by Tasneem Zehra Husain
There are some questions we just can't shake; the nature of space and time, or the identity of the building blocks of the universe; they pester us until we answer them, and then, as if on cue, the Universe proceeds to demonstrate the inadequacy of our proposed solutions. One such question, the asking and answering of which has spurred on the progress of science for millennia, is that of the vacuum. Almost universally, the human race seems to find the concept of complete emptiness fascinating. We have fantasized about this gaping void and spoken of it often, in science, philosophy and folklore, but while in principle it is possible to postulate a complete void – the physical equivalent of the mathematical concept of zero – in practice, this perfect nothingness eludes us.
The argument can be traced back at least to (circa) 500 B.C, when Parmenides declared that a vacuum – i.e. a region of space completely devoid of matter – simply could not exist. The Greek natural philosophers debated this possibility for decades, some declaring the void to be indispensable, others finding it repugnant, until a hundred or so years later, Aristotle issued the now famous dictum ‘horror vacui', or, ‘Nature abhors a vacuum'.
Two thousand years later, when experimental science had advanced sufficiently for abstract ideas to be put to the test, the vacuum was duly investigated. Scientists like Galileo, Pascal, von Guericke and Boyle devised mechanisms to pump the air out of glass vessels, creating vacua in order that their properties could be studied, and some rather striking demonstrations ensued. There were, for instance, the Magdeburg hemispheres designed by von Guericke in 1656.
These large copper hemispheres were joined together their rims sealed with grease, and the air within pumped out so that a vacuum was created within. The hemispheres could then no longer be pulled apart, even by thirty horses, until a valve was opened and air let back in. The incredible strength with which the metal globe clung together was attributable to atmospheric pressure; in other words, the ‘weight' of air – a force we feel all the time and yet are insensible of, because in most situations, the push and pull balances each other out. A vessel devoid of air, however, exerts no outward force – it only feels the air outside bearing down on it from all sides, holding it in an invisible vice.
