Fringe Dream of Virtual Particles

Last night I had a vividly strange science fiction dream. Like with most of my dreams, and dreams in general, I guess, it was hard to recall all the details in the morning, and this one was no exception, but in a nutshell, the scene started with me in some science lab, describing the idea of how to effectively make a tiny hole in the universe. It was pretty simple—I was using four Tesla coils, perfectly positioned in the corners of the large square with edges of about a couple of meters long and with two small, battery-sized metal plates positioned in the center of the square. The experiment was that at the precise moment, Tesla coils fired four filaments of thunder, reaching the center point exactly between two metal plates at the same time, initiating a process that in the end created a tiny breach in the universe that I was describing in the dream as a brane between dimensions and within the void between multiverses. Anyway, in the process, one plate goes from metallic through dark and eventually invisible, while the other started immediately to glow and emit light and other sorts of radiation.

I was explaining in my dream that the breach positioned one plate just outside of our universe while the other stood here. Most of the pairs of virtual particles that were popping between two plates all the time out of vacuum are torn apart by the invisible plate, making them real particles from that point and attracting one toward itself, while the second particle is always attracted by the other plate, creating radiation and the glow in the process. Very similar to the Hawking radiation emitting from the event horizon of the black hole. Even though those two plates were positioned very near to each other, after the Tesla coils did the job by breaching the universe, they stayed in different realms from that point, keeping a relatively close distance between them and finding new equilibrium even when the coils were shut down.

Our plate was then taken out of the square center, wrapped in the bigger case, and used as a battery that never drains. Or, to be precise, not until the invisible plate in the system that is always outside of our universe depletes itself by doing its job of separating the particles, but it was explained in the dream to be an extremely slow process that takes centuries, even if the battery is used to generate lots of power, like empowering entire city blocks.

I know, having a geeky or nerdy dream can be weird for most people, but it's not that we can choose what to dream, can we? It is surely a product of my daydreams, so to speak, and definitely an outcome from my daily interests in astrophysics by watching various documentaries and reading articles online. The novel-like storyline was definitely the consequence of all of my science fiction fascination in both movies and books, which I enjoy from time to time as well. In this very case, the background of the entire story from the last night and today's post is all about the most intriguing feature of the universe. The one that might change everything one day. Virtual particles. They are one of those scientific theories that has extraordinary potential for the future. If we find a way to capture and control them. Hopefully not by poking our universe with bolts of lightning. :-)

But seriously, and sci-fi aside, let's see why virtual particles are one of those quantum properties I think we still wait to understand fully. First of all, they are not really virtual per se; they differ from real particles only by their short existence in time. Aside from that, they can have some or even all properties of the real particles, including mass, but so far it is not really possible to observe virtual particles due to their short lives. However, in the subatomic world, virtual particles are often found in diagrams invented by Richard Feynman that revolutionized theoretical physics by their simplicity to explain what was really happening during the quantum events.

For example, take the Feynman diagram above. It shows how two electrons collide. The internal line is a virtual photon, which is in this case a representation of the excitation of the electromagnetic field caused by electrons and their interaction. We can observe both electrons, their velocities, and paths, but we are helpless to spot the virtual particle. In this very case, whether this virtual photon is really a particle, lasting only a tiny fraction of time during collision, which would give it the title of an actual mediator of the force, just like what its counterpart, the real photon, is, or it is used just as a calculation aid, it is not really certain, but in the end any particle, real or virtual, is only a representation of the excitations of the underlying quantum fields. However, even though they are called "virtual" because of their unobservability, and even though we can't see how they "look" and "act," in one experiment we are definitely able to observe what they do. Experiment proposed by Hendrick Casimir in 1948 and confirmed by Steven Lamoreaux in 1996. The experiment is probably responsible for my dream in the first place. The Casimir effect of the virtual particle-powered machine is just by using two metal plates positioned very near each other. But to understand the Casimir effect, we need to understand one simple thing. Timespace itself. I am not kidding. This is mandatory and a requirement for further reading. Easy. ;-)

Well, I am not pretending that I understand what really happens in the universe, but mainstream science of the current date says, and I am trying to paraphrase it, that all that is around us and within us and at any point in time is just one soup of various fields. Like the Higgs field I talked about once earlier on the blog. Or gravitational field. Or in this post's story and this particular case, electromagnetic field. Any field, by definition, is a region in space (and time?) that is affected by some force. At any point in the field. It also means that a field is a region in space that contains energy. Now, an electromagnetic field is not something that can occupy a certain part of space. It is literally everywhere. It is a fundamental field that is actually in the background of the entire universe and not just in places with matter. Everywhere. Even in the vacuum, where nothing tangible exists. Some places contain more energy than others, with a vacuum being a place with the electromagnetic field in its lowest energy state. Not zero. Now, keep with me; it gets interesting—let's compare this field with actual soup that is always boiling.

