I promise this will be a really simple introduction in which we will just have to dig into a bit of 10th class Physics and Chemistry. The motivation to do so: to understand the greatest discovery made in our life time; and be able to share with our friends and children the significance of this great discovery.
Last Wednesday (27 Jun 2012), experimental scientists at the Large Hadron Collidor at CERN somewhere on Swiss – Italian border confirmed the identification of a particle called Higgs-Boson; or informally, The God Particle.
…Errr…. in fact no one, even the physicists like it to be referred as ‘The God Particle’..except for the media… just the real name.. Higgs-Boson.. more later on this..
Terminology Update: Large Hadron Collidor. suffices to say the collidor is just a machine (http://www.dailymail.co.uk/sciencetech/article-1368107/Is-Large-Hadron-Collider-world-s-time-machine.html) to smash protons at near the speed of light to see what is inside them or what gets created. When particles collide in such extreme situation, it creates a situation very similar to what may have existed when the universe was born from nothing (The Big Bang).
The LHC has a small loop and a larger 27 km loop through which protons can be accelerated and smashed together at 99.9999999% the speed of light…
Terminology Update: CERN. Some French for the organization that manages nuclear research in Europe.
Terminology Update: The Big Bang. One of the greatest discovery of the previous century. American astronomer Edwin Hubble found, to his shock, that every galaxy in the universe is moving away from all other galaxies. Thus, the universe is stretching much like dots on a balloon when it blown with air. This means that at some point, it must have been a point. Subsequently, this theory was proven through discovery of Cosmic Microwave Background Radiation(CMBR) – which is out of scope of this article.
Now let’s get down to the central topic of this article: The God Particle (ooops!!).
Believe me, the pre-requisites to understanding this topic are very simple. For completeness, I am skimming over them below…
- Matter is made of molecules; almost everything we see/experience.
- Molecules are made of atoms. Atoms combine in different ways electrically to give different properties to molecules.
- Atoms are made of a small dense center called nucleus.
- Electrons ‘orbit’ around nucleus (not entirely accurate; electrons exist as probablistic wave function; not important here).
- Nucleus is made of positively charged protons and neutral charged neutrons. Positive charge of proton is balanced by negative charge of electron.
- Atoms connect to other atoms to form molecules. This is due to electrical forces, e.g. Oxygen shares one electron with one Hydrogen atom each and achieves a stabler existence i.e. H2O, while maintaining overall zero charge.
- See simplified diagram of atom below…
If the nucleus exists as a dot in the middle of a football field, electrons will be found all over the football field. So the atom is largely emp
ty! Also, neutrons a about 1% heavier that protons, and electrons are about 1/1000 size of protons.
Sounds simple so far. Now let us come down to Higgs Boson, why it is needed, how it was predicted and why we can’t do without it.
The Need for Higgs-Boson
This is not easy to explain; but can be well explained with an >>analogy<<.
Somewhere in 1870s, J J Thomson was investigating the structure of atom by bombarding them with negatively charged cathode rays (http://www.aip.org/history/electron/jj1897.htm). He postulated the nucleus which he said was positively charged and heavy, and that most of atom was empty (reason, most of the cathode rays went right through to a photograph plate behind and much less than 1% had massive deflection). Subsequently, Rutherford predicted that there ought to be negatively charged particles too.. since the atom has no net charge. The operative word here is >>prediction<<. The model of atom, put forth by Rutherford, that it has a small dense positively charged nucleus with negatively charged electrons hanging around the nucleus cannot be complete until electrons are discovered.
To emphasize the importance, science was confined to deduction; i.e. why does the sun rise in the east….. earth rotates… ear
th spherical… blah blah blah. So science gives explanation to phenomenon around us. But……….. here about a 100 years ago, science took the great leap forward and became predictive. So Rutherford said that xyz is the model of the atom, and we need to find a negatively charged super small particle hanging around the nucleus. Now JUST FIND IT. 20 years later, it was found and the Rutherford model of atom as shown by the image above was accepted by the scientific community as the truth.
Analogy Number 2. Does the diagram of atom and its explanation above evoke some basic doubts? Really basic, if we look at the nucleus? Stop….. Think…… Two oddities emerge…
- How do the protons live with eash other in such a densely packed nucleus. Aren’t they supposed to repel each other? The electrical repulsion being stronger the closer they get..
- How do protons stick with neutrons? there is zero electrical affinity since neutron is neutrally charged.
This leads to more >>predictions<<. There must be a new force which attacts proton to proton, works at only very short distances, and is much more powerful than electrical forces over that short distance. This
is the strong nuclear force. If we separate two protons by bombarding them with neutrons, massive amount of energy is released which is known as nuclear fission… that is the strong nuclear force energy being released.. and is used to generate energy in nuclear plants.. or do a Hiroshima.
The prediction was that the strong nuclear force must have a corresponding particle which carries the force from proton to proton and proton to neutron. Thus a new particle was predicted called gluon. STOP.. isn’t this paragraph confusing? So I will take a few lines to explain this paragraph…..
