Relativity of time - Topics

The Andromeda paradox: two walkers passing each other disagree about whether a fleet has already launched Michelson and Morley found nothing in 1887 and that null result became physics' most useful measurement Light cones: why saying now about Alpha Centauri is a convention and not a fact The twin paradox: the traveller really is younger and acceleration is what breaks the symmetry The train and the two lightning strikes: how Einstein's 1905 thought experiment killed absolute simultaneity Hafele and Keating flew caesium clocks around the world in 1971 and the two directions were wrong in opposite ways The speed of light is not really about light: it is the exchange rate between space and time Two observers disagree about distance and duration but always agree on the spacetime interval Gravity Probe B's gyroscopes and the dragging of spacetime by a rotating Earth Why length contraction is a convention about simultaneity and not a physical squash Why one-way light signals cannot synchronise two clocks without a convention Proper time is the only time your body actually experiences Rossi and Hall in 1941: cosmic-ray muons reach sea level because their lifetime stretches Why free fall and weightlessness are locally indistinguishable and what that does to clocks Distant Type Ia supernovae run slow by exactly their redshift factor GPS satellites gain about 38 microseconds a day: uncorrected that is 10 kilometres of drift NIST raised an optical clock by 33 centimetres and it measurably ticked faster Interstellar's Miller planet: does one hour near a black hole really cost seven years? What you see through a telescope is not what remains after correcting for light travel Minkowski in 1908: space by itself and time by itself are doomed to fade into mere shadows Muons in a storage ring live about 29 times longer than their 2.2 microsecond lifetime Does modern physics still support one universal line that everyone shares Scott Kelly came home 5 milliseconds younger than his twin brother How far apart can two nows be before they stop being the same moment? Presentism has no observer-independent now to hang on once relativity is in play How much younger would you be after a round trip to Proxima Centauri at 0.9c? In special relativity a cause can be simultaneous with its effect for some observers Godel's 1949 rotating universe contains closed timelike curves Forward time travel is settled physics and muons already prove it Does the present exist for a photon travelling at light speed?