First Spectrum Of Anti-Hydrogen Atom Observed By CERN

The first spectrum of anti-hydrogen has just been obtained by CERN’s ALPHA team and studies are on-going to find differences between its spectrum and that of ordinary hydrogen. Hanging in the balance are answers to crucial questions on the nature of anti-matter and why matter supersedes anti-matter in the visible Universe.

Trapping anti-hydrogen (Courtesy: ALPHA, CERN)

Mysteries of the Universe

The fundamental mystery is this: why is there more matter than anti-matter in the Universe, even though all equations of physics predict that the two are exactly the same. If we lived in a Universe made up of anti-matter particles, we wouldn’t know the difference. Or would we? A hypothesis, involving two discrete symmetries of nature – Charge (you reverse the charge on a particle), denoted by C and Parity (you take the mirror image of a particle), denoted by P – taken together and called CP symmetry, could be broken giving rise to more matter particles than anti-matter particles. However, this still doesn’t violate another symmetry called CPT symmetry, in which Charge and Parity are joined by Time reversal symmetry.

The object of study is this: There is an anti-proton about which a positron (anti-electron) orbits. As is well known, such a system will have energy levels like those of the hydrogen atom, composed of a proton orbited by an electron. The question is how similar are the two systems. How much is CP symmetry violated? What about CPT symmetry?

How is the study done?

The study, published in Nature, describes the very first attempts at studying resonances in this bound system. They attempted to flip the magnetic moment of the atoms using a microwave laser radiation. This is basically flipping the poles of a tiny atomic magnet. Now, the trapping of the anti-atoms, perfected by the same team at ALPHA, CERN, depends on the magnetic moment. If that is flipped, the anti-atoms leave the trap, escape and get annihilated. This happens at a particular energy. If the laser is tuned to this energy, most of the laser energy will be absorbed. This signifies a resonance.

This is just the first among, surely, several tests that will be performed on anti-hydrogen, now that it can be produced and trapped easily. 

Discovered : A Belt of Antimatter Surrounding Earth

Anti-particles are not as exotic as many think and here’s further proof. The PAMELA spacecraft has detected a ring of anti-protons around the Earth, confined in that region by Earth’s magnetic field. These may be confined in that small region for hours before annihilating with matter and producing radiation.

This ground-breaking discovery was reported by PAMELA spacecraft recently. PAMELA, acronym for Payload for Anti-Matter Exploration and Light-nuclei Astrophysics, is a satellite that was launched to further cosmic ray astrophysics on 15th June 2006. It was specifically built to focus on the occurrence and interactions of positrons (anti-electrons) and anti-protons in the space around Earth.

The PAMELA spacecraft

Some theoretical considerations

Anti-matter is a theoretical necessity, which can be deduced from the symmetry of theories in physics. It was first predicted by the great Paul Dirac in 1931, following the interpretation of results given by his own equation (unsurprisingly called, the Dirac Equation) to describe the electron. His wild prediction of the positron was soon experimentally verified the following year by Carl Anderson, who detected it in his lab. (Remember, that the neutron was not yet known. It was also discovered in 1932 late in the year.) The scientific impact and importance can be gauged from the fact that Anderson went onto win the Nobel Prize in 1936, just four years after the discovery. Now, we know that every particle must have its anti-particle.

When particles and anti-particles collide, they annihilate producing (two) gamma rays. As always in physics, the reverse can also happen. Given certain conditions, a gamma ray can give rise to two particles a particle and an anti-particle obeying Einstein’s famous equation E=mc2. (Due to other strong constraints imposed by symmetries of physics, two particles or two anti-particles cannot be produced.)

The Van Allen Radiation Belts (Courtesy: Addison Wesley Longman)

In our atmosphere too, the same phenomenon happens. High energy cosmic rays bombard the Earth’s atmosphere producing matter and anti-matter particles. These can be kept separated out from each other due to the presence of Earth’s magnetic field, since moving particles of opposite charge behave very differently in magnetic fields. Furthermore, magnetic fields can confine these particles in pockets. They can remain stable for hours on average, before encountering matter particles and annihilating. Theoreticians have long predicted the presence of anti-protons in the Van Allen Belts (belts of charged particles surrounding Earth), in addition to positrons, because of the high energy of the bombarding cosmic rays. Anti-protons are much more massive than anti-electrons and thus require more energy to be produced. Most radiation can produce electron-positron pairs, but do not have enough energy to produce proton-antiproton pairs.

Enter PAMELA

PAMELA collected data over 850 days from the South Atlantic anomaly (a region over the South Atlantic ocean, where the Van Allen belts come closest to the Earth’s surface) and confirmed this theoretical prediction.

As this news spreads, there will be inevitable attempts at grabbing eyeballs by projecting this as the new cheap, easily available energy source. You can lend an ear to that at your own risk.