For those who may be mystified by Fahim's very clever joke, Werner Heisenberg is credited with an important relationship of quantum mechanics, often called the uncertainty principle, which we can simplistically say tells us that the precision with which we can determine the position of a particle, and the precision with which we can determine its momentum (the product of its speed and mass) are in opposition: if we can determine the position at a very high precision, we can determine the momentum to a lesser precision, and vice-versa.
In Fahim's joke, we in effect speak of knowing the position of an object "exactly" (that is, to infinite precision) and thus know the object's momentum (as thus its speed) to no precision whatsoever.
Of course, in the real rigorous application of the principle, we must recognize that we never know, for example, the position of a particle exactly (that is, to infinite precision).
But if we're not that rigorous, it makes a cute joke.
The Heisenberg principle is often confused with the notion that the very act of determining, for example, the position of a particle must necessarily disturb its position (that is, cause uncertainty in its position). The crude model is that if I touch an object with a tape measure to determine its exact position, that will move it a little bit. Of course, the principle is far more subtle than that.
Best regards,
Doug
