## Paraclimbing World championship – Paris, 2016

UPDATE: I ended fourth in my category. That’s less than I had hoped for, but a lot more than I had expected (I was the only Dutch finalist). The next worldchampionship (Innsbruck, 2018) I’ll do better!

Five days to go and then… showtime! On Tuesday I will leave the Netherlands for almost a week and try not to think too much about science, philosophy, PhD’s and all that. I need to focus, because I’m going to compete in the 2016 world championship paraclimbing in Paris

A month ago I had to sign up for this event. I had to promise that I wasn’t going to use doping of any kind and that I won’t be doing any betting concerning my own matches. I also had to fill in which disability-category I’ll be competing in. That was a tough choice. There are three overarching categories: one for people with visual impairments, one for people with (or without?) amputated limbs and one category for paraclimbers with limited power, range or stability (RP). Sounds pretty straightforward, right?

None of my limbs are amputated. Nor am I blind; I do have double-vision (diplopia), colour-blindness (dichromacy) and nearsightedness (myopia) but I still have more than 20% of my visual field, so I don’t belong in the category of visually impaired climbers. I decided to sign up for the RP category. The RP category is itself subdivided into four smaller categories, each of which is again divided in yet smaller categories – now I know what Zeno’s Achilles must have felt like. In the end I couldn’t decide between RP2 and RP3 (most of the deficiencies listed apply to me) so I just picked one at random.

When I’m in Paris on Wednesday (the 14th) there’ll be an examination by a bunch of French doctors to determine whether my own idea of the category I’m in is right. At the end of the examination they will not only determine the category I’m in, but they will also give me a ‘correction factor’. Such a correction factor works like a ‘handicap’ in golfing: the score one attains is multiplied by the correction factor to even out an unwanted advantage. For example, suppose that me and mr X are in the same category but he has a correction factor of 2 and I have one of 1.5. Say we climb to the same height (say, we both reach the 5th grip) then his final score will be higher than mine because his score is multiplied with a larger factor (and $2 \times 5 > 1.5 \times 5$).

I have to admit I was somewhat worried when I first learned about these categories. Even if they make many categories, I thought, there is always quite a lot of room within the categories so that I would have to compete against people that, while they have the same disability, are less disabled (for example, someone who is spastic but has perfect balance). While I was thus convinced that these categories would never give me a fair chance, the correction factor made me hopeful again. Imagine, for a moment, that the doctors on Wednesday put me in a procrustean category. And then they give me a very high correction factor, because I don’t really fit into the category. My disadvantage will get me onto the podium!

Posted in paraclimbing, Personal, Travels | | 3 Comments

## Does Science Describe Reality?

In the philosophy of science there is a debate about whether scientific theories tell us what the world is really like, or whether scientific theories are nothing more than ‘tools’ or ‘instruments’ – useful for making predictions, but not for telling us what the world is really like. This debate is called the realism-debate. Most working scientists are realists: they believe that scientific theories tell us what the world is really like. They argue that realism is the only philosophy of science that can explain the success (in terms of the accuracy of predictions) of science. For example, they argue that “the theory of atoms allows us to predict that a gas expands when it is heated; wouldn’t that be a mystery if atoms did’t exist?”

Most realists would admit that we can never be 100% certain that our scientific theories tell us what the world is really like. “But”, they argue “science gets better and better at making predictions, and that shows us that we’re on the right track – we’re getting closer to the truth.” The idea that our realists defend is that of convergent realism. The assumption of convergent realists is that as science progresses, it gives us a better picture of what the world is really like. Often without being aware of it, convergent realists assume that better prediction goes hand in hand with a more truth-like description (because that’s what ‘being on the right track’ means).

