Studying The Weight and Gravitational Behavior of Antimatter

Weighing Antimatter

Physicists at the University of California, Berkeley are studying the difference between matter and antimatter in relation to how it interacts with gravity.

Particles that have the same mass but with the opposite charge and quantum spin are called antimatter. Antimatter was predicted to exist in 1928 through equations by Paul Dirac. The next year, it was first observed by two physicists but considered it an anomaly and was not studied further.

Three years later, in 1932, Carl D. Anderson also observed the same thing in his experiments but instead of treating it as an error, studied it further. Bt using gamma rays, he created an anti-particle; a positively charged electron. Electrons are negatively charged and his discovery proved Dirac was right and antimatter does exist.

Anderson was awarded the Nobel Prize for Physics in 1936 for this discovery.

All particles has its antiparticle counterpart. The antiparticle of the electron is the positron. It carries a positive charge rather than a negative one. The proton's version is the anti-proton and it carries a positive charge. Despite the neutron having a neutral charge, there is an antineutron which is made up of antiquarks (the antiparticle of the quark).

Compact Neutral Particle Accelerator Using Lasers Developed

Highly charged Argon ions (orange) exploding from a nanocluster are reduced to neutrals (blue) in a mm accelerator due to dense excited clusters (green).
Credit: Dr. Rajeev Rajendran, TIFR

Neutral atoms are unaffected by magnetic and electrical fields generated by standard particle accelerators. A new class of accelerators have been developed using lasers to accelerate neutral particles, in this case, Argon ions.

A particle accelerator is a device that accelerate and propel subatomic particles to tremendous speeds. The particles are accelerated to either hit a surface or other particles. Electric fields increase the speed of the particles while magnetic fields control the direction.

There are two kinds of accelerators; linear and circular. Linear accelerators direct a particle from one end to another. They are usually used to hit surfaces of objects with the particles. A cathode ray tube (like the ones in a television screen) can be an example of a linear accelerator. Electrons are sped up and hit the screen to light it up and ultimately form the image.

Circular ones let the particle travel round and round in a loop. They are used to collide two particles, each going in opposite directions. The Large Hadron Collider is an example of a circular particle accelerator.

What Is Antimatter?

Antimatter has been a popular concept in science fiction. But contrary to popular belief, antimatter has been observed and even created as early as 1932 and was theorized to exist years earlier.

What is Antimatter?

Antimatter are particles (antiparticles) that have the same mass as its counterpart but carry the opposite charge and quantum spin. Spin can be compared to how the Earth rotates on its axis while orbiting the Sun.

The antiparticle counter part of the electron is the positron. It carries a positive charge rather than a negative one. The proton's version is the anti-proton and it carries a positive charge.

There is also the antineutron despite the neutron having a neutral charge. This antineutron is made up of antiquarks (the antiparticle of the quark).

A Brief History of Antimatter

In 1929, two scientists in two different experiments observed a particle that exhibited a peculiar behavior. They saw what they believed to be an electron that travelled as if it had a positive charge. Electrons are negatively charged. The two physicists, Dmitri Skobeltsyn and Chung-Yao Chao, disregarded the anomaly and never pursued it afterwards.

Three years later, in 1932, Carl D. Anderson who was studying cosmic rays at the time noticed the same thing in his experiments. Believing this to be an electron but with a positive charge, he successfully created a positron by shooting gamma rays into other materials.

Anderson was awarded the Nobel Prize for Physics in 1936 for this discovery.

This validated Paul Dirac's theory from 1928 on the existence of positrons. At the time, he called them anti-electrons. It was Anderson who named them positrons; short for positive electrons.

The antiproton was discovered in 1955 by physicists Emilio Segrè and Owen Chamberlain while the antineutron by Bruce Cork in 1956.

MIT News: Bending Light To Cloak Objects Lead To Better Electron Transfer For Thermoelectric Devices

A new approach that allows objects to become “invisible” has now been applied to an entirely different area: letting particles “hide” from passing electrons, which could lead to more efficient thermoelectric devices and new kinds of electronics.

Diagram shows the 'probability flux' of electrons, a representation of the paths of electrons as they pass through an 'invisible' nanoparticle. While the paths are bent as they enter the particle, they are subsequently bent back so that they re-emerge from the other side on the same trajectory they started with — just as if the particle wasn't there.
Image courtesy Bolin Liao et al.

The concept — developed by MIT graduate student Bolin Liao, former postdoc Mona Zebarjadi (now an assistant professor at Rutgers University), research scientist Keivan Esfarjani, and mechanical engineering professor Gang Chen — is described in a paper in the journal Physical Review Letters.