The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
We can create matter from energy in the lab. Particle accelerators do this all the time. When we do, half of what is created is matter and the other half antimatter. There is a symmetry in physics that requires matter and antimatter to appear in equal amounts. But when we look around the universe, what we see is matter. So how did the big bang create all the matter we see without creating an equal amount of antimatter? The answer could be neutrinos.
Neutrino detection by the Kamioka Observatory. Credit: Kamioka Observatory/ICRR/The University of Tokyo
Although neutrinos are mysterious particles, they are remarkably common. Billions of neutrinos pass through your body every second. But neutrinos rarely interact with regular matter, so detecting them is a big engineering challenge. Even when we do detect them, the results don’t always make sense. For example, we’ve recently detected neutrinos that have so much energy we have no idea how they are created.
The NUmI (Neutrinos from the Main Injector) horn at Fermilab, which fires protons that degrade into neutrinos. (Image: Caltech)
The Standard Model of Particle Physics is one of science’s most impressive feats. It’s a rigorous, precise effort to understand and describe three of the four fundamental forces of the Universe: the electromagnetic force, the strong nuclear force, and the weak nuclear force. Gravity is absent because so far, fitting it into the Standard Model has been extremely challenging.
But there are some holes in the Standard Model, and one of them involves the mass of the neutrino.
One of the Daya Bay detectors.
Roy Kaltschmidt, Lawrence Berkeley National Laboratory
In 1960, famed theoretical physicist Freeman Dyson made a radical proposal. In a paper titled “Search for Artificial Stellar Sources of Infrared Radiation” he suggested that advanced extra-terrestrial intelligences (ETIs) could be found by looking for signs of artificial structures so large, they encompassed entire star systems (aka. megastructures). Since then, many scientists have come up with their own ideas for possible megastructures.
Like Dyson’s proposed Sphere, these ideas were suggested as a way of giving scientists engaged in the Search for Extra-Terrestrial Intelligence (SETI) something to look for. Adding to this fascinating field, Dr. Albert Jackson of the Houston-based technology company Triton Systems recently released a study where he proposed how an advanced ETI could use rely on a neutron star or black hole to focus neutrino beams to create a beacon.
Since the 1960s, scientists have theorized that the Universe is filled with a mysterious, invisible mass. Known as “dark matter“, this mass is estimated to make up roughly 85% of the matter in the Universe and a quarter of its energy density. While this mass has been indirectly observed and studied, all attempts at determining its true nature have so far failed.
To address this, multiple experiments are being carried out that rely on immensely sophisticated instruments. One of these, called XENON, recently observed a process that had previously avoided multiple attempts at detection. These results could help scientists to improve their understanding of neutrinos, which some scientists believe is what dark matter is made up of.
This image shows a visual representation of one of the highest-energy neutrino detections superimposed on a view of the IceCube Lab at the South Pole. Credit: IceCube Collaboration
At the Amundsen–Scott South Pole Station in Antarctica lies the IceCube Neutrino Observatory – a facility dedicated to the study of elementary particles known as neutrino. This array consists of 5,160 spherical optical sensors – Digital Optical Modules (DOMs) – buried within a cubic kilometer of clear ice. At present, this observatory is the largest neutrino detector in the world and has spent the past seven years studying how these particles behave and interact.
The most recent study released by the IceCube collaboration, with the assistance of physicists from Pennsylvania State University, has measured the Earth’s ability to block neutrinos for the first time. Consistent with the Standard Model of Particle Physics, they determined that while trillions of neutrinos pass through Earth (and us) on a regular basis, some are occasionally stopped by it.
The IceCube Neutrino Observatory at the South Pole. Credit: Emanuel Jacobi/NSF
Back in 2013, the first detections of high-energy neutrinos were made by IceCube collaboration. These neutrinos – which were believed to be astrophysical in origin – were in the peta-electron volt range, making them the highest energy neutrinos discovered to date. IceCube searches for signs of these interactions by looking for Cherenkov radiation, which is produced after fast-moving charged particles are slowed down by interacting with normal matter.
