Archive | November, 2011

Symmetry violations and the standard model

28 Nov

The theory that governs the elementary particles (see this post) and the forces that affect them (see this post) is called the Standard Model. The Standard Model calls for some degree of symmetry in the Universe. There should be spacial symmetry called parity and symmetry under charge conjugation, meaning that the laws of physics should stay the same if you put a negative sign in the charge or change the right- or left-handedness of the system. Violations of these symmetries are called C-P violations (C for charge and P for parity).

Part of the symmetry called for by the Standard Model is that particles and antiparticles should have similar decay rates. Recent findings from the LHCb show that this may not be the case for charm quarks and antiquarks. It is an early result, but it is exciting. The LHCb is the part of the LHC that detects mesons, a particle that contains a heavy quark (strange, charm, top or bottom). The “b” stands for “beauty” which is another name for the bottom quark.

We’re particularly interested in the symmetry of particle and antiparticle decay rates, because it pertains to one of the big questions in physics: Why is it that there is so much more matter than antimatter in the Universe? When matter and its corresponding antimatter come into contact, they annihilate one another. So it makes sense that there is an abundance of one and not the other. Eventually one or the other would win out if there are to be large, stable structures, but why did matter win? Is there something fundamentally different about matter that made it win the cosmic fight for dominance in the Universe? This discrepancy between charm quark and antiquark decay rates may shed some light on this question some day.

LHCb announcement here.


The Force(s of nature)

23 Nov

There are four fundamental forces in the Universe (and love is not one of them). They are: gravity, the electromagnetic force, the strong force and the weak force. Gravity and electromagnetism you are probably familiar with. Gravity is actually the weakest of the four forces (which is a good thing for us). The force of gravity is so weak that it is negligible when we’re talking about particles. But gravity does have the furthest range of all the forces.

The electromagnetic force is the second strongest force, and acts with the second longest range. The electromagnetic force is much, much stronger than gravity. The electromagnetic force between our atoms is what keeps us from falling down through the floor straight to the center of the earth.

The strong force is sometimes called the “strong nuclear force” or the “strong nuclear interaction,” and is responsible for holding protons and neutrons together in the nucleus, and quarks together to form hadrons. It is the strongest of the four forces, but acts at very short distances.

The weak force, sometimes called the “weak interaction,” is the weakest force except for gravity, and it acts on a very short range. The weak force is responsible for radioactive decay.

I bet you’re wondering why we call some of these forces “interactions.” Good question! It turns out that at least three (and probably all four) of these forces are actually the result of an exchange of particles. Each fundamental force has a corresponding boson (sometimes called a “gauge boson”) that is the carrier of that force. For the electromagnetic force, it is a photon. When two particles with electromagnetic charge interact, they exchange discreet amounts of energy in the form of photons. The gluon is the carrier particle for the strong force, and the weak force is carried by W and Z bosons. It has not been discovered yet, but we suspect there exists a “graviton” that is the carrier particle for gravity.

The theory about the fundamental forces, their carrier particles, and how they all act on the particles that make up matter, is called the “Standard Model.” It works remarkably well in describing how the world works. There is a strange sort of similarity between the weak and electromagnetic forces that hints at further connections between the fundamental forces. And there is an overall symmetry that is kind of beautiful about the Standard Model. Gravity, however, is the fly in the ointment. Gravity isn’t part of the Standard Model and we don’t understand how it fits in with the other forces. Luckily, gravity is a large-scale force and is negligible at the small scale of the other forces, so its absence isn’t felt too strongly.

So there you have it. We live in a strange world where everything that ever acts on anything else does so by exchanging energy in the form of these crazy little particles.

Elementary particle crash course

22 Nov

We used to think atoms were the smallest things in the universe and that they couldn’t be divided up into smaller parts. Then we learned that protons, neutrons and electrons are what atoms are made up of. Quarks are what protons and neutrons are made up of.

Quarks are elementary particles. There are six different flavors of quark: up, down, charm, strange, top and bottom (hey, we needed to call them something). Quarks have properties like mass, charge and spin. Up and down quarks have the smallest masses of the quarks, and they are the most stable, abundant quarks in the universe. The other, larger mass quarks decay into up and down quarks. We have only observed these other quarks (charm, strange, top and bottom) in high energy collisions. As with most elementary particles, there are antimatter equivalents of quarks called antiquarks. Antimatter isn’t as mysterious as it sounds. Antiquarks have all the same properties of quarks, except that some of the properties are reversed (meaning they have the opposite sign).

