# Physics: a brief history

Classical physics began in outline with the ancient Greeks, notably Socrates who laid some of the foundations of epistemology, and Aristotle, who developed that area, stated his attempt at a set of laws of motion, and realized that the planet Earth was roughly a sphere, for which he and others calculated its radius. This was not far wrong, given that all they had to work on was the length of the shadow cast by a stick.

The basic study of motion continued about 1800 years later at the Renaissance (hence that name), with Nicolaus Copernicus and Galileo Galilei deducing stuff from astronomy, and seeing planetary positions and movement with the first telescopes.

The laws of motion, still today used for everyday things (just not for cosmology, with huge distances and speeds, or for quantum physics stuff), were set out in Isaac Newton’s great work Philosophiæ Naturalis Principia Mathematica (1687). That created classical mechanics.

Then there were generations of great individuals like Michael Faraday who developed knowledge of electricity in the 19th century, and hence telephone and audio, then light radiation. Then Albert Einstein and also Henri Poincaré (separately!) realized some results about what is known as special relativity, Albert first (1905); but he was never given a Nobel prize for it, which some sources allege was influenced by antisemitic prejudice, and not solely based on lack of empirical proof till too late (after his death in 1955). After special relativity there came general relativity.

The other major new element in the first half of the 20th century was that guys like Werner Heisenberg (1927) discovered an area of the quantum physics level of reality where his uncertainty principle kicks in, which (sadly) Einstein refused to accept — which was the situation until he died.

The problem, which persisted for the rest of the 20th century, was that — as the leading physicists realized — the descriptions of reality that emerged as relativity theory and quantum theory are different: they say different things, and each is used only for describing what happens in suitable contexts. Both are different from the Newtonian description, which is still what is used to describe ordinary, everyday situation (such as if you want to do a calculation about a car driving along a road). The relativity theory version is used for very large distances and high speeds, such as when examining situations with interplanetary or interstellar distances and speeds comparable to the speed of light. Quantum theory is used for measurements and movements of subatomic particles. The search therefore began for what came to be called the Grand Unified Theory or the Theory of Everything. There is something called relativistic quantum mechanics which is reportedly applied to any attempt to achieve such unification.

Physicists working at the frontier of this have struggled with various possible ways to achieve such a unified theory for decades, and various possible strategies and related topics came to the public attention. These include, as two examples, string theory, and black holes.

Some physicists hoped that what was called string theory would produce a unification of theory covering the two extreme domains of reality, and the everyday classic realm as well; however, others disagreed with the belief or hope that it would ever do that.

The concept of entities known as black holes also divided the world of advanced physics. In 1974 Stephen Hawking showed that quantum field theory predicts that black holes should radiate like a black body, with a temperature proportional to the surface gravity of the black hole. He famously proposed something else on this topic, and there arose another famous disagreement that lasted 30 years. Different areas of theory appeared to predict conflicting propositions about black holes, and his suggestion was one idea for addressing that; but other physicists, including his avowed friend Leonard Susskind, disagreed. That was what was known as the black hole information paradox. After 30 years, Hawking appeared and spoke at a conference, apparently offering a solution but in fact conceding the point.

The work goes on; there is still a lot to do in fundamental physics.