The third property of a particle, spin, has a very significant importance as it divides subatomic particles into two main groups.
Many particles have their spin, which is quite restricted, and it can come as spin of 1/2, 1 and a 1/2, 2 and a 1/2 integers and so on. So spin can come in a half of a whole number. However, a particle can have a full spin of 1 integer, 2, 3 integers and so on.
Electron spin is only ½ an integer, for example.
All particles that spin ½ an integer, as an electron, or 3 times the spin of electron (which is 1 and a ½ integers) or 5 times the spin of electron (which is 2 and a half integers) belong to categories of particles, which are called fermions. Their name is given in honour of Italian physicist Enrico Fermi.
Fermion is what all matter in the universe we can see and detect, involving ourselves, is made of.
Fermion is subject to the Pauli exclusion principle, which means that there is a very limited number of fermions that can be placed in a confined space. For example, only 2 electrons can occupy orbitals around an atom.
The first shell around an atom has only 1 orbital and can accommodate only 2 electrons. The second shell has 2 subshells. The first subshell is the so- called S orbital, which can have only 2 electrons. The second subshell within the second shell has 3, so- called P orbitals, each of which can accommodate 2 electrons. With 3 P orbitals in the second subshell and 1 S orbital in the first subshell, the second shell around an atom has altogether 4 orbitals and therefore can have up to 8 electrons around but not more.
The particles can have spin twice that of the spin of an electron, a spin of 1 (1/2 + 1/2 = 1). Such particles with a spin of full integer are called bosons. The name was given in honour of Indian mathematician and physicist Satyendra Bose.
With such spin, a boson has a property that is not subject to the Pauli exclusion principle. It means that there is no limitation on how many bosons can be accommodated in a confined space. Before elaborating a little bit more on these differences between fermions and bosons, I would like to clarify what we mean by integer.
Integer comes from the Latin word meaning untouchable. In mathematics, integer refers to a whole number. The whole number is every number, which is not decimal, or a fraction. It is also 0 or a positive or a negative number, but it has to be a whole number. Numbers 1, 3, 564, or 53952 are integers as they are whole numbers. Minus numbers are integers as long as they are whole numbers such as –1, –3, –35728 and so on.
Subtraction among integer numbers can take place giving an integer number, irrelevant whether it is a + or – number.
For example 10-20 = –10 or 30 –30 = 0. All of these 6 numbers (10, –20, –10, 30, –30, 0) are integer numbers, including 0.
1/2 , 3/2, 5/2, 7/2 are not integer numbers as they are not whole numbers. Obviously, 2/2, 4/2 and 6/2 are integer numbers as they are actually whole numbers (2 divided by 2 gives 1 as a whole number; 4 divided by 2 gives 2 and 6 divided by 2 gives 3 as a whole number).
FERMION has a spin of a half of an integer number which is ½ and forms matter of which all the universe is made, including ourselves. Fermion is subject to the Pauli exclusion principle which is a principle which in the most simplistic way means that two things cannot be in the same place at the same time. As a fermion is subject to such principle, matter which is composed of fermions cannot be in the same place at the same time with another mother.
BOSON has a spin of 1 integer and as such is not subject to the Pauli exclusion principle. Two bosons therefore can be in the same place at the same time. To illustrate the difference between fermions and bosons in that sense, I will use the example of a popular film Ghost with Patrick Swayze. He plays Sam, a character who was murdered, but his ghost remained on Earth to resolve the case which was behind his murder. Before Sam died, he was made up of fermion as we all are. As such, he was not able to go through closed doors, or occupied space at the same time as somebody else was sitting there. When he died, his soul remained around as a ghost. Ghosts, for the purpose of understanding this topic, can be described as having a boson property. As boson is not subject to the Pauli exclusion principle, it can go through a closed door because it can be at the same time and place as the other matter.
That boson has such property has been proven in science, in my opinion, by creating superfluid, which was achieved in 1995.
Groups of scientists, including Eric Allin Cornell, Carl Edwin Wieman and Wolgang Ketterle, were awarded the Nobel Prize in Physics in 2001 for achieving the so-called Bose-Einstein condensation.
In a very simplistic way, the way how I understand this, is that the property of fermions and bosons, or rather to say their behaviour, can be studied at microscopic level using the logic of quantum mechanics, or quantum physics.
If, however, it is possible to reduce the temperature of a matter to a temperature very close to absolute zero then the fermion starts behaving as a boson and this property can be experienced at macroscopic scale.
I can imagine this or try to understand it in the following way. Electrons, which are fermions, have a spin of ½ of an integer and, as such, only 2 electrons are allowed to occupied each orbit, one with upper ½ of a spin and one with down ½ of a spin. The second shell has 4 orbitals with 2 electrons, which are allowed in each orbital. Therefore,the first shell of an atom can have 2 electrons while the second shell can have up to 8 but no more electrons. If an atom is cooled down close to absolute zero, electrons from upper shells would tend to contract towards the centre of the atom. (The reason I am trying to understand this in that way is that I can understand easily that all things expand at a higher temperature and contract at a lower temperature.) If electrons at a temperature close to absolute zero go towards the centre then they move from the upper shell to the lower shell where ½ of the upper spin of one electron is coupling with ½ of the down spin of another electron, creating the spin of 1 integer, which is the property of a boson.
This is achieved in Bose-Einstein condensation where at such a low temperature particles coalesce into a low quantum state where they become bosons. This allows the microscopic property of a boson to be experienced at a macroscopic scale.
Eric Allin Cornell, Carl Edwin Wieman and Wolgang Ketterle were able to create a superfluid which has a boson property. Such superfluid looks like it is going through the wall of the vessel (Picture 1.07), like Sam’s ghost went through closed doors or occupied the body of Whoopi Goldberg towards the end of the movie.
Picture 1.07
This is not exactly what has happened here. An unlimited number of bosons can occupy the same place at the same time. However, a boson does not occupy the same place a fermion occupies at the same time. If that was the case it would be understandable for superfluid to go through the wall of the vessel. Here, however, we have a different property of superfluid which is the result of reduced viscosity of that fluid to nil and preserved kinetic energy of such fluid. If we stir up superfluid, the created whirlpool will last forever. With such reduced viscosity and preserved kinetic energy, the superfluid tends to climb up the wall of the vessel, come on the other side and go down to the bottom of the vessel until it eventually completely leaves the vessel, dropping out drop by drop from the bottom of the vessel.
ELEMENTARY PARTICLES
Subatomic particles are not the same as elementary particles. Elementary particles are those particles which cannot further subdivide. Before progress in the science of subatomic particles was made there was a time when it was believed that protons were elementary particles which means they cannot be further divided. Today we know that matter is made of only two types of elementary particles or fundamental particles: quarks and leptons (electrons belong to leptons). Both of them are fermions.
There are 6 quarks and 6 leptons.
Quarks are:
Up
Down
Top
Bottom
Charm
Strange
Leptons are:
Electron
Muon
Tau
Electron neutrino
Muon neutrino
Tau neutrino
There are 6 quarks and 6 leptons, altogether 12 elementary particles from which all ordinary matter is made.
The main difference between quarks and leptons is that quarks are affected by strong nuclear force while leptons or electrons are not.
Quarks unite together to create protons and neutrons. Quarks cannot exist on their own and come as 3 united together, creating neutrons or protons. Neutrons consist of 2 down and 1 up quark. The down quark is slightly heavier which is the reason that neutrons are slightly heavier than protons. Protons consist of 3 quarks as well, but 2 up and 1 down quark.
Quarks also come in pairs, consisting of quark and antiquark. This is a structure of mesons, which are actually bosons, and a carrier of force.
As there are some more names such as hadron and baryon, I would like to outline again that particles can be divided into two main categories depending on whether they are affected by strong nuclear force.
LEPTONS are fundamental particles, which are not affected by strong nuclear force but are affected by weak nuclear force, electromagnetic and gravitational force, the three remaining fundamental forces.
HADRONS are subatomic particles affected by strong nuclear force. They are divided into:
BARYONS, which are fermions, made of 3 quarks such as protons and neutrons.
MESONS are made of a quark and an antiquark. They have a very short life. Their integer is 1 spin and they are bosons.
There are some rules which exist in the world of particles and which cannot be broken. This refers to three conserved quantities. They are: electric charge, Byron number and Lepton number.
1.Electric Charge is conserved in a sense that it never changes and always remains zero. An atom has an equal number of protons (positively charged particles) and electrons (negatively charged particles). If ions and cautions are created, they bond together, becoming neutral again with zero charge.
On a large scale it is gravitational force that has a significant effect in reaction among particles according to the quantity of their masses. Gravitational force has nothing to do with the charge of a particle. If, however, we do not have a zero charge conserved in the universe but different charges among mass in the universe then our universe would look much different to how it is now. We should not forget that electromagnetic force is only 100 times weaker than strong nuclear force and much stronger than gravitational force.
If we are at the top of a high storey building and stretch our hand over the top window with a magnet in our hand with a piece of metal attached to it, we know that this piece of metal will not drop as electromagnetic force is much stronger than gravitational force.
2.Baryonic numbers and
3.Lepton numbers are also conserved quantity in a sense that the total number of baryons – antibaryons as well as the total number of leptons – antileptons, remains a constant and never changes.
It means that if a baryon is involved in a reaction, then the final result of this reaction is the same number of baryons as at the beginning of the reaction.
An example is a Beta radioactive decay where a neutron is transformed into a proton giving an electron and antineutrino.
N (neutron) = p (proton) + e- (electron) + antineutrino
In this equation we have 1 baryon before the reaction (neutron) and again 1 baryon (proton) after the reaction.
Zero charge is at the beginning of the reaction (neutron is neutral) and zero charge is after the reaction( it is created + proton and -electron which cancels each other out, giving zero charge).
The baryon or lepton number has to remain uncharged so if we have a reaction which initially did not start with a presence of baryon or lepton, then, even if they appear during the reaction, they have to be in a pair with an antibaryon or antilepton which will result in the cancelling of each other or their annihilation so that the end reaction will not have a baryon or lepton as it was not present at the beginning of the reaction.
In the above example there was only a neutron, baryon at the beginning of the reaction but no lepton present before the reaction. The neutron decayed into a proton and electron (lepton). A lepton is therefore created but also an antineutrino, which is antilepton to electron. Electron (lepton) + antineutrino (antilepton) annihilate each other out with the end result of no lepton present as was the case at the beginning of the reaction.
We know similarly that photons at a particular condition when they collide with each other can create matter. However, every creation of matter in that way has to be accompanied by the creation of antimatter where collision of those two converts them again into energy (photons) from which they were created. The end result will be as at the beginning.
photon + photon = matter + antimatter = photon + photon
Similarly: 0 = 1 – 1 which = 0
Mesons are composed of quarks and antiquarks. They are bosons, as they have a spin of 1 integer. They are carriers of forces for particular fundamental interactions for which they are responsible.
As we mentioned earlier, mesons are made of 2 quarks, actually 1 quark and 1 antiquark. As such, they last an incredibly short time because they annihilate each other. Due to such a short time of their existence they almost cannot be detected. They are called virtual particles. It is accepted theory that particles communicate with each other with the help of virtual particles, which are responsible for carrying and exchanging the information among particles. These virtual particles are therefore the means of communication between particles in a particular fundamental interaction, which takes place between particles. What sort of meson or virtual particle will be involved in an exchange of communication between particles depends on what sort of fundamental interaction between particles is in question. If it is an electromagnetic fundamental interaction, then the virtual particle is a photon. In the case of weak nuclear interaction, the virtual particles are W and Z bosons. With strong nuclear interaction, it is gluon and with gravitational interaction, it is graviton.
The main characteristic of a virtual particle is that its life is very limited and short in duration compared with ordinary particles. It is based on the theory of quantum mechanics and quantum fluctuation in the vacuum.
Quantum fluctuation in the vacuum is referred to as an energy oscillation in a vacuum, which appears to violate a low preservation of energy; also, it is not exactly that preservation of the energy is broken. I have to elaborate a bit on this.
First of all, we have to imagine a container which has been completely emptied in such a way that all atoms are removed from this container. Atoms contain energy. As the container is completely empty it means that it contains zero mass and zero energy. In other words, we have a vacuum where nothing is happening. Well, quantum theory and quantum mechanics state that this statement is wrong and actually so many things are happening in the vacuum. It actually keeps creating matter and antimatter, but as they annihilate immediately the space again remains a vacuum with zero energy, and zero mass.
It looks like something is created from nothing where conservation of energy appears to be violating.
We were describing earlier conservation of charges and baryon and lepton numbers. We demonstrated that if a baryon or lepton number was not present at the beginning of a reaction then the final result of reaction also has to be zero number of baryons or leptons.
If we have created an electron negatively char
ged and at the same time a positron, which is positively charged (electron antimatter), then they will annihilate each other, giving zero mass and zero charge. In both cases we have preserved charge and mass as before the creation of an electron there was zero mass and zero charge. In both cases, however, both charges (positive and negative) and masses(matter and antimatter) exist for a limited time. This is the same rule for virtual particles which are created as a particle with a positive energy which is immediately cancelled out and annihilated with antiparticle and negative energy bringing final result to zero mass and zero energy as it was before a virtual particle was created for a very, very, very limited time. In principle, therefore, the law of conservation of energy has not been violated.
Conservation of matter refers to a statement that matter cannot be created or destroyed in chemical or physical reactions. In other words, the amount of matter is not changing in our universe but is preserved.
It does sound very logical. We can look back at the conservation of baryonic and lepton numbers which is very much another way of making the same statement. Baryons (protons and neutrons) together with leptons (electrons) make atoms. An atom itself is a very stable structure. When atoms of hydrogen combine with atoms of oxygen to create a molecule of water, they do not disappear but just become a part of a water molecule. It means that the sum of masses of 2 hydrogens and mass of 1 oxygen (number of those atoms in a molecule of water) is equal to mass of molecule of water.
Journey Through Time Page 3
