Talking about 2001: a Space Odyssey reminds me of a puzzle I've ruminated over for decades. This query is for physicists on FFL. If you're not a physicist stop reading now - unless maybe you live in Fairfield and are a friend of John Hagelin. In which case can you tap him on the shoulder, ask him for his thoughts on my conundrum and let me know what he says. At the start of the film we are approaching a doughnut-shaped space station. The station is rotating. Why? Well, think of a schoolboy with a conker on a string. He twirls his conker and the centrifugal force keeps the string taut. The concept is that a circular space station is set in circular motion. The centrifugal effect means that those inhabitants living on the edge of the circle would find themselves in a pseudo-gravitational force so could walk around as if they were on the surface of the Earth. Neat, yes? But here's the thing: how does the space station "know" it is rotating? Why shouldn't we regard it as stationary and the planets around it are the one's in motion? https://www.youtube.com/watch?v=q3oHmVhviO8 https://www.youtube.com/watch?v=q3oHmVhviO8
Isaac Newton came up with a "thought experiment": suppose a bucket containing water being spun on the end of a rope. The centrifugal force would make the water creep up the sides of the bucket. That's basic and acceptable. But suppose the bucket on the end of the string was suspended in outer space? Why would the water creep up the side of the bucket? Newton's answer was that there is a background of Absolute Space - ie, a really existing environment of three-dimensional space in which we live. The rotating bucket/conker/space station rotates in reference to Absolute Space so that ensures the effects we expect. That's nice. But what makes us twitchy is this thought: if a god was to decide to move the Universe exactly 30 metres in some direction what difference would we notice? And we see immediately we would notice no difference whatsoever. So it's a difference that doesn't make a difference! But doesn't that suggest Absolute Space is a redundant concept? Then along came Einstein. He rejected Newton's concept and replaced it with relativity and space time. The position of an object only makes sense with respect to another object to which it has a relative position. That's the new orthodoxy. But then the obvious question is: in Einstein's universe would Newton's spinning bucket see the water rising when the bucket was spun? In other words, would a rotating space station give its inhabitants the sense of gravity? Austrian physicist Ernst Mach thought the answer was "Yes". He believed that just as a spun conker was spinning in relation to the gravitational pull of the Earth, a rotating bucket in space was spinning in relation to the surrounding galaxies. The problem with his answer is that 1) the gravitational effects of distant galaxies is minute; and 2) if Einstein had thrown out Absolute Space as a theoretical theory then, for all practical purposes, Mach was re-introducing Absolute Space a de facto reality. So would Kubrick's rotating space station actually work as a viable environment? I'm not aware of any plans to build rotating space stations. That suggests confidence is low. Given the number of space launches has anyone ever carried out experiments by either spinning buckets of water or (more likely) carried out some simpler, equivalent experiment to see if the idea is right or wrong? Not as far as I'm aware. If you know the answer to my puzzle can you send the solution to : Space Habitats NASA Headquarters Washington DC 20546-0001 I'm sure they'd be grateful to know what to concentrate on for space stations of the future . . .
