this took place between Steven Weinberg and Philip Anderson. Impossibility of calculation Weinberg points out that calculating the precise motion of an actual projectile in the Earth's atmosphere is impossible. So how can we know we have an adequate theory for describing the motion of projectiles? Weinberg suggests that we know principles (Newton's laws of motion and gravitation) that work "well enough" for simple examples, like the motion of planets in empty space. These principles have worked so well on simple examples that we can be reasonably confident they will work for more complex examples. For example, although general relativity includes equations that do not have exact solutions, it is widely accepted as a valid theory because all of its equations with exact solutions have been experimentally verified. Likewise, a theory of everything must work for a wide range of simple examples in such a way that we can be reasonably confident it will work for every situation in physics. See also Absolute (philosophy) Argument from beauty Attractor Beyond black holes Beyond the standard model cGh physics Chronology of the universe ER=EPR Grand Unified Theory Holographic principle Mathematical beauty Mathematical universe hypothesis Multiverse Penrose interpretation Standard Model (mathematical formulation) Superfluid vacuum theory (SVT) The Theory of Everything (2014 film) Timeline of the Big Bang Zero-energy universe References Bibliography Pais, Abraham (1982) Subtle is the Lord: The Science and the Life of Albert Einstein (Oxford University Press, Oxford, . Ch. 17, Weinberg, Steven (1993) Dreams of a Final Theory: The Search for the Fundamental Laws of Nature, Hutchinson Radius, London, Corey S. Powell Relativity versus quantum mechanics: the battle for the universe, The Guardian (2015) https://www.theguardian.com/news/2015/nov/04/relativity-quantum-mechanics-universe-physicists External links The Elegant Universe, Nova episode about the search for the theory of everything and string theory. Theory of Everything, freeview video by the Vega Science Trust, BBC and Open University. The Theory of Everything: Are we getting closer, or is a final theory of matter and the universe impossible? Debate between John Ellis (physicist), Frank Close and Nicholas Maxwell. Why The World Exists, a discussion between physicist Laura Mersini-Houghton, cosmologist George Francis Rayner Ellis and philosopher David Wallace about dark matter, parallel universes and explaining why these and the present Universe exist. Theories of Everything, BBC Radio 4 discussion with Brian Greene, John Barrow & Val Gibson (In Our Time, Mar. 25, 2004) Physics beyond the Standard Model Theoretical physics Theories of gravity