Lawrence Krauss - The Greatest Story Ever Told--So Far Read online

  drives almost every device we use.

  Two years after Davy’s death in 1829, and six years after Faraday

  had become director of the laboratory of the Royal Institution, he

  made the discovery that cemented his reputation as perhaps the

  greatest experimental physicist of the nineteenth century—magnetic

  induction. Since 1824, he had tried to see if magnetism could alter

  the current flowing in a nearby wire or otherwise produce some kind

  of electric force on charged particles. He primarily wanted to see if

  magnetism could induce electricity, just as Oersted had shown that

  electricity, and electric currents in particular, could produce

  magnetism.

  On October 28, 1831, Faraday recorded in his laboratory

  notebook a remarkable observation. While closing the switch to turn

  on a current in a wire wound around an iron ring to magnetize the

  iron, he noticed a current flow momentarily in another wire

  wrapped around the same iron ring. Clearly the mere presence of a

  nearby magnet could not cause an electric current to flow in a wire

  —but turning the magnet on or off could. Subsequently he showed

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  that the same effect occurred if he moved a magnet near a wire. As

  the magnet came closer or moved away, a current would flow in the

  wire. Just as a moving charge created a magnet, somehow a moving

  magnet—or a magnet of changing strength—created an electric

  force in the nearby wire and produced a current.

  If the profound theoretical implication of this simple and

  surprising result is not immediately apparent, you can be forgiven,

  because the implication is subtle, and it took the greatest theoretical

  mind of the nineteenth century to unravel it.

  To properly frame it, we need a concept that Faraday himself

  introduced. Faraday had little formal schooling and was largely self-

  taught and thus was never comfortable with mathematics. In

  another probably apocryphal story, Faraday boasted of using a

  mathematical equation only one time in all of his publications.

  Certainly, he never described the important discovery of magnetic

  induction in mathematical terms.

  Because of his lack of comfort with formal mathematics, Faraday

  was forced to think in pictures to gain intuition about the physics

  behind his observations. As a result he invented an idea that forms

  the cornerstone of all modern physics theory and resolved a

  conundrum that had puzzled Newton until the end of his days.

  Faraday asked himself, How does one electric charge “know” how

  to respond to the presence of another, distant electric charge? The

  same question had been posed by Newton in terms of gravity, where

  he earlier wondered how the Earth “knew” to respond as it did to the

  gravitational pull of the Sun. How was the gravitational force

  conveyed from one body to another? To this, he gave his famous

  response “Hypotheses non fingo,” “I frame no hypotheses,” suggesting

  that he had worked out the force law of gravity and showed that his

  predictions matched observations, and that was good enough. Many

  of us physicists have subsequently used this defense when asked to

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  explain various strange physics results—especially in quantum

  mechanics, where the mathematics works, but the physical picture

  often seems crazy.

  Faraday imagined that each electric charge would be surrounded

  by an electric “field,” which he could picture in his head. He saw the

  field as a bunch of lines emanating radially outward from the charge.

  The field lines would have arrows on them, pointing outward if the

  charge was positive, and inward if it was negative:

  He further imagined that the number of field lines increased as

  the magnitude of the charge increased:

  The utility of this mental picture was that Faraday could now

  intuitively understand both what would happen when another test

  charge was put near the first charge and why. (Whenever I use the

  colloquial why, I mean “how.”) The test charge would feel the “field”

  of the first charge wherever the second charge was located, with the

  strength of the force being proportional to the number of field lines

  in the region, and the direction of the force being along the direction

  of the field lines. Thus, for example, the test charge in question

  would be pushed outward in the direction shown:

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  One can do more than this with Faraday’s pictures. Imagine

  placing two charges near each other. Since field lines begin at a

  positive charge and end on a negative charge and can never cross, it

  is almost intuitive that the field lines in between two positive charges

  should appear to repel each other and be pushed apart, whereas

  between a positive and a negative charge they should connect

  together:

  Once again, if a test charge is placed anywhere near these two

  charges, it would feel a force in the direction of the field lines, with a

  strength proportional to the number of field lines in that region.

  Faraday thus pictured the nature of electric forces between

  particles in a way that would otherwise require solving the algebraic

  equations that describe electrical forces. What is most amazing

  about these pictures is that they capture the mathematics exactly,

  not merely approximately.

