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States of Matter
How many states of matter are there? Well, you have likely heard of solid, liquid and gas states, and maybe plasma as well, but in reality, there are more states still. The reason these are not so obvious to most of us is that they tend to require conditions that we don't normally experience directly in everyday life, such as extremely cold temperatures. The following is a chart of some known or suspected states of matter as of late 2009.
Let's consider for a moment the scales that are used to measure temperature. Most people are familiar with degrees centigrade, and if you live in the US, you are probably familiar with the Fahrenheit scale. There is another scale that is less common in everyday use, but is often used by scientists that is called the Kelvin scale.
When you hear of condensation, you might think of water vapour from a kettle condensing on a cool surface, or perhaps cloud formation in the atmosphere. When the molecules in the gas get colder, they move around less and take up less space. This causes water vapour to condense into a lower energy state and become liquid water. This is exactly what Bose-Einstein condensation is about, but at a much colder level.
One result of the study of very cold temperatures is the discovery of a new state of matter called a superfluid. Superfluids have some bizarre characteristics, such as having the ability to flow through solid matter and zero viscosity among others.
Superconductors are metals or oxides that, when cooled to very low temperatures, have the property of zero electrical resistance and a reduced interior magnetic field. There are two types of superconductors: type I and type II. Type I work at the lowest of temperatures (7.1 degrees Kelvin and lower, depending on the material) and include metals and metalloids, and type II work at higher temperatures (at or below 130 degrees Kelvin, depending on the material) and include alloys and complex oxide ceramics. These are the ones you will see in popular science demonstrations.
How do they work?
When an electron moves between ionized atoms, there is a slight attraction because the ions are slightly positively charged and the electron is negatively charged. This causes the atoms on either side to move a bit towards the electron. This action creates Cooper pairs, which have the property of being superconductors.
Here is a demonstration comparing electrons flowing through ions in high and low temperatures http://www.supraconductivite.fr/en/index.php?p=supra-explication-cooper-more
Recently, physicists were able to create a negative Kelvin temperature state. If you're like me, you may be wondering how this could be possible, and if you're as old as or older than I am, you may be envisioning Kurt Vonnegut's infamous "ice nine". While headlines everywhere read about the breaking of the thermodynamic laws of physics, it would seem that this is a misunderstanding of the way thermodynamics defines temperature.
While most of us would be challenged to find a cheap and reliable source of liquid nitrogen for home use, we can find sources of dry ice. Many party suppliers as well as medical supply companies will sell dry ice to the public. Be certain to follow proper handling procedures as dry ice can give severe burns and may explode if stored in a sealed container. You can also make dry ice yourself with a fire extinguisher. Here is an "Instructables" clip to show you how. A word of warning however: the video shows someone handling dry ice with bare hands--unless you want frostbite, you should be advised that this is not a good idea! http://www.instructables.com/id/How-to-Make-Dry-Ice-With-a-Fire-Extinguisher/
Recently, scientists in the U.S. were able to use gases cooled to just above absolute zero to cause two photons to interact and become a molecule. Although not quite a light sabre nor a holodeck, the ability to make such molecules may lead to breakthroughs in quantum computing. More about this can be found at this Physics World link.