A. Space-time is the union of the ordinary three-dimensional space together with time,
that represents the fourth dimension of the physical world.
Space-time is like an immense roll of ribbon, that at the moment of the creation of the
universe was all wound.
During the evolution of the universe, the ribbon,that represents the space,unrolled in the
past,is unrolling in the present and will unroll in the future,until the universe will
exist.
Even if the ribbon has only two dimensions, length and breadth, this model gives us well
the image of the time that passes, while the ribbon is unrolling.
To represent more clearly the evolving of the universe in space-time, we can think to a
sphere of an elastic material, that, being point-like at the moment of the creation (the big
bang) of the universe, expanded uniformly, until it represents the universe as we see it
today, with some hundreds of billions of galaxies,whose distances are increasing continously,
making the universe always less dense and always less bright (the universe expansion was
discovered by the astronomer Hubble in twenties ).
The whole history of the universe is written in space-time, that has the same age of the
universe (this age is esteemed currently to be 15 billions of years ).
A. The measure of the duration of any physical phenomenon, for example of the flash
emitted by a light source, when is determinated, independently, from an observer who is at
rest with respect to the source and by an observer who is moving with respect to it (for
example an observer aboard an airplane ), furnishes values that are the more different,
the greater is the velocity of the moving observer .
In particular, the duration measured by the observer in motion with reference to the
source results greater of the duration measured by the observer stationary with respect to
it.
According to Galileo and Newton's theory, the measure of a time interval is absolute,
since it is independent from the motion of anyone observing a physical phenomenon, whereas
in the context of Einstein' relativity theory, the measure of a time interval depends from
the velocity of the observer ; therefore it is spoken of a one's own time (or local time) Dtp ,that is measured
by an observer at rest, and of a non-local time Dtnl, if it is measured by a
moving observer .
Obviously the differences among the measured values result meaningful only if the
velocity v of the observer is not too little with respect to
the one of light in vacuum
(c = 300000 km/s):
Dtnl
= Dtp : square
root of (1 - v2/c2). .
Because the measure of a time interval depends on the observer's frame of reference,one
cannot consider a time measure is absolute, as in the prerelativistic physics ; therefore,
are introduced the concepts of space-time and of space-time event, which is a point
individuated in space-time by 4 parameters, that are the 3 spatial co-ordinates and
the temporal coordinate.
The measures of length and time made in an experiment (for example, the measure of the
length and of the oscillation period of a pendulum ), we plane to performe in a railway
carriage, are valid with respect to the train, that represents our frame of reference.
Another observer, standing on a car in motion with respect to the train, could observe the
experiment at a distance by binoculars and measure the length and the period of the
pendulum with respect to his own frame of reference, the car,which is in moving with
respect to the train.
The observer on the car would notice a slightly smaller length ( the so-called contraction
of lengths ) and a slightly greater period (the so-called expansion of time) in
comparison with the values measured by the observer on the train.
In fact the observer aboard the car, to effect the measures used the light rays coming
from the pendulum, and the delay associated with the path of the light rays moving with
velocity c = 300000 Km/s, even if it is too little, influenced both the evaluation of the
length and the one of the period of oscillation.
The dependence of the measure of a time interval and of a length from the frame of reference
couldn't take place if the velocity of light were infinite, that is, if the electromagnetic waves and
the light, that consists of electromagnetic waves, were propagating instantly.
In such a case a stationary observer and another one in motion would measure the same
times and lenghts relating to a physical phenomenon .
A. A body or a living creature is made of matter, and the matter is made of microsystems,
the atoms of the 92 chemical elements existing in nature, from hydrogen atom,which is
the most light one, to uranium atom,which is the most heavy one .
Atoms are bound among them according to the laws of chemistry to form the molecules and crystals of
all the chemical compounds of which are made all the bodies and the living creatures.
The molecules of elements, that is of metals ( copper, silver, zinc, etc...) and
metalloids (carbon, phosphorus, oxygen, sulphur, etc...), consist of one or more atoms,
according to the chemical element to be considered; for example the molecules of gases
(hydrogen, chlorine, nitrogen, etc...) consist of two atoms, whereas the ones of
metals consist of only one atom.
