A shorter post today to break up what have been quite a series of length editions. So we’re about to talk about a concept fundamental to the subject of Physics and explain what it is – the field.
Fields were first conceptualised by Michael Faraday in the 19th Century and later immortalised into mathematical equations by James Clerk Maxwell. Faraday’s thoughts regarding fields were provoked by his tinkering with glass rods, needles, pins and magnets which repel and attract. Before Faraday the forces between objects such as a pin and a magnet or the moon and the earth were thought of as spooky ‘action at a distance’ – there was clearly some interaction between these objects but being separated by space it was unclear exactly how or rather what was mediating that interaction. This mediator was Faraday’s conceptual leap, the existence of a entity in the space between bodies which is distorted by electric and magnetic bodies and itself acts upon the bodies. This is the field.
The field is visualised as being composed of lines, ‘field lines’ which fill the space between objects. to use Rovelli’s metaphor, fields are like ‘a gigantic cobwebs filling everything around us.’ The lines (electromagnetic ones in this case) are distorted by electric or magnetic objects and in turn transmit the electric and magnetic forces from one object to another through this distortion. Therefore, it is not the objects that attract or repel each other directly it is the effect they have on their surrounding field lines which is then transmitted through the medium of the field lines themselves from one to the other- no more spooky ‘action at a distance’. The field lines can wobble and fluctuate, just like waves on the surface of a choppy sea.
You can see an example of the distortion in the field lines produced by two electrical charges below. When the charges are two of the same, +,+ the field lines are seen to diverge away from each other which is what we would expect from knowing that like charges repel each other (put two north poles of a magnetic together and feel the outward push). When the two charges are opposite, -,+ the field lines are seen to converge which again is what we expect knowing that opposite charges attract. (Maybe this is the cause for the saying opposites attract, although this might be true with particles I personally don’t find it the case with people..) When mathematically modelling the field we can assign value and direction to every point in space, which can be visually represented by the size and direction of the field line. Any particle susceptible to the field will then experience a force with corresponding strength and direction.
The next great stroke of genius came in the realisation that speed at which these field lines move is the same as the speed of light! James Clerk Maxwell realised that light itself is just a product of the fluctuations of Faraday’s field lines! Light and colours are simply oscillations of lines of the electromagnetic field at a particular frequency. Moreover other oscillations of the field lines at lower frequencies produce different types of electromagnetic waves such a radio waves or infrared waves – 20th century technology is born. (Quick note: we do not see the field lines themselves, only the vibrations/oscillations of the lines.)
But, it doesn’t stop here with the electromagnetic field, oh no all of the fundamental interactions have a field associated with them to mediate their dynamics. Electricity and magnetism – the electromagnetic field, gravity – the gravitational field, the strong force – the strong field, the weak force – the weak field. The fundamental interactions are also characterised by their particular fundamental particle, whose general term is a gauge boson. More specifically these are, photons for electromagnetic, gravitons for gravitational, gluons for strong and W and Z bosons for weak. In fact in 2012 a pivotal discovery at CERN was made of a new fundamental particle – the Higgs Boson. This particle is the particle that is suspected to give mass to other particles – Joseph is about to do a post on it imminently so I won’t tread on his toes but it also has an associated field – the Higgs field. The Higgs field is an energy field that is thought to exist everywhere in the universe and be responsible for giving mass to the other gauge bosons (apart from the photon which doesn’t interact with it, hence is massless!). So there we have it all the fundamental fields which mediate all the fundamental forces in nature. But there is just one more revolutionary step to be mentioned.
Up till now the universe consisted of space, fields and particles. The stroke of genius came from Einstein (of course it did) in 1915 with his theory of General Relativity. Einstein realised that the gravitational field was not just another one of the fields, the gravitational field was so much more, the gravitational field was space itself. There was no longer this mysterious nothingness of space ‘between’ field lines, the gravitational field line was the space. Just as with other field lines the gravitational field lines respond, move and bend in the presence of matter. So our everyday word ‘space’ does too as they are the same thing. Though I doubt we’ll all drop our colloquial convention and starting calling space the gravitational field, bit of a mouth full. Anyway, we have seen this idea with the visual depiction of space ‘bending’ in presence of heavy masses.
There we have it, space is no longer a separate entity, space is a field and the universe now consists of fields and particles alone. We are not trapped in rigid container filled with material but a malleable, flexible shell which curves and distorts in the presence of matter. Such was the powerful and revolutionary introduction of the field which not only allowed us to invent the lightbulb and create the radio but drastically changed our understanding of the fundamental constitutions of the universe and the nature of space itself.