ElShamah - Reason & Science: Defending ID and the Christian Worldview
Would you like to react to this message? Create an account in a few clicks or log in to continue.
ElShamah - Reason & Science: Defending ID and the Christian Worldview

Otangelo Grasso: This is my library, where I collect information and present arguments developed by myself that lead, in my view, to the Christian faith, creationism, and Intelligent Design as the best explanation for the origin of the physical world.

You are not connected. Please login or register

Matter/Antimatter Asymmetry

Go down  Message [Page 1 of 1]

1Matter/Antimatter Asymmetry Empty Matter/Antimatter Asymmetry Fri Feb 27, 2015 12:54 pm



Matter-Antimatter Asymmetry 


Leonard Susskind The Cosmic Landscape: String Theory and the Illusion of Intelligent Design 2006, page 183
When the universe was very young and hot, it was filled with plasma that contained almost exactly equal amounts of matter and antimatter. The imbalance was extremely small. For every 100,000,000 antiprotons, there were 100,000,001 protons. Then, as the universe cooled, particles and antiparticles combined in pairs and annihilated into photons. One hundred million antiprotons found 100,000,000 partners and, together, they committed suicide, leaving 200,000,000 photons and just 1 leftover proton. These leftovers are the stuff we are made of. Today, if you take a cubic meter of intergalactic space, it will contain about 1 proton and 200,000,000photons. Without the slight initial imbalance, I would not be here to tell you (who would not be here to read) these things. 

Open Questions: Matter/Antimatter Asymmetry

Quarks and anti-quarks form via matter-antimatter pair production. Because of their nature, these particles instantly annihilate each other. However, during the Big Bang, a slight asymmetry in this pair production resulted in approximately 1 extra particle of matter for every 10 billion produced.
It turns out that this 1 in 10 billion ratio of “leftover particles” happens to be the exact amount of mass necessary for the formation of stars, galaxies, and planets. As much as 2 in 10 billion, and the universe would have just been filled with black holes. As little as 0.5 in 10 billion, and there wouldn’t have been enough density for galaxies to form.

The matter-antimatter asymmetry problem 
Researchers have observed spontaneous transformations between particles and their antiparticles, occurring millions of times per second before they decay. Some unknown entity intervening in this process in the early universe could have caused these "oscillating" particles to decay as matter more often than they decayed as antimatter.

Matter-antimatter mystery remains unsolved 
There is little wiggle room for disparities between matter and antimatter protons, according to a new study published by the BASE experiment at CERN.
Charged matter particles, such as protons and electrons, all have an antimatter counterpart. These antiparticles appear identical in every respect to their matter siblings, but they have an opposite charge and an opposite magnetic property. This recalcitrant parity is a head-scratcher for cosmologists who want to know why matter triumphed over antimatter in the early universe.
“We’re looking for hints,” says Stefan Ulmer, spokesperson of the BASE collaboration. “If we find a slight difference between matter and antimatter particles, it won’t tell us why the universe is made of matter and not antimatter, but it would be an important clue.”
Ulmer and his colleagues working on the BASE experiment at CERN closely scrutinize the properties of antiprotons to look for any miniscule divergences from protons. In a paper published today in the journal Nature Communications, the BASE collaboration at CERN reports the most precise measurement ever made of the magnetic moment of the antiproton.

“Each spin-carrying charged particle is like a small magnet,” Ulmer says. “The magnetic moment is a fundamental property which tells us the strength of that magnet.”

The BASE measurement shows that the magnetic moments of the proton and antiproton are identical, apart from their opposite signs, within the experimental uncertainty of 0.8 parts per million. The result improves the precision of the previous best measurement by the ATRAP collaboration in 2013, also at CERN, by a factor of six. This new measurement shows an almost perfect symmetry between matter and antimatter particles, thus further constricting leeway for incongruencies which might have explained the cosmic asymmetry between matter and antimatter.
The measurement was made at the Antimatter Factory at CERN, which generates antiprotons by first crashing normal protons into a target and then focusing and slowing the resulting antimatter particles using the Antiproton Decelerator. Because matter and antimatter annihilate upon contact, the BASE experiment first traps antiprotons in a vacuum using sophisticated electromagnetics and then cools them to about 1 degree Celsius above absolute zero. These electromagnetic reservoirs can store antiparticles for long periods of time; in some cases, over a year. Once in the reservoir, the antiprotons are fed one-by-one into a trap with a superimposed magnetic bottle, in which the antiprotons oscillate along the magnetic field lines. Depending on their North-South alignment in the magnetic bottle, the antiprotons will vibrate at two slightly different rates. From these oscillations (combined with nuclear magnetic resonance methods), physicists can determine the magnetic moment.
The challenge with this new measurement was developing a technique sensitive to the miniscule differences between antiprotons aligned with the magnetic field versus those anti-aligned.

