President Theodore Roosevelt strengthened the Monroe Doctrine by establishing the Roosevelt Corollary which stated the policy that the United States would

Heisenberg's uncertainty principle enunciated in 1927, postulates that the fact that each particle has a wave associated with it, imposes restrictions on the ability to determine its position and speed at the same time.  

In other words:  

It is impossible to measure simultaneously (according to quantum physics), and with absolute precision, the value of the position and the momentum (linear momentum) of a particle.  

So, the greater certainty is seeked in determining the position of a particle, the less is known its linear momentum and, therefore, its mass and velocity.  

In general, the greater the precision in the measurement of one of these magnitudes, the greater the uncertainty in the measure of the other complementary variable.  

This principle is one of the fundamentals of quantum mechanics that differentiates it from Newtonian mechanics, which stablishes a physical macroscopic model to describe the movement of bodies in space with fixed properties, whereas according to quantum mechanics it is not so.

Both theories offer very different descriptions of the world, incompatible with each other, but both are valid in their fields of application.