What's Happening With Antimatter at CERN? Scientists Are Stumped Again

Summary

The video explores the enigmatic world of antimatter, delving into its discovery, theoretical predictions, and experimental observations. It highlights the historical detection of antimatter, the predictions made by Dirac's quantum field theory, and the subsequent experimental confirmations. The video also discusses the baryonic asymmetry of the universe and the ongoing quest to understand the differences between matter and antimatter, focusing on the weak force's distinct interaction with particles and antiparticles. The discussion culminates with the ALPHA experiment at CERN, which investigates the gravitational pull on antimatter, revealing that it behaves similarly to matter, thus dismissing speculative theories of antimatter falling upwards.

Takeaways

• 🌌 The fundamental building blocks of matter, protons, neutrons, and electrons, are consistent across the observable universe, including distant galaxies like Andromeda.
• 🔍 The mystery of the universe lies not in unknown phenomena but in the unexpected scarcity of antimatter, which is a significant part of the Standard Model of particle physics.
• 🏅 Antimatter's existence was first detected in 1932 by Carl D. Anderson, who observed positively charged particles with the mass of an electron but opposite charge, known as positrons.
• 📈 Paul Dirac's quantum field theory predicted the existence of antimatter before its experimental detection, leading to the understanding of particles and their corresponding antiparticles.
• ⚛️ Antimatter can theoretically form entire celestial bodies, appearing similar to matter构成的 planets, but the asymmetry between matter and antimatter in the universe remains unexplained.
• 🔬 Experiments at CERN aim to uncover differences between matter and antimatter, focusing on the properties of antiparticles and their interactions with the four fundamental forces of nature.
• 🔄 The weak nuclear force affects particles and antiparticles differently, with 'handedness' playing a key role in their interaction, but this doesn't sufficiently explain the universe's matter-antimatter imbalance.
• ⚖️ The strong nuclear force, contrary to early predictions, appears to treat particles and antiparticles identically, further deepening the mystery of the baryonic asymmetry.
• 🌐 Gravitational experiments at CERN, such as those conducted by the ALPHA group, suggest that gravity may not differentiate between matter and antimatter, as previously assumed in the Equivalence Principle.
• 🔵 The ALPHA experiment found that antimatter experiences gravitational acceleration at 75% the rate of matter, with a margin of error that still allows for the possibility of a full 1g of gravitational force.
• 🚀 Continued research into the gravitational effects on antimatter is necessary for a more precise understanding, and the search for new forces and particles that could explain the baryonic asymmetry persists.

Q & A

What are the three building blocks of matter mentioned in the script?

The three building blocks of matter are protons, neutrons, and electrons.

What is the significance of the discovery of anti-electrons or positrons?

The discovery of anti-electrons or positrons is significant because it confirmed the existence of antimatter, which is a critical part of the Standard Model of particle physics and has been observed in experiments for nearly a century.

How did Paul Dirac predict the existence of antimatter?

Paul Dirac predicted the existence of antimatter by realizing that in order to describe electrons as quantum fields in a way that was physically consistent with special relativity, they had to be part of a larger mathematical structure known as a Dirac spinor, which inevitably gave rise to both positively and negatively charged versions of the same particle.

What is the 'baryonic asymmetry of the universe' and why is it a mystery?

The 'baryonic asymmetry of the universe' refers to the observed dominance of matter over antimatter in the universe. It is a mystery because if antimatter were too similar to matter, it would be impossible to explain why our universe contains so much of one and so little of the other.

What are the four fundamental forces of nature?

The four fundamental forces of nature are electromagnetism, gravity, the weak nuclear force, and the strong nuclear force.

How do particles and antiparticles interact differently with the weak force?

Particles and antiparticles interact differently with the weak force in that ordinary particles can only feel the weak force if they are 'left-handed' and antiparticles can only feel it if they are 'right-handed.' Additionally, right-handed antiparticles experience a different strength of the weak force compared to left-handed ordinary particles.

What was the result of the 1963 experiment by James Cronin and Val Fitch?

The 1963 experiment by James Cronin and Val Fitch observed a fundamental asymmetry between particles and antiparticles in their interactions with the weak force. This discovery earned them a Nobel Prize.

