able to separate out the unit of measurement from our own nature. But such philosophical conundrums do not trouble most scientists. (‘Shut up and calculate!’) Though we cannot be sure what we are doing when we measure time and space, science goes ahead and measures them anyway."(53)
"You believe there is something because you know you exist. You believe in your own ego. Science is a way of translating that individual experience of the world into a collective experience. We can personally validate a scientific description of reality by repeating an experiment, or by believing that experiments are repeatable, or, most apparently, by simply noting the changing nature of the world that technology creates around us. Technology is our evidence that science is getting somewhere."(55)
"Curiously, the one fact that we think we know of the world – the certainty of our own existence – is not open to scientific examination, as it is by definition not public."(56)
"Why nature is describable in mathematics is perhaps the greatest of all science’s mysteries. The buck stops there: our ultimate scientific faith rests in mathematics and the web of phenomena that mathematical description includes. Technology is the outward and visible sign of that faith."(56)
"Science is consistent measurement. We expect the world to look the same when we measure it again, or, indeed, if anyone else makes the same measurement. Science requires repeatability. Phenomena that arise out of rogue conditions through the mediation of rogue individuals are not suitable subjects for scientific enquiry. But we are all rogue individuals. Complex, individualistic humans are always going to be the most intractable objects of scientific enquiry. It is our own nature that presents the greatest measurement problem."(57)
De natuurfilosofie en kosmologie van de klassieke Oudheid en de perioden daarna.
"Any theory that has an earth that moves must account for the fact that the stars appear to be held in a fixed pattern (the constellations) that circles the earth every 24 hours. The fact is that there is parallax between the earth and the stars, but because the stars are so very far away they appear not to move. The tiny change of perspective is so difficult to measure that stellar parallax was not observed until the nineteenth century, when there were telescopes sufficiently powerful to make the sensitive measurements required."(76)
"Modern science could be said to have begun in that year 1543 when Copernicus removed the earth from the centre of the universe and put the sun there. With this single act he set out a principle by which science has been guided ever since: that not only is mankind not at the physical centre of the universe it is not at the centre in any fashion, literally or metaphorically. What launched the scientific revolution was not the placing of the sun at the centre of the cosmos (from where, anyway, it is later removed) so much as the removal of the earth. It’s not about us."(79-80)
Galileo, Newton, Einstein en zo.
"It was Galileo, not Einstein, who first realised that all motion is relative. In another thought experiment, he imagined two boats each travelling at a steady speed on a perfectly flat and empty sea (a scenario that could only exist in a Platonic world). By thought alone he saw that it would be impossible as a passenger on either boat to tell where the true motion is, only the relative motion between the boats is apparent. There is no experiment that can be performed that will tell me if I am moving, if it is you who is moving in the other boat, or if we are both moving. We need a shoreline, or something fixed, to measure absolute motion against. The universe, however, does not have a shoreline, not even in the so-called fixed stars, which are not fixed at all, but only appear so because they are so far away. The best we can say about the motion of all the bodies in the universe is that they are seen to be moving relative to each other."(82)
"With his three laws, Newton set out a mathematical description of a physical world in which there are concepts like mass, velocity, acceleration and momentum. To this new world he introduced a new and particular kind of force, and which he described separately in his theory of universal gravitation."(83)
"Can we conceive what the world looked like before Newton described it in terms of velocity, mass and gravity, when gravity was a mood and not a force? Newton’s conceptual world has become so real to us that we may be cut off from it in ways we will never be able to quite grasp."(84)
"Einstein came up with a new idea of what motion is. He realised that all motion is the same as the motion that light has. What this means takes some getting used to. We have such a strong idea of what we think motion is that to conceive it differently is almost beyond our imagining. We are so comfortable with Newton’s idea that time and space are absolute and that things move relative to that fixed framework that Einstein’s theory still shocks us over a hundred years later."(87)
"It was Einstein, however, who realised that the speed of light must also be the fastest possible speed in the universe. This single assertion undermines the Newtonian idea of relative motion. Einstein is telling us that the motion of light cannot be relative."(88)
"Einstein unhinges the absolute and eternal reality of Newton’s space and time and replaces it with a new absolute: the unchanging nature of light. Time and space become relative qualities because the speed of light is not."(90)
"Around objects with relatively low masses, like our sun, the distortion of space-time is more apparent as a distortion of space. Around the more massive objects the universe has to offer, like a neutron star, it would also be apparent that time is dilated."(92)
"Modern cosmology began with the general theory of relativity, but the mathematics is so complex that it wasn’t initially clear how the theory was to be interpreted physically."(92-93)
"Without a physical interpretation science is reduced to mathematical abstraction."(94)
[Mij lijkt dat er toch ook een groot gevaar schuilt in die complexe mathematische beschrijving van de dingen. Wie kan die beschrijving nog begrijpen en controleren? Zitten er geen fouten in die niemand kan zien bijvoorbeeld? Zitten degenen die die complexiteit naar voren brengen niet te bluffen, omdat ze heel goed weten dat niemand hen kan controleren? En wordt de mathematische beschrijving niet te snel aangezien voor de fysieke realiteit?]
