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Because the relative uncertainties in the values of conjugate variables are so small, they seem to have little direct impact on our normal experiences. For example, the uncertainty in speed of a pitched baseball has much less to do with the uncertainty of its location on its way to a batter, than it does with wind, wear, and how hard the ball has been hit before. But they do have something profound to say about the basic nature of our universe.
Historically, theories that attempt to understand the basic nature of our universe, space, and time, have been "Euclidean," or classical theories. That is, they use the fundamental ideas of Euclid's geometry and thereby propose that space and time are smooth and continuous properties of the universe. The size of space and time intervals (or distances) can be any value from zero to infinite. One prominent, and useful, example of such a theory is Einstein's General Theory of Relativity which explains the force of gravity in terms of the basic structure of our universe. A feature predicted by this theory, popularly known as a black hole, considers a real object collapsing to zero size as a geometric point. But, if it collapses to a point, then its location is known with absolute precision. According to Heisenberg, this also means that the uncertainty in our knowledge of its momentum is absolute, or infinite! Since the momentum of a massive object is related to the motion part of its energy, its energy can also be viewed as classically infinite.
This is typical of the type of problem that arises when classical theories extend into the range where quantum principles are important. Largely because of the Heisenberg uncertainty principle, classical and quantum theories are essentially incompatible. And the primary incompatibility lies in taking the geometric concepts of points and continuity as the basic building blocks of our physical universe.
Since Einstein has shown that space, time, and gravity are inextricably related to each other, we will let gravity set a quantum scale for us - something known as the Planck length.
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