Distances and Measurement
The universe is really
quite a large place. In
fact, it is so large that it really doesn't make sense to measure it
using familiar units such as inches, feet, or even miles. The problem
with measuring the universe in miles is that the numbers will be so
large, that they just don't make sense to the average
In order to make
distances in the universe more understandable, new units had to be
chosen. Scientists decided to use the speed of light as a way of
measuring the vast distances in the universe. We
know that nothing is faster than the speed at which light is able to
carefully calculating how far light can travel in a second, or a
minute or even a year, we an use those values to measure
The following values
have been established for the speed of light.
- A beam of light
miles, or 300,000 kilometers in one second.
This distance is referred to as one light-second.
- A beam of light
(6 trillion) miles, or 10,000,000,000,000 (10 trillion) kilometers
in one year.
This distance is
called a light year.
- In other words, a
beam of light will travel around
the world about seven times in one second.
That's about 12
million miles a minute!
And that's the fastest speed there is! Nothing
can move faster than light!
(As far as we know!)
Using these values, we
know that our sun is about 8 light minutes or (92,000,000 miles) away
from the Earth. That means that it would take abeam of light coming
from the sun a full eight minutes to reach the Earth.
We also know that the
most distant objects that can be seen from Earth are about 15 billion
(15,000,000,000) light years away! That means that a beam of light
leaving these objects will take about 15 billion years to reach our
Theory of Spacetime
The famous scientist,
Theory of Spacetime based on these facts. His theory states
that "as you look
into space, it's like you're looking back in
time". He knew that
because the universe is so large, it takes a while to get a message,
(or a beam of light) from one place to another. By the time that the
message gets to its destination, it will be "old news". If you look
at our sun for example, which is only 8 light minutes away, the image
that you see is already eight minutes old by the time it arrives
here. When you look at the sun, you're not seeing it as it is
RIGHT NOW, but you're looking at it as it appeared eight
minutes ago. The sun probably isn't going to change much in only
eight minutes, but it might. Things get stranger as you move further
and further from Earth. Let's say that a star is one million light
years from Earth. By the time a beam of light from that star reaches
this wonderful planet, it's already a million years old. That star
might not even exist today. When you look upon that star at night,
you're looking at it as it looked a million years ago. This is
what the theory of spacetime is all about. The stars that you see in
the sky at night might not even be there today. When you look at the
stars at night, you're literally looking into the past. It is also
interesting to consider what a creature on a planet a million or more
light years from Earth would see when he/she/it looks at the Earth.
Would they see the Earth as it is today?