are observable events which are explained by physics
or raise some question about matter
, or spacetime
. For example, it was observed, by Isaac Newton
, that while an apple might fall from a tree, the moon, very large and massive, does not fall. See gravity
A related observation, made by Johannes Kepler after painstaking observations, was that the Planet Mars traveled in an elliptical orbit.
Another related observation, first made by James Bradley, an astronomer, is that by carefully plotting the position of a nearby star it appears to move in an elipse over the course of a year.
It is a rather commonplace observation that some things are heavier than others, see mass.
If an object is not moving it stays that way until something moves it; if it is moving it keeps on moving, see inertia.
It is hard to get a heavy object moving; it is hard to stop or change the course of a heavy object once it is moving, see momentum.
Niels Bohr, one of the fathers of quantum mechanics, said "no phenomenon is a phenomenon until it is an observed phenomenon".
- Jeremy Bernstein, A Theory for Everything, Copernicus, An imprint of Springer-Verlag, New York, 1996, hardback, ISBN: 0-387-94700-0
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