"With the cosmological constant removed, a new solution – the so-called Big Bang theory – is plucked from the mathematics of general relativity, though once again after initial resistance from the theory’s author."(97)
"When the universe began there was only high-energy light, out of which all the matter that is in the universe was created. The universe is light that has evolved."(98)
[Dat soort abstracties zijn even gevaarlijk. Hoe kan licht materie scheppen?]
"But if everything was once light, it seems reasonable to ask how some of that light became stuff and how that stuff became us. And science does ask, and has answers to, these questions."(98)
[Precies. Nou, laat maar horen dan :-)]
De microkosmos tot aan de allerkleinste deeltjes.
"The seventeenth century saw the opening up of the universe at the largest and smallest dimensions, but it wasn’t until the twentieth century that the astonishing smallness of the world figured in our physical understanding of the universe as a whole.(...)
We have a notion that some day we might travel the universe to see for ourselves that it is as we have described it, but how could we ever explore the world of atoms and subatomic particles? There is no access to the microscopic (unless we imagine ourselves as smaller versions of ourselves, like Alice shrunk to get through a tinier-sized garden door), except as passive observers using our ingenuity artificially to extend our ability to see. "(101)
"It appears to be increasingly apparent that life is not a hard boundary between the animate and the inanimate but something diffuse like the edge of the solar system or, indeed, the edge of the universe. Life begins to look like it may be some arbitrary label we impose on a phenomenon that is not entirely discrete, and whose meaning only gradually emerges out of an evolutionary process that must, ultimately, merge with whatever descriptions we have for the smallest structures in the universe."(105)
"All large-scale, or macroscopic, matter is made of molecules and all molecules are made out of atoms of the 94 different naturally occurring elements. There are other elements that only exist in laboratories. We can reduce nature to this modest number of differences: the elements that are familiarly arranged in the periodic table.
Atoms were meant to be the last word in a physical descrip- tion of matter, the word ‘atom’ meaning indivisible. We now know that they are far from indivisible, though we also know that they not easily divided. Atoms make a strong barrier not easily breached that runs between the familiar world of ‘things’ and the curious world that lies beyond."(107)
"Faraday imagined that each electrical and magnetic particle is surrounded by ‘an atmosphere of force’, a sort of condition of space that he later called a field. Faraday, like Einstein, was a strong adherent of the idea that nature is unified. Though Faraday’s grasp of mathematics was notoriously poor (nor was he much interested in it), he invented the concept of a ‘field’ (fundamental to how we understand the particle nature of the universe) in order to unite these phenomena in an explanation. It is this field of influence that tells the particle how to move. It can be envisaged as arrows, at every point in space, that indicate the direction of the force. Whether it is purely a mathematical description or something real, it is hard to say. The field doesn’t explain in a deep way why the particles at a distance know which way to go; it is an ad hoc addition, as are aether and charge, that makes the explanation work. But by giving the field some properties, we find that we can explain other phenomena that would otherwise have remained unexplained. The field description is so successful at this that we gradually grow comfortable with the idea of fields, as we did with gravity, and eventually even grant the field a physical presence in the world. The epicycle was an ad hoc addition, but in Ptolemy’s cosmology every finer measurement of planetary motion required the addition of yet another epicycle, whereas Faraday’s field idea uses a single ad hoc concept to unify a multiplicity of phenomena. [mijn nadruk]"(118-119)
