Why Quarks?

I have already explained in a previous post why I chose the word “finches” to be included in my blog’s name.  But, why quarks?  Is it because it’s the name of the adorable dog in “Honey, I Shrunk the Kids?”  While that may have been a bonus, I actually had a more science-based reason.  In a similar way to the effect of Darwin’s finches on the field of biology, the discovery of quarks has been revolutionary for the field of physics, especially when looking at the sub-field of particle physics.  Because it has been so revolutionary and so well-ingrained in today’s theories about particle physics, the word “quarks” has somehow made its way into public discussion.  Granted, we may not exactly understand, well, anything about quarks, but most of us who have heard of the term at least know it is related to the field of physics and that they are very, very small.  By the end of this article, I hope to show all of you why quarks are such a big deal, how they relate to the history of matter itself, and what they could mean for perhaps the future of our universe.

What Are Quarks?

Most of us grew up learning that atoms are the fundamental building blocks of all matter.  You may even have learned, depending on your school and how much you paid attention in science class, that atoms are made up of three main types of particles:  protons, neutrons and electrons.  However, what you likely didn’t learn is that protons and neutrons (and actually almost all of the particles that we know of) are made up of these quirky things called quarks.

A quark is a fundamental particle that makes up the vast majority of matter that we interact with on a daily basis.  Fundamental in this sense means that quarks do not have a sub-structure and cannot be split into smaller pieces.  Quarks are not the only fundamental particles, however. 

Note:  From this point on I am going to be introducing a lot of scientific, Star Trek-sounding terms that will likely get a little confusing.  To make it a little easier to distinguish one brand new, strange-sounding word from another, I’ll be including different pictures throughout this post to help explain how all of the terms are related to one another.

There are two main types of fundamental particles:  fermions and bosons.  Quarks are one of the four fundamental fermions.  The other three are leptons (which include electrons), antiquarks and antileptons.  The last two members of the fermion group are examples of antimatter.  We will go further into detail about antimatter in a later post, but for now just know that for every particle in our universe there is an antimatter particle.  Antimatter can be just as stable as their regular matter counterparts, unless they come into contact with each other.  Like an evil twin in a soap opera, if a particle comes into contact with its antiparticle counterpart, they will annihilate one another.  This is where the soap opera analogy ends unfortunately, because particles don’t come back to life looking completely different after a miraculous medical procedure.

More About Quarks

There are six types of quarks that we already know of.  If you thought physicists seemed to have fun with naming the types of particles above, just wait until you see what they have in store for you when it comes to the types of quarks. In fact, physicists don’t even call them quark types, they call them quark “flavors.”  That’s right, like ice cream but much, much smaller than an ice cream cone and I doubt it tastes as good.  The first two quarks to be discovered were the “up” and the “down” quarks.  It’s not really a surprise that these were the first two identified because they are the only quarks that are stable in our universe (meaning these are the only quarks you are really likely to see in your house).  They were therefore significantly easier to identify than the other four. 

The “strange” quark was the next flavor to be discovered, and it was named “strange” because when a particle contains a strange quark, it has a strangely long life time.  Interestingly, this strangely long life time is less than a nanosecond, but I guess it’s still longer than normal.  Followed by strange, was the charm quark.  It was named “charm” because its discovery absolutely fascinated physicists at the time.  Cute, right?  The last two quarks that were identified had even more adorable names originally.  They were known as “beauty” and “truth.”  At some point, I guess physicists decided these names were too cute and their names were changed to “bottom” and “top” to coincide with the original up and down quarks.  To make it easier to remember each flavor of quark, I have given them each an emoji-like personality in the image below.

 

Okay, so we now know what the flavors of quarks are, and that they belong to a set of fundamental particles that make up all matter ever.  But, how do they actually make up matter?  Quarks are social little guys at heart – they are never found alone.  Instead, they join together to make up “composite particles,” which are particles that are made up of two or more smaller particles.  Think of it like a compound word.  “Campground” is a word all on its own, but it is made up of two fundamental words “camp” and “ground” that are words all on their own.   

Hadrons are the most important compound particles that are made up of quarks.  There are two major types of hadrons:  baryons and mesons.  The weird names just keep on coming.  I’m not even including them all.  Anyway, baryons are made up of three quarks, while mesons are made up of only two (a quark and an antiquark).  Baryons are arguably the more important of the two, as these include protons and neutrons (the things that make up most of the matter in the universe). 