“It’s the equivalent of determining if a particle has vibrated 5 million times or 5 million-plus-one times over the course of a second,” Ulmer says. “Because this measurement is so sensitive, we  stored antiprotons in the reservoir and performed the measurement when the antiproton decelerator was off and the lab was quiet.”

BASE now plans to measure the antiproton magnetic moment using a new trapping technique that should enable a precision at the level of a few parts per billion—that is, a factor of 200 to 800 improvement.
Members of the BASE experiment hope that a higher level of precision might provide clues as to why matter flourishes while cosmic antimatter lingers on the brink of extinction.

“Every new precision measurement helps us complete the framework and further refine our understanding of antimatter’s relationship with matter,” Ulmer says.

Davies: Goldilocks enigma 
What Happened to All the Antimatter?
The possibility that protons might not be absolutely stable is also germane to the origin of the universe. If matter can disappear, then it can also appear (by the reverse process). This yields a clue to one of the deepest puzzles of cosmology: the origin of matter. Somehow it was made, in a flash, from the heat energy of the big bang. But cosmologists want to know exactly how it happened and why that particular amount (10^50 tons in the observable universe) got made. When matter is made in the lab by high-energy collisions, the same quantity of antimatter appears too. If the universe contained equal amounts of matter and antimatter, we’d be in for trouble. Whenever antimatter and matter mingle, they quickly annihilate in a burst of gamma rays. Even in outer space, lots of mingling happens, when gas clouds collide, for example. Unless matter and antimatter are quarantined on a very large scale (much larger than the size of a galaxy), the universe would be flooded with distinctive gamma radiation. Astronomers have looked for it, without success, and so have concluded that less than one millionth of our galaxy is in the form of antimatter. Most cosmologists assume that the entire observable universe is made overwhelmingly of matter. So that presents a puzzle: how did the big bang make 10^50 tons of matter without also making 10^50 tons of antimatter? Evidently the symmetry between matter and antimatter cannot be exact. Something must have broken it, slightly favoring matter over antimatter. Grand unified theories naturally encompass the necessary symmetry-breaking. If a proton can turn into a positron, then (by going the other way) an electron-positron pair can turn into an electron-proton pair—in effect, a hydrogen atom with no antihydrogen atom accompanying it. But however it is done, the story of the origin of matter would go something like this.

The heat radiation released after the big bang created copious quantities of both matter and antimatter, all mixed together, but containing a slight excess of matter. As the universe cooled, the antimatter would be totally destroyed by virtue of its being in intimate contact with matter, leaving unscathed the small residue of excess matter—about one part in a billion. The wholesale annihilation of the antimatter, and most of the matter, flooded the universe with gamma-ray photons. Where are they now? The answer is that they lost most of their energy as the universe expanded and cooled, eventually be coming microwave photons. They constitute the cosmic microwave background radiation. So this radiation is a fading remnant of the primordial extermination visited on antimatter at the dawn of time. Viewed this way, matter is almost a cosmic afterthought. But what an important afterthought it is! Without matter there could be no life. Therefore our very existence, not to mention the existence of the visible universe, hinges on the minute degree of symmetry-breaking between matter and antimatter, which in turn depends on how quarks, leptons, and the forces that act between them are amalgamated together in some as yet undetermined grand unification.