What is the current understanding of how the strong nuclear force affects particles and antiparticles?

Current understanding and experiments suggest that the strong nuclear force treats particles and antiparticles exactly the same, which is surprising given the differences observed in other fundamental forces.

What is the ALPHA experiment at CERN investigating?

The ALPHA experiment at CERN is investigating the gravitational properties of antimatter, specifically the gravitational acceleration of antimatter on Earth's surface.

What was the outcome of the ALPHA experiment regarding the gravitational acceleration of antimatter?

The ALPHA experiment found that antimatter experiences a gravitational acceleration that is approximately 0.75g of the strength of gravity acting on ordinary matter, indicating that gravity does not treat matter and antimatter differently, at least to the extent observed in the experiment.

What are the two major sources of uncertainty in the ALPHA experiment's results?

The two major sources of uncertainty in the ALPHA experiment's results are the uncertainty in the applied magnetic field bias and possible errors in alignment, as well as other systematic and statistical uncertainties.

What implications do the results of the ALPHA experiment have for theories of gravity and antimatter?

The results of the ALPHA experiment rule out speculative theories that suggest antimatter might have a negative gravitational charge or that it might fall upwards instead of downwards. The findings also confirm that, aside from the weak force, the other fundamental forces, including gravity, appear to treat particles and antiparticles in a similar manner.

Outlines

00:00

🌌 The Building Blocks of Matter and the Mystery of Antimatter

This paragraph introduces the fundamental particles that make up all matter, protons, neutrons, and electrons, and extends the discussion to the cosmic scale, highlighting that matter is composed of these same particles throughout the observable universe. The central mystery presented is the unexpected absence of an equally abundant presence of antimatter. The video's host, Alex McColgan, sets the stage for an exploration of antimatter, its interactions with particles and gravity, and the frustration among physicists that antimatter isn't as 'weird' as it should be to explain the observed scarcity of it in the universe. The historical context is established with the mention of Carl D. Anderson's 1932 experiment that first detected antimatter, specifically positrons, and his subsequent Nobel Prize for this discovery. The paragraph also introduces Paul Dirac's theoretical prediction of antimatter as part of his quantum field theory, which posited that every particle has a corresponding antiparticle with the same mass but opposite charge. This theoretical framework was confirmed just four years later by Anderson's experiment.

05:05

🔬 Experiments and Theories: Unraveling the Properties of Antimatter

This paragraph delves into the scientific understanding of antimatter, summarizing what is currently known about its properties and how they compare to those of regular matter. It explains that while the intrinsic properties of antiparticles, such as mass, mirror those of their matter counterparts, their behavior under electromagnetic forces is characterized by their opposite charge, as demonstrated by Anderson's cloud chamber experiment. The discussion then moves to the weak nuclear force, which affects particles and antiparticles differently based on their 'handedness' or chirality, and the surprising discovery that these two types of particles experience the weak force with different strengths. This asymmetry was first observed by James Cronin and Val Fitch, earning them a Nobel Prize. The paragraph also touches on the strong nuclear force, which, contrary to early theoretical predictions, appears to treat particles and antiparticles identically. The focus then shifts to the ongoing experiments at CERN aimed at understanding the gravitational interaction with antimatter, questioning whether it could differ from that with matter and potentially offering insights into the baryonic asymmetry of the universe.

10:09

🧪 CERN's Experiments on Antimatter and Gravity

This paragraph discusses the experimental efforts at CERN to study the gravitational properties of antimatter, questioning the long-standing assumption that antimatter falls downward under the influence of gravity, just like matter. It describes the intricate experimental setup involving the creation of antihydrogen atoms, which are composed of positrons and antiprotons, and their behavior within a magnetic field trap. The experiment aimed to measure whether the gravitational acceleration experienced by antimatter is the same as that experienced by matter. The ALPHA experiment's results indicated that antimatter does indeed fall downward, with approximately 75% of the antihydrogen atoms escaping through the bottom of the chamber. However, the gravitational acceleration measured for antimatter was found to be 0.75g, suggesting it could be three-quarters the strength of gravity acting on matter. The paragraph also addresses the limitations and uncertainties of the experiment, such as the applied magnetic bias and systematic errors, which prevent a definitive conclusion but rule out the speculative theories that antimatter might have a negative gravitational charge.

