The Cosmic Landscape: String Theory And The Illusion Of Intelligent Design (2008) - Plot & Excerpts
- A review of Feyman diagrams, propagators and vertex diagrams.- The fine structure constant (alpha = 1/137 or 0.007297351) is an important constant of nature. It represents the probability that an electron will emit a photon as it moves along its trajectory.- Feyman developed Quantum Electrodynamics (QED) which predicts the probability of any event based upon the propagators and the vertex diagrams, and upon coupling constants such as the fine structure constant.- Quantum Chromodynamics (QCD) is the theory of quarks and gluons.- There are 6 quarks - up, down, strange, charmed, top and bottom.- Only the up and down quarks form the stable nuclei.- A proton is 2 u and 1 d: Charge is 2/3 + 2/3 - 1/3 = 1- A neutron is 2 u and 1 d: Charge is 2/3 - 1/3 - 1/3 = 0.- QCD is the theory of strong interactions where gluons tie the quarks together.- The numerical constant governing the emission of gluons is called the alpha-QCD and is 100 times larger than the fine structure constant.- Weak interactions are another part of the Standard Model. Nothing in QED or QCD explains how a neutron can emit an electron and become a proton.- Quarks and electrons can emit w-bosons, as can the neutrino.- One of the 2 d quarks in a neutron can emit a w-boson and become a u quark, turning the neutron into a proton. The w-boson then splits into an electron and an anti-neutrino.- The Standard Model makes use of about 30 fundamental constants. Extensions to the Standard Model and cosmological theory bring the number of constants to over a hundred.- All evidence suggests that the constants do not vary over the observable universe.- Einstein thought the universe to be stable and determined that an extra term was possible under General Relativity that would represent a force that would counteract gravity, which would otherwise act to pull the universe together. He denoted this cosmological constant as lambda. Unfortunately this resulted in an unstable equilibrium.- Hubble discovered that the universe is expanding and the cosmological constant could be set to zero.- Quantum mechanics predicts that empty space will be filled with fluctuations where particle pairs are created and annihilated over very short times (billion-trillionth of a second). These short lived particles are termed virtual particles and represent a vacuum energy.- Fermions, such as electrons, contribute negative vacuum energy while bosons, such as photons, contribute positive energy.- The vacuum energy exerts a force that is indistinguishable from the cosmological constant.- Calculations of the vacuum energy produce a result that is vastly larger than what would be consistent with the observable universe.- Super-symmetry (fermi-bose symmetry) suggests that there is a boson corresponding to every fermion (and vice versa) such that the vacuum energy nets to zero. However, there is no super-partner for the electron or other elementary particles.- There are no viable theories as to why the vacuum energy is essentially zero.- Steven Weinberg: The Anthropic principle: Some property of the Laws of Physics must be true, because if it wasn't we would not exist.- Calculations show that if the cosmological constant is much different from what is empirically observed, the universe would not be suitable for our existence.- The Planck mass, time and length are described.- The quantum jitters of space occur on the scale of the Planck length and time. The Planck mass turns out to be equal to the smallest possible black hole.- To a physicist a vacuum denotes a space where physics can take place.- The Laws of Physics depend upon the values of the physical constants of a space.- A field is the result of the coordinated movement of particles. Each particle has an associated field.- Physicists discovered that the Standard Model is mathematically inconsistent, but could be made consistent by adding the Higgs particle.- The mass / inertia of particles depend upon the value of the Higgs field. The exceptions are the two massless particles - the photon and the graviton.- In the 80's, String Theory looked to be an elegant theory that would merge the Standard Model with gravity. However, since then 3 problems have emerged:1. The number of mathematically consistent versions increased dramatically, opening up a stupendous Landscape.2. The models became increasingly complex and less elegant.3. All versions produce a non-zero cosmological constant.- The Cosmological Principle - the large scale structure of the universe is homogeneous and isotropic.- The galaxies are receding with a velocity equal to the product of their distance and the Hubble constant.- Three possible geometries for space: zero, negative and positive curvature:1. If the mass density is great enough to reverse the outgoing expansion, it will distort space into a 3 sphere. This is a closed and bounded universe or k=1 universe.2. If the mass density is less than what is required to close the universe, it is insufficient to reverse the motion. It distorts space into a hyperbolic geometry. The universe expands forever, or k= -1 universe.3. If right on the knife edge, the geometry of space is flat and uncurved. The universe endlessly expands, but at a diminishing rate. This is the flat or k=0 universe.- A megaparsec is about 3 million light years, or 30 million trillion km - a little more than the distance to our neighboring galaxy Andromeda.- The Hubble constant is about 75 km/sec per megaparsec.- According to Hubble's Law, the Andromeda galaxy should be receding at 50 km / sec, but is moving toward us due to gravity.- It would take only 10 E-25 kg/m3 to reverse the outward flow of the galaxies. This is roughly 50 protons / m3.- The average cosmic density is around 1 proton / m3.- Therefore, we appear to be living in an infinite open (k= -1) universe.- The mass of the galaxies can be determined from their movement. Each galaxy is 10 times more massive than all of the visible stars and gas. The remaining mass is almost certainly not made up of ordinary matter. It is termed dark matter as it gives off no light. Dark matter is likely composed of some new, heavy elementary particles that have not yet been discovered.- When including the dark matter, the amount of mass in the universe appears to be 5 times too small to attain a flat universe.Hubbel calculated the age of the universe from the distances and speeds of the recession of the galaxies. Unfortunately, he calculated a billion years and rocks had been found that were 2 billion years old.- Modern calculations put the age of the universe at 10 billion years. However, there are stars that appear to be 13 billion years old.