By detecting neutrinos that interact with the clear ice, the IceCube instruments were able to estimate the energy and direction of travel of the neutrinos. Despite these detections, however, the mystery remained as to whether or not any kind of matter could stop a neutrino as it journeyed through space. In accordance with the Standard Model of Particle Physics, this is something that should happen on occasion.
After observing interactions at IceCube for a year, the science team found that the neutrinos that had to travel the farthest through Earth were less likely to reach the detector. As Doug Cowen, a professor of physics and astronomy/astrophysics at Penn State, explained in a Penn State press release:
“This achievement is important because it shows, for the first time, that very-high-energy neutrinos can be absorbed by something – in this case, the Earth. We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything.”
The Icetop Tank, the neutrino detectors at the heart of the IceCube Neutrino Observatory. Credit: Dan Hubert
The existence of neutrinos was first proposed in 1930 by theoretical physicist Wolfgang Pauli, who postulated their existence as a way of explaining beta decay in terms of the conservation of energy law. They are so-named because they are electrically neutral, and only interact with matter very weakly – i.e. through the weak subatomic force and gravity. Because of this, neutrinos pass through normal matter on a regular basis.
Whereas neutrinos are produced regularly by stars and nuclear reactors here on Earth, the first neutrinos were formed during the Big Bang. The study of their interaction with normal matter can therefore tell us much about how the Universe evolved over the course of billions of years. Many scientists anticipate that the study of neutrinos will indicate the existence of new physics, ones which go beyond the Standard Model.
Because of this, the science team was somewhat surprised (and perhaps disappointed) with their results. As Francis Halzen – the principal investigator for the IceCube Neutrino Observatory and a professor of physics at the University of Wisconsin-Madison – explained:
“Understanding how neutrinos interact is key to the operation of IceCube. We were of course hoping for some new physics to appear, but we unfortunately find that the Standard Model, as usual, withstands the test.
Looking down one of IceCube’s detector bore holes. Credit: IceCube Collaboration/NSF
For the most part, the neutrinos selected for this study were more than one million times more energetic than those that are produced by our Sun or nuclear power plants. The analysis also included some that were astrophysical in nature – i.e. produced beyond Earth’s atmosphere – and may have been accelerated towards Earth by supermassive black holes (SMBHs).
Darren Grant, a professor of physics at the University of Alberta, is also the spokesperson for the IceCube Collaboration. As he indicated, this latest interaction study opens doors for future neutrino research. “Neutrinos have quite a well-earned reputation of surprising us with their behavior,” he said. “It is incredibly exciting to see this first measurement and the potential it holds for future precision tests.”
This study not only provided the first measurement of the Earth’s absorption of neutrinos, it also offers opportunities for geophysical researchers who are hoping to use neutrinos to explore Earth’s interior. Given that Earth is capable of stopping some of the billions of high-energy particles that routinely pass through it, scientists could develop a method for studying the Earth’s inner and outer core, placing more accurate constraints on their sizes and densities.
It also shows that the IceCube Observatory is capable of reaching beyond its original purpose, which was particle physics research and the study of neutrinos. As this latest study clearly shows, it is capable of contributing to planetary science research and nuclear physics as well. Physicists also hope to use the full 86-string IceCube array to conduct a multi-year analysis, examining even higher ranges of neutrino energies.
This event display shows “Bert,” one of two neutrino events discovered at IceCube whose energies exceeded one petaelectronvolt (PeV). Credit: Berkeley Labs.
As James Whitmore – the program director in the National Science Foundation’s (NSF) physics division (which provides support for IceCube) – indicated, this could allow them to truly search for physics that go beyond the Standard Model.
“IceCube was built to both explore the frontiers of physics and, in doing so, possibly challenge existing perceptions of the nature of universe. This new finding and others yet to come are in that spirit of scientific discovery.”
Ever since the discovery of the Higgs boson in 2012, physicists have been secure in the knowledge that the long journey to confirm the Standard Model was now complete. Since then, they have set their sets farther, hoping to find new physics that could resolve some of the deeper mysteries of the Universe – i.e. supersymmetry, a Theory of Everything (ToE), etc.
This, as well as studying how physics work at the highest energy levels (similar to those that existed during the Big Bang) is the current preoccupation of physicists. If they are successful, we might just come to understand how this massive thing known as the Universe works.
The Spallation Neutron Source, located at the Oak Ridge National Laboratory. Credit: neutrons.ornl.gov
Neutrinos are one of the fundamental particles that make up the Universe. Compared to other types of particles, they have very little mass, no charge, and only interact with others via the weak nuclear force and gravity. As such, finding evidence of their interactions is extremely difficult, requiring massive instruments located deep underground to shield them from any interference.
However, using the Spallation Neutron Source (SNS), a research facility located at the Oak Ridge National Laboratory (ORNL) – an international team of researchers recently made a historic discovery about neutrinos using an entirely different method. As part of the COHERENT experiment, these results confirm a prediction made 43 years ago and offers new possibilities for neutrino research.
The Standard Model of particle physics has been the predominant means of explaining what the basic building blocks of matter are and how they interact for decades. First proposed in the 1970s, the model claims that for every particle created, there is an anti-particle. As such, an enduring mystery posed by this model is why the Universe can exist if it is theoretically made up of equal parts of matter and antimatter.
This seeming disparity, known as the charge-parity (CP) violation, has been the subject of experiments for many years. But so far, no definitive demonstration has been made for this violation, or how so much matter can exist in the Universe without its counterpart. But thanks to new findings released by the international Tokai-to-Kamioka (T2K) collaboration, we may be one step closer to understanding why this disparity exists.
First observed in 1964, CP violation proposes that under certain conditions, the laws of charge-symmetry and parity-symmetry (aka. CP-symmetry) do not apply. These laws state that the physics governing a particle should be the same if it were interchanged with its antiparticle, while its spatial coordinates would be inverted. From this observation, one of the greatest cosmological mysteries emerged.
If the laws governing matter and antimatter are the same, then why is it that the Universe is so matter-dominated? Alternately, if matter and antimatter are fundamentally different, then how does this accord with our notions of symmetry? Answering these questions is not only important as far as our predominant cosmological theories go, they are also intrinsic to understanding how the weak interactions that govern particles work.
Established in June of 2011, the international T2K collaboration is the first experiment in the world dedicated to answering this mystery by studying neutrino and anti-neutrino oscillations. The experiment begins with high-intensity beams of muon neutrinos (or muon anti-neutrinos) being generated at the Japan Proton Accelerator Research Complex (J-PARC), which are then fired towards the Super-Kamiokande detector 295 km away.
This detector is currently one of the world’s largest and most sophisticated, dedicated to the detection and study of solar and atmospheric neutrinos. As neutrinos travel between the two facilities, they change “flavor” – going from muon neutrinos or anti-neutrinos to electron neutrinos or anti-neutrinos. In monitoring these neutrino and anti-neutrino beams, the experiment watches for different rates of oscillation.
This difference in oscillation would show that there is an imbalance between particles and antiparticles, and thus provide the first definitive evidence of CP violation for the first time. It would also indicate that there are physics beyond the Standard Model that scientists have yet to probe. This past April, the first data set produced by T2K was released, which provided some telling results.
The detected pattern of an electron neutrino candidate event observed by Super-Kamiokande. Credit: Kavli IMPU
As Mark Hartz, a T2K collaborator and the Kavli IPMU Project Assistant Professor, said in a recent press release:
“While the data sets are still too small to make a conclusive statement, we have seen a weak preference for large CP violation and we are excited to continue to collect data and make a more sensitive search for CP violation.”
These results, which were recently published in the Physical Review Letters, include all data runs from between January 2010 to May 2016. In total, this data comprised 7.482 x 1020 protons (in neutrino mode), which yielded 32 electron neutrino and 135 muon neutrino events, and 7.471×1020 protons (in antineutrino mode), which yielded 4 electron anti-neutrino and 66 muon neutrino events.
In other words, the first batch of data has provided some evidence for CP violation, and with a confidence interval of 90%. But this is just the beginning, and the experiment is expected to run for another ten years before wrapping up. “If we are lucky and the CP violation effect is large, we may expect 3 sigma evidence, or about 99.7% confidence level, for CP violation by 2026,” said Hartz.
