1 Introduction
3
Returning to the ‘naïve’ point of ultimate building blocks one might ask whether
the quarks and leptons are fundamental indivisible particles or whether they have a
substructure. Here we are running into a dilemma which was recognised already by
the philosopher Immanuel Kant. 2 Either ultimate building blocks are mathematical
points and cannot be divided, but then it is difficult to understand how they can have
a mass and carry charges and spin. Alternatively, the building blocks might have
spatial extension, but then it is hard to understand why they could not be divided into
smaller parts. Whenever one meets such a paradox in science it is usually resolved
by recognising that a wrong question was asked.
Indeed the recent developments of particle physics indicate that the naïve concept
of ultimate building blocks of matter has to be abandoned. The smaller the ‘building
blocks’ are, the higher energies are necessary to break them up. This is simply a
consequence of the Heisenberg uncertainty principle of quantum mechanics. In the
case of quarks their binding energies become so strong that any energy applied
to break them apart is used to produce new quark-antiquark pairs. 3 The existence
of antimatter implies also that matter does not have an ‘eternal’ existence. When
matter meets antimatter the two annihilate by being converted into ‘pure’ energy and
in the reverse mode matter can be produced 4 from energy in the form of particleantiparticle pairs.
One of the most exciting development of physics or in science in general is a
change of paradigms. Instead of using building blocks and forces acting between
them, it was progressively recognised that symmetry principles are at the basis of
our understanding of nature. It seems obvious that laws of nature should be invariant
against certain transformations since ‘nature does not know’ how we observe it.
When we make experiments we have to choose the origin of the coordinate system,
its orientation in space and the moment in time when we start the observation. These
choices are arbitrary and the laws deduced from the observations should not depend
on them. It is known since a long time that the invariance of laws of nature against
the continuous transformations, i.e. translations and rotations in space and time,
give rise to the conservation of momentum, angular momentum and energy, the
most basic laws of classical physics. 5 The mirror transitions (i.e. spatial reflection,
particle-antiparticle exchange and time reversal) lead to the conservation of parity
P, charge parity C and detailed balance rules in reactions, all of which are essential
ingredients of quantum mechanics.
The detection of complete parity violation in weak interactions in 1957 was one
of the most surprising observations. Many eminent physicists, including Wolfgang
2 Immanuel Kant, Kritik der reinen Vernunft, 1781, see, e.g., Meiner Verlag, Hamburg 1998, or
translation by N.K. Smith, London, MacMillan 1929.
3 The binding energies are comparable to mc 2 , where m is the rest mass of a quark and c is the
velocity of light.
4 When Pope Paul John II visited CERN and I explained to him that we can ‘create’ matter his
response was: you can ‘produce’ matter, but ‘creation’ is my business.
5 Emmy Noether, Nachr. d. königl. Gesellschaft d. Wissenschaften zu Göttingen, 1918, page 235.
3
Returning to the ‘naïve’ point of ultimate building blocks one might ask whether
the quarks and leptons are fundamental indivisible particles or whether they have a
substructure. Here we are running into a dilemma which was recognised already by
the philosopher Immanuel Kant. 2 Either ultimate building blocks are mathematical
points and cannot be divided, but then it is difficult to understand how they can have
a mass and carry charges and spin. Alternatively, the building blocks might have
spatial extension, but then it is hard to understand why they could not be divided into
smaller parts. Whenever one meets such a paradox in science it is usually resolved
by recognising that a wrong question was asked.
Indeed the recent developments of particle physics indicate that the naïve concept
of ultimate building blocks of matter has to be abandoned. The smaller the ‘building
blocks’ are, the higher energies are necessary to break them up. This is simply a
consequence of the Heisenberg uncertainty principle of quantum mechanics. In the
case of quarks their binding energies become so strong that any energy applied
to break them apart is used to produce new quark-antiquark pairs. 3 The existence
of antimatter implies also that matter does not have an ‘eternal’ existence. When
matter meets antimatter the two annihilate by being converted into ‘pure’ energy and
in the reverse mode matter can be produced 4 from energy in the form of particleantiparticle pairs.
One of the most exciting development of physics or in science in general is a
change of paradigms. Instead of using building blocks and forces acting between
them, it was progressively recognised that symmetry principles are at the basis of
our understanding of nature. It seems obvious that laws of nature should be invariant
against certain transformations since ‘nature does not know’ how we observe it.
When we make experiments we have to choose the origin of the coordinate system,
its orientation in space and the moment in time when we start the observation. These
choices are arbitrary and the laws deduced from the observations should not depend
on them. It is known since a long time that the invariance of laws of nature against
the continuous transformations, i.e. translations and rotations in space and time,
give rise to the conservation of momentum, angular momentum and energy, the
most basic laws of classical physics. 5 The mirror transitions (i.e. spatial reflection,
particle-antiparticle exchange and time reversal) lead to the conservation of parity
P, charge parity C and detailed balance rules in reactions, all of which are essential
ingredients of quantum mechanics.
The detection of complete parity violation in weak interactions in 1957 was one
of the most surprising observations. Many eminent physicists, including Wolfgang
2 Immanuel Kant, Kritik der reinen Vernunft, 1781, see, e.g., Meiner Verlag, Hamburg 1998, or
translation by N.K. Smith, London, MacMillan 1929.
3 The binding energies are comparable to mc 2 , where m is the rest mass of a quark and c is the
velocity of light.
4 When Pope Paul John II visited CERN and I explained to him that we can ‘create’ matter his
response was: you can ‘produce’ matter, but ‘creation’ is my business.
5 Emmy Noether, Nachr. d. königl. Gesellschaft d. Wissenschaften zu Göttingen, 1918, page 235.