15:12

🔄 The Search for the Baryonic Asymmetry Solution Continues

The final paragraph wraps up the video's exploration of antimatter by reflecting on the experimental findings and their implications for understanding the baryonic asymmetry of the universe. It acknowledges that while the weak force has been shown to differentiate between particles and antiparticles, the observed differences are not sufficient to explain the predominance of matter over antimatter in the universe. The paragraph leaves open the possibility of undiscovered forces or particles that could provide a more significant distinction between matter and antimatter interactions. It invites the viewer to consider whether the preponderance of matter is merely a coincidence and encourages further exploration into the mysteries of antimatter. The video concludes with a call to action for viewers to share their thoughts and interests in the topic, fostering engagement and a sense of community around the scientific pursuit of knowledge.

Keywords

💡Antimatter

Antimatter refers to a fundamental class of particles that are the counterparts of the particles构成物质的粒子，but with opposite charge. In the video, antimatter is introduced as a real and crucial part of the Standard Model of particle physics, with its first detection dating back to 1932. The video discusses the mystery of the universe's asymmetry between matter and antimatter and explores whether antimatter interacts differently with gravity compared to matter.

💡Protons, Neutrons, and Electrons

Protons, neutrons, and electrons are the three basic building blocks of matter. Protons and neutrons reside in the nucleus of an atom, while electrons orbit around the nucleus. These particles are made up of even smaller particles called quarks and are fundamental to the structure of all visible matter in the universe, as explained in the video.

💡Standard Model

The Standard Model is a theoretical framework that describes the fundamental particles and forces that make up the universe, except for gravity. In the context of the video, antimatter is a critical component of the Standard Model, and the study of antimatter helps to test and refine this model.

💡Quantum Field Theory

Quantum Field Theory is a theoretical framework in modern physics that combines quantum mechanics and special relativity to describe the behavior of subatomic particles as quantum fields. The video mentions Paul Dirac's work on electron theory, which was one of the first instances where quantum field theory predicted the existence of antimatter.

💡Dirac Spinor

A Dirac Spinor is a mathematical object used in quantum field theory to describe particles with spin, such as electrons. The video explains that Dirac's theory predicted the existence of antimatter because his equations naturally included both positive and negative energy solutions, which correspond to matter and antimatter particles, respectively.

💡Baryonic Asymmetry of the Universe

The Baryonic Asymmetry of the Universe is the observed imbalance between the amounts of matter and antimatter in the universe. The video discusses this cosmic mystery and the quest to understand why there is so much more matter than antimatter, which has led to decades of research and experiments in particle physics.

💡Weak Force

The Weak Force is one of the four fundamental forces of nature, responsible for processes like radioactive decay. In the video, it is explained that the weak force affects particles and antiparticles differently, with 'left-handed' particles and 'right-handed' antiparticles experiencing the weak force with different strengths. This asymmetry was first observed in a 1963 experiment and is crucial for understanding the behavior of subatomic particles.

💡Gravitational Acceleration

Gravitational acceleration is the rate at which an object accelerates due to gravity. In the context of the video, the ALPHA experiment at CERN aims to measure the gravitational acceleration of antimatter to determine if it behaves differently than matter under the influence of gravity.

💡AEgIS, GBAR, ALPHA

AEgIS, GBAR, and ALPHA are experiments at CERN designed to test the gravitational properties of antimatter. These experiments aim to determine if there are any differences in how gravity affects matter and antimatter, which could provide insights into the baryonic asymmetry of the universe.

💡Equivalence Principle

The Equivalence Principle is a fundamental concept in the theory of General Relativity, which states that in a local frame of reference, the effects of gravity are indistinguishable from the effects of acceleration. In the video, this principle is mentioned as the foundation for the expectation that gravity should treat matter and antimatter in the same way.

💡Antihydrogen

Antihydrogen is an isotope of hydrogen where the protons and electrons are replaced by their antimatter counterparts, antiprotons and positrons. In the video, antihydrogen atoms are created by combining positrons and antiprotons, and their behavior under the influence of gravity is studied to gain insights into the properties of antimatter.

