What is Fundamental?

 

Why do so many things in this world share the same characteristics? People have come to realize that the matter of the world is made from a few fundamental building blocks of nature. The word "fundamental" is key here. By fundamental building blocks we mean objects that are simple and structureless -- not made of anything smaller. Even in ancient times, people sought to organize the world around them into fundamental elements, such as earth, air, fire, and water.

 

 

Is the Atom Fundamental?

 

People soon realized that they could categorize atoms into groups that shared similar chemical properties (as in the Periodic Table of the Elements). This indicated that atoms were made up of simpler building blocks, and that it was these simpler building blocks in different combinations that determined which atoms had which chemical properties.

Moreover, experiments which "looked" into an atom using particle probes indicated that atoms had structure and were not just squishy balls. These experiments helped scientists determine that atoms have a tiny but dense, positive nucleus and a cloud of negative electrons (e-).

Trivia: The term "atom" is a misnomer. Why?
The Greek root for the word atom, "atomon," means "that which cannot be divided." But the entities we call atoms are made from more fundamental particles!


http://particleadventure.org/frameless/images/proton-quark4.jpg                                        Is the Nucleus Fundamental?


Because it appeared small, solid, and dense, scientists originally thought that the nucleus was fundamental. Later, they discovered that it was made of protons (p+ ), which are positively charged, and neutrons (n), which have no charge. So, then, are protons and neutrons fundamental? Are Protons and Neutrons Fundamental? After extensively testing this theory, scientists now suspect that quarks and the electron (and a few other things we'll see in a minute) are fundamental.

 

                                               The Scale of the Atom

 

 

 

http://particleadventure.org/frameless/images/scale.jpg

 

 

 

 

 

 

 

 

 




We don't know exactly how small quarks and electrons are; they are definitely smaller than 10-18 meters, and they might literally be points, but we do not know.

It is also possible that quarks and electrons are not fundamental after all, and will turn out to be made up of other, more fundamental particles.

What are we looking for?

Physicists constantly look for new particles. When they find them, they categorize them and try to find patterns that tell us about how the fundamental building blocks of the universe interact.

We have now discovered about two hundred particles (most of which aren't fundamental). To keep track of all of these particles, they are named with letters from the Greek and Roman alphabets.

Of course, the names of particles are but a small part of any physical theory. You should not be discouraged if you have trouble remembering them. Take heart: even the great Enrico Fermi once said to his student (and future Nobel Laureate) Leon Lederman,

"Young man, if I could remember the names of these particles, I would have been a botanist!"

Physicists have discovered that protons and neutrons are composed of even smaller particles called quarks . As far as we know, quarks are like points in geometry. They're not made up of anything else. After extensively testing this theory, scientists now suspect that quarks and the electron (and a few other things we'll see in a minute) are fundamental.

The Standard Model

Physicists have developed a theory called The Standard Model that explains what the world is and what holds it together. It is a simple and comprehensive theory that explains all the hundreds of particles and complex interactions with only:

•  6 quarks .

•  6 leptons . The best-known lepton is the electron. We will talk about leptons in just a few pages.

•  Force carrier particles , like the photon. We will talk about these particles later.

All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles.

The Standard Model is a good theory . Experiments have verified its predictions to incredible precision, and all the particles predicted by this theory have been found. But it does not explain everything. For example, gravity is not included in the Standard Model.

This site will explore the Standard Model in greater detail and will describe the experimental techniques that gave us the data to support this theory. We will also explore the intriguing questions that lie outside our current understanding of how the universe works.

 

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For more advanced readers (scroll down if you do not feel like reading this paragraph):

Higgs Physics

One part of the Standard Model is not yet well established. We do not know what causes the fundamental particles to have masses. The simplest idea is called the Higgs mechanism . This mechanism involves one additional particle, called the Higgs boson, and one additional force type , mediated by exchanges of this boson.

The Higgs particle has not yet been observed. Today we can only say that if it exists, it must have a mass greater than about 80GeV/c2 . Searches for a more massive the Higgs boson are beyond the scope of the present facilities at SLAC or elsewhere. Future facilities, such as the Large Hadron Collider at CERN , or upgrades of present facilities to higher energies are intended to search for the Higgs particle and distinguish between competing concepts.

Thus, this one aspect of the Standard Model does not yet have the status of " theory " but still remains in the realm of hypothesis or model.

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Question:

It is known that the 100s of particles are all made from how many fundamental particles?

            6 quarks, 6 leptons, 6 antiquarks, 6 antileptons, and the force carriers.

Trivia Question:

For how many years have physicists known that there were more than just protons, neutrons, electrons, and photons? 5? 25? 60? 100?

           60 years! In the 1930's physicists found muons, but hundreds more were found with high energy accelerators in the 1960's and 1970's.