We’ll see that the realist’s assumption that better prediction implies a more truth-like description is problematic. Consider, as an analogy, a map of some city-centre, on which all the streets and buildings are represented by lines on a flat surface. We will call the city map a ‘model’ of the city. Imagine that there is a second model of the city, and that the walls in this second model are made out of real stone (as perhaps in a scale model); they are not flat lines on a piece of paper as the walls in the first model are. Suppose also that the second model is very incomplete and that it has only several streets and buildings in it. Now we ask: which model is better?

Scale model of ancient Rome

We are going to test the models. Suppose that we are actually in the city-centre and start walking in a certain direction. Suppose that both models tell us that there’s a wall ahead. I don’t know about you, but I’d like to be able to predict what actually happens if I cross something that looks like a line on the map! Okay, perhaps the first model has the advantage that you can use it anywhere in the city-centre, but the second model helps you predict what actually happens if you bump into a wall. We see that the question of which is the better model is not easy to answer. We could of course assume that the best model is the one that yields the best predictions. But then the scientist’s claim that better predictions show that we are closer to a true picture (the perfect model) becomes a tautology: better predictions show that we have a better model, which, in turn, means nothing else than making better predictions. So better predictions show us that we make better predictions – we don’t have to be convergent realists to know that.

What goes for city-maps also goes for scientific theories: some of them are great for making predictions, but that does not mean that they tell us ‘what the world is really like’. This shows that if scientists say that the better their theories predict, the more accurately these theories represent reality, they’d better scratch their heads some more.

Street map of ancient Rome

## This Is What Climbing With A Hemiparesis Looks Like

There remains a lot to be learned…😉

Posted in paraclimbing | 1 Comment

## Olympic paraclimbing

Besides physics and philosophy I invest quite a lot of time and energy in sports. Several years ago a friend of mine asked me to join him to go climbing in a gym. When he saw me wavering he spoke the magic words “perhaps it’s not such a good idea. Your disability will make it very difficult for you to get up there”. That’s when I was sure that I was going to go climbing. And so it started. Now, almost four and a half years later, I go climbing every week and I have made some nice rock climbing trips abroad.

September last year the Olympic Committee announced that sport climbing is to have a place at the Olympic games in Tokyo in 2020. For any branch of sports at the Olympics there is always a ‘para’-branch; a competition solely for athletes with a disability. For climbing there is paraclimbing. Some of my climbing friends told me about this when they had heard the news and jokingly asked me whether I was going to compete in the Olympics. It was an absurd idea of course…. or was it? I decided to do some asking around and I was lucky. While in the countries surrounding the Netherlands paraclimbing involves a fierce competition due to the large number of competitors, in the Netherlands paraclimbing is relatively unknown. As a matter of fact there are in the Netherlands in the official competition only two paraclimbers… one of whom is me.

I am not exceedingly good at climbing. If it hadn’t been for my braintumour I would never have been admitted into an official training program. I realise that, but I also know that it has always been the olympic adage that ‘participating is more important than winning’.

For me climbing has always been a hobby – time-consuming, yet not as important as my PhD or my editorship at Foundations of Physics. It stays that way. But now that I am officially a top-athlete (I don’t feel like I’m one) I’ll have to start training many times a week and I have to follow a very strict diet. The Olympics are still very far away. The first upcoming competition that is relevant for me is the world championship in paraclimbing in Paris in September this year. I’ve got four months to seriously improve my climbing skills – per aspera ad astra!

## What Is A Dimension?

In sci-fi movies there is often talk of “going to another dimension” as if there is some kind of barrier in between dimensions that can be crossed only if the circumstances are very special – usually the filmmakers are wise enough not to specify what these very special circumstances are. I will show in this blogpost that “Travelling to another dimension” is not only physically impossible; the phrase makes no sense from a logical point of view either.

