| MadSci Network: Physics |
Dear Meghan: Thank you very much for your kind question. It is really nice to know that there are young fellows interested in the social implications of science. Temperature is the quantity most widely measured in science and industry. Currently 30% of all the measurements are temperature measurements. This is due that a large fraction of the final properties of a product are temperature dependent. Why measure low temperatures? Well, try to imagine a world with no refrigeration in it. Food will spoil quickly. A lot of places will be very hot to live in. Some foodstuff will be available only in short seassons. There is a very nice book: Absolute Zero and the Conquest of Cold by Tom Shachtman in which there is a very compehensive tratement of this subject. There are some excerpts of it in the Amazon webpage. How low we can go in our temperature quest? In the very nice website http://www.pa.msu .edu/~sciencet/ask_st/012992.html an answer to the question: What is absolute zero? Is provided. In http://www.pa.msu.edu/sciencet/ask_st/012992.html we can read some interesting facts about low temperatures, although it is a little technical. And htt p://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980301b.html answers the question: How cold is the outer space? What will happen to a gas at absolute zero?. The answer ,as provided by http://www.ph yslink.com/Education/AskExperts/ae380.cfm reads: “First of all, the gas will no longer be a gas at absolute zero, but rather a solid. As the gas is cooled, it will make a phase transition from gas into liquid, and upon further cooling from liquid to solid (ie. freezing). Some gases, such as carbon dioxide, skip the liquid phase altogether and go directly from gas to solid. Now the question is: what are the atoms in the solid doing (if anything) at absolute zero. Are they totally motionless? The answer is no. Atoms, being very tiny particles, must be analyzed using quantum mechanics, and one of the cornerstones of this theory is the Heisenberg Uncertainty Principle (HUP). The HUP states that the uncertainty of a particle's position and momentum (mass times velocity) are not independent of each other; the product of these uncertainties must be greater than a certain value. In equation-ese : (position uncertainty)*(momentum uncertainty) > h “The number 'h' is called Planck's constant, and pops up throughout quantum mechanics. This equation requires the atoms in the solid to have a certain amount of intrinsic jitteriness, even at absolute zero. If the atoms were totally motionless, then both the position and momentum uncertainties would be zero, disobeying HUP. ”A pathological example of this is the element helium. Because helium is a noble gas (that is, it cannot form covalent bonds) and it is very light, HUP requires the uncertainty in its velocity to be quite high compared to other atoms. This makes the helium atoms so jittery, in fact, that they refuse to solidify at all-- at reasonable pressures, it remains a liquid even at absolute zero!” A cautionary note, provided in the same web site tells us that: “First off, 0K can never be achieved, since the amount of entropy in a system can never be equal to zero, which is the statement of the second law of thermodynamics. This can be nicely illustrated by your question: ”Using the state equation for an ideal gas: PV = nRT T, the thermodynamic temperature will be equal to 0, so the product of the molar gas constant R (8.31 J/mol/K) and the amount of moles n, will also be zero. ”Therefore the product of PV must be zero also. the pressure of the gas must be zero or volume of the gas must be zero. ”Since neither of these can be true, the second law of thermodynamics is observed.” Although we can not reach the zero temperature, it is possible to have negative temperatures. Such temperatures are briefly described in: ucr.edu Low and very low temperatures are very useful for technical applications. I will name just three of them: 1. Superconductors. http://superconductors.org/ Gives a nice glimpse of the importance of superconductors and its technical applications 2. Atomic clocks (clocks so precise that they will lag a second in a million years).In harvard.edu There is a nice description of low temperature atomic clocks. A state of the art research is optical atomic clocks. They are described in the following website http://newton.ex.ac.uk/ aip/physnews.551.html 3. Low temperature sterilization systems. They have a remarkable application for health care purposes. There are some highlights of them on ht tp://p2library.nfesc.navy.mil/P2_Opportunity_Handbook/12_3.html I hope this helps Jaime
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