today think that our universe is somewhere between 12 and 15
billion years old. The Big Bang Theory says
that, in a tiny part of a second,
all the matter in the universe came into being. This matter was
so hot that there were no atoms -- just a great, cloud
of very hot plasma that was expanding at incredible speeds. In
less than two minutes this plasma cooled down to a billion degrees,
and the atoms of the lightest elements, hydrogen and helium,
began to form. The matter continued to expand, and is still expanding
today. As the plasma continued to cool, stars and
We cannot even begin to imagine
the size of the universe. Objects in the universe are separated
by huge stretches of essentially empty space.
Scientists wonder if
the universe is
infinite, which means
that there would be no
limit to its size.
telescopes have found
no end to the stars,
or the huge flocks of
stars that we call
In space, distances
are measured in light years -- the distance that light in
space can travel in a year. Light travels at 186,000 miles a
second. It takes light a little over 8 minutes to reach us from
our sun. It takes light from our sun more than four years
to reach the nearest star, Proxima Centauri.
Scientists think that the universe
is governed by the same natural laws everywhere. There is gravity
everywhere, and it works in the same way. The structure of the
atoms of elements is the same everywhere. Light travels at the
same speed under the same conditions everywhere. This means that
your world, no matter where it is located, will obey the same
laws of physics and chemistry as the earth.
One of the questions that interests
me is whether, just as there are physical and chemical laws,
there are also universal biological laws. We cannot know this
by studying a single planet, but we can think about it.
Now, let's start thinking about how your planet took form.
Though stars, planets, comets,
and moons engage our attention, the universe is mostly empty.
In the spaces between the stars, you might be able to find one
tiny hydrogen atom in a cubic yard of the vacuum. It is difficult
to imagine such an absence of matter -- here on earth we have
air, that fills emptiness as we commonly think of it.
However, the vacuum of space
does have matter in it. Gravity causes the material objects in
space to attract each other. The more massive the lump of matter,
the more pull it exerts on anything around it. As little clumps
of space dust collect, they exert more gravitational force on
everything near them. In time, huge clouds of dust can accumulate.
As gravity pulls the atoms more closely together, the dust heats
up. Eventually a huge mass of hot matter can become a star, surrounded
by a swirling, flattened disk of dust that may have smaller lumps
of matter accumulating in it. These smaller lumps may become
planets and their satellites. They, too, may be hot for a time.
The relationship of the planet
to its sun determines such characteristics as temperature, year
length, and gravitational forces. We can calculate how much solar
energy the planet receives. Newtonian physics has provided formulas
that allow us to work out these relationships. We can do at least
rough calculations that will help us to describe these relationships
For more information, check
Lesson 1 of your Science Notes
or visit some of the helpful
web sites out on the web. Or you may Return
to Lesson 1 and check on the assignments.