A material called spacetime

A material called spacetime Ralf Greve Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan Credit: bornscientist.com Ralf Greve: A material called spacetime 2/21 The classical concept of space and time Space: Empty space = three-dimensional “nothing”, but can be filled with matter. Time: Describes the continued progress of existence and events. Exists independently of anything else. Progresses uniformly from –∞to +∞. Ralf Greve: A material called spacetime 3/21 Concept of absolute space and time works well in everyday life Newtonian mechanics in general, celestial mechanics, continuum mechanics… Ralf Greve: A material called spacetime 4/21 Galilei transformation Credit: User:Krea @ Wikimedia Commons Frames of reference: Transformation equations for any point (“event”) P: Ralf Greve: A material called spacetime 5/21 The nature of light Particle theory vs. wave theory: Wave theory triumphs: Young, Fresnel (early 19th century): Newton’s rings, double-slit experiments → interference! Light is a transverse wave. Credit: www.olympus-lifescience.com Credit: U. Seifert @ Wikimedia Commons Ralf Greve: A material called spacetime 6/21 Aether Waves need a medium for propagation → “aether”: Filling entire space. Invisible, massless, no viscosity. Much more rigid than steel to support the high frequencies (4–8 ×1014 Hz !) of light waves. ????? ? Ralf Greve: A material called spacetime 7/21 Electromagnetic theory Faraday, Maxwell (mid-19th century): Light is an electromagnetic wave. Doesn’t need a mechanical medium, propagates through empty space. Credit: E. Boutet @ Wikimedia Commons Ralf Greve: A material called spacetime 8/21 Maxwell’s (macroscopic) equations Gauss’s law: Gauss’s law for magnetism: Faraday’s law of induction: Ampère’s law: E: electric field D: electric displacement field ρf: free charge density B: magnetic B-field (flux density) H: magnetic H-field Jf: free current density Ralf Greve: A material called spacetime 9/21 Closure requires constitutive equations In vacuum (= empty space): ε0: permittivity of free space μ0: permeability of free space → Wave equations: c: speed of light in free space (c= 299,792,458 m/s) Ralf Greve: A material called spacetime 16/21 Indirect detection of gravitational waves Hulse–Taylor binary Binary pulsar, discovered in 1974. Gradual decay of its 7.75-hour orbit due to radiation of gravitational waves (power ~ 7 × 1024 W). (Solar system only ~ 5 kW) 1993 Nobel Prize in Physics Credit: Shane L. Larson, NASA/GSFC Ralf Greve: A material called spacetime 17/21 Direct detection of gravitational waves Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) – 2 observatories in the US LIGO Livingston (LA) Observatory. Credit: www.ligo.caltech.edu Ralf Greve: A material called spacetime 18/21 Direct detection of gravitational waves Ralf Greve: A material called spacetime 19/21 Direct detection of gravitational waves 20xx Nobel Prize in Physics ? Ralf Greve: A material called spacetime 20/21 Summary Spacetime itself can be considered a material: physical properties, constitutive equations. Alternative interpretation: spacetime = aether. Open questions, speculations Physics of black holes & Big Bang: General relativity + quantum mechanics. Other spacetimes (or something completely different)? Thank you THANK YOU Credit: dansalisbury.com