Chasing Ghosts of the Universe

You probably heard that matter is pretty much an empty space. It's true. Everything is made of tiny particles with nucleus in their centers and cloud of electrons orbiting around. If we take Hydrogen (H) for example - the smallest atom with just one proton in nucleus orbiting by just one electron and if we scale the proton to be the basketball size, the orbit of the electron in diameter would be something about 15km. Both, nucleus and electrons are electromagnetically charged, keeping everything in stable equilibrium and also inside nucleus two more fundamental forces - strong and week nuclear interactions are keeping all the matter and energy in line. However, the smallest atom in the Universe is not the smallest, standalone system we know of. According to standard model, all atoms and complex molecules found in nature or artificially produced are made of fundamental particles. Something we cannot cut into smaller pieces. Electron is one of them. But there are more. So far, as far as we know, if we count all of those basic particles inside protons or neutrons and those that represents force carriers with addition to the "god" particle that makes all the mass possible, there are exactly 17 of them. But one of them deserves its own story to tell. It's nickname is "the ghost particle" and it is literally capable of passing through any mountain like it is made of cheese.


You probably guessed, this will be short story about neutrinos, the most elusive particles in the universe we can play with. They are product of radioactive beta decay in heavy nucleus where proton or neutron decays into other sub-atomic particles, i.e. if proton decays in a process knows as 'beta plus decay', it transforms into a neutron, a positron, and a neutrino. In the moment of its creation, even if it happens in the center of the Sun it escapes entire star immediately. There are many different beta decay types and I mentioned just one - others helps as classified neutrinos. Just like with other fundamental particles that comes in three flavors - with charged leptons (electron, muon, tau), the up-type quarks (up, charm, top), and the down-type quarks (down, strange, bottom), neutrinos also can be different in mass and property. The one created in previous example with creation of positron is called electron neutrino, but if anti-tau or anti-muon are created in the process, neutrinos that emerge on the other side of the decay will be tau or muon-neutrinos respectively. Neutrino, no matter which type it is, belongs to leptons as well. This means it is not affected with strong nuclear force at all and it only interacts with weak nuclear force and because of being particle with mass it also follows gravity as well. To simply illustrate its ghostly manner I will just note that its tiny mass is about 4 millionths of the electron mass (and electron mass is 1837 times less heavier than entire mass of Hydrogen). Furthermore it is not electromagnetically charged and therefore not affected with this fundamental force as well. In other words if you like to watch horror movies or believe in ghosts, the obvious conclusion is that they are made of neutrinos. That would perfectly explain how ghost travels through walls and doors just like Patrick Swayze did in the movie "Ghost" couple of decades ago.

Well, kidding aside and thankfully to these neutrino's features, they are really one ghostly particles that is extremely hard to either control or detect. However, this phantom behavior of theirs, immediately triggers some extraordinary ideas. If we could embed messages into neutrinos and control path of their beam we might literally send them through anything. If some neutrino based portable device is possible to be built, and you are located, for example in Buenos Aries, Argentina and you want to send message to Beijing, China, you would have to point your neutrino device slightly toward the center of the Earth* and neutrinos would reach the receiver with speed of light all the way through the planet. But before we glimpse into obvious possibility of whether or not is possible to use neutrinos in some sort of communications let's check some more facts about them.


Basically, neutrinos, strictly speaking belong to the radiation realm. They are indeed carriers of radioactive energy. The same as alpha and beta particles, gamma rays, muon radiations and tons of other types of particles floating around the universe as a result of different types of particle decays or some other processes in the universe. Actually, we are living in a soup of radioactive energy on daily basis from various sources as pretty much everything in the universe is decaying or decomposing toward the ultimate fate of the universe which will in the end be just one giant soup of basic ingredients, if the ever-lasting expansion of the universe is correct theory, that is. Therefore, the choice between usage of paper and plastic bags has nothing green in potential answer. Either way, both bags will eventually decompose. Just give them enough time. Humans are also radioactive - we also emit radioactive particles thanks to radioactive food we are consuming. Technically speaking, all food is radioactive because all organic food contains Carbon-14 or radiocarbon as it is nicknamed. Many other radioactive elements can be found in other products and the most notable one is Potassium-40. This one is actually radioactive isotope that undergoes all three types of beta decay. In one of them it emits neutrinos as well. So, if you like eating bananas, rest assured that you are one of neutrino producers as well as bananas are very rich in Potassium. Believe it or not, large container shipments full of bananas at ports or airports regularly trigger radiation alarms. Well, if you have not eaten entire container full of bananas, you are safe. Radiation form couple of bananas is harmless, way below the edge and potassium is actually very good for you and if you emit a neutrino here and there nobody will notice. Believe me. Well, on second thought, don't believe me. Even though neutrinos are very hard to be detected, still, after all, there is a way to do it.

