Relativity and the Birth of Quantum Physics: Two Major Problems for Physics in the Year 1900

Max-Planck-[1]In the year 1900, two critical questions haunted physicists, and both involved that elusive entity, light. The ultimate answers to these troublesome questions materialized during the dawn of the twentieth century and resulted in the most recent two of the four major upheavals in the history of physics. Albert Einstein was responsible for the third of those four upheavals in the form of his theory of special relativity which he published in 1905. Einstein’s revolutionary theory was his response to one of those two critical questions facing physics in the year 1900. A German scientist named Max Planck addressed the second critical question while igniting the fourth great upheaval in the history of physics. Max Planck began his Nobel Prize-winning investigation into the nature of heat/light radiation in the year 1894. His later discovery of the quantized nature of such radiation gave birth to the new realm of quantum physics which, in turn, led to a new picture of the atom and its behavior. Planck’s work directly addressed the second critical question nagging science in 1900. The aftermath of his findings ultimately changed physics and man’s view of physical reality, forever.

What were the two nagging problems in physics in 1900?

The nature of light and its behavior had long challenged the best minds in physics. For example: Is light composed of “particles,” or does it manifest itself as “waves” travelling through space? By the eighteenth century, two of science’s greatest names had voiced their opinions. Isaac Newton said that light is “particle” in nature. His brilliant French contemporary, Christian Huygens, claimed that light is comprised of “waves.”

Newton_Kneller_ 1702_1         huygens[1]

                  Isaac Newton                                                      Christian Huygens

By 1865, the great Scottish physicist, James Clerk Maxwell, had deduced that light, indeed, acted as an electromagnetic wave traveling at a speed of roughly 186,000 miles per second! Maxwell’s groundbreaking establishment of an all-encompassing electromagnetic theory represents the second of the four major historical revolutions in physics of which we speak. Ironically, this second great advance in the history of physics with its theoretically established speed of light led directly to the first of the two nagging issues facing physics in 1900. To understand that dilemma, a bit of easily digestible background is in order!

Maxwell began by determining that visible light is merely a small slice of the greater electromagnetic wave frequency spectrum which, today, includes radio waves at the low frequency end and x-rays at the high frequency end. Although the speed of light (thus all electromagnetic waves) had been determined fairly accurately by experiments made by others prior to 1865, Maxwell’s ability to theoretically predict the speed of light through space using the mathematics of his new science of electrodynamics was a tribute to his supreme command of physics and mathematics. The existence of Maxwell’s purely theoretical (at that time) electromagnetic waves was verified in 1887 via laboratory experiment conducted by the German scientist, Heinrich Hertz.

The first of the two quandaries on physicist’s minds in 1900 had been brewing during the latter part of the nineteenth century as physicists struggled to define the “medium” through which Maxwell’s electromagnetic waves of light propagated across seemingly empty space. Visualize a small pebble dropped into a still pond: Its entry into the water causes waves, or ripples, to propagate circularly from the point of disturbance. These “waves” of water represent mechanical energy being propagated across the water. Light is also a wave, but it propagates through space and carries electromagnetic energy.

Here is the key question which arose from Maxwell’s work and so roiled physics: What is the nature of the medium in presumably “empty space” which supports electromagnetic wave propagation…and can we detect it? Water is the obvious medium for transmitting the mechanical energy waves created by a pebble dropped into it. Air is the medium which is necessary to propagate mechanical sound-pressure waves to our ears – no air, no sound! Yet light waves travel readily through “empty space” and vacuums!

Lacking any evidence concerning the nature of a medium suitable for electromagnetic wave propagation, physicists nevertheless came up with a name for it….the “ether,” and pressed on to learn more about its presumed reality. Clever but futile attempts were made to detect the “ether sea” through which light appears to propagate. The famous Michelson-Morley experiments of 1881 and 1887 conclusively failed to detect ether’s existence. Science was forced to conclude that there is no detectable/describable medium! Rather, the cross-coupled waves of Maxwell’s electric and magnetic fields which comprise light (and all electromagnetic waves) “condition” the empty space of a perfect vacuum in such a manner as to allow the waves to propagate through that space. In expressing the seeming lack of an identifiable transmission medium and what to do about it, the best advice to physicists seemed: “It is what it is….deal with it!”