Protons are made up of two up quarks and one down quark, while neutrons are made up of one up quark and two down quarks.  If you can reach back into your memory bank, deep in the forgotten corner where you stored your knowledge of basic chemistry, you may remember that protons have a charge of positive one (+1) and neutrons have no charge at all (0).  These nicely rounded charges are actually determined by the sum of the individual charges of the quarks within the particles.  Up quarks have a charge of positive 2/3 the charge of an electron (+2/3e), while down quarks have a charge of negative 1/3 the charge of an electron (-1/3e).  As you can see in the picture below, when the two up quark charges are combined with the down quark charge in a proton, you get a nice whole number of +1.  In the case of the neutron, the charges completely cancel out, leaving a net charge of zero.  The partial charges of quarks make the charges of protons and neutrons work, but they also made sense when looking at all of the known baryons and mesons.  The math came out perfectly.

If you’d like more information on the different flavors of quarks, and how the math works, check out the video by the Fuse School below.

How Did We Find Quarks?

In 1964, two physicists (Murray Gell-Mann and George Zweig) independently suggested that most of the particles scientists knew of at the time could actually be combinations of even smaller, truly fundamental particles.  Zweig suggested these particles came in sets of three and gave them the name “aces.”  Gell-Mann developed a way to classify and group such particles, known as the SU3 scheme, and suggested the name “quarks.”  Gell-Mann’s name stuck, and the name “aces” faded into scientific obscurity.

As an aside, Murray Gell-Mann has apparently always had a fascination with words.  He enjoys giving names to things or ideas that have yet to be named, and he has said he corrects strangers’ pronunciations of their own names.  So, when he first theorized that small particles could be making up the things we already knew about, like protons and neutrons, he was excited to attach a name to these tiny, obscure things.  He came up with the sound “qwork.”  Soon after this, however, he changed the name to be spelled “quark” after the line in James Joyce’s book Finnegans Wake from 1939:

Three quarks for Muster Mark! 

Sure he hasn’t got much of a bark

And sure any he has it’s all beside the mark.

But O, Wreneagle Almighty, wouldn’t un be a shy of a lark

To see that old buzzard whooping about for uns shirt in the dark

And he hunting round for uns speckled trousers around by Palmers-town Park?

Did that make sense to you?  No?  It’s probably because this book is heralded as one of the most difficult works of fiction in the English language.  Apparently Joyce used stream of consciousness writing, puns in different languages and linguistic blends of words to illustrate the experience of sleep and dreams… critics think…  Because this book is so hard to read, let alone understand, the majority of the public has never heard of it, let alone read it.  I therefore think the name quark is pretty fitting, considering the concept of particle physics is so difficult for most of us normal people to understand.  Anyway, there remains a divide in the physics community to this day as to whether the word is pronounced “qwork” or “quark.”

The idea that most matter is composed of quarks is now universally accepted across the scientific community.  However, it didn’t start this way.  At first, the concept really rubbed physicists the wrong way.  The major reason for this was, while protons, neutrons and electrons all have nicely rounded charges (+1, 0 and -1, respectively), these quarks would have to have fractional charges to make the math work, like we discussed above.  Fractional charges had never been seen before.  Gell-Mann and Zweig (and many other physicists as well) failed for years to find physical evidence of the existence of these “quarks” with non-whole number charges.  Therefore, soon after the quark theory was suggested, the leading physicists of the day basically said it was a nice thought, and made sense mathematically, but did not exist in our universe’s physical reality.

That is, until the Massachusetts Institute of Technology (MIT) and the Stanford Linear Accelerator (SLAC) decided to do a series of experiments between 1967 and 1973, where they hurled electrons towards protons at ridiculously fast speeds.  When asked during an interview if these particle smashing experiments were like a game of pool, with electrons being the cue ball, Murray Gell-Mann answered “At very high energies, two particles that smash together do not bounce off each other but create a vast number of particles.  You would have all sorts of little chips flying off in all directions – that would be a little more like it.”  Because these experiments were done in a specially-designed room, the scientists were able to track the paths that all of these new particles took after collision.  By looking at these tracks, the physicists were able to figure out exactly what particle was leaving each track and confirm the existence of quarks as real, physical entities!

The physics community as a whole did not really get on board with all this until the mid-1970’s.  There was a slew of evidence from different experiments in 1975 that was so overwhelming (at least in the physics community) that this time was dubbed the “November Revolution.”  Scientists could no longer ignore the quark theory of particle physics, and while the theory has been modified and expanded to include more and more particles as they are discovered, it has pretty much held its own against the pressures of time, improved technology, and scientific scrutiny.

