Chapter 11 10. Antimatter and antiuniverse
" (I found out!), but "That's weird..."
In Dan Brown's book (Angel and Demons), a previous bestseller, a small group of extremist "Illuminati" hatch a plot to use a piece of antimatter stolen from the nuclear laboratory CERN outside Geneva to The bomb destroyed the Vatican.Conspirators know that when matter and antimatter collide there is a huge explosion many times more powerful than a hydrogen bomb.While antimatter bombs are pure fiction, antimatter is real.
Only about 1% of the full astonishing power of an atomic bomb is effective.Only a very small fraction of the uranium is converted into energy.But if an antimatter bomb could be built, it would convert 100% of its mass into an energy disk, making it far more effective than an atomic bomb (to be more precise, 50% of the material in an antimatter bomb could be converted into energy explosive energy used. The rest will be carried away in the form of undetectable particles called neutrinos).
Antimatter has long been the focus of intense speculation.Although antimatter bombs don't exist, physicists have used powerful nuclear particle accelerators to create tiny amounts of antimatter for study.
In the early 20th century, physicists realized that atoms consist of electrically charged subatomic particles with electrons (negatively charged) orbiting a tiny nucleus (positively charged).The nucleus, in turn, is made up of protons (positively charged) and neutrons (neutrally charged).
So it was a shock when physicists realized in the 1930s that every particle has a twin — an antiparticle, but with the opposite charge.The first antiparticle to be discovered was the antielectron (called a positron), which has a positive charge.A positron is exactly like an electron in all respects except that it carries an opposite charge.It was first discovered in cosmic ray photographs taken in cloud chambers (positron trajectories can be seen fairly easily in cloud chambers. When placed in a strong magnetic field, they turn in the opposite direction to ordinary electrons .in fact, I photographed such antimatter trails when I was in high school).
In 1955, the Bevatron particle accelerator at the University of California, Berkeley produced the first antiproton.As expected, it's exactly the same as a proton -- except it has a negative charge.This means that we can create antiatoms (positrons orbiting antiprotons).In fact, in theory, anti-element, anti-chemical, anti-human, anti-earth and even anti-universe are all possible.
Tiny amounts of antihydrogen are already being produced at CERN and at the giant particle accelerators at Fermi lab outside Chicago (this is done by using a particle accelerator to launch a beam of high-energy protons into a target, thereby creating large amounts of subatomic hydrogen. Atoms are formed from the remains of atoms. Powerful magnets separate antiprotons, they are slowed to very low velocities, and they are then exposed to antielectrons naturally emitted by sodium-22. As antiprotons orbit antiprotons, they Antihydrogen was created, since a hydrogen atom is made of a proton and an electron).In a pure vacuum, these antiatoms could exist forever, but due to impurities and collisions with walls, these antiatoms will eventually hit ordinary atoms, get canceled out, and release energy.
In 1995, CERN made history when it announced that it had produced nine atoms of antihydrogen.Fermilab quickly followed suit and produced 100 antihydrogen atoms? In principle, nothing prevents us from producing higher-level antielements as well, except for the incredible cost.Creating even a few ounces of anti-atoms would bankrupt any country.The current production of antimatter is between 1/10 billion gram and 1/1 billion gram per year.This output may triple by 2020.The economics of antimatter are very poor.In 2004, CERN spent $20 million to create a few trillionths of a gram of antimatter.At this rate, it would cost 1,000 trillion times $100 to produce 1 gram of antimatter, and the antimatter factory would have to run non-stop for 100 billion years!This makes antimatter the most precious substance in the world.
"If we could take all the antimatter we've produced at CERN and make it cancel out with matter," says a report from CERN, "we'd have enough energy to light a light bulb for a few minutes. .”
Dealing with antimatter presents unusual problems, since any contact between matter and antimatter would cause an explosion.Putting antimatter in an ordinary container is suicide.When the antimatter hits the walls of the container, it explodes.If antimatter is so unstable, what should be done with it?One approach is to first ionize antimatter into a gaseous state, or ions, and then keep it safely enclosed in a "magnetic bottle."The magnetic field prevents the antimatter from touching the walls of the container.
