- How did Minkowski's geometric language later become foundational to Einstein's general relativity?
General Relativity
Einstein's theory of gravity as spacetime curvature.
- How do Einstein's field equations describe gravity as a property of spacetime rather than a force?
- Why was correctly predicting the advance of Mercury's perihelion such a decisive test for Einstein's theory?
- What role did Eddington's 1919 eclipse expedition play in confirming a theory Einstein had already completed in 1915?
- Why would GPS satellite navigation drift by kilometres a day without correcting for general relativistic effects?
- What did Karl Schwarzschild's exact solution to Einstein's field equations actually describe?
- What is the Schwarzschild radius and why do the equations become singular there?
- How was Schwarzschild able to derive the solution while serving as an artillery officer on the Russian front?
- Why did Eddington need a total solar eclipse to measure the bending of starlight by the Sun's gravity?
- How did the 1.75 arcsecond deflection Einstein predicted differ from the Newtonian expectation, and how was the difference measured?
- Where were the two expedition teams stationed in 1919, and why was having two sites important for the result?
- How did the November 1919 announcement transform Einstein into a global celebrity almost overnight?
- How did extending general relativity to five dimensions cause Maxwell's equations for electromagnetism to fall out naturally?
- Why did Einstein wait two years before presenting Theodor Kaluza's paper to the Prussian Academy?
- Why did Millikan spend years trying to disprove Einstein's photoelectric equation before his own measurements ended up confirming it?
- Why were Einstein's original papers on general relativity so difficult for even professional physicists to work with?
- How did Eddington's 1919 eclipse expedition help confirm general relativity's prediction that light bends around mass?
- What made Eddington's 1923 textbook different from earlier popularizations of relativity?
- How did Einstein extend Bose's statistics from photons to atoms?
- What did Lemaître derive from Einstein's field equations in 1927?
- Why did Einstein add a cosmological constant to his equations, and what did he later call it?
- When did Albert Einstein sign the manifesto relative to his death, and who else signed alongside him?
- What medical condition caused Einstein's death, and why did he refuse surgery that might have extended his life?
- What unified field theory was Einstein still searching for at the end of his life, and why did it elude him?
- How was the Mössbauer effect sensitive enough to detect the gravitational redshift predicted by general relativity using a source moved only a few feet?
- Why did the Schwarzschild metric fail to describe most real astrophysical objects?
- What made finding an exact solution for a rotating mass so difficult for four and a half decades?
- What is the ergosphere, and what does the Kerr metric say can be extracted from it?
- How is the Kerr metric still used in modern black hole observations like the Event Horizon Telescope?
- What 1917 observation by Einstein made the maser theoretically possible three decades before it was built?
- What did Einstein, Podolsky, and Rosen argue in 1935 about hidden variables and quantum mechanics?
- Why can't X-rays be focused with conventional mirrors, and how did grazing-angle mirrors solve the problem?
- What new kinds of astronomical objects did the Einstein Observatory reveal that earlier X-ray detectors could not?
- Why does a shrinking orbital period between two neutron stars count as evidence for gravitational waves?
- How closely did the observed decay of PSR B1913+16's orbit match Einstein's prediction?
- What job was Einstein working when he wrote these four papers, and how did his employer regard him at the time?
- What rare planetary alignment made Voyager 1's grand tour of the outer planets possible?
- Why did Einstein himself doubt gravitational waves could ever be observed?
- Why did Einstein doubt that gravitational waves could ever be detected?
- How long after Einstein's general relativity predicted black holes did it take to produce an actual image of one?
- What did Roger Penrose prove in 1965 about black holes that even Einstein had doubted?