Antimatter sounds like the stuff of science fiction, but it’s very real. It is, however, elusive.
Antimatter particles are subatomic particles with properties opposite those of normal matter particles. So a positron (positively charged) is the antiparticle equivalent of the electron (negatively charged). When a particle and its antiparticle meet, they annihilate (are destroyed), releasing a lot of energy.
Antimatter particles are created in ultra high-speed collisions. There was a lot of it after the Big Bang. But today antimatter is rare.1
How rare is antimatter? Lawrence Krauss puts it this way:
I like to say that while antimatter may seem strange, it is strange in the sense that Belgians are strange. They are not really strange; it is just that one rarely meets them.2
In the sentences before making that statement, Krauss tells us something interesting about antimatter:
Because antiparticles otherwise have the same properties as particles, a world made of antimatter would behave the same way as a world of matter, with antilovers sitting in anticars making love under an anti-Moon. It is merely an accident of our circumstances, due, we think, to rather more profound factors…that we live in a universe that is made up of matter and not antimatter or one with equal amounts of both.3
That’s pretty awesome! You might be wondering then, how can we know that this universe is made of matter and not antimatter? If they behave the same way, how can we tell the difference? Antimatter has an opposite charge and quantum spin4; those are the subtle differences that let us know that we live in a universe comprised of matter. Well, there’s that and the possibility that it falls up.5
Every particle in existence has an antiparticle equivalent, which is almost identical except it carries the opposite electric charge. Matter is composed of normal particles and antimatter is composed of antiparticles—for example, while a proton and an electron form an ordinary hydrogen atom, an antiproton and a positron form an antihydrogen atom. Antimatter is created all the time in high-energy collisions, like when cosmic rays impact Earth’s atmosphere, but it immediately disappears because when matter and antimatter collide, they annihilate in a flash of pure energy. This makes it difficult to study experimentally, and neither can we find any evidence of a significant concentration of antimatter in the wider universe. The universe we know is dominated by ordinary matter—it makes up every person and planet and star—and yet if matter and antimatter were created equally at the birth of the universe, where has all the antimatter gone? This asymmetry is a perplexing question in physics, and several theories have been proposed to explain it. Perhaps nature favours matter reactions over antimatter ones; or perhaps matter and antimatter particles decay differently; or perhaps there are far flung regions composed primarily of antimatter, but they’re just beyond our visible universe. Researchers are currently trying to determine if such regions exist by studying colliding superclusters for high-energy signatures of annihilation, and by studying decay patterns in quarks.
The universe is a weird place. Here’s a look at some of the strangest things in the cosmos.
Like Superman’s alter-ego, Bizzaro, the particles making up normal matter also have opposite versions of themselves. An electron has a negative charge, for example, but its antimatter equivalent, the positron, is positive. Matter and antimatter annihilate each other when they collide and their mass is converted into pure energy by Einstein’s equation E=mc2. Some futuristic spacecraft designs incorporate anti-matter engines.
2. Mini-Black Holes
If a radical new “braneworld” theory of gravity is correct, then scattered throughout our solar system are thousands of tiny black holes, each about the size of an atomic nucleus. Unlike their larger brethren, these mini-black holes are primordial leftovers from the Big Bang and affect space-time differently because of their close association with a fifth dimension.
3. Cosmic Microwave Background
Also known as the CMB, this radiation is a primordial leftover from the Big Bang that birthed the universe. It was first detected during the 1960s as a radio noise that seemed to emanate from everywhere in space. The CMB is regarded as one of the best pieces of evidence for the theoretical Big Bang. Recent precise measurements by the WMAP project place the CMB temperature at -455 degrees Fahrenheit (-270 Celsius).
4. Dark Matter
Scientists think it makes up the bulk of matter in the universe, but it can neither be seen nor detected directly using current technologies. Candidates range from light-weight neutrinos to invisible black holes. Some scientists question whether dark matter is even real, and suggest that the mysteries it was conjured to solve could be explained by a better understanding of gravity.
