Tag Archives: Quantum Physics

The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom, by Graham Farmelo

P.A.M. Dirac has always been mysterious to me.  I knew his name, and that he was a theoretical physicist who made contributions to quantum theory, but very little else.  What was he like?  Where did he live and work?  What were his contributions to science?  And I really wanted to know what those initials stood for, so I could stop thinking of him as “Pam.”  Farmelo’s book answers all these questions.

Dirac was born in Bristol in 1902.  He was exceedingly quiet, almost unresponsive, giving one-word responses to those questions he deemed worth answering, and no response at all to small talk.  Those who knew him described him as lacking empathy, as being tactless, awkward, and taciturn.  He was influenced by the famous verification of Einstein’s relativity theory in 1919, when bending of light by the sun’s gravity was observed during an eclipse.  Around the age of 20 he developed a new hobby – taking equations from Newtonian physics and converting them to their relativistic versions.

After earning engineering and mathematics degrees in Bristol, he was accepted into a graduate program at St. John’s College, Cambridge, studying quantum physics and relativity.  Here he interacted with some of the most famous scientists of the twentieth century – Eddington, Rutherford, Kapitza, and Oppenheimer.  The names of those he worked with or competed against are an indication both of his ability and of the exciting early days of quantum theory during which he worked – names like Bohr, Heisenberg, Born, Pauli, Schrödinger, Ehrenfest, and Fermi.

Among his contributions was a mathematical description of atoms and electrons that didn’t rely on an incorrect visualization, as does the Bohr model of electrons as particles orbiting a nucleus.  He completed the first PhD anywhere on the subject of quantum mechanics, found the relationship between Schrodinger’s wave equation and Heisenberg’s quantum theory, and developed a quantum theory of light reconciling its wave and particle nature.  He was barely beaten into print by other researchers for several important contributions to quantum theory.

More famously, he developed a quantum theory of the electron,  consistent with the electron’s spin and magnetism.  The theory was criticized for having negative energy states that seemed to be meaningless, until they turned out to predict antimatter.  Later he predicted the existence of magnetic monopoles, which have yet to be discovered.

Dirac’s contributions were recognized when he was offered the Lucasian Professorship of Mathematics at Cambridge (a post formerly held by Isaac Newton and later by Stephen Hawking), and when he shared the 1933 Nobel Prize in Physics with Erwin Schrodinger.  But you really know you’ve made it when your textbook is used as a reference by Albert Einstein, as was Dirac’s “The Principles of Quantum Mechanics.”  When Einstein had a difficult quantum problem, he’d mutter, “Where’s my Dirac?”

Dirac had an intuition about the structure of reality, a form of visualization using geometrical methods, that he never articulated.  He could not, or simply refused – “To draw its picture is like a blind man sensing a snowflake.  One touch and it’s gone.”


Reality is Not What it Seems: The Journey to Quantum Gravity, by Carlo Rovelli

Carlo Rovelli is the author of the best-selling book “Seven Brief Lessons on Physics,” published in 2015.  “Reality is Not What it Seems” was actually written first, but not translated from Italian into English until now.  It provides more detail, more depth, and more historical context than “Lessons”.

Rovelli lays it out very clearly, with little tables showing what the universe was thought to have consisted of through history.  Let’s start with the Newtonian view of the world: there are particles, changing position in space as time passes.  This is the world most of us think we live in, with 3-dimensional space providing a stage or framework in which thing move around with time.  Faraday and Maxwell added the concept of fields, such as electromagnetic fields; these are modifications of the properties of space that change the way particles move.  With his theory of Special Relativity, Einstein showed that space and time are not separate, but a unified “spacetime”, so now particles were understood to move through spacetime under the influence of fields.

Then it starts to get weird.  General Relativity says that the gravitational field IS space.  And it’s not a fixed frame, it gets warped by mass.  So we’ve gone from thinking of the universe as being made of space, time, and particles (Newton); to space, time, particles, and fields (Faraday and Maxwell); to spacetime, particles and fields (Einstein); to (since space is a field), just fields and particles (Einstein again).

And then it gets weirder still.  Quantum Mechanics says that fields are granular; they are quantized; and particles are really the quanta of a field.  Dirac wrote the equations for those fields for electrons and other elementary particles.  Now all we have are quantum fields.  No space, no time, no particles.

This is the historical foundation that provides the jumping off point for more speculative theories about quantum gravity.  Given the historical development as provided by Rovelli, it seems almost inevitable that space must be quantized.  If fields are quantized, and gravity is a field, and gravity is space, then space is quantized!  Now we’re really through the looking glass, dealing with loop theory, quantum spin foams, black holes, and the eradication of time.  Rovelli has a knack for explaining things clearly, even poetically, to the point where you almost think you understand it.

