Saturday, December 31, 2011

Subatomic Particles and The Standard Model

As the name might suggest, subatomic particles are particles that are smaller than an atom... Which is an interesting conundrum for the atom: The Greek root for the word atom, "atomon," means "that which cannot be divided." 
When atoms were first decidedly discovered, they were thought to be fundamental, a not-dividable particle that made up all elements. But as compounds and solutions were broken down into elements, and these elements became more categorical, it seemed that even individual atoms had to possess smaller building blocks.

"...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-)."(Berkeley Lab, 2011)

Picture credit: wikispace History of the Atom

Soon enough, scientists had determined that an atom is made up of three sub-atomic particles: Protons and Neutrons in the nucleus and that cloud made up of the much smaller elementary particle, the electrons. But are these three particles fundamental? Well, the electrons are. 

So electrons are (to date considered) fundamental subatomic particles. But what, then, are protons and neutrons made of? 
Protons, it turns out, are made of two "up" quarks and one "down" quark, held together with a "cloud of gluons" (R. Nave).
Neutrons are made up of two "down" quarks and one "up" quark. 

What scientists have developed to determine fundamental particles is the Standard Model Theory. This theory has been supported through experimentation in particle accelerators such as the Large Hadron Collider(LHC) at CERN. 
The Standard Model has 12 fundamental matter particles: six quarks and six leptons. The up and down quarks are just two of the quarks; there are also: charm, strange, top and bottom quarks.
Leptons include the electron as well as the following: neutrino electron, muon, tau, muon-neutrino and tau-neutrino.
picture credit: Cern,

These particles are members of multiple generations, 1st, 2nd and 3rd. Up and down quarks, for example, make up the first generation of quarks. The second and third generation particles are heavy and unstable and quickly decay to the more stable first generation. This is why our protons and neutrons are made of first generation quarks, and why it is electrons that occupy the cloud surrounding the atom's nucleus.

The Standard Model Theory does include forces and carrier particles which play a role in keeping atoms together. Carrier particles are carrying three of the four forces known: strong and weak nuclear forces and electromagnetism. Note that gravity is not included which is part of the reason that this model is not considered complete enough for the science community. These forces hold together the matter particles and the carrier particles include bosons, photons and gluons. Photons carry electromagnetism, bosons carry the weak force and gluons carry the strong force. Now if gravity could be added to the Standard Model, a carrier particle called a graviton could be included, but so far, scientists have not been able to produce any results to add the force and its carrier. This is one of many goals of the LHC and it's collaborators. 

Berkeley Labs. accessed 29Dec2011

Nave, C. R. and Sheridan, John, The Microwave and Infrared Spectra and Structure of Hydrothiophosphoryl Difluoride, Journal of Molecular Structure 15, 391, 1973. (

CERN, European Organization for Nuclear Research . 2008.

Sunday, December 11, 2011

Nobel Prize 2011 Physics: Dark Energy and Accelerating Expansion of the Universe

When you throw a ball into the air, gravity will eventually cause it to stop it's upward movement and accelerate it back toward you, right? Well, what if that ball kept going up? For that matter, what if it kept going up and increasing its speed as it did so? 
We would have to assume that something, some force, is working harder then the force of gravity. This is not so hard to believe as far as the forces go...of the four known basic forces (weak and strong nuclear forces, electro-magnetic force and gravity), gravity is observably the weakest. But lets assume the ball is not fitted with a magnet headed toward a massive piece of iron and that we have not fitted it with nuclear reactor boosters...what, then, could be working against the gravity?

This is the conundrum that Nobel Laureates Saul Perlmutter, Brian Schmidt and Adam Reiss faced when they discovered that the universe was an accelerated rate. 

For a long time, scientists believed that the universe was static; this was due to a paradox that Newton was aware of after his discovery of the force of gravity. According to his law, Newton realized that if the universe were finite, that it should be collapsing due to stars attracting one another...but that did not appear to be the case and so the universe was determined to be static. 
Olbers’ paradox is the argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. It is one of the pieces of evidence for a non-static universe such as the current Big Bang model. 
The problem with this was that a static universe would make an infinite universe and that could not be...if the universe were infinite, our night sky would be as bright as day from all the stars shining from the endless reaches of space (whether the light came from close by or gazillions of light-years away, an infinite universe means stars "forever").
 Newton was aware of the paradox, but decidedly stuck by the static universe theory. Years later, Einstein also realized that according to his theory of General Relativity, the universe should be expanding or collapsing, but to fix that, he came up with the cosmological constant, cancelling the effect of gravity on a large scale, thus keeping a static universe as the rule (SDSS, Expanding Universe). 

Image credit: 
Edwin Hubble, with the assistance of "larger telescopes...being built that were able to accurately measure the spectra, or the intensity of light as a function of wavelength, of faint objects (SDSS, Expanding Universe)," then discovered the universe was indeed expanding. Through the observations of distant galaxies, Hubble discovered that the redshift of these galaxies increased the further they were from the earth. This led Einstein to call his cosmological constant his "biggest blunder." Now scientists knew that the universe was not only finite, but that because it was expanding, there was a point in time and space where the universe was incredibly small and dense; it had a beginning...a "Big Bang.

Enter Nobel Laureates, Brian Schmidt, Adam Reiss and Saul Perlmutter. From's popular information:

 "Saul Perlmutter headed one of the two research teams, the Supernova Cosmology Project, initiated a decade earlier in 1988. Brian Schmidt headed another team of scientists, which towards the end of 1994 launched a competing project, the High-z Supernova Search Team, in which Adam Riess was to play a crucial role."

Using IA supernovae (the death of white dwarf stars in a binary star system, to be specific) as basis for their measurements, the two competing teams came to the same surprising conclusion: Yes the universe is expanding, but it was not slowing down as previously believed. While trying to determine the fate of our universe, the teams had found that the supernovae were becoming much fainter then expected. This find was to be the key to the roles that the mysterious dark energy and dark matter play in the cosmos. Where a vacuum of nothing in space should be, there is something. That something must be working against? or with? gravity to accelerate expansion in a universe that is supposed to be slowing down. Dark energy and dark matter are believed to make up 95% of our universe, while we, the earth, the moon, the sun and all the stars...all other matter...only comprise the last 5%. 

With the discovery of acceleration came the true value of Einstein's cosmological constant. Without the cosmological constant, the formula for expansion would not allow for acceleration. So Einstein's blunder could turn out to be the value of that vacuum of space that contains "something."

So, as a toddler who continues to ask why with each answered question, our universe presents new unknowns with each discovery!

Sloan Digital Sky Survey (SDSS). . viewed on 12/11/2011.

"The Nobel Prize in Physics 2011 - Popular Information". 11 Dec 2011

Perlmutter, S. (2003) Supernovae, Dark Energy and the Accelerating Universe, Physics Today, vol. 56,no.