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The Mystery of Temperature: What is Absolute Zero? Do you know?
Temperature is a physical quantity that quantitatively expresses how hot or cold an object is. We usually use thermometers to measure, and the scale of the thermometer depends on different temperature standards. These standards contain various reference points and materials for heat measurement. The most commonly used temperature scales are Celsius (°C), Fahrenheit (°F) and Kelvin (K). Among them, Kelvin is mainly used in scientific research and is regarded as one of the seven base units in the International System of Units. Absolute zero on this scale, zero Kelvin or −273.15 °C, is the lowest point on the thermodynamic temperature scale. Experimentally, although absolute zero cannot be actually reached, we can get very close to it.
At absolute zero, there is no longer any macroscopic thermal energy in matter, but quantum mechanical zero-point energy still exists.
The Importance of Temperature
Temperature has a wide range of effects, involving the physical properties of matter, such as phase change (solid, liquid, gas or plasma), density, solubility, conductivity, etc. Furthermore, temperature directly affects the rate and extent of chemical reactions and even has a profound effect on the behavior of all living organisms. For example, the speed of sound in a gas is proportional to the square root of the absolute temperature.
Evolution of temperature scales
A temperature scale requires two values to be defined: the chosen zero point and the size of the temperature increment. The Celsius (°C) scale is the most widely used temperature measurement scale worldwide, with its zero point determined by the freezing and boiling points of water; while the Fahrenheit scale is widely used in the United States, with a freezing point of 32 °F and a boiling point of 212 °F. The zero point of the Kelvin scale is absolute zero.
Definition of Absolute Zero
Absolute zero is a key concept in physics, marking the state of matter when thermal energy is completely removed. In this state, the particles of matter will cease their macroscopic motion and, according to the third law of thermodynamics, the net thermodynamic energy is zero. People cannot cool objects to this temperature and can only explore its boundaries as closely as possible.
From an experimental point of view, absolute zero can only be approached but not reached. The lowest experimental temperature to date is 38 pK.
Absolute and relative temperature standards
Among temperature standards, the Kelvin scale is considered an absolute scale because it does not rely on any specific heat-measuring substance or instrument. Since 2019, the definition of Kelvin has been based on microscopic phenomena and is related to the Boltzmann constant, which allows for more precise measurements of temperature.
Relationship between statistical mechanics and thermodynamics
The current Kelvin scale is no longer clearly defined as a reference standard, but relies on determining the exact Boltzmann constant. Historically, Kelvin's definition was based on the thermodynamic properties of the Carnot engine, rather than relying on a microscopic description of motion. This allows us to create a more universal standard for describing temperature.
Classic and modern measurement methods
Temperature has historically been measured using empirical standards such as the triple point of water (defined as 273.16 K), but has increasingly relied on statistics and an understanding of microscopic dynamics. This shows that temperature is not only a macroscopic measurement, but also the result of microscopic and quantum behavior.
Future Development
With further research into thermodynamics and statistical physics, scientists may seek more precise measurements. For example, using the molar volume of a gas or the spectrum of blackbody radiation to measure temperature is promising future research directions.
Through our understanding of quantum behavior, we may be able to have a deeper understanding and more accurate measurement of absolute zero in the future.