# Do dragons exist?

After having written this question I began to ponder what answer would my readers expect. For God's sake, not a simple "no", I hope? (At this point I would expect from many a reader an impulse of protest: "Has the author forgotten that we are not kids any more and we cannot be made to believe in fairy tales?" - to which I would reply: "Oh, really?".) The matter is not that simple at all. It relies heavily on
• the definition of a dragon,
• the definition of the word "exist",
• on the possibility of verifying or falsifying any possible answer to the basic question.

First of all, everything I (and maybe others) think of as existing at this very moment indeed exists, in some sense. Therefore - in this sense - not only dragons exist, but also Mr.Pickwick or Apollo. For instance, when I think of Mr.Pickwick, he exists; his existence depends on me, but nevertheless he is not me. He is not an act of my consciousness, for of no act of my consciousness can I ever say with reason that it walks around with an umbrella. In the same sense I can say that dragons exist, too. This point of view seems to be to trivial, though, and we shall therefore not spend any more of our time on it. I shall now be only interested in `serious` existence, such as the existence of the desk at which I am writing this article right now.

Second, everything depends on the definition of a dragon. If looking at a dog I say `This dragon could devour anything it finds on its way', then I am applying a definition of a dragon due to which dragons exist no less than desks do. But this seems to be too easy an answer again. So let a dragon be a creature covered by scales, with lizardlike feet, bat's wings and seven fire-belching mouths. Do such dragons exist? With some hesitation I reply - probably not. What makes me think so? To begin with, nobody has ever seen such a monster. The second reason is that its existence in the form postulated by the definition seems to be in total opposition to the known laws of biology. The first reason - important as it is - does not seem to be very convincing. After all, up to a certain moment nobody has ever seen radium. Would it be justified to conclude that radium did not exist until that moment? This would have been a very risky statement indeed. Every discovery makes us see something that we did not know before. Hence only the second reason, more important to my opinion, remains. To my knowledge, the existence of dragons contradicts the laws of biology. But these laws, as any other laws, may change with time. How can I be sure that some extended laws of astrobiology will not admit the existence of dragons in some hidden corner of our Galaxy? At the present state of knowledge I can only say today that the existence of dragons seems to be very, very improbable.

Well then, let's now turn to the other end of our cognizance and ask whether desks exist. Do they exist more than just my conception of a desk? I am inclined to say yes, they probably exist. What are my reasons now to give such an answer? Well, first - I perceive various sense impressions: visual, tactile, maybe aural (if I tap the desk with my fingers), perhaps some other kind of impressions, too. Second, my impressions have the property of being coherent, they are consistent with each other. Third, this group of impressions is very stable. I go away from the desk, I turn my back to it and then I look at it again - and there it is, as if nothing had changed. Everyone can try this experiment.

You may easily notice that in my argument I used both sensorial data and my knowledge (superstitions?) on what the world should be like. There must be some consistency! some causality! some intrinsic coherence! It is absolutely necessary! As in the case of dragons, our conviction on existence or non-existence was based on two factors - sensorial data and our theories on what the world is like, theories which stem from our will to grasp an understanding of the world. I say: the desk probably exists - and the word `probably' leaves room for a theoretical possiblity of a longlasting sensorial illusion or of a sudden failure of the causality principle right here in this corner of my apartment.

What am I aiming at? I would just like to make everyone realize that no theorem of science nor of our everyday knowledge has the value of an absolute truth; it is always a more or less probable hypothesis. I agree - it is sometimes very probable indeed. Nevertheless, there is always a possibility of fundamental doubts. Human's subjective certainty should not be confused with the basically hypothetical character of science. The same applies to judgments on existence. If we say, for instance, that atoms exist, we express our conviction that the hypothesis on their existence has become probable enough to be transformed into our subjective certainty. However, this was not always so. Eminent philosopher and physicist Ernest Mach wrote by the end of the 19th century: `it does not befit science to assign real existence to variable economical means like particles and atoms which it had itself created'. In other words, atoms are useful as economical means for the description of phenomena, but in fact they do not exist! It was only when the results of research on Brownian movement (Einstein and Smoluchowski) and Jean Perrin's admirable experiments on the behaviour of resin emulsion became known that the conviction on the existence of atoms prevailed.

It is time now to admit with all sincerity that the Editors of Delta have asked me to write an article not on dragons and not even on atoms, but on quarks. The title of the paper was originally intended to be Do quarks exist? However, I would not be able to present the topic properly if I had not previously made this introduction, which is now almost over.

