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Push or Pull of Gravity
Name: Katrina C.
Status: student
Age: 14
Location: N/A
Country: N/A
Date: May 2001
Question:
Why does gravity pull?
Why doesn't gravity push?
Replies:
On all the sizes and distances overwhich gravity has been measured, it
always pulls, although very weakly compared to other forces like electrical
or magnetic. I do not think anyone has an answer to the question: WHY?
Some very recent astrophysical observations and theory seen to "need" to
have gravity be repulsive on the scale of the Universe. It seems that some
of the very furthest/oldest objects in the Universe are expanding faster
than they "should". One idea put forth is that on the Cosmic scale gravity
is also repulsive, but so far as I know it is not the only possible
explanation.
Vince Calder
Good question! But it's more philosophy than physics. If the
gravitational force were repulsive instead of attractive, life
as we know it would, of course, not be possible. Matter would
not congregate in stars, planets, etc., but would be rather
uniformly spread throughout space.
Electrical charges of like sign do, as you know, repel, but thank
goodness there are two signs of charge and opposites attract.
This allows neutral atoms to attract one another and causes
matter to form hard pieces (like iron) and crystals (like diamonds).
It is interesting to note that gravity has only one charge and always
attracts, electricity has two charges (+ and -) and so can repel or
attract. The strong force that keeps nuclei together seems to have
basically three charges and is complicated.
On the other hand, not having done all possible experiments, we
cannot be sure that there isn't some kind of gravity somewhere
in the universe that repels (pushes). You may have heard that
Einstein found an equation that predicted that, but he thought
that made no sense and rejected the idea. Now, however, there
is some experimental evidence for such an effect and it may even
help explain why the universe is expanding!!!!
Keep thinking up good questions!
Best, Dick Plano...
Richard J. Plano
Katrina -
An excellent question. Others have asked this question, too. I don't
have an answer for you, but rather a further question. If gravity pulls
should it not also push? Magnets do. Static charges do. Could there
be two poles or polarities for gravity also? Keep thinking.
Larry Krengel
Katrina,
We do not know why gravity pulls. We do not even know why gravity must
exist. The universe we live in seems to have a force that pulls objects
together. The heavier the objects are, the harder they pull together.
Scientists decided to call it gravity. Experiments were done to figure out
how it worked. We do not even know if our ideas about it are perfectly
correct. It is something that agrees with real-life experience.
All of science is like this. First, there is reality. Then, there are
scientists trying to figure out how reality works. They come up with
experiments to test reality, and with ideas (usually called theories) that
agree with the experiments. New scientists try new experiments to test
these theories. If they agree, nothing happens. If they disagree, the
theories are changed.
The science we learn in school is the set of theories that work best. They
could be correct, or incorrect. They are the best we have. Some very basic
theories agree with more advanced theories. The basic ones can be called
the reasons for the others. Still, the reality is the reason for the
science: the science is just a possible description of how reality works.
Science cannot tell us why reality happens to be as it is.
Dr. Ken Mellendorf
Illinois Central College
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