10. Gravity - A Conclusion

Though quantum theory of gravity defines gravity in terms of gravitons, it's still not resolved mathematically compared to how general theory of relativity resolve gravity hypothetically as well as mathematically. That's because there is a catch/problem in defining gravity and mathematically resolving the same. We have two definitions for gravity, one from general theory of relativity in terms of macroscopic objects and another one is from quantum theory in terms of microscopic objects. Quantum physicists can only claim that they could explain gravity in terms of quantums only when their mathematical model support or explain in terms of both microscopic and macroscopic world.

For a quantum field theory to be well-defined, it must be asymptotically free or asymptotically safe. The theory must be characterized by a choice of finitely many parameters, which could, in principle, be set by experiment. For example, in quantum electrodynamics, these parameters are the charge and mass of the electron, as measured at a particular energy scale.

On the other hand, in quantizing gravity, there are infinitely many independent parameters needed to define the theory. The process of mathematically reducing the infinite number of parameters to a finite set of parameters is called renormalization. For a given choice of those parameters, one could make sense of the theory, but since we can never do infinitely many experiments to fix the values of every parameter, we do not have a meaningful physical theory:

• At low energies, the logic of the renormalization group tells us that, despite the unknown choices of these infinitely many parameters, quantum gravity will reduce to the usual Einstein theory of general relativity.
• On the other hand, if we could probe very high energies where quantum effects take over, then every one of the infinitely many unknown parameters would begin to matter, and we could make no predictions at all.

There is another major difference between general theory of relativity and quantum theory of gravity. A basic lesson of general relativity is that there is no fixed space-time background, as found in Newtonian mechanics and special relativity; the space-time geometry is dynamic. To a certain extent, general relativity can be seen to be a relational theory in which space and time are always relative to the reference frame of the observer. On the other hand, quantum mechanics has depended since its inception on a fixed background of space (non-dynamic) structure. In the case of quantum mechanics, it is time that is given and not dynamic, just as in Newtonian classical mechanics.

As explained below, there is a way around this problem by treating quantum gravity as an effective field theory. Since quantum mechanics couldn't reduce the number of parameters quantum gravity is termed as non-re-normalizable!There are a number of other approaches to quantum gravity. The approaches differ depending on which features of general relativity and quantum theory are accepted unchanged, and which features are modified. Examples include the following,

• Supergravity
• Path-integral based models of quantum cosmology
• Causal Dynamical Triangulation
• Regge calculus
• Causal sets
• Asymptotic safety
• Twistor models
• Noncommutative geometry.
• String-nets giving rise to gapless helicity ±2 excitations with no other gapless excitations
• Acoustic metric and other analog models of gravity
• MacDowell–Mansouri action
• An Exceptionally Simple Theory of Everything
• Group field theory

Ultimately any meaningful theory of quantum gravity that makes sense and is predictive at all energy scales must have some deep principle that reduces the infinitely many unknown parameters to a finite number that can then be measured!

Anyway, I don't want to just simply close this chapter at this point. I would like to step back here and give it a second thought on gravity because after going through all these concepts, theories, hypothesis one thought keep rolling into my mind. Every time I read about general theory of relativity or quantum gravity or theories like String theory or M theory or whenever I see physicists trying to define Grand Unified Theory, so called, GUT, which will be capable of defining everything in this universe.

I ask myself 'What's wrong with science? Why should mathematics fail if we are on right track? Why is it so hard for physicists, who resolved the other three forces and united them into one single theory, to resolve gravity in terms of quantums? Why does it make physicist to dream about so many complications and come up with theories like Super-string theory, Membrane theory and loop quantum gravity theory, etc? Are they not starting physics all over again with their new complicated theories? After all these, what I could finally think of is that the basic understanding of the gravity itself may be wrong!

Conclusion:
According to me, Gravity can be a special force but it cannot be too special to demand such complications. If you consolidate the inventions of the other three fundamental forces, it goes as follows.
1. Strong force was found and that is happening because they internally share photons during their interactions. Hence it could be united with electromagnetic force.
2. Next, weak force was found and that is at higher temperature and high energy environment, it is nothing but another form of electromagnetic force because it was found that photons are shared during weak interactions.

Then what could be stopping gravity to be like Strong force or weak force? Since strong is the strongest of all the fundamental forces, we will ignore it for the analysis. Lets consider the weak force. We have seen that this force is no longer weak at high energy environments but it became weaker when the temperature and energy goes down. We all also know that objects would have not been formed if the weak force is not weaker.

