Astrologers and other inhabitants of parallel universes

Constellation of Monoceros the Unicorn with Canis Major and Minor by James Thornhill (1725). Photograph: Stapleton Collection/Corbis 

 " The "argument from spurious similarity" was first explicitly described by Daisie and Michael Radner in their slim but influential volume, Science and Unreason. As they point out, pseudoscientists are fond of claiming that the principles upon which their claim is based are, in fact, already part of established science and that the claim should therefore be accepted. One of the examples that the Radners discuss is astrology. Not all astrology believers claim that it is scientifically based, but many do. They will often point out that science already accepts that celestial bodies exert numerous effects on the Earth, implying that their own claims are simply another example of such effects. The most common effect they cite is the tides, which are caused by the gravitational pull of the sun and the moon. Given that gravity can cause whole oceans to rise and fall, isn't it obvious that our bodies, which are composed mainly of water, will also be subject to tidal forces? The answer is no. Tidal forces are caused by the differences in gravitational pull on a body of water due to the fact that different points on the Earth are different distances from the moon and sun. The size of these differences with respect to ocean tides is orders of magnitude higher than those relating to the water in your body. The proposed mechanism just could not work. Astrologers might object that even if an explanation in terms of tidal forces does not work, it is undeniable that all celestial bodies exert a gravitational pull on each other and that astrological effects are produced by gravity in some other, as yet unspecified, way. But again, this just does not work. The gravitational pull on a newborn baby as a result of being held by its mother is greater than the gravitational pull on the baby from most celestial bodies. Attempts to explain astrological effects in terms of electromagnetic influences don't work either. The sun's electromagnetic activity can have effects on the Earth, such as the aurora borealis. Massive solar flares have even been known to knock out power supplies. But many bodies of supposed astrological significance, such as the moon, Venus and Mars, have negligible magnetic fields. Astrologers also point to cycles in nature. From circadian rhythms relating to temperature and hormone levels to the widespread effects of the changing of the seasons, many biological processes follow such cycles. Their reality is indisputable, as is the reality of the astronomical cycles relating to celestial bodies – which astrologers rely on to cast their horoscopes – but there is no evidence that astrology can use the latter to describe someone's personality or make accurate predictions about future events on Earth. "
By Chris French /more