Highlights

Everything from the skin of your hand to the screen you're watching this video on is made of the same three building blocks of matter: protons, neutrons, and electrons.

The mystery of the universe is not that we've seen something we can't explain, but rather that we haven't seen something we were expecting: a universe full of antimatter.

Antimatter is very real and forms a critical part of the Standard Model of particle physics, with particles of antimatter having been observed in experiments for nearly a century.

The first detection of antimatter dates back to 1932 when Carl D. Anderson discovered anti-electrons, or positrons, for which he won the Nobel Prize in Physics in 1936.

Paul Dirac predicted the existence of positrons in 1928 as part of a larger mathematical structure, the Dirac spinor, which gives rise to both positively and negatively charged versions of the same particle.

Other particles of matter, like quarks, each have their own anti-quark counterparts, allowing for the formation of anti-protons, anti-neutrons, anti-atoms, and anti-molecules.

The cosmic mystery known as the 'baryonic asymmetry of the universe' has sent physicists on a quest to find differences between matter and antimatter.

In the 1960s, it was discovered that particles and antiparticles are affected differently by the weak force, with 'handedness' playing a role in how they experience this force.

The famous experiment by James Cronin and Val Fitch in 1963 observed a fundamental asymmetry between particles and antiparticles, for which they were awarded a Nobel Prize.

Theoretical models predicted differences in how left-handed particles and right-handed antiparticles feel the strong force, but experiments to date suggest that the strong force treats them the same.

The ALPHA experiment at CERN has provided real-world data on the gravitational acceleration of antimatter on Earth's surface, challenging assumptions after decades.

Antihydrogen atoms, composed of positrons and antiprotons, were used in the ALPHA experiment to measure the effects of gravity on antimatter.

The ALPHA experiment found that roughly 75% of antihydrogen atoms escaped through the bottom of the chamber, indicating a preference for downward-pulling gravity.

The best-fit gravitational acceleration for antimatter was reported as 0.75g, meaning three-quarters of the strength of gravity acting on ordinary matter.

Despite the experimental results, a full 1g of gravitational acceleration is still fairly consistent with the collected data due to uncertainties in the applied bias and other factors.

The ALPHA experiment rules out speculative theories that antimatter falls up instead of down, and the weak force is the only fundamental force that applies differently to particles and antiparticles.

The search continues for new forces and particles that interact more weirdly with antimatter, as explaining the baryonic asymmetry of the universe would require more drastic differences between matter and antimatter.

Transcripts

Have a look around you. Everything you see,  from the skin of your hand to the screen you’re  

watching this video on, is a different combination  of the same three building blocks of matter:  

protons, neutrons, and electrons. Now let’s look  a little farther, say at Mars, or the Andromeda  

galaxy, or even halfway across the observable  universe… and still, there is matter made of  

protons, neutrons, and electrons, as far as the  eye can see. At first, this might not sound all  

that surprising—but for once, the mystery here  isn’t that we’ve seen something we can’t explain,  

but rather that we haven’t seen something we were  expecting: a universe just as full of antimatter.

I’m Alex McColgan, and you’re watching  Astrum. Join me today as we explore the  

world of antimatter and learn about its  interactions with other particles and even  

with gravity. By the end of this video, you’ll  probably agree that antimatter is a bit weird,  

but you’ll also see why some physicists  are frustrated that it isn’t weird enough.

Let’s get one thing out of the way first: although  it might sound like something straight out of  

science fiction, antimatter is very real. It  forms a critical part of the Standard Model of  

particle physics, and particles of antimatter have  been observed in experiments going back nearly a  

century. The very first detection of antimatter  dates back to a 1932 experiment conducted by Carl  

D. Anderson at Caltech using a cloud chamber  immersed in a magnetic field. When charged  

particles from outer space—broadly called cosmic  rays—intercept the Earth’s orbit and fly through  

this chamber, the magnetic field curves their  paths according to the charge and mass of each  

particle, and the clouds show a visible imprint  of their resulting trajectories. Anderson was  

hoping this experiment would help determine  just what kinds of particles were streaming  

into the Earth from the cosmos, and he may have  found just a little bit more than he bargained  

for! What Anderson saw was that these cosmic rays  included both positively and negatively charged  

particles. The masses of the negatively charged  particles lined up exactly with the known mass of  

an electron, but some of the positively charged  particles were far too light to be protons.  