Now, my point here is to consider gravity just like another weak force, probably, we can name it as the weakest force of all. This force could also be another form of electromagnetic force but it became weaker and weaker under low energy environments. We also know that on moon, there is no life is formed because the gravitational force of the moon is not enough to support it like how earth does it.

This approach demands one more possibility. We all know that gravitational force interacts with masses. Science has not found how the objects gain their masses. Hopefully, the Large Hydron Collider would find the Higgs boson and explain mass. However, lets consider that it is Higgs boson that caused the objects to gain the mass. If this is true, then according to me, gravitational force interacts with Higgs boson.

Lets consider the interaction is happening with Higgs bosons, then that tells us that gravitational force also involves carrier particles which are familiar to Higgs bosons. Quantum physics says that Higgs bosons are another sub-atomic carrier particle evolved from the electromagnetic force.

Just for record, earth also behaves as a gigantic magnet due to it's electromagnetic force radiating from it's burning core. Taking all these into consideration, I personally believe that gravity is another form of electromagnetic force, the only hard-stop is that we haven't resolved the mystery behind the Mass. If we do, then gravity will no longer be a mystery!

9. Gravity Vs Quantum Gravity

So far, science has discovered four fundamental secrets of the nature, the four fundamental forces. Among those, science has defined theortically, mathematically and also practically explained the first three forces, so called, 'Strong', 'Weak', 'Electromagnetic' forces. Can this be interpreted as science has understood 75% of the nature? It seems like it did but if you look further into facts, it hasn't done and science has long way to go.

Gravity by Newton:
In classical physics, gravity is the most famous topic and also it is the most familiar force among laymen, as compared to other three fundamental forces. Around 300 years ago, Sir Isaac Newton described gravity as the character of an object that has a non zero mass. He is the father of the definition of gravitational force (g) and also for the gravitational constant (G).

According to Newton, Gravity is always a force that exists between two objects. Please don't forget that 300 years ago there was no atoms, no photons and no quantums. Everything is just an object. So, he came up with a formula that explains the gravitational force as it is directly proportional to the masses of two interacting objects and inversely proportional to the square of the distance between those objects; and also introduces the gravitational constant.

G, the gravitational constant is nothing but the gravitational force of the Earth and it's a constant value because on earth most of the objects have very less mass as compared to the mass of the earth and the distance is almost equal to the earth's radius. Hence the final outcome of the formula, approximately, stays as a constant. If m1 is the mass of object1, m2 is the mass of object 2 andd is the distance between the objects1 & 2. Then, the gravitational force F, acting between those two objects, can be calculated as F = m1. m2/d*d. In other words, on earth F will be g * m2 or F = mg. This is how gravity was defined 300 years ago.


Gravity by Einstein:
In 1916, Einstein re-defined gravity in his general theory of relativity in a brand new dimension. He was the person who also introduced Time as the 4th dimension. So, his perspective and mathematical theories are defined in his three dimensional space with Time as a 4th dimension. So, his models are viewed in the space-time matrix or fabric. The way how he had done mathematical models and defined the gravity is an amazing and interesting one.

According to Einstein, universe is nothing but the fabric which is made up of 3dimensional space and time. When we talk about gravity, it just remains the property or attribute of the planets in our galaxy. So, he demands that the planets resting on the fabric and rotating on their positions. Planets are massive and so due to their heavier masses, they push the fabric down at their positions. This creates slope around the heavier planet and it in turn makes the other smaller planets to roll around the heavier planet.

Hence in our solar system, Due to Sun's heavier mass, all other planets and satellites revolve around the Sun. As per Newton's formula, Sun pulls each planet with a unique amount of force based on the distance and the mass of the planet and make them revolving around.

If you take a closer look, such model demand and at the same time proves few other facts as follows:
1. Empty space or vacuum is not really empty in the outer space.
2. When Sun rays come through outer space, it carries the electromagnetic force, which creates energy and forms the fabric of 3-dimensional space.
3. So when Sun dies after burning all of its fuel, the fabric will no longer exist between Sun. In other words, there won't be any gravitational force from Sun and eventually other planets would be free from their path and slip through outer space until it's acceleration comes to zero; but this means earth may even stop rotating. If that happens then that would destroy everything on earth as everything on earth is pushed in opposite direction due to the acceleration that the objects gained from earth's rotational force. This is similar to the effect that the passenger is pushed front when brake is applied.