While the Standard Model of particle physics has proven true over the years, even with countless discoveries of new particles, this theory may need to be changed, or at the very least adjusted, according to the latest scientific discoveries.  Quarks have always been known to exist in groups of two’s or three’s within composite particles (like with mesons and baryons).  However, in 2013, scientists discovered the first four-quark particle.  They called it Zc(3900)… yes, I was disappointed with the name as well, especially considering how many cool names have been in this post so far.  I guess that’s what happens when more and more new particles are being discovered every year.  In any case, boring old Zc(3900) set off a new series of discoveries, this time all centering around four-quark particles.  Around 160 of these particles have already been discovered, suggesting it is not actually a fluke and the Standard Model will need to start taking them into account.  Updating our theory of particle physics would actually have major implications for our understanding of the universe.  This research will not lay waste to the Standard Model of particle physics, but it will make us stop and think what could be on the horizon.

The discovery of quarks and leptons as fundamental particles that make up all matter may have taken a couple of decades, but it has led to an “era of discovery” that has never been seen before.  The importance of quarks can be seen by the sheer number of Nobel Prizes that have been awarded for research in this topic.  Murray Gell-Mann was the first to receive the prize, in 1969.  This prize was awarded for his amazing work in particle physics, but the term “quarks” was never actually mentioned since the physics community had yet to believe Gell-Mann and Zweig.  Five other physicists have shared two additional prizes for their work in quarks since then (in 1990 and 2008).  Controversy is not unknown to the world of Nobel Prizes, and the prizes in quarks are no different.  Though both Gell-Mann and Zweig were nominated for their work in first discovering and describing quarks (which became the foundation of the Standard Model of particle physics that still holds to this day) in 1977, this nomination was unsuccessful and one of the pioneering names in quarks (George Zweig) has never been awarded a prize for his groundbreaking research.

 

Why We Should Care

For some of the tiniest particles in our known universe, quarks can have major implications for the future of life itself.  The first quarks appeared less than a nanosecond after the Big Bang.  At this time, the world was a hot mess, for lack of a better term.  Everything was orderless.  Particles that we now can only find in our universe under extreme conditions (like in a huge vacuum chamber when particles are hurled at each other at ridiculously high speeds) were free, somewhat stable particles at this time.  Unraveling the details about these particles could give us information about these earliest moments in our universe’s history.  They could help us answer humanity’s biggest question, the question that seems to affect everyone regardless of their beliefs:  where do we come from?

Quarks could not only give us insight into the beginning of everything.  They can also tell us about the fate of our universe, and what our future may hold.  The biggest topic of interest takes place billions of years in the future and the answer lies in the secrets of the top quark.  Remember him?  The mass (amount of matter in an object) of the top quark is unknown so far.  Physicists have an approximate value that they feel somewhat comfortable with, but the quest is on to find scientific evidence of the true mass of the top quark.  As long as the physicists are right, there isn’t anything universe-shattering about the top quark.  If, however, the top quark is oh so slightly heavier than physicists expect, the universe could end in 10 billion years.  And it will end in a blaze of glory, with all of the energy in the universe collapsing in upon itself like a giant black hole.  

On the other, slightly weirder hand, if the top quark is slightly lighter than expected, we could find ourselves surrounded by alien lifeforms (assuming we are still around in billions of years).  Basically, as our universe stands today, it is much, much more likely for groups of atoms that randomly come together to form a brainless, consciousness-less hunk of matter than it is for those atoms to organize themselves into a self-aware, conscious entity.  It’s one of the reasons life on Earth is such a wonder, because in math terms, the probability of life is very, very low.  Now, if the top quark is just the tiniest bit lighter than we think, this universal truth could disappear, making it more likely for atoms to come together to form sentient beings than to form random bits of matter.  This isn’t science fiction folks, just science.

I hope you enjoyed this post – it’s been my favorite to write so far.  If you did enjoy it, please click the “like” button below or share the content using your favorite social media platform.  You can follow us on Twitter, like us on Facebook or join our Finches&Quarks Community for weekly updates so you never miss that “Aha!” moment.  If you have anything to add, have any questions or would like to request a topic, please leave us a comment below the resources or contact us!  

 

Resources

Title	Author(s)	Publication Type
“7 Strange Facts About Quarks”	Live Science (Elizabeth Howell)	Website
“Classification of Particles”	PhysicsNet	Website
“The Discovery of Quarks”	Science (Michael Riordan)	Peer-reviewed journal article
“Fifty Years of Quarks”	CERN	Website
“How a New Discovery in the World of Quarks Could Change Everything”	Futurism (Jolene Creighton)	Website
“The Man Who Found Quarks and Made Sense of the Universe”	Discover (Susan Kruglinski)	Magazine Article
“Quarks and Leptons for Beginners”	Roger Linsell	Youtube Video
“What are Quarks?”	FuseSchool – Global Education	Youtube Video