To create an antimatter engine, a steady stream of antimatter is injected into a reaction chamber where it is carefully combined with ordinary matter to create a controlled explosion, similar to that produced by chemical rockets. explode.Ions from this explosion are then fired from one end of the antimatter rocket, creating thrust.Because of how efficiently an antimatter engine converts matter into energy, it is theoretically one of the most intriguing engine designs for future stellar spacecraft.In the "Star Trek" series, antimatter is the energy source of the "Enterprise", and its engines are powered by the controlled collision of matter and antimatter.
Penn State physicist Gerald Smith is one of the leading advocates of antimatter rockets.In the short term, he believes, as little as 4 milligrams of positrons will be enough to send an antimatter rocket to Mars in a few weeks.He noticed that the energy contained in antimatter is a billion times greater than that contained in ordinary rocket fuel.
The first step in making the fuel is to create beams of antiprotons in a particle accelerator and store them in a "Penning trap" that Smith built.During construction, the Penning trap will weigh 220 pounds (mostly the weight of liquid nitrogen and liquid helium) and will store about 1 trillion antiprotons in a magnetic field (at very low temperatures, antiprotons have wavelengths shorter than The wavelengths of the atoms in the container walls are several times longer, so the antiprotons mostly reflect off the walls instead of canceling themselves out).Such a Penning trap should be able to hold antiprotons for about 5 years (until they eventually mix with ordinary atoms, canceling out), he said.His Penning trap should be able to store about a billionth of a gram of antiproton.His goal is to create Penning traps capable of storing up to 1 microgram (one millionth of a gram) of antiprotons.
Although antimatter is the most precious substance on Earth, its cost continues to drop dramatically every year (1 milligram currently costs about $62.5 trillion).A particle injector being built at Fermilab outside Chicago should be able to increase antimatter production by a factor of 10, from 1.5 to 15 micrograms per year, which should drive down the price of antimatter.However, NASA's Harold Gerrish believes that with further improvements, the price could realistically drop to $5,000 per microgram.Dr Steven Howe of Synergistics Technologies in Los Alamos, New Mexico, said: "Our goal is to transfer antimatter, which is in the radical category of science fiction, to applications in transportation and medicine. business scope."
Until now, particle accelerators capable of producing antiprotons were not specifically designed for this purpose, so they were not very efficient.Such particle accelerators are primarily intended as research tools, not antimatter factories.That's why Smith imagined building a new type of particle accelerator specifically designed to produce large numbers of antiprotons at a reduced cost.
If the price of antimatter can be further reduced through technological improvement and mass production, Smith hopes that antimatter rockets will one day become a common vehicle for interplanetary and (perhaps) interstellar travel.Until that day, however, antimatter rockets will remain on paper.
Antimatter is so difficult to make on earth, will it be easier to find antimatter in the universe?Unfortunately, the search for antimatter in the universe has yielded so little, much to the surprise of physicists.The fact that our universe is made of matter, not antimatter, is difficult to explain.We can naively assume that the universe started with equal, symmetrical amounts of matter and antimatter.So the absence of antimatter is puzzling.
The most likely explanation was first proposed by Andrei Sakharov, who designed the hydrogen bomb for the Soviet Union in the 1950s.Sakharov's theory says that at the beginning of the universe, the amounts of matter and antimatter were slightly asymmetric at the Big Bang.This slight symmetry violation is called "CP violation," and the phenomenon is currently at the center of many active research topics.In fact, Sakharov's theory states that all the atoms in the universe today are left over from a near-complete cancellation between matter and antimatter, the Big Bang causing a cosmic cancellation between the two.Small bits of leftover matter created the remnants that make up the visible universe today.All the atoms in our bodies are remnants of this gigantic collision between matter and antimatter.
This theory leaves open the possibility that small amounts of antimatter exist naturally.If so, finding its source would drastically reduce the cost of using antimatter inside an antimatter engine.In theory, deposits of natural antimatter would be easy to spot.When an electron and a positron meet, they cancel and become gamma rays with energies of 1.02 MeV or more.Thus, by scanning the universe for gamma rays with such energies, we can discover the "fingerprint" of natural antimatter.
