Einstein time made easy!

QUESTION As a non-physicist, I have a very basic understanding of Einstein’s theories but don’t quite gather how they revolutionised our understanding of the world. How do they affect our everyday lives? EinstEin’s abstract thoughts on light, space and time have led to many innovations.

One such is GPs navigation, enabled by a network of 24 satellites placed into orbit, each carrying a precise atomic clock.

Einstein’s theory of special relativity tells us that moving clocks run more slowly with respect to a stationary observer. this slowing of time becomes more obvious as something approaches the speed of light.

General relativity states that the closer you are to a heavy mass, such as Earth, the slower time will move for you. this means that a clock on a satellite orbiting the Earth, at about one quarter of our gravity, will run faster relative to one on the ground.

GPs satellites travel at about 8,700 mph with respect to Earth. this means time runs 7,200 nanoseconds per day slower for a satellite relative to us on Earth as described by special relativity.

However, using general relativity it is possible to calculate that time goes faster for a GPs satellite by 45,900 nanoseconds a day, as the satellite is 12,000 miles above Earth. this means time runs 38,700 (45,900-7,200) nanoseconds faster a day for a satellite relative to us stationary on Earth.

Relativistic offset in the rates of the satellite clocks is so large that, if left uncompensated, it would cause navigational errors, making the technology useless. T. White, Belfast.

QUESTION Did David Bowie ever visit Somalia, the birthplace of his wife Iman? FURTHER to the earlier answer, David Bowie was at the Mombasa Beach Hotel, Kenya, in 1977.

As a shy 18-year- old, i did not know what to say to him. He played table tennis constantly with his assistant Corinne and no one would have recognised this unkempt man until he spoke.

At one point, his little son Zowie came near and i asked what his name was. He showed me a crayon drawing then ran off.

Gary McBar, Tavistock, Devon.