Until about the early 1990s, the only known planets in the universe were the familiar ones in our solar system. Astronomers have since identified more than 500 extrasolar planets (as of November 2010). They range from gargantuan gas worlds whose masses are just shy of being stars to small, rocky ones orbiting dim, red dwarfs. Searches for a second Earth, however, are still ongoing. Astronomers generally believe that better technology is likely to eventually reveal worlds similar to our own.
6. Gravity Waves
Gravity waves are distortions in the fabric of space-time predicted by Albert Einstein’s theory of general relativity. The gravitational waves travel at the speed of light, but they are so weak that scientists expect to detect only those created during colossal cosmic events, such as black hole mergers like the one shown above. LIGO and LISA are two detectors designed to spot the elusive waves.
7. Galactic Cannibalism
Like life on Earth, galaxies can “eat” each other and evolve over time. The Milky Way’s neighbor, Andromeda, is currently dining on one of its satellites. More than a dozen star clusters are scattered throughout Andromeda, the cosmic remains of past meals. The image above is from a simulation of Andromeda and our galaxy colliding, an event that will take place in about 3 billion years.
Neutrinos are electrically neutral, virtually mass-less elementary particles that can pass through miles of lead unhindered. Some are passing through your body as you read this. These “phantom” particles are produced in the inner fires of burning, healthy stars as well as in the supernova explosions of dying stars. Detectors are being embedded underground, beneath the sea, or into a large chunk of ice as part of IceCube, a neutrino-detecting project.
These bright beacons shine to us from the edges of the visible universe and are reminders to scientists of our universe’s chaotic infancy. Quasars release more energy than hundreds of galaxies combined. The general consensus is that they aremonstrous black holes in the hearts of distant galaxies. This image is of quasar 3C 273, photographed in 1979.
10. Vacuum Energy
Quantum physics tells us that contrary to appearances, empty space is a bubbling brew of “virtual” subatomic particles that are constantly being created and destroyed. The fleeting particles endow every cubic centimeter of space with a certain energy that, according to general relativity, produces an anti-gravitational force that pushes space apart. Nobody knows what’s really causing the accelerated expansion of the universe, however.
A Black Hole Doesn’t Die – It Does Something A Lot Weirder
Black holes are basically “game over, man,” for anything that gets too close to them, but they aren’t invincible. In fact, they’re always in the process of self-destructing. We’ll look at how they fizzle out, and see if we can help them do it faster.
The Event Horizon
Realistically speaking, you are dead as soon as you get anywhere near a black hole. You’ll be snapped like a rubber band by the differences in the gravitational pull on your top and bottom half, or you’ll be fried by radiation (more on that later). No one in the foreseeable future (even if we try to foresee multiple millennia into the future) will get close to a black hole. Pass the event horizon, however, and you don’t even have an unforeseeable future. Once material gets beyond the event horizon, it’s being pulled into the black hole with such force that it doesn’t escape. Not even light gets out. Once something has gone beyond the event horizon, it no longer really “counts” as part of the universe anymore.
“This is right at the frontiers of what is known, and is my bet for the next of the greatest unsolved problems in theoretical physics to fall. With any luck, we’ll finally be able to explain why there’s more matter than antimatter in our Universe very soon.”
UCLA physicists discover apparent departure from the laws of thermodynamics
According to the basic laws of thermodynamics, if you leave a warm apple pie in a winter window eventually the pie would cool down to the same temperature as the surrounding air.
For chemists and physicists, cooling samples of charged particles, also called ions, makes them easier to control and study. So they use a similar approach – called buffer gas cooling – to lower the temperature of ions by trapping them and then immersing them in clouds of cold atoms. Collisions with the atoms cool the originally hot ions by transferring energy from the ions to the atoms – much the same way a warm pie is cooled next to the cold window, said Eric Hudson, associate professor of physics at UCLA.
But new research by Hudson and his team, published in the journal Nature Communications, demonstrates that ions never truly cool to the temperature of the surrounding gas. Also, very surprisingly, they discovered that under certain conditions, two final temperatures exist, and the temperature that the ions choose depends on their starting temperature.
“This apparent departure from the familiar laws of thermodynamics is akin to our warm apple pie either cooling as expected or spontaneously bursting into flames, depending on the pie’s exact temperature when it is placed in the window,” said Hudson, the senior author of the study.