Quantum Gravity:
When we say quantum gravity, we still mean the gravitational force. Then what is the difference? While gravity has always been described as the property of macroscopic world, such as planets and solar system, quantum gravity is explained in terms of objects and entities from the microscopic world, in other words, quantums. Either in classical physics or quantum physics, all the phenomena have been described not only in theories but also mathematically and proved experimentally.

Quantum mechanics claims that gravity is another fundamental force caused by new set of sub-atomic particles, named as gravitons. While there is no concrete proof of the existence of gravitons, quantized theories of matter necessitate their existence. Supporting this theory is the observation that all other fundamental forces have one or more carrier particles, except gravity, leading researchers to believe that at least one most likely does exist; they have dubbed these hypothetical particles gravitons.

Many of the accepted notions of a unified theory of physics since the 1970s, including string theory, super-string theory, M-theory, loop quantum gravity, all assume, and to some degree depend upon, the existence of the graviton. It is clear that the detection of the graviton as vital to validating all of these theories up to the decent extent. While quantum mechanics demands that the gravitons would be theoretical spin-2 mass less particles, quantum physicists are trying to define gravity in quantum theories. In order to succeed, they also need to resolve gravity in their mathematical models!

8. Matter Vs Anti-Matter

We know that matter is made up of subatomic particles such as protons, neutrons & electrons and they, in turn, are also made up of tiny particles called quarks. All these are referred as matter. Then what is Anti-Matter? Originally it sounded to me like something opposite to the matter, probably like spirits or ghosts. In fact, antimatter is also a matter. It's just another set of particles that also belongs to the subatomic world. In 1932, anti-electrons were discovered by Carl D. Anderson even though the term was already used by Arthur Schuster in 1898.

What is anti-electron? Is it some spirit form of electron matter?! No, not at all. It's also an electron but with a positive charge! Usually laymen like me get confused that a particle with positive charge is a proton, isn't it?! Yes, but there are other differences. Protons are also heavier than electrons. So when we say anti-electron, it means an electron but with positive charge! Anti-electrons were found and eventually named as 'Positrons' by Carl D. Anderson himself.

Like matter, apart from the electric charge, antimatter also also have their spins. Spin is a unit-less attribute. It refers the angular momentum of the particle. In fact, in real subatomic world, no particles spin to right or left. Feynman referred spin as the direction of time in which particles move! Forward or Backward! This actually leads to further confusions and questions about time! So, the standard way of seeing the direction of spin remains clockwise and anticlockwise to avoid further complications on 'Time'.

Creation:
Antiparticles are created everywhere in the universe where high-energy particle collisions take place. High-energy cosmic rays impacting Earth like atmosphere produce antiparticles, which are immediately annihilated by contact with nearby matter. Antiparticles are also produced in any environment with a sufficiently high temperature where mean particle energy greater than the pair production threshold.

1. Positrons were reported^[11] in November 2008 to have been generated by Lawrence Livermore National Laboratory in larger numbers than by any previous synthetic process. A laser drove ionized electrons through a millimeter radius gold target's nuclei, which caused the incoming electrons to emit energy quanta, that decayed into both matter and antimatter.
2.  In 1995 CERN announced that it had successfully brought into existence nine antihydrogen atoms by implementing the SLAC/Fermilab concept during the PS210 experiment.
3. A small number of antihelium-3 (³He) nuclei have been created in collision experiments.

Interaction:
a positron (the antiparticle of the electron) and an antiproton can form an antihydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom. Antimatter that is composed of charged particles can be contained by a combination of an electric field and a magnetic field in a device known as a Penning trap. There are also particles with no charge, for which atomic traps are used. In particular, such a trap may use the dipole moment of the trapped particles; at high vacuum, the matter or antimatter particles can be trapped and cooled with slightly off-resonant laser radiation because just an intensive laser beam also could suspend few small antimatter particles.

Annihilation:
Mixing matter and antimatter can lead to the annihilation of both by giving rise to high-energy photons. Antimatter cannot be stored in a container made of ordinary matter because antimatter reacts with any matter it touches, annihilating itself and an equal amount of the matter, I mean the container.

Before we conclude, lets consider the positive beta decay. We had seen this activity in the previous post while talking about strong force. While proton decays into neutron, it releases positron with it's positive charge if there is enough energy is available. Antimatter is the byproduct of fundamental interactions. Even though we try to create antimatter for medical and scientific uses because of its high energy states, antimatter is not easily reproducible and stored in matter based environment and hence antimatter can exist in abundance to form antimolecules only in burning star or center of the galaxy where the energy is too high.

