Thermodynamics is a branch of physics that studies the movement of energy and how energy instills movement. More precisely, it studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. 19th century physicists defined three Laws of thermodynamics to sum up the basic principles of the subject; in the 20th century, an unofficial "zeroth law" was added.

Sourced

• Isn’t thermodynamics considered a fine intellectual structure, bequeathed by past decades, whose every subtlety only experts in the art of handling Hamiltonians would be able to appreciate?
  • Pierre Perrot, "A to Z Dictionary of Thermodynamics"

• Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by that time you are so used to it, it doesn't bother you any more.
  • Arnold Sommerfeld

• Nothing in life is certain except death, taxes and the second law of thermodynamics. All three are processes in which useful or accessible forms of some quantity, such as energy or money, are transformed into useless, inaccessible forms of the same quantity. That is not to say that these three processes don't have fringe benefits: taxes pay for roads and schools; the second law of thermodynamics drives cars, computers and metabolism; and death, at the very least, opens up tenured faculty positions.
  • Seth Lloyd, writing in Nature 430, 971 (26 August 2004); doi:10.1038/430971a

• If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
  • Sir Arthur Stanley Eddington, The Nature of the Physical World (1915), chapter 4

• A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative.
  • C. P. Snow, 1959 Rede Lecture entitled "The Two Cultures and the Scientific Revolution".

• The second law of thermodynamics is, without a doubt, one of the most perfect laws in physics. Any reproducible violation of it, however small, would bring the discoverer great riches as well as a trip to Stockholm. The world’s energy problems would be solved at one stroke. It is not possible to find any other law (except, perhaps, for super selection rules such as charge conservation) for which a proposed violation would bring more skepticism than this one. Not even Maxwell’s laws of electricity or Newton’s law of gravitation are so sacrosanct, for each has measurable corrections coming from quantum effects or general relativity. The law has caught the attention of poets and philosophers and has been called the greatest scientific achievement of the nineteenth century. Engels disliked it, for it supported opposition to Dialectical Materialism, while Pope Pius XII regarded it as proving the existence of a higher being.
  • Ivan P. Bazarov, "Thermodynamics" (1964)

• A theory is the more impressive the greater the simplicity of its premises, the more different kinds of things it relates, and the more extended its area of applicability. Therefore the deep impression that classical thermodynamics made upon me. It is the only physical theory of universal content which I am convinced will never be overthrown, within the framework of applicability of its basic concepts.
  • Albert Einstein (author), Paul Arthur, Schilpp (editor). Autobiographical Notes. A Centennial Edition. Open Court Publishing Company. 1979. p. 31 [As quoted by Don Howard, John Stachel. Einstein: The Formative Years, 1879-1909 (Einstein Studies, vol. 8). Birkhäuser Boston. 2000. p. 1]

Unsourced

• Every mathematician knows it is impossible to understand an elementary course in thermodynamics.
  • V.I. Arnold

Humor

• In this house, we obey the laws of thermodynamics!
  • Homer Simpson, after Lisa constructs a perpetual motion machine whose energy increases with time, in The Simpsons.

• S happens.
  • Bumper sticker on the second law of thermodynamics.

• How does bear know about thermodynamics?
  • Image macro showing a bear eating apples, after one showing a bear trying to get at apples frozen in ice.

• Zeroth: You must play the game.
  First: You can't win.
  Second: You can't break even.
  Third: You can't quit the game.
  • A common scientific joke expressing the laws of thermodynamics.
    • Variant:

      You can't win; you can only break even.
      You can only break even at absolute zero.
      You can't reach absolute zero.

    • Another variant:

      Zeroth: You must play the game.
      First: You can't win.
      Second: You can't break even, except on a very cold day.
      Third: It doesn't get that cold.

    • Yet another variant:

      Zeroth: There is a game.
      First: You can't win.
      Second: You must lose.
      Third: You can't quit.

    • An old US undergraduate version of the previous variant concludes:

      Second: You can't break even – except at absolute zero.
      Third: You can't get to absolute zero.

• It’s the Second Law of Thermodynamics: Sooner or later everything turns to shit.
  • Woody Allen, in Husbands and wives (1992).

• Murphy's Law about Thermodynamics: Things get worse under pressure.

• If you think things are in a mess now, JUST WAIT! (unknown)

Other

• A common scientific joke, as stated by C. P. Snow, expresses the four laws simply and surprisingly accurately as:

Zeroth: "You must play the game."

First: "You can't win."

Second: "You can't break even."

Third: "You can't quit the game."

• The parody rapper MC Hawking makes several references to the Second Law in his songs, usually in references to creationist claims about the Second Law. In his song "Entropy", he makes a reference to the C.P. Snow joke above: "You can't win, you can't break even, you can't leave the game".

• "Old Chemists never die: they reach thermodynamical equilibrium" (unknown).