Tag: Anti-Matter

Does our Universe have a twin, an anti-matter Universe that is running backward in time? It would answer a lot of the questions we have about this Universe.    

Physicists are always fascinated by symmetries in the world around us. For example there appears to be exactly the same number of positively charged particles as there are negatively charged particles. At the same time there are just as many north magnetic poles as south magnetic poles.

Our hands are of course the best example of symmetry. They look identical but in fact are exact opposites, mirror images of each other. (Credit: Charlie Fox Signs)
One of the most fundamental symmetries in the Universe is that all magnets have both a north and a south pole. (Credit: Northeastern University)

Another big symmetry appears when we look at the distribution of galaxies throughout the Universe as a whole. In whatever direction we look there are the same sorts of galaxies in roughly the same density. In terms of space the Universe appears to be very symmetrical.

The Hubble Deep Field Image. In whatever direction we look the Universe is filled with countless galaxies, a symmetric Universe. (Credit: Hubble Space Telescope)

Not so in time. We know that the Universe is expanding; Carl Hubble made that discovery more than 90 years ago now. So in the distant past, billions of years ago, all of those galaxies would have been much closer together than they are today. And going even further back all of the matter in the Universe would have formed one big, dense hot cloud, a big bang. So why should time be different from space.

Starting with the Big Bang itself the Universe has changed over time, evolved. The Universe may be symmetric in space but it definitely not symmetric in time. (Credit: Owlcation)

After all Einstein’s Theory of Relativity tells us that time should really be treated mathematically in the same way as space, a principal know as covariance. And all of the experiments we perform in big atom smashers like the ones at CERN or Fermilab confirm Einstein’s ideas.

The Large Hadron Collider (LHC) at CERN is the world’s largest and most powerful scientific instrument. Smashing elementary particles together at tremendous energies accelerators like the LHC have taught us much about the way the Universe works. (Credit: Forbes)

Another big lack of symmetry that has physicists confounded is that between matter and anti-matter, those mysterious mirror particles that have the same mass but opposite charge of the matter particles that form everything we know. Another curious fact about anti-particles are that when they come in contact with their ‘normal’ matter counterpart the two annihilate each other becoming photons of light. Matter into energy, just as Einstein said. Again, both our theories and the experiments performed at high-energy physics labs all tell us that anti-particles should be generated just as often as particles, that there should be just as much anti-matter in the Universe as matter.

The first evidence for the existence of anti-matter. The streak in this could chamber is an anti-electron, also known as a positron. (Credit: Twitter)

But there isn’t, certainly not in our Solar System because since the solar wind touches every planet, moon and etc. we’d see the energy from matter anti-matter annihilation if say Jupiter were anti-matter. And that also means that our galaxy can’t contain anti-matter since the interstellar medium touches every star system and again, we don’t see any sign of matter anti-matter annihilation.

Matter and anti-matter don’t get along. Whenever a particle meets its anti-particle the two annihilate each other to produce photons of light, pure energy. (Credit: Center for Astrophysics and Supercomputing)

What about different galaxies you ask? Couldn’t some of them be composed of anti-matter? Well maybe, but astronomers have also seen a number of galaxies that are colliding with other galaxies and once more there are no signs of the type of energy release that would indicate matter and anti-matter in contact. That leaves physicists with the question, where is all of the anti-matter?

So physicists are faced with two instances of non-symmetry, in time and in matter / anti-matter. And since physicists are clever people it isn’t surprising that someone thought to use one problem to solve the other. You see back in the 1950s physicist Richard Feynman suggested that the best way to think about anti-particles, his paper was explicitly about anti-electrons, was to consider them as normal electrons going backward in time. That way when an electron, going forward in time, collides with an anti-electron, going backward in time they turn into photons who, according to relativity, do not travel in time, perfect symmetry.

Feynman diagram of electron-positron annihilation. The positron. the anti-electron is the e+ portrayed as going down, that is backward in time. (Credit: Physics Stack Exchange)

So let’s go with that thought, let’s assume that all anti-matter is just normal matter going backward in time. Then what happened to all of the anti-matter that should have been created by the big bang? Well it went backward in time and exists before the big bang. The Universe before the big bang was made up of an amount of anti-matter equal to the matter in the Universe after the big bang. Perfect symmetry.

The anti-matter Universe on the left perfectly balances the matter Universe on the right, restoring symmetry in both time and matter/anti-matter. (Credit: Semantic Scholar)

Time symmetry is restored as well because whatever the Universe looks like at a certain time t after the big bang the Universe looked exactly the same way, on a large scale at least, at the same time t before the big bang. This new model of the Universe uses its anti-matter component as a mirror to fully restore symmetry.

