William Thomson declared the end of the development of physics, but the 20th century saw the emergence of elementary particle research and quantum mechanics, which overcame the limitations of classical physics. Modern physics still has many limitations, and we are far from being able to fully explain the world.
In 1900, the British physicist William Thomson declared at the British Association for the Advancement of Science “There is now no possibility of new discoveries in physics. By the end of the 19th century, physicists believed that the logical system of physics, or classical physics, was complete and that all that remained was to increase the precision of observations and calculations. However, in the 20th century and beyond, as technology and scholarship advanced, physicists conducted experiments involving elementary particles, and when they tried to explain the results of these experiments using Newton’s classical system, contradictions arose. The need for a new mechanics began to emerge.
Finally, in December 1900, Max Planck solved the problem of ultraviolet breakdown in an attempt to explain blackbody radiation by departing from the classical framework of energy as continuous and thinking of energy as small chunks with distinct values. In 1905, Einstein pointed out the compatibility of the atomic theory, which states that all matter has a minimum unit, and Maxwell’s electromagnetic theory, which describes radiated waves, and identified the photoelectric effect through the photon theory, which states that the energy of light is proportional to an integer multiple of its frequency, marking the beginning of quantum mechanics.
Later, through De Broglie’s wave hypothesis of matter and Niels Bohr’s model of the hydrogen atom, Schrödinger derived the Schrödinger equation from the wave function of classical mechanics. In 1927, Bohr, Schrödinger, and Heisenberg gathered in Copenhagen to present the Copenhagen interpretation of the meaning of the wavefunction based on the principle of complementarity and the principle of indeterminacy. Shortly after its publication, the interpretation faced numerous objections and paradoxes from scientists, including Einstein’s thought experiment with a photon box, Schrödinger’s cat, and the EPR paradox, but it eventually succeeded in explaining them all adequately and remains the most widely accepted interpretation to this day.
Based on the Copenhagen interpretation of quantum mechanics, physicists studied various quantum theories (quantum field theory, quantum color theory, etc.) and established the theoretical framework of the Standard Model, which describes the particles that make up matter and the interactions between them. In addition, several fundamental particles predicted to exist in this model were actually confirmed by experiments using particle accelerators from the mid-1900s to the present, and the discovery of the Higgs boson, the last remaining particle, in 2013 completed the Standard Model, a theory that describes the fundamental particles of nature and their interactions except for gravity. This is one of the greatest achievements of modern physics, as it has helped mankind overcome the limitations of classical physics, and has helped explain many microscopic phenomena that classical physics could never explain.
However, we are still far from being able to fully explain our world. This is because even the Standard Model has many limitations.
Unlike the weak and electromagnetic forces, which can be combined into the electromagnetic weak force under certain circumstances, such as high temperatures, the strong force is a completely separate interaction from the other forces in the Standard Model. Many complementary theories have yet to be experimentally verified. Even the graviton, the expected particle that mediates gravity, is not included in the Standard Model at all. Gravity is a force that we feel as intimately as electromagnetism, and yet the inability of the Standard Model, the most complete and experimentally verified of the many theories that humans have created to explain our world, to account for it, suggests that we do not have a sufficient theoretical background to understand the physics of the microscopic world. Quantum gravity theories, which introduce gravitons as gravitational mediators along with a quantum field theory of gravity to describe gravity quantum mechanically, have also so far proven impossible to renormalize. Mankind’s dream of a complete description of the universe’s three-dimensional landscape has been thwarted by the first interaction discovered: gravity.
In addition, the Standard Model has too many particles and too many constants – as many as 20. There are 18 types of quarks alone, with six flavors and three colors, and 24 types of fermionic particles in nature, including electrons, muons, tau particles, and their counterparts, the neutrinos. In addition, every particle has an antiparticle partner, so there are 48 different types of fermions, and 61 types of particles in the Standard Model, including photons, W+, W-, Z0, gluons, and the Higgs boson, which gives mass to the fundamental particles. But that’s a lot of elementary particles, and why they have specific numbers and generations, why the values of the 20 constants have specific values, and how they relate to each other are not predicted by theory and can only be determined by experiment. The standard model cannot even explain why the values of the important constants should have the specific values they do.
Another reason is that the various theories that have been proposed to address these limitations of the standard model have their own major and minor problems, and experiments to verify whether they are correct or incorrect are not possible with current technology. The most promising candidate to date, which is expected to solve the limitations of the Standard Model and become the Theory Of Everything (TOE), is superstring theory, which solves the problems of point particle theory by thinking of elementary particles as one-dimensional strings. However, American mathematician and theoretical physicist Peter Woit argues in his book The Truth About Superstring Theory that it has never made any concrete experimental predictions, does not explain any phenomena on the macroscopic scale, and is merely a collection of unrealized wishful thinking.
For one thing, discovering and experimentally proving the particles predicted by superstring theory would require astronomical amounts of energy – between 100 billion and 10 trillion times the power of the LHC, the world’s largest particle accelerator – and a particle accelerator capable of producing such power would be about the size of the solar system, making a number of assumptions that are impossible to verify in practice. In addition, the background theories needed to advance the study of superstring theory are so lacking that it is still not possible to even begin to study it properly. In extreme cases, it is even treated as a pseudoscience.
The Standard Model is a theory that describes the interactions of all particles almost perfectly, and was considered the golden tower of human intellect along with general relativity, and is still the most accurate description of real-world physical phenomena among experimentally verified theories. However, even the Standard Model suffers from the same problems as the above, and as a result, it remains an incomplete theory, and even the various theories that compensate for the deficiencies of the Standard Model are currently impossible to test. Therefore, the day when humanity can explain the world perfectly is still far away.