“Dealing with it” was easier said than done, because one huge problem remained. Maxwell and his four famous “Maxwell’s equations” which form the framework for all electromagnetic phenomena calculate one and only ONE value for the speed of light – everywhere, for all observers in the universe. One single value for the speed of light would have worked for describing its propagation speed relative to an “ether sea,” but there is no detectable ether sea!

The Great “Ether Conundrum” – Addressed by Einstein’s Relativity

In the absence of an ether sea through which to measure the speed of light as derived by Maxwell, here is the problem which results, as illustrated by two distant observers, A and B, who are rapidly traveling toward each other at half the speed of light: How can a single, consistent value for the speed of light apply both to the light measured by observer A as it leaves his flashlight (pointed directly at observer B) and observer B who will measure the incoming speed of the very same light beam as he receives it? Maxwell’s equations imply that each observer must measure the same beam of light at 186,000 miles per second, measured with respect to themselves and their surroundings – no matter what the relative speed between the two observers. This made no sense and represented a very big problem for physicists!

The Solution and Third Great Revolution in Physics:
 Einstein’s Relativity Theories

As already mentioned, the solution to this “ether dilemma” involving the speed of light was provided by Albert Einstein in his 1905 theory of special relativity – the third great revolution in physics. Special relativity completely revamped the widely accepted but untenable notions of absolute space and absolute time – holdovers from Newtonian physics – and time and space are the underpinnings of any notion/definition of “speed.” Einstein showed that a strange universe of slowing clocks and shrinking yardsticks is required to accommodate the constant speed of light for all observers regardless of their relative motion to each other. Einstein declared the constant speed of light for all observers to be a new, inviolable law of physics. Furthermore, he proved that nothing can travel faster than the speed of light.

The constant speed of light for all observers coupled with Einstein’s insistence that there is no way to measure one’s position or speed/velocity through empty space are the two notions which anchor special relativity and all its startling ramifications.

 The Year is 1900: Enter Max Planck and Quantum Physics –
The Fourth Great Revolution in Physics

The second nagging question facing the physics community in 1900 involved the spectral nature of radiation emanating from a so-called black-body radiator as it is heated to higher and higher temperatures. Objects that are increasingly made hotter emanate light whose colors change from predominately red to orange to white to a bluish color as the temperature rises. A big problem in 1900 was this: There is little experimental evidence indicating large levels of ultraviolet radiation produced at high temperatures – a situation completely contrary to the theoretical predictions of physics based on our scientific knowledge in the year 1900. Physics at that time predicted a so-called “ultraviolet catastrophe” at high temperatures generating huge levels of ultraviolet radiation – enough to damage the eyes with any significant exposure. The fact that there was no evidence of such levels of ultraviolet radiation was, in itself, a catastrophe for physics because it called into serious question our knowledge and assumptions of the atomic/molecular realm.

The German physicist, Max Planck, began tackling the so-called “ultraviolet catastrophe” disconnect as early as 1894. Using the experimental data available to him, Planck attempted to discern a new theory of spectral radiation for heated bodies which would match the observed results. Planck worked diligently on the problem but could not find a solution by working along conventional lines.

Finally, he explored an extremely radical approach – a technique which reflected his desperation. The resulting new theory matched the empirical results perfectly!

When Planck had completed formulation of his new theory in 1900, he called his son into his study and stated that he had just made a discovery which would change science forever – a rather startling proclamation for a conservative, methodical scientist. Planck’s new theory ultimately proved as revolutionary to physics as was Einstein’s theory of relativity which would come a mere five years later.