In the exact sciences, when we want to describe a physical situation we need a number of variables to do so. For example, if we wish to describe the fall of a stone then we need a minimum of three numbers to pinpoint the location of the stone in space (the space coordinates), and one number to locate the stone in time (the time coordinate). With the aid of these four numbers we can describe all possible developments of the situation. Viceversa, all possible states the stone can be in can be described in terms of these four numbers. The same goes for all material things that science is about: not only stones, but also houses and – in the case of sci-fi movies, spaceships – are described with the help of this minimal number of variables. Because those variables are needed to measure [1] they are called dimensions (from the Latin dimensio – a measuring). In our example of the falling stone every point in space and time is necessarily characterised by all dimensions because every dimension is by definition one of the minimal number of variables needed to describe a physical state (intuitively put:  a dimension must be everywhere [You can’t have a stone with length and height but without breadth]).

Someone might argue that the number of dimensions we believe to exist changes as science progresses. In certain extensions of Einstein’s relativity theory (such as the Kaluza–Klein theory) there exists a fifth spatial dimension; and in string theory – the theory that has been a promising candidate for the unification of relativity and quantum theory for at least 50 years – there are perhaps as many as 11 spatial dimensions.

That’s right: whereas it’s logically impossible to travel to alternate dimensions; it’s not logically impossible to discover alternate dimensions. The following example will show that.

Consider a bunch of very smart ants on a soccer ball. Suppose that these ants cannot look up due to some inheritable neck disease. Now if one of those ants were to come up with an antidote to this disease the ants would suddenly be able to look up and discover a third dimension. What they discover is not a third dimension into which they can now travel but rather that they have been living in three dimensions all the time (even before the antidote was discovered).

[1] It is an unanswered question in the philosophy of science whether these numbers are merely needed to measure or whether they are the ‘realm’ in which is measured. Perhaps the latter choice is the more intuitive, but that choice incorporates the metaphysical claim that space is more than what is measured by a yardstick – a claim that Einstein was unwilling to make.

Posted in Philosophy of Physics | Tagged , , | 1 Comment

## Conference Vienna – lunchtime!

[disability as a networking skill]

When abroad I use a wheelchair because it’s quite a hassle to take a tricycle with you on an airplane. When I visit conferences on my own I cannot use a wheelchair because my left hand doesn’t work (and I don’t want to go in circles all the time). Being on foot at a conference can be a challenge for me because often you have to cover distances of over 100 or 200 meters in between speaker sessions for which you only have five minutes. It is also challenging when the conference-organised lunch consists in a DIY buffet, because I can’t even walk with a cup of coffee in my hands; let alone with a tray filled with food! I often have to ask total strangers for help. This can be a bit of a nuisance because I like being independent. But on the other hand it is also a great advantage because it allows me to come into contact with other conference-goers (without being obtrusive) whom I wouldn’t have met otherwise. In short: it allows me to extend my academic network.

## How Natural Is The Natural Logarithm?

I want to show in this post that the natural logarithm is not natural – it is not a characteristic of objective nature.

The natural logarithm pops up everywhere in science: biology, sociology, economics… and the list goes on. Every student of physics knows that many of the calculations in physics (for example in electrodynamics and quantum mechanics) would be undoable if it weren’t for the natural logarithm. The universal applicability of the natural logarithm suggests that it is something that exists in the world in which we live; that it is a characteristic of the physical world. We will see, however, that the naturalness of the natural logarithm (having base $e$) is a characteristic of the definition of derivative – and of any logarithm to which this definition can be applied.

### Wherever there’s derivation, there’s $\bold{e}$

The natural logarithm is a logarithm with as its base the mathematical constant $e$. $e$ is a number such that the function $e^t$ for every $t$ has a value that is equal to its rate of growth $[e^t=\frac{de^t}{dt}]$. The existence of a number with that characteristic follows logically from our definition of derivative.

The derivative of a function $f(t)$ is defined as follows:

$\frac{df(t)}{dt}=\lim_{h \to0}\frac{f(t+h)-f(t)}{h}$.

