Physics Talk

Saya Kimura:  https://www.pexels.com/photo/bright-clear-close-up-dark-401107/ 3 x 10 8 ms -1 . This is a value ingrained into the minds of all physicists: the speed of light (to one significant figure). Special relativity reveals that this is the ultimate speed limit of the universe. However, in the past, many believed that light propagates instantaneously. Danish astronomer, Ole Rømer, made the first quantitative measurement of the speed of light in 1676, demonstrating that light travels at a finite speed. The Earth, the Sun and Jupiter Rømer noticed that the distance between the Earth and Jupiter affected the time at which Io, the gas giant’s innermost moon, seemed to emerge. [1] When the Earth is closest to Jupiter in its orbit around the Sun, Io appeared from behind Jupiter earlier than expected. Meanwhile, when Earth was at its farthest point from Jupiter, Io emerged later than expected. [1] Light took longer to travel from Io to the Earth when the distance between the two

Pbroks13 / Public domain; https://commons.wikimedia.org/wiki/File:Doppler_effect.svg ‘It may […] be more than apt to call the Doppler Effect […] the effect of the millennium.’ – Anton Zeilinger, Wolf Prize in Physics recipient and President of the Austrian Academy of Sciences, July 2007. Have you ever noticed how the pitch of a passing ambulance siren seems to change? This is the Doppler effect at work: the observed frequency of a wave depends on the relative motion of the source and detector.   Picture ripples on the surface of a pond after a pebble has been cast, where the circular wavefronts are equally separated. Since a wave’s velocity is determined by the medium through which it propagates, the wavefronts travel at a fixed speed. Now imagine a duck is swimming in the pond. The wavefronts created are no longer evenly spaced because the centre of each new wavefront is slightly displaced in the direction of travel. If it approaches an unmoving swan, from the swan’s perspecti