The Fabric of Reality, by David Deutsch

David Deutsch has presented his understanding of the fundamental nature of reality.  He weaves together the dominant theories from four fields: quantum physics, epistemology, computation theory, and evolution, and he is utterly fearless in accepting the implications from each field.

In quantum physics, results from experiments like the double slit experiment can be interpreted to imply there are infinitely many parallel universes, which interact only weakly with our universe.  Deutsch rejects explanations that say things behave “as if” there is a multiverse; instead, he fully accepts the implications of the theory, and accepts the multiverse as real.  As he says, “To understand our best theories, we must take them seriously as explanations of reality, and not regard them as mere summaries of existing observations.”  His matter-of-fact explanation and acceptance of parallel universes is enough to blow your mind more than it has been since you read Douglas R. Hofstadter’s “Godel, Escher, Bach” in high school.

Having accepted the reality of the multiverse, he goes on to examine implications from computation theory, extending the Turing principle (that it is possible to build a universal computer; one that can perform any computation that any other physical object can perform) to include quantum computers and virtual-reality machines.

Then he looks at life.  Living brains are a sort of virtual-reality generator (they construct versions of reality for us from sensory input).  Genes manipulate their own environments to cause themselves to be replicated.  The better adapted the genes are, the more influence they have on whether they get copied in their environment.  As environments vary across similar multiverses, genes will stay constant, while other things vary randomly.  Genes encode information (“knowledge”) about their environments, so there are links among quantum physics (the multiverse), life and genes (knowledge and evolution), and computation (virtual reality).

And there you have it: the fabric of reality.  There’s a lot more to it than this, of course, and Deutsch takes the time to provide examples and address possible criticisms.  He debunks solipsism (it’s literally indefensible – who is a solipsist trying to convince?) and scientific inductivism, explores the implications for time travel (yes, it’s possible), and speculates about super-intelligences controlling the final stages of the end of the universe.  Whoooa.

The Universe Within: From Quantum to Cosmos, by Neil Turok

Niel Turok is the director of the Perimeter Institute for Theoretical Physics based in Waterloo, Ontario, and delivered the Massey Lectures in 2012.  This is a publication in book form of those lectures.  It’s a masterful summary of our understanding of physics to date, tracing the history of science from the time of the ancient Greeks to the modern day.

The history of discoveries in mechanics, electricity and magnetism, and light are all presented, along with the personalities involved in those discoveries.  Weird results from relativity and quantum physics are described, and there’s an excellent explanation of the importance of the double slit experiment.  The big bang is explained, and even the question, “What banged?” is considered, as well as the influence of big bang processes on the structure of the universe.  Dark matter, dark energy, and quantum computing make an appearance, too.  Turok does not neglect the human side of the equation either, examining the potential for harm or benefit to mankind depending on how scientific understanding is pursued and how the results are used.

This is a thoroughly engaging and readable account of the current state of understanding in physics, delivered by a world-class expert in the field.

Genius: The Life and Science of Richard Feynman, by James Gleick

I was interested in learning more about Richard Feynman because I had heard he was an original thinker, someone with his own unique style of learning, understanding, and teaching.  Gleick has explored Feynman’s life in detail, searching in part for a satisfactory definition of genius.

Richard Feynman was a 20th century theoretical physicist.  The very name of his field – theoretical physics – was invented during his career.  Even Einstein was known as a mathematician until physicists became prominent after the creation of the atomic bomb.  Feynman grew up in the twenties and thirties, when theories of quantum mechanics were developing, creating “a vision of reality so fractured, accidental and tenuous that it frightened those few older American physicists who saw it coming.”  Feynman made original contributions to the field in graduate school and throughout his career, and worked on the development of nuclear weapons at Los Alamos during the Second World War.

Feynman tried to understand things from a fundamental level.  He would refuse to read the work of others, preferring to work it out for himself.  He would read about or listen to a problem someone was trying to solve, but just enough so he understood the question.  Then he would go away and come up with his own solution, which often provided startling new insights.  By working this way, he also contributed to an understanding of what it really means to know something.

Gleick reminds us of the weirdness of reality as revealed by relativity and quantum physics.  For example, we should not think of reality as a bunch of matter distributed in space and evolving with time.  “The laws of nature are not rules controlling the metamorphosis of what is into what will be.  They are descriptions of patterns that exist, all at once, in the whole tapestry.”

So what is genius?  There are some who think like everyone else, but are simply much smarter than the rest.  We would be like them if we were only much, much better.  That’s one kind of genius.  The other kind is a wizard.  This kind of genius thinks in a way that others don’t, and produces results using what seems like magic.

Schrodinger’s Kittens and the Search for Reality, by John Gribbin

More quantum weirdness.  Gribbin updates ideas about the deeper meaning of quantum physics, starting with detailed descriptions of double slit experiments, which show conclusively the dual wave-particle nature of light, electrons, and even atoms.  Then he dives into a good historical summary of scientific ideas about light, from the ancient Greeks through Newton, Faraday, and Maxwell to Einstein.

Einstein showed that light has some very strange properties.  You may have heard of time dilation, where moving clocks run more slowly, or of Lorentz contraction, which describes the shortened length scales of moving bodies.  In the extreme, for something moving at light speed, time stands still, and there is no distance between objects.  An electromagnetic wave touches everything at once, or exists everywhere along its path at the same time.  For an entity like this, interfering with itself in a double slit experiment is easy!

A photon can spontaneously become an electron and a positron, and when an electron meets its anti-matter counterpart, they annihilate to produce a photon.  But we can equally view this process as involving an electron that meets a photon, sending the electron back in time (looking like a positron to us), until it meets another photon, which sends it forward in time again as an electron.

The vacuum of space is not empty at all, but consists of a superposition of many states of the electromagnetic field.  (Indeed, Einstein said it’s meaningless to talk of space in the absence of the fields that fill it).  When an atom emits a photon, it affects the surrounding  vacuum state.

These are strange phenomena, and Gribbin describes many more before exploring the underlying implications for the nature of reality.  He shows why the Copenhagen Interpretation cannot be the last word, and presents other interpretations (like the many worlds interpretation), labelling some of them “desperate remedies.”  The most reassuring analysis is in the section about what we mean when we say we know something.  There is only so far the reductionist approach to science can take us.  Are atoms the fundamental particles of reality?  Protons and neutrons?  Quarks?  Strings?  Photons?  In the end, the descriptions we use for quantum phenomena are all based on analogies to help us visualize, understand, and predict what’s going on.  None of them really say what a photon, electron, or quark really “is”, and each explanation is helpful in the specific circumstances to which it applies.

In Search of Schrodinger’s Cat, by John Gribbin

Talk about things that don’t make sense.  Nothing about quantum physics makes sense.  It seems impossibly weird, and yet it’s true.

The book was recommended by an acquaintance after learning I had enjoyed reading Walter Isaacson’s biography of Einstein.  He also suggested I read a more recent book by Gribbin, Schrödinger’s Kittens, which I plan to do.

In his acknowledgements, Gribbin mentions a disappointing aspect of his university physics education:  “…the simplicity and beauty of the underlying ideas was smothered in a wealth of detail and mathematical recipes for solving specific problems with the aid of the equations of quantum mechanics.”  They were probably unrealistically simplified problems, too.  Using mathematical recipes in what Gribbin later calls “quantum cookery” successfully solves many problems, but can interfere with contemplating the utterly bizarre nature of quantum reality.  Gribbin wrote this book in part to compensate for that deficiency in his university physics education.

Consider the properties of light.  In some situations light behaves like a wave, and in others like a particle.  “Particles” like electrons also have wave-like properties in some situations.  But how can they be both?  Gribbin says they’re not, they never exhibit both wave-like and particle-like behaviour at the same time, and really they’re neither waves nor particles, but something…different.

If that seems strange, quantum physics also undermines the classical notion of causality.  Atomic nuclei can decay spontaneously, without anything to trigger the event and the associated emission of particles and energy.  Except that to a photon, time stands still, so instead of thinking of the atom as having emitted a photon, we can equally well view the photon as having travelled backwards in time to trigger the event.  It is equivalent.  That’s so strange, I have to repeat it: the two ways of viewing the event are equivalent.

The uncertainty principle tells us we cannot measure with absolute accuracy, and at the same time, both elements of certain pairs of complementary properties, such as position and momentum, or energy and time; there will always be an inherent uncertainty.  But it’s worse than that – until we measure it, the object does not have a definite position or momentum.  Our observations crystallize reality at the quantum level, and some say our observations have crystallized the reality of the entire universe.

The uncertainty principle allows particles to appear out of nothing.  Mass is energy, and there is uncertainty in the amount of energy available to a particle  for a short enough time, so there is uncertainty about whether a particle exists or not for that time.  A group of particles can appear out of vacuum, then recombine with one another and disappear.

And it just keeps getting weirder.  The cat in Schrödinger’s famous thought experiment really is alive and dead at the same time, or, equally consistent with quantum mechanics, the universe has split into two; one in which the cat is alive, and one in which it is dead.  We don’t know which one we’re in until we lift the lid and check on the cat.

We live in a very weird universe.