Conclusion:
On Earth, antimatter always ends upon annihilation with matter considering how much it costs if we try to protect them from matter and produce them in abundance! However given such high temperature and pressures, there is almost zero possibility of forming matter like us. In order to form the matter like the one on Earth, temperature should be drastically low and water should be formed.

Provided these facts, I could only think of some organisms(!), which are made up of antiparticles with high energy, can live at those high temperatures and pressures. Would that be some kind of spirit form!? Even if it is true, then it will not be the same as the spirit form of living being that is defined by worldly religions! Hence antimatter is not the idea that a meta-physicist would be interested in to explain the spiritualistic view of our world!

7. Quantum Theories

We had seen the details of the first three fundamental forces and now I am jumping into the Quantum theories that explain these forces. For now, we miss gravity because gravity is still unresolved mystery from quantum physics's perspective. Unlike classical physics, Quantum physics doesn't see the forces as individual forces but see them in terms of commonality between them. That's why Quantum physicists keep attempting to unify all the forces into one theory based on the relationship or commonality between them at the quantized level.

1. Strong Force - Theory of Quantum Chromo Dynamics
2. Weak Force & Electromagnetic Force - Electroweak Theory

Theory of Quantum Chromo Dynamics (QCD):
From the word 'chromo', you might have guessed that this is something to do with 'color'! Yes but this is nothing to do with the colors which we see. We know that strong force shares quarks between neutrons and protons to form the nucleus. This theory explains how that is happening but first, we need to understand quarks better.

Flavors: Quarks can be found in one of the following six states or types.
1. Up (u), 2. Down (d), 3. Charm (c), 4. Strange (s), 5. Top (t), 6. Bottom (b).

Though there are 6 types, Protons and Neutrons are formed only by 2 types of the quarks. They are Up and Down. Proton consists of 'u-d-u' and a Neutron consists of 'u-d-d'. These states are called as 'Flavors' in Quantum physics.

Colors:
Also, quarks have three type of charges. These charges are called as 'Colors'. Don't let the name confuse you with the real colors that we see. Though these charges are defined as 'red', 'green', 'blue', they don't really mean it. But their behavior matches them. Like, mixing three of them gives you a neutral-charge. At the same time, there are anti charges like '-' and '+'. They are called 'anti-red', 'anti-green', 'anti-blue' and all three of them produce neutral-charge. Please note that, red and anti-green does neutral the charges it happens only with the anti-quark of it's own.

Interactions:
Quarks interact with other quarks by sharing 'gluons' between themselves. The gluon is the one that is responsible for the color-charge. Also, it's possible that gluon share gluons with other gluons. I mean gluon can absorb or emit gluons. So, if you take an incident of a strong force, you might see a huge number of interactions, happening within a short period of time and space and that is filled with sharing of gluons and quarks. Yes, it's complicated and impossible to draw Feynman diagrams (Famous diagrams used to explain quantum activities) using perturbation theory.

Electroweak Theory:
Although the electromagnetic force and weak force appear very different at everyday low energies, the theory models them as two different aspects of the same force. Above the unification energy, on the order of 100 GeV, they would merge into a single Electroweak force. Thus if the universe is hot enough (approximately 10¹⁵ K, a temperature reached shortly after the Big Bang) then these two forces will merge into a combined Electroweak force. In other words, the weak force will no longer be weak at high energy environment. So, there will be only one force so called electroweak force that causes both beta-decays and attraction/repelling of the charges.

Weak interactions:
There are three types of bosons that mediates the weak force. They are W⁺, W⁻, and Z⁰. Electroweak theory says that during beta decay, neutron releases it's excessive mass in the form of energy as W & Z bosons. As we have seen in my initial posts, these are the heaviest bosons among all. Hence this moves slowly during the interaction and makes the force weaker compared to other forces. Also, this is the only force which occurs or involves change of 'flavor'. We had seen two interactions happen via weak force. 

1. n⁰ → p⁺ + e⁻ + ν_e - Neutron becomes Proton by releasing a heavy boson W⁻. It changes up quark to a down quark. Hence electron get it's negative charge from W⁻. This decaying process is called as negative beta decay (β^-) as electron, with negative charge, is emitted.

