The Standing Invitation

Posts Tagged ‘Dennett

The Origin of Opacity

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A while back I wrote a post about vision and why it is that some things simply can not, even in principle, be described in visual terms. I focused (see how hard it is to avoid metaphors of sight?) on things smaller than atoms, but I didn’t need to go that far. Right now, you are reading these words through at least several inches of air – real-world, macroscale stuff that you are able to feel or hear when it moves, but are unable to see.

Transparency is something magical. As a child I was fascinated by glass: solid, hard, heavier than water – and yet invisible. I asked how this could be possible, and was never really satisfied with any answer I got. And it turns out this is because I was asking the wrong question. It turns out that glass’s seemingly magical transparency is not the phenomenon demanding an explanation. To gain the deep understanding I missed as a child, we must consider the origin of opacity.

Ranked in order of wavelength, the electromagnetic spectrum begins with radiowaves and continues (decreasing wavelength) with microwaves, the infrared, the ultraviolet, x-rays, and gamma rays. Note the omission: I have deliberately excluded visible light. Why?

The portion of the electromagnetic spectrum that we can actually see is vanishingly small. You could blink and miss it, though of course if you blink you do miss it. Visible light – colour – is an astoundingly narrow selection of the available wavelengths between infrared and ultraviolet. One might wonder why this particular chunk of real estate, between 390 and 750 nm, happens to be the one that we can see. And if you ask it in these terms, you are still asking the wrong question.

Recall that you “seeing” something corresponds to your brain detecting a chemical change in a substance called 11-cis-retinal in your eyeball. 11-cis-retinal only absorbs radiation with wavelengths between 390 nm and 750 nm; anything outside this range has no effect, and so is invisible. So this is why only some of the light gets “seen”. But this only pushes the question back one step further. Why do our eyes employ 11-cis-retinal, and not some other chemical with absorbance in another wavelength range?

We can narrow the possibilities using an understanding of chemistry. There are no known chemical compounds that undergo a chemical change on exposure to radiowaves. This means that no organism dependent on chemistry as we know it could ever treat radiowaves as its own personal “visible light”.  The same appears to go for microwaves, though this is contested. X-rays and gamma rays do cause chemical changes in molecules, but with wavelengths such as this it would be quite a challenge to evolve an eye that could handle them (an essay by Arthur C Clarke suggests an animal with a metal box for an eye and a microscopic pinhole to focus it, but only to illustrate the difficulties involved). So from the restrictions of photochemistry we’re limited to a window about 3500 nm wide available for seeing – and yet evolution has caused us to see only a fraction of that. Why? And why did it “choose” for us the wavelength range that it did?

Well, consider some possibilities. What if we saw in the range of about 100 to 200 nm? Chemically it’s possible. But no organism on Earth would evolve to see in that wavelength. Our atmosphere is 80% nitrogen, and nitrogen absorbs light at about 100 nm. If we saw in that range, air would not be transparent: it would be totally opaque. The ability to see in this wavelength range would be worthless, just as it would be worthless to see around 1450 nm, where water absorbs; we evolved from creatures that needed to see in water. Here is the answer to the problem of transparency, and the problem is revealed to be that the question was backwards. Air (or water, or glass) is not transparent by itself; it is transparent to us because eyes that don’t find air transparent would be of no use to us. The transparency of air is the result of the environment our genes have designed us to live in. Of course, a subterranean creature like a mole might welcome a design of eye that makes soil transparent – while simultaneously leaving worms opaque and visible. But the chemistry for that does not exist, and moles have to make do with being blind.

Practical considerations aside, it’s interesting to ask if X-ray vision might have been useful on evolutionary terms. If we saw in the X-ray region, most matter would be transparent to us, including our own bodies. This would be useful for some things, like spotting tumours or broken bones. But we would struggle to pick fruit, or detect approaching thunderclouds, or build tools out of wood. As a species, we are better off with the kind of eyes that can detect the chemical difference between an unripe fruit (green) and a ripe one (red). Evolution has selected for us a sense of vision that operates in the part of the spectrum that is richest in information relevant to our survival. Other animals make use of slightly different wavelength ranges, like bees, who prefer the shorter ultraviolet wavelengths rich in information about the availability of nectar in flowers.

In fact, it’s arresting to imagine an alien world, lit by sun that emits different wavelengths of light to our own – populated by aliens based on very different chemistry to our own, with strange eyes for detecting wavelengths we cannot ever hope to see. If ever they came to visit us, their children might well look at us in fascination, wondering why it is that we humans are as transparent to them as glass…


Daniel C Dennett: Consciousness Explained

Richard Dawkins: Unweaving the Rainbow

Arthur C Clarke: Report on Planet Three and Other Speculations

Written by The S I

May 6, 2012 at 1:10 am

Thank Goodness!

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I’m away from the computer just now, so here’s an excellent essay by Daniel C Dennett describing how his life was saved by a heart operation – and what it really means when an atheist says “Thank goodness!