In fact, the "source" of antimatter has been discovered by Dr. William Purcel of Northwestern University in the Milky Way, not far from the center of the galaxy.Apparently, there exists a stream of antimatter that created this typical 1.02 MeV gamma ray when it collided with ordinary hydrogen gas.If this strand of antimatter exists in nature, then other swarms of antimatter that were not destroyed in the Big Bang may also exist in the universe.
In order to search for naturally occurring antimatter more systematically, the PAMELA (Payload for Antimatter-Matter Exploration and LigHT-Nuclei Astrophysics) satellite was put into orbit in 2006. This is a Russian, A collaborative project between Italy, Germany and Sweden to search for antimatter.Earlier missions to search for antimatter were carried out using high-altitude balloons and space shuttles, so data were collected over a period of no more than a week.Instead, PAMELA will stay in orbit for at least 3 years. "It's the best detector ever built, and we're going to use it for a long time," said Piergiorgio Picozza of the University of Rome.
The purpose of PAMELA is to detect cosmic rays from common sources, such as supernovae, as well as from unusual sources, such as stars composed entirely of antimatter. PAMELA will specifically look for hints of antihelium, which may be produced inside antistars.Although most physicists today believe that the Big Bang caused a near-perfect cancellation between matter and antimatter, according to Sakharov, PAMELA is based on a different assumption — that the entire antimatter universe has no Lived through that cancellation, and thus exists today as an anti-stellar.
If antimatter exists in small amounts in outer space, it is possible to "harvest" some antimatter to propel a spacecraft. NASA's Institute for Advanced Concepts has taken the idea of harvesting antimatter in space very seriously. NASA recently provided a pilot program with the concept of funding research. "Essentially, what you want to do is weave a net, like you do when you're fishing," says Gerald Jackson of Hbar Technologies, the company responsible for the project. leading organization.
The Antimatter Harvester is based on three concentric spheres, each made from a sheet of gridded wire mesh.The outermost sphere is 16 kilometers in diameter and is positively charged, so it will repel any protons, which are positively charged, and it will attract antiprotons, which are negatively charged.Antiprotons will be collected by the outer sphere, then slowed down as they pass through a second sphere, and finally stop when they reach the innermost sphere, which is 100 meters in diameter.The antiprotons are then captured in a magnetic bottle and mixed with the positrons to create antihydrogen.
Jackson estimates that a controlled matter-antimatter reaction in a spacecraft could fuel a solar sail to Pluto using only 30 milligrams of antimatter. "Seventeen grams of antimatter," Jackson said, "is enough to power a stellar spacecraft to Alpha Centauri." Between the orbits of Venus and Mars, Jackson claims, there may be 80 grams that could be collected by space probes of antimatter.However, due to the complexity and enormous expense of bringing such a giant antimatter collector into service, it may not be possible before the end of this century or later.
Some scientists dream of harvesting antimatter from a meteor floating in space (the Flash Gordon comic strip once rendered a rogue meteor floating in space whose contact with any planet would create a horror explosion).If natural antimatter goes undiscovered in space, we'll have to wait decades or even centuries until we're able to produce huge quantities of antimatter here on Earth.But assuming the technical problems of producing antimatter can be solved, it might be possible for antimatter rockets to take us to the stars someday.
Because of our current knowledge of antimatter, and the foreseeable evolution of this technology, I classify antimatter rocket ships as "incredible first class".
What is antimatter?It seems odd that nature would double the number of subatomic particles in the universe for no good reason.Nature is usually very frugal, but now that we understand antimatter, nature seems extremely redundant and wasteful.If antimatter exists, can an antiuniverse exist?