Max Planck declared that the radiation energy emanating from heated bodies is not continuous in nature; that is, the energy radiates in “bundles” which he referred to as “quanta.” Furthermore, Planck formulated the precise numerical values of these bundles through his famous equation which states:

 E = h times Frequency

where “h” is his newly-declared “Planck’s constant” and “Frequency” is the spectral frequency of the radiation being considered. Here is a helpful analogy: The radiation energy from heated bodies was always considered to be continuous – like water flowing through a garden hose. Planck’s new assertion maintained that radiation comes in bundles whose “size” is proportional to the frequency of radiation being considered. Visualize water emanating from a garden hose in distinct bursts rather than a continuous flow! Planck’s new theory of the energy “quanta” was the only way he saw fit to resolve the existing dilemma between theory and experiment.

The following chart reveals the empirical spectral nature of black-body radiation at different temperatures. Included is a curve which illustrates the “ultraviolet catastrophe” at 5000 degrees Kelvin predicted by (1900) classical physics. The catastrophe is represented by off-the-chart values of radiation in the “UV” range of short wavelength (high frequency).

Black_body copy

This chart plots radiated energy (vertical axis) versus radiation wavelength (horizontal axis) plotted for each of three temperatures in degrees K (degrees Kelvin). The wavelength of radiation is inversely proportional to the frequency of radiation. Higher frequency ultraviolet radiation (beyond the purple side of the visible spectrum) is thus portrayed at the left side of the graph (shorter wavelengths).

Note the part of the radiation spectrum which consists of frequencies in the visible light range. The purple curve for 5000 degrees Kelvin has a peak radiation “value” in the middle of the visible spectrum and proceeds to zero at higher frequencies (shorter wavelengths). This experimental purple curve is consistent with Planck’s new theory and is drastically different from the black curve on the plot which shows the predicted radiation at 5000 degrees Kelvin using the scientific theories in place prior to 1900 and Planck’s revolutionary findings. Clearly, the high frequency (short wavelength) portion of that curve heads toward infinite radiation energy in the ultraviolet range – a non-plausible possibility. Planck’s simple but revolutionary new radiation law expressed by E = h times Frequency served to perfectly match theory with experiment.

Why Max Planck Won the 1918 Nobel Prize
in Physics for His Discovery of the Energy Quanta

One might be tempted to ask why the work of Max Planck is rated so highly relative to Einstein’s theories of relativity which restructured no less than all of our assumptions regarding space and time! Here is the reason in a nutshell: Planck’s discovery led quickly to the subsequent work of Neils Bohr, Rutherford, De Broglie, Schrodinger, Pauli, Heisenberg, Dirac, and others who followed the clues inherent in Planck’s most unusual discovery and built the superstructure of atomic physics as we know it today. Our knowledge of the atom and its constituent particles stems directly from that subsequent work which was born of Planck and his discovery. The puzzling non-presence of the “ultraviolet catastrophe” predicted by pre-1900 physics was duly answered by the ultimate disclosure that the atom itself radiates in discrete manners thus preventing the high ultraviolet content of heated body radiation as predicted by the old, classical theories of physics.

Albert Einstein in 1905: The Photoelectric Effect –
Light and its Particle Nature

Published in the same 1905 volume of the German scientific journal, Annalen Der Physik, as Einstein’s revolutionary theory of special relativity, was his paper on the photoelectric effect. In that paper, Einstein described light’s seeming particle behavior. Electrons were knocked free of their atoms in metal targets by bombarding the targets with light in the form of energy bundles called “photons.” These photons were determined by Einstein to represent light energy at its most basic level – as discrete bundles of light energy. The governing effect which proved revolutionary was the fact that the intensity of light (the number of photons) impinging on the metal target was not the determining factor in their ability to knock electrons free of the target: The frequency of the light source was the governing factor. Increasing the intensity of light had no effect on the liberation of electrons from their metal atoms: The frequency of the light source had a direct and obvious effect. Einstein proved that these photons, these bundles of light energy which acted like bullets for displacing electrons from their metal targets, have discrete energies whose values depend only on the frequency of the light itself. The higher the frequency of the light, the greater is the energy of the photons emitted. As with Planck’s characterization of heat radiation from heated bodies, photon energies involve Planck’s constant and frequency. Einstein’s findings went beyond the quanta energy conceptualizations of Planck by establishing the physical reality of light photons. Planck interpreted his findings on energy quanta as atomic reactions to stimulation as opposed to discrete realities. Einstein’s findings earned him the 1921 Nobel Prize in physics for his paper on the photoelectric effect….and not for his work on relativity!

