Physique Quantique/
Quantum Physics

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Table of Contents


Introduction


What is Quantum Physics?        


Why Should I Care About Quantum Physics?


Vocabulary and Other Important Stuff


Keep an Open Mind! (Read Me! Read Me! I'm Important!)

    "Let's start at the very beginning. That's a very good place to start". Let's follow Julie Andrew's advice and clear up a few things before we delve into the heart of the subject. In order to understand the basic concepts of quantum physics, we must first understand a few basic concepts of physics. It’s also good to know a little bit of vocabulary (Don't worry, you can always refer back to this section so you don't have to learn it by heart!) and a little bit about what quantum physics really is. Even if you are already familiar with quantum physics, I suggest you look at the “Vocabulary” and "Keep an Open Mind" sections, just so we're all on the same page. An asterisk (*) indicates a note or comment at the end of the section. 

 

What is quantum physics?

    You might have heard about Albert Einstein's Theory of Relativity*. That's good. You might also have heard that this theory explains everything in the universe. Unfortunately, that's not true. In fact, Relativity explains everything that is big: from solar systems to particles of sand! (Yes, they're considered big too ... at least in the realm of quantum physics!). But while Einstein's theory has yet to be faulted when we're talking about the "big stuff", it falls apart when we try to apply it to little things (like electrons, quarks and other subatomic particles). That's where quantum theory comes in. Quantum Physics explains (or tries to explain) the movements and interactions of atoms and subatomic particles. 


* If you're interested in learning more about Einstein's theory, here's a website that contains the great man's original work! http://www.bartleby.com/173/

Why should I care about quantum physics?

   The answer to this question is quite simple: quantum physics is important because it explains the basis of our entire world. It explains what we're made of, where we come from, what happened in the very beginning of the universe, why we exist and how we might exist in the future - among other things. Obvious - right? Well, not all that obvious, because that still doesn't explain why you would need to know it. That's great for scientists, but why should "normal" people take time to learn it? Personally, I'd be tempted to simply answer “curiosity”, but again, that doesn't always justify the time and effort you have to put in to understand quantum physics. So here are a couple "motivational reminders", just to keep you going (or get you started!)


  • News: Undoubtedly, you're going to be hearing a lot about quantum physics in the next few years. It's no wonder: a lot of people are saying that quantum physics is the future of physics. So next time you hear about something coming from the CERN about the Higgs-Boson or anything else quantum-related, you'll understand it too. No more excuses not to read that article you wanted to read and aren't brave enough to read because you're scared you won't understand. Extra credit when you get to impress your friends and family!

  • Self-Confidence: This may sound silly, but it is true. A few years ago, no one could even conceive of understanding rocket science. That's because it was new. A little while after that, rocket science became quite accessible to the average person - just like that! Rocket science didn't get any easier to understand, it just got easier to get information about it and it more present in people's lives. The same thing happened with neuroscience and brain surgery. Quantum physics isn't impossible to understand, just new and not very present in our lives. So take the chance! 
Vocabulary and Other Important Stuff

Knowing this will certainly help you to understand the rest of the site. Don't overlook words that you think you know the meaning of, you might just be surprised!


Atom: Small particle made up of electrons, protons and neutrons. The protons and neutrons make up what we call the "heart", or nucleus of the atom and the electrons orbit around the heart. There are always the same number of electrons and protons in an atom with no charge because the positive charges of the protons must balance out the negative charges of the electrons to make an electrically neutral atom.

Subatomic particle: particle that makes up an atom. 

Electron: The electron in a subatomic particle with a -1*** electrical charge. That means that it is negatively charged. Electrons orbit around the heart of the atom randomly and have a negligible masse when compared to that of the atom. 

Proton: The proton is a subatomic particle with a +1*** electrical charge. That means that it is positively charged. Protons are situated in the heart of the atom* and have a mass of 1,6726 x 10E-27 kg. 
*Well ... technically not. But we'll talk more about that in the section about Uncertainty,. Don'y worry about it for now. 