Geraint F. Lewis A universe made for me? 18 December 2016
Symmetry:  In everyday life the word symmetry describes how something stays the same when you change your viewpoint; think of the appearance of a perfect vase as you circumnavigate the table it’s sitting on. It demonstrates rotational symmetry. In physics, we find other types of symmetries hidden in mathematics. For instance, there is a symmetry that ensures the conservation of electric charge: in every experiment we perform, equal amounts of positive and negative charges are produced. Other symmetries dictate the conservation of momentum, and there are others for a whole host of quantum properties. Some symmetries are perfect, others contain slight imperfections. And we would not be here without them. In a perfectly symmetric universe, the hot fires of the Big Bang would have produced equal amounts of matter and antimatter. This means protons and antiprotons would have completely annihilated each other as the universe cooled leaving a universe empty of its atomic hydrogen building block. Somewhere hidden in the physics of protons there must be a slight asymmetry that resulted in protons outnumbering antiprotons by one in a billion. But why does our universe possess a perfect symmetry with respect to charge but a slight asymmetry with respect to matter and antimatter? Nobody knows! If the situation was reversed and our universe was born with zero protons, but with a net excess of charge, the immense repulsive action of the electromagnetic force would prevent matter present from collapsing into anything resembling stars and galaxies. No matter which way we turn, the properties of our universe have finely tuned values that allow us to be here. Deviate ever so slightly from them and the universe would be sterile – or it may never have existed at all. What explanation can there be for this fine-tuning? Unfortunately, if you are expecting an answer, there is none. But there is much speculation.

The hand of God
While this is a scientific article, we cannot ignore the fact that to many, the fact that the universe is finely tuned for intelligent life shows the hand of the creator who set the dials.

Ethan Siegel How The Big Bang Failed To Set The Universe Up For The Emergence Of Life  Aug 11, 2021
If you imagine starting off the Universe in a very hot, dense, and uniform state, but one that’s expanding very rapidly, the laws of physics themselves will paint a remarkable picture of what’s to come.

In the initial stages, every quantum of energy that exists will be so hot that it will be traveling at speeds indistinguishable from the speed of light, smashing into other quanta countless times per second due to the overwhelming densities.
When a collision occurs, there’s a substantial chance that any particle-antiparticle pair that can get created — restricted only by the quantum mechanical conservation laws that govern the Universe and the amount of energy available for particle creation from Einstein’s famous E = mc2 relation — will come into existence.
Similarly, whenever a particle-antiparticle pair happen to collide, there’s a substantial chance that they’ll annihilate back into photons.
So long as you have an initially hot, dense, expanding Universe filled with interacting quanta of energy, those quanta will populate the Universe with all the various types of particles and antiparticles that are permitted to exist.

Matter/Antimatter Asymmetry Https_30
As matter and antimatter annihilate away in the early Universe, the leftover quarks and gluons cool to form stable protons and neutrons. Somehow, in the very early stages of the hot Big Bang, a slight imbalance of matter over antimatter was created, with the remainder annihilating away. Today, photons outnumber protons-and-neutrons by approximately 1.4 billion to one.

But what happens next? As the Universe expands, everything cools: massive particles lose kinetic energy while massless particles get redshifted to longer wavelengths. Early on, at very high energies, everything was in equilibrium: particles and antiparticles got created at the same rate they got annihilated. But as the Universe cools, the “forward” reaction rates, where you create new particles-and-antiparticles based on collisions, begin to occur less rapidly than the “backwards” reaction rates, where particles-and-antiparticles annihilate away back into massless particles, such as photons.

At very high energies, all of the known particles and antiparticles of the Standard Model are easy to create in large quantities. As the Universe cools, however, the more massive particles and antiparticles become more difficult to create, and they eventually annihilate away until there’s a negligible amount left. This winds up leading to a Universe filled with radiation, with just a tiny bit of leftover matter: protons, neutrons, and electrons, which somehow came to exist slightly more abundantly — about 1 extra matter particle per 1.4 billion photons — than antimatter. (How, exactly, that occurred is still an open area of research, and is known as the baryogenesis problem.)

Matter/Antimatter Asymmetry Https_31
A logarithmic scale showing the masses of the Standard Model's fermions: the quarks and leptons. Note the tininess of the neutrino masses. Data from the early Universe indicates that the sum of all three neutrino masses can be no greater than 0.17 eV. Meanwhile, in the early hot Big Bang stages, the heavier particles (and antiparticles) stop getting created earlier, while the lighter particles and antiparticles can continue to be created as long as there's enough available energy via Einstein's E=mc^2.

About 1 second after the Big Bang, the Universe is still very hot, with temperatures in the tens of billions of degrees: about ~1000 times hotter than in the center of our Sun. The Universe still has a little bit of antimatter left, because it’s still hot enough for electron-positron pairs to be created as quickly as they’re destroyed, and because neutrinos and antineutrinos are as equally copious as one another, and almost as copious as photons. The Universe is hot and dense enough for the remnant protons and neutrons to begin the process of nuclear fusion, building their way up the periodic table to create the heavy elements. If the Universe could do precisely this, then as soon as the Universe becomes cool enough to form neutral atoms and enough time passes so that the gravitational imperfections can attract enough matter to form stars and star systems, we’d have chances for life. The atoms necessary for life — the raw ingredients — can bind together into all sorts of molecular configurations all on their own, through natural, abiotic processes, just like we find today all throughout interstellar space. If we could begin building elements in these early stages of the hot Big Bang, the high temperatures and densities could permit not just fusion of hydrogen into helium, but helium into carbon, and so on into nitrogen, oxygen, and many of the heavier elements found all throughout the modern cosmos.

Matter/Antimatter Asymmetry Https_32
In a Universe loaded with neutrons and protons, it seems like building elements would be a cinch. All you have to do is start off with that first step: building deuterium, and the rest will follow from there. But making deuterium is easy; not destroying it is particularly hard. To avoid destruction, you have to wait until the Universe is cool enough so that there aren't sufficiently energetic photons around to destroy the deuterons.

This is the problem: deuterium. The Universe is full of protons and neutrons, and it’s hot and dense. Whenever a proton and neutron find one another, they’ll fuse into a deuteron, which is a heavy isotope of hydrogen, and is also more stable than a free proton and neutron separately; each time you form a deuteron from a proton and neutron, you liberate 2.2 million electron-volts of energy. (You can also form deuterium from nuclear reactions involving two protons, but the reaction rate is much lower than from a proton and a neutron.) So why, then, can’t you add protons or neutrons to each deuteron, building your way up to heavier isotopes and elements? The same hot, dense conditions lead to a “backwards” reaction that swamps the “forward” creation of deuterium by fusing protons with neutrons: the fact that enough photons, which outnumber protons and neutrons by more than a billion-to-one, have more than 2.2 million electron-volts of energy themselves. When they collide with a deuteron, which occurs far more frequently than a deuteron colliding with anything else made out of protons-and-neutrons, they immediately blast it apart. The inability of the cosmos to maintain deuterium in the early Universe for long enough periods to build up to heavier elements is the primary reason that the Big Bang can’t create the ingredients for life on its own.

Matter/Antimatter Asymmetry Https_33
From beginning with just protons and neutrons, the Universe builds up helium-4 rapidly, with small but calculable amounts of deuterium, helium-3, and lithium-7 left over as well. In the aftermath of the first few minutes of the Big Bang, the Universe winds up being populated, in terms of normal matter, with over 99.99999% hydrogen and helium alone.

So, what can the Universe do? It’s compelled to wait until it’s expanded and cooled enough so that deuterium isn’t immediately blasted apart. But in the meanwhile, a whole slew of other things happen while we wait for the Universe to cool sufficiently. They include:

1. neutrinos and antineutrinos stop efficiently participating in interactions with other particles, also known as the freeze-out of the weak interactions,
2. electrons and positrons, like other species of matter and antimatter, annihilate away, leaving only the excess electrons, and the free neutrons, being unable to bind themselves up in heavier nuclei, begin to decay away into protons, electrons, and anti-electron neutrinos.
3. Finally, after a little more than about ~200 seconds, we can finally form deuterium without immediately blasting it apart. But at this point, it’s too late. The Universe has cooled but become much less dense: only about one-billionth the density found in the central core of our Sun. The deuterons can fuse with other protons, neutrons, and deuterons to build up copious amounts of helium, but that’s where the chain reaction ends.

With less energy per particle, with strong repulsive forces between the helium nuclei, and with every combination of:

helium-4 and a proton,
helium-4 and a neutron,
and helium-4 and helium-4,

being unstable, that’s pretty much the end of the line. The Universe, in the immediate aftermath of the Big Bang, is made of 99.99999%+ hydrogen and helium, exclusively.

Matter/Antimatter Asymmetry Https_34
The most current, up-to-date image showing the primary origin of each of the elements that occur naturally in the periodic table. Neutron star mergers, white dwarf collisions, and core-collapse supernovae may allow us to climb even higher than this table shows. The Big Bang gives us almost all of the hydrogen and helium in the Universe, and almost none of everything else combined.

Even though we’re talking about cosmic scales, it’s actually the laws that govern subatomic particles — nuclear and particle physics — that prevents the Universe from forming the heavy elements required for life in the early stages of the Big Bang. If the rules were a little bit different, like deuterium was more stable, there were much greater numbers of protons and neutrons, or there were fewer photons at high energies, nuclear fusion could have built up large quantities of heavy elements in the first few seconds of the Universe.

But the easily-destroyed nature of deuterium, combined with the enormous numbers of photons present in the early Universe, kills our dreams of having the necessary raw ingredients right at the beginning. Instead, it’s just hydrogen and helium, and we’ll have to wait stars to form before we build up any substantial quantities of anything heavier. The Big Bang was a great start to our Universe, but couldn’t set us up for life all on its own. For that, we need stars that enrich the interstellar medium with the heavier elements that all biochemical processes require. When it comes to your existence, the Big Bang absolutely isn’t enough to give rise to you. For that to occur, you can literally thank your lucky the creator of stars: the ones that lived, died, and created the essential elements still inside you today.

Johan Hansson: The 10 Biggest Unsolved Problems in Physics March 26, 2015
The Matter-Antimatter Asymmetry: The question of why there is so much more matter than its oppositely charged mirror image, antimatter, is actually the crucial question of why anything exists at all. It is assumed that the universe when it is born treats matter and antimatter symmetrically. Thus, the Big Bang should have produced equal parts matter and antimatter. This should then have resulted in a total annihilation of the two: protons would have annihilated with antiprotons, electrons with antielectrons (positrons), neutrons with antineutrons, and so on, which would have left behind a structure-less sea of photons in a matterless void. For some reason there remained a tiny excess of matter that was not annihilated. And here we are. This has not yet any explanation. Because what we mean by matter is only a definition, we see that we could just as well have obtained a universe dominated by antimatter. But that in turn means that the answer to this riddle must contain a fundamental time direction, the universe cannot be run backwards because two completely different final states (matter or antimatter) would have arisen from the same initial state. A more complicated way of saying the same thing is that today’s most fundamental theory is CPT-invariant, i.e. the same when simultaneously changing the particle charges (C), mirrorreflecting their state (P) and re- versing the direction of time (T). And because we know that CP is broken for some reactions, this means that also T is broken, i.e., that the theory (or nature itself) is asymmetrical in the time direction. The problem is that the known CP-violation is far too weak and insignificant to explain why we today have only matter.

Matter/Antimatter Asymmetry Matter10

Whenever any two particles collide, which happens with increasing frequency the farther back in time you look, there are a number of possible ways in which they can interact with one another. They can collide elastically, bouncing off of one another and turning all of that initial energy from before the collision into the kinetic energy of the outgoing particles. They can collide inelastically, perhaps causing one of the particles to explode apart or perhaps causing both of them to stick together. Or, if the energies are high enough, they can spontaneously cause the creation of new particles: a combination of matter and antimatter in equal amounts. This is something that happens without any provocation so long as there is enough energy, and the amount of energy required to do so is given simply by Einstein’s most famous equation: E = mc2 .

How could this creation of more matter than antimatter have happened? 
 If we wanted to begin in a high-energy state where matter and antimatter existed in equal amounts and wind up in a low-energy state with slightly more matter than antimatter, something must have happened as the Universe expanded and cooled to create that asymmetry. It was a Soviet physicist, Andrei Sakharov, who in 1967 became the first to work out that there are only three things that need to be true in general for this to happen. These three properties that the Universe must have, today known as the Sakharov conditions, are as follows (and do not worry; we will explain them): 

1) The Universe must be out of thermal equilibrium. 
2) Two of the three fundamental symmetries in the Universe — charge conjugation (C) and charge conjugation plus parity (CP) — must be violated.
3) And finally, there must be interactions that violate the conservation of baryon number.

Before we talk about what these mean individually, we should emphasize that all three of these things need to occur together, otherwise you would not generate a difference in the amount of matter vs. antimatter present in the Universe. Thermal equilibrium is the easiest one to understand: it is the same idea that, if you turn on a heater in one part of a cold room, eventually the entire room becomes the same temperature. In the case of the room with a heater in it, the reason why the temperature equilibrates is that the heater gives energy to the molecules closest to it, which in turn speed up, collide with the molecules that are further away and give energy to them, which then in turn collide with molecules even further away and exchange energy, and so on. Given enough time (and given a room where no heat is exchanged through the walls, ceiling or floor), the room will eventually reach a state of thermal equilibrium, where every part and component of it has the same, stable temperature. But the Universe is not a stable, static system: it is both expanding and cooling! A region of the Universe that is a slightly higher temperature than a region just a short distance away might not be able to exchange heat (or any type of information) with that region for hundreds, thousands or even millions of years thanks to the Universe’s expansion. On top of that, the fact that the Universe is non-uniform and cooling means that different regions of space will have different relative abundances of particle– antiparticle pairs at any given time, dependent on how much energy is available for particle–antiparticle creation as the Universe cools down. In short, this condition is the easiest one to satisfy: the expanding Universe is perhaps the ultimate out-of-thermal-equilibrium system! What about the violation of two of the three fundamental symmetries at once? This one is a little harder to understand, so I want you to picture a particle of matter. Imagine this particle as a little sphere and that it spins counterclockwise around its North Pole as we move forward in time. There are three types of fundamental symmetries that we can apply to this particle:

