Since Aristotle finished his book, Physics, it has already passed more than 2000 years. There are 3 ages in the?2000 years. In the same time, they belong to 3 special “creature” of physics. The first age, maybe we can call it, the Aristotle’s age, and it represent a long speculation time. I think the Zeno’s Tortoise is more likely the totem in that time. But that age is finished by Galileo. Than comes the second, the classical physics age. Based on Newton’s 3 lows of dynamics, we arrived at homeland of “Laplace’s demon”, a determinism area. But now, we are in the third, the modern physics age, it’s under the rule of Schr?dinger’s cat. This mysterious cat is still walking on this world step by step, and left a string footprints since 1900 to now. those footprints are the confusing puzzles. The history of solving those puzzles is also the history of modern physics. And there are so many puzzles significant, so I only write some interesting briefly in this article.

Two clusters above the physics field in 1900

Michelson Morley experiment and Black body radiation explanation, the two famous “clusters”, one is for proving the existence of “ether”, and the another is defensing the “ridiculous” quantization of energy. And the ether represents an absolute reference frame, both of them are failed. We have to accepted that the speed of light is invariant and the energy is quantized in micro field. That is means the classical physics is not perfect. The fact of experiment will not cheat people, those “clusters” give the birth of relativity and quantum mechanics, the two pillars of modern physics.

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Does God play dice? The birth of the very “cat”.

After learning the quantum mechanics, we always confused by superposition state and uncertainty principle. It is incredible in classical physics. Everything appears by probability. Just like the Schr?dinger’s cat, it is horrible observation can determine the cat’s life. No wonder Einstein doubt that the God don’t play dice. And the more incredible thing is the uncertainty principle,?, and it is completely comes from theoretical result. It shows that, in the limit when either??or??is completely determined, the other is completely undetermined. Both of them show a confusing world of probability. And the birth of quantum mechanics time is the gold time of modern physics. Lots of subjects likes condensed matter physics can back to this famous equation, the Schr?dinger equation.

“Aesthetics” of equations?

Science is very different from art, but I am very convinced about the “aesthetics” of equations. I mean, the beautiful equations always have some “metaphysical characters”, like symmetry, brevity or concordance. Such like the Maxwell equations under the Canonical quantization.

□Aμ=0

That equations is much brief and unified than the 4 equations which we all know. I believe a successful theory must include everything in one brief sentences. Let’s back to see the Schr?dinger equation, it seem not symmetrical in time and space, one order differential set at time term, but two order at space. Here comes the Dirac equation γ·pψ=0. Dirac equation predicted the anti-particles and negative energy. Now, we realized the vacuum does not mean nothing, there still many particle and anti-particle pairs here. Base on Dirac equation, we open the gate of quantum electrodynamics and QED.?

It seems we can describe the electromagnetic interaction very well here. But we still have a big question. That is:?↓

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How can we hold the protons and neutrons together?

Why the protons and neutrons can bind together, or not divided by the electromagnetic force? Now, we know the answer is the strong interaction. In the early time before the quark model, is Yang-Mills Theory. Then goes to the gauge theory, quark model and QCD. Finally, the stand model, with 3 generations quark and 3 generations lepton to contribute the matter, and 4 kinds boson to deliver the interactions. But we still need a particle to coupling with other particles to explain the region of mass. That is Higgs boson. For a long time, we were searching the Higgs, until the CERN announce they found. Now, the stand model seem prefect, because we can explain everything except the gravity. How to unify the gravity to 3 others? That is another big theory, because Einstein say only the distortion of space-time by General Relativity.

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Beyond Stand Model?

Neutrino oscillation, neutrino mass?

According to the stand model, the neutrinos is massless particles. But Super-K observed ?can oscillate to ?in 1998. That is the evidence of neutrinos have mass, although it is very small. And we also know that , ?and ?are the superposition state.

X17, the fifth interaction, dark matter?

It is the recent thing that we find a new particle with mass in 17 GeV in ?decay. It has been proved as a boson. That might mean the fifth interactions. Because the interaction always mediated?by the gauge boson. But there is no place in the stand model particle table for X17.

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There still lots of puzzles in modern physics, like the asymmetry of matter and anti-matter, the cosmic acceleration, the great attractor, CMB, primary gravitational wave…it is that puzzles that push our big ship of civilization forward in the universe. Maybe the ghost like cat will fall down someday, and that will be a new age of physics. But that “footprints” will print for long in the history.