In ‘Alice through the Looking Glass’ by Lewis Carroll Tweedle-Dee and Tweedle-Dum are not twins but rather right and left versions of each other, perfectly symmetric. (Credit: Vanity Fair)

This is the basis of a new paper by physicists Latham Boyle, Kieran Finn and Neill Turok of the Perimeter Institute for Theoretical Physics in Waterloo Ontario in Canada along with the University of Manchester in the UK. In doing their calculations the physicists also discovered that their new, symmetric model of the Universe had a couple of other advantages as well. For one thing the period of rapid expansion called inflation immediately after the big bang proposed by Alan Guth back in the 1970s to account for the almost perfect flatness of the Universe is simply not needed. The model proposed by Boyle, Finn and Turok provides a flat Universe full of particles naturally, without the ‘ad hoc’ insertion of inflation.

In order to provide the flat Universe we see today Alan Guth invoked what he described as ‘cosmic inflation’, but no one has been able to determine exactly what caused the inflation. The new matter / anti-matter symmetric Universe doesn’t need inflation to be flat. (Credit: Medium)

Another feature of the model is that it requires a fourth type of neutrino, those mysterious ‘ghost’ particles that very rarely interact with more normal particles. The researchers think that their fourth neutrino species could provide the basis for the missing dark matter, maybe solving yet another problem in astrophysics.

In order to observe any neutrinos physicists have to build enormous chambers whose walls are covered with detectors. Such experiments capture maybe one or two neutrinos a day! (Credit: Nature)

So, how do we go about proving that this new model is the correct one? After all it seems like new models of the Universe are being proposed nearly every week. Well, finding that neutrino would be a good start but physicists have been looking for ‘sterile’ neutrinos for a long time now without success.

The researchers also propose another way. Theories of inflation all predict that the rapid expansion at the beginning of the Universe should have produced large amounts gravitational waves, waves that the scientists at LIGO and Virgo gravity wave observatories may soon be able to detect. But if inflation didn’t happen, if the Universe is symmetric instead, then the search for primordial gravity waves will fail.

It is hoped that soon gravity wave detectors such as Virgo here in Italy may soon be able to detect gravity from the early Universe itself. That data may provide evidence for the Matter / Anti-matter Universe. (Credit: ResearchGate)

Of course it would be so much simpler if we could somehow look back before the big bang to see if there was an anti-matter Universe back then. But that’s impossible! Isn’t it?

For the last ten years an experiment aboard the International Space Station (ISS) has been counting cosmic ray events. What has it discovered about those mysterious high-energy particles.

At the beginning of the 20th century physicists were shocked to discover various substances that were emitting particles sub-atomic in size yet possessed energies that per particle were enormous, far greater than could be explained by the chemical reactions that were known at the time. The alpha and beta particles that were found coming from Uranium and other heavy elements defied everything that ‘classical physics’ understood. Remember at this time an atom meant something indivisible, nothing smaller and the concept of nuclear energy had to wait for the concept of a nucleus.

Antoine Henri Becquerel (l) visiting the Curies Pierre (m) and Marie (R). These three scientists would be awarded the 1903 Nobel Prize in Physics for their discovery of radioactivity. (Credit: Linda Hall Library)

An even bigger shock came when such particles were found to be shooting through the very air around us. At first scientists thought this radiation had to be coming from substances in the ground. To test that theory in 1912 physicist Victor Hess equipped a balloon with instruments that could detect the particles. He rode the balloon several kilometers into the air expecting that the intensity of the radiation would decrease as the balloon rose. Instead it got stronger. At an altitude of five kilometers Hess found that the intensity was twice as strong as at sea level. The particles were coming from outer space. They were cosmic rays!

Victor Hess preparing to take one of the balloon flights where he proved the radiation was coming to Earth from Outer Space. (Credit: The New York Times)

  Ever since then physicists have studied these mysterious particles hoping to learn where they come from and how they were accelerated to such enormous velocities and energies. In 1932 another mystery was added when the first ever anti-particle, an anti-electron was found in cosmic rays by the physicist Carl Anderson. For their work on cosmic rays Hess and Anderson would share the 1936 Nobel Prize in physics.

