The past couple of weeks have been busy as usual. Work is always busy, of course, but the weekends have been packed as well. Last weekend was the Memorial Day holiday so I took the train down to St. Louis to visit some family. Yep, that’s right, the train. Its no secret that the inter-city train system in the US pales in comparison to its European counterpart, but fortunately Amtrak is still around serving major cities.
The week before, my father didn’t tell me what it was about, but he let on that he was super excited to ask me about something when he saw me. So my last Quantum Diaries post I mentioned was inspired by a 6th grader. Well, I guess this one is inspired by a 60 year old, because the question my dad could not wait to ask me, that had him practically giddy with excitement, was, “What is antimatter?” Guess what. My parents saw Angels and Demons last week!
Fortunately, I was well prepared to answer my father’s question, as I had just attended Marcela Carena’s public lecture last Thursday at Fermilab (here’s the full video stream of the event). As others have mentioned in several places, public lectures were organized around the country to coincide with the release of the film in order to answer just this question being asked by my dad and others like him.
The event at Fermilab was a great success with a packed Ramsey Auditorium and a fun-filled and informative lecture from Marcela. She began by welcoming the audience to the biggest antimatter factory in the world, Fermilab! which pretty much answered the first question on many people’s minds, “Is antimatter even real?”
The term ‘antimatter’ refers to otherwise normal particles, but whose various quantum properties are all reversed from their normal matter counterparts. The most obvious and most important of these is electric charge. So an antielectron is just like the regular electron except it has positive charge (hence, we call it the positron). An antiquark is just like a regular quark except its charge is opposite. And a regular ol’ proton is made of three quarks which add up to positive one charge (up+up+down = 2/3Q + 2/3Q – 1/3Q = +1Q) and an antiproton is made up of the three corresonding antiquarks (antiup+antiup+antidown = -2/3Q – 2/3Q + 1/3Q = -1Q). Its sorta just that simple. In principle, you can take this logic further. Just like a proton and electron bound together makes hydrogen, an antiproton and positron bound would make antihydrogen. 6 antiprotons, 6 antineutrons, and 6 positrons would make anticarbon, and so on. I suppose enough antiwood and antiglue could be assembled into an antichair for an antiperson to sit on. (incidentally, antihydrogen is as far as we have gotten in the science laboratory and they managed to make just 9 antihydrogen atoms each lasting a fraction of a second).
What the book and movie exploit in the story is the rather thrilling fact that when a bit of matter meets its antimatter counterpart, !PUFF!, they annihilate into a tiny burst of energy. Here at Fermilab we are constantly creating antiprotons to push into our particle accelerators and send on a collision course with a bunch of regular protons moving in the opposite direction. When they collide, !PUFF!, a tiny burst of energy (Okay, so you can add energy to the annihilation effect if the particles are moving when they collide. Most of the energy here is actually from the protons and antiprotons tremendous velocities, 99.9999 percent of the speed of light in a vacuum or about the speed of light – 700 mph, which is why we work so hard to get them going so fast). Einstein’s famous equation tells us that this energy E can convert into mass since E = mc^2. This mass is the particles we see and study in our detectors.
So what is the difference between these matter/antimatter collisions at Fermilab and the ones in the movie which are capable of releasing enough energy to destroy multiple square miles of buildings in Rome? Quantity. In the movie they use 1/4 of a gram of antimatter as a weapon. It turns out this modest enough sounding number is an incredible amount of antimatter! Perhaps the most fun fact in Marcela’s talk last week: in the entire history of Fermilab running the antiproton source for several decades, 24 hours a day, 7 days a week, we have produced only about 2 billionths of one gram of antiprotons! Instead of a huge explosion you might be able to power a light bulb for a few moments.
Another important difference between the movie and real life antimatter is containment and storage. Of the 2 billionths of a gram created over the decades at the Lab, none of it is still around. It all harmlessly collided with regular matter and !PUFF! is gone – most of it in the center of our particle detectors. But even when it didn’t, to an antiproton, the world just so happens to be made of a huge amount of very dangerous regular matter!
Which brings me to one of the really exciting open questions in particle physics research today. Where in the world did all the antimatter go? Physicists believe strongly that matter and antimatter would have been produced in symmetric, equal amounts in the earliest moments of the Universe. All of our theories and experimental results point to this conclusion. Yet here we are, safely living in a matter dominated Universe with no threat of being annihilated by stray antimatter. It could have been different. We could all be made of positively charged electrons circling around negatively charged protons. If it were that way we wouldn’t know the difference. It seems even more likely that all of the intense energy in the early moments after the Big Bang would have created matter and antimatter in equal numbers which immediately would have annihilated against itself back into intense energy – but then we wouldn’t be here today to blog about it, so we know that’s not how it went down.
Instead, something in the way the Universe works at the most basic level prefers negative electrons and positive protons (matter). Some asymmetry must exist between the opposing forms such that matter ultimately won out and was able to form the Universe we inhabit. Experiments have actually provided clues, but revealed nothing strong enough to have let matter win out totally as it seems to have done. But where is always the last place we look? Why, among the elusive neutrinos, of course.
It turns out this is the Holy Grail of modern neutrino physics research. It is possible that neutrinos violate the matter/antimatter symmetry in such a way as to explain the Universe that we live in. And the next generation of huge experiments which will send intense beams of neutrinos 100’s of miles through the Earth hope to take a peak at exactly this issue: can neutrinos explain why only one variety of matter has come to dominate our Universe and allowed us the opportunity to be here to ask the question in the first place?