EAS-134 Is Earth Unique?
Fundamental Physics
This section is from Brian Greene, The Elegant Universe, 2000, Vantage Books
Fundamental Particles.
Physics now recognizes 3 families of fundamental particles that were discovered during the 20th century (Table 1.1). Each family consists of an electron (or equivalent), an electron-neutrino (or equivalent) and 2 quarks.
Table 1.1 The fundamental particles of
physics.
Masses are relative to the proton mass of
1.
|
Family 1 |
Family 2 |
Family 3 |
|||
|
Particle |
Mass |
Particle |
Mass |
Particle |
Mass |
Electron |
0.00054 |
Muon |
0.11 |
Tau |
1.9 |
|
Electron- neutrino |
< 10-8 |
Muon- neutrino |
< 0.0003 |
Tau- neutrino |
< 0.033 |
Up-quark |
0.0047 |
Charm quark |
1.6 |
Top quark |
189 |
Down-quark |
0.0074 |
Strange quark |
0.16 |
Bottom quark |
5.2 |
“Physicists have now probed the structure of matter to scales of a billionth of a billionth of a meter (10-18 m) and shown that everything encountered to date – whether it occurs naturally or is produced artificially with giant atom smashers – consists of some combination of particles from these 3 families and their anti-matter particles”.
Fundamental Forces
Physics also recognizes four fundamental forces, established conclusively by 1984. Only the graviton remains to be determined experimentally. Each force is moderated by a particle, whose exchange between other particles gives rise to the force.
Mass is relative to the proton mass and strength relative to the EM force.
|
Force |
Force particle |
Mass |
Relative Strength |
|
Strong (nuclear) |
Gluon |
0 |
100 |
|
Electromagnetic (EM) |
Photon |
0 |
1 |
|
Weak (nuclear) |
Weak gauge bosons |
86, 97 |
0.001 |
|
Gravity |
Graviton |
0 |
10-42 |
In our everyday world, only the gravity and electromagnetic forces are evident; the nuclear forces only play a role at subatomic distances. Gravity is an additive force (all particles have positive mass) and so becomes the dominant force at masses comparable to moons, planets and stars.
The nature of our universe depends crucially on the relative strengths of the various forces and the masses of the particles.
The ratio of the strong force to the EM force governs the existence of the stable nuclei forming the main elements of the periodic table.
The ratio of the electron to proton mass governs the stability of atoms, allowing electrons to form stable orbits around the nucleus.
The gravitational force is just strong enough to condense stellar interiors sufficiently for thermonuclear fusion, but not to exhaust the material too quickly.
The universe is the way it is because the matter and force particles have the particular properties they do. But is there a scientific explanation for why they have these properties? Maybe in another universe the laws of physics would be different.
Why Physics?
Of the 3 classical hard sciences – physics, chemistry, and biology – it is clear that physics is the most fundamental because it is concerned with the structure properties of matter and energy. Chemistry is largely concerned with the properties of atoms and molecules, and how they combine, and biology is concerned with the life of organisms. Without physics there would be no chemistry, and without chemistry there would be no biology. In a sense, once physics is understood, then chemistry and biology are in principle understood, except for the complexity that comes with the interactions between the huge numbers of atoms and molecules that make up our macro-world.
Commentary
The purpose of reviewing these aspects of physics is first to demonstrate how far physics has come, especially between the discovery of the atom (Lord Rutherford and Niels Bohr, 1911-1914) and 1984. Second it is clear that the structure and properties of the universe itself is delicately balanced according to the laws of physics. This adds to the mystery of how delicately balanced is complex life on Earth.