The intense debate between Leibniz and Newton about the nature of space-time has impacted the nature of physics to this day.
Leibniz said that "space-time" (i.e., space and time) does not have an independent, real existence of its own. Rather, it exists only relative to objects. If we removed all energy and matter from the universe, there would be no space or time, Leibniz says.
Newton says that space-time is real, that it has an existence all of its own, independent of material objects. So Newton says that if we removed all matter and energy from the universe, we would be left with empty space and empty time.
Leibniz says that there is no such thing as "empty space-time", and produces the following argument for this view. If, Leibniz says, we moved everything in the universe five feet in one direction, there would be no discernable difference between the state affairs before the move and the state of affairs after the move. Thus, Leibniz continues, there is no absolute location, but rather, location is merely relative. Therefore, space-time exists merely relative to objects, and does not have a real independent existence of its own.
Newton disagrees. Newton says that, if we removed all matter and energy from the universe, and in its place we placed a bucket of water, and then we gradually begin to spin that bucket of water, eventually the water would spill over the edge. This would prove that the bucket is spinning. But, if the universe were devoid of all matter and energy in this experiment, the bucket would have to be spinning relative to something, and, Newton continues, that "something" would be the absolute, independently-existing space-time matrix.
Newton later revised this thought experiment to go as follows: in a universe emptied of all matter and energy, place two rocks connected by a string. If we spin these rocks around an axis point between them, tension will be detected on the string. This would prove that the rocks are indeed spinning. But they must be spinning relative to something, which would be the absolute independently-existing space-time matrix.
A very good account of this debate, describing both sides, can be found the following book:
Author: Sklar, Lawrence
Title: Space, Time, and Spacetime
Berkeley, Los Angeles, and London: University of California Press, 1974, 1976, 1977
ISBN 0-520-03174-1
The book was written by a professor at the U of M, and is used in U of M physics courses. I strongly recommend this book. The section on the Leibniz-Newton debate is only part of the book; it discusses many other topics.
If you are taking a physics course this semester, you might ask your physics teacher about this.
So, who was correct? Leibniz or Newton?