To answer these questions, we must examine the source of antimatter itself.The discovery of antimatter dates back to the pioneering work of Paul Dirac in 1928.He was one of the most brilliant physicists of the 20th century.He holds the Lucasian Chair of Mathematics at the University of Cambridge, which was once held by Newton and is currently held by Stephen Hawking.Born in 1902, Dirac was a tall, thin 20-something when the quantum revolution broke out in 1925.Although he was studying electrical engineering at the time, he was suddenly swept up by a wave of interest in quantum theory.
Quantum theory is based on the notion that particles like electrons can be described not as point-like particles, but as some type of wave using Schrödinger's famous equation (the wave represents the energy that can be found at that point. particle possibility).
But Dirac realized that Schrödinger's equation had a shortcoming.It only describes electrons moving at low speeds.For fast-moving electrons, the equation fails because it doesn't obey the laws of fast-moving objects, the theory of relativity discovered by Albert Einstein.
The challenge for the young Dirac was to fix Schrödinger's equation to fit the theory of relativity.In 1928, Dirac proposed a radical modification of Schrödinger's equation that fully obeyed Einstein's theory of relativity.The physics community was shocked.Dirac discovered his famous relative equations for electrons purely by manipulating a higher mathematical object called a spinor.A mathematical curiosity suddenly became the center of the universe. (Unlike many of the physicists before him who insisted that major breakthroughs in physics should be based firmly on experimental data, Dirac took the opposite tack. For him, pure mathematics of sufficient beauty was the gateway to major breakthroughs He writes: "Having beauty in one's equations is more important than fitting them to experimental results, and if one has really sound insight, one is on the sure path to progress .”)
In the process of developing new equations for the electron, Dirac realized that Einstein's famous equation E=mc2 was not very accurate.Even though it's all over Madison Avenue, on kids' t-shirts, in cartoons, and even on superhero costumes, Einstein's equation is only partially correct, and the correct equation is actually E=±me2 (the reason why The minus sign, because we have to consider the square root of a certain quantity. Considering the square root of a quantity always introduces a positive or negative ambiguity.)
But physicists abhor negative energy.There is an axiom of physics which states that objects always tend towards the lowest energy state (this is why water always tries to stay at the lowest level - sea level).Since matter perpetually descends to its lowest energy level, the prospect of negative energies can be disastrous.It meant that all electrons would eventually jump sharply down to infinitely negative energy levels, whereby Dirac's theory would become unstable.Therefore, Dirac invented the concept of "Dirac sea".He imagined that all negative energy conditions would have been filled, so that electrons could not jump down to negative energy levels, and the universe would be stable.Likewise, a gamma ray may accidentally collide with an electron in a negative energy state and raise it to a positive energy state.We then see that the gamma ray turns into an electron and creates a "hole" in the Dirac sea.The hole would behave like a bubble in vacuum, ie: it would have a positive charge and the same mass as the original electron.In other words, the hole would behave like a positron.So, in this picture, antimatter consists of "bubbles" in a Dirac sea.
Only a few years after Dirac made this astonishing prediction, Carl Anderson actually discovered the positron (for which Dirac won the Nobel Prize in 1933).
In other words, antimatter exists because Dirac's equation has two solutions, one for matter and one for antimatter (and, in turn, this is a consequence of special relativity).
The Dirac equation not only predicts the existence of antimatter, but also the "spin" of electrons.Subatomic particles can spin, much like a spinning top.In turn, the spin of electrons is crucial to understanding electron flow in transistors and semiconductors, which underlies modern electronics.
Stephen Hawking lamented that Dirac did not patent his own equations.He wrote: "If Dirac patented the Dirac equation, he would make a fortune. He would collect royalties on every television, every Walkman, every video game, and every computer. "
Today, Dirac's famous equation is engraved on a stone tablet in West Westminster, not far from Isaac Newton's tomb.It is perhaps the only equation in the world to be awarded such a unique honor.
Historians of science have tried to understand how Dirac arrived at his revolutionary equations, and the concept of antimatter has often led him to be compared to Newton.Oddly enough, Newton has a lot in common with Dirac.Both were in their 20s when they completed their seminal work at Cambridge, both were mathematicians, and both shared another distinguishing trait: a complete lack of social skills to the point of pathology.Both had their reputations tarnished for their inability to join small conversations and basic social graces, Dirac was embarrassingly shy and would never say anything unless asked directly, after which he would answer "yes ’ or ‘No’, or ‘I don’t know’.