- If the vacuum energy were to amount to 30 protons / m3, it would solve the 2 biggest problems in cosmology:1. A small cosmological constant would result, giving a flat universe which is what we observe.2. The repulsive force would cause the expansion of the universe to accelerate. Run backward, the age would be calculated at 14 billion years, consistent with the ages of the stars.- Type I supernovae always generate the same luminosity, and so observation gives both the distance and the rate of recession. The more distant supernovae are older, because of the time it takes light to reach earth. We observe a larger Hubble constant for older supernovae. These show that the expansion of the universe is accelerating. The value of the cosmological constant is just what Weinberg had predicted.- The oldest light reaching earth has been Doppler shifted to microwave frequencies. The Cosmic Background Radiation (CMB) is very cold at 3 deg K.- When detected from high altitude balloons, oscillating blobs can be seen. These are well enough known in theory that their size is known. Comparison of their known sizewith their apparent size allows measurement of a triangle and establishes that space is flat on scales of 10-20 billion light years,- It appears that the universe inflated exponentially for a period in its earliest phases, and this has resulted in the surprisingly homogeneous nature of space.- While expansion of the universe results in decreasing density of matter, that is not true of vacuum energy which is constant per volume of space.- A chapter on the Anthropic Principle, how it requires a landscape of possible universes, and whether it is a valid scientific theory.- Hadrons are the particles made up of quarks, anti-quarks and gluons.- All hadrons belong to one of three families - baryons, mesons and glueballs.- Baryons include protons and neutrons, and are made up of three quarks connected by strings.- Energy can only be added in discrete steps.- Mesons are made up of a quark and an anti-quark joined by a string.- Glueballs are closed strings and can be formed when the quark and the anti-quark of a meson connect.- A point particle moving through space-time gives a world line.- A meson moving through space-time gives a world sheet and a close string gives a pipe. Junctions result where particles combine or separate.- Particles exchange gluons so these sheets are made up of a fabric of lies representing the exchanges.- String Theory requires 9 + 1 dimensions.- Forces are the result of exchanging particles: gravity - graviton electromagnetic - photon weak nuclear - pion strong nuclear - gluon- The strength of the forces depends on the mass of the messenger particle.- The strings of String Theory vibrate at all modes (harmonics) of oscillation due to the quantum jitters. They appear to oscillate to the ends of the universe.- String Theory was originally developed to describe hadrons. However, it has been expanded to describe all particles and forces, including gravity.- Leptons are fermions that do not have strong interactions like quarks.- Compactification - some dimensions are closed and compacted towards the size of the Planck length.- Some particles move only in the compacted dimensions. Strings can be wound once or more around a compact dimension (winding number).- The distance around a compact dimension is termed the winding scale, and is typically a few Planck lengths.- The compact scale fixes properties such as the electronic charge and the masses of the particles. In effect, the compact scale determines the Laws of Physics.- The 6 compact dimensions are rolled up in what are called Calabi-Yau spaces. Millions of possible C-Y spaces exist.- The parameters that determine the shape of the C-Y spaces are called moduli, and number in the hundreds.- The spaces can taper so that the dimensions vary from point to point. This is equivalent to saying that the Laws of Physics vary from point to point. Thus the C-Y spaces allow a Landscape of possibilities.- Super symmetry is a concept whereby each fermion has a boson twin and vice-versa. However, there is no twin observed for the electron and other proposed particles do not appear to exist.- Distortion may cause the twin partners to be different, perhaps very heavy. It may be that super symmetry may yet be applicable.- Branes are membranes - 0-branes are points, 1-branes are surfaces, etc.- String Theory may involve multi-dimensional branes that are compacted into the extra 6 dimensions.- Fluxes, akin to fields, are now included in String Theory.- de Sitter described an exponentially growing space. It would feature an event horizon representing the furthest distance at which points could be observed.- Eternal Inflation is the idea that islands of vacuum energy form in an inflating meta-stable de Sitter space.-These islands or bubbles could have Laws of Physics corresponding to any of the possibilities given in the Landscape of String Theory.- The many worlds idea is that parallel universes have formed in these bubbles. This is the mega-verse.- A review of complementarity and the Holographic Principle as applied to black holes.- A review of various contemporary physicists and their views on String Theory and the Anthropic Principle.- Susskind says that there are no serious alternatives to String Theory. Lee Smolin has a Loop Gravity theory but it may be an alternate formulation of String Theory, rather than an alternate theory.- Many dislike the Anthropic Principle because it is too easy and may be akin to giving up. It may reduce the drive to explore more deeply.- That the laws of nature are emergent is the idea of Robert Laughlin. He pictures a universe composed of a material like superfluid helium where the properties emerge only at the macroscopic levels. However, black holes do not work with this theory and Laughlin argues against some of the generally accepted properties of black holes such as Hawking radiation.- Lee Smolin proposes a natural selection of universes whereby baby universes form inside black holes which are inside universes, etc. This repeated replication results in an evolution toward maximally fit universes.- One problem with the Landscape is that String Theory loses it's predictive power. There are too many valleys in the Landscape to predict, for example, the mass of the top quark.- Early inflation of the universe resulted in vacuum energy being converted to heat and particles. It is also theorized that some vacuum energy was converted to vast collections of entangled strings. These strings would not be visible as light or other electromagnetic radiation, but they would emit gravity waves. They may be detectable in the coming decade. - Susskind sums up saying that there may yet be possibilities for testing String Theory that are not apparent today.
This book is one of the best physics/cosmology books I've ever read (read 3 times in fact). The most interesting parts, for me, were related to the Anthropic Principle and the discussion of the Landscape and Multiverse theories. As I understood it the biggest issue was with the cosmological constant he discussed. If it were exactly zero, as Einstein believed, we would live in a "flat" (read: not-curved) universe and everyone would be OK with that. But better and better measurements show that the cosmological constant only appears to be zero...after some 120 decimal places it suddenly is not zero anymore. Why exactly this means our universe is "fine-tuned" for us to live in...I'm not exactly sure. I just understood the more surface level explanation of the weirdness of something that appears to be zero for 119 digits suddenly not being zero anymore. Like if the digits of Pi started repeating your phone number after a billion decimal places.Other anthropic issues are discussed as well: why is our planet in Goldilocks zone, why are we so lucky to have a large moon to stabilize our rotation, why are we so lucky to have Jupiter sweeping up our solar system's debris, why is the life of proton so remarkably stable, why is the gauge constant exactly where it needs to be to enable chemistry to happen, and on and on. The combination of all these "coincidences" is what Susskind argues gives the APPEARANCE of intelligent design or a benevolent God tuning the dials on our universe. But string theory's multiverse allows such a mind boggling number of different universes with different physical laws that when we ask "Why do we live in a universe so perfectly tailored to allow us to exist?" then the answer becomes "Because obviously if we didn't then we wouldn't be asking the question." Why does our planet have liquid water and atmospheric oxygen??? Because if not, we'd be dead and never have asked the question in the first place. At least that was my understanding of it.eric
What do You think about The Cosmic Landscape: String Theory And The Illusion Of Intelligent Design (2008)?
This was a very good book. Susskind is a good story teller, able to lay on the heavy duty scientific theory, the implications for its meaning and his own biography as a physicist. I enjoyed several aspects of the book, particularly the argument that we live in one of several universes, that the universe that we live in follows only one of an infinite number of possible laws, and the anthropic principle which evaluates the conditions for life on a planet, solar system or universe. Very good stuff.
—Michael
This book is about one of the most shocking ideas in modern physics. Susskind's argument goes a little something like this: There are certain measurable physical constants in the universe that we inhabit that can be quantified. These constants represent things like how strongly particles are attracted to one another or how far an electron is from the nucleus of an atom. Lately, some physicists have come to the conclusion that if even one of these numbers was even minutely different, then life an
—Micah Johnson
THE COSMIC LANDSCAPE tells the intriguing story of the gradual acceptance by physicists of the implications of certain weird aspects of quantum mechanics, implications that entail an infinite multiverse or megaverse comprising endless populations of universes of every conceivable form and variety. Here, too, is the story of the battle between the proponents of Intelligent Design, who draw on quantum mechanics to try to show that our universe is uniquely fashioned for life and intelligence, and scientists who believe that our universe arose as a result of natural processes, its hospitability to life and intelligence a product of scientifically comprehensible phenomena. When Susskind was a student, he was laughed at by his scientific idols for his ideas -- ideas which are now the solid stuff of physics. Over the last century, physical science has growth from Newtonian mechanics to Einsteinian relativity to a quantum-mechanical wonderland, a process that Susskind details beautifully in this fascinating book. For newcomers to quantum mechanics, it's slow going at first, but Susskind's patient, step-by-step discussion of basic concepts is understandable to any intelligent reader, and soon the novice has enough of the new concepts under his belt such that the reading begins to go faster and faster. By the end, one is whizzing through the brave new multiverse the author has introduced to us, delighting in every parsec of it. I got my copy through the Science Fiction Book Club; that's how accessible it is even to laymen. I loved it.
—Yael