What has particles got to do with force. It seems force is ethereal, like light. It has no particles, and is unlike sand or sawdust or chalk particles. Not entirely true. A magnet lying on ground with no attention will do nothing, but a magnetic field exists. Enter a metallic item, and the magnetic field will be excited, there will an attraction, and this will be manifested by exchange of particles called photons. When force is exerted between two particles, e.g. an electron and a proton (electrical force in this case), the force is manifested by particle exchange. In case of electrical force, the particle is photon. Suffices to say that ALL forces have associated particle which act as the force carriers. Like I said above, a simple example is of light which is simply electrical force with a frequency which can be observed by human eye. Light can travel in space i.e. through nothing. Thus it must be particles travelling, unlike waves in water which move due to rippling of water where water acts acts as a medium to transmit force (remember the Tsunami? or a vacation at Goa..).
Thus, gluons became force carriers for strong nuclear force, much like photons for electrical force including light.
After two decades, indeed, the gluon was disc
overed and the theory of atom was validated again. Experimental Scientists keep trying more and more ways of proving a theory postulated by theoritical physicists. Even now they conduct new experiments to validate special theory of relativity more than a 100 years old. They obsessive compulsive maniacs.. never at rest.
The Standard Model
As particle physicists started discovering/predicting more and more particles, they developed a standard model. This model organized particles in a logical table. This model has been tested by hundreds of experiments and stood the test of time. See image below for a look at the standard model…
All our understanding and predictions are based on this model. Let us have a brief look at only those things that we need for this article…
- if you look at the columns at the top, there are two groups… Fermions and Bosons.
- Fermions are particles which make everyday stuff like protons, electrons, neutrons etc. They are further divided into quarks and leptons. Quarks make up neutrons and protons, and leptons make up electrons and a host of other particles.
- No further need to go into more details. All one should know is that nature is heavily economical, and each particle exists for a reason. If even one is not found, the standard model will collapse and we need a new model.
- Bosons are force carrying particles… e.g. photon for electrical/light waves, and gluons for strong nuclear force. Ignore W and Z boson.
- Interesting fact: Bosons are named after Indian Mathematician S N Bose. In those times (just 80 years ago), India produced a great number of mathematicians who had international repute in research. Fermions were named after Italian Mathetician Enrico Fermi.
- All particles are found. Most were predicted and then found.
- Higgs-Boson was the only one not found so far. It is a Boson i.e. represents force, and was predicted by Prof Higgs; thus the name.
- All higher level particles e.g. protons, neutrons (and dozens of others, not important here) are composed of these basic particles.
Prof Higgs welcomed by Director CERN for the announcement
Focus on Higgs-Boson now
So why is the Higgs-Boson needed. Why was it predicted? So that particle physicists could make a living out of it?
In the standard model above, the Fermions have a mass and related inertia. If your car breaks down, and unfortunately you have to push it, it starts slowly, and then picks up speed. So there is a resistance to movement. If your office bus breaks down, you dont even bother to push. Too heavy. Resistance is much higher. Ever wondered why? ……………….
An ordinary day to day question, but not easy to answer. One answer could be that friction has to be overcome. The more the weight, the more the friction. Friction itself is a result of electrical force. So let us take a frictionless environment to cut out the confusing factors. If you have to push a 10 ton space shuttle in space, it will need more effort as compared to pushing a small 100 kg weather satellite. The physics.. force = mass * accelaration. To achieve same acceleration for two bodies, one 100 kg in weight and another 10000, you need 100 units of force and 10000 units of force repective… even in frictionless space. Why this resistence to motion? So there is something which acts on Fermions (particles that make the matter around us) which slows its movement. If you throw a brick from top storey of your office building, it moves towards the ground due to gravity. But why doesn’t it move at the speed of light towards ground? Why does it start slowly and then pick up speed? Why the resistance? What is resisting the movement? Newtons first law: every body tends to stay in state of rest or uniform recti linear motion unless unbalanced external force is applied. But every body resists the movement of rest or linear motion.
Enter the Higgs-Boson. Higgs field permeates the entire universe. When it interacts with Fermions, it slows them down restricting their movement. If Higgs field was not a property of our universe, all mass would be moving at each other at the speed of light and would end up forming one big clump with massive thermonuclear fusion in the center. Fortunately, due to Higgs field, the movement of particles is slowed down.
Another try by giving an >>analogy<<. Consider a large room with a couple of hundred ordinary folks and photographers milling around and chatting randomly. Then a Bollywood star makes an appearance. A number of people would stick around restricting forward movement and trying to get the best angles. Here the ordinary folks represent the Higgs Boson. In absence of these people, the star could have moved at max possible speed (speed of light; for our universe). If the star is Johnny Depp, he will get slowed down more. If the star is less weightier (less famous, more ordinary, less mass) like Kim Kardashian (more ‘mass’ as we know it, actually ! ), then he can move comparatively more easily. Thus bodies of higher mass are more difficult to move e.g. a bus compared to a car.