Neutrinos are tiny particles but few of them on rarely occasions still collide with atom nucleus of the material they are passing through. And by few I mean the literal meaning of the word. The Sun is producing extremely large number of neutrinos - 60 billion per square centimeter are passing through Earth and .. us .. each second. That is maybe around 100 trillions of neutrinos passing average human. To detect that few, several extremely large detectors are created and one of them is shown in above image - Super-Kamiokande under mount Ikeno in Japan. It utilizes Cherenkov radiation, optical equivalent to a sonic boom, to detect collision. If neutrino collides with the electron or nuclei of water - neutrino only changes direction but particle that was struck recoils in sudden motion and faster than the speed of light in water (which is slower than maximum speed of light in vacuum). This creates a flash of light which is amplified with photo detectors (those round bulbs all over the water pool). This flashes provide information on the direction and type of the neutrino. SK is located in the old zinc mine 1km below the surface in order to exclude all other radiation to reach the water and ensure that only neutrinos are detected. To illustrate small number of neutrinos detected with this approach states the fact that total number of collisions detected from supernova SN1987A in Kamiokande was only 19 out of trillions of neutrinos emitted by the supernova. Small amount of neutrinos are regularly detected from the Sun and their number is way smaller than predicted by the number of estimated nuclear reactions in the star, which provides a proof that neutrinos are able to change their flavor during their travel and as it seems especially during their travel through solid matter. Different number of solar neutrinos are detected during night as they passes long way through the solid matter of entire planet Earth while on daylight they need to penetrate only those 1000 meters to reach the mine chamber.


Poorly detection of neutrinos due to their week interaction with matter is only the start of bad news regarding potential communication device we are trying to build. More difficulties follow. For example artificial production of desirable type of neutrinos is either with nuclear reaction or in particle accelerators which is either too large or too dangerous to build. Encoded information in beamed neutrinos can also be lost with their oscillation between flavors during travel. Creating desirable beam and path is still not perfect and last but not least there are too much noise on the way as billions and billions of other neutrinos are also there either created in stars, supernovas or those created in the very beginning during the big bang. Even so, scientists with powerful proton accelerators developed a procedure to develop stable beams of neutrinos or anti-neutrinos** which are then directed toward near and/or distant detectors. Two experiments emerged with potential scientific value - in first one neutrino beam at Fermilab was sent with short, encoded message through 240 meters of rock toward MINERvA neutrino detector and the word "neutrino" which was binary encoded within beam sequence was successfully decoded. Second and the most challenging one was performed in Japan. Within the "T2K experiment", both neutrino and anti-neutrino beams are created in J-PARC laboratory and sent toward 295km distant Super-Kamiokande. Both are successfully detected and in return opened first working neutrino beamline on large distances.

So in both, theory and practice, neutrino communication might be possible and current experiments confirm it with working proof of concept made in large neutrino observatories and accelerators. Actually, it resembles the state of computers as they were some half a century ago when they were large and limited in mathematical computation built with bulky vacuum tubes. With invention of semi-conductors and transistors everything changed and result is pretty much in front of you either on your desc, lap or palm. Perhaps similar breakthrough is waiting to be invented so we could equip our smartphones of the future with neutrino messaging when we would be finally able to send texts to Mars from our living room without enormous satellite dishes. Who knows, maybe search for extraterrestrials would gain completely new angle and perhaps many of those neutrinos that are passing through our bodies right now could be complex messages from E.T. and neutrino communication in the future might be our ticket into Milky Way alien internet. Universe's WiFi. So to speak.


Speaking about E.T. and science fiction in general, this neutrino story remanded me about two more things I love to share in conclusion for this post. First one is John Cramer, experimental and theoretical physicist and professor at Department of Physics, University of Washington, Seattle. Some seven or eight years ago, Cramer intended to perform an experiment with two quantum entangled laser beams pointed in different directions. He was trying to prove that by fiddling one beam that was sent into circuitous detour miles away through optical cable would be detectable on the second beam that was ended in detector much earlier in different location. Detection of this form of laser beam fiddling would be indication that quantum entanglement is a phenomenon not only between spacial distant particles but also distant in time. When asked what he expects in the outcome, John Cramer, being a science fiction author as well, said: "If this experiment we're doing works, then I will follow up and push it as hard as possible. And if it doesn't work, I will write a science-fiction novel where it does work. It's a win-win situation."

The second thing and in recent tradition of MPJ and its "books" thread, what hinted me partially for this post is great novel "Signal", written by Patrick Lee, with entire plot triggered by the neutrino based portable device, capable to catch radio waves from the future by harvesting neutrinos that move against the direction of time. The device able to hook into radio stations 10 hours ahead. Just try to imagine all the implications and applications of this kind of fictitious device. If you can't, I am encouraging you to grab Patrick's novel and read it. I literally swallowed it and during reading eagerly waited for another chapter. I really can't emphasize what is better, the thriller plot, scifi or the intense writing. I will say no more.

Image refs:
http://motherboard.vice.com/read/why-neutrino-detectors-look-so-cool
http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/
http://www.patrickleefiction.com/
http://www.nuclear-power.net/nuclear-power/fundamental-particles/antineutrino/
http://particleadventure.org/neutrinos.html

In text refs:
* http://www.antipodesmap.com/
** http://www.symmetrymagazine.org/article/november-2012/how-to-make-a-neutrino-beam

Refs:
http://physics.info/standard/practice.shtml
http://chemistry.about.com/od/foodcookingchemistry/tp/Radioactive-Foods.htm
http://discovermagazine.com/2007/jun/life-is-rad
http://www2.lbl.gov/abc/wallchart/chapters/03/2.html
https://profmattstrassler.com/articles-and-posts/particle-physics-basics/neutrinos/neutrino-types/
http://timeblimp.com/?page_id=1033
http://cosmiclog.nbcnews.com/_news/2007/07/17/4350992-backward-research-goes-forward
http://faculty.washington.edu/jcramer/cramer.html


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