Atoms consist of a central nucleus, made of positively charged particles, the protons,
and electrically neutral particles,the neutrons, and of a cloud of negatively charged
electrons, that are distributed around the nucleus with a density depending on the own
structure of the chemical element, which is considered .
The number of electrons (the so-called atomic number Z), that in the non-ionized atoms
coincides with the one of the protons of the nucleus, determines the chemical properties
characterizing an element.
The quantity of matter that forms an inert body or a living creature,defines a basic physical
property: the mass or inertia.
A lorry or an elephant have a mass much greater of the one of a little tennis ball, and
that involves a different effect (the acceleration) determined by a force of the same
intensity .
In fact the second fundamental law of mechanics ( discovered by Galileo and formulated
by Isaac Newton in his "Principia mathematica philosophiae naturalis" )
affirms that the variation of velocity per second, impressed by a force to a body, initially at rest
or moving with a rectilinear motion with a certain initial velocity, is directly
proportional to the intensity of the force applied to the body, and that, on the other
hand, by applying the same force to bodies of different mass, variations of
velocity per second happen that are inversely proportional to the mass of the body.
When applying a thrust of 200 kg to a body with a mass of 1000 kg, and after
to a body with a double mass, in the second case the variation of velocity per second is
halved.
The mass of a body, said more precisely its inertial mass, represents the aptitude of a
body to withstand to the acceleration (that is the variation of velocity per second)
produced by a force.
How much smaller is the mass of a body, much more the body is accelerated (or decelerated
) by a force.
The second fundamental law of mechanics can be expressed by the following approximate
formula, since we consider the mean acceleration of the body instead of the instantaneous
one:
F = M a = M ( Vfin-Vin )/( Tfin-Tin ),
where a is the mean acceleration, that is expressed
by the ratio between the variation ( increase or diminution ) of velocity ( final velocity
- initial velocity ) and the duration
( Tfin-Tin )
that this variation is referred to.
It can be observed that, by keeping constant the force F
applied to the body, if the mass of the body doubles, then the acceleration a halves and if, viceversa, M
halves, a duplicates.
A practical example that is a direct consequence of this law, can be furnished by thinking
about the force F necessary to brake the motion of a
vehicle: with constant values of velocity and of braking time, the friction force (the
resistant force ) the brakes have to effect, is directly proportional to the mass M of the vehicle.
Likewise, the motive force that has to be produced by the engine to accelerate the vehicle
from the rest state to a certain velocity in an assigned time, is directly proportional to
the mass M of the vehicle.
Likewise the impulsive forces acting in the collision of the vehicle against an obstacle
or another vehicle, is directly proportional to M,
with an assigned velocity .
It is said commonly that a vehicle, in the acceleration or deceleration phase , is
subjected to the inertial force F = Ma, which is
directly proportional to the mass (inertia) M and
has, respectively, the same direction of the motion or the opposite one.
If are required smaller time and space to brake the vehicle, it is necessary to
increase proportionally the braking force F to get
an equal variation of the velocity
v ( and of the
momentum Mv) within a smaller time interval.
With the same considerations can be explained the protection that is provided by an
elastic body interposed between a moving body and a rigid obstacle (let's think to a
rubber pneumatic mattress used to reduce the effects of the bump produced from the free
fall of a person to the ground from an height of a few meters).
Although the free fall velocity is too high, the elasticity and the softness of the medium
determine an increase of the time necessary to slow down the velocity during the bump;
consequently, during the bump it is possible to decrease considerably the deceleration a (the negative acceleration) and the impulsive force F = Ma, which is directly proportional to a.
A. When we work manually, for example lifting a much heavy object, we are getting tired
and feeling that our body has spent "something" that has been necessary to lift
the body; that "something" is energy.
In this case the manual work has been performed by using the muscles of our body, that are
perfect biochemical engines that convert into mechanical work the energy stored by means
of complex biochemical reactions that take place every time we eat to feed ourselves.
