have used many devices to
measure time. The sundial
was one of the earliest
dispositivos; sundial: reloj de sol; earliest: más
A sundial measures the movement of the sun
across the sky each day.
It has a stick or other
object that rises above a
flat surface. The stick,
blocking sunlight, creates a
shadow. As the sun
moves, so does the shadow of the stick across the flat surface. Marks on
the surface show the passing of hours, and
perhaps, minutes. The
sundial works well only
when the sun is shining.
So, other ways were invented to measure the passing of time.
a través de; stick: vara; rises above: se eleva sobre;
flat surface: superficie plana; shadow: sombra; as: a
medida que; perhaps: tal vez, quizás; works well: funciona
bien; shining: brillando;
One device is the hourglass.
It uses a thin stream of
falling sand to measure
time. The hourglass is shaped
like the number eight –
wide at the top and bottom, but very thin in the middle. In a
true "hour" glass, it takes exactly one hour for all the sand
to drop from the top to
the bottom through a very
small opening in the middle. When the hourglass
is turned with the upside down,
it begins to mark the passing of another hour.
reloj de arena; thin stream: flujo fino; falling sand:
arena en caída; is shaped like: tiene la forma de; wide:
ancho; to drop: caer; through: a través de; is turned
with the upside down: se lo da vuelta;
By the eighteenth century, people
had developed mechanical
clocks and watches. And today, many of our clocks and watches are
electronic. So, we have devices to mark the passing of time. But what
time is it now? Clocks in different parts of the world do not show
the same time at the same
time. This is because time on Earth is
set by the sun's position
in the sky above.
developed: había desarrollado; the same: la misma; set by:
We all have a twelve o'clock
noon each day. Noon is the time the sun is highest in the sky.
But when it is twelve o'clock noon where I am, it may be ten o'clock at
night where you are.
As international communications and travel
became clear that it
would be necessary to establish a common time for all parts of the world.
se incrementó; became clear: fue evidente;
In 1884, an international conference divided the world into twenty-four
time areas, or zones. Each zone represents one hour. The astronomical
observatory in Greenwich, England, was
chosen as the
starting point for the
time zones. Twelve zones are west of Greenwich. Twelve are east.
elegido; starting point: punto de partida;
The time at Greenwich – as measured by the sun – is called Universal
Time. For many years it was called Greenwich
Some scientists say time is governed by the movement of
matter in our universe.
They say time flows forward
because the universe is expanding. Some say it will stop expanding some
day and will begin to move in the opposite direction,
to grow smaller. Some
believe time will also begin to flow in the opposite direction – from
the future to the past. Can time move
materia; flows forward: fluye hacia adelante; to grow smaller:
para encogerse; backward: hacia atrás;
Most people have no trouble
agreeing that time moves forward. We see people born and then grow old.
We remember the past, but we do not know the future. We know a film is
moving forward if it shows a glass falling off a table and breaking into
many pieces. If the film were moving backward, the pieces would
re-join to form a glass
and jump back up onto the
table. No one has ever seen
this happen. Except in a film.
problema, inconveniente (en); re-join: reagruparse; jump back
up: saltar hacia atrás; has ever seen: ha visto jamás (que);
Some scientists believe there is one reason why time only moves forward.
It is a well-known
scientific law – the second law of thermodynamics. That law says
disorder increases with time. In
fact, there are more conditions of disorder than of order.
famosa, bien conocida; in fact: en realidad;
For example, there are many ways
a glass can break into pieces. That is disorder. But there is only one
way the broken pieces can be organized to make a glass. That is order.
If time moved backward, the broken pieces
could come together in a
great many ways. Only one of these many ways,
however, would re-form
the glass. It is almost
impossible to believe this would happen.
many ways: existen muchas maneras (en las que); could come
together: podrían unirse; however: sin embargo; almost:
Not all scientists believe time is governed by the second law of
thermodynamics. They do not agree that time
must always move forward.
The debate will continue about the nature of time. And time
will remain a mystery.
must: debe; will remain: continuará siendo
Our program was written by Marilyn Christiano and read by Sarah Long and
Bob Doughty. I'm Steve Ember. Listen again next week for "Science in the
News" in VOA Special English.