Dirac was also deeply humble and abhorred public knowledge.When he was awarded the Nobel Prize in Physics, he seriously considered turning down the award because of the visibility and trouble it would bring.But when it was pointed out to him that rejecting the Nobel would draw more publicity, he decided to accept it.
Numerous books have been written about Newton's eccentric personality, with numerous hypotheses - ranging from mercury poisoning to psychosis.But recently Cambridge psychologist Simon Baron-Cohen has come up with a new theory that may explain the strange personalities of Newton and Dirac.Barron-Curhoun announced that both may have Asperger's syndrome, which is close to autism, like the moron genius in the film "Rain Man."People with Asperger's syndrome are extremely unrevealing, socially awkward, and sometimes gifted with extreme computational abilities.But unlike people with autism, they can cope in society and hold productive jobs.If this speculation is correct, then the miraculous mathematical abilities of Newton and Dirac may have come at the cost of social isolation from other people.
Using Dirac's theory, we are now able to answer many questions: What is the antimatter counterpart of gravity?Do anti-universes exist?
As we've discussed, antiparticles have the opposite charge to ordinary matter, but particles that have no charge at all (such as photons, the particles of light; or gravitons, the particles of gravitation) can be their own antiparticles.We can see that gravity is its own antimatter, in other words, gravity and antigravity are the same thing.Therefore, antimatter would lie down under gravity instead of standing up (this is widely believed by physicists, but it has never been proven in the laboratory in fact).
Dirac's theory also answered deep questions: Why does nature allow antimatter to exist?Could this mean that anti-universes exist?
In some science fiction novels, the protagonist discovers a planet in outer space that is similar to Earth. In fact, that new planet is identical to Earth in every way except that everything is made of antimatter.We have anti-matter twins on this planet, have anti-children, live in anti-cities.Since the laws of antichemistry are the same as those of chemistry except that the charges are opposite, people living in such a world would never know that they are made of antimatter (physicists call this an inverse charge universe, or , because in this antiverse universe all charges are opposite, but everything else remains the same).
In other sci-fi stories, scientists discover Earth's twin brother in outer space, the difference being that it is a mirror universe.There, everything is reversed left and right.Everyone's heart is on the right side, and most people are left-handed.They spend their entire lives unaware that they live in a mirror universe that is upside down (physicists refer to such a mirror universe as a parity inverse universe, or ).
Is it really possible for such antimatter and equivalent reverse universe to exist?Physicists take the question of twin universes very seriously.Because when we simply flip the charge of all our subatomic particles, or reverse the orientation of left and right, the equations of Newton and Einstein remain the same.Thus, C-reverse and P-reverse universes are possible in principle.
Nobel laureate Richard Feynman posed an interesting question about these universes: "Suppose that one day we were in radio contact with aliens on a distant planet, but could not see them, could we Does the radio explain to them the difference between 'left' and 'right'?" he asked.If the laws of physics allow a P-verse universe to exist, it should be impossible to convey these concepts.
Certain things, he reasoned, are easy to communicate, such as the shape of our bodies and how many fingers, arms, and legs we have.We could even explain the laws of chemistry and biology to aliens.But if we try to explain to them the concepts of "left" and "right" (or "clockwise" and "counterclockwise"), we fail again and again.We will never be able to explain to them that our heart is on the left side of our body, which is the direction the Earth spins, or the direction the DNA molecule spirals.
Therefore, Yang Zhenning and Li Zhengdao, both at Columbia University, caused a sensation when they proved this precious proposition wrong.By carefully observing the properties of subatomic particles, they proved that mirror universes, P reverse universes, cannot exist.After learning of this revolutionary result, a physicist said: "God must have made a mistake." Due to the significance of this research conclusion called "overthrow of parity", Yang Zhenning and Li Zhengdao won the Nobel Prize in Physics in 1957.