If the experiment proves successful, physicists may finally be able to answer how it is that the early Universe didn’t annihilate itself. It is also likely help to reveal aspects of the Universe that particle physicists are anxious to get into! For it here that the answers to the deepest secrets of the Universe, like how all of its fundamental forces fit together, are likely to be found.
One of the Daya Bay detectors.
Roy Kaltschmidt, Lawrence Berkeley National Laboratory
It is no easy thing to search for signs of intelligent life beyond our Solar System. In addition to the incredible distances involved and the fact that we really only have indirect methods at our disposal, there is also the small problem of not knowing exactly what to look for. If intelligent life does exist beyond our Solar System, would they even communicate as we do, using radio transmitters and similar forms of technology?
Such has been the preoccupation of groups like the Search for Extra Terrestrial Intelligence (SETI) Institute and, more recently, organizations like Messaging Extraterrestrial Intelligence (METI) International. A non-profit dedicated to communicating with extra-terrestrial intelligence (ETI), the organization recently suggested that looking for neutrinos and other exotic particles could help us find signals as well.
First, some clarification should be made as to what SETI and METI are all about it and what sets them apart. The term METI was coined by Russian scientist Alexander Zaitsev, who sought to draw a distinction between SETI and METI. As he explained in a 2006 paper on the subject:
“The science known as SETI deals with searching for messages from aliens. METI science deals with the creation of messages to aliens. Thus, SETI and METI proponents have quite different perspectives. SETI scientists are in a position to address only the local question “does Active SETI make sense?” In other words, would it be reasonable, for SETI success, to transmit with the object of attracting ETI’s attention? In contrast to Active SETI, METI pursues not a local and lucrative impulse, but a more global and unselfish one – to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation ‘You are not alone!'”
One of the 42 dishes in the Allen Telescope Array that searches for signals from space. Credit: Seth Shostak/SETI Institute.
In short, METI looks for ways in which we might be able to contact aliens instead of waiting to hear from them. However, this does not mean that organizations like METI International are without ideas on how me might better listen to our (potential) alien neighbors. After all, communication goes beyond mere messages, and also requires that a medium exist with which to convey the message.
Such is the recommendation put forth by Dr. Morris Jones, a space analyst and writer who serves on the METI advisory council. In a recent article published on METI International’s website, he addressed the two main challenges when it comes to looking for ETI. On the one hand, you have the need for multiple methodologies to increase the odds of finding something. But as he indicates, there’s also the problem of knowing what to look for:
“We are not really sure of how extraterrestrials would communicate with us. Would they use radio waves, lasers, or something more exotic? Perhaps the universe is awash in extraterrestrial signals that we cannot even receive. SETI and METI practitioners spend a lot of time wondering how a message would be encoded in terms of language and content. It’s also important to consider the medium of transmission.”
In the past, says Jones, SETI searches were based on radio astronomy because that was the only practical means of doing so. Since then, efforts have expanded to include optical telescopes and the search for laser signals. This is due to the fact that in the past few decades, human beings have developed the technology to use laser for the sake of communications.
An artist’s illustration of a light-sail powered by a radio beam (red) generated on the surface of a planet. Could the part of the beam that misses the sail be our mysterious Fast Radio Bursts? Image Credit: M. Weiss/CfA
In a 2016 SETI paper, Dr. Philip Lubin of the University of California, Santa Barbara, explained how the development of directed-energy propulsion could help us search for evidence of aliens. As one of the scientific minds behind Breakthrough Starshot – a laser-driven lightsail that would be fast enough to make the trip to Alpha Centauri in just 20 years – he believes it’s a safe bet that ETI could be using similar technology to travel or communicate.
In addition, Dr. Avi Loeb from the Harvard-Smithsonian Center for Astrophysics (also one of the minds behind Starshot) has also suggested that fast-radio bursts (FRBs) could be evidence of alien activity. FRBs have been a subject of fascination to scientists since they were first detected in 2007 (the “Lorimer Burst“), and could also be a sign of alien communications or a means of propulsion.
Another means involves searching for artefacts – i.e. looking for evidence of physical infrastructure in other star systems. Case in point, since 2015, astronomers have been seeking to determine what is responsible for the periodic dimming of KIC 8462852 (aka. Tabby’s Star). Whereas most studies have sought to explain this in terms of natural causes, others have suggested it could be evidence of an alien megastructure.
To this array of search methods, Dr. Jones offers a few other possibilities. One way is to look for neutrinos, a type of subatomic particle that is produced by the decay of radioactive elements and interacts with matter very weakly. This allows them to pass through solid matter and also makes them very difficult to detect. Neutrinos are produced in large quantities by our Sun and astronomical sources, but they can also be produced artificially by nuclear reactors.
Ever since it was first announced in 2015, there has been speculation as to what could account for the dimming of KIC 8462852. Credit: SentientDevelopments.com
These, claims Jones, could be used for the sake of communications. The only problem is that looking for them would require some specialized equipment. Currently, all means of detecting neutrinos involve expensive facilities that have to be built either underground or in extremely isolated locations to ensure that they are not subject to any kind of electromagnetic interference.
Another possibility is searching for evidence of communications that rely on gravitational waves. Predicted by Einstein’s Theory of General Relativity, the first detection of these mysterious waves was first made in February 2016. And in the coming years and decades, it is expected that gravitational wave observatories will be established so the presence of these “ripples” in spacetime can be visualized.
However, compared to neutrinos, Jones admits that this seems like a long shot. “It’s hard to conceive with our current grasp of physics,” he writes. “They are extremely difficult to generate at a detectable level. You would need abilities similar to those of superheroes, and be able to smash neutron stars and black holes together at will. There are probably easier ways to get a message across the stars.”
Breakthrough Listen will monitor the 1 million closest stars to Earth over a ten year period. Credit: Breakthrough Initiatives
Beyond these, there is the even more exotic possibility of “Zeta Rays”, which Dr. Jones is not prepared to rule out. Basically, “Zeta Rays” is a term used by physicists to describe physics that go beyond the Standard Model. As scientists are currently looking for evidence of new particles with the Large Hadron Collider and other particle accelerators, it stands to reason that anything they discover will be the added to the SETI and METI search manifest.
But could such physics entail new forms of communication? Hard to say, but definitely worth considering. After all, the physics that power our current technology certainly existed before we did. Or as Jones put it:,
“Is it possible to transmit with something better than we already have? Until we know a lot more physics, we just won’t know. Humanity in the twenty-first century could be like an isolated tribe in the Amazon jungle a century ago, unaware that the air around them was filled with radio signals. SETI uses the science and technology provided to us by other disciplines. Thus, we must wait until physics itself makes some more major breakthroughs. Only then can we consider such exotic methods of searching. We think a lot about the message. But we should also think about the medium.”
Other projects that are dedicated to METI include Breakthrough Listen, a ten-year initiative launched by Breakthrough Initiatives to conduct the largest survey to date for extraterrestrial communications – encompassing the 1,000,000 closest stars and 100 closest galaxies. Back in April of 2017, the scientists behind this project shared their analysis of the first year of Listen data. No definitive results have been announced yet, but they are just getting started!
Ever since Drake proposed his famous equation, human beings have eagerly sought to find evidence of extra-terrestrial intelligence. Unfortunately, all of our efforts have been haunted by Fermi’s equally-famous paradox! But of course, as space exploration goes, we’ve really only begun to scratch the surface of our Universe. And the only way we can ever expect to find evidence of intelligent life out there is to keep looking.
And with greater knowledge and increasingly sophisticated methods at our disposal, we can be sure that if intelligent life is out there somewhere, we will find it eventually. One can always hope, right? And be sure to check out this video of Dr. Jones 2014 presentation at the SETI Institute, titled “A Journalistic Perspective on SETI-Related Message Composition“:
Super-Kamiokande, a neutrino detector in Japan, holds 50,000 tons of ultrapure water surrounded by light tubes. Credit: Super-Kamiokande Observatory
Under Mount Ikeno, Japan, in an old mine that sits one-thousand meters (3,300 feet) beneath the surface, lies the Super-Kamiokande Observatory (SKO). Since 1996, when it began conducting observations, researchers have been using this facility’s Cherenkov detector to look for signs of proton decay and neutrinos in our galaxy. This is no easy task, since neutrinos are very difficult to detect.
But thanks to a new computer system that will be able to monitor neutrinos in real-time, the researchers at the SKO will be able to research these mysteries particles more closely in the near future. In so doing, they hope to understand how stars form and eventually collapse into black holes, and sneak a peak at how matter was created in the early Universe.
Neutrinos, put simply, are one of the fundamental particles that make up the Universe. Compared to other fundamental particles, they have very little mass, no charge, and only interact with other types of particles via the weak nuclear force and gravity. They are created in a number of ways, most notably through radioactive decay, the nuclear reactions that power a star, and in supernovae.
Timeline of the Big Bang, which unleashed cosmic neutrinos that can still be detected today. Credit: NASA / JPL-Caltech / A. Kashlinsky (GSFC).
In accordance with the standard Big Bang model, the neutrinos left over from the creation of the Universe are the most abundant particles in existence. At any given moment, trillions of these particles are believed to be moving around us and through us. But because of the way they interact with matter (i.e. only weakly) they are extremely difficult to detect.
For this reason, neutrino observatories are built deep underground to avoid interference from cosmic rays. They also rely on Cherenkov detectors, which are essentially massive water tanks that have thousands of sensors lining their walls. These attempt to detect particles as they are slowed down to the local speed of light (i.e. the speed of light in water), which is made evident by the presence of a glow – known as Cherenkov radiation.
The detector at the SKO is currently the largest in the world. It consists of a cylindrical stainless steel tank that is 41.4 m (136 ft) tall and 39.3 m (129 ft) in diameter, and holds over 45,000 metric tons (50,000 US tons) of ultra-pure water. In the interior, 11,146 photomultiplier tubes are mounted, which detect light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum with extreme sensitivity.
For years, researchers at the SKO have used the facility to examine solar neutrinos, atmospheric neutrinos and man-made neutrinos. However, those that are created by supernovas are very difficult to detect, since they appear suddenly and difficult to distinguish from other kinds. However, with the newly-added computer system, the Super Komiokande researchers are hoping that will change.
Cherenkov radiation glowing in the core of the Advanced Test Reactor at the Idaho National Laboratory Credit: Wikipedia Commons/Argonne National Laboratory
“Supernova explosions are one of the most energetic phenomena in the universe and most of this energy is released in the form of neutrinos. This is why detecting and analyzing neutrinos emitted in these cases, other than those from the Sun or other sources, is very important for understanding the mechanisms in the formation of neutron stars –a type of stellar remnant– and black holes”.
Basically, the new computer system is designed to analyze the events recorded in the depths of the observatory in real-time. If it detects an abnormally large flows of neutrinos, it will quickly alert the experts manning the controls. They will then be able to assess the significance of the signal within minutes and see if it is actually coming from a nearby supernova.
“During supernova explosions an enormous number of neutrinos is generated in an extremely small space of time – a few seconds – and this why we need to be ready,” Labarga added. “This allows us to research the fundamental properties of these fascinating particles, such as their interactions, their hierarchy and the absolute value of their mass, their half-life, and surely other properties that we still cannot even imagine.”
The Super-Kamiokande experiment is located at the Kamioka Observatory, 1,000 m below ground in a mine near the Japanese city of Kamioka. Credit: Kamioka Observatory/ICRR/University of Toky
Equally as important is the fact this system will give the SKO the ability to issue early warnings to research centers around the world. Ground-based observatories, where astronomers are keen to watch the creation of cosmic neutrinos by supernova, will then be able to point all of their optical instruments towards the source in advance (since the electromagnetic signal will take longer to arrive).
Through this collaborative effort, astrophysicists may be able to better understand some of the most elusive neutrinos of all. Discerning how these fundamental particles interact with others could bring us one step closer to a Grand Unified Theory – one of the major goals of the Super-Kamiokande Observatory.
To date, only a few neutrino detectors exist in the world. These include the Irvine-Michigan-Brookhaven (IMB) detector in Ohio, the Subdury Neutrino Observatory (SNOLAB) in Ontario, Canada, and the Super Kamiokande Observatory in Japan.
