Supporters claim that astrology is a science, or at least a field of study based on structured systems and predictable outcomes. If this is so, we should be able to test the underlying theory of these systems and see if it makes sense. Even if we can't prove or disprove it, it should at least make sense and be consistent in it's own way.
At the heart of astrology is the claim that the positions of celestial bodies influence the environment on earth and the people inhabiting this planet. There is assumed to be some type of force which emanates from these bodies and affects life here.
First of all, let's discuss what we know. There are four known forces of nature. These forces are are reasonably well understood, at least in terms of the influence they can have on surrounding objects.
None of the known forces can influence human matters from distant celestial locations — even most astrologers acknowledge this. This means that astrological effects must be due to some unknown force(s). This is where things become controversial, as scientists and astrologers argue over whether such unknown forces could exist.
Although it is difficult to make a case for the existence of any new forces, it is nonetheless fair to say that science is imperfect and such forces could exist, however unlikely that may seem. For the sake of this discussion let us assume that there could be a mysterious force generated by celestial bodies, which extends across interplanetary distances, which cannot be detected or measured, but which has some effect on living organisms.
At this point science has an ace up it's sleeve: The question of size and distance.
Astrology places essentially the same importance on celestial objects whether they are large, small, nearby or distant. This is a legacy of the time when people didn't understand the real structure of the Universe and assumed that most celestial bodies were a similar size and distance from earth.
According to astrology then, the size and distance of a celestial body are not related to the influence they exert. If this is true, it follows that every celestial body in the Universe would have a similar amount of influence on humans. This results in a chaotic situation which cannot be reconciled with the way astrology is claimed to operate. It would actually mean that similar forces are being applied to us from every single direction in the Universe simultaneously.
Humans can only see a tiny fraction of the objects out there in space — the night sky is literally filled with celestial bodies we can't see. There are around 100 billion stars in our galaxy alone, most of them probably home to orbiting planets and/or other bodies. If they all exert similar forces, as astrology says they must, where do they fit into astrological charts?
So the basic problem of astrology is that there is no type of force which could be excerpted upon us by all the planets in our solar system, without also being exerted upon us by countless billions of other celestial bodies. In short, any theory which would explain how celestial bodies influence the earth would also contain an inherent paradox which means it cannot be true.
At this point astrology supporters are likely to say "But it does work, even if you say it can't". I actually think it's fair to raise this claim and I think it's worth investigating. It's not unheard of for scientists to think something couldn't happen and then it does — what if astrology is the same?
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