I recall back to my first days in physics class where I read the quotation “Nature abhors a vacuum”. The phrase was accompanied by an image of two teams of horses trying to pull two hollow hemispheres apart after the air was pumped out from inside.
These were called Magdeburg hemispheres and the experiment was performed by Otto von Guericke. I didn’t realize this, but according to Wikipedia it was Aristotle’s theory Horror Vacui that von Guericke was trying to disprove. This theory suggested that nature hates a vacuum and that the vacuum will suck material in to fill it. Von Guericke demonstrated that it is not a sucking force, but a pushing force from the outside air. However, as I recall from the physics text, the presentation was written as if this experiment was a demonstration of this “principle”. I imagine that this misconception is why you still see the phrase commonly used today. This is one of the science myths that keeps floating around.
A more accurate viewpoint is that Nature Abhors a Gradient. It isn’t that there is a vacuum that is holding the hemispheres together. Nor is it that there is air surrounding the hemispheres that is holding the hemispheres together. Rather it is that there is an enormous gradient in the air density outside the hemispheres with respect to the inside. The result of this gradient is a force.
Gradients in potential energy cause forces.
More generally, gradients in any scalar field result in generalized forces.
The gradient of the electric potential is the electric field. The gradient of the gravitational potential energy is the gravitational force. Over and over again these ideas reappear. In physics, we learn them as separate concepts, and then later in the abstract topic of statistical mechanics we are expected to put it all together. But each of these gradients resides in its own little box in the student’s cortex, and statistical mechanics is in its own little box. Rarely do these ideas merge to form a unified concept.
Temperature gradients are responsible for our weather.
Huge temperature gradients are responsible for hurricanes. The temperature of the extremely warm air at the sea surface in the Gulf of Mexico drops quickly as one rises higher into the atmosphere. This enormous gradient powers the heat engine known as a hurricane. Nature abhors gradients, and will do something about them. The gradients will result in forces that tend to eradicate the gradient. Watching this NASA video of satellite imagery during the 2005 hurricane season, one can clearly see that hurricanes are designed to cool the sea surface.
Our weather here in Albany is due mainly to cyclonic storms that act to relieve the temperature gradient between the Earth’s equator and the poles. Forces due to this gradient brings parcels of warm air north from the south and exchanges them with parcels of cold air from the north. The spinning of the Earth results in the Coriolis force which deflects the northbound warm air eastward and the colder southbound air westward. This creates a counter-clockwise rotating structure that brings warm air north on the eastern front and cold air south on the western front. The result is that the extremely warm weather we had a few days ago had to be followed by the extremely cold weather as this cyclonic structure moved over us from the west.
However, the weather is not the only system driven by the Earth’s energy gradients. Life itself is driven by these forces. The “purpose” of life is to relieve gradients. This is why forests are cooler, they are working to dissipate thermal gradients induced by incoming light heating the surface. During the process of relieving these thermal gradients, the plants grow. This excess organic matter results in residual chemical potential energy, which again creates a gradient. The herbivores devour the plant matter to further relieve the chemical potential gradients. This works up to a point, but again there is a residual chemical potential, of which the carnivores take advantage. The cycles of life are driven by energy gradients.
But it doesn’t stop here. There are other scalar fields that have gradients. Wealth gradients result in generalized forces. In cites where there are enormous gradients between the wealthy and the poor one sees violence. Across the southern U.S. border there is another enormous gradient in wealth. This gradient results in forces that drive Mexican immigrants into this country. Building a wall won’t help because it doesn’t eliminate the gradient. The gradient will merely increase until new forces become strong enough to eliminate it.
How does one solve the problem?
Eliminate the gradient.
Nature abhors a gradient.
Kevin Knuth
Albany NY
Posted under Biology, Climate, Energy, Evolution, Philosophy, Physics, Social Justice
This post was written by drknuth on November 27, 2007