2. energy + p⁺ → n⁰ + e⁺ + ν_e - Proton becomes Neutron by absorbing energy of . It changes down quark to an up quark. Since positron takes away the positive charge with itself Neutron ends up with no charge. This is called as positive beta decay (β⁺) since the positron, with positive charge, is emitted. Here, in all the cases where β⁺ decay is allowed energetically (and the proton is a part of a nucleus with electron shells), it is accompanied by the electron capture process, when an atomic electron is captured by a nucleus with the emission of a neutrino:

energy

+

p

+

e−

→

n

+

νe

But if the energy difference between initial and final states is less than 2m_ec², then β⁺ decay is not energetically possible, and electron capture is the sole decay mode. For low-energy decays, electron capture is energetically favored by 2m_ec² = 1.022 MeV, since the final state has an electron removed rather than a positron added.

This decay is also called K-capture, because the 'inner most' electron of an atom belongs to the K-shell of the atom and this has the highest probability to interact with the nucleus. By changing the number of protons, electron capture transforms the nuclide into a new element. The atom moves into an excited state with the inner shell missing an electron. When transiting to the ground state, the atom will emit an X-ray photon (a type of electromagnetic radiation) and/or Auger electrons.

Electromagnetic interaction (Theory of Quantum Electrodynamics, QED):
Quantum physics states that the mass-less photon γ, which is also charge-less and has 1 spin, mediates the electromagnetic force. Photons can be shared between two electrons, two protons or between electrons and protons, etc. QED explains that sharing of photons is the reason for attraction and repelling forces. The basic approach of QED is to determine the probability of finding a photon, an electron or their interactions in a certain point of space and time.

For an interaction that involves one electron and one photon, the probability of the outcome (Po) can be determined by multiplying the individual probabilities for an electron (Pe) and a photon (Pp) to exist in their specific points of space and time. There is a certain possibility of an electron or photon at position 'A' moving as a basic action to any other place and time in the universe. That includes places that could only be reached at speeds greater than that of light and also earlier times. Also, quantum mechanics say that an electron moving backwards in time can be viewed as a positron moving forward in time. No particle can move backward in time in reality.

I would say that concept like 'moving backward in Time' should only be used for mathematical purpose. In reality, Time doesn't flow in backward. It's all new topic to discuss. Please refer my other blog on science of Time -> http://scienceoftime.blogspot.com

To calculate the probability of any interactive process between electrons and photons it is a matter of first noting, with Feynman diagrams, all the possible ways in which the process can be constructed from the three basic elements. Each diagram involves some calculation involving definite rules to find the associated probability. From the details, QED doesn't quite sound like a typical 'Theory' to explain a natural phenomena rather it's an approach that helps us to determine the behavior or outcome of electrons/photons interactions.

Like any other theory, quantum theories are also associated with symmetries, gauges, fields and models that are mathematical aspects of natural phenomena. Unlike classical physics, quantum physics can't yet explain things in laymen terms because the submicroscopic world is not yet completely understood for laymen interpretation. Still, mysteries like uncertainty principle, gravitons, etc are yet to be explained in order to form the Grand Unified Theory of everything!

6. Electromagnetic force or Light

Welcome back..

In this post, we are going to explore what the physics behind light or electromagnetic force is. In previous posts, we had seen how the strong force formed the nucleus and how the weak force formed the atoms. Now, what is next? No doubt.. Molecules!

Molecules are the reasons for matter to gain certain form in this universe. Atoms are combined together to form a molecule. In order for atoms to get together, we need a force that can operate between atoms. Such force is called intermolecular force. When we are talking about atoms and molecules formation, our interest is mainly on the electric form of the electromagnetism or the electric fields. We will keep the magnetic fields aside for now.

So, let's see how electric fields help in the formation of molecules. In fact, without electromagnetic force, even protons and electrons will not have charges and even atom might not have been formed! Though we had seen that strong & weak forces form atoms, without electric charges or fields, it's impossible for atomic nuclei to hold the electrons surrounding them.

What do atoms have to do to mingle with each other? Electromagnetism is the force that results when charged particles exchange photons. As we all know that atoms have electrons readily available. These electrons are negatively (e-) charged. Now, when two atoms comes closer, there are several actions happen. I have listed them out below for better understanding.

1. The protons from both atomic nuclei repel each other due to same charge.
2. The electrons, which stays at the entrance of one atom, easily get attracted by the protons inside the other nucleus.
(Attraction/Repelling are resulted from the exchange of photons, the electromagnetic force!)
3. Since electrons cover the most of the area in an atom, it keeps the protons far apart from each other.
4. At the same time, electrons, which are more in count compared to proton and neutron, move closer to the protons (nucleus) from other atom
5. Since the attractive force overwhelms the repulsive force, due to sharing and transfer of electrons, a bond is formed between those two atom.

