Thirty. One.

                Here we are.  Today, the 31^st day of August, is also my 31^st birthday and, coincidentally, the publishing of my 31^st blog post.  We have a theme.

                Let’s talk about the number 31.  

                It’s a prime number.  No other number will divide evenly into 31 other than 1.

                The element on the periodic table corresponding to the atomic number of 31 is gallium.  I hate to tell you that I know nothing about gallium except that is sits between zinc and germanium, and above indium but below aluminum on the periodic table.  To quench my ignorance, I did some reading.  This particular element was discovered by Paul Emile Lecoq de Boisbaudran.  It was joked for a long time that he named this element after himself.  Lecoq, meaning rooster in French (if you put a space between the e and c), is gallus in Latin.  However, he adamantly denies this and claims it was really after the Latin word Gallia, a historic region of Western Europe that included present day France.

                I looked for notable scientific achievements that occurred in 1531, 1631, 1731, 1831, and 1931.  I came up mostly empty.

                However, I learned that several Nobel Prize winners were 31: Tsung-Dao Lee (Physics, 1957), Carl D. Anderson (Physics, 1936), Paul A. M. Dirac (Physics, 1933) and the man that spawned the rest of this post: Werner Heisenberg (Physics, 1932).

                Born December 5, 1901, Heisenberg published his theory of quantum mechanics in 1925.  He won the Nobel Prize in 1932 “for the creation of quantum mechanics, the application of which has, inter alia, lead to the discovery of allotropic forms of hydrogen.”

                Do not fear – I’m not going to spend the rest of this post describing quantum mechanics in any detail.  That would be … difficult.  Instead, I’m going to just talk about one little part of it: waves and particles.

                Let’s first set the scene on how scientists were viewing the world prior to quantum mechanics.  The macroscopic world (trees, cars, people, baseballs, etc) all behaved in ways that well-defined classical physics equations could predict.  For example, if a cannonball was shot at a particular degree from the ground with a particular initial velocity, classical physics could do the math and say (rather accurately) where it would land.  They could use math and initial conditions to predict future events.

 However, the microscopic world (atoms, electrons) did not follow these equations.  Try as they might, scientists could not explain the microscopic world.  It was a head scratcher for awhile.   

Finally, the theory of quantum mechanics was proposed as a model of the microscopic world.  It allowed scientists to use math and initial conditions to predict future events.  It works reasonable well and, as a chemistry major in college with a particular penchant for physical chemistry, I spent a great deal of time learning the equations and theory behind this excessively complicated model.  I’ll spare you the details!

Before quantum mechanics could be developed, however, scientists had to learn to think about things differently.  And now!  So shall you.

Think about a baseball.  If you had to define it as a particle or a wave – what would you choose?

Now think about light.  If you had to define it as a particle or a wave – what would you choose?

Classically, a baseball would be particle and light would be a wave.  That should seem familiar, yes?  A baseball is an object that can be seen, held, and touched.  Light, on the other hand, flies through the air at the fastest speed possible, we cannot hold light in our hands and we talk about light in terms of wavelengths.

But … what if we flipped it?  

What if we asked: Does a baseball ever act like a wave?  Does light ever behave like a particle?

The answer is yes on both fronts.  I can even give you examples.

Waves Behave like Particles

                The best example of this is the photoelectric effect, which was explained by Albert Einstein in 1905 when he published his theory detailing quanta of light.  These quanta are now known as photons.  

            

                In the experiment, light was shone on a piece of metal.  When the metal was exposed to lower energy RED light, nothing happened.  In contrast, when the metal was exposed to higher energy VIOLET light, electrons started moving across the surface.  Why?

                A metal surface is really rows and rows of metal atoms.  Atoms are composed of protons and neutrons in their nuclei and electrons spinning around the outside.  Shining VIOLET light on the metal was actually allowing electrons to be pulled away from their metal atom and move independently.  The RED light could not do this.  In order for an electron to be pulled from its nuclei, it had to be given some energy (the same is true if you want to hit a baseball really far – you have to put a lot of energy into a really awesome swing).

                Energy is associated with light.  That was understood.  It was also know that shorter wavelength of light (such as VIOLET light) has more energy than longer wavelength (like RED light).  Okay – it becomes obvious at this point that the energy associated with each color of light is playing a part here.  But, do the waves carry the energy?  That doesn’t make sense.

                And so this is where the understanding of the experiment ended until Einstein came along.  He said, rather succinctly, that the energy associated with each light is carried in small packets called photons.  The photons from VIOLET light hit the metal, transfers their energy to some metal electrons, and those electrons now have enough energy to get away from their nuclei.  The photons associated with RED light just don’t have enough energy for the electron to get way so nothing happens. It is an eloquent theory and a beautiful explanation.

                By definition, photons are particles.  Light has been traditionally treated as a wave.  This experiment could not be explained with waves but could be explained if we treated light as full of particles instead.  

Huh.

Particles Behave like Waves

                I think most people are familiar with the idea that waves can interact with each other to create new waves.  If two waves are moving identically, their peaks can add together and their troughs can add together and you get a newer, bigger wave.  This is called constructive interference.  If the two waves are completely out of sync, the peaks will add with the troughs and a flat line will result.  This is called destructive interference. 

                If you shine light on a piece of paper with two slits, you will get a pretty light pattern (called an interference pattern) displayed on your wall.  This is due to the light waves constructively and destructively interfering with each from each slit.  This experiment was explained quite well by the English physicist Thomas Young in the 19^th century.  

                Let’s say – just for fun – that you shine one electron at a time on the piece of paper with two slits.  What do you think would happen?  An electron is a particle.  It’s quite a bit smaller than the slit so, in theory, it should just pass through.

                Oddly, weirdly, totally against common sense-ly, you will see is a diffraction pattern.  That particle, an electron, is behaving like a wave.  I kid you not.  

                What have we learned?  Waves can behave like particles and particles can behave like waves.  This idea was fundamental to setting up quantum mechanics (along with a lot of other stuff that I won’t get into).  How to explain an atom, where electrons were located and what energy would do to these microscopic systems became infinitely easier to explain if we stopped thinking about electrons as strictly as particles and started thinking about them as having wave-like properties as well.  This is called wave/particle duality.

                Sooo… do you have a wavelength associated with you?  Why, yes indeed!

                You can figure it out using the below equation, which was developed by Louis-Victor-Pierre Raymond, the 7^th Duke of de Broglie.  It’s called, quite simply, the de Broglie equation.

               

                 

                Happy last day of August!

Clarification: Yes, I realize my blog archive says 35 posts.  I was counting science posts only (not announcements that I'll be away or my initial "what in the world is this blog?" post).  Unfortunately, I forgot to add in one post so this appears to be my 32nd science post.  Close enough.  :-)

Photons: packets of energy that is associated with light.

REFERENCES

Zumdahl, Steven S. “Chemical Principles, 4^th Edition” (2002) Houghton Mifflin Company, Boston, MA.

Oxtoby, David W. “Principles of Modern Chemistry, 6^th Edition”

Weeks, Mary Elvira. Journal of Chemical Education (1932). 9 (9) pgs 1605 - 1619.

http://www.nobelprize.org/faq/nobel_laureates.html