In a study published a few days ago in Nature, a team of physicists at CERN report that they have successfully used a laser to induce a change of energy state for an atom of antimatter. Antimatter is notoriously difficult to produce, contain, and manipulate, so the experiment is monumental as it represents a great advance in scientists’ ability to experimentally manipulate antimatter, one of the more mysterious and rarer substances in our universe.
In particular, scientists successfully induced what is known as a Lyman-alpha transition in an atom of anti-hydrogen. The Lyman-alpha transition is one of the fundamental energy-involving processes in normal hydrogen atoms, so the ability to successfully manipulate anti-hydrogen like its normal hydrogen counterpart “opens up a new era in antimatter science” according to Takamasa Momose, a particle physicist at University of British Columbia and lead researcher for the team that developed the laser. “This approach is a gateway to cooling down antihydrogen, which will greatly improve the precision of our measurements and allow us test how antimatter and gravity interact, which is still a mystery.”
It is thought that advances in such experimental technologies will help investigate fundamental symmetries and anti-symmetries between matter and antimatter, possibly answering longstanding cosmological questions regarding the presence of unequal amounts of matter and anti-matter in the observable universe.
Matter And Antimatter
We are all familiar with normal matter, consisting of three types of particles; positively charged protons, neutral charge neutrons, and negatively charged electrons. Antimatter is then defined as matter composed of antiparticles—particles of the same mass but opposite electric charge or quantum number of the ordinary matter particles. For example, an antiproton is a particle the same mass as a regular proton, but with a negative electrical charge.
Similarly, an antielectron (often called “positron”) has the same mass as an electron, but a positive electrical charge. In other words, one can consider antimatter as a sort of mirror-image of ordinary matter; the size and shape are the same but other properties have been flipped. In fact, physicists theorize that antiparticles should be able to combine in exactly the same way as normal particles, leading to a whole catalog of “anti” substances and chemical compounds like anti-oxygen, anti-water, and anti-methane, etc.
When matter and antimatter make contact, both are completely annihilated and 100% of the mass is converted into energy. For contrast, the most efficient possible nuclear fusion bombs would only convert about 7-10% of the original reactants’ mass into energy. Using Einstein’s handy equation for mass-energy equivalence E=mc2, we can determine that just a single gram of matter and a single gram of antimatter interacting would produce .002 kg×(2.98×108)2 = ~1.8×1014 joules of energy—roughly the equivalent of 43 thousand tons of TNT. This high energy potential has made antimatter of interest to physicists and speculative high-energy antimatter tech has been a staple of sci-fi authors for decades.
Given that cosmological equations predict that equal amounts matter and antimatter should have been created at the big bang, it is strange that the observable universe is composed almost entirely of normal matter. Antimatter is sometimes created during high energy events, such as solar flares, or high-energy particle collisions, but those antiparticles are immediately annihilated once they come into contact with ordinary matter. The asymmetry of matter and antimatter in the observable universe is one of the great unsolved problems in physics.
Lasers And Antimatter
The Lyman transition is measured as a series of ultraviolet spectral lines, emitted when an electron of hydrogen transitions from a low orbital to a high orbital. The Lyman transition is one of the most fundamental processes in nature and forms an integral part of modern quantum theory. By using a series of precisely timed laser bursts, the team was able to induce a similar transition in the positron of an atom of anti-hydrogen.
By using powerful magnetic fields, the team was able to trap a few hundred atoms of anti-hydrogen and suspend them in a vacuum. The laser used is noteworthy as it represents great advancements of the technology; having a solid state source and being capable of generating nanosecond long pulses. As the laser went through its cycles, the team recorded the emitted photons, the characteristic emission for when an excited particle changes energy state. What they found was that the recorded spectral line measurements coincided with the measurements for an atom of normal hydrogen to a precision of 8 significant figures, one of the most accurate measurements of the properties of antimatter to date. The researchers report that they successfully induced a Lyman transition in approximately 966 atoms of anti-hydrogen over a 2-hour period.
In particular, the team is hopeful that their new techniques will provide ways to test for CPT symmetry, the fundamental theory that charge reversal, parity reversal, and time reversal are symmetric; that is, a “mirror image” of our universe would operate exactly the same. CPT symmetry seems to be implied by both quantum mechanics and relativity theory, but some exceptions may exist. In particular, the prevalence of matter over antimatter in the early universe could have resulted from some process that violates CPT symmetry. What has been needed is a way to manipulate antimatter in a precise enough way to test for symmetries and any possible asymmetries between matter and antimatter.
The next step for the team is to refine their method to allow for the production of quantities of cooled anti-hydrogen sufficient for precise mass spectroscopy and gravity measurement. The advancement of such experimental methods will go lengths to exploring the fundamental symmetries and asymmetries of matter and antimatter. Said Momose, “This gets us just a bit closer to answering some of these big questions in physics.”