When we make a mechanical work on a body, we do nothing but apply to it a force (a
motive force) increasing its velocity and having an opposite direction to the one of the sum of
the resistant forces that make the velocity be decreasing.
In the case of a body that is being lifted to a certain height, the force opposing to the
motion is the weight P (the gravitational force),
that has to be exceeded by the muscular force so that the body can be lifted.
Also, the greater is the height h (vertical
displacement of the body ), the greater are the energy and the mechanical work L = Fh that must be spent, by taking account, in this
particular case, that L must be greater than the
product of the weight P of the body by
the vertical displacement h.
If, for instance, we lift a body of 50 kg from the ground to an height of 2 meters,
we
execute a work greater than 50 kg x 2 meters = 100 kgm (1 kgm = 1 kg x 1 meter), by spending an
energy greater than 100 kgm.
Therefore a body or a system ( in our case the system is our body ) have an amount of energy, if they are
able to execute some work on one or several bodies or on another system.
Vice-versa, if on a body or on a system is performed some mechanical work by one or
several bodies or by another system, some energy is accumulated, that can be used
subsequently.
A. The most simple way to accumulate energy consists in making a body gain velocity
; we speak in this case of kinetic or motion energy , because any mass M, accelerated by a force until reach a certain velocity V, when collides against one or several bodies, it is able
to execute some work , by accelerating them during the collision and giving up them a
share of its kinetic energy, according to the masses and of the type of collision.
The kinetic energy Ec stored in a moving body is
directly proportional to its velocity V and is given
by the formula
Ec = ( 1/2 ) M V2 .
If the velocity of a body duplicates, the kinetic energy quadruples.
So we can explaine why it is necessary to slow down a vehicle to limit the damages in
collisions against other vehicles.
The collisions are defined elastic, if is preserved the total kinetic energy stored in the
bodies before the collision, that is if the total kinetic energy after a collision is
equal to the initial one.
Practically the collisions are never entirely elastic, because a share of the total
kinetic energy of the bodies before the collision, is spent to deform the structure of the
bodies in an irreversible mode, as it takes place in the head-on violent crashes between
two vehicles or in the crash of a vehicle against a wall.
The work made by the intense impulsive forces acting during an inelastic collision is
converted into heat according to the first principle of thermodynamics, as when we beat a
nail with an hammer or fold up several times a piece of metal; the deformation work
transforms into heat.
Approximately elastic collisions are considered the ones among the billiard-balls or among
the molecules of a gas.
Let us remember that the kinetic energy of winds and of the water bodies has been largely
exploited in past centuries to produce motive power, before the industrial use of the heat
and electric engines.
The energy can be accumulated in several forms:
It accumulates as potential energy ( or position energy ) in all the systems that consist of masses keeped at a distance each other in the space (systems of heavenly bodies, solid masses and liquid masses raised above the ground);
It accumulates as potential energy in a spring or in a cylinder containing a compressed gas;
It is released by chemical reactions, because of the bond energy among the atoms interacting each other to form chemical compounds;
It corresponds to the kinetic energy of the molecules of matter, and it
determines the energy exchanges that take place among solids, liquids, gases and vapors
because of temperature differences, that correspond to differences of both molecular
velocity and kinetic energy.
In particular the heat energy that accumulates in a fluid ( liquid, gas or vapor ), that
functions as a thermal accumulator, can be transformed into mechanical energy in the
thermal engines ( that is the vapor and internal combustion engines ), exploiting the
difference of temperature between the thermal source heating the fluid and the
environment.
In refrigerators and in air-conditioning plants is exploited the principle of the heat
pump, that consists in transferring heat from an environment to another at an higher
temperature, by means of the compression of a gas or of a vapor, obtained at expenses of
some mechanical energy (furnished by an electric motor ).
In the first phase of the thermodynamic cycle, the environment at a lower temperature,
across the serpentine of the evaporator releases heat to a liquefied gas or vapor,
causing its transition in the gaseous state; subsequently the gas or the vapor is
liquefied while it is being compressed, at expenses of the absorbed electric power
necessary to make operate the compresser, with an heat release to the environment at
a greater temperature, across the serpentine of the condenser.