Physicist Carl Anderson with the first photograph of a cosmic ray Anti-electron. (Credit: Famous Scientists)

After a lot of hard work researchers recognized one thing, the cosmic ray particles they were studying at the Earth’s surface were not the original particles. You see when a particle moving through space at nearly the speed of light enters the Earth’s atmosphere it will quickly strike the nucleus of either an oxygen or nitrogen atom, often smashing that nucleus to bits. Those bits receive energy and momentum from the original particle and so continue downward, sometimes striking other nuclei in a cascading reaction. The bits from the collisions are what physicists see down here at Earth’s surface, only rarely does the original particle reach our instruments. (Actually that’s a good thing, our atmosphere acts as a shield protecting life down here at sea level from most of the radiation.)

The high energy particles we see here at Earth’s surface are actually not the primary cosmic rays but rather the fragments of numerous collisions triggered by the original particle. (Credit: CERN)

So in order to study the primary cosmic ray particles physicists have to get their detectors above the atmosphere and ever since the beginning of the space age they’ve tried to do just that. Early instruments put aboard the Skylab Station and taken into space by the Space Shuttle discovered that there were two distinct types of cosmic rays; one type came from the particles that make up the solar wind. The other type, which are usually more energetic, come from outside our solar system, some perhaps even from outside our galaxy.

The first Alpha Magnetic Spectrometer (AMS-1) was carried into orbit aboard the space shuttle. (Credit: Symettry Magazine)

The most sophisticated instrument sent into orbit thus far is the Alpha Magnetic Spectrometer-2 (AMS-2) which for the last ten years has been attached to the outside of the International Space Station (ISS). During that time the AMS-2 has detected, measured and recorded over 44 million cosmic ray events every day. More than 160 billion cosmic ray particles have been cataloged by the instrument.

The Alpha Magnetic Spectrometer 2 (AMS-2) instrument has been attached to the outside of the International Space Station (ISS) for ten years now.

As a cosmic ray particle enters the AMS-2 its velocity is measured by either a Transition Radiation Detector (TRD) for high-energy particles or a Time of Flight Counter (TOF) for low energy particles. Inside the AMS-2 a permanent magnet causes the particle’s path to curve, the degree of curvature giving information about the particle’s mass. Finally a calorimeter measures the particle’s total energy. Using these pieces of data the physicists can both identify the cosmic particle, element and isotope, as well as its total energy.

The AMS-2 is a highly complex and sophisticated instrument that has measure the properties of over 160 billion cosmic ray particles. (Credit: ESA Earth Online)

What the AMS-2 has discovered about the cosmic rays coming from outside our solar system is first of all that they broadly fall into three categories, electrons, atomic nuclei and anti-matter particles; I’ll save the anti-matter for later. Electron intensity at high energy has been shown to be largely suppressed and we have a pretty good idea of why. You see because of their tiny mass, 1/2000th that of a proton, high-energy electrons traveling through interstellar space get pushed around by the magnetic field of the galaxy causing them to lose their energy and they cease to be part of the cosmic rays after only a few hundred light years.

Some of the results from AMS-2 for electrons and positrons (anti-electrons). (Credit: AMS Collaboration)

Protons and atomic nuclei manage to maintain their energies much further, 2000 times further or more. And keeping in mind that a proton is also the nucleus of a hydrogen atom what the measurements made by AMS-2 tell us is that cosmic ray particles are pretty much just normal stellar matter. That is about 80% of cosmic rays by mass are hydrogen nuclei (Protons) about 20% by mass are helium nuclei while all of the remaining elements make up less than 1% by mass. In fact this is just about the proportions we see when we measure the constituency of the matter in our Sun and nearby stars. The majority of cosmic rays are simply the nuclei the normal atoms that have somehow been accelerated to enormous velocities.

The cosmic ray spectrum, flux of particles versus energy as measured by AMS-2 and other experiments. Since we now have good measurements of how much energy these particles have the question is now, where do they get that energy? (Credit: SpringerLink)

Then there are the anti-matter particles and in truth the real purpose, the juicy meat of the AMS-2’s program was to detect and measure as many anti-particles as possible. You see most of the theories about how the big bang happened say that our Universe should consist equally of matter and anti-matter, but there’s virtually no anti-matter here on Earth or in our solar system. What anti-matter there is comes from high-energy collisions, like those from cosmic rays, and the anti-particles don’t last long.

All of our experiments at atom smashers, along with all our theories tell us the there should be as much anti-matter as matter in our Universe. So where is it? (Credit: Science Notes)

Our observations of the Milky Way also rule out any large amounts of anti-matter in our galaxy. In fact most astronomers think it highly unlikely that there are any anti-matter galaxies within at least 100 million light years. So where is all of the anti-matter, are there anti-matter galaxies anywhere in the observable Universe? That’s one of the big questions it was hoped that AMS-2 would help to answer.

