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FIND OUT MORE. Light 178–179 • Quantum Theory 159 • Space 10 • Universe 26

158 Science and Technology

HOW DO WE MEASURE TIME?

The steady ticking of a clock marks the passing

of time. An accurate clock is controlled by

something that repeats at a precise, unchanging

interval. Early clocks were set by the swing of

a pendulum. Modern clocks are set by the

vibrations of a quartz crystal.

DOES TIME BEGIN AND END?

Time began when the Universe was created

in the Big Bang about 14 billion years ago.

The Universe is currently expanding. Scientists are

not sure if the Universe will expand forever, so that

time never ends, or if it will collapse in a “Big

Crunch”, stopping time for good.

HOW DOES RELATIVITY WORK?

If a person watches two identical clocks, one

stationary and one travelling at high speed, the

moving clock ticks more slowly. To another person

travelling with the moving clock, the other clock

appears to be moving, and ticking, more slowly.

Einstein’s theory of relativity states that

time is not the same for everyone. Time

passes more slowly if you are travelling

very fast, almost at the speed of light.

4 SHORTCUT THROUGH SPACE AND TIME

Scientists have shown that, in theory, two distant parts of the Universe

could be linked by a tunnel through space and time called a wormhole.

A wormhole might work as a time machine. By making a return journey

through the tunnel you could arrive home before you left.

1 ATOMIC CLOCK, USA

This accurate clock uses the

regular vibrations of caesium

atoms to measure time. It is so

accurate, it will be less than three

seconds out in a million years.

RELATIVITY

1 RADAR

A radar system locates

ships in space and time.

Using radars helps to

prevent collisions in

busy shipping lanes.

Co-ordinates

locate the

object’s

position at a

given time Coastline

Harbour

where the ship

is docked

Time

We use time to say when an event happened or how

long it lasted. Time seems to pass at the same rate for

everyone, but Einstein’s theory of. RELATIVITY shows

that time is not constant throughout the Universe.

ALBERT EINSTEIN

German, 1879–1955

Albert Einstein did not do

very well at school, but was

fascinated by mathematics

and science. The Special

Theory of Relativity (1905),

the General Theory of

Relativity (1916), and his work

on the quantum theory of

light established him as one

of the most original and

creative thinkers of all time.

He was awarded the Nobel

Prize for Physics in 1921.

time