For Feynman, this conclusion meant that if you were talking to aliens by radio, you couldn't build an experiment that would allow you to tell the difference between left-handed and right-handed universes just on the radio (e.g., Electrons emitted by radioactive cobalt-60 do not spin in equal numbers clockwise and counterclockwise, but in fact spin in a preferential direction, thus breaking parity).
Feynman even imagined a historic meeting between aliens and humans that would eventually take place.We ask the aliens to hold out their right hands when we first meet, and we will shake hands.If the aliens do extend their right hand, then we know we have successfully taught them the concepts of "left and right" and "clockwise and counterclockwise".
But then Feynman had a disturbing idea.What if the aliens held out their left hands?This means that we made a fatal mistake, we failed to make them understand the concept of "left" and "right".Worse, this means that the aliens are in fact made of antimatter, and they performed all the experiments in reverse, thus confusing "left" and "right".That means we explode when we shake their hands!
That was our understanding before the 1960s.It's impossible to tell the difference between our universe and a universe where everything is made of anti-universes and parity is flipped.If you reverse both parity and charge, the resulting universe obeys the laws of physics.The parity itself is reversed, but the charge and parity are still nicely symmetric in that universe.So one is still possible.
This means that we talk to aliens on the phone, and we cannot account for a normal universe and a universe with reversed parity and reversed charge (that is, left and right are swapped and all matter becomes antimatter ) between different.
Then, in 1964, physicists received a second shock: CP reverse universes cannot exist.By analyzing the properties of subatomic particles, it is still possible to tell the difference between left and right, clockwise and counterclockwise while talking over the radio with another CP reverse universe.For this work, James Cronin and Val Fitch were awarded the Nobel Prize in 1980.
(While many physicists were saddened when a CP reverse universe was shown to defy the laws of physics, it is good to see this discovery in hindsight, as we discussed earlier. If a CP reverse universe might exist, Then the original big bang should have involved exactly the same amount of matter and antimatter, and therefore 100% cancellation should have occurred, then our atoms could not exist! We act as a cancellation between uneven amounts of matter and antimatter The fact that the CP exists as a residue is evidence that CP is not conserved.)
Are any reverse anti-universes possible?The answer is: yes.Even if reverse-parity and reverse-charge universes are impossible, anti-universes are still possible, but it would be a strange universe.If we reverse the order of charge, parity, and time, the resulting universe obeys all the laws of physics.is allowed to exist.
Time reversal is a weird symmetry.In one, a fried egg jumps off a dinner plate, reforms in a frying pan, then jumps back into the egg, sealing the cracks; their mother's womb.
Common sense tells us that T reverse universe is impossible.But the mathematical equations for subatomic particles tell us otherwise.Newton's laws work perfectly both forwards and backwards.Imagine filming a game of pool, where every collision of the balls obeys Newton's laws of motion.Playing such a tape would make for a wacky game, but Newton's laws allowed for it.
In quantum theory, things are more complicated. The T inverse itself violates the laws of quantum mechanics, but the complete CPT inverse universe is allowed.This means that a universe where the left and right are reversed, matter becomes antimatter, and time runs backwards follows the laws of physics, which is perfectly fine.
(The irony is that we cannot communicate with such a reverse CPT world. If time runs backwards on their planet, that means everything we tell them over the radio is part of their future, so they will Forget everything as soon as we talk to them. So, although the CPT reverse universe is allowed under the laws of physics, we cannot talk to any CPT reverse universe aliens by radio.)
Overall, if enough antimatter could be produced on Earth, or found in outer space, antimatter engines might give us the definite possibility of fueling distant starships.Since CP is not conserved, there is a slight imbalance between matter and antimatter, which may in turn mean that there is a large amount of antimatter still present and able to be harvested.
However, due to the technical difficulties involved in antimatter engines, it may take a century or more to develop this technology, making it a "first-class incredible".
However, let's face another question: Will faster-than-light stellar spacecraft be possible thousands of years from now?Is there a loophole in Einstein's famous quote "Nothing goes faster than light"?Surprisingly, the answer is yes.
Notes:
Notes: