Hyper-thermal Rifle

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Lore & Background

Thermodynamic temperature can be defined in purely thermodynamic terms using the Carnot cycle, and was rigorously defined historically long before particles such as atoms, molecules, and electrons were fully understood. The International System of Units (SI) specifies the absolute scale for measuring temperature, and the unit of measure kelvin (symbol: K) for specific values along the scale. A temperature interval of one degree Celsius is the same as one kelvin. Since the 2019 revision of the SI, the kelvin has been defined in relation to the kinetic energy of atomic free particle motion, fixing the Boltzmann constant at exactly 1.380649×10−23 J⋅K−1. The property that imbues material substances with a temperature can be understood by examining the ideal gas law, which relates, through the Boltzmann constant, how heat energy causes precisely defined changes in the pressure and temperature of certain gases. Monatomic gases like helium and argon behave kinetically like freely moving perfectly elastic and spherical billiard balls that move only in the three translational degrees of freedom, which is why the noble gases all have the same heat capacity per atom and why that value is lowest of all the gases. Molecules, however, have internal structure and additional internal degrees of freedom, so they absorb more heat energy for any given rise in temperature than do monatomic gases. Heat energy is born in all available degrees of freedom in accordance with the equipartition theorem, so all available internal degrees of freedom have the same average energy as do their three external degrees of freedom. However, the property that gives all gases their pressure is a function of the kinetic energy borne in the freely moving atoms' and molecules' three translational degrees of freedom. Fixing the Boltzmann constant at a specific value had the effect of precisely establishing the magnitude of the kelvin in terms of the average kinetic behavior of the noble gases. Moreover, the starting point of the thermodynamic temperature scale, absolute zero, was reaffirmed as the point at which zero average kinetic energy remains in a sample; the only remaining particle motion being that comprising random vibrations due to zero-point energy.

In Their Own Story

Temperature scales are numerical. The numerical zero of a temperature scale is not bound to the absolute zero of temperature. Nevertheless, some temperature scales have their numerical zero coincident with the absolute zero of temperature, such as the Kelvin temperature scale and the Rankine temperature scale. Other temperature scales have their numerical zero far from the absolute zero of temperature, such as the Celsius scale and the Fahrenheit scale. At the zero point of thermodynamic temperature, absolute zero, the particle constituents of matter have minimal motion and can become no colder. Absolute zero, which is a temperature of zero kelvins (0 K), precisely corresponds to −273.15 °C and −459.67 °F. Matter at absolute zero has no remaining transferable average kinetic energy and the only remaining particle motion is due to an ever-pervasive quantum mechanical phenomenon called ZPE (zero-point energy). Though the atoms in, for instance, a container of liquid helium that was precisely at absolute zero would still jostle slightly due to zero-point energy, a theoretically perfect heat engine with such helium as one of its working fluids could never transfer any net kinetic energy (heat energy) to the other working fluid and no thermodynamic work could occur. Temperature is generally expressed in absolute terms when scientifically examining temperature's interrelationships with certain other physical properties of matter such as its volume or pressure (see Gay-Lussac's law), or the wavelength of its emitted black-body radiation. Absolute temperature is also useful when calculating chemical reaction rates (see Arrhenius equation). Furthermore, absolute temperature is typically used in cryogenics and related phenomena like superconductivity, as per the following example usage: 'Conveniently, tantalum's transition temperature (Tc) of 4.4924 kelvins is slightly above the 4.2221 K boiling point of helium.'

Reader's Guide

Though there have been many other temperature scales throughout history, there have been only two scales for measuring thermodynamic temperature which have absolute zero as their null point (0): The Kelvin scale and the Rankine scale. Throughout the scientific world where modern measurements are nearly always made using the International System of Units, thermodynamic temperature is measured using the Kelvin scale. The Rankine scale is part of English engineering units and finds use in certain engineering fields, particularly in legacy reference works. The Rankine scale uses the degree Rankine (symbol: °R) as its unit, which is the same magnitude as the degree Fahrenheit (symbol: °F). A unit increment of one kelvin is exactly 1.8 times one degree Rankine; thus, to convert a specific temperature on the Kelvin scale to the Rankine scale, x K = 1.8 x °R, and to convert from a temperature on the Rankine scale to the Kelvin scale, x °R = x/1.8 K. Consequently, absolute zero is '0' for both scales, but the melting point of water ice (0 °C and 273.15 K) is 491.67 °R. To convert temperature intervals (a span or difference between two temperatures), the formulas from the preceding paragraph are applicable; for instance, an interval of 5 kelvins is precisely equal to an interval of 9 degrees Rankine. For 65 years, between 1954 and the 2019 revision of the SI, a temperature interval of one kelvin was defined as 1/273.16 of the temperature difference between the triple point of water and absolute zero. The 1954 resolution by the International Bureau of Weights and Measures (BIPM), plus later resolutions and publications, defined the triple point of water as precisely 273.16 K and acknowledged that it was 'common practice' to accept that due to previous conventions (namely, that 0 °C had long been defined as the melting point of water and that the triple point of water had long been experimentally determined to be indistinguishably close to 0.01 °C), the difference between the Celsius scale and Kelvin scale is accepted as 273.15 K; which is to say, 0 °C corresponds to 273.15 K. The net effect of this as well as later resolutions was twofold: 1) they defined absolute zero as precisely 0 K, and 2) they defined that the triple point of special isotopically controlled water called Vienna Standard Mean Ocean Water occurred at precisely 273.16 K and 0.01 °C. One effect of the aforementioned resolutions was that the melting point of water, while very close to 273.15 K and 0 °C, was not a defining value and was subject to refinement with more precise measurements. The 1954 BIPM standard did a good job of establishing—within the uncertainties due to isotopic variations between water samples—temperatures around the freezing and triple points of water, but required that intermediate values between the triple point and absolute zero, as well as extrapolated values from room temperature and beyond, to be experimentally determined via apparatus and procedures in individual labs. This shortcoming was addressed by the International Temperature Scale of 1990, or ITS‑90, which defined 13 additional points, from 13.8033 K, to 1,357.77 K. While definitional, ITS‑90 had—and still has—some challenges, partly because eight of its extrapolated values depend upon the melting or freezing points of metal samples, which must remain exceedingly pure lest their melting or freezing points be affected—usually depressed. The 2019 revision of the SI was primarily for the purpose of decoupling much of the SI system's definitional underpinnings from the kilogram, which was the last physical artifact defining an SI base unit (a platinum/iridium cylinder stored under three nested bell jars in a safe located in France) and which had highly questionable stability. The solution required that four physical constants, including the Boltzmann constant, be definitionally fixed. Assigning the Boltzmann constant a precisely defined value had no practical effect on modern thermometry except for the m

Did You Know?

• Thermodynamic temperature starts from absolute zero, the point at which particles have minimal thermal motion.
• A temperature of 295 K corresponds to 21.85 °C and 71.33 °F.
• The Rankine scale is based on the Fahrenheit degree interval and has absolute zero as its null point.
• The kelvin was redefined in 2019 in terms of the kinetic energy of free motion of particles such as atoms, molecules, and electrons.
• Absolute zero precisely corresponds to −273.15 °C and −459.67 °F.