New insight into elusive antimatter can help unravel universe's mysteries

December 20, 2016 by Niels Madsen, The Conversation
When particles collide. Credit: Andrey VP/www.shutterstock.com

Physicists have believed that the universe is made of both matter and antimatter since the 1930s. While we are well aware of what the physical matter is, antimatter has remained an elusive substance.

But that is about to change: our newly-published research on antihydrogen – the antimatter counterpart of hydrogen – heralds a new era in the effort to understand more about antimatter and how it has managed to evade us.

So what is antimatter? In the late 1920s, Paul Dirac predicted the existence of "mirror" particles – opposite counterparts to the already known electrons and protons. These mirror particles had opposite charge so they were a positive electron and a negative proton – later named positron and antiproton. The positron was discovered a few years later in 1932, but it took scientists until 1955 to discover the antiproton.

The discovery was tricky as antimatter doesn't seem to be prevalent in the universe. In fact, the antiproton was only discovered because a particle accelerator was built specifically to create them.

According to Einstein's famous equation E=mc² mass can be converted to and vice versa. The accelerator worked by supplying enough energy to create antiprotons by converting energy to mass. Mass is a compact holder of energy, but not all of it can normally be released – even a nuclear weapon only releases a tiny fraction of the energy of its mass.

When a particle and its antiparticle are brought together, they annihilate each other – that is they collide and disappear – and all their mass energy is released in a burst of light. The opposite is also true: with sufficient energy, we can create matter, but like annihilation, this process is also symmetric, so matter and antimatter will always be created in equal quantities.

This is the process by which the first antiproton was created, and it is still what we use today. But it is incredibly inefficient: in a typical creation process at the CERN antiproton decelerator, about 1m protons are collided with a metal target to yield a single antiproton.

Why does it matter?

Physicists believe that the universe was created in the Big Bang billions of years ago, and in particular that it started out so hot and tiny that no particles could form at the very start. As this primordial energy soup cooled, particles and antiparticles formed in equal quantities. But less than a second after the Big Bang, something happened that caused an asymmetry, leaving a small excess of matter behind. So where did all the antimatter go? We simply don't know – this is one of the greatest mysteries of physics.

There is no explanation for this asymmetry, in fact we cannot explain how we can be here, as this asymmetry is required for the universe we know to exist.

Despite many lifetimes of careful observation of the skies, so far no clues have been found to tell us why there is this asymmetry between matter and antimatter. Many scientists have looked in various ways at antimatter, to try to unravel if there is some fundamental difference between it and matter that could have caused this asymmetry. The traditional method is to look at the results of high energy collisions, for example by using the large hadron collider at CERN. However, we are now pursuing a very promising alternative to this.

Hydrogen is the most abundant substance in the universe and consists of just one electron and one proton. It's fair to say that it is the best understood system in physics, both experimentally and theoretically. It also played a key role in the discoveries that led to quantum mechanics. The internal properties of hydrogen have been studied to staggering precision using lasers, and the energy difference between its ground state and the first – where it has excess energy – is known in detail. It is similar to a guitar string – its means the string is not vibrating and an excited state means it is. The more it is vibrating, the more excited it is.

For more than 30 years, researchers have been working to unravel the mystery of antimatter using antihydrogen, and we have just accomplished a major breakthrough.

What we have just done is to shine laser light on trapped antihydrogen atoms and excite them to their first excited state. We can study their behaviour as they gain energy from the laser light (get excited). Eventually, they break apart – that's how we could tell they had absorbed the energy.

One reason it has been so hard to do this is that antimatter is always annihilated when it encounters matter. This makes it challenging to store – you can't just put it in a bottle. However, we have already managed to make and hold antihydrogen using an array of electromagnets that can constrain it, which allowed us to do this research.

This very first measurement allows us to compare hydrogen and antihydrogen with unprecedented precision – indeed, it is the most precise comparison of an atom and an antiatom ever made.

Using this measurement, they look identical, and though that was to be expected, it is the first experimental confirmation. For now, the mystery of the elusive continues – but it is something we are continuing to pursue.

Explore further: ALPHA observes light spectrum of antimatter for first time

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Seeker2
1 / 5 (1) Dec 20, 2016
Antimatter was banned to the outermost reaches of spacetime during baryogenesis when the U was much smaller. Like when you could go from any two points in the U in less than a second. It was banned because its energy density is less than that of the dark energy it was created from. As spacetime expanded and cooled, or does expand and cool, its energy density drops below that of antimatter, in which case antimatter will become attractive. That is it switches from being antigravitational to normal gravitation. But its energy density is less than that of normal matter so it will still be less gravitational. Detecting this difference is going to be very interesting if it can ever be. Anyway we may all be collected into black holes before antimatter becomes gravitational. But it will come back. And when it does watch out.
Seeker2
1 / 5 (1) Dec 20, 2016
Just to push this speculation a bit further, and why not? During inflation the U was an expanding white hole and antimatter collected at the event horizon inside this white hole. At present we are in exponential expansion which explains the accelerating expansion if I got the math correct. Actually I don't even know if a white hole has an event horizon. Makes a good story anyway.
Benni
2.3 / 5 (3) Dec 20, 2016
Actually I don't even know if a white hole has an event horizon. Makes a good story anyway.
......glad you cleared that up in a hurry, for a few seconds there you had me sitting on the edge of my chair.
Elmo_McGillicutty
1 / 5 (3) Dec 21, 2016
Antimatter is just regular matter that has been inverted. There is no mystery here.

antialias_physorg
4.2 / 5 (5) Dec 21, 2016
Antimatter is just regular matter that has been inverted.

...gets my vote of most information-free comment of the year.
Do you have any more of these gems? Feel free to post them (anywhere but here, that is.)
Elmo_McGillicutty
1 / 5 (5) Dec 21, 2016
Academic dogma is our science today. If you are willing to abandon this religion.....and get back to science......I am willing to explain all phenomena to you. But it requires a very scarce entity. And that is common sense and an open mind.

I can not tell you how the universe came into existence, nor when it happened. But I can explain ALL the components of the cosmos and how they interact. There is no such thing as randomness or probability. Only an puzzled mind needs such concepts.
Seeker2
5 / 5 (1) Dec 21, 2016
...I am willing to explain all phenomena to you.
Another Oh Great Swami? David Letterman would love it.
antialias_physorg
4 / 5 (4) Dec 21, 2016
But I can explain ALL the components of the cosmos and how they interact.

Please. Do. This we've all got to hear. (*grabs popcorn*)
Elmo_McGillicutty
1 / 5 (3) Dec 22, 2016
My pleasure. The self repulsiveness of charge is the primal force of nature. A charged particle is a suspended explosion. The explosion is not frozen or locked.......it is continuously turned. A charge is a rotating electric field trying to explode out, during which, generates a magnetic field, which confines and turns all of the explosion in a common direction. It has two perpendicular rotations at the same time. These counter-balancing forces result in a structure similar to a stripe on a hula hoop. Not the hoop....the stripe. The two fields of this structure rotate at c. The perpendicular rotating fields are what you call inertia. The density of those fields is what you call mass. This density and inertia is controlled by the number of turns on the stripe. When a magnetic turn is added (number of turns on stripe) ....it compresses the diameter of the hoop. As the energy and density of the charge increases.....the size of the particle decreases. Continued......
Elmo_McGillicutty
1 / 5 (3) Dec 22, 2016
If the particle stripe (stripe, not hoop) is rotating to the right, the magnetic momentum is parallel to the electric momentum. This has a self locking effect, which cause a proton to keep it's mass, which is it's field density. If the particle stripe rotates left.....the magnetic momentum is anti-parallel to the electric momentum and has a self un-locking effect. This causes an electron to shed it's mass. The proton is about 300 to 500 times smaller than an electron. 99% of all cosmic energy and mass is in the proton. With the proper polarity and speed of either an electric or magnetic field, we can unfold or expand a proton. You call it a positron. We can also greatly contract an electron....you call that an anti-proton.

If you were more familiar with true particle dynamics...you could understand dipole dynamics. And if you were familiar with true dipole action, I would explain gravity to you. Gravity comes from dipole action, not mass.
antialias_physorg
4 / 5 (4) Dec 22, 2016
You do realize you are completely insane? That is the most crazy garble of words I have had the displeasure to skim.
Seeker2
not rated yet Dec 22, 2016
The Irish patron saint of fire. I guess.
Seeker2
not rated yet Dec 23, 2016
Antimatter was banned to the outermost reaches of spacetime during baryogenesis when the U was much smaller. Like when you could go from any two points in the U in less than a second. It was banned because its energy density is less than that of the dark energy it was created from.
How could I make such a claim? Suppose instead of particle/antiparticle pair creation think of miniature black hole/white hole pair creation, if such a thing is possible, sharing the same event horizon. Energy in one hole is trapped inside the event horizon and in the other an equal amount is trapped outside the horizon, spinning I suppose in the opposite directions thus having different charge. The one outside the horizon is going to require more volume or displacement of space than the one inside the horizon. Hence it will have a lower energy density. Just a thought.
Seeker2
not rated yet Dec 23, 2016
cont
It should be radiation not dark energy. Maharishi will get it right eventually.
Seeker2
not rated yet Dec 23, 2016
...The one outside the horizon is going to require more volume or displacement of space than the one inside the horizon. Hence it will have a lower energy density.
As a matter of fact if they didn't have different energy densities then the particle and antiparticle would probably never separate under radiation pressure and form real particles.
nikola_milovic_378
Dec 29, 2016
This comment has been removed by a moderator.
nikola_milovic_378
Dec 29, 2016
This comment has been removed by a moderator.

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