The 2017 Nobel Prize in Physics "for decisive contributions to the LIGO detector and the observation of gravitational waves" Peter Berg Department of Science University of Alberta www.peterberg.net Source: https://www.mpg.de/11646260/neutron-star-merger-gravitational-waves

Gravitational waves: Three ingredients Clocks can tick at different rates (time is relative) Gravitational fields can warp space (space is relative) Accelerating masses keep changing space-time How? https://physics.aps.org/articles/v9/17

We observe time dilation! Time is relative The speed of light, c, is constant. It has the same value in all reference frames. We observe time dilation! https://physics.aps.org/articles/v9/17

https://physics.aps.org/articles/v9/17 Warping space Gedankenexperiment #1: Equivalence Principle https://faraday.physics.utoronto.ca/PVB/Key/relgen.htm https://claesjohnsonmathscience.wordpress.com/2012/01/17/questioning-relativity-3-the-equivalence-principle/ The accelerated observer, or equivalently an observer in a gravitational field, observes bent light trajectories! https://physics.aps.org/articles/v9/17

Time in a gravitational field Gedankenexperiment #2: Free fall in a gravitational field https://faraday.physics.utoronto.ca/PVB/Harrison/GenRel/TimeDilation.html We observe different time dilation in a gravitational field! https://physics.aps.org/articles/v9/17

Einstein’s field equations of general relativity “Simple” concept: mass-momentum distribution determines space-time: Equations have “just” the right (relativistic) form! Everything moves according to a minimization principle ⇒ new distribution of matter ⇒ new space-time metric And so forth… Above equations allow for gravitational waves, moving at speed of light & produced by accelerated masses, similar to electro-magnetic waves, moving at c & produced by accelerating charges. Causing minuscule changes in distance of objects (𝟏 in 𝟏𝟎 𝟐𝟐 ) Einstein: “This can never be measured!” https://physics.aps.org/articles/v9/17

Physics Nobel Prize Winners 2017 Reiner Weiss (*1932, Berlin, Germany) PhD from MIT LIGO/VIRGO Collaboration, MIT interferometer, noise reduction, data collection (1/2) Barry Barish (*1936, Omaha, USA) PhD from University of California, Berkeley LIGO/VIRGO Collaboration, Caltech PI & Director, LIGO (Hanford, WA; Livingston, LA); LIGO collaboration (1/4) Kip Thorne (*1940, Logan, USA) PhD from Princeton University LIGO/VIRGO Collaboration, Caltech prediction of signature; wormholes & time travel; Interstellar (1/4) https://www.nobelprize.org/ https://physics.aps.org/articles/v9/17

LIGO: Observing gravitational waves Tiny effect amidst a lot of noise ⇒ gigantic interferometer! Laser Interferometer Gravitational- wave Observatory https://physics.aps.org/articles/v9/17

What was observed first? 14 Sep 2015: (5x by now) Two black holes merging (predicted theoretically) 1.3 billion years ago. Happens very quickly (0.1s). Correlation between several interferometers. https://physics.aps.org/articles/v9/17

What was observed first? . https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/advanced-physicsprize2017.pdf https://physics.aps.org/articles/v9/17

What is so special about this? Gravitational waves pass through all matter, electro-magnetic waves do not. ⇒ Looking deeper into space, i.e. further back in time (closer to Big Bang), then currently possible (Cosmic Microwave Background Radiation; 𝑡=380,000 years) Proof of existence of black holes Study new dynamics https://physics.aps.org/articles/v9/17

What is so special about this? . https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/advanced-physicsprize2017.pdf https://physics.aps.org/articles/v9/17

Observing gravitational waves: The future Besides several current interferometers (2x USA, 1x Germany, 1x Italy), there is space: LISA And then there is the Warp Drive… https://en.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna https://physics.aps.org/articles/v9/17