In mathematics all exponential functions are of the form $f(t)=ca^t$  Therefore, if $f(t)$ is an exponential function then the following holds:

$\frac{df(t)}{dt}=\lim_{h\to0}\frac{ca^{t+h}-ca^t}{h}$

We can move $ca^t$ outside the limit so that the limit no longer depends on the variable $t$ (and it is therefore a constant in $f(t)$):

$\frac{dca^t}{dt}=\lim_{h\to0}\frac{ca^{t+h}-ca^t}{h}=ca^t[\lim_{h\to0}\frac{a^{h}-1}{h}]$.

Let’s take a closer look at the latter limit. In it there are the two functions $f_1(h)=a^h-1$ and $f_2(h)=h$. We may calculate the value of the limit with the help of l’Hôpital’s rule:  by determining the derivatives of $f_1$ and $f_2$ and computing $\frac{f_1'}{f_2'}(0)$. Determining $f_2'$ is easy; $f_2'=\frac{dh}{dh}=1$. The value of $f_1'$ is less straightforward, because it depends on the value of $a$. If $a$ in $f_1$ has the value $e$ then $\frac{f_1'}{f_2'}(0)=\frac{e^h}{1}(0)=1$ (in the figure you can see that for $h=0$ $f_1$ and $f_2$ have both the same value and the same slope; $f_1'$ and $f_2'$ also have the same value). Returning with our findings about this limit to the equation for $\frac{da^t}{dt}$ we see that the only exponential function for which $\frac{df(t)}{dt}=f(t)$ is the exponential with base $e$; $\frac{dca^t}{dt}=ca^t$ only if $a=e$.

### Every exponential can be expressed as a natural exponential

Consider again the general form of the exponential function, $f(x)=ca^x$. There are two ways in which we can transform any function of the form $ca^x$ into a natural exponential function.

1. Firstly, we can choose a suitable variable transformation ($t \rightarrow x$, where $x=\log_a e^t$) so that we may write $f(x)=ca^x$ as $f(t)=ce^t$.
2. Alternatively, if we don’t want to adjust the variable, we may rewrite $ca^x$ as $ce^{c_1x}$ (for $a=e^{c_1}$) and then let $e^{c_1}$ merge with $c$ into some other constant $c_2$ so that we end up with $f(x)=c_2e^x$

Suppose for example that a biologist, let’s call her Fleur, studies a colony of bacteria in a Petri dish. Fleur finds that the number of bacteria in the Petri dish grows exponentially with a linear increase in time. Say she counts the time, $t$, in seconds and formulates the function $n(t)=ca^t$ to describe the number of bacteria. If $a\neq e$ then n(t) is cumbersome to work with mathematically. If Fleur could rewrite $n(t)$ in terms of a natural logarithm then any differential equation with $n(t)$ in it would become much easier to solve.

Suppose Fleur indeed wants to rewrite $n(t)$ in terms of a natural logarithm. She has measured the number of bacteria at $t=0$ and found it to be $n(0)=c$. It would be a bad idea for Fleur to use the second method (2) of naturalising $n(t)$ because that would change $n(0)$ and then $n(t)$ would conflict with her initial measument. Fleur, being the clever biologist that she is, realises that and therefore opts for method (1). Suppose that she sees that $n(t)$ doubles every 2.5 seconds. Then she might try substituting the variable $t$ for a variable $x$ for which each unit-step is not 1 second but 2.5 seconds ($x=\frac{1}{2.5}t$). The function $n(t)$ can now be rewritten into a function $n(x)$ which has a natural exponential form: $n(x)=ce^x$. This will make Fleur’s life much easier.

Now we may ask the question whether the natural exponential growth-rate is a characteristic of the system that is studied or a characteristic of the way we describe that system. The facts that $e$ is a characteristic of the definition of derivative and that any exponential function can be written as a natural exponential might suggest that $e$ is a characteristic of our number system and not of nature. Such a conclusion, however, disregards a distinguishing feature of logarithmic functions.

### But not every phenomenon can be described by an exponential

The distinguishing feature of logarithmic functions is that their rate of growth at a certain moment scales with the value of the function at that moment. A natural logarithmic function is a special case of this in that the scaling is very simple: the rate of growth is at every moment exactly equal to the value of the function at that moment.

