The cosmic view of albert einstein
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So if you imagined the extreme situation of a black hole, then light would be reduced to zero speed, apparently, and time would apparently have been stopped completely at the surface. Gravity has the apparent effect of reducing the speed of light and slowing down time.
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Perhaps the most useful thing I ever did as a science writer was to persuade the distinguished Oxford theorist Roger Penrose to own up to all this, on prime-time television. The velocity of light measured locally never changes, but it can certainly appear to do so for a distant onlooker. Why? Because time passes more slowly in the Sun’s strong gravity than it does for radar physicists on the less massive Earth.
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The radio waves, an invisible form of light travelling in the near-vacuum of interplanetary space, slowed down as they grazed the Sun and felt its gravity.įor atoms in the Sun’s atmosphere the radio waves still seemed to be travelling at the correct speed. “ The velocity of light never varies” became a mantra of the theorists dealing with GR and its inscrutable mathematics, to make clear what was necessary to keep the cosmos safe.īut in the late 1960s radar experiments by Irwin Shapiro of MIT showed that radio pulses going to and from Venus or Mercury were delayed when those planets were passing across the far side of the Sun. The theory’s beauty is that it saves the Universe from the mayhem that would result if the speed of light in empty space were able to change – for a start, atoms would behave differently. Specially made for the programme and flown out from London was a billiard table configured so that a ball representing a planet could orbit in the warped space around the Sun, or fall into a black hole. This was the actor Peter Ustinov, who also spoke Einstein’s own words and twice acted the part of a time traveller. Months of fun followed, in the course of which Martin Freeth, producer-director for the BBC, borrowed the McDonald Observatory in Texas and brought to it the eminent physicists and astronomers who were to explain Einstein’s ideas to a genuine layman. Filming for “Einstein's Universe”: Sidney Drell, John Archibald Wheeler and Peter Ustinov, with a younger Nigel Calder.