And AMS-2 has provided quite a bit of data that has given physicists a lot to think about. The intensity of anti-electrons for one thing is about five times higher than can be accounted for by established theories. This has raised the possibility that the excess anti-electrons are produced by ‘physics beyond the standard model’ such as the decay of ‘dark matter’ particles.

AMS-2 has also found an excess number of anti-protons in the cosmic ray flux and physicists are trying to determine how well their models predict the number and energy spectrum. Remember single anti-particles are regularly produced in cosmic ray collisions. The big news however has to be the ‘preliminary’ detection of eight anti-helium nuclei. Now because of its importance these detections are being carefully scrutinized, any possible kind of contamination eliminated, nevertheless the data has physicists very excited.

The Anti-Proton to Proton ratio in the primary cosmic rays. There are about one anti-proton for every 10,000 protons but the ratio is pretty flat as a function of energy. (Credit: CERN Document Server)

After all, if the discovery of anti-helium is confirmed that would mean that somewhere in the universe there is an anti-star, a star composed entirely of anti-matter, producing anti-helium by the process of fusion, just as our Sun produces helium by fusing hydrogen. Somewhere, a billion light years or more away, there are anti-galaxies with anti-stars and anti-planets, maybe with anti-people living on them.

Is there an entire Universe composed of anti-matter, and how would we ever know? (Credit: American Physical Society)

Or are they the real people and we’re the anti-people?

Oh, you may have noticed that I’ve haven’t discussed the theories physicists have concerning how cosmic ray particles ever get so much energy. I’m saving that for a later post!

The Alpha Magnetic Spectrometer aboard The International Space Station and its search for an Anti-Atom.

It was some ninety years ago now that physicist Paul Dirac first suggested the existance of anti-matter and only a little more than a year later that another physicist, Carl Anderson observed anti-electrons (he called them positrons) in cosmic rays striking the Earth. In the years since then physicists have not only observed many different anti-particles but actually produced them using particle accelerators like the Large Hadron Collider (LHC) at CERN. We also know that the collisions of cosmic ray particles in outer space produce single anti-particles because we often observe them as well.

Anti-Matter differs from ordinary Matter by a switching of the charge. (Credit: Popular Mechanics)

In fact all of the experiments we have performed with our particle accelerators, and all of the theories we have developed tell us that there should be exactly as much anti-matter in the Universe as there is matter. The big bang should have produced just as much anti-matter as matter. But there certainly aren’t large amounts of anti-matter, not anywhere around Earth at least.

The logic goes like this: The Earth is made of matter and since the solar wind is in contact with the Earth’s upper atmosphere without causing matter/anti-matter annihilation it must be made of matter as well, so the Sun is made of matter. Since the solar wind is also in contact with everything else in our solar system as well all of the planets; moons and etc must be made of matter just as the Earth is. (Let’s not forget that we have now landed probes on several other bodies so they certainly aren’t anti-matter)

Matter and Anti-Matter annihilate each other producing Energy (Credit: Fandom)

We can even go further because the solar wind reaches out into the interstellar medium where the gas and dust particles must be made of matter or again they would interact with the solar wind. Finally that means that, since all the solar winds from all of the other stars in our galaxy are also in contact with the interstellar medium all of the stars in our galaxy must be made of matter.

What about other galaxies? You may ask. Could there be entire anti-galaxies made of anti-matter out there? And if so, how would we know? That question has been the subject of much debate over the last half a century.

Again, here’s the logic: if anti-galaxies do exist then they must have anti-supernova that produce anti-cosmic ray nuclei just as normal cosmic ray nuclei are produced in our galaxy. Eventually a very few of those anti-cosmic ray nuclei will find their way to Earth and if our scientists could find a single undeniable anti-nucleus that would be strong evidence that there are anti-galaxies with anti-stars out somewhere out there.

That’s the goal of the Alpha Magnetic Spectrometer (AMS-02) currently operating aboard the International Space Station (ISS). Launched into space by the space shuttle on the 16th of May in 2011 the AMS-02 has been observing cosmic ray particles above our atmosphere now for eight years.

The AMS-02 Mounted on the International Space Station (Credit: NASA)

(By the way, yes there was an APS-01, a Proof-of-Concept model that went into space with the Space Shuttle Discovery in 1998.)

The AMS-02 operates in many ways like one of the detectors at CERN or one of the other high energy physics labs. First ignoring any particles that do not pass from the top to the bottom the AMS-02 measures the time each particle takes passing through, that gives particles velocity. At the bottom the particle then enters a calorimeter which measures the particles energy. Once you know the velocity and energy you can calculate the mass and together they tell you what kind of particle it is.

Breakdown of the Components of the AMS-02 (Credit: NASA)

Finally the whole detector is surrounded by a large permanent magnet. The magnetic field will bend the path of charged particles and if you know what kind of particle it is, and the direction it bends you know whether it’s matter or anti-matter.

AMS-02 has spent the last eight years searching for an anti-helium nucleus and so far found nothing. Physicists feel that this result puts a very strong constraint on the possibility of large amounts of anti-matter existing anywhere in the observable Universe. It really appears that for some reason still unknown the big bang produced only matter, even though much less powerful interactions since then have always produced matter and anti-matter in equal parts.

If you’d like to learn more about the Alpha Magnetic Spectrometer (AMS-02) click on the link below to be taken to NASA’s webpage for AMS-02.

https://ams.nasa.gov/

There is obviously still a lot to be learned about how our Universe came into being.

Scientists at CERN take Anti-Matter for a Sunday Drive, and just what is Anti-Matter anyway.

We’ve all heard about anti-matter. We’ve been told that anti-matter is made up of anti-particles which are some weird mirror images of familiar particles like the electron or proton. We’ve also know that whenever a particle and its anti-particle come in contact they annihilate each other leaving only a burst of energy.

I know that anti-matter seems like the stuff of science fiction, after all doesn’t the starship Enterprise in Star Trek have matter / anti-matter engines. Anti-matter isn’t real, it’s just some strange theory that Einstein or some other physicist thought up, right?

It’s true that the English physicist Paul Dirac predicted the existence of anti-matter in 1926 as he was trying to mathematically combine Einstein’s special theory of relativity with quantum mechanics. What Dirac’s calculations told him was that for every kind of particle there should be another particle, having the same mass but the opposite charge. Even Dirac wasn’t certain what to make of his own prediction.

It was only six years later in 1932 however that the first picture of an anti-particle was taken by the American physicist Carl Anderson who was doing research on the cosmic ray particles striking our planet from outer space. That first evidence of the reality of anti-matter is shown below in a picture made in what is known as a cloud chamber.

First Photograph of an Anti-Particle taken by Carl Anderson (Credit: Public Domain)

Since the time of Dirac and Anderson physicists have continued to study anti-matter in cosmic rays. Not only that but they have also used their high-energy atom smashers; we call them particle accelerators nowadays, to actually manufacture anti-matter.

How do they manufacture anti-matter you ask? Well if a particle and anti-particle annihilate each other leaving only energy, then energy can be separated into a particle and its particular anti-particle. Out of the debris that comes from collisions in particle accelerators we have found the anti-particle of nearly every known particle. The photon of light is an exception because it is actually its own anti-particle! Below is an image taken of the products of some of these collisions along with a breakdown of what is happening.

Bubble Chamber Photograph from CERN (left) along with analysis of interactions (Credit: CERN)

Handling the anti-matter is obviously a delicate task but slowly scientists are learning how to confine charged anti-particles in a vacuum bottle with a magnetic field that keeps the particles from even touching the bottle’s walls. Using such a magnetic bottle the physicists at CERN now plan for the first time to transport anti-protons from the labouratory where they were produced to another labouratory at the CERN facility.

You see the physicists working on the PUMA experiment (that’s the anti-Proton Unstable Matter Annihilation experiment) are studying the structure of Protons and Neutrons in large, unstable nuclei. The researchers working on PUMA intend to use the anti-protons as probes that can tell them a great deal about the arrangement of the protons and neutrons in the nuclei that they study.

You remember from high school that the nucleus of every atom is made up of protons and neutrons. You may also recall that the lighter, more stable nuclei like Carbon-12 have six protons and six neutrons, an equal number of each. However large unstable nuclei like Uranium have more neutrons, 146 than protons 92 and physicists want to learn the details of how the different particles arrange themselves.

Now an anti-proton will annihilate a proton but it will also react with a neutron in a different way so observing the reactions will paint a picture of the structure of the target nucleus. The planned setup for the PUMA experiments is shown in the image below.

Outline of PUMA experiment at CERN (Credit: Nature)

There are still a lot of things we don’t know about anti-matter and scientists will continue to study these mirror particles for years to come. However it is a measure of how much we’ve learned that we are now using anti-matter to study other phenomenon.