Any dataset that can be described in terms of exponentials can also be described in terms of natural exponentials (any exponential function can be transformed such that its base is $e$), but we have stumbled upon an objective fact about nature (as it comes to us in our observations) whenever we discover that some phenomenon allows a description in terms of exponentials at all.

The fact that we can describe nature in terms of natural logarithms is a consequence of the way we describe nature, but the fact that we can use logarithms at all tells us something about nature’s dynamics.

## Kant & Modern Physics

The part of Kant’s philosophy that I’ll be discussing in this post is Kant’s view on human knowledge. The central idea of Kant is rather straightforward: the world must be such that knowledge is possible. The world, according to Kant, must be structured in such a way that our knowledge of that world is possible. And since we have knowledge (otherwise we couldn’t live our lives) the world must have certain structural features that make this knowledge possible.

It sounds like Kant is stating the obvious here. We have knowledge of everyday objects; for example, we know that heavy objects (such as stones) fall. In Kant’s view it follows from this that it must be possible to think about heavy objects and about ‘falling’. Ok, so there must be the possibility of knowledge in order to have knowledge – sounds pretty simple, doesn’t it?

Immanuel Kant (1724-1804)

Things become complicated when Kant tries to specify what it means to be able to think about objects and processes. Thinking about a falling stone is impossible, Kant believed, without thinking about this process in terms of causal laws. Kant’s argument therefore boils down to the following: causal laws are inherent in knowledge; we have knowledge, so causal laws must exist.

When Kant wrote about these matters (in the 18th century) he had in mind Newton’s physics as a model for human knowledge. The possibility of knowledge therefore went hand in hand with the possibility of Newton’s physics. Causal laws are essential elements in Newton’s physics (manifesting themselves as the conservation of momentum) so it shouldn’t surprise us that Kant identified causal laws as essential elements in knowledge.

Modern science presents numerous challenges to Kant’s and Newton’s view on causal laws. In the theory of special relativity the concept of time loses its absolute character and it therefore becomes impossible to say which events precede which events. What does it mean to say that some event causes another if there is no ‘earlier-than’ relation? Causes in quantum theory are even more problematic: in quantum theory there are events which have no cause in the Newtonian sense at all.

These scientific developments suggest that Kant was mistaken when he said that causal laws necessarily exist. Modern science shows that knowledge (in the form of scientific theories) is still possible without causal laws. And yet Kant’s central idea – that the world must be such that knowledge is possible – is still a truism. It’s just that we’ve come to realise that our knowledge does not coincide with knowledge in Newton’s physics. How should we make sense of Kant’s idea in the face of modern physics? One option is to replace Newton’s causal relations between events with relations of probability. That works as follows.

Suppose a scientist repeats a measurement a number of times. For example, she repeatedly measures the length of a stick. No matter how accurate the measurements are, they never yield exactly the same results because there are always infinitely many possible disturbing influences (the wind, a varying temperature of the stick, ambient air temperature, quaking due to seismic activity; you name it). If the results of the measurements were put in a graph then we would not find a straight line (representing equal measurement-results), but a normal distribution (a Gaussian, or bell-shaped, curve; see graph). Someone with a strict belief that everything in nature follows the same causal laws may believe that different measurement-outcomes are due to measurement disturbances, but she may as well believe that the different measurement-outcomes refer to differently sized sticks (compare a sociologist who is not sure whether the variations in her data are due to variations pertaining to one individual or to variations within a population of individuals).

A normal distribution, which is symmetrical around some average value$\mu$.