Such a bond is called a 'Chemical bond'. Similarly more chemical bonds are formed to create bigger molecules and eventually matter gets its form. This is the basic for H2O, O2, CO2, N2, SiO2, etc.. I mean all the fundamental molecules are formed due to this electromagnetic force. Quantum physics went one step further and explain what makes electromagnetic force to attract or repel the opposite or same charged particles respectively. Let's explore them in my next post.

5. Weak Nuclear force

Hello.. thanks for coming back..

In my previous post, we had seen how Strong force is contributing to the formation of Nucleus. Now what? To form a complete atom, we need set of electrons swirling around the nucleus. So, our next objective is to understand how an atom is formed on top of the nucleus.

Particle physics say that 98% of the total mass of an atom is from the mass of its nucleus! So, once the nucleus is formed, it becomes heavy. Once again, nature exhibits its intelligence here. Neutrons are basically heavier (0.2%) than protons and it has no charge or it is neutral in charge. So, neutrons start releasing part of its mass (0.2% of its mass) in the form 'W⁻ bosons' with the energy of 1.29 MeV. Since W⁻ bosons are unstable they immediately break down into a negative charged particle and a positive charged particle. They are nothing but an electron and an anti-electron neutrino!

We can indicate the above reaction by the below equation. This process is called 'Beta decay'.

n⁰ → p⁺ + e⁻ + ν_e

There are two important points to be observed:
1. Neutron gets transformed into a Proton.
2. An electron is created out of Neutron.

So, as per the above reaction, in a nucleus, all the neutrons should have transformed into protons and all the electrons might have been created simultaneously. Ideally we would think that nucleus would then be filled only with Protons and no neutrons would exist; but in every atoms, population of protons and neutrons in it's nucleus is same. How is it possible?

In a same way how neutron gets transformed into a proton, a proton can also get transformed into a neutron if it receives an energy of 1.29 MeV. This is a reverse process of neutron's beta decay. In the early stages of big bang when the energy was so high, protons and neutrons were able to freely get transformed vice versa and so there were equal number of protons and neutrons in the atomic nuclei.

Sometime, when the size of the nucleus grows too big or too heavy, strong force start repel hadrons from each other due to collective positive (+) charges of protons in the nucleus. At some point, the nucleus gets broken into multiple smaller nucleus; eventually weak forces plays its role and creates smaller atoms out of those smaller nuclei by release electrons.

It's simple and obvious to realize why the electrons swirl around nucleus instead of traveling into the space. Yes, it's the attractive force that is generated between positively charged protons that is inside the nucleus and the negatively charged electrons that swirls around the nucleus. If you ask me what made electrons to swirl instead of just hang around the nucleus, I would surmise that it could be due to the effect of Big Bang that bursts out and left each and every subatomic and atomic particles in this universe to spin as a result of its kinetic energy and it's angular momentum!

Why is this called as weak force? because it is weaker than strong and electromagnetic forces. However without this force, there was no chance for the formation of electrons, eventually, atoms. Also this force plays a vital role in keeping the pace, at which Sun burns helium, very low and so Earth could get enough time to support the formation of lives. If such force would be stronger, then Sun might have burned all the helium very early, probably even before lives might have been formed on Earth. Hence weak force is as unique and important as any other fundamental force in this universe!

4. Strong force and Nuclear force

There is a reason why I ordered the forces starting from Strong force to Gravitational force. It's because of their purpose and how they contribute to form things that we see around us, including us. Once we explore the forces in detail, you would also understand the same.

Before proceeding into details, let's understand the reality. At any given space & time, all these fundamental forces are always acting on each other. We can also says that any activity or incident that occur in this universe is a final outcome of the resultant force derived from all four participating fundamental forces.

Let's see why it strong force is. Considering the above fact, we see this force has more control and cancel out all other forces that act on a quark or hadron. To understand it better, first we need to understand what this strong force does. This force acts on the nucleus and it has two different forms. 1. As strong force between the quarks. 2. Residual strong force between the nucleons. Nucleon is the common term for protons and neutrons. Hence, this residual force is also called as 'Nuclear force'. Let's get into the details now.

