Poincaré's DinganSich
Princeton's Graduate College 
If Bertrand Russell (18721970) of England had said the same thing to me about mathematics, I could not have told him to go away. Russel was one of the great thinkers of the past century and I like his history books. Russell told Herni Poincaré (18541912) that mathematics is only a tool of logic and nothing else, but Poincaré repeatedly disagreed.

 Like Einstein, Poincaré was heavily influenced by
Immanuel Kant. One object
or event could appear differently to different observers, but there is one and
only one absolute entity. Kant used the word "DinganSich" (thing in itself).
From Poincaré's point of view, mathematics could have been his "DinganSich."
If Russel and Poincaré are both right, nothing is everything. Even without those two great names, we usually complain that nothing is everything according to philosophers.
In preparation for this webpage, I made a trip to Paris 2012 in order to have a photo of myself at Poincaré's grave. He was buried at the Montparnasse Cemetery 1912.
 This is his grave, one hundred years old in 2012. Many people came here and left their used Metro tickets on the stone.
 Henri Poincaré was buried in his family grave.
 I was there in 2012.
 This young Australian came to this cemetery to visit the graves of the people dear to her heart. Her list should have included
 Guy de Maupassant, who wrote a number of important stories about women.
 JeanPaul Sartre was also buried there, together with Simone de Beauvoir. I like Sartre and I have a webpage dedicated to him.
 Where is the Montparnasse Cemetery? It is one block east of Montparnasse Tower.
 The Cemetery seen from the top of the Montparnasse Tower.
 The Montparnasse Tower is one of the tallest structures in Paris. This is a nontraditional buildings in Paris.
 From the top of the Arch of Triumph, we can see how tall this structure is compared with other buildings in Paris. Underneath of the golden dome seen in this photo is Napoleon's gasket. The building is called "Hotel des Invalides" meaning hospital for wounded soldiers.
 The Hotel des Invalides seen from the top of the Montparnasse Tower.
 The Eiffel Tower seen from the top of the Montparnasse Tower. Modern buildings in the district of Defense are also seen. These buildings are for banks and other moneymanaging institutions.
 The Basilica of the Sacré Coeur can also be seen from the top of this Tower. This photo was taken on a cloudy day, and became an impressionist photo.
 From the Sartre Square, the Montparnasse Tower looks like this. The Sartre square is the area with the Cafe Flores and the Cafe Deux Magots where Sartre used to preach his philosophy. Click here for the Sartre Square in Paris.
Let us go back to physics. Speaking of the role of mathematics in physics, Poincaré started with the threebythree rotation matrix applicable to the threedimensional space. He expanded it to fourbyfour by augmenting the time variable. He then came up with fivebyfive matrices in order to take into account the spacetime translational variables. This is the way in which he completed the formulation of the Poincaré group.
 Here is what Raymond Streater says about Poincaré. Go to his web page on Henri Poincaré. According to him, Poincaré formulated the Lorentzcovariant spacetime symmetry before Einstein completed special relativity as a new physical theory. Streater is not only an outstanding physicist but also a very critical history writer. I had two overlapping years with him in Princeton (196062).
Poincaré and Einstein
 Einstein's Relativity.
While many people were worrying about transformation properties
of velocities, Einstein was interested in transformation properties of momentum and
energy, and cameup with the concept of fourmomentum. In so doing he obtained one
mathematical formula the energymomentum relation, leading to his celebrated
E = mc^{2}.
 By 1904, Lorentz and Poincaré proved the equations of electromagnetism,
with the velocity of light as an invariant constant, are invariant under Lorentz
transformations. Then, the question is why Newton's
equation is not. Here, Einstein had to face a Hegelian problem: how to make
Newton's equation and Maxwell's equations obey the same transformation law.
He solved this problem and came up with a relativistic form Newton's equation.
During this process, Einstein found out the momentum and energy can become a
fourvector transforming like the spacetime fourvector.
 Hermann Minkowski was born in
Lithuania and studied in Koenigsberg. He was a devoted Kantianist, and a also
a creative mathematician. He was one of Einstein's teachers.
In 1907, he published a paper where he gave a geometrical interpretation
Lorentz transformations. He was particularly interested in expressing
everything in terms of quadratic forms.
Lorentz transformations in the fourdimensional Minkowskian space include both rotations and squeeze transformations. Rotations are quite familiar to physicists. The squeeze is one of the standard deformations in engineering, but this transformation is still strange to physicists.
 Let us go back to Kant. It is easy to say that Einstein's relativity is inconsistent
with Kant's DinganSich which is the absolute coordinate frame. Let us see what Einstein
did more closely. He divided many different observations into two groups (as in the
case of Taoism). He then combined these two into one. Yes, Einstein was a Kantianist
with the Lorentzcovariant energymomentum relation as his DinganSich. Einstein's
DinganSich is different from Kant's DinganSich. It appears as a mathematical formula.
 Click here for an illustration of how Einstein
reached his DinganSich. He had to go through Taoism and Hegelianism.
 This image will illustrate how Kantianism
and Taoism were developed from the same geographical environment. Kantianism is a
product of the geographical condition of
Koenigsberg. Like Venice, Koenigsberg
was the traffic center for the ships navigating in the Baltic Sea. Many people came
there with different ideas. The city had to find common ground to entertain those
people. This is what Kant's DinganSich is all about.
China was created as a collection of many isolated population pockets with different backgrounds. They came to one place with different ideas. They divided those ideas into two opposing groups. This is what Taoism is all about.
 Twoparty system of American government was developed in the same way as Taoism was developed in ancient China.
 This image will illustrate how Kantianism
and Taoism were developed from the same geographical environment. Kantianism is a
product of the geographical condition of
Koenigsberg. Like Venice, Koenigsberg
was the traffic center for the ships navigating in the Baltic Sea. Many people came
there with different ideas. The city had to find common ground to entertain those
people. This is what Kant's DinganSich is all about.
 From these illustrations, we now have a clearer picture of what Kantianism is all about. From Poincaré's point of view, Einstein's DinganSich is mathematics. The mathematical expression of Einstein's energymomentum relation is much more than an instrument of logic.
Poincaré Group after Einstein
When Einstein formulated his special relativity in 1905 and derived his energymomentum relation, he did not take into consideration of the fact that particles have internal spacetime symmetries. Then how can we define these symmetries?
How about momentum? Indeed, Einstein's fourmomentum is associated with spacetime translations in the Minkowskian space. If the momentum variable is to play a role, we have to resort to the inhomogeneous Lorentz group where the translational degrees of freedom are augmented to the Lorentz group with the rotation and boost generators. This inhomogeneous Lorentz group is commonly called the Poincaré group.
In order to discuss this problem, we need many webpages. You may go to this page for a brief survey of this field. You will note there that this subject has been my main business since 1973.
Poincaré's Geometry and Topology
 Poincaré was quite fond of drawing pictures when he was thinking.
He used the surface of a sphere to describe the polarization of light.
This sphere is known as the Poincaré sphere, and discussed in
every optics textbooks. Like the Eulier angles, this sphere carries
three variables.
The sphere has its radius. If it is allowed to vary, the sphere has four variables. In this case, did you know that the sphere can be used for representations of the Lorentz group which Poincaré formulated? I talked about this aspect in one of my earlir.
 Click here for
one of the webpages.
 Click here for a paper
I presented at the Fedorov Memorial Symposium: International
Conference "Spins and Photonic Beams at Interface," dedicated to the 100th
anniversary of F. I. Fedorov (Minsk, Belarus, 2011). Academian Fedorov
was one on the pioneers in applications of the Lorentz group in optical sciences.
 One mathematics for two
different branches of physics. The damped harmomic oscillator and the LCR circuit are two different manifestations
of the seconddegree differential equation. Likewise, special relativity
and polarization phyiscs are two different manifestations of the Lorentz
group.
The Lorentz group is applicable to many other branches of optical sciences. For a list my paper on this subject, go to this page.
 Here again, Poincaré had enough reason to think mathematics is his DinganSich.
 Click here for
one of the webpages.
 Poincaré was also interested in circles. He was particularly interested
in under what circumstances we can shrink a circle continuously to a point.
 Is there a physical application of this topology?
Click here.
 We would not be working against his wishes if we worry about how a
circle can be deformed while preserving its area. It can become an ellipse and
eventually become a straight line.
Click here for the ellipse, and
here for a detailed story. Here again, we are talking about the
Lorentz group formulated first by Poincaré.
 Here again, in the spirit of Poincaré, we can worry about
to what extent a hyperbola is the same as an ellipse. I studied this aspect
in this webpage. We know one can
be continuously transformed into the other, but art they the same?