But wait! Such a normal distribution is actually an approximation of what is measured. The real results form a dotted line which (if the scientist has done a proper job) only roughly follows a smooth, normal distribution. Before we can use experimental results to construct a mathematical model of the experiment we must assume that the experimental results can be extrapolated to a smooth curve. That’s the first assumption we need to make. But that is not enough. Suppose our scientist is asked by a fellow scientist what is the length of the stick. It would not be satisfactory if our scientist could only point at the normal distribution and say “the actual length of the stick is somewhere in that graph”. No, what the scientist must also assume is that the average value of the normal distribution corresponds to the length of the actual physical stick. To be able to construct useful mathematical models using experimental results we must make at least these two assumptions: 1) experimental data can be extrapolated to a smooth, normal distribution, and 2) the average value of this distribution corresponds to something real.

Hans Reichenbach (1891-1953)

Back to Kant and to his possibility of knowledge. After our analysis of the role of probability in science, we might now determine how assumptions about probability theory make knowledge possible. The philosopher/physicist Hans Reichenbach (early 20th century) diagnosed a deficit in Kant’s philosophy: Kant’s idea is relevant not for knowledge per se, but for scientific knowledge. The above considerations show that the possibility of scientific knowledge requires that the scientist makes certain assumptions about the theory of probability. Probability theory serves to flesh out the import of Kant’s philosophy for modern science.

Posted in Probability | | 1 Comment

## Probability “0” Is Not Impossibility

The probability that a dart will hit any specific point of a dartboard is zero because there are infinitely many points on the board. And yet if you throw a dart at a dartboard you’ll always hit some point (assuming you hit the dartboard). Hitting a specific point at a dartboard is highly improbable, but not impossible.

The responses to a similar statement in a previous post were mixed. Some people were delighted by its counterintuitiveness, whereas others were skeptical – what if we assume that the tip of the dart has a size that is not a mathematical point? What if it were, say, 0.1 square mm? That wouldn’t change the probability of hitting any one point, because there would still be an infinite number of points on the board. True, the probability of hitting any one of those points would increase by a certain factor, but no matter how large this factor is, the probability of $\frac{1}{\infty}$ is still $\frac{1}{\infty}$ – zero-probability.

What we can do is divide the area of the dartboard into a (finite) number of smaller areas and assume that if two of such areas are equal in size, then the probability of hitting them is also equal. There are two fundamental problems with such an approach:

1. How do we know that equal areas have equal probabilities?
2. There are infinitely many ways to subdivide an area. How do we know which one is the correct one?

To grasp the second of these problems it might be helpful to realise that this problem occurs whenever we try to subdivide an infinite set. Just think of the set of positive integers (1, 2, 3, 4, 5…etc.) and try to subdivide it into equal subsets. These equal subsets may have any size we choose. For example, we can choose subsets each of which contains two elements, like this: (1, 2), (3, 4), (5, 6), (7, 8)…(etc.). But we might also opt for the smaller subsets (1), (2), (3), (4)…(etc.) or the larger subsets (1, 2, 3), (4, 5, 6), (7, 8, 9), (10, 11, 12)…(etc.). There are infinitely many choices, because we’ll never run out of integers! The same argument goes for areas (just assign an integer to every point) or any other infinite set.

Both of the questions facing the probability theorist can only be answered by adopting a suitable convention. The scientist must assume that equal areas have equal probability of being hit and she must assume that there is a preferred way to divide up a continuous area that is shared by other scientists. This shows that statements of probability do not have universal validity. The probabilistic problem of uniquely dividing up infinite sets has become known as Bertrand’s paradox.

If probability is in its core subjective, as we’ve seen, then why does science seem to possess an objective quality? One may suspect, perhaps, that the crux lies in finding the right convention. But that is not the case, since different conventions are logically equivalent; none of them is objectively better than the others. All we can do is what scientists have done ever since the dawn of science: find out by trial and error what are the most useful conventions in different situations.

For a thrower of darts the situation is simple because the conventions have already been decided upon. All players know beforehand that equal areas have equal probabilities (without being aware that this is a convention). The other convention, about the subdivision of the surface of the dartboard, has already been decided upon by the manufacturer of the dartboard; all players tacitly agree upon this conventional subdivision of the surface of the dartboard.

