Wednesday, 23 May 2012

Intuitive deceptions

As the years pass, and I mull over various philosophical or scientific ideas, it's becoming increasingly obvious to me that our human intuitions lead us astray all to often. We have uncovered numerous phenomena in the scientific world where reality is stranger than our intuitions suppose. In some cases, the nature of reality stretches the capability of our imaginations past breaking point.

Let's look at some examples.

Our intuition tells us that the world is flat and that the sun, moon and planets are smaller objects which orbit us. While the latter idea was held to be true for most of history, it's actually a misconception that the former was ever widespread among the educated members of the world's civilisations. Even so, the uneducated would have believed in a flat earth. I remember as a child being surprised to learn that the earth was spherical, and wondered why the Australians didn't fall off the "bottom" of the earth.

Because even the concept of gravity is so wired into our intuitive understanding of the world that it took Newton to recognise that it was a force attracting us towards the centre of the earth. Thinking about this also confused me as a child. If the earth wasn't there to hold us up, surely we'd fall down? Surely an unsupported object must fall. Why? Because there's nothing holding it up!

After the initial confusion, I soon came to understand that we wouldn't fall down if the earth disappeared, because there would be no "down". Unsupported objects will only fall down if there is a gravitational force acting on them.

Sometimes the incorrect intuitions we hold dear are not so much instinctive as a product of culture. As a child, I had no difficulty accepting the theory of natural selection. I was big into dinosaurs and ate up anything that discussed prehistoric life and evolution. The ideas seemed natural and exciting to me.

It was not so easy for the majority of Darwin's contemporaries to accept his heretical idea. This was in large part due to its disagreement with religious doctrine, but I believe it was also due to the fact that people just couldn't accept the unintuitive idea that any of their ancestors could have been animals. They were deeply enculturated with the intuitive and mutually exclusive categories of "human" and "animal".

This attitude has persisted even to the modern day. I remember vividly a discussion I had with two great-aunts of mine when I was a teenager, perhaps fifteen years ago. I don't recall how it started, but somehow the topic of evolution came up. I was shocked to discover than my elderly relatives seemed entirely ignorant of it, and would entertain no notion that it was possible. I explained to them that we had evolved from apes, and if you traced the ancestry back further you'd find smaller rat-like mammals, then reptiles, then amphibians, fish etc.

They were having none of it. As devout Catholics, like most elderly Irish Kerry women, religion alone was unlikely to be the motivation for their disbelief. The Catholic faith holds that the pope is infallible, and the papacy has long accepted that evolution has occurred. I told them about this but they were not impressed.

When I asked them to explain their doubt, all they could say was "No Booth is descended from any rat!".

As a child grows he or she learns that in some cases new knowledge can trump intuition. These first challenges to our instinctive understanding of the world are relatively simple to overcome, but as we learn more, the challenges become greater. Sometimes we may fail to overcome our intuitive obstacles as we attempt to understanding the most difficult truths.

The discoveries of twentieth-century physics have provided plenty of challenges for our intuitions. Einstein is responsible for at least two of them in the forms of special and general relativity.

Special relativity introduces the idea that the universe has a speed limit -- nothing can move faster than the speed of light. This is tremendously unintuitive because we imagine that if we continue to accelerate at a constant rate, then of course we can achieve any finite velocity in a finite time. It's inconceivable that we would suddenly hit some kind of ceiling to our velocity.

And yet Einstein was right, and this has been demonstrated in countless experiments. After the initial intuitive rebellion agains the proposition, we learn that there is no hard "barrier" to acceleration as we might at first suppose, but that as you speed up time slows down and space distorts such that you can never quite get to the speed of light, even though you perceive your acceleration as constant.

This is a tough idea to grasp, and I confess I do not have a particularly well realised mental model of how all this works. I am already reaching the limits of the capabilities of my imagination. I expect that in the case of special relativity, this could be overcome with a little more education on the subject.

But it just gets weirder. General relativity brings gravitation into the mix, and now we have to understand that our flat three-dimensional space is an illusion. What we really find ourselves in is four-dimensional space-time that can be distorted and bent by the gravitational effects of mass and energy in all sorts of ways we don't usually perceive. This means, among other things that light can be bent by gravity, that black holes can form, and that time slows down more the deeper you are in a gravitational well.

Just think about that! Time passes more slowly for you on the ground floor of a building than it does at the top! The effect is miniscule, but highly unintuitive nonetheless.

And four-dimensional space-time is difficult enough even without the strange effects of gravity. No-one alive can truly, honestly picture a four-dimensional shape the same way they can picture two- or three-dimensional shapes. But space-time is weirder yet. It's not even Euclidean space, it's a different kind of space entirely called Minkowski space, which I really don't understand at all.

Thankfully, mathematics doesn't require an intuitive understanding, and we can reason about such things even if we have a hard time picturing them. By using such mathematics, Hawking argued that time itself could have been created at the Big Bang. Our intuition will not accept this, as we can always ask what happened before the Big Bang. The answer that this question is meaningless is rather unsatisfying. Hawking explains that it's like asking what's south of the South Pole.

It turns out that the Big Bang singularity is now rather uncertain, thanks to quantum mechanics. And what a raft of unintuitive consequences quantum mechanics imply! The unintuitive consequences of quantum mechanics could easily fill another post the size of this one. I'll just list some of them out without discussing them.
  • Everything is composed of "stuff" which is both wave-like and particle-like at the same time.
  • Particles can in some ways be in more than one place at a time. In fact they can be in all places at once.
  • Particles can move backwards in time.
  • Space and time are quantised, by which I mean there are both a shortest possible duration and a shortest possible distance.
  • Schrödinger's cat is arguably both alive and dead at the same time!
  • There are either an infinite number of universes or there is some other equally unlikely explanation for what we observe.
  • The mere act of observation appears to change the state of a system.
  • The empty vacuum is actually fizzing with virtual particles which constantly pop into and out of existence.

Finally, it seems clear to me that our intuitions can also mislead us in the domain of philosophy. I have already argued that our moral intuitions do not imply that morality is actually objective, and I have argued that the Big Bang does not constitute the universe's springing into existence as our temporal intuitions might suggest. Our intuition that a whole must be more complex than its part has also been shown to be wrong.

But this is just the beginning. There are many more philosophical points I will argue in future posts which are even more unintuitive, so I ask that you bear with me and subject your intuitive doubts to the same skepticism you apply to my arguments.

Don't trust your gut. Trust your reason.

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