The heat transferred to the environment at an higher temperature is equal to the sum of the
heat absorbed from the environment at a lower temperature and of the electric work
trasformed into mechanical work, neglecting the losses of the system caused by the
friction forces and by the heat generated (Joule effect) inside the windings of the electric motor
( electric work that hasn't converted into mechanical energy ).
It is produced by the electric generators exploiting various forms of primary energy
(kinetic, gravitational, thermal, chemical, nuclear, solar ).
It is stored by accumulators (secondary batteries ) or capacitors.
It accumulates in permanent (natural or artificial) magnets and in electromagnets by using electric power.
It is produced by fission and fusion nuclear reactions.
In the unstable nuclei of the heavy elements (uranium, plutonium, thorium ) the electric
forces by which the protons ( nuclei of hydrogen atoms with one positive elementary electric
charge ) repulse each other causing the nucleus to break up, are balanced precariously by
the attractive nuclear forces that act among all the nucleons ( protons and neutrons ),
keeping compact the nucleus.
Therefore, provided that the nucleus is excited by absorption of a slow neutron, the
repulsive electric forces among protons prevail on the attractive ones, causing the
fission of the nucleus in two fragments ( less heavy nuclei ) more 1 or 2 neutrons, with
the emission of a considerable quantity of kinetic energy, that subsequently is converted
into heat.
The nuclei of the light elements ( hydrogen, deuterium, tritium ) undergo instead , at
very high temperatures ( at least about tens of millions of °C degrees), the
thermonuclear fusion to form neutrons and helium nuclei and release a very high energy,
corresponding to the bond energy of the helium nuclei that are formed.
A. Before the formulation of Einstein's theory, were considered separately the
fundamental principles of conservation of the mass and the one of the energy.
The conservation principle of the mass, formulated in the eighteenth century by the
chemist Lavoisier and already expressed by Lucretius in the poem "De rerum natura",
consists in considering constant and indestructible the quantity of matter existing in
nature; that is, in any system and, by extension, in the universe the total quantity of
matter is always the same.
Matter is subjected to physical-chemical transformations, but it is not destroied
("in nature nothing is destroied, everything transforms " ).
The energy conservation principle, formulated in the nineteenth century, affirms that,
whatever is the form of energy that is considered ( mechanical, thermal, electric,
etc...) in any system and, by extension, in the universe, the total energy is constant.
Einstein showed that both principles are nothing but two faces of the same medal, the
conservation principle of both the mass and the energy, that affirms that in any system
and, by extension, in the universe, the mass transforms into energy and, vice-versa the
energy transforms into mass, as in practice it happens in the nuclear reactions and in the
ones among subnuclear particles.
In short, in the energy balancing of any system it is necessary to include the term mc2, where m
is the sum of the rest-masses , that is the masses, measured at a zero velocity, of all
the bodies forming the system.
The rest-mass term mo derives from the
fact that Einstein showed that the mass of a body depends on its velocity, referred to a
particular frame of reference, that is the frame in which the mass is at rest.
If we consider the mass of a body keeped at rest in a moving car, the mass of the
body, measured aboard the car is the rest-mass mo,
being the body stationary in comparison with the car; if instead we consider the mass m(v) of the body in comparison with the road, we speak of
motion-mass, that is the greater than the rest-mass, the greater is the velocity of the
body, that in this case coincides with the velocity of the car.
Practically, the difference between both masses is so little to result meaningless for
a macroscopic body, whose velocity is much smaller of the velocity (c) of the light in
vacuum (300000 Km/s), unless we consider microscopic bodies, as the elementary particles (
electrons, protons, neutrons ), that are able to reach, because of their extremely small
rest-mass, velocities nearly equal to c, such that
the relativistic effects are much meaningful.
If during a transformation of a physical system, takes place a diminution of the total
mass of the bodies constituting the system, it means that the difference Dm (the so-called mass
deficiency) transforms into energy according to the law E = Dm c2,
where Dm
represents in this case the difference between the initial mass and the final one.