For the scientist – perhaps working in the field of particle physics or in cosmology – it is not obvious which conventions are useful: perhaps there is a particle for which equal size does not imply equal probability. Or perhaps two cosmologists from opposite points on the earth’s surface study some galaxy without knowing the angle from which they observe the galaxy. These cosmologists will disagree on which areas on the distant galaxy are equal (and hence they might disagree on the exact source or intensity of incoming radiation).

Science is, in the end, a capricious affair.

Posted in Probability | | 2 Comments

## Conference Vienna, part II – customs, Kant and quantum mechanics

When I had exchanged email addresses with the Japanese girl and we had said goodbye to each other, our wheelchairs were pushed off by one of the airport’s employees. With great dexterity he steered both wheelchairs at the same time to our next stop: customs. The customs check is one of the most unpredictable parts of a journey in a wheelchair. Sometimes the check is very thorough: the douaniers check every inch of the wheelchair; frisk me while I remain seated and even swab the wheelchair’s tires for explosive residue. At other times merely seeing the wheelchair is enough to just let me pass and wishing me a pleasant journey. The only constancy that I can detect is that never once have they checked the tubes in the frame of my wheelchair – I wonder what could fit in there.

When we had passed customs the wheelchair pusher dropped me off before the gate from which my plane was to leave. I was lucky, I thought, because the gate was straightly opposite from a coffee bar, so I wouldn’t have to walk very far for my ‘daily worship of the black gold’. Neither were the toilets very far from my gate. I sat down and made myself comfortable. Out of my bag I took a sandwich and the book I wanted to read. To get into the spirit of the conference I had chosen a German book on Kantianism. At the conference I was going to give a talk on something I’ve been working on the past few years. I’ve been working on the role of Kant’s philosophy in modern philosophy of physics. Many physicists see little value in philosophical systems, no matter how well thought-out, of over two centuries old. At the other extreme there are those who believe that modern physics, and particularly quantum mechanics, present philosophers and physicists alike with problems that can only be resolved within a Kantian approach.

Looking up from my book, rather sleepily, I noticed on the view screen that the regular boarding was to be preceded by what they call ‘priority boarding’. People with babies or other disabilities or people who are willing to pay for priority boarding are allowed to board the airplane before the horde of regular passengers. Since I fall in the category of people with disabilities I’m allowed to make use of priority boarding.

By the time the actual boarding of the airplane begins I’m not in a wheelchair anymore, and as long as I’m not walking I don’t really look disabled so I always try to make sure that the people behind the boarding-counter see me walk up to them so that they’ll allow me to ‘board with priority’.

When I walked up to the counter to tell the lady behind it that I wanted to make use of priority boarding she had been very busy with a conversation up until that moment and hence had not seen me walking up to her desk. So when I asked her whether it be possible to make use of priority boarding I could hear her starting a sentence “but why do you need…” As I was quickly trying to think of a way to convince her of my disability (should I show her the scar on the back of my head, which was due to the latest brain surgery I’d had?) I almost fell over backwards. When I had regained my balance the lady behind the counter was a lot more willing to accept that I belong in the disability priority class.

The stewardess behind the counter, made anxious by her experience, now wanted me to board the plane with extra priority – even over the other priority passengers (she was probably afraid that I would fall). Once in the plane I could relax: “if anything goes wrong now it’s not my fault” I thought. I always like flying because on a flight you can read or work without being disturbed. But not only that. Not only without being disturbed but also without the possibility of distracting yourself with Google or Facebook or what-have-you: you can sort of force yourself to do the work that you have taken with you. For most people this strategy will not work because it will only make them stare out of the window of the airplane. For me the situation is somewhat different because I have so much double vision (because of the spasticity of the muscles moving my left eye) that staring out the window while actually seeing things requires a lot more effort than reading. For me the strategy works perfectly: often I look forward to a flight for weeks because I have already decided upon what to read.