The UCLA researchers have, for the first time, placed fundamental limits on the use of buffer gas cooling in “ion traps.” To perform their experiment, the researchers prepared a microscopic sample of laser cooled ions of the chemical element barium and immersed them in clouds of roughly 3 million laser-cooled calcium atoms. The researchers make molecules extremely cold under highly controlled conditions to reveal the quantum mechanical properties that are normally hidden.
The ions were trapped in an apparatus that levitates charged particles by using electric fields that oscillate millions of times per second, confining the ions to a region smaller than the width of a human hair. Both the atomic and ionic samples were brought to ultra-cold temperatures –just one-thousandth of a degree above absolute zero – via a technique in which the momentum of light in a laser is used to slow particle motion.
After allowing collisions between the atoms and ions to occur and the system to reach its final temperature, the physicists removed the calcium atoms and measured the temperature of the barium ions. The results, which show the existence of multiple final temperatures based on ion number and initial temperature, suggest that subtle non-equilibrium physics is at play.
The researchers trace these strange features to the heating and cooling rates which exist in the system – the peculiar temperature dependence of the interaction among multiple ions in an ion trap. Both simulation and theory support their experimental findings, and paint the buffer-gas cooling process as a fundamentally nuanced, non-equilibrium process rather than the straightforward equilibrium process it was originally understood to be.
Lead author Steven Schowalter, a graduate student researcher in Hudson’s laboratory and now a staff scientist at NASA’s Jet Propulsion Laboratory, said, “Our results demonstrate that you can’t just throw any buffer gas into your device – no matter how cold it is – and expect it to work as an effective coolant.”
Buffer gas cooling is crucial in fields ranging from forensics to the production of antimatter. Hudson’s research group has discovered important nuances that revise the current understanding of the cooling process, explain the difficulties encountered in previous cooling experiments and show a new path forward for creating ultra-cold ion samples. With this framework the researchers showed how troublesome effects can be overcome and even exploited to study the mechanisms at play in molecular motors and single-atom heat engines in a precisely controlled manner.
“Of course, this work does not violate the laws of thermodynamics, but it does demonstrate there are still some interesting, potentially useful things to learn about buffer gas cooling,” said John Gillaspy, a physics division program director at the National Science Foundation, which funds the research. “This is the sort of fundamental research that can really guide a wide range of more applied research efforts, helping other scientists and engineers to avoid going down dead-end paths and illuminating more fruitful directions they might take instead.”
Quirky Quarks: ‘Charming’ Particle Mixes with Bizarre Cousin
An experiment that offers a peek inside the behavior of subatomic particles called quarks could help answer questions about why the universe is made of matter, and might even be evidence of new, previously unseen particles.
At the Fermi National Accelerator Laboratory (Fermilab) in Illinois, an international team of scientists published the first observation of a charm quark (quarks come in several “flavors”) decaying into its antiparticle, a phenomenon called “mixing,” first predicted in 1974.
While the Large Hadron Collider is looking for the Higgs boson, we’re on the verge of two huge antimatter-related breakthroughs. One could finally solve the universe’s oldest mystery, while the other could reveal strange new particles that are perfect for quantum computers.
The first result comes from CDF, one of the two long-running experiments at the now deactivated Tevatron accelerator at Fermilab. CDF physicists had been studying the decay of subatomic particles called D-mesons - particles made up of massive charm quarks that form in the decay of even heavier bottom quarks, which in turn decay into kaons and pions.
The other big antimatter-related result hasn’t come from a big particle accelerator but instead a nanowire in a Dutch laboratory. According to a team led by Leo Kouwenhoven of the Delft University of Technology, they have spotted what could be the first experimental evidence of Majorana particles, first proposed by Ettore Majorana over 70 years ago. These theoretical particles are a unique exception to the standard relationship of matter and antimatter, in that they don’t annihilate each other when they come into contact. Majorana realized in 1937 that a fermion with no electric charge would have a completely identical antiparticle, meaning pairs of these particles would be able to exist together without destroying one another. They’re remained strictly theoretical until now, when Kouwenhoven reported the first tentative evidence of their existence.