"Changing electric and magnetic fields cannot be described independently of each other. A changing magnetic field produces an electric field and a changing electric field generates a magnetic field. When they reinforce each other, electromagnetism – or light – is the result.(...) Light, by which we once meant visible light, as from the sun or a candle, turns out to be part of a continuous range, or spectrum, of radiation called electromagnetic radiation. Visible light is just a tiny part of that spectrum, which we sense with our eyes as being separate from other parts of the spectrum: infrared radiation is felt as heat, ultraviolet radiation tans the skin, X-rays destroy cells. By naming them, we have separated them out as separate phenomena with different properties, but underlying this separation is a continuity of energy that moves from radio waves with the lowest energy to gamma rays with the highest. Nature doesn’t know that we have named little parts of it. As far as she is concerned, light is one continuous form. Casually, scientists use the word ‘light’ to mean any part of the electromagnetic spectrum. "(120)
"In 1861 the eccentric Scottish mathematician and physicist James Clerk Maxwell (1831–1879), known as Dafty at university, published a paper that contained four equations that fully described the mathematics of electromagnetic radiation and that showed that such radiation would travel at the speed of light. Maxwell guessed that electromagnetic radiation is the same thing as light, but at that time there was no experimental evidence. The German physicist Heinrich Hertz (1857–1894) provided the physical evidence when he produced the first radio waves and microwaves and showed that all electromagnetic waves travel at the speed of light. Although Maxwell’s equations are less well known than Newton’s laws of motion and Einstein’s relativistic equations, they are just as significant in the history of science. These seemingly abstract equations, together with Hertz’s physical evidence, unified electricity, magnetism and optics into a single description [mijn nadruk]."(121)
Volgt nog meer geschiedenis van de fysica.
"All the visible matter in the world is made up of just four particles: two sorts of quark (called up and down), the electron and a particle associated with the electron called a neutrino. Unfortunately, in order to account for these four particles, the existence of hundreds of other particles is required (plus their corresponding antiparticles). All of these particles have been found by inserting large amounts of energy into the vacuum, from which they can be briefly brought into some kind of existence. There are so many of these particles – seen as evanescent spikes of energy in particle accelerators – that they have been collectively named the particle zoo. The Italian physicist Enrico Fermi (1901–1954) was heard to say to a questioning student: ‘Young man, if I could remember the names of these particles, I would have become a botanist.’
This profligacy is troubling, and the search for elegant laws underpinning nature has seemingly taken a reversal. The most convincing evidence that current field and particle descriptions are on to something comes from the fact that these theories are the most accurately tested theories in the history of science, more accurately tested, even, than Einstein’s relativity theories. Quantum field descriptions have been tested to within an accuracy of one part in a billion, as if the distance between New York and LA were measured to within the thickness of a hair. The inelegance of these quantum field theories, collectively called the Standard Model, is, however, profoundly troubling. The theoretical physicist Thomas Kibble (b.1932) has gone so far as to say of the Standard Model that it is ‘such an extraordinary ad hoc and ugly theory it [is] clearly nonsense’. And even its fans admit that it is cobbled together. If the Standard Model is itself ugly, it is at least suggestive of deeper symmetries."(132-133)
"Sometime in the 1940s, Einstein was walking through Princeton in conversation with the Russian-born theoretical physicist and cosmologist George Gamow (1904–1968), who happened to mention that he had come to the realisation, while pondering Einstein’s discovery that energy and matter are equivalent, that a star could be created out of nothing at all since the energy of its mass is exactly balanced by the energy of its gravitational field. Einstein was so taken aback by this insight that, as Gamow reported, ‘since we were crossing a street, several cars had to stop to avoid running us down’. If the universe, as large as it is, is merely a hierarchy of stars, then it too could have emerged out of nothing. Its overall energy is zero. Parmenides and King Lear were wrong: the universe is something that comes from nothing."(151)
Over supersymmetrie en de deeltjes die daar weer bij horen.