The great value of c involves that is very huge the
energy that is released, even if is very small the mass that disappears, as it happens
in the nuclear fission reactors and in the thermonuclear fusion reactions that take place
inside the Sun and the other stars.
A. Because the motion mass m(v) of a body grows with the
increasing velocity v, becoming very huge, theoretically
infinite, while the velocity is approaching to c.
The formula giving the dependence of the motion-mass m(v) on
the velocity v is: m(v)
= mo : square root of (1 - v2/c2 ) .
Moreover, since mass and energy are equivalent, it would be necessary to furnish to the body
an infinite energy, and that is physically impossible.
A. The electric charge , the weak subnuclear charge and the strong subnuclear charge.
They correspond to as many fundamental forces (interactions) of nature, provided we
consider separately the gravitational force, that acts on the mass of any body,
independently from the type of charge that it possesses.
It is easy to speak of the electric forces that, together with the gravitational ones, are
well known to everyone, because they determine the chemical reactions, the existence of
any form of life, the natural electric phenomena, and the many applications of the
electromagnetism that permitted to realize the technological wonders of today world.
Much less known are the weak subnuclear forces, that determine the radioactive
b decay
phenomena of the natural and artificial radioelements, and that control the velocity
of the thermonuclear fusion reactions.
We quote finally the strong subnuclear forces, from which depend the operation of the nuclear
fission reactors and the stability of atomic nuclei, that otherwise would disintegrate, if
the intense repulsive electric forces among the protons weren't counterbalanced by the
intense attractive nuclear forces among the nucleons
( protons and neutrons).
A. The wide diffusion of cellular telephones has involved the frequent use of the term
"field" in common speechs, because we often hear people say "in that zone
there is no field ", in relation to the impossibility to receive electromagnetic
signals of intensity enough to the good operation of a cellular telephone.
In the case of the cellular telephones and of the
radio and telediffusion systems we speak of electromagnetic fields always with reference
to the current laws preventing environmental electromagnetic pollution.
Practically,what is a field ?
If we start from the example concerning the cellular telephones, we associate to an
electromagnetic field something invisible that is moving from the transmitter to the
receiver, "imbuing" the space, as in effect it happens.
A field is a physical quantity, as temperature, pressure, force of gravity , velocity,
whose value is variable in a certain region of the space.
A force field (electric, magnetic or gravitational ) acts on the bodies that are
sensitive to it, because they have charges that are able to evidence the forces owing to
the field.
The "fundamental charge" sensitive to the electromagnetic field is the electric
charge, that in the macroscopic world is always equivalent to a multiple of the elementary
electric charge, the negative electric charge of electron.
Likewise, the nucleons ( protons and neutrons ) are carriers of a "strong subnuclear
charge" that makes them sensitive to the field of the so-called "strong
force", that is a rough expression used to point out strong nuclear
force, that is the most intense one of all the natural forces.
Similarly we speak of the "weak subnuclear charge" of subnuclear particles
(electrons, positrons, muons and neutrinos ) sensitive to the field of the weak subnuclear
force, that is less intense than the other two, but more intense of the gravitational one,
that is the most weak of all the forces of nature and becomes very intense
only on a very large scale, when are considered the quantities of matter that form
heavenly bodies (asteroids, planets, satellites, stars and galaxies ).
On the Earth the gravity force is very intense because of the big mass of our planet and
the relatively little distance (~6400 km) between the bodies subjected to the gravity and
the Earth center, in which we consider to be concentrated all the mass of the planet,
as it is shown in Newton's gravitation theory.
A. In the first three decades of the twentieth century the physicists succeeded to
elaborate a theory much sophisticated, the quantum mechanics or wave-mechanics, that
explains entirely all the atomic phenomena that the classical physics, founded on Galileo
and Newton's mechanics and on Maxwell's electromagnetism, was not able to explain.
The atomic-molecular microcosm evidences that all the elementary particles behave as waves
with a De Broglie wavelength l = h/( mv ) , which is inversely proportional to the momentum p = mv, and they obey to Heisenberg's uncertainty
principle ( 1927 ), by which, when a particle is confined in a space region with
dimensions comparable with its associated wavelength l,
the uncertainty (error) that characterizes the measure of its momentum p, varies in inverse relation to the uncertainty which characterizes
the measure of its position in the region of confinement.
This is equivalent to affirm that elementary particles, taking account of their wave-like
behaviour, are as less locatable in the space, as better is known their velocity , and
then their linear momentum.
Therefore there is no meaning for the trajectory concept of a particle,which is
fundamental instead in classical physics, within which, when a body is moving,it is
possible to determine at the same time its position and its velocity ,with all the precision
that is required.
The impossibility to define the trajectory is replaced by the possibility to define in
every point of the space the probability to find the particle.
On the other hand, it can be shown theoretically that, if a particle is confined in a well
delimited region of the space, as in the case of an atomic electron, the request of no
probability to find the particle outside the zone of confinement, implicates the
impossibility to assign to the energy of the particle any value: from this request derives
in fact the quantization of energy, already introduced in the primitive version of
Planck (1900) and Bohr's (1913) quantum physics.
Not all the values of the energy are permitted to an electron inside an atom, but only some
well determinate values that represent the energetic levels of the atom.
Likewise we speak of quantization of the momentum of a particle confined to move in a
well-delimited region of the space.
We ask how to explain the origin of the values of the masses and the electric charges of
the elementary particles (electrons, protons and neutrons) ? They have well-determinated
values, but still we don't know why it is so.
We are able only to say that the masses and the electric charges of the particles depend
on the structure of the universe, and precisely from the values of the three fundamental
constants that determine the characteristics of the physical world: the Newton's universal
gravitation constant G, the velocity c
of light in the vacuum and the Planck constant h.
In this context, even the fields are quantized,since their energy is always multiple of an
elementary energy quantity that they exchange with the particles that are able to
interacting with them.
Einstein expressed the hypothesis of photons (said even quanta of light ) to
explain the photoelectric effect.
By considering that a photon is a quantum of the electromagnetic field that transports an
energy E = hf, where f
is the frequency of the electromagnetic waves, it can be observed that the energy of the
electromagnetic radiation, in the interaction with the particles of the microcosm, is
divided in a flux of packets, each containing the same energy, that are just the quanta or
photons.
The quanta of the electromagnetic field can be considered as special "particles"
that, having a rest-mass equal to zero, are always moving with the velocity of light in
the vacuum.
In quantum electrodynamics, that has been developed subsequently to the formulation of the
relativistic quantum mechanics by Paul Dirac ( 1928 ), the attractive or repulsive force
between two electric charges is determined by the fact that a charged particle is entirely
screened by a cloud of virtual photons that are continually emitted and absorbed by the particle.
The attractive or repulsive force is the more intense, the more the particles are near
each other (according to the Coulomb law ), because, with the decreasing distance,
decreases the time D
t requested to photons pass from a particle to another.
If, to give an intuitive
elementary explanation, we consider the second fundamental law of dynamics
F = DP/
D t ,then , with the decreasing
Dt ,
increases the variation of the momentum per second; then the force increases.
In 1935 the Japanese physicist Yukawa proposed to extend this mechanism to a nucleon
pair ( protons and neutrons ), expressing the hypothesis that strong subnuclear attraction
forces between two nucleons, that is between two protons, between two neutrons and between
proton and neutron ( Heisenberg-Maiorana's forces ), are determined by the continuous
exchange of virtual particles, the mesons, that are positively or negatively charged or
neutral and with a rest-mass between the rest-mass of proton and the
one of electron (~270 times the electronic mass ).
When in 1947 Powell and Occhialini discovered in cosmic radiation some charged particles
with a rest-mass equal to 270 times the one of electron, that were identified with
the p mesons (pions), Yukawa's theory was definitely
confirmed.
The exchange of a virtual pion between two nucleons implicates a temporary violation of
the energy conservation principle, since, during the flight of the pion, the total
mass-energy of the system consisting of both nucleons and the virtual pion,
is greater than the total mass-energy of the system before and after the
flight, when it is made of only two nucleons.
However, this violation
can be allowed, provided it is compatible with Heisenberg's uncertainty
principle, that states that, the shorter is the flight time, the heavier is
the mass-energy of the exchanged particle.
Because of the very short
flight time t ( the time
characteristic of the strong subnuclear interactions is 10-23
seconds), the distance R = c t at which two nucleons are subjected to the strong subnuclear force, is very small:
R = 3 .1010cm/s x 10-23 s =
3 .10-13cm = 3 fermi .
Therefore, Heisenberg's principle requires
that must be exchanged a virtual particle that, differently from the virtual
photon in electromagnetic interactions, has a non-zero rest-mass.
The
strong subnuclear force has a very short range and is 1000 times more intense than
the electromagnetic one, which instead is extended to a huge distance,
theoretically infinite.
To the strong subnuclear force are sensitive not only protons and neutrons, but all the other
hadrons ( barions and mesons ) that were discovered in cosmic radiation and
were produced artificially in particle accelerators.
The quanta of the
strong subnuclear field are just the pions, whose role is like the one of
photons for the electromagnetic field.
In 1968 the model based on the "ping pong" of virtual particles was extended
by Salam, Weinberg and Glashow to the weak subnuclear forces, that determine the phenomena
of radioactive decay (beta decay), for which Enrico Fermi in 1934 formulated the first
theory, founded on the hypothesis of the existence of neutrino, introduced by Pauli.
Salam, Weinberg and Glashow formulated a theory of the weak interactions, introducing the
particles W ( positive and negative ) and Zo, with masses much greater than the one of
pion and a very short interaction range (10-15
cm).
Besides they succeeded to show that the weak subnuclear quantum and electromagnetic
fields, studied at high energy, trend to identify in an only type of quantum field
"the electro-weak field" , for effect of which the W and Zo particles,
denominated intermediary vectorial bosons, produce an unified interaction with the same
intensity of the electromagnetic one.
A. The elementary particles that constitute matter can be represented as spheres of
ultramicroscopic dimensions, with a radius of the order of tenths of millionth of
millionth of centimetre, and they can be neutral or with a positive or negative electric
charge.
Besides exists another property, typical of the microcosm, that differentiates a particle
from another: the spin.
A particle can have a zero or a non-zero spin, if it is characterized or not by an
intrinsic rotation around an its axis; if a particle has an angular momentum is said to
have the spin, and behaves as an ultramicroscopic spinning top.
Besides, an electrically charged particle as, for example, electron or proton, or
a neutral one, as neutron, can be considered, provided it has the spin, as a spinning
top containing virtual charged particles that are rotating inside it around its axis, so
that the particle is equivalent, because of the Ampere equivalence theorem, to an
elementary magnet of microscopic dimensions.
The particles behave in different modes, according to the value of the spin: if the
particles have spin 0, as the pions ( p mesons),or an integer
spin, as,for example, the photon, that has spin 1, they are defined bosons, from the name
of the Indian physicist Bose that studied, independently from Einstein, the statistic of
these particles (the Bose-Einstein statistics) ; if they have instead a fractional spin (
1/2, 3/2, 5/2, etc...), as it happens for electrons, positrons, protons and neutrons,
whose spin is 1/2, they are defined fermions, from the name of Enrico Fermi that studied
their statistic, independently from Dirac (the Fermi-Dirac statistics).
The difference of behaviour between bosons and fermions is in the fact that, while two or
many bosons, even in a great number, are able to occupy the same quantum state,
individuated for every particle by a combination of quantum numbers, in relation to the
energy and the angular momentum , two fermions instead, for the exclusion principle of
Pauli, aren't be able to have the same quantum numbers.
A notable example of the behaviour of the bosons ( condensation in an only quantum state )
is shown by the liquid helium, that, keeped at temperatures smaller or equal to 4 °K
above the absolute zero ( -273,16 °C or 0 °K ),evidences a behaviour much unusual: the
superfluidity, what consists in the fact that the superfluid helium is able to go up again
in the capillary pipes and in the containers, against the gravity , to give rise to the so
called "fountain effect".
In fact the helium nucleus, formed by 2 protons and 2 neutrons, whose totale spin is equal
to zero, behave as zero-spin bosons (scalar bosons).
The fermions instead, since aren't able to be in the same quantum state, spread their
energy in an interval of quantum energetic levels, that is the wider, the greater is the
number of particles.
If for the atomic electrons, that have spin 1/2, weren't worth the Pauli
exclusion principle, they would condense in an only quantum state, in proximity of the
atomic nucleus, with a consequent compression of whole the matter.
The density of matter would increase enormously, reaching values nearly equal to the
ones that are typical of nuclear matter ( collapse of the atomic structure ).
A. All the bodies and the living creatures, that originated and are evolving in the space-time, are made of :
It is the mass-energy of the protons, neutrons and electrons of which are made atoms of matter.
The fundamental charges of the particles forming atoms are of three types and
determine the stability of matter with respect to the conversion of mass into energy:
1) Electric charges:
Leptons (electron, muon,tauon), baryons (proton,hyperon and other particles heavier than
proton ), mesons (pions, kaons,etc...) and the respective antiparticles, have an electric
charge with the absolute value of 1,6*10-19C (the elementary electric
charge e).
To quarks and antiquarks is assigned instead a fractional electric charge
with the values,depending on the quark type, of +/-( 2/3 )e or +/- ( 1/3 )e.
Electric charge are the sources of the electromagnetic forces determining
the atomic structure,the binding energy among atoms forming molecules and crystals,
and the absorption and emission phenomena of electromagnetic energy
(by photons ) in atoms, molecules and crystals.
2) Weak subnuclear charges (flavours) :
-six for quarks (up,down,strange,charm,bottom and top )
-six for leptons (electron,electron neutrino, muon, muon neutrino,tauon,
tauon neutrino).
They are the sources of the weak subnuclear forces ( Fermi forces ) and of the
electroweak ones ( of Salam, Weinberg, Glashow ), that produce as the change
of flavour of quarks ( for instance, from charm into strange or from down into up ) and of
leptons ( for instance, from electron into electronic neutrino by the exchange of
a W boson ), as the b radioactive decay
phenomena that take place in atomic nuclei and consist in the transformation of
a proton into a neutron, with the emission of a positron
( positive electron ) and a neutrino, or in the transformation of a neutron into a proton,
with the emission of an electron and an antineutrino.
3) Strong subnuclear charges
They are the sources of the strong subnuclear forces determining the binding energy
of protons and neutrons inside the atomic nucleus, and the strong interaction of
quarks , antiquarks and of all the hadrons ( mesons and baryons ).
According to the standard model ( quantum cromo-dynamics ,Q.C.D ), the strong
subnuclear charges are the colour charges (red, green,blue) of quarks, of the respective antiquarks
and of gluons (the quanta of gluon field determining the strong
subnuclear forces to which are subjected quarks and antiquarks.
The quantum fields associated to the forces acting among the particles forming atoms, are of three types:
1) Electromagnetic field , mediated by the exchange of
virtual photons ( that cannot be detected experimentally ) among particles having an electric
charge> .
Since the photons, without electric charge and with zero mass, that determine electromagnetic forces,
have spin = 1, their field is said boson quantum field.
2) Electroweak field (of Salam, Weinberg, Glashow ) ,
mediated by the exchange of virtual bosons ( W+ and W- electrically charged and Z°
neutral ) with non-zero mass, among leptons and among quarks and antiquarks forming hadrons.
Since the bosons producing weak forces have spin = 1, their field is said boson quantum field.
3) Gluon field ( from the Latin glus = glue ),
mediated by the exchange of eight types of virtual gluons.
Gluons, that determine the strong subnuclear forces to which are subjected quarks and antiquarks, have
zero mass and zero electric charge, but six of them are furnished with two color charges.
Even in this case, since the exchanged gluons have spin = 1, their field is said boson quantum field.
