The concept of an "absolute cold" was first presented by Robert Boyle in his 1665 New Experiments and Observations touching Cold.
Various physicists explored this phenomenon, until Lord Kelvin derived his thermodynamic temperature scale, extrapolating backward to absolute zero based purely on the laws of thermodynamics.
Some substances, when cooled to near-absolute zero temperatures, reach a state of matter known as a superfluid and exhibit strange properties.Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15° on the Celsius scale (International System of Units),[1][2] which equates to −459.67° on the Fahrenheit scale (United States customary units or Imperial units).[3] The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.
It is commonly thought of as the lowest temperature possible, but it is not the lowest enthalpy state possible, because all real substances begin to depart from the ideal gas when cooled as they approach the change of state to liquid, and then to solid; and the sum of the enthalpy of vaporization (gas to liquid) and enthalpy of fusion (liquid to solid) exceeds the ideal gas's change in enthalpy to absolute zero. In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy.
The laws of thermodynamics indicate that absolute zero cannot be reached using only thermodynamic means, because the temperature of the substance being cooled approaches the temperature of the cooling agent asymptotically. And a system at absolute zero still possesses quantum mechanical zero-point energy, the energy of its ground state at absolute zero. The kinetic energy of the ground state cannot be removed
Definition
As you remove heat from a substance, its temperature drops. The particles of the substance move slower and slower. What happens if you keep removing heat from the substance? You will reach a temperature at which all particle motion almost stops. The temperature is called absolute zero, and it's the lowest possible temperature. It is equal to -273oC (-459oF). You cannot have a temperature lower than absolute zero. You can think of absolute zero as the temperature where molecules are completely frozen, with no motion. Technically, molecules never become absolutely motionless, but the kinetic energy is so small it might as will be zero.Temperature Limits
You might say that a fire is hot and a freezer is cold. But the temperatures of everyday objects are only a small part of the wide range of temperatures present in the universe, as shown in this figure: |
Temperatures do, however, have a lower limit. Generally, materials contract as they cool. If an ideal atomic gas in a balloon were cooled to -273.15oC, it would contract in such a way that it occupied a volume that is only the size of the atoms, and the atoms would become motionless. At this temperature, all the thermal energy that could be removed has been removed from the gas, and the temperature cannot be reduced any further. Therefore, there can be no temperature less than -273.15oC, which is called absolute zero.
Examples
The Fahrenheit and Celsius temperature scales have little or nothing to do with the fundamental nature of the concept of temperature. After all, the freezing point of water at Earth's atmospheric pressure has no obvious relationship to any basic aspect of the Universe. Presumably, an alien scientist on a planet that has no water will devise a thermometer that measures temperature equally well. More to the point, could there be a universal zero of temperature linked to the very essence of matter and energy, a zero that all scientists (human or otherwise) might discover? The answer is yes, and it is called the absolute zero of temperature.Let's look at the history of temperature measurements to better understand the nature of absolute zero. Like so many other physical quantities, temperature was measured long before it was understood. Galileo appears to have invented (ca.1592) the first device for indicating 'degrees of hotness'. As shown in the image below, he simply placed the end of an inverted narrow-necked flask, warmed in his hands, into a bowl of water (or wine). As it cooled, the liquid was drawn up, partially filling the neck.
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Air captured in the bulb at the top either expanded or contracted when subsequently heated or cooled, and the column fell or rose proportionately. Much the same effect can be seen by putting an inflated balloon in the freezer. The gas molecules inside the balloon keep it puffed up by constantly bombarding the inner walls. Cooling the gas, removing kinetic energy from its molecules, lessens their bouncing and causing the balloon to collapse.
The medical applications of the thermometer were recognized almost immediately, and normal body temperature became a focus of interest. In 1631, J. Rey, a French physician, inverted Galileo's device, filling the bulb with water and leaving much of the stem with air in it. In that configuration, which is more like today's thermometer, the liquid's expansion operates the device. Within 70 years of Galileo's invention, sealed pocket-sized thermometers containing either alcohol or mercury were in use.
By exploring the behavior of matter with the aid of the thermometer, it soon became evident that there were a number of physical occurrences that happened at fixed temperatures. In 1665, Boyle, Hooke, and Huygens, European natural scientists, independently recognized that that fact could provide a reliable reference point for any thermometer. Hooke suggested using the freezing point of water, and Huygens offered its boiling point. In 1694, an Italian scientist Carlo Rinaldini used both the freezing and boiling points of water to standardize two widely spaced points on his thermometer.
As we will see, the manner in which any material - mercury, alcohol, water, glass, whatever - expands on heating is characteristic of that material. What this means practically is that thermometers that differ in their physical construction and yet have the same two fixed reference points, will necessarily agree exactly only at those two points.
The range of temperatures we deal with is extensive, and there is now a whole arsenal of different kinds of thermometers, each with its own virtues. The familiar mercury-in-glass instrument is only useful between the points where mercury freezes and glass melts. Moreover, it can be used reliably only when its presence doesn't affect the temperature being determined. If you want to measure the temperature of a flea or a thermonuclear fireball, the old mercury-in-glass standby will not be of much help. Accordingly, there are electrical resistance thermometers, optical thermometers, thermocouples, and constant-volume gas thermometers, to name a few. Of these, the standard for accuracy and reproducibility is still the constant-volume gas instrument as shown in the figure below, though it is large, slow, delicate, and inconvenient.
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