Antimatter
I read an article one day that someone asked in an scientific conference that “What happens if an irresistible force meets an immovable Object?”, well that’s a pretty big question isn’t it, just like why did Issac Newton is satisfied with 3 laws of motion or why Beethoven is one symphony isn’t?
The idea of something that would first consume its container has awesome implications : why stop there? having destroyed its container it would go to the surroundings and also destroy everything in the way into oblivion, including eventually us. This would be a truly a irrestible force, and also a nightmare..!!
Antimatter is a wierd topsy shadow of the matter, where left becomes right and positive becomes negative. Antimatter’s main ability to destroy matter in a flash of light is the source of facination. Antimatter is truly an Anti-Matter.
It is eighty eight years since the possible existence of such wierd stuff was proposed by Paul Dirac and discovery of positron as the first example of such thing was seen. and yet we are still here, happily, because antimatter is extremly rare almost nonexistence in fact. It seems that the destruction of antimatter was one of the first acts after the Big Bang. Today as the Universe we know is the left-over remnants of the great Annihilation between antimatter and matter, still after fourteen billion years ‘Microwave Background’ radiation fills the universe even today. After big bang there might be some antimatter that has escaped and is still lurking out in universe, what if a volume no bigger than a car comes in contact with earth? If that were to happen, then antimatter will destroy matter indeed, but at the expence of destroying itself, it’s like a cancer that in killing its host has self-destructed. The result may be an Explosive flash of radiation, which fly away from the site at speed of light. That is why no antimatter survives, atleast around here.
In large scale the antimatter is being produced in sun’s core, matter-of-fact the sunshine is due to the positron that is being created. In its center where the temperature exceeds 10 million degrees, the Hydrogen atoms, protons and swarm of electrons are moving independently at random. As the protons occasionally bumps into one another and through a fusion process helium is formed, but it has less mass than the protons the were ised to make it and energy loss is E=MC². So what does the positron has to do with this? well, a He nucleus has 2 protons and two neutrons. Under suitable conditions a neutron would change into a proton and positron.
The positron finds itself in the middle of sun where swarm of electrons are moving at random, and is instantly destroyed, turned into gamma rays. These rays travel towards surface of sun, by that time they reach surface they have lost lot of energy and will becomes visible rays. So daylight is the result of antimatter being produced in the heart of the sun. A gamma ray would take hundreds of years before it reaches surface, yeah, That’s a long time..!!
In 1928 when the story of antimatter began, the knowledge as understood on Atoms by Paul Dirac and others principle players in antimatter saga, consisted of dense protons and lightweight electrons in a cosmic waltz*. And laws of electro-magnetism still holds good with antimatter because we just swapped the charges in the subatomic particle. Such swapping would result in different thing called antimatter, this prediction that such mirror image of matter should exist, leads to Nobel Prize for Dirac in 1933.
The first glimpse of the antiworld came not from experiment, but from the beautiful equation that Dirac had derived. To those who learned to read the hieroglyphs of mathematics can compare his equations to Beethoven..!!
(Notice the Equation)
Memorial in Westminister Abbey.
Image source – http://www.westminister-abbey.com
A Cosmic Discovery
In 1923 first photo of cosmic rays showed signs of positron, but no one realized the fact. Then after Paul dirac prediction, he came to know about this new particle. In 1923 Dmitri Skobelzyn used gamma rays to investigate white lines in Cloud Chamber. He didn’t know what it was but after comparing his images of electron going in wrong way to paul’s work and then he realise that’s a positron. But it was Anderson who identify it and Patrick Blackett and Giuseppe Occhialini to explain it.
Although Dirac’s equation is for electrons but it also explains antiprotons, antineutrons and fremions. But you may notice that neutron has no charge how is antineutrino possible? Actually neutron is made up of quarks which has fractional charges and spins, so antineutron likewise has the same mas as neutron and zero charge. After positron hunt for antiproton begins in 1950. So they built a machine called BeVatron – BeV, which is a typical proton accelerator with billion electron volts energy capacity after many tests and collision of protons they finally discovered antiproton, they discovered antineutron in the same way by colliding in accelerator.
But the story doesn’t end there, these anti particles are made up of smaller anti particles called antiquarks. With the help of bubble chamber invented in 1952 strange particles are discovered from cosmic rays and collision of proton and neutrons such as Lambda(Λ), Omega(Ω), Sigma(Σ), Xi(χ), Delta(Δ) etcetra. The anti part of these strange particles have been discovered, it reminds me a statement by Rutherford that the Science consists of physics, all else being stamp collecting, was turning into extreme irony.
The standard model of Particle Physics.
After the discoveries of the particles we have to study them for properties using large machines such as CERN’s large hadron collider and Fermi lab in US.
Well after reading all these things you may wonder what is the use of this antimatter?
Collision of matter and antimatter as a power source.
As you read earlier when matter meets anti matter it annihilates, as the velocity is high their kinetic energy is also high resulting in explosion, so this could be used as power source or a potential bomb.But antimatter is also used in Medicines, PET Scanner – Positron Emission Tomography. It is used in scanning body, this can paradoxically be a life saver.
You may wonder if matter meets antimatter it will destroy itself but it is being used in PET scanners, how it is being stored?. Storing these destructive materials is difficult job and also costly, in CERN they have underground tunnel, 27 km long inside that they have vaccum and magnetic lining that will keep the charged particles moving with the speed relatively close to speed of light, it all started with the Lawrence’s ‘Cyclotron’. The first application to this obvious idea was in 1959 an american team built ‘storage rings’, using magnetic field to steer the particles around them. Largest one is being operated at CERN called LEP- Large Electron Positron collider. The fact that machines like these work at all shows the remarkable symmetry between matter and antimatter. Beams of electrons and positrons travelled around LEP over and over again and arrived at their rendezvous point on time. This is a result of the precise counterbalanced electric charges and their identical masses causeing them to follow their pre-assigned paths in opposite directions and the collision takes place, the chances of collision is one in 2,50,000, so its a bummer. Similarly we can compare the times for a proton or an antiproton to complete a circle in the magnetic field, from which we know that the proton and antiproton are alike to better that one part in a billion.
There is one method called Antimatter Trap, The trap is about 15cm long tube, when an antiparticle enters, the voltage is raised so that it would stay there and cooled to negative temperatures. In 1986 Gabrielse’s team managed to trap antiproton and hold it for four days. After the trap they studied its behaviour in the electric and magnetic fields, this shows that they are just a mirror of each other. In another line of research with trapped particles question of whether there is antigravity. These things fall under higher physics and mathematics so i’m not going to talk about them.
Anti-Hydrogen Trap – https://home.cern/about/experiments/atrap
Further Reading – https://goo.gl/HqNb6o
Today, 88 years after the discovery of the positron and 61 years after that of antiproton, everything confirms the suspicion that antiparticle are nature’s mirror of particles, however, as to wheather antimatter would interact with normal gravity, we still don’t know.
Thanks for reading.
Srivatsa Subramanya 
Very Nicely documented and explained!!
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