Rel­a­tiv­ity in five steps

Focus-Science and Technology - - Guide to the Cosmos -


The speed of light as it moves through empty space is the same for ev­ery­one, which means it would be im­pos­si­ble to catch up with a beam of light, no mat­ter how fast you might, hy­po­thet­i­cally, be trav­el­ling.


It’s also im­pos­si­ble to tell the dif­fer­ence be­tween mov­ing uni­formly and not mov­ing at all – this is known as the prin­ci­ple of rel­a­tiv­ity. Ein­stein’s prin­ci­ple was pre- empted by Galileo in the 17th Cen­tury.


From these two ideas, Ein­stein con­cluded that time and dis­tance are not con­stants: mov­ing clocks run slow, mov­ing rulers shrink. So some­one zip­ping around in a space­ship will age slower than some­one on Earth.


Grav­ity also af­fects the pas­sage of time. Clocks slow down un­der the in­flu­ence of grav­ity so, for ex­am­ple, clocks tick faster at the top of Mount Ever­est. This is a key re­sult of Ein­stein’s Gen­eral The­ory of Rel­a­tiv­ity.


Space and time are not fixed – they are mal­leable and sub­jec­tive, and to­gether they form a uni­ver­sal, four- di­men­sional fab­ric called space-time. This idea is cen­tral to physics.

ABOVE: Jo­drell Bank’s Lovell Tele­scope played a part in con­firm­ing the ex­is­tence of grav­i­ta­tional waves, and so con­firm­ing Ein­stein’s the­o­ries

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