  A similar pictorial view could be applied to magnets, and

  magnetic fields, reproducing the magnetic force law between

  magnets, experimentally verified by Coulomb, or current-carrying

  wires, derived by André-Marie Ampere. (Up until Faraday, all the

  heavy lifting in discovering the laws of electricity and magnetism

  was done by the French.)

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  Using these mental crutches, we can then reexpress Faraday’s

  discovery of magnetic induction as follows: an increase or decrease

  in the number of magnetic field lines going through a loop of wire

  will cause a current to flow in the wire.

  Faraday recognized quickly that his discovery would allow the

  conversion of mechanical power into electrical power. If a loop of

  wire was attached to a blade that was made to rotate by, say, a flow

  of water, such as a waterwheel, and the whole thing was surrounded

  by a magnet, then as the blade turned the number of magnetic field

  lines going through the wire would continuously change, and a

  current would continuously be generated in the wire. Voilà, Niagara

  Falls, hydroelectricity, and the modern world!

  This alone might be good enough to cement Faraday’s reputation

  as the greatest experimental physicist of the nineteenth century. But

  technology wasn’t what motivated Faraday, which is why he stands

  so tall in my estimation; it was his deep sense of wonder and his

  eagerness to share his discoveries as broadly as possible that I admire

  most. I am convinced that he would agree that the chief benefit of

  science lies in its impact in changing our fundamental understanding

  of our place in the cosmos. And ultimately, this is what he did.

  I cannot help but be reminded of another mo
re recent great

  experimental physicist, Robert R. Wilson—who, at age twenty-nine,

  was head of the Research Division at Los Alamos, which developed

  the atomic bomb during the Manhattan Project. Many years later he

  was the first director of the Fermi National Accelerator Laboratory

  in Batavia, Illinois. When Fermilab was being built, in 1969 Wilson

  was summoned before Congress to defend the expenditure of

  significant funds on this exotic new accelerator, which was to study

  the fundamental interactions of elementary particles. Asked if it

  contributed to national security (which would have easily justified

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  the expenditure in the eyes of the congressional committee

  members), he bravely said no. Rather:

  It only has to do with the respect with which we regard one

  another, the dignity of men, our love of culture. . . . It has to do

  with, are we good painters, good sculptors, great poets? I mean all

  the things that we really venerate and honor in our country and

  are patriotic about. In that sense, this new knowledge has all to do

  with honor and country, but it has nothing to do directly with

  defending our country except to help make it worth defending.

  Faraday’s discoveries allowed us to power and create our

  civilization, to light up our cities and our streets, and to run our

  electric devices. It is hard to imagine any discovery that is more

  deeply ingrained in the workings of modern society. But more

  deeply, what makes his contribution to our story so remarkable is

  that he discovered a missing piece of the puzzle that changed the

  way we think about virtually everything in the physical world today,

  starting with light itself. If Newton was the last of the magicians,

  Faraday was the last of the modern scientists to live in the dark,

  regarding light. After his work, the key to uncovering the true nature

  of our main window on the world lay in the open waiting for the

  right person to find it.

  • • •

  Within a decade, a young Scottish theoretical physicist, down on his

  luck, took the next step.

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  C h a p t e r 3

  T H R O U G H

  A

  G L A S S,

  L I G H T LY

  Nothing is too wonderful to be true, if it be consistent with the

  laws of nature; and in such things as these, experiment is the

  best test of such consistency.

  —FARADAY, LABORATORY JOURNAL ENTRY #10,040 (MARCH 18,

  1849)

  The greatest theoretical physicist of the nineteenth century,

  James Clerk Maxwell, whom Einstein would later compare to

  Newton for his impact on physics, was coincidentally born in the

  same year that Michael Faraday made his great experimental

  discovery of induction.

  Like Newton, Maxwell also began his scientific career fascinated

  by color and light. Newton had explored the spectrum of visible

  colors into which white light splits when traversing a prism, but

  Maxwell, while still a student, investigated the reverse question:

  What is the minimal combination of primary colors that would

  reproduce for human perception all the visible colors contained in

  white light? Using a collection of colored spinning tops, he

  demonstrated that essentially all colors we perceive can result from

  mixtures of red, green, and blue—a fact familiar to anyone who has

  plugged RGB cables into a color television. Maxwell used this

  realization to produce the world’s first, rudimentary color

  photograph. Later he became fascinated with polarized light, which

  results from light waves whose electric and magnetic fields oscillate

  only in certain directions. He sandwiched blocks of gelatin between

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  polarizing prisms and shined light through them. If the two prisms

  allowed only light to pass that was polarized in different

  perpendicular directions, then if one was placed behind the other, no

  light would make it through. However, if stresses were present in the

  gelatin, then the light could have its axis of polarization rotated as it

  passed through the material, so that some light might then make it

  through the second prism. By searching for such fringes of light

  passing through the second prism, Maxwell could explore for

  stresses in the material. This has become a useful tool today for

  exploring possible material stresses in complex structures.