I have created a Facebook page for this blog, which those of you who are so inclined may wish to like.

Also, on yet another note, for times like this when I physically cannot get to a computer to update this place, I am thinking of recruiting some guest contributors so I have something to fall back on. If you’re interested in writing a post here on practically any topic, for a general audience and in under 500 words, drop me a comment and we’ll see what we can work out.

Written by The S I

October 11, 2011 at 11:59 pm

Service Announcement

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Folks, for two weeks starting from today I will be away in parts foreign. Rest assured, however, that the S I’s candles are always burning, and regular posts will continue in my absence, although I may be slow responding to your comments.

Meanwhile, if you find yourself with an hour or so to spare, make yourself some tea and toast and watch this talk about free will. Science is showing us that our minds are purely biological phenomena, governed ultimately by the laws physics. Does this mean we have free will?

Written by The S I

August 31, 2011 at 4:32 pm

A Common Tragedy

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The Tragedy of the Commons occurs when a number of people using a finite resource realise that they each stand to gain from taking more than their fair share. You know everybody else benefits from taking more, so that’s probably what they are doing; the more likely they are to be taking more, the more sense it makes for you to take more. And since everybody knows that it makes sense for you to take more… and so on, until the resource is depleted.

Fishers often know that their overfishing will lead to extinction of certain species of fish, and farmers often know that overfarming will leave the land infertile; but cessation is simply not feasible for them as individuals competition.

In a way the problem of short-term benefits outweighing long-term disadvantages resembles addiction. An chocoholic knows chocolate will make him fat; but it’s just too tasty to say no to! His willpower isn’t strong enough.

But our chocoholic friend has an option: he can employ a willpower-assisting strategy. He might not feel he needs chocolate just now, but can imagine a future point when the craving really sets in, when his willpower won’t be enough. So he acts now, while he can, and flushes the chocolate down the toilet, removing the temptation in advance. He enacts policy that anticipates future temptations. Sometimes people entrust this to others. “Don’t bring me any chocolate, I’ll only end up eating it.”

This is one solution to the Tragedy of the Commons. The consumers make a pact: they all agree to how much they can safely extract from the resource, and agree to be punished if they take more, even if ­– especially if ­– it later becomes profitable in the short term to do so. This leads to the creation of national parks, protected areas, one-child policies, fishing quotas and so on.

This kind of contract exploits a very human difference in our valuation of rewards depending on how far away in the future they are. Agreeing to protect a resource is easy when the resource is plentiful.

The trouble is that a sufficiently plentiful resource might not even be seen as a resource. What value do you place, for example, on air? Not much, until you start to see it polluted.

There was a time when the Earth was seen by most people as an infinite source and an infinite sink. Why regulate things that will never run out? It is only after we realise that something is in danger that it makes sense to protect it ­– but if the realisation comes late, and we see that the resource is actually scarce, then the short-term benefits of looting it faster than the other fella become very real to us indeed.

There is a time window between thinking something too free to regulate and thinking it too precious to regulate, and the window is often narrow. What have we missed it for? And what do we still have time to protect from our future, greedier selves?


This was written on a train having just finished The Logic of Life by Tim Harford, and with Dennett’s Freedom Evolves fresh in memory. Both very worth reading.

Written by The S I

August 25, 2011 at 11:59 pm

Ideas Worthy of Nurture

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For human failing/strength/preference/proclivity x, which is more important, nature or nurture?

Nothing could be more of an empirical question. Science can’t explain everything, but there are some things that are absolutely slap-bang in the centre of what science can explain.* This is one of them. The methodology is well laid-out. Take a group of people who have similar a genetic makeup but different environments (like identical twins raised apart), and another group have a shared environment but different genes (like adopted children). See how much variation in x there is between groups, and compare that to the variation within the groups. Perform the necessary statistical tests, see what the outcome is.

This should be as simple, or as complicated or imperfect or conclusive or vague, as any other scientific enquiry. Nevertheless, the nature/nurture question is different. No other issue has more power to fog the process of rational investigation, because it is so intimately involved in how we apportion blame.

It is easy to blame people for things they choose. But it is much harder to blame them for what they are.

For human trait x, whichever one you’re interested in, the research will exist ­– or it won’t. It will be a well-planned experiment or something so poorly executed you’d be amazed it snuck through peer review. It’ll tell you one thing or another, or something in between, or nothing. But in a lot of cases, this won’t matter. In a world of conflicting information, complicated science and a lack of understanding of the relationship between how we were born and what we can become, a lot of people will select the evidence that suits the prejudices of the time. And sometimes great harm results.

To an extent, this is a question of who speaks loudest. The voice of a scientist with graphs and facts is too easily drowned out by a hysterical politician’s claims that people are born violent or raised gay, brought up female or psychotic from birth (or the other way around, as suits). The scientist’s problem is not just making herself heard: she must also overcome the public’s misunderstandings about what exactly we mean when we say that a gene influences behaviour.