Higgs-Boson (which I am also referring to as Higgs field now due to wave particle duality and convenience of expression) does not interact with bosons like photon. Thus, photons can move at max possible speed.
Thus, as per standard model, it cannot be validated completely unless such a particle is found which lends inertial resistance to fermions based on their mass. It has to exist to maintain the universe in its present state where things are not flying at each other at 300,000 km/sec due to gravitational force. If it doesn’t exist, then the standard model is wrong. Thus, it was predicted… very much like electron or gluon was predicted.. and must be found.
Finally it is found at a level of certainty of 5 SIGMA or 99.999% (5 nines). This is equal to you getting a heads consecutively 21 times when you toss a coin. As of now this is considered the highest level of certainty.
So how do we find find the Higgs-Boson with the Collider
basically, accelerate two groups of protons; one clockwise, and second anti clockwise. After enough rotations, switch the controlling electrical field to make them collide. If energy levels are high enough, traces of existend of Higgs-Boson will be noted in the readings. See this cartoon (http://www.youtube.com/watch?feature=player_embedded&v=EVwEZXhEWbo).
This poor guy below is stuck with a bunch of protons(who have been suitably fooled into thinking they are on a picnic) in the collidor
So now how do we define Mass.. now that Higgs-Boson is Here?
Surprise. All the 12 Fermions plus the 5 Bosons are considered point particles. They have zero volume; i.e. zero length, zero width and zero height. That is why they cannot be divided further and are thus considered fundamental. If some sort of volume was recordable, then it lends to the idea that they could be further divided. So they are not really some sort of golf ball like things. Just points.
How do they make up higher level particles. As an example, two quarks of +2/3 charge and one quark of -1/3 charge combine to make a proton with net
+1 charge. This can be proven by bombarding protons with positrons (positively charged electron) and observing the pattern as it traverses inbetween the three quarks of the proton. To clarify, three quarks dont combine and become a golf ball sort of proton, but align with each other with large space inbetween, and are bound by strong nuclear force. No more forey into such details is needed, because next would be how these quarks exchange gluons with other quarks of other protons and neutrons to bind together etc.
Now the proton gets its volume by the space occupied by three quarks, which are points with vast empty region between them. So how dows matter get volume and heaviness?
- Volume: answered. Particles bind with each other and have vast space inbetween them. This gives volume to protons and neutrons. Next, at molecular level, atoms bind with other atoms and have vast space between them which gives volume to molecule, and so on.
- Heaviness: See cartoon “you are fat” above. This is how Higgs-Boson is used to explain mass. The interaction of particles with Higgs field gives it mass. The more a particle interacts with Higgs field, the more is it’s mass. Thus mass is simply a degree of measure of interaction between particle and higgs field. If a particle has a property of zero interaction with Higgs field, it will zip at the speed of light and will be considered to have zero mass e.g. photons.
Birth of Higgs-Boson
When the universe was born, it was in complete state of symmetry. All forces had same power and all particles were massless and zipping at speed of light. Withing a trillionth of second, the Higgs field switched on which started interacting with mass of fermions because of which assymetry was created as a result of which galaxies etc were formed.
Some clunky places…
- I have been mentioning gravity, and also other forces like electric and strong nuclear forces… and that there are photon bosons for electric forces and gluon boson, but by a similar correlation shouldn’t there be a boson for gravity? Well, a graviton is predicted. But scientists have not been able to integrate gravity with standard model. So as of now, standard model is independent of gravity and does not explain how it fits in with the other forces.
- 5% of universe is observable e.g. stars etc that we see in the night. 25% is dark matter, it does not reflect light.. everything passes right thought it, since it consists of all neutral particles. If you punch it, your hand will go right through. There is an image of a galaxy collinding with a mass of dark matter, and the galaxy went right through. what particles is it made of? and the dark matter is 5 times heavier than normal matter! but just like cotton. Zero electrical forces. The balance 70%… unknown universe… we dont know what it is made of and >>where it is<< !!!.
- Anti matter: out of scope again. When the universe was born, matter and anti matter was created in equal quantities. In normal course of things, they should have anhillated each other in a short time and our universe should have been full of photons and nothing more. However, a small twist was added which skewed things slightly in favor of matter, and after about 99% or so of matter was anhillated by anti matter, less than a percent survived which makes our universe (with billions of galaxies, each galaxy with billions of stars and their puny planets in dozens). The architect of this twist is a ghostly particle called neutrino. See the standard model above. It is almost massless and almost travels at speed of light. If you look at the sun and stop its rays with your palm, in a second a billion neutrinos would have passed through your palm. This story is another interesting one and out of scope.
Human beings have the remarkable power to think like God. The discovery of Higgs-Boson marks the beginning of the last phase in our quest to know His plan.
“First gulp from the goblet makes you an atheist, but at the bottom, God is waiting”. – Werner Heisenberg
Higgs Boson explained by a cartoon:- http://vimeo.com/41038445
An adventure in the world of particles:- http://www.particleadventure.org/eternal-questions.html