Instead, they appeared to also have the mass of  an electron, despite having the opposite charge,  

and so these never-before-seen particles came to  be known as anti-electrons, or later positrons  

for short. In 1936, Anderson would win the  Nobel Prize in Physics for this discovery.

Meanwhile, a British physicist, who  was also destined to win a Nobel,  

had been developing a description of electrons  that would fit nicely within the framework of  

quantum field theory. His name was Paul Dirac. By  1928, Dirac had realized that in order to describe  

electrons as quantum fields in a way that was  physically consistent with special relativity,  

they had to be a part of a larger mathematical  structure— later known as a Dirac spinor—that  

inevitably gave rise to both positively  and negatively charged versions of the same  

particle. In this way, Dirac had predicted  the existence of positrons before Anderson  

had even built the cloud chamber that  would detect them four years later.

What’s even more incredible is that electrons  aren’t the only fundamental particle to come  

in a two-for-one "Dirac spinor" package. Other  particles of matter, like the quarks that make  

up protons and neutrons, each have their own  anti-quark counterparts. These anti-quarks can  

come together to form anti-protons and  anti-neutrons, which can then bond with  

positrons to form anti-atoms and anti-molecules.  You could make a whole planet out of antimatter,  

and from the outside, it would look quite similar  to an ordinary planet made of ordinary matter!

But if anti-matter were too similar to  matter—if the only difference were the  

sign of its charge—then it would  be impossible to explain why our  

universe contains so much of one and so  little of the other. This cosmic mystery,  

known as the “baryonic asymmetry of the universe,”  sent physicists on a decades-long quest to try and  

find as many differences as they could between  matter and antimatter. That quest lives on today,  

spearheaded by particle colliders at CERN  that are capable of producing, trapping,  

and studying both positrons and anti-protons.  But before we talk about these experiments,  

let’s try to summarize what we already  know about the properties of antimatter.

When studying antiparticles in isolation,  experiments have confirmed with ever-greater  

precision that their intrinsic properties -  namely their masses - are exactly the same as  

for ordinary particles. And when studying how  antiparticles are affected by electromagnetic  

forces, experiments have again found that they  behave the same exact way as ordinary particles,  

except with the opposite electric charge -  just as Anderson had observed in his cloud  

chamber. But electromagnetism is just one  of the four fundamental forces of nature,  

alongside gravity and the weak  and strong nuclear forces. And as  

physicists began to better understand  the weak force in the 1950s and ‘60s,  

they realized that particles and antiparticles  are actually affected by it quite differently.

The first surprise was that ordinary particles  could only feel the weak force if they were  

"left-handed" and antiparticles could only feel  it if they were "right-handed." The concept of  

handedness (or "chirality") is subtle and  difficult to conceptualize for particles  

with mass. But a loose analogy can be drawn with  a particle's helicity, which describes whether  

a particle is spin-up or spin-down along  its direction of motion. In this analogy,  

a spin-up particle is called right-handed, while  a spin-down particle is called left-handed.

The second and even crazier surprise was that  right-handed antiparticles experienced a different  

strength of the weak force, as compared to  left-handed ordinary particles. In practice,  

this means that the quantum probabilities  for radioactive decay in ordinary nuclei are  

somewhat different from the probabilities of the  analogous decay processes in anti-nuclei. This  

fundamental asymmetry between particles  and antiparticles was first observed in  

a 1963 experiment run by James Cronin  and Val Fitch of Princeton University,  

who would be awarded yet another  Nobel Prize for their discovery.

When this asymmetry was discovered, there was some  hope that it would explain the baryonic asymmetry  

of the universe: perhaps these differences  in the weak force were responsible for the  

abundance of matter and utter lack of antimatter  around us. But the maths didn't quite work out.  

There simply wasn’t enough of a difference  between the strength of the weak force acting  

on particles versus antiparticles. That was  when physicists began to turn their attention  

to the strong nuclear force. Theoretical models  predicted that, just like in the weak interaction,  

there should be some differences in how  left-handed particles and right-handed  

antiparticles feel the strong force. But  antimatter just keeps surprising us! Every  

experiment to date suggests that the strong force  treats particles and antiparticles just the same.