If something is genetically determined, that does not make it inevitable. And just because a thing is natural, that doesn’t make it good. Until these two ideas are widely understood, a society built on an accurate understanding of human nature will always face hostility from people who won’t be told what they don’t want to hear.



All of this and more (and better) in The Blank Slate: The Modern Denial of Human Nature by Steven Pinker. See also Freedom Evolves by Daniel C Dennett for the difference between determined and inevitable.

* Don’t even get me started on homeopathy.

Written by The S I

August 23, 2011 at 11:59 pm

A Few Comments On Your Wallpaper

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Here’s another one drawn from Dennett’s Consciousness Explained. Before reading on, find yourself a pack of cards. Go ahead, I’ll wait.

Got the cards? Obviously you found them using your eyes. Human vision is pretty good for mammals. Reflect for a moment on how much detail you can see right now: you see a whole page of words, on your computer screen, in full colour. Probably you are aware of what objects are behind your monitor, colour the wallpaper is, what its texture is. It’s pretty impressive.

Now take your pack of cards, shuffle them and select one at random without looking. Keep your eyes focused on one point directly in front of you. Without turning your eyes to look at it, hold the card at arm’s length to one side, with the picture-side turned towards you. It’s in your peripheral vision. You probably can’t see it very clearly, and have no idea what card it is.

Now move your arm a few degrees closer to the centre of your field of vision. Can you identify the card now? Can you even see what colour it is? Move it a little closer. Black or red? Face card or number? Keep moving it closer, without looking directly at it. It really is surprising how close it has to get to the centre of your field of vision before you can confidently identify it; up till then, it’s a blur.

The clear patch in the centre of your vision corresponds with your fovea, the densest concentration of rods and cones in your retina. This is the only part of your eye that can see in detail and colour. The rest is devoted to picking up motion, change; it is the early warning system that tells you where to point your fovea.

You don’t see the world. You see a description of the world that is provided by your eyes. Your fovea flicks from one point of interest to another, gathering information with which to update your brain’s virtual-reality reconstruction of your surroundings. The brain’s editing process is seamless: it’s only when you deliberately prevent your eyes from moving that you realise just how patchy your vision really is.

Dennett goes further: imagine you have some really garish wallpaper, in the style of Andy Warhol, that consists of thousands of identical pictures of Marilyn Monroe. When you look at the wallpaper, how much of it do you really see? Every Marilyn in detail? Or does your brain just ‘fill in’ the rest, based on inspection of one or two. Either way, you can’t tell the difference.

The unsettling conclusion of all this is that you actually perceive the world in more detail than your eyes are providing. The sense of vision is not a window on the world: it is a cobbled-together bag of cheats, tricks and shortcuts. Fortunately, this seems to be enough.

Written by The S I

July 18, 2011 at 8:05 pm

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You Just Think You Are

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We’re big fans of Daniel C Dennett here at the S I. This magnificently bearded Tufts philosopher has spent much of his career trying to solve the ancient puzzle of what the mind is, and how it relates to the brain. His slogan: “Yes, we have a soul, but it’s made up of lots of tiny robots.”

How is it, he asks in his book Consciousness Explained, that a collection of unthinking nerve cells can somehow go to make up a thinking, feeling being? No single brain cell knows or cares who you are. So how can the ensemble be different? What is the magic step that turns robotic components into a human whole? To try to make sense of this emergence of the self, he introduces the idea of the centre of narrative gravity.

In physics, gravity is potentially a tricky business. Consider a football. Drop a football, and any physicist will tell you it will fall. How do they know this?

It is theoretically possible to go back to first principles: calculate the gravitational attraction between all atoms in the ball and on Earth, work out the details of their interactions, then, millisecond by millisecond, determine that every atom in the ball will ultimately move downwards. But of course this is not what they do. There is a much easier way: give the football a centre of gravity. This is a single, imaginary point that stands for the whole ball. It averages out the incredible complexity of the atoms in the ball, and allows physicists to treat it as a unified entity.

Note that the centre of gravity is fictitious. Although it is located at the centre of the ball, it is not associated with an atom at the centre, or indeed any one atom. A football’s centre of gravity exists only in the minds of people who study footballs.

In the brain, Dennett argues, we have something similar. There are billions of brain cells, all firing all the time, each one telling its own story. Every time a cell fires, a set of conditions is reported – information about what a retinal cell is saying, or what the balance organs of the inner ear are saying, or what other brain cells are saying to each other. To run an efficient organism, these narratives have to be made sense of – and quickly, before the sabre-toothed tiger mentioned by one brain cell has a chance to eat you. The neurons can’t be addressed individually. Wouldn’t it be better to treat them as one thing? This is where the self comes in.

Who are you? You are your brain’s centre of narrative gravity: you are the point in space around which the experiences reported by your brain cells cluster. You, unified, singular you, are a fiction generated by your brain, as flag to rally defences around.

It is your brain cells, working together, that are reading these words right now. You, the person, are not. You just think you are.

Written by The S I

July 14, 2011 at 8:25 pm

Posted in Science

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