Neutron: The neutron is a subatomic particle with no electrical charge. It's charge is 0. Neutrons are situated in the heart of the atom* and have a mass of 1,6749 x 10E-27 kg. 
*Again ... technically not. But we'll talk more about that in the section about Uncertainty,. Don'y worry about it for now. 

***The actual charge of the electron and proton are respectively -e and +e, where e = 1,602 x 10E-19 coulombs. A coulomb is a unit of electrical charge. For this website, we will consider that a +1 charge is a charge worth +e to make things simple. 

Fermion: A fermion is a type of subatomic particle. Usually referred to as matter particles, fermions have a half-integer spin (see below) and contain an odd number of quarks and or leptons. Protons, neutrons and electrons are fermions. This type of particle obeys Pauli's exclusion principle (see below). 


Boson: A boson is a type of subatomic particle. Usually referred to as force carriers, bosons are not made of matter (therefore, they have no mass). They have an integer spin (see below) and contain an even number of quarks and/or leptons. Photons and gluons are bosons. This type of particle obeys the Bose-Einstein Statistics (see below). 


Spin: Spin is one of the many characteristics that we use to distinguish one particle from another. A Half-Integer spin is a spin that we describe with numbers like -3/2, -1/2, 1/2, 3/2, 5/2, etc. An Integer spin is a spin that we describe with numbers such as -1, 0, 1, 2, 3, etc. As for the specifics, you don't really need to know them in order to understand anything you'll find on this site, but if you're curious, there are many other websites out there you could check out. 


Photon: Boson which makes up light. The photon has no mass is usually represented by the Greek letter gamma (γ). 


Plank's constant: Represented by the letter h, Plank's constant is a very, very small number ( something like 6.626068 × 10E-34 to be precise). It represents one quanta, or lump. 


Volume: Volume is how much space something occupies. It is usually made up of three dimensional measurements. For example, if I want to give the volume of a die that measures 2cm x 2cm x 2cm, I would say it had a volume of 2x2x2 or 8 cm3. Raising the units to the third power shows us that there are three measurements being multiplied, or three dimensions being considered.


Coordinate Grid: A coordinate grid is an imaginary set of lines that intersect in a crisscross pattern. It can have any number of dimensions, but is usually used to chart two or three-dimensional space. Each line represents a number and the distance between each line is equal. The numbers that the lines represent and the difference between these numbers is arbitrarily determined, but must stay constant throughout the grid. 


Mass: Mass is different from weight. This is the first thing to understand. Weight can vary, depending on gravity, mass is constant, always. In short, mass is a measure of how much matter everything around us is made up of and weight is a measure of how much gravity pulls on that matter. Weight is measured in newtons while mass is measured in kilograms, or pounds. 


Pauli's Exclusion Principle: Pauli's exclusion principle applies only to fermions. It states that no two identical fermions can occupy the same quantum state. 


Bose-Einstein Principle: The Bose-Einstein Principle states that more than one boson can occupy the same quantum state and that all particles that follow this principle will tend towards the lowest energy stage. 


Keep an Open Mind! (Read me! Read me! I'm Important!)


    Here are a few things to keep in mind while reading this website. These thoughts are very important because the key to understanding is believing you can understand it and keeping an open mind. 


  1. You can understand everything you read: remember, you're smarter than your computer screen. 
  2. Forget everything you think you know about the world around you: it probably doesn't apply to quantum theory. 
  3. If you understand it but can't seem to completely grasp it, you're normal. Don't let this discourage you! Remember that M. Richard Feynman (Cornell University and California Institute of Technology), a very smart and influential physicist and physics teacher once said: "You see my physics students don't understand it ... That is because I don't understand it. Nobody does!" (QED, The Strange Theory of Light and Matter -- for full reference, see Sources.)
  4. This is complicated stuff. Don't get discouraged if you don't understand it the first time: try, try again ... or just skip it and come back later. Remember: there is no shame in reading again  rereading! 
  5. Have fun! Whether you're looking to understand the last newspaper article you read or just find this interesting, there won't be a test at the end so don't stress over it too much!