Let's look at a proton first. Do protons exist? Contrary to desks, nobody can claim having perceived sense impressions coming `directly' from a proton. `Well - may somebody ask - and what about proton traces on photographic emulsion or in a cloud chamber? Are they not photographs of protons?' Let's consider this important problem. What do we see on a photograph, in fact? On the negative we can see dark areas, which are the result of some simple chemical reactions in the emulsion due to its processing. These grains come from a decomposition of silver bromide and liberation of metallic silver. The decomposition of the molecules of bromide has been caused by the action of electric forces exerted on the molecules by a particle running through the emulsion. These forces decrease with an increase of distance, so their strongest action corresponds to places where the probability of finding a particle is the greatest. Thus an evaluation of the density of grains along the trajectory can yield an estimation of the electric charge of the running object. And so on. We can see now that our argument has gone a long way from the initial sense impressions to final conclusions. It had to cross the land of ionization theory as well as that of the theory of chemical reactions of a rather special kind. Moreover, the counting of grains (needed to evaluate the degree of ionization) requiring a microscope, we also depend on the laws of optics. As you can now see, in this case, too, our conviction on the existence of protons is based not only on sensory data, but also on our knowledge about nature. We might say that the assumption on the existence of protons saves our faith on the rationality of our world, which - without protons - would remain a paradoxical mystery.

Well, and what about neutrons? A neutron leaves no trace on a plate, does it? In this case - leaving aside for the moment all information which comes from an interpretation of data on the structure of an atomic nucleus - we analyse some special events. They are characterized by the fact that in one particular point of space we can observe a process in which there is clearly no preservation of energy nor momentum, whereas after some time and at another point some energy and momentum reappear - from nowhere. In addition to all the factors we have been considering before, we must also take into account our firm belief in the correctness of principles which govern the behaviour of the above mentioned mechanical entities. Our faith in the rationality of the world requires much more effort now - we must assume the existence of neutrons even if there is no visible trace of them, not even in the sense which made us see protons.

Some elementary particles live surprisingly short - their average lifetime is of the order of $\left\{10\right\}^\left\{-24\right\}$ s. In such cases we never see their traces, even if sometimes these particles are charged. For a particle with such a short lifetime to cover the distance of 1 mm in a chamber it would need a momentum \${10}^{21}\$ times greater than its mass (in a unit system in which c=1). This is not attainable at present and maybe never will. Even cosmic radiation exhibits no energy greater than approximately \${10}^{22}\$ times the mass of an electron. When do we see, then, that makes us believe in the existence of such objects? It turns out that an observation of one particular event involving a particle provides no information at all. We must assemble many such `suspected' events, make an appropriate chart and perhaps then we might be able to discover some features which would sustain the hypothesis on the existence of the particle. This method would appeal only to those who realize that the hypothesis on the existence of such a particle is the only known possibility of explaining events, which otherwise would become an irrational chaos. A `known' possibility? Well, yes, and that is why it is a hypothesis and not a certainty, that is why such a hypothesis is accepted with great caution at first and the existence of the particle is accepted only when there is enough data to support this claim. It is accepted, however, under a tacit assumption: `within the limits of our present knowledge of the world'. Well, and where do the quarks come in? I believe we can all gues what it is all about and why Delta has asked me to consider the question of their existence. To put it in simple terms, nobody has ever seen a free quark with sufficient certainty yet, though there were many who believed that they have trapped it with their instruments just like a butterfly. But this must have certainly been an illusion, supported by their good (very good!) will to observe that extraodrinary object. In other words, if a quark exists, it can never live outside a hadron. Thus we have no chance of `seeing' it, though most probably at least one quark would be absolutely stable. And electrically charged, too.

What do we base our conviction on the existence of quarks on? The situation is quite analogous to all the previous cases. Some experiments provide some sensory data which are then analysed with all the rigour of the presently valid physical knowledge and the conclusion is: the only explanation for the observed phenomena is the existence of quarks.

There have been many such experiences which make the hypothesis on the existence of quarks more probable. What follows is a very incomplete list of them.

1. Only those elementary particles exist, which can be composed of a pair quark-antiquark (mezons) or of three quarks (barions) - i.e. no exotic particles can be observed in nature, where "exotic" means having a different quark structure than one of the two above.
2. Facts related to some properties of barions - their mass, magnetic moments etc., which can be only explained under the assumption of the existence of quarks (using various theoretical models).
3. Facts related to several processes occurring in the world of elementary particles - processes of deeply nonelastic collisions of leptons with hadrons (in practice - with nucleons) as well as processes of annihilation of pairs electron-positron into systems of hadrons.In this latter case a measurement of the proportion of the probability of annihilation into hadron systems to the probability of annihilation into a pair mion-antimion can provide a very simple experimental proof for the existence of quarks.
4. Facts explained by a homogeneous theory of weak and electromagnetic interactions, which could not be developed without assuming that quarks exist.
And many others, too.

I have already written everything I wanted to include in this article, but let me make a brief summary. We cannot say that quarks exist with the same probability as a desk or even a proton does. But we can certainly state that the existence of quarks is by far more probable than the existence of dragons. Therefore, if you believe in dragons, you should also believe in quarks. And more - you should do so even if you have ceased to believe in dragons long time ago.

Grzegorz Bia³kowski