How Do We Know Quarks Exist If They Have Never Been Directly Detected?

January 8, 2016 | Joanne Kennell

Artist's realisation of three quarks
Photo credit: Brianzero/Wikimedia (CC BY-SA 3.0)

They are pronounced “kworks.”

Quarks — the building blocks of matter — are not only impossible to see, but they are extremely difficult to measure.  They are fundamental particles that make up subatomic particles called hadrons, the most stable of which are protons and neutrons.  But how do we even know they exist if one has never been directly detected?  It comes down to indirect effects — how quarks influence their surroundings.  

The idea of quarks first came around in the 1960s when researchers using the Stanford Linear Accelerator Center found that electrons were scattering from each other more widely than their calculations suggested — indicating that protons and neutrons were made of even smaller particles.

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According to physicists, quarks first appeared 10-12 (0.000000000001) seconds after the Big Bang when two of four fundamental forces (the weak force and the electromagnetic force) separated.  The antiparticles of quarks, or antiquarks, also appeared around this time.

Surprisingly, there are six different “flavors” of quarks: up, down, strange, charm, bottom, and top.  The major difference between these flavors is their mass, however, some also differ by charge.  For example, all quarks have the same spin of ½ with up, charm, and top having charges of ⅔, and down, strange and bottom having charges of -⅓.  Quarks can also change from one form to another — meaning up quarks can become down quarks, according to LiveScience.  A very interesting quality.





Approx. Mass





1.7-3.3 MeV





4.1-5.8 MeV





1270 MeV





101 MeV





172 GeV





4.19 GeV

4.67 GeV

So why are quarks so difficult to measure?  

They can never be seen alone due to a property known as color confinement.  The energy required to remove a quark from a proton or separate two quarks immediately produces an antiquark, which quickly turns a single quark back into a hadron.  Computer models have to be used to determine their mass by simulating the interaction between quarks and gluons — the particles that glue quarks together.

Now this strange fact about quarks may surprise you.  The fate of the universe may rest in the hands of the top quark — which plays a very important role in both the weak and strong fundamental forces of the universe.  It will determine whether the universe is in a high or low energy state.  If the mass of the top quark is found to be heavier than expected, meaning the universe has high energy, the energy carried through space could collapse in as little as 10 billion years.  However, if its mass is lower than expected, than due to something known as Boltzmann Brain, self-aware entities could literally pop out of nowhere.  

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