This brings us to the last of  the four fundamental forces and  

the subject of today's ongoing  experiments at CERN: gravity.

To be honest, suggesting that gravity might  treat matter and antimatter differently is  

kind of a long shot. Think back to the popular  legend of Galileo tossing stones of different  

sizes and materials from the Tower of  Pisa: they all fell at the same rate,  

because the gravitational acceleration on Earth  is 9.8 meters per second squared, regardless  

of which object is falling. Of course, the  experiment works even better in a vacuum chamber,  

where air resistance is taken out of the equation.  Newton expanded on this idea and showed in the  

17th century that your gravitational acceleration  anywhere in space depends only on the mass of the  

object pulling you and your distance from it,  but not on any of your personal properties—not  

even your own mass. This famous result—known as  the Equivalence Principle—is the foundation of  

Einstein’s theory of General Relativity, our most  accurate and successful model of gravity to date.

With that in mind, physics is still  an experimental science at its core,  

and we can’t know for sure whether  matter and antimatter obey the same  

laws of gravity unless we check for ourselves.  The physicists at CERN set out to do just that,  

motivated not only by the baryonic asymmetry  of the universe, but also by a few speculative  

papers suggesting that the cosmological  mysteries of dark matter and dark energy  

could be more easily explained if antimatter  were to have a negative gravitational charge—or  

put more simply, if antimatter were to  fall up, rather than down. There are  

several ongoing experiments at CERN testing  the gravitational properties of antimatter,  

including AEgIS (“Aegis”), GBAR (“g-bar”),  and ALPHA (“Alpha”). Today we will focus  

specifically on a key experiment coming out  of the ALPHA group that was published in the  

journal Nature this past September. After  decades of assumptions, this experiment has  

brought us real-world data on the gravitational  acceleration of antimatter on Earth’s surface.  

But before we show you the results, let’s take  a moment to appreciate just how intricately  

this experiment was designed in order to  isolate and measure the effects of gravity.

The first step in the experiment is to secure  a beam of several million positrons per second  

emitted from a radioactive isotope of  sodium (Na-22). Most of these positrons  

end up colliding with ordinary matter in the  experiment, causing miniature explosions in  

which positrons and electrons annihilate each  other and release place a small burst of energy  

in the form of light. But a small fraction of the  positrons survive as they are guided through the  

experimental apparatus [figure below], where they  are cooled by low-pressure gases and trapped by  

electric and magnetic fields. But observing the  effects of gravity on these positrons would be  

nearly impossible: their masses are so small, that  the tiny force of gravity felt by each particle  

is overshadowed by even the smallest fluctuations  in the surrounding electromagnetic fields. That’s  

why this collection of positrons is merged with a  separate container of antiprotons, where they bond  

and form neutral anti-hydrogen atoms that are much  less responsive to stray electromagnetic fields.  

And where did the antiprotons come from? Suffice  it to say that they were produced by firing  

ordinary protons into a block of metal really,  really fast. Yeah—Physics is awesome like that. 

Once the antihydrogen atoms are created, they  behave like tiny, weak magnets that can remain  

trapped by a complicated arrangement of  external magnetic fields. But now, this  

magnetic interaction is weak enough that it no  longer overwhelms the gravitational effects that  

we’re trying to measure. The chamber containing  these antihydrogen atoms is nearly a vacuum:  

there are just about 200,000 atoms of ordinary  gas per cubic centimeter, compared to a typical  

atmospheric density of 20 quintillion atoms  per cubic centimeter. Under these conditions,  

the trapped antihydrogen atoms almost never  collide or annihilate with atoms of ordinary  

matter. Instead, they can more or less just float  around the chamber for minutes or longer. But  

as the magnetic fields used to vertically  trap the antihydrogen atoms are weakened,  

this random floating eventually allows the  antihydrogen atoms to escape through either the  

top or bottom of the chamber [figure below], where  they can collide with a wall of the apparatus,  

annihilate with some ordinary atoms, and release  a small burst of light. In the ALPHA experiment,  

this happens over the course of about 20 seconds.

