In this modern world it is often confusing to consider how things work. What keeps a plane in the sky? It shouldn't be there. It's wrong.
I can't answer that one.
But I have a theory about how tube trains manage to get from one place to another.
I think they run on dignity.
Let me explain.
We all need energy to get us moving around. We get this energy by consuming food or fuel. We use this food to create energy and then we excrete the stuff that is of no use to us.
So logically a tube train must work the same way. What does it consume? Commuters. A tube train eats millions of innocent commuters a day.
However, the train appears to excrete those commuters unchanged at unspecified toilets along its path and the commuters appear to be the same.
So what has the train taken from them? What has it consumed to make itself run?
Of course the only thing that has gone is the commuters' dignity.
When they were eaten by the train they had pride, poise and self-esteem, but after half an hour of being pressed against the body of a foul smelling stranger at temperatures approaching 40 degrees celsius, they leave the train humbled and humiliated.
The tube has ingested that dignity and transformed it into the energy it needs to run along a rail.
Occasionally there is not enough dignity lost and the train will grind to a halt in a tunnel. Brilliantly, this is the solution to the problem. The additional heat, frustration, bodily odours and fights that will ensue squeeze the commuters dry of their last drops of dignity, allowing the train to continue.
It is weird that London underground don't explain this to passengers. If we knew that the humiliation we receive by travelling on the underground was necessary to keep it going, then the whole experience would be much less annoying.
Of course, if we knew that that was the case the journey would no longer be humiliating and our dignity would remain intact and the whole transport system in London would grind to a halt.
Similarly buses are fuelled by aggression (provided by drunken yobs fighting on night buses and old ladies scrabbling for a seat during the day) and taxis operate thanks to hot air.