By the end of the 19th century, our knowledge of the structure of matter looked more or less complete – so much so that smart people were actually discouraged from joining this dead field of theoretical physics. 실제로, there were some loose ends – like radioactivity, subatomic structure etc., but they were expected to be minor extensions of the theories that enjoyed currency at that point in time.
Before getting into modern physics, and why it was needed, we need to set the boundaries of what classical physics is. It is the physics of things we can see or imagine. It describes and (even explains in terms of simple or general laws) the behavior of this of human scale. The term “human scale” is vague and deeply unscientific, but it is a fairly generous bracket of lengths, speeds and masses. It will easily encompass anything from a microbe to a planet in size (from microns to thousands of km in length). The bracket in speed will easily include the fastest object we are likely to encounter, such as the fastest meteorite that was clocked at over 100,000 km/h. 물론, I am ignoring the particles (and light itself) that we are bombarded with all the time – classical physics cannot handle those. But it can handle even the largest object, like our planets and even the sun, very nicely.
사실, classical physics has been spectacular in describing almost everything we knew until the turn of the 20th century. It includes everything that you learned in physics through high school.
Heat, optics, 소리, waves etc.
Radioactivity, 알파, 베타, gamma radiations, x-rays.
그림에서 4, I have drawn a pictorial representation of what kind of physics we need to apply when we go beyond human scales. On the x-axis we have size or scale, on the y-axis, the speed.
일반 상대성, Quantum Gravity, string theory etc. are not needed to appreciate our current state of knowledge of particle physics. But I will touch upon those monsters as well, for the sake of completeness.