If you are looking at the surface of the boiling soup, you will see bubbles and fluid filaments all over the surface, but at some places they are heavier and more powerful, and at other places they are calmer and more peaceful, but always boiling and moving. If we were able to glimpse a closer look and magnify the surface to see it on an even smaller scale, we would see that the entire surface is in a chaotic state of constant wibbling, wabbling, wobbling, blooping, and bubbling*. The same is with electromagnetic fields. The stronger wabbles are what we identify as electromagnetic radiation that propagates forward (and in the case of our soup, outside the pot to the kitchen floor), while the tiny wibbles are just a short-lived emission of photons or failed radiation, if you will.

That tiny failed radiation is possible thanks to quantum mechanics that allows temporary violations of conservation of energy, so one smaller particle can become a pair of heavier particles, and in the case of a photon, it goes from changes of being a wave, a mediator particle with no mass, or a pair of heavier particles—a couple of electrons and positrons (or a pair of quarks and antiquarks with radiation of one gluon). What exactly it is and when it happens is dependent on the ongoing process and energy levels of the system, but in the case of the lowest energy state of vacuum, we know that heavier particles are popping all the time, and due to the uncertainty principle, those virtual particles always appear in pairs. They are borrowing the energy from the vacuum and immediately collide and annihilate themselves, repaying the energy in order not to violate the laws of thermodynamics. These streams of virtual particles "coming out of vacuum and diving back" are well-known quantum features known as quantum fluctuations of the electromagnetic field.

Now, those virtual particles popping out into short existence are coming pretty randomly—and in all possible wavelengths—which brings to "the surface" a vast amount of energy due to their short life, normally invisible to us. If we position two uncharged metal plates very near to each other (less than a micrometer), only those virtual particles whose wavelengths fit a whole number of times into the gap emerge between the plates, while outside, without limitations, all possible wavelengths are accounted for. The result is that energy density between the plates is way less than the energy density of the surrounding space, and immediately a tiny force appears and starts pulling the plates toward each other. This force is named the "Casimir force", and the entire system the "Casimir effect". On first glance, it doesn't look strange—the same effect can be made with two plates in water that, with small waves created by a sonic generator**, are pulling toward each other as well—but keep in mind that the actual Casimir experiment is performed in a vacuum with no single atom of matter between or outside the monitoring system, and the plates are uncharged. So the "only effort" we need to make is to put them very near to each other, and they will start moving. The force is tiny, though; for example, for the one-square-meter plates apart by just one micron, the force is 1.3 mN*** (the weight of 1 kg is about 10N). The force is stronger for bigger plates and with shorter distances in between.

However, one potential propulsion engine, built on the principles of the Casimir effect with even a tiny but constant push like this one, is comparable with ion engines that create thrust by accelerating ions with electricity. For example, in "Dawn", the spacecraft that recently arrived in the asteroid belt was propelled by three xenon-ion thrusters, each with a force of only 90 mN. Eventually, after more than 8 years of travel, it accumulated acceleration over the mission to more than 10 km/s (41,260 km/h), which is pretty fast for a tiny push (even though it used other means of acceleration like gravity boost while transiting Mars). It carried almost 400 kg of xenon for the ion thrust engine, but the potential Casimir engine of the future would need none of such a payload. Its propellant would be the very vacuum of spacetime and its pairs of virtual particles.

Of course, the real application would come with separating virtual particles like in my dream or what black holes seem to do**** on a daily basis. If there is a way to make virtual particles real, the millinewtons will instantly lose that 'milli' prefix and be equipped with one more powerful (perhaps 'kilo' or 'mega'), and that will be something extraordinary. Something that in science fiction has a cool acronym. ZPE. Zero Point Energy. Surely, we must find other means to deal with this than by creating tiny black holes to do the job for us, but thankfully, the quantum world is always full of surprises, and perhaps one day we will build a machine that is capable of taking the energy out of a vacuum safely and is small in size, relatively speaking. Perhaps another quantum effect will be helpful for this job, the one that uses interactions between hydrogen electrons and virtual particles called the Lamb shift. But that is a story for another time.

Image refs:
https://www.nasa.gov/mission_pages/dawn/main/index.html
http://www.livescience.com/50119-superconductors-physicists-gravity-particles.html
http://pics-about-space.com/black-hole-hawking-radiation-diagram?p=3

Refs:
http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html
* https://www.youtube.com/watch?v=Kn5PMa5xRq4
https://en.wikipedia.org/wiki/Zero-energy_universe
https://briankoberlein.com/2015/03/06/nothing-but-net/
** https://www.youtube.com/watch?v=PS8Lbq2VYIk
https://www.scientificamerican.com/article/are-virtual-particles-rea/
http://physics.stackexchange.com/questions/147096/are-virtual-particles-tool
***http://math.ucr.edu/home/baez/physics/Quantum/casimir.html
https://en.wikipedia.org/wiki/Virtual_particle
****https://en.wikipedia.org/wiki/Hawking_radiation

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 nuclei in their centers and clouds of electrons orbiting around. If we take hydrogen (H), for example, the smallest atom with just one proton in the nucleus orbited by just one electron, and if we scale the proton to be the size of a basketball, the orbit of the electron in diameter would be something about 15 km. Both the nucleus and electrons are electromagnetically charged, keeping everything in stable equilibrium, and also inside the nucleus, two more fundamental forces—strong and weak 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 the 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 represent force carriers in 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. Its 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 a short story about neutrinos, the most elusive particles in the universe we can play with. They are products of radioactive beta decay in heavy nuclei where a proton or neutron decays into other subatomic particles, i.e., if a proton decays in a process known 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 the entire star immediately. There are many different beta decay types, and I mentioned just one; others help as classified neutrinos. Just like with other fundamental particles that come in three flavors—the charged leptons (electron, muon, tau), the up-type quarks (up, charm, top), and the down-type quarks (down, strange, bottom), bottom)—neutrinos can also be different in mass and property. The one created in the previous example with the creation of positrons is called an electron neutrino, but if anti-tau or anti-muons are created in the process, neutrinos that emerge on the other side of the decay will be tau or muon neutrinos, respectively. A neutrino, no matter which type it is, belongs to leptons as well. This means it is not affected by strong nuclear force at all, and it only interacts with weak nuclear force, and because it is a 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 heavy than the entire mass of hydrogen). Furthermore, it is not electromagnetically charged and therefore not affected by 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 ghosts travel through walls and doors just like Patrick Swayze did in the movie "Ghost" a couple of decades ago.

Well, kidding aside, and thankfully for these neutrino features, they are really one ghostly particle 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 the 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 Aires, Argentina, and you want to send a 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 the speed of light all the way through the planet. But before we glimpse into the obvious possibility of whether or not it is possible to use neutrinos in some sort of communication, 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 a 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 everlasting expansion of the universe is the correct theory, that is. Therefore, the choice between usage of paper and plastic bags has nothing green in the 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 the 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 a 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 the 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 the entire container full of bananas, you are safe. Radiation from a 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 detect, there is still, after all, a way to do it.

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

Poor detection of neutrinos due to their weak interaction with matter is only the start of bad news regarding the potential communication device we are trying to build. More difficulties follow. For example, artificial production of desirable types of neutrinos is either with nuclear reactions or in particle accelerators, which are 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 beams and paths is still not perfect, and last but not least, there is 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 the first, a neutrino beam at Fermilab was sent with a short, encoded message through 240 meters of rock toward the MINERvA neutrino detector, and the word "neutrino", which was binary encoded within the beam sequence, was successfully decoded. The second and most challenging one was performed in Japan. Within the "T2K experiment", both neutrino and anti-neutrino beams are created in the J-PARC laboratory and sent toward the 295 km distant Super-Kamiokande. Both are successfully detected and, in return, opened the first working neutrino beamline over large distances.

So in both theory and practice, neutrino communication might be possible, and current experiments confirm it with working proof of concepts 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 and built with bulky vacuum tubes. With the invention of semiconductors and transistors, everything changed, and the result is pretty much in front of you, either on your desk, lap, or palm. Perhaps a 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 the search for extraterrestrials would gain a 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 the Milky Way alien internet. Universe's WiFi. So to speak.

Speaking about E.T. and science fiction in general, this neutrino story reminded me about two more things I love to share in conclusion for this post. The first one is John Cramer, an experimental and theoretical physicist and professor at the 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 with one beam that was sent into a circuitous detour miles away through optical cable, it would be detectable on the second beam that ended in a detector much earlier in a different location. Detection of this form of laser beam fiddling would be an indication that quantum entanglement is a phenomenon not only between spatially 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 the recent tradition of MPJ and its "books" thread, what partially hinted at this post is the great novel "Signal", written by Patrick Lee, with the entire plot triggered by the neutrino-based portable device capable of catching radio waves from the future by harvesting neutrinos that move against the direction of time. The device is 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, the sci-fi, 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