Deja Vu All Over Again: Is Light a Particle or a Wave?

My EinsteinAlong with Planck, Einstein is considered to be “the father of quantum physics.” The subsequent development by others of quantum mechanics (the methods of dealing with quantum physics) left Einstein sharply skeptical. For one, quantum physics and its principle of particle/wave duality dictates that light behaves both as particle and wave – depending on the experiment conducted. That, in itself, would trouble a physicist like Einstein for whom deterministic (cause and effect) physics was paramount, but there were other, startling ramifications of quantum mechanics which repulsed Einstein. The notion that events in the sub-atomic world could be statistical in nature rather than cause-and-effect left Einstein cold. “God does not play dice with the universe,” was Einstein’s opinion. Others, like the father of atomic theory, Neils Bohr, believed the evidence undeniable that nature is governed at some level by chance.

In one of the great ironies of physics, Einstein, one of the two fathers of quantum physics, felt compelled to abandon his brain-child because of philosophical/scientific conflicts within his own psyche. He never completely came to terms with the new science of quantum physics – a situation which left him somewhat outside the greater mainstream of physics in his later years.

Like Einstein’s relativity theories, quantum physics has stood the test of time. Quantum mechanics works, and no experiments have ever been conducted to prove the method wrong. Despite the truly mysterious realm of the energy quanta and quantum physics, the science works beautifully. Perhaps Einstein was right: Quantum mechanics, as currently formulated, may work just fine, but it is not the final, complete picture of the sub-atomic world. No one could appreciate that possibility in the pursuit of physics more than Einstein. After all, it was his general theory of relativity in 1916 which replaced Isaac Newton’s long-held and supremely useful force-at-a-distance theory of gravity with the more complete and definitive concept of four-dimensional, curved space-time.

By the way, and in conclusion, it is Newton’s mathematics-based science of dynamics (the science of force and motion) that defines the very first major upheaval in the history of physics – as recorded in his masterwork book from 1687, the Principia – the greatest scientific book ever written. Stay tuned.

Chance Encounters: I Wish I Knew Then What I Know Now!

Just a bit of background: The Danish postage stamp pictured was issued in honor of Niels Bohr, Nobel Prize Laureate in physics from Denmark and father of the scientific quantum theory of the atom. A close colleague and contemporary of Einstein’s, Bohr’s role in physics and his work on quantum theory share the highest pedestal in physics along with Einstein’s relativity theories and Newton’s mechanics. No, I never met Niels Bohr, but I did have a chance encounter with someone who knew him very well and who contributed to quantum theory.

Bohr Stamp_1

It occurred many years ago, 1960 to be exact. I had just transferred to Stanford University from San Jose State College to begin my junior year there. On a September afternoon in 1960, I moved into Stern Hall, the on-campus dormitory at Stanford, with much anticipation (and many qualms) about the great adventure ahead. Being the first in my entire extended family to ever go to college, I had a great number of those qualms and, just like two years prior when first enrolling at San Jose State, I was continually “learning on the fly.”

Checking in at the dormitory desk, I was handed a key to room 102 which was not yet occupied by my (unknown) roommate. It was nice to have first choice of the beds and desks, even though the room was symmetrically arranged. Who will be my roommate and where, in this great United States, will he be from: Perhaps a proper Bostonian with an eastern accent? Maybe a southerner…with an even stronger accent. Because my home in San Mateo was only twenty miles away from the Stanford campus, I was excited about meeting someone from a completely different part of the country.

The day wore on and still…no roommate: I thought that was somewhat odd. Finally, my roommate, Bob, strode through the open door carrying surprisingly little luggage. No wonder! Bob was from…Palo Alto, the home of Stanford University! “Well, so much for the cultural exchange,” I thought to myself, but I could readily see that Bob was a good guy and we would get along fine. That proved to be true even though he was a music major and I, an engineering student going in rather different directions.

But this meeting of roommates is not the subject of this post; the particular encounter which I want relate was Bob’s doing one evening, not far from campus. His mother lived literally just a mile across the El Camino Real which borders the 9600 acres (not a typo!) of the Stanford campus. One evening, we jumped into his Volkswagon beatle and drove over to the house. From there, we drove several blocks in the same residential area to visit two boyhood friends of  Bob’s who he must have known at nearby Palo Alto High School.

As we pulled into the large driveway, he related that Dan and George were twins. He also gave me a heads-up that their father worked at Stanford – a very smart man who won a Nobel Prize in physics, he told me! Despite my youthful naivete, even I  knew at the time that a Nobel Prize in physics is a pretty big deal. I knew little else. We walked in to a very warm, friendly living area which featured a full-size pool table.

Bob introduced me to his friends and to their father, Mr. Bloch, who was relaxing in a large easy chair and puffing on a pipe. We probably shook hands although I cannot recall for certain – at least I hope so.

I hope I shook his hand because Felix Bloch was, in his early years, one of the great young European physicists who ushered-in the scientific revolution called “quantum physics.” The great unveiling of the atom and its mysteries took place in the first three decades of the last century, and Felix Bloch was there when it happened and contributed to it. He worked with and knew, personally, some of the greatest European names in science: The “Great Dane,” Niels Bohr, the father of the quantum atom; The German, Werner Heisenberg of “uncertainty principle” fame; the Austrian whose innate genius was said by colleagues to be second only to Einstein’s, Wolfgang Pauli; and most of the others in the famous cast of roughly two dozen. This revolution, this peeling-back of atomic physics and its mysteries, took place almost exclusively in Europe because that is where the greatest talent in physics resided.

 Atom_1

Felix Bloch was Swiss-born, talented enough and fortunate enough in circumstance to participate in one of the great epochs of science. A young Felix Bloch can be seen in the illustrious company of Bohr and the others at Bohr’s Institute for Physics in Copenhagen, posing on the long auditorium benches in the famous lecture hall where assaults on the mysteries of quantum physics were launched and often won. These period photos date from around 1930 when brilliant young physicists received invitations from Bohr for extended working visits at the Institute. It is no exaggeration to say that the atom grudgingly yielded many of its secrets as the result of the myriad gatherings and collaborations that emanated from Bohr’s circle of brilliant young minds. 

Have you ever had a medical MRI (Magnetic Resonance Imaging)? If so, then you, along with millions of others have benefitted from the talent and fundamental research of Felix Bloch…and many others. My wife’s bout with cancer (complete recovery) several years ago invoked the miracle of MRI many times. It was in recognition of his research on Nuclear Magnetic Resonance, or NMR, that Bloch shared the Nobel Prize for physics in 1952. The beginnings of that research date back to the original work of Bohr, Heisenberg, Pauli, and Paul Dirac who first endeavored to understand the atom and its mysteries. The seminal paper of Bohr’s which first cast a quantum light on the then-mysterious atom was published by the very young physicist in 1913. It followed on the heels of the 1900 paper of Max Planck which revealed the quantum nature of radiated energy and the 1905 paper of Einstein’s on the quantum photoelectric effect (Nobel Prize, 1921). My wife’s benefit from MRI technology was a first-class connection with the man I met way back in 1960.

One other personal connection to Mr. Bloch and his contributions comes to mind: My first real job, ever, came through my high school physics teacher at San Mateo High School. He recommended me for a summer position at the Stanford University Microwave Lab that summer between graduation and college. While there, I assisted two physics post-docs with their research projects in …NMR, nuclear magnetic resonance – well before its advent as a medical tool and two years before meeting the man so instrumental in the field. Felix Bloch had come to Stanford in 1934, so it was not surprising that the university would be well-versed in and actively pursuing the physics and the technology in the Microwave Lab and elsewhere on campus. For those interested, I add a humorous postscript at the end of this post.

In summary: I had no clue about the importance and historical significance of the gentleman that I met that evening in 1960. I never would have guessed that he came to reside in familiar, nearby Palo Alto only after an early life spent travelling between the intellectual centers of early European physics, working with many of the greatest names in modern physics!

Since retiring from engineering twelve years ago, I have become very interested in science and science history, as most of you have surmised, so I learned about much of this over the years since. I delved quite deeply into Einstein’s relativity several years ago, but it is only now that I have generated the courage to really learn something in detail about quantum mechanics, a revolution in physics which is just as strange and equally challenging as Einstein’s relativity. Ironically, and surprising, the old textbook for one of my physics courses at Stanford is where I expect to get my firmest footing in the theory (again!). I re-discovered that old text by thumbing through my library (I almost got rid of it once!). Too bad that I did not have the requisite perspective and drive back then to better learn and recall what I now appreciate is contained in that textbook.

Equally regrettable is the fact I did not realize, at the time, my great good fortune in personally meeting Felix Bloch. If I had any inkling back then of what I know today, I would love to have bought lunch and a bottle of fine wine at the best bistro in Palo Alto and discussed with him his recollections of those weeks and months spent in the company of physics’ elite at the Bohr Institute of Physics in Copenhagen. I would certainly have made sure that I at least shook his hand when introduced! As the old Pennsylvania Dutch saying goes, “Too soon oldt; too late schmart!” Ah, so true.

Quantum book

Several days ago, I pulled a recently purchased book off of my “must read” shelf and dove-in. The book is titled “Quantum” by Manjit Kumar, an historical/scientific account of quantum mechanics. Reading the richly-detailed historical account of this scientific revolution revitalized the memory of my introduction to Felix Bloch and prompted the post you have just read. One need not have much of a science background to benefit from Mr. Kumar’s outstanding account of those colorful days and events in the intellectual centers of European science. His recounting is as much a story of the human spirit as it is a scientific overview. I heartily recommend this book; it truly captures the golden years of physics during the first decades of the twentieth century. Google any of the names mentioned, above, and the internet will provide a treasure-trove of both historical and scientific information. “Niels Bohr” would be where I would start! He was at the center of the quantum revolution; everyone else who orbited around quantum physics, including Felix Bloch, was heavily influenced by the “pull” of his persona and acumen.

A Humorous Postscript: My contributions to NMR (Nuclear Magnetic Resonance) technology during a summer job in the Stanford Microwave Lab – 1958. My job as a student intern that summer was to help two physics post-doctoral students with their lab experiments involving NMR in ferrite materials. One of the assignments was to grind “chips” of this black rock-like substance into very tiny, round ferrite balls for magnetic resonance testing.

This was accomplished by using cylindrical “wells” bored about an inch deep into blocks of wood. Each well had a small inlet pipe through which compressed air could be used to blow the small ferrite chips around the walls of the capped cylindrical wells. Different wells were lined with different grades of sandpaper. The idea was to “start the ball rolling” using a rough grade of sandpaper, progressively polishing the forming sphere using finer and finer grades.

This particular day, I had eight different, tiny samples to prepare. It was tedious work, efforts for which there is no Nobel Prize! After a full day spent forming ferrite spheres and polishing them to precise diameters as measured with a micrometer, I had my ferrite mini-menagerie. I carefully used tweezers to place them on a twice-creased sheet of paper where they nestled in the apex of the folds. I proceeded to deliver my ferrites and started across the open courtyard between buildings when a sudden gust of wind lifted my paper. My tiny ferrites were now nowhere to be seen. I was standing on the grass at that instant, so forget about finding them. Sorry, no Nobel Prize for me that day; instead, I felt like dummy-of-the-day. My post-doc was quite sympathetic; he probably had a good laugh once I slunk out of sight. Who said doing science was easy?