x^{2}  y^{2} = 1.
We can write this as

(x + y)(x  y ) = 1.
Here, if (x + y) becomes larger, (x  y) has to becomes smaller. What does this mean?
Let us start with a circle

x^{2} + y^{2} = 1,
which can also be written as

(x + y)^{2} + (x  y)^{2} = 2.
If (x + y) becomes larger, (x  y) has to becomes smaller, it is an elliptic deformation of the above equation. Thus, the circle is the same as the hyperbola to the extent that the first hypergolic equation leads to an elliptic deformation of the cricle. Click here for a story. What physics can you do with this? Click here.
I am very happy to say that I was able to reach this conclusion based on analytic geometry I learned during my highschool senior year (195354) in Korea.
 Is there a physical application of this topology?
Click here.
Two and Three
However, I am not the first one to see this point. Henri Poincaré was the first one to recognize the significance of this number. I am encouraged, and I have to do some more work to understand my own papers before making a meaningful statement about Poincaré's work on this subject. Please come again.
Conclusion
 Poincaré's DinganSich was mathematics. This is the reason why Bertrand
Russell said Henri Poincaré was the greatest man France had ever produced,
even though he insisted that mathematics does not have its own content. After all,
philosophers are right. Nothing is everything.
Since I have been writing papers for more than fifty years, I am entitled to organize my publications within some framework. It appears that they could fit into Poincaré's world. Thus, Henri Poincaré is my DinganSich.
It is very easy for young physicists to get lost these days. If you think you are lost in physics, find out your own DinganSich. If you thinks you are an established physicist, but you are not sure about whether your work will remain in history, find out what your DinganSich is.
Other Poincaré Papers
 Wigner's Little Groups dictate
internal spacetime symmetries of elementary particles. Wigner's work is based
on the Poincaré group governing both Lorentz transformations and translations.
This group is called the inhomogenous Lorentz group.
 Raymond Poincaré was Henri's
cousin. He was the president of France from 1913 to 1920, covering the period
of World War I. I am not able to write a story about him. Perhaps we can
rely on his
Wikipage.
copyright@2013,2015 by Y. S. Kim, unless otherwise specified.
Click here for his home page.
Why is he with Einstein? 
 Click here for Y.S.Kim's home page.
 His Einstein page.
 His Einstein page.
 His style page.