"Though supersymmetry lacks physical evidence, the mathematics predicts a unification of all the forces of nature at very high energies: at around 1019 electronvolts."(153)
"String theory requires a plunge downwards to a world made out of strings of vibrating energy 10–35 metres across, 17 orders of size smaller than the maximum size of the electron and quark. A string is as small compared to an electron as a mouse is compared to the solar system."(153)
"Theories that hope to make such a unification are called TOEs (theories of everything). It isn’t yet clear if string theory is such a theory or not."(154)
"In scientific discourse the poetry is in the mathematics, and the same language judges them alike: symmetry, elegance, simplicity, brevity, subtlety, profundity are the highest qualities of both means of apprehending reality. Mathematics has been the language of science ever since. But that language is increasingly untranslatable even among large groups of scientists. It is not even a single arcane language but many arcane languages each spoken by some small tribe of specialists. [mijn nadruk]"(159)
Volgt een soort van geschiedenis van het universum aan de hand van toenemende tijd.
[Ik vind het allemaal nogal speculatief en oncontroleerbaar, zowel wiskundig als op een reële manier.]
"The predicted proportion of neutrons and protons in the early universe is spectacularly confirmed by the measurement of the quantities of hydrogen and helium existing in interstellar space today. This experimental confirmation is proof that particle physics and astrophysics describe the same reality. Here is further evidence that our separate descriptions of small and large things can be reconciled."(170)
"A few hundred thousand years after the Big Bang the universe is more recognisably as we know it today: there is matter and there is light. An expanding universe of matter and light evolves over a period of 13.7 billion years into the universe as it mani- fests itself around us today."(172)
"Scientists love vulnerability in a theory (particularly in someone else’s theory): it provides a great opportunity to test the theory. Apparent weakness can turn out to be a way forward. It is this provisional quality of science that is often misunderstood. Science’s provisional nature is its strength, not a weakness. Calling something a theory doesn’t mean to say that it is merely an idea; a theory is the highest form of scientific explanation. Provisionally is how science proceeds; that is its nature."(181)
"In spite of the lack of observational evidence for the existence of Population III stars and the uncertainty surrounding the formation of quasars, the physical description of how Population I and II stars are formed is one of the triumphs of modern physics, bringing together in a single description theories of the very small and the very large.(...) The failure fully to unify light and gravity at the theoretical level is also manifest in the universe at the physical level of stars. When we check the content of the physical universe using our two ways of seeing – by light and by gravity – a strikingly different picture emerges."(185-186)
"Cycles of star formation and explosion are a chemistry laboratory that manufactures ever more complex molecules. Hundreds of hydrocarbons (molecules made either entirely or mostly out of hydrogen and carbon) appear for the first time in star forming nebulae; formaldehyde and hydrocyanic acid and other so-called prebiotic molecules are among them. They are called prebiotic because they seem to be essential to life, but by what mechanism is still unclear. Some complex compounds found in outer space, glycoaldehyde for example, have been made to react in laboratories to make a sugar called ribose, a key ingredient of ribonucleic acid (RNA). If an oxygen atom is removed from RNA it becomes deoxyribonucleic acid (DNA)."(193)
"The earth and the solar system have been dated using various radioactive isotopes found in meteorites and from rocks collected from the moon. They are in agreement with the first accurate dating of the earth made in 1953 by the American geochemist Clair Patterson (1922–1995) of 4,567 million years with a small error bar."(197)
"The chance strike that knocked off a part of the earth and made the moon, also seems to be necessary to the presence of life as we know it. The moon stops the earth swinging wildly on its axis, reducing this wildness to a wobble. Without a large moon the earth would topple over, even more dramatically than Mars does. The modest wobble of the earth, taken together with the inclination of the earth to the sun, accounts for the moderate change in the seasons, which would otherwise be too dramatically changeable to support the kind of complex life found here. Without the ameliorating presence of the moon, life would have to have taken a very different form, which is not to say that life is ruled out, just that we cannot yet imagine what a different sort of life might look like."(203)
"Because the earth has an iron core and is spinning, it generates a magnetic field that protects it from the damaging effects of radiation – damaging, that is, to the kind of life that exists here. Cosmic rays, emitted by the sun as winds of protons and electrons blowing at 400 kilometres a second (three times faster in a solar storm), are deflected by the earth’s magnetic field."(204)
"So much for some of the physical conditions of the earth, that may or may not be prerequisites for the emergence of life elsewhere. But before we can begin to decide on the necessity of those conditions for life as we know it, we must work out how the physical earth became a living earth in order to understand more fully what we even mean by life."(210)
De verschillende geologische perioden en zo.