The gluon’s responsibility is to make sure that this combination of colour always exists within a baryon.
Unlike a photon, which is neutral, a gluon is colour charged and in its interaction with a quark, it radiates colour itself.
The particular characteristic of strong fundamental interaction is that it gets stronger with the increasing distance. That is not the case with electromagnetic and gravitational interaction, as their strength gets weaker with the distance (their strength is inversely proportional to the square of distance between particles). The force of strong nuclear interaction can be compared to an elastic band attached to quarks which is relaxed when quarks are close to each other but if they move apart, the elastic gets stretched and pulls them back. In other words, gluons present within baryons are not felt or detected when quacks are close together. In such a situation the quark can behave like an independent particle. This effect is called asymptotic freedom.
David J. Gross, H. David Politzer and Frank Wilczek, American physicists, were awarded the Nobel Prize in 2004 for work in related strong nuclear interaction. They discovered that strong forces become weaker at smaller distances and that they become stronger as the quarks move apart.
Quarks come in triplets within protons and neutrons when a red, blue and green colour has to be present to give zero net colour. They can also come in a combination of quark-antiquark where one quark has a colour and antiquark anticolour, which brings again zero net colour. In reality, it is impossible to separate quarks on their own as they always come as three quarks within a baryon. If they pull apart from each other and reach the distance which is within the size of a hadron or baryon, the strong force reaches and remains at strength of 10 000 newtons. (Newton is the unit of force. 1 Newton is a force needed to apply to move 1 kg in a distance of 1 metre with an acceleration of 1 metre in a second per second.) That is the strength of the force, which keeps quarks together in a baryon. If we apply such an amount of work against this force to neutralise it in order to get free quark , we cannot get it as with that amount of work we can easily create particle-antiparticle pair. So that energy used with an intention to separate quarks will create new quarks, which will pair up again with the original one. This inability to get a free quark out of a baryon is called colour confinement.
3
ENERGY
We all have a rough idea in our minds what energy means and although we might not be able to accurately define energy, we more or less understand this notion of what we refer to when we talk about energy. To define it more precisely from the aspect of physics, we need help from physics. Physics defines energy as a capacity to do work. Work is a force used to move an object a particular distance or to displace an object at a particular distance. The equation for work in physics is therefore:
work = force x distance
Energy is therefore tightly related to work, as without energy, work cannot be done. In our everyday lives we know that the more physical exercise we do, the more energy we spend. If we additionally eat less or reasonably, then we will be able to keep ourselves fit, slim and healthy. This, of course, refers to middle-aged people who around that time usually start having a problem to balance intake of food or energy and the output of calories brought in. One of the reasons that middle-aged people are usually heavier or have more fat than when they were younger is a decrease of metabolism, which comes with age. Metabolism is regulated by the thyroid gland. This, however, is not a topic of this book and we can move away from this discussion as quickly as possible.
Energy is measured in joules.
1 joule is equal to 1 Newton (1 kg m/s on power of 2) times metre or:
S= second
M= meter
There is an old system of measuring energy, which is still in use when we measure the level of energy taken by food, and that is the calorie.
The calorie is used for two units of energy:
Gram calorie symbol of cal(small calorie) which is the amount of energy needed to raise the temperature of 1 gram of water by 1 degree celsius.
Kilogram calorie with the symbol of cal or kcal, which is the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree celsius.
A gram calorie is equal to 4.2 joules and this old system of energy measure is still used in chemistry.
A kilocalorie is equal to 4.2 kilojoules and is still used to measure energy levels food contains itself. Otherwise, an official agreement is to use the International System of Units, which in the case of measuring energy is in joules.
There are many different forms of energy. We are familiar with many of them such as kinetic, which is the energy of a moving object; potential energy, which is stored energy (gravitational or elastic, for instance) and radiant energy which is carried by electromagnetic waves, electric energy and so on.
Energy can be transferred from one form to another. This transfer can be done by work or heat. I will elaborate more on these two ways of energy transferral, looking at these from a molecular level.
In Chapter 1, under the subsection of subatomic particles, we have outlined some conservation rules in relation to particles such as conservation of baryon and lepton numbers as well as conservation to charges of particles where we have zero net charges in a whole.
This rule is also applied to energy; but before stating this rule, which is the formulation of the first law of thermodynamics, I would like to introduce some concepts which might be helpful to make better sense of this rule.
For this purpose the whole universe can be divided into two compartments. On one side we have a numerous number of systems where each system makes one compartment. On the other side we have surrounding of the system, which makes another compartment. We are each individually one system which is separated from its surroundings by our skin. A football is another example of the system; one single biological cell is another system. A pot of water prepared to be heated up for making soup is another example of the system and so on.
Every system has its own internal energy, which is a total amount of all energy, which this system contains within itself.
The total amount of all energy in the system or internal energy can be increased or decreased if there are transfers of energy between the system and its surroundings. If energy goes in the system from the surroundings, then the total energy of that system will increase. If it goes out, then the total energy of the system will decrease. This change of internal energy in the system is possible only thanks to the existence of its surroundings. These will allow transferral of energy between the two compartments.
The universe as a whole is a closed and isolated system. It does not have surroundings. It does not have outside or other compartments from where energy can be injected into the system and so increase the internal energy of the universe or where transferring energy from the universe to its surroundings can decrease the internal energy of the universe. As the universe is isolated with no outside, we have the first law of thermodynamics, which can be formulated as follows:
The internal energy of an isolated system is constant.
From there we can say that energy cannot be created or destroyed but only transferred from one form to another. As mentioned before, this transferral takes place by work or heat.
Looking from the molecular level, work transfers energy by using organised motion of the molecules.
Work is force multiplied by distance. When we kick a football, we inject or transfer energy into the football, which is manifested as kinetic energy of motion. The football as a system moves upwards against the force of gravity. In this process all atoms or molecules of the football move in the same direction, meaning that work use organised motion of particles, molecules.
Heat uses disordered motion of molecules to transfer energy. When we heat up a pot of water to make soup, we are doing this by applying thermal motion of the surroundings on the system. Disorderl
y motion of the molecules is called thermal motion. In the case of our pot of water, our hob starts producing disordered motion of the molecules, which stimulates disordered motion of the molecules of water inside the pot and in doing so, increases the temperature in the system where, with the help of heat, the energy of the system increases.
As stated before, energy cannot be lost or created but only transferred from one form to another.
Before it was kicked, the football had its own internal energy. Once energy was transferred to it by work, the football’s internal energy increased, which was manifested as a kinetic energy. The football will go up but its movement will slow down by Earth’s gravity. In one moment, for a split second, the ball will stop in the air. The whole injected energy will be now transferred to a potential energy. Potential energy is nothing more than stored energy (if we just remind ourselves of an electron jumping from an inner shell to an outer shell, absorbing a photon and gaining potential energy which is stored in the shape of a photon being absorbed). The ball will now head towards Earth, transforming potential energy to kinetic energy. (The same happened with an excited atom where an electron now goes back to the inner shell and emits that photon which was absorbed to go up to the higher shell.)
Based on the conservation of energy or the first law of thermodynamics, we cannot have or construct any perpetual motion. Perpetual motion means continued motion indefinitely with no external source of energy. A ball will not go upwards in the air unless it is kicked (external energy injected as kinetic energy). It will not continue to move upwards indefinitely as it will be slowed down by gravitational force and the friction it has in contact with molecules of air. In this friction, kinetic energy is reduced by being transferred to molecules of air. As this increases the movement of these molecules of air, their energy (referred to as molecules of air) is increased. In other words, a part of the kinetic energy of the ball is transferred in its surroundings or air by heat. So in order for the ball to continue to move upwards, the ball needs the constant input of external energy and, therefore, perpetual motion is not possible.
The internal energy of the system is the sum of all energy which is within the system. It is usually the sum of kinetic and potential energy. Kinetic energy is manifested with the presence of the movement of atoms, molecules. There are all sorts of movements, which take place at molecular level. Atoms can vibrate jiggles within molecular structures. Molecules can move randomly within the system. Electrons can jump on a higher level, having a potential energy, for example. In essence, every system has its own internal energy and as such, it can transfer this energy to its surroundings. Such transferral of internal energy to the outside of the system is called thermal energy transfer.
This can be achieved in three ways:
1.By conduction: when we hold one side of a wire while the other is heating up, we will quickly start to feel the heat as molecules or atoms of the wire transfer energy by touch to each other until it reaches the end of the wire we hold
2.By convection: where molecules move around transferring energy such as in the case of air where hot air moves upwards while cold goes down, creating circulation
3.By radiation: where internal energy is transferred by radiation or electromagnetic waves
Basically, all matter radiates energy as long as it has energy inside itself. It will stop doing so if it reaches a temperature of absolute zero, which is -274 degree celsius or 0 Kelvin. At this temperature there will be no movement and energy will be equal to zero. We should remember that an atom has its own energy due to its own structure as its electrons go around the shells. Each shell is at a particular energy level but when electrons go down to the inner shell, it loses or radiates this energy. We also have protons and neutrons within a nucleus, which have some form of energy level. That is how gamma radiation is explained,which is emitted when protons and neutrons go back to ground state or lower energy level. However, as the temperature approaches absolute zero, electrons lose their energy levels, so do protons and neutrons. They radiate this energy away and coalesce with each other at the lowest energy level or ground state creating bosons; Bose-Einstein condensate.
We can ask the question, if energy is equal zero, where has all this energy disappeared to? Is that the break of the first law of thermodynamics? The answer is no, as we are decreasing the temperature in the system which has its surroundings. We are doing this by decreasing the temperature of its surroundings which makes the system radiate its energy out to its surroundings. In this process, the energy is taking away from the system and if the system is brought to near the absolute zero (we cannot achieve absolute zero) the energy of the system still exists but is transferred from the system to outside as heat and in doing so, the temperature of the system decreases while the temperature of its surroundings increases. Obviously, when the temperature of the surroundings increases, due to energy being radiated from the system, equilibrium will be established at one point. This means that the temperatures will equalise between the system and their surroundings. Once this happens, we need to find a way to cool down the surroundings again to allow further radiation of energy from the system until a temperature of zero is reached. This also means that the whole process of cooling the system down to the temperature of absolute zero will take place in stages as the surroundings need to be cooled down again. To achieve this, we need a machine which will operate in that way. In other words, we need an extra energy.
We have just described the second law of thermodynamics, which can be formulated as:
Heat always flows from a hot object to cold and never from cold to hot.
This is one way of formulating the second law, but it is not complete. To complete it, we need to look at the first law which says that energy is always constant but only changes or converts from one form to another. While this is true, the initial form of energy or work used is never going to be completely transformed into another form of useful energy. It will always be a waste of energy as heat. If a car engine produces work or energy to move a car, this energy is never going to be completely converted to kinetic energy or motion of the car, but part of it will be lost as heat. In order to produce car motion or work, we always need to input more work into it as during conversion of our work to a different sort of work, we have a waste of energy as heat.
Work in (external energy) = work out (transferred energy) + heat (waste energy)
The general rule or tendency in the universe is that transfer from one type of energy always goes from the most useful kind of energy to the less useful kind of energy. This is where we come to the notion called entropy.
Before going to entropy, just to state that cooling the system to the absolute zero of -273 Celsius or Kelvin can never be achieved. It can come close but never completely, which is the third law of thermodynamics.
Entropy is the measure of the amount of disorder in a system. As the amount of disorder increases in the system, so does the amount of energy. However, the amount of usefulness of energy is reducing.
In the universe as a whole, entropy is spontaneously increasing and with it the usefulness of energy is decreasing. Energy is not disappearing but is becoming less useful every time the entropy increases.
Perhaps the best way to describe an increase of disorder or entropy with reduction of order and useful energy or work is if we are led by the definition of work at a molecular level where work is a way of transferral of energy by using organised motion of the molecules which is also a type of useful energy.
If we look at the phase state of the matter, taking the water as an example, we can state that ice (solid state of the water) has the lower entropy as water molecules are in a higher order. We can use ice to produce useful work, which is force multiplied by distance. We can throw sphere-shaped ice instead of a ball in bowling to knock over pins. When the temperature increases, the water melts, becoming a liquid, which has higher entropy end energy, but that energy is no
w less useful. We can still knock over pins with water, but we need more water to flow towards them. We can succeed in this only if we have a sort of tube which contains water and creates a condition for a stream of water to take place. If the flow of water is strong enough, it might knock over the pins. The energy of water will be less useful. Finally, with increasing temperatures, water will reach the higher entropy by evaporating in air. Energy will be higher but completely useless for the purpose of knocking down pins.
In essence, an increase in entropy inevitably reduces the amount of useful energy, which ultimately means that such a process will bring the universe to the end where the universe will consist of all the energy, as it does today, but all this energy will be useless.
We mentioned before that all matter has energy and can radiate this energy unless it reaches absolute zero. Once we have an absolute zero, then we have zero energy and zero entropy. But in any other situation, the system has internal energy, which can be transferred by radiation. It is done by electromagnetic waves. Waves are therefore the way of energy transferral. They are energy carriers. Electromagnetic waves are photons, which are carriers of energy or force in electromagnetic fundamental interaction between particles. We can simplify this and say that energy structure is an electromagnetic wave or photons while matter structure is quarks and leptons. Now it is the right place to give just simple general characteristics of waves.
Journey Through Time Page 7