  Even these ingenious experiments do not adequately represent

  the power of Maxwell’s voracious intellect or his mathematical

  ability, which were both manifest at a remarkably early age.

  Tragically, Maxwell died at the age of forty-eight and had precious

  little time to accomplish all that he did. His inquisitive nature was

  reflected in a passage his mother added to a letter from his father to

  his sister-in-law when Maxwell was only three:

  He is a very happy man, and has improved much since the

  weather got moderate; he has great work with doors, locks, keys,

  etc., and “show me how it doos” is ever out of his mouth. He also

  investigates the hidden course of streams and bell-wires, the way

  the water gets from the pond through the wall.

  After his mother’s untimely death (of stomach cancer, to which

  Maxwell would later succumb at the same age), his education was

  interrupted, but by the age of thirteen he had hit his stride at the

  prestigious Edinburgh Academy, where he won the prize for

  mathematics, and also for English and poetry. He then published his

  first scientific paper—concerning the properties of mathematical

  curves—which was presented at the Royal Society of Edinburgh

  when he was only fourteen.

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  After this precocious start, Maxwell thrived at university. He

  graduated from Cambridge, becoming a fellow of the college within

  a year after graduation, which was far sooner than average for most

  graduates. He left shortly thereafter and returned to his native

  Scotland to take up a chair in natural philosophy in Aberdeen.

  At only twenty-five, he was head of a department and teaching

  fifteen hours a week plus an extra free lecture for a nearby college for

  working men (something that would be unheard of for a chaired

  professor today, and something that I find difficult to imagine doing

  myself and still having any energy left for research). Yet Maxwell

  nevertheless found time to solve a problem that was two centuries

  old: How could Saturn’s rings remain stable? He concluded that the

  rings must be made of small particles, which garnered him a major

  prize that had been set up to encourage an answer to this question.

  His theory was confirmed more than a hundred years later when

  Voyager provided the first close-up view of the planet.

  You would think that, after his remarkable output, he would have

  been able to remain secure in his professorship. However, in 1860,

  the same year that he was awarded the Royal Society’s prestigious

  Rumford Medal for his work on color, the college where he lectured

  merged with another college and had no room for two professors of
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  natural philosophy. In what must surely go down in history as one of

  the dumbest academic decisions ever made (and that is a tough list

  to top), Maxwell was unceremoniously laid off. He tried to get a

  chair in Edinburgh, but again the position was given to another

  candidate. Finally, he found a position down south, at King’s College,

  London.

  One might expect Maxwell to have been depressed or

  disconsolate because of these developments, but if he was, his work

  reflected no signs of it. The next five years at King’s were the most

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  productive period in his life. During this time he changed the world

  —four times.

  The first three contributions were the development of the first

  light-fast color photograph; the development of the theory of how

  particles in a gas behave (which helped establish the foundations of

  the field now known as statistical mechanics—essential for

  understanding the properties of matter and radiation); and finally his

  development of “dimensional analysis,” which is perhaps the tool

  most frequently used by modern physicists to establish deep

  relationships between physical quantities. I just used it last year, for

  example, with my colleague Frank Wilczek, to demonstrate a

  fundamental property of gravity relevant to understanding the

  creation of our universe.

  Each contribution on its own would have firmly established

  Maxwell among the greatest physicists of his day. However, his

  fourth contribution ultimately changed everything, including our

  notions of space and time.

  During his period at King’s, Maxwell frequented the Royal

  Institution, where he came in contact with Michael Faraday, who

  was forty years older but still inspirational. Perhaps these meetings

  encouraged Maxwell to return his focus to the exciting

  developments in electricity and magnetism, a subject he had begun

  to investigate five years earlier. Maxwell used his considerable

  mathematical talents to describe and understand the phenomena

  explored by Faraday. He began by putting Faraday’s hypothesized

  lines of force on a firmer mathematical footing, which allowed him

  to explore in more depth Faraday’s discovery of induction. Over the

  dozen years between 1861 and 1873, Maxwell put the final touches