The theory behind the experiment is that if  gravity really pulls antimatter downwards,  

more of the antihydrogen atoms escape through  the bottom than the top. The stronger the  

gravitational force, the more atoms escape  through the bottom. The simulations the ALPHA  

team ran showed that under normal gravitational  attraction, about 85% of the antihydrogen atoms  

should escape through the bottom, whereas  only 20% of them would escape through the  

bottom if gravity pulled antimatter upwards.  If there were no gravitational force at all,  

the simulations showed a more even distribution  of 55% escape through the bottom (probably only  

differing from 50% due to asymmetries  in the experimental apparatus itself).

What did the actual experiment find? Well,  roughly 75% of antihydrogen atoms escaped  

through the bottom of the chamber, showing a  clear preference for downward-pulling gravity.

As any thorough scientist would, the ALPHA team  repeated this experiment to collect a variety  

of data points that tell a more complete story.  They redid the procedure under various levels of  

magnetic field bias, which applied external  upward or downward magnetic forces on the  

antihydrogen atoms. On this graph, a bias of -1g  means that just enough magnetic force is applied  

to counteract normal gravity, while a bias of +1g  means an extra “g” of magnetic force is applied to  

push the antihydrogen atoms downward, and so on.  The team made predictions through simulations for  

each bias and for various possible gravitational  interactions, which produced the orange, green,  

and purple curves shown here [figure below]. As you can see, the experimental data points,  

shown in blue, best match the orange  curve, which represents the “normal”  

simulation where gravity pulls antimatter  downwards. But because the data falls  

just a bit below this curve, the best-fit  gravitational acceleration was only 0.75g:  

three-quarters of the strength of  gravity acting on ordinary matter.  

Does this mean that gravity affects matter and  antimatter particles differently after all?

Not necessarily. Let’s have a quick look  at the error bars. They indicate that there  

are two major sources of uncertainty in  the results, including an uncertainty in  

the applied bias (highlight horizontal error  bars on screen), possible errors in alignment,  

and other systematic and statistical uncertainties  (highlight vertical error bars for these last 3).

When accounting for these uncertainties, the  best-fit gravitational acceleration is actually  

reported as 0.75g±0.13g±0.16g. This means that  a full 1g of gravitational acceleration is still  

fairly consistent with the collected data. Future experiments will be able to determine  

more precisely how strongly gravity acts  on antimatter. But … we can already rule  

out speculative theories that rely on  antimatter falling up instead of down.

In the end, despite how weird and backwards the  world of antimatter is, it seems that only the  

weak force actually applies differently to  particles and antiparticles. But explaining  

the baryonic asymmetry of the universe would  require much more drastic differences between  

the two— so scientists aren’t done looking for  them. Could there be new forces and particles  

that interact even more weirdly with antimatter?  Or would you be willing to accept that having so  

much more matter than antimatter around  us is a mere coincidence? In any case,  

let us know if you’ve learned something new about  antimatter from watching this video, and whether  

this is a topic you’d like to hear more on! We generally applaud it when hundreds of eyes turn  

their telescopes to the Stars to learn everything  they can about the cosmos however it feels a  

little less celebratory when similar number of  eyes look at you learning everything they can  

about you from your intim traffic habits to your  passwords and sensitive data but thankfully the  

sponsor of today's video NordVPN can keep unwanted  eyes off you while you browse provided they're not  

using a telescope to do it you're on your own  there for online threats NordVPN is the fastest  

VPN on the planet and stops what you're doing  online from being tracked and shared giving you  

a feeling of safety and privacy again. with just a click you can jump between regions allowing  

you to access content outside of where you are one  account can can protect up to six devices and even  

comes with threat protection to keep viruses  and malware out of your computer why not give  

nordvpn a try by scanning my QR code or using my  link nordvpn.com/astrum in the description below  

to get 4 months free on your 2-year subscription  it's free risk with nordvpn's 30-day money back

guarantee thanks for watching if you like this  imagery based video you may like my others in  

this playlist a big thanks to my patrons and  members if you want to support and have your  

name added to the end of every ashon video check  the links below all the best and see you next time