Quarks:
It's a sub-elementary particle and it also consists sub-elementary particles called 'gluons'. They get together and form the elementary particles called hadrons. Protons and Neutrons are examples of hadrons.

Strong Force:
In other words, when quarks and gluons are shared between hadrons, we can say that there is the strong force acting. One specialty about this force is that unlike any other force that we studied in physics, it's strength is proportional to the distance between the two particles! Yes, the force increases by distance. That's interesting, isn't it! That means when the hadrons come too close it repels each other or the force becomes weak. This helps to keep the hadrons not too far and not too close to each other and ultimately form the nucleons.

Nuclear Force:
We had seen that the strong force is acting between hadrons sharing quarks and gluons. If this is strong force, then what is holding the nucleons? Population of neutrons and protons is always conserved because in a nucleus, the number of protons and neutrons are always same! As a result of such a strong force inside nucleons, it extends it's field outside the nucleons and acts between nucleons as a residual force. This force also increases by distance as it's simply an extension of the strong force. It holds the nucleons not too far and not too close to each other. Hence it forms the nucleus at the center of the atom with high density.

As I said above, any activity or incident that occur in this universe is a final outcome of the resultant force derived from all four participating fundamental forces. So, considering all other forces, this force has to be the strongest one in order to form the sub-atomic particles as a first step of the creation process, the creation of an atomic nucleus!

3. Why are we what we are?

We all know what/how we are, at least from what we observe through our senses but do we know why we are what we are? That's what we are going to see in this post.

After centuries of research, Scientists came up with four fundamental forces that drive the whole universe, what we know. Also, there are theories that explain each force both theoretically and mathematically. They are as follows,

1. Strong force - Quantum Chromo Dynamics theory.
2. Weak force - Weak theory.
3. Electromagnetic force - Quantum Electromagnetic Dynamics theory.
4. Gravitational force - Unfortunately, there are so many theories which try to explain Gravity by combining Einstein's general theory of relativity with Quantum Mechanics.

Let's see a brief introduction to each of these forces.

1. Strong Force:
This is responsible for the stability of the nucleus of an atom. The strong force acts between nucleons and holding the nucleus together.

2. Weak Force:
This is responsible for the stability of an atom itself. This force acts between neutrons, protons and electrons. A neutron releases an electron and becomes a proton at smaller distances.

3. Electromagnetic Force:
This is responsible for most of the daily activities that we encounter. Starting right from seeing, hearing, feeling and anything that involves chemical bonds and reactions.

4. Gravitational Force:
 As we all know that this is responsible holding us tight to the earth otherwise we would be flying around (funny!) but the interesting fact is that without the correct amount of gravitational force no living being might have formed on earth!

You take any action or incident that occurs in this universe and it can be proven as an outcome of the interactions due to one or more of the above fundamental forces. Let us discuss them in detail in my next posts.

2. Is Light continuous or discrete?

How do we define Light in simple words?

1. Light is an outcome of rays that originated from Sun.
2. It can penetrate through objects which have less opacity.
3. It can bend
4. It can get reflected.
5. It is continuous.

Are we done? I don't think so because Light is the most primary source of life in our universe and so it's characteristics can't be limited to this short basic list. All the above statements are true except that the 5th one is partially true or it's not always the case! So, when we say 'Light can be continuous' it becomes complete.

Why 'can be'? To put this clearly, Light can also be a series of discontinuous packets! Analog had always been the idea before digital was formed in every field. It was also true for Light! For centuries, Light was understood as a continuous ray emitted from Sun. In 1877, Ludwig Boltzmann's suggestion to the black body radiation problem stated that energy states of a physical system can be discrete. Eventually, the 1900 hypothesis of Max Planck about Light energy confirms the discreteness of the energy states of Light.

So, which is true? Is Light a continuous wave or discrete particles? The answer is 'both are true based on how it is observed'. To explain this further, let's see the scientific proof for this claim. It's called 'Double-slit Experiment' where light is emitted from a source and it passes through a double slit filter and it's observed on the other end on a screen. The results came out as one of major inventions in quantum physics! The test cases are as follows,

1. The slits are open -> Light creates a pattern of crossing waves on the screen proving wave like behavior!
2. The slits are open and also an apparatus is kept to observe the wave -> Light creates lines instead of the pattern of crossing waves, proving particle like behavior!

