Sunday, 7 February 2010

Physical Resonances

This post is going to stray a tad from the physical 'concept' of the blog into the arena of theory and economic theory at that. This is intended to be a suggestion for further thought and is not based on anything in particular that I have come across from anyone else. If others have noticed the same connections, I am not at all surprised. I am a landscape architect and not an economist, so the thoughts have yet to be tested.

In the year 2000 London's newest bridge across the Thames was opened and promptly closed 3 days later. It was a footbridge and had been designed through a multiple committee process using what appear to have been primarily wheeled traffic models to calculate the forces of weight and wind that were likely to impact upon it. Of course it was a pedestrian bridge and pedestrians don't behave like cars. Useful as it would be to have our own wheels, we have feet and we have rhythm. According to Wikipedia here the first day of opening also coincided with a charity race that meant up to 2,000 people were on the bridge at any one time for most of the day. While not marching like soldiers, people who walk together often share a walking pace and frequency. The bridge started to respond to the resonance of the people walking. The people walking started to respond to the resonance of the bridge and the inevitable happened. The bridge started to bounce.

Quite a few people have had the amazing privelege to walk on overhead walkways in rainforest or jungle environments. These bridges are notorious for their resonance from single foot passengers. This can be quite marked because there are no damping devices possible on such simple structures. On the Millenium Bridge in London it was possible for the damping devices to be placed at intervals across the bridge and when it opened again 2 years later it was possible for large numbers of people to walk across the bridge with no discernible effects and therefore no bringing on of the rhythm that caused feet to fall together and accelerate the bounces.

In our economy we have economic models constructed in a similar way to that of the bridge. They assume the behaviour of the traffic to be consistent at all times, when we as frustrated bystanders know only too well from our own experiences how incredibly vulnerable stock holding is to the effects of the bounces in the market. Intelligence doesn't always work in the markets, fear is a far greater influence. The effect is of course also exaggerated on occasions by the comments made by others who may not have obvious reasons for saying what they do. Confidence works in a way that does seem to me to be remarkably akin to the accelerated bounces on the Millenium Bridge. It would do no harm if models could be built to look at this effect and to see if the parallels could in fact help build a resolution for such a long running problem. I have worked on historic landscapes where the effects of previous economic fallout have affected the layout of veteran trees. One historic park that I can think of has a strange young series of avenues, where the trees are 150 years younger than the design period they belong to. This turns out to be as the result of a benefactor reinstating a predecessors wholescale felling of the site caused by the need to recover funds lost in a large scale economic disaster.


  1. It is a truism that no model can account for the vagaries of human nature - thus are only based on average reactions.
    Economic models are based on the assumption that reactions will average out. the fact is that the markets are sheep and fear is the main factor is deciding how to react - not why someone has done something but the fear that they know something others do not and therefore act or react without time for effective evaluation - a person seen as influential can therefore have a disproportionate effect to someone seen as average - rogue traders spring to mind.
    Also the average age of traders is under 30 so no one can remember the last time things went wrong - they burn out or get out early having made a fortune without understanding how

  2. The point about the bouncing bridge is to do with resonance, isn't it? I remember when doing Sound in O Level physics, we were told that soldiers had to break step, and not march in step when they crossed bridges in order to prevent just what happened to the Millenium Bridge. I guess the lack of conscription means that nowadays, such generally known information has been forgotten, unlike the use of raw carrots to improve night vision (to cover up the air force having radar during the war).