Quarks combine to form hadrons, which are held together by the strong force (insert Star Wars reference here). Hadrons made up of three quarks are called baryons, and hadrons made out of one quark and one antiquark are called mesons. Protons and neutrons are both baryons. A proton is made up of two up quarks and one down quark. A neutron is two down and one up.

Leptons are another type of elementary particle. Electrons, muons and tau particles, along with their corresponding neutrinos, make up the six types of leptons. Together, leptons and quarks are the building blocks for all matter, and what we usually think of when we say “elementary particles.”

Phew. So now you know exactly what a hadron is. It’s time to talk LHC. The Large Hadron Collider is a big machine that collides hadrons (either protons or lead ions), and the world’s largest at that. At full power, protons race around the enormous circular pathway at 99.9999991% of the speed of light. Two of these beams travel in opposite directions around the path and then collide. These high energy collisions are the only place to look for some of these elementary particles, as well as some elementary particles that are predicted to exist but we haven’t found yet (*cough* Higgs boson). These collisions are also the only way to get a glimpse at the kind of conditions that existed in our Universe during those first critical moments of the big bang.

More LHC fun facts here.

Sense of scale and Saturn’s storm

18 Nov

It’s difficult to comprehend the size of objects when they are very large or very small. Check out this site that gives you a sense of the size of cells, viruses, and other biological bits and bobs (you must be flash enabled).

Also, there are some very cool photos of a giant storm on Saturn here. To be honest, I’m not exactly sure what it means to be a storm on a gaseous planet where there are large-scale currents and violent swirling eddies in the different layers of gas all the time. But the pictures are very cool. It looks just like the experiment you see at science centers where you have a big flat circle full of a colored liquid, and you spin it in different directions to see the chaotic motion.

World’s smallest electric car

15 Nov

Scientists have created a molecule that can “drive” in one direction across a conducting surface. It is the world’s smallest electric car. It is all one molecule. It has four wheels–though they’re really more like small planes–attached to a hub by a carbon double bond. Electrons cause this double bond to rotate, and a molecule next to the hub acts like a ratchet keeping the wheels rotating only in one direction. Electrons are delivered by a scanning tunneling microscope tip. The conducting surface provides somewhere for the electrons to go. And the result is the world’s smallest vehicle that can travel in one direction across a surface. There have been molecules in the past that travel, but mostly it was diffusion in a single direction, or movement in an uncontrolled direction. This is the first molecule exhibiting controllable single-directional autonomous movement.

Amazingly, it works! One of the cars traveled 6 nanometers with 10 pulses of electrons. Of course, assembling the molecule is a bit tricky: you cannot control the way the ratchet part of the molecule is attached so some of the molecules end up with front and back ends that go in opposite directions. It’s a long way from a nano machine that can enter your body and repair your cells, but it may be a first step.

Read the article here. Image by Randy Wind/Martin Roelfs.

Russian probe stranded in earth orbit

11 Nov

The Russian probe Phobos-Grunt was intended to go to Mars, orbit it for awhile, then land on Mars’ moon Phobos, where it would have collected soil samples and then returned to earth in 2014. But the probe is currently stranded in orbit around the earth. The craft experienced engine failure very soon after launch. The Russian Space Agency says that they have 3 days to remotely get the engine running again and the probe back on track before its batteries die. Russian has had 3 failed attempts to land on the moon Phobos in the last 25 years, and all hopes are riding on this probe. Hopefully they will get this thing working again.

Phobos-Grunt is also carrying a Chinese satellite, and an experiment being conducted by the Planetary Society trying to see if extremophiles can survive in the low pressures of space.

Image courtesy of Russian Space Agency

Graphene and DNA sequencing

8 Nov

One of the most exciting applications for graphene is DNA sequencing. Some clever folks at the Kavli Institute of Nanoscience are using graphene to read genetic codes in an entirely new way. They drew a little hole in a sheet of graphene, called a nanopore, and then they use that graphene to separate two liquid chambers. This whole is so small that things go through it one at a time. By monitoring the voltage changes across the sheet of graphene as molecules pass through the nanopore, they can get a pretty good idea of what is passing through, nucleotides for example. The DNA strand gets pulled through the nanopore like a thread in sewing, and the DNA sequence can be read as it passes through. It’s so simple! Incredible.

This could allow forensics analysts to do DNA testing in a matter of hours, instead of days. Which would mean a world of difference to real life detectives, and faster-moving tv detective drama plots for the rest of us.

Graphene and DNA sequencing article here.

Also, here is a video if you want to learn a little more about graphene: how to make it (the simple version), and some of its amazing properties and applications.