Adding an apparatus into the experiment changes the behavior of the photons! Yes, this is the base for all of the modern age theories like Cosmic/Universal Consciousness, Multiple Universes, etc. For better visual understanding of this test, I would recommend you to look at the below animated video.
http://www.youtube.com/watch?v=DfPeprQ7oGc

I would say that Light can be either wave or particles depends on the 'contributors' (We will come back on this term later!) involved in the outcome or experience. Now, let's see how we calculate the energy if light possess sometimes wave-like and sometimes particle-like behavior. If Light is treated as a wave, then we can calculate the energy from its frequency f (f=c/λ, where λ is wavelength and c is speed of Light) using the following formula. We also know that energy is proportional to the frequency and so,

E = hf, where E is energy and h is the Planck constant.

If the Light is of discrete particles, then how do we determine the frequency without wave-length? because only waves have wave-length! Yes, we can't find wave-length but definitely the frequency. The frequency is determined by the energy released by an energetic photon when it comes down from its higher energy state to the lower energy state by losing a bit of energy.

Hence, f = (E2-E1) / h, where h is the Planck constant.

So, irrespective of whether Light behaves as waves or particles, the energy E is the same and hence you can determine the missing factors using the other formula. To explore more about wave characteristics of Light, you may refer this site http://www.astronomynotes.com/light/s3.htm which I found interesting and informative!

1. Welcome to Quantum World!

Hello friends... Welcome to Quantum World! If you are a Quantum Freak, then you are in the right place!

Here we will discuss all kinds of topics, theories, concepts that are related to Quantum Physics! Let's start with the brief introduction to Quantum Physics or Quantum Mechanics or Quantum Dynamics, whatever you want to call!

Quantum is the finest entity of any object that you can find in this universe. Quanta (in plural) are the discrete entities filled with energy. This is a new microscopic world that lies inside an atom's fundamental particles such as electron, proton or neutron. Quanta can be released as energy packets and can be observed as well. In a atom, if there is an energy exchange or transfer of fermions or photons or bosons, then that atom can be said as quantized. For example we can say if an electron is bound to an atom, it is quantized because an unbound electron is not involved in any energy transfer. Hence it's unbound!

Quanta can be released or observed by protons, neutrons and baryons, etc. One of the important findings in quantum mechanics is that the physical characteristics of an entity varies or can be changed only by discrete amounts of energy rather than a continuously varying or arbitrary values. Doesn't this mean that there might be a common factor or a constant to support this behavior? Yes, that's what called as 'Plank Constant'.

There are varieties of quanta found, named and arranged in a matrix. Also, there are characteristics recorded for each of these quanta. They can be described in terms of the following characteristics.
1. Charge - can be one of these values -1, -1/3, 0, 1, 2/3.
2. Mass - can vary from less than 2.2 eV up to 171.2 GeV (eV is for Electron Volt)
3. Spin - can be one of these values 0, 1/2, 1. (it can be clock wise or anti-clock wise)

I am not much interested in numbers but still this would help you to have an general idea when we talk about quanta. Among these quanta, two of them differ from all others but match with each other in characteristics. Those are photon & gluon. Both of them  have zero Mass, zero Charge but 1 Spin and both of them behave as transmitters or force carriers. Having no Mass, they are can travel at the maximum possible speed! Anyway, what does then differentiate or set them apart?

Their purpose! Yes, photon mediate electromagnetic interaction while gluon mediate the strong interaction. Just like photon & gluon, every quantum has it's purpose and is involved in corresponding activities. There are theories which explain such interactions. Usually, in scientific world, most of the time, theories are formed first and are proven later but in quantum mechanics, it's the other way around. It's really interesting how finding of quanta formed these theories. All such theories are grouped together and named as Quantum Theory! Let's say Q.T in short.

Q.T. categorizes all the events that occur, in this universe, into 4 fundamental interactions and each one is supported by a theory. Now, let's get into the details. The fundamental interactions are Electromagnetic interaction, Weak interaction, Strong interaction and Gravity. Among these, only 3 of them are mathematically proven.Yes, the pending theory is nothing but the famous subject, 'Gravity'.

Mr. Albert Einstein explained Gravity in terms of his spectacular space-time curvature in his General Theory of Relativity in 1915 and he was also one of the worldly famous personalities who criticized the quantum theories. He called it as 'Quantum Spookiness'! As an attempt to define the whole universe from start to end, we need Q.T. to explain Gravity in terms of quanta and in order to complete the theory it has become a necessity for Quantum Physicists to explain Gravity in terms of Quanta.

Ultimately, the objective is to have 'An Unified Theory of Everything' about our universe!