I’m not ruling out unicorns.
It is impossible to prove that something does not exist. Unless you have looked everywhere, you can’t be 100% sure that whatever you were looking for doesn’t exist. And if you did look everywhere then you couldn’t be sure that it hadn’t walked around behind you, making faces behind your back (as I believe the Loch Ness monster does every time they run sonar up and down the loch).
Not only that, but there’s always the possibility of things we don’t know how to detect (like, say, neutrinos until recently), or things that look like something else, or even the sceptical equivalent of the atom bomb – we could be brains in a jar (although I believe that nowadays the brain in a jar gets to wear cool clothing and learn Kung-Fu, so it’s not all bad).
So, given that we can’t disprove the existence of unicorns, it therefore makes perfect sense that if someone declares that Black Holes could be full of unicorns that we give them the benefit of the doubt. After all, we can’t see into a black hole, there could be _anything_ in there, couldn’t there?
But you’ll excuse me if I don’t believe it. Because if I believe it (and I’m not even talking about certainty here – not 100% pure, positive, unshakeable belief, just your common-or-garden, “My history teacher said it so it must be true”) then by the same reasoning I have to believe there could be pixies in there or an army of Nicole Kidman clones or Great Cthulu himself.
Eventually, when you get right down to it, all we have to go on is what seems right to us. We can’t have definitive proof, we can’t be completely sure; there will always be room for scepticism on anything before the basic Cogito Ergo Sum (and even that is arguable, for certain values of “Ergo” and “Sum”). This means that we are left to pick and choose based on what fits into our worldview.
Which doesn’t mean that you’ve got free rein to decide that the sky is yellow, cats bark and Paris is near Tokyo, because believing things that are clearly contradictory to your perceptions will quickly make it impossible to deal with anyone not living in your personal world. But when you discover that the US is invading Iraq (something for which we have clear evidence) then it’s your worldview that tells you that whether he’s doing it for the oil, to free Iraqis, to stabilise the Middle East, because Saddam had his dad shot, to bring about the Rapture or because Vladimir Putin bet him he wouldn’t. The evidence is always open for interpretation.
Evidence varies in how much interpretation it allows; experiments have shown that witnesses are far less accurate in their perceptions than used to be thought. People fill in information from a few glimpses, taking in a few cues and then adding layers of detail based on their expectations. We use shortcuts to leap to conclusions, choose evidence selectively to prove whatever points we are attached to and then remember the stories we tell as the truth. Once we’ve repeated a story a few times as if it were truth it becomes very hard to remember the original embellishments we applied.
Given all of this, deciding what fits your worldview is fraught with peril. How can you tell that you’re not just playing to your own prejudices? For instance, I have a liking for superstring theory because it plays to my appreciation for simplicity. But I wouldn’t say I believed it any more than one of the other quantum theories because there’s no decisive evidence for it. When it comes to deciding what to believe I am generally very happy to turn to science. But why should science be privileged over, say, Christianity?
When you learn science at school you largely conduct experiments and then interpret them. This leads people to think that these two stages are what make up ‘science’. And if that’s all there is to it – do something, decide what it means – then why should the opinion of said scientist matter any more than yours when it comes to announcing what’s really going on?
The answer is that science demands more than that – the scientific method means that when you come up with a hypothesis that you design an experiment whose results will be different if your hypothesis is true than if it is not. If a scientist thinks that the speed of light varies depending on height above sea level, then they have to design an experiment that measures it at various heights and show the difference. They also have to defend the design of his experiment against other scientists who think something different. And when, 50 years later, someone designs an experiment that shows that the speed of light varies depending on air pressure, not height, they have to face up to the fact that their work was merely transitory, giving an approximation to reality that’s been superseded.
Science isn’t a doctrine of facts to be believed. It’s a method of discovering approximations to reality, of constructing models of reality, of producing rigorous evidence for a particular view of reality. It’s not perfect, of course, no system ever is, especially not one that involves people. Scientists hold onto theories that are terribly outdated, attack each other in print (and occasionally in person) and occasionally behave like spoiled brats. But when the evidence is sufficient the vast majority of scientists can be persuaded and minds can be changed.
Scientifically you don’t have much of a theory unless you have some way of differentiating it from other possibilities. If you don’t have a way of looking into the black hole to see whether there are unicorns inside then saying that there might be is just meaningless supposition. It may feel right to you. You may have a gut feeling that they are there. But unless it’s possible to look in some way, assuming their existence is taking a step out of rationality.
So, returning to the original example, when people say “But black holes could be caused by unicorns.” I look at whether this fits in with whatever I already know, I factor in whether there is any new evidence for the claim, whether people whose judgement I value (either personally or by reputation) agree with it, whether the people making the claim have any obvious ulterior motive for doing so and whether there is any way of checking to see if the claim is correct.
So, having never seen any proof of unicorns, lacking any credible people in favour of the claim, noticing that the unicorn claimants have a strong emotional attachment to the existence of unicorns and that there’s no way of telling if there are unicorns in the black hole, I don’t consider there to be any reason to add the claim to my list of beliefs. Which doesn’t mean I’m ruling it out permanently; many claims have seemed incredible, weren’t believed at first and were uncheckable at the time later turned out to be valid. But this doesn’t mean that I’m willing to commit to it at any point before there is a strong reason to do so.
This was, by the way, inspired by the post on the journal of green_amber here