• C-symmetry, known as charge conjugation. This is the same as replacing our particle with an antiparticle: it has the same mass and spin, but certain other properties — electric charge, color charge, baryon number, lepton number and lepton family number — have the exact opposite value. 
• P-symmetry, known as parity, or mirror-symmetry. This is the same as reflecting our particle in a mirror: all its properties remain the same except spin (and, for multi-particle systems, orbital angular momentum), which has the exact opposite value. For example, a particle spinning clockwise would have a reflection spinning counterclockwise in a mirror. 
• And T-symmetry, or time-reversal symmetry. Instead of a particle moving forward through time as it interacts with the Universe around it, it would move backwards through time when time-reversal symmetry is applied.

Of all the particles and interactions known, we have never violated either baryon number or lepton number by themselves in the lab, nor do we know how to create the conditions to do so. But according to the Standard Model of elementary particles and their interactions, it should be possible to violate both baryon number (B) conservation and lepton number (L) conservation, so long as the combination of baryon number minus lepton number (B − L = 0) is conserved. This last of the Sakharov conditions is the source of our greatest uncertainty concerning the matter–antimatter asymmetry, and is the only condition that has yet to be confirmed experimentally. if we want to account for the observed matter–antimatter asymmetry, it likely requires some new physics (and most likely, some new particles as well) beyond what is currently known.

Matter/Antimatter Asymmetry Antima10

Last edited by Otangelo on Wed Aug 18, 2021 2:12 pm; edited 13 times in total


2Matter/Antimatter Asymmetry Empty Re: Matter/Antimatter Asymmetry Sun Nov 29, 2020 8:01 am



University of Sussex Why is there any matter in the universe at all? New study sheds light February 28, 2020

Scientists at the University of Sussex have measured a property of the neutron -- a fundamental particle in the universe -- more precisely than ever before. Their research is part of an investigation into why there is matter left over in the universe, that is, why all the antimatter created in the Big Bang didn't just cancel out the matter.

The team -- which included the Science and Technology Facilities Council's (STFC) Rutherford Appleton Laboratory in the UK, the Paul Scherrer Institute (PSI) in Switzerland, and a number of other institutions -- was looking into whether or not the neutron acts like an "electric compass." Neutrons are believed to be slightly asymmetrical in shape, being slightly positive at one end and slightly negative at the other -- a bit like the electrical equivalent of a bar magnet. This is the so-called "electric dipole moment" (EDM), and is what the team was looking for.
This is an important piece of the puzzle in the mystery of why matter remains in the Universe, because scientific theories about why there is matter left over also predict that neutrons have the "electric compass" property, to a greater or lesser extent. Measuring it then it helps scientists to get closer to the truth about why matter remains.
The team of physicists found that the neutron has a significantly smaller EDM than predicted by various theories about why matter remains in the universe; this makes these theories less likely to be correct, so they have to be altered, or new theories found. In fact it's been said in the literature that over the years, these EDM measurements, considered as a set, have probably disproved more theories than any other experiment in the history of physics. The results are reported today, Friday 28 February 2020, in the journal Physical Review Letters.
Professor Philip Harris, Head of the School of Mathematical and Physical Sciences and leader of the EDM group at the University of Sussex, said:
"After more than two decades of work by researchers at the University of Sussex and elsewhere, a final result has emerged from an experiment designed to address one of the most profound problems in cosmology for the last fifty years: namely, the question of why the Universe contains so much more matter than antimatter, and, indeed, why it now contains any matter at all. Why didn't the antimatter cancel out all the matter? Why is there any matter left?
"The answer relates to a structural asymmetry that should appear in fundamental particles like neutrons. This is what we've been looking for. We've found that the "electric dipole moment" is smaller than previously believed. This helps us to rule out theories about why there is matter left over -- because the theories governing the two things are linked.
"We have set a new international standard for the sensitivity of this experiment. What we're searching for in the neutron -- the asymmetry which shows that it is positive at one end and negative at the other -- is incredibly tiny. Our experiment was able to measure this in such detail that if the asymmetry could be scaled up to the size of a football, then a football scaled up by the same amount would fill the visible Universe."
The experiment is an upgraded version of apparatus originally designed by researchers at the University of Sussex and the Rutherford Appleton Laboratory (RAL), and which has held the world sensitivity record continuously from 1999 until now.
Dr Maurits van der Grinten, from the neutron EDM group at the Rutherford Appleton Laboratory (RAL), said:
"The experiment combines various state of the art technologies that all need to perform simultaneously. We're pleased that the equipment, technology and expertise developed by scientists from RAL has contributed to the work to push the limit on this important parameter"
Dr Clark Griffith, Lecturer in Physics from the School of Mathematical and Physical Sciences at the University of Sussex, said:
"This experiment brings together techniques from atomic and low energy nuclear physics, including laser-based optical magnetometry and quantum-spin manipulation. By using these multi-disciplinary tools to measure the properties of the neutron extremely precisely, we are able to probe questions relevant to high-energy particle physics and the fundamental nature of the symmetries underlying the universe. "

50,000 measurements
Any electric dipole moment that a neutron may have is tiny, and so is extremely difficult to measure. Previous measurements by other researchers have borne this out. In particular, the team had to go to great lengths to keep the local magnetic field very constant during their latest measurement. For example, every truck that drove by on the road next to the institute disturbed the magnetic field on a scale that would have been significant for the experiment, so this effect had to be compensated for during the measurement.
Also, the number of neutrons observed needed to be large enough to provide a chance to measure the electric dipole moment. The measurements ran over a period of two years. So-called ultracold neutrons, that is, neutrons with a comparatively slow speed, were measured. Every 300 seconds, a bunch of more than 10,000 neutrons was directed to the experiment and examined in detail. The researchers measured a total of 50,000 such bunches.

A new international standard is set
The researchers' latest results supported and enhanced those of their predecessors: a new international standard has been set. The size of the EDM is still too small to measure with the instruments that have been used up until now, so some theories that attempted to explain the excess of matter have become less likely. The mystery therefore remains, for the time being.
The next, more precise, measurement is already being constructed at PSI. The PSI collaboration expects to start their next series of measurements by 2021.

Search for "new physics"
The new result was determined by a group of researchers at 18 institutes and universities in Europe and the USA on the basis of data collected at PSI's ultracold neutron source. The researchers collected measurement data there over a period of two years, evaluated it very carefully in two separate teams, and were then able to obtain a more accurate result than ever before.
The research project is part of the search for "new physics" that would go beyond the so-called Standard Model of Physics, which sets out the properties of all known particles. This is also a major goal of experiments at larger facilities such as the Large Hadron Collider (LHC) at CERN.
The techniques originally developed for the first EDM measurement in the 1950s led to world-changing developments such as atomic clocks and MRI scanners, and to this day it retains its huge and ongoing impact in the field of particle physics.


Paul Davies, God and the new physics:  
Under laboratory conditions the creation of matter and antimatter is always symmetric, in the ultra-high temperatures of the big bang it is possible that a very slight excess of matter was permitted. The idea stems from a programme of theoretical work that seeks to provide a unified description of nature's four fundamental forces. According to the theoretical calculations, at a temperature of a billion billion billion degrees, which could have been attained only during the first billion-billion-billion-billionth of a second, for every billion antiprotons, one-billion-and-one protons were created. Similarly, electrons would have outnumbered positrons by one part in a billion. Such an excess, while minute, would be crucially significant. In the subsequent carnage, the billion matched pairs of protons and antiprotons would have annihilated each other, but the single unpaired proton would have survived, along with a solitary electron. These left-over particles — almost an afterthought of nature — became the material that eventually formed all the galaxies, all the stars and planets — and us. According to this theory, our universe is built out of a tiny residue of unbalanced matter that survives as a relic of the first unthinkably brief moment of existence.

The average lifetime of a proton is at least ten thousand billion billion billion years.

The processes described here do not represent the creation of matter out of nothing, but the conversion of preexisting energy into material form. We still have to account for where the energy came from in the first place. This surely requires a supernatural explanation? What is energy? It can take many different forms. It might simply be motion, for example. In the laboratory, particles can collide at high speed and four appear where previously there were only two. The newcomers are paid for by reducing the speed of the two original particles. The conversion of motion, which is intangible, into stuff, which can be kicked, comes very close to the spirit of creation out of nothing.

There is a still more remarkable possibility, which is the creation of matter from a state of zero energy. This possibility arises because energy can be both positive and negative. The energy of motion or the energy of mass is always positive, but the energy of attraction, such as that due to certain types of gravitational or electromagnetic field, is negative. Circumstances can arise in which the positive energy that goes to make up the mass of newly-created particles of matter is exactly offset by the negative energy of gravity or electromagnetism. For example, in the vicinity of an atomic nucleus the electric field is intense. If a nucleus containing 200 protons could be made (possible but diffcult), then the system becomes unstable against the spontaneous production of electron–positron pairs, without any energy input at all. The reason is that the negative electric energy generated by the new pair of particles can exactly offset the energy of their masses.

In the gravitational case the situation is still more bizarre, for the gravitational field is only a space warp — curved space. The energy locked up in a spacewarp can be converted into particles of matter and antimatter. This occurs, for example, near a black hole, and was probably also the most important source of particles in the big bang. Thus, matter appears spontaneously out of empty space. The question then arises, did the primeval bang possess energy, or is the entire universe a state of zero energy, with the energy of all the material offset by negative energy of gravitational attraction?

It is possible to settle the issue by a simple calculation. Astronomers can measure the masses of galaxies, their average separation, and their speeds of recession. Putting these numbers into a formula yields a quantity which some physicists have interpreted as the total energy of the universe. The answer does indeed come out to be zero within the observational accuracy. The reason for this distinctive result has long been a source of puzzlement to
cosmologists. Some have suggested that there is a deep cosmic principle at work which requires the universe to have exactly zero energy. If that is so the cosmos can follow the path of least resistence, coming into existence without requiring any input of matter or energy at all. Matters are further complicated by the fact that energy is not even properly defined when gravity is present. In some cases it is possible to make sense of the total energy in an isolated system by considering its gravitational influence a great (in fact infinite) distance away. But this strategy fails completely in the case of a universe that is spatially finite, such as the model proposed by
Einstein and discussed briefly in the previous chapter. In such a closed universe, the total energy is a meaningless quantity.

Do these examples, such as the natural creation of matter out of empty space, perhaps with no need for even an energy input, amount to the creation ex nihilo of theology? It could be argued that science has still not explained the existence of space (and time). Granted that the creation of matter, for so long considered the result of divine action, can now (perhaps) be understood in ordinary scientific terms, is it only by an appeal to God that one can explain why there is a universe at all — why space and time exist in the first place, that matter may emerge from them?

The belief that the universe as a whole must have a cause, that cause being God, was enunciated by Plato and Aristotle, developed by Thomas Aquinas, and reached its most cogent form with Gottfried Wilhelm von Leibniz and Samuel Clarke in the eighteenth century. It is usually known as the cosmological argument for the existence of God. There are two versions of the cosmological argument: the causal argument, to be considered here, and the
argument from contingency which will be discussed in the next chapter. The cosmological argument was treated with scepticism by David Hume and Immanuel Kant and has been bitterly attacked by Bertrand Russell.

The goal of the cosmological argument is two-fold. The first is to establish the existence of a ‘prime mover’ — a being that in turn accounts for the existence of the world. The second is to prove that this being is indeed the God as usually understood in Christian doctrine.

Can something be created out of nothing? We saw how particles can be created out of empty space, but in that case the spacewarp was the cause. We still have to explain where space came from (if it hasn't always existed).

Some people might question whether space is a thing. Certainly it is hard to imagine Thomas Aquinas or Leibniz regarding it as part of the causal chain. Still, let us press on. What caused space to suddenly appear in the big bang? The singularity? But a singularity is most certainly not a thing. It is the boundary of a thing (spacetime). Impasse.

Aquinas: No one being in this infinite succession is supposed to be self-existent or necessary… but every one dependent on the foregoing… An infinite succession therefore of merely dependent beings, without any original independent cause; is a series of beings that has neither necessity nor cause… either within itself or from without That is, 'tis an express contradiction and impossibility.

Last edited by Otangelo on Mon Jul 05, 2021 12:48 pm; edited 2 times in total


Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum