Chritiaaan Huygens (1629-1695)

Waves are as important as particles. We all know this, and we all know where Christiaan Huygens stands in the history of physics.

• As far as mechanics is concerned, did you know that Huygens derived the following formulas before Newton?

for the pendulum and the centrifugal force.

• We learn these formulas during the high school years, before learning Newton's second law based on calculus.

Before talking about why Newton ranks higher than Huygens in physics, let us look at some photos of the House of the Huygens, known as Huygens’ Hofwijck, in Voorburg near Rotterdam. You know where Rotterdam is.

 Statue of Christiaan with his father at the entrance of the House of the Huygens.
• This house was built by Christiaan's father named Constantijn Huygens who was a powerful politician. Based on the items displayed in this house, his family made their fortune from the trades with Indonesia. Those "flying Dutchmen" imported spices from Southeast Asia. Black pepper was introduced to the Western world at that time. Can you think of a dining table without pepper dispenser?

• In front of this house, there is a statue of Christiaan with his father. I am sitting there in this photo.
1. This house is built upon a lake.
2. This house looks like this from the Voorburg railway station. However, it is not possible to walk directly to the house. It is separated by a lake.
3. You have to go though this road between the trees to enter the house ground.
4. This is how the railway station appears from the entrance to the House.

• The house door says Huygens Museum Hofwijck. Let us look at some of the precious items his family owned.
1. One of the jewelry boxes. Here is another one.
2. One of the book cases with rare items.
3. Precious materials from Indonesia.
4. Elegant fireplace. Here is another one.
5. One of the old Dutch currencies carrying a portrait of Christiaan Huygens. They use Euros these days in the Netherlands.

• The most interesting items are the machines Huygens built to find out physical laws.
1. With this machine, Huygens proved the pendulum period does not depend on the mass. I did this experiment in 1949 when I was the first-year middle school student. I am standing next to this machine in this photo.
2. With this machine, he studied acceleration of falling bodies. He was of course interested in whether it depends on the mass.
3. I was not able to spot rotating instrument to measure the centrifugal force. I am still curious.

4. Huygens was interested in the planetary system, with this figure, especially the rings of the saturn.
5. I am not able to figure out what he was doing with this elegant gadget.
6. He was interested in jumping from the sky with a parachute.
7. He was also interested in chemistry. I did not know.
8. Whatever he did, he described his observation mathematically and graphically.

 Projector with a gaslight. No electric lights available at that time. With this kind of environment, it is not possible to avoid the wave nature of everything.

• Did he build optical instruments indicating wave nature of light? I was not able to spot any.
1. This glass box includes a telescope.
2. He built this projector with gas light. There were no electric bulbs during his time. This projector does not any hint of wave nature of light?

3. How did he become interested in waves? His house is sounded by a serene water surface. If a bird drops a thing, the wave propagates with a circular front. It is safe to assume that this effect led him to the wave nature of light.
4. Another reason: He did not like Newton's corpuscular nature of light. Newton did not get along with anyone.
5. Did he say anything about the wavelength of the light wave. No. He died in 1695. More than one hundred years later, in 1801, Thomas Young (1773-1839) performed the first double-slit experiment to measure the wavelength.

•  Isaac Newton. Nobody liked him during his time.
As far as I could see, Huygens spent most of energy to figure out mechanical aspects of this world. His formulas for pendulum and centrifugal force played pivotal role in the development of mechanics. Yet, Isaac Newton gets all the credits. The reason is very simple. He came with one formula that produces both formulas, and many more.

1. The point is that physics is an art of synthesis. In addition to the two formula by Huygens, Newton's equation synthesizes both elliptic orbits of planets and hyperbolic orbits of comets.

2. Maxwell's equations synthesize electricity and magnetism, leading the present world of wireless world.

3. Einstein synthesized the energy-momentum relations for massive and massless particles. His formula is commonly known as E = mc2.

4. Werner Heisenberg gets the credit for synthesizing the particle nature and wave nature of matter.

• The remaining question is whether we can find a single mathematical framework which produces both quantum mechanics and special relativity. Don't worry. I am not the first person to ask this question.

 Niels Bohr Institute in Copenhagen. Dirac and Heisenberg (1930s).
1. When I was at the Niels Bohr Institute in Copenhagen in 2015, I noted Einstein visited the place occasionally. I asked a young man there whether there has been any effort to synthesize quantum mechanics and special relativity. He said "Dirac," and ran away. I thought I was a hopeless old man asking a hopeless question, and he did not want to waste any more seconds with me.

2. He was right in mentioning Dirac. He was also right in regarding me as a hopeless man, because he could not make money or get promotions by worrying about this problem. However, I am different. I do not have to worry about promotions, and my economic base is stable.

3. Furthermore, he did not know I met Dirac in 1962, and became converted like Nicodemus after meeting Jesus (story in the Gospel of John). Since then I wrote my papers mostly on this Dirac issue.

4. Yes, I published many papers on squeezed states of light, and developed one of the major conferences in quantum optics. What does this have to do with Dirac?

The answer in very simple. Dirac was the first one to worry two oscillator states (or two-photon states) in his 1963 paper. I met him right after he completed this paper and submitted it to the Journal of Mathematical Physics. Click here for the story.

 I like this machine, and I like Dirac. Photo taken at the Fine Hall Libray of Princeton University (2000).

5. The harmonic oscillator is the language of quantum mechanics. According to Dirac, two coupled oscillators produce the symmetry of the Lorentz group applicable to three space-like dimensions and two time-like dimensions.

If one of the those two time-like coordinates is contracted as the Lorentz group contracted group to Galilei group (Inonu and Wigner, the two-oscillator system produces the symmetry of the inhomogeneous Lorentz group. Again, according to Dirac's 1949 paper entitled Forms of Relativistic Dynamics, the Lie algebra of the ionospheres Lorentz group is extension of Heisenberg's Poisson brackets to the Lorentz-covariant world.

• Paul A. M. Dirac published many great papers. His papers are like poems, but they do not contain figures or diagrams. Another serious problem is that he seldom quotes his own earlier papers. It is thus fun to fill in these gaps. This has been my major business for many years. You may click here for my latest published paper on this subject. I hope to write more papers along this line. Here is my ultimate wisdom:

 How did he talk to Einstein?
copyright@2019 by Y. S. Kim, unless otherwise specified.
The photo of Dirac and Heisenberg is from the AIP Emilio Segre Visual Archives.