Monday, January 28, 2013

Natura sum vacuum

We usually credit Aristotle with the phrase “natura abhorret vacuum” Nature abhors a vacuum. That was the sum of our thinking on nothing for over a thousand years. We have nothing everywhere today. Every vacuum tube is filled with a an air void.  It's in space all around us, it's in your TV, computer monitor, tubes in your guitar amp, the top half of the thermometer and in empty space all around our planet. So how did we get from something to nothing

Indeed later on Philo of Alexandria and even ten centuries later Adelard of Bath and Peter of Abano were busily draining water out of buckets and sucking it out with straws dutifully noting that nothing failed to occur. At the time this was just another proof: horror vacui. Some writers credit Aristotle with the phrase but no such original writing has come down to us. But his opinion is well known from his work De Caelo. There he made observations on fire, air and water regarding the lack of a vacuum as these "elements" exchanged places to prevent a vacuum from occurring. This had practical application. They used a clepsydra in that era to pump water. It was a primitive suction pump with a single plunger like a syringe. For thinkers of that era, this exchange of water for air preserved the continuity of the universe and that took on a religious connotation. It just happened to be totally wrong.

Lucretius around 100 BC thought that a vacuum could exist but only for a fleeting instant. If two surfaces were hypothetically sealed then separated a vacuum had to exist in order for matter to rush into it.  This wasn't staunch opposition. he was just arguing that it existed on the most minute level so that nature could abhor it.  The book Much Ado about Nothing by Edward Grant covers this in excellent detail even if the book is grotesquely over priced.

Around 1330 Nicholas of Autrecourt theorized that Aristotle might have been a teensy bit wrong. He observed that the density of matter varied in reaction to changes in pressure and that this had certain implications. the experiment usually involves a candle, a jar and some kind of hose to water. When the candle expends the remaining air the pressure decreases siphoning in some water. He credited it all to mysterious properties of atoms. He was condemned by Pope Clement VI as heretic. So these and other writings earned him some time in court after which he had to recant many of his writings. But others kept tinkering with this experiment. But largely conclusions still remained in the anti-vacuum camp.

Then Adrianus Turnebus proposed an experiment around 1530 that caused a ruckus. He suggested that a siphon could be sealed with a glass ball and caulked. Then if suction was applied a vacuum would be created and that this could be tested by breaking the seal under water which would then rush in to fill the void. There was much debate and unlike Nicolas he was not declared a heretic.

Evangelista Torricelli produced the first vacuum in 1643.  He had previously been pondering why water could not be pumped from a well more than 32 feet deep. In his experiments he filled a tall glass tube closed at one end with mercury. He then sealed the open end, then opened it under the surface of a bowl of mercury. The level of mercury dropped inside the glass tube, but not all the way. At the top of the glass was a vacuum.  We call it  Torricelli's Vacuum. More here. He noticed that the level of the mercury varied.  It is the weight of the atmosphere that determines what level the mercury rises to in the glass aka barometric pressure. Galileo had been condemned only 10 year earlier to he avoided drawing conclusions he wrote "Many have said that the vacuum does not exist, others that it can exist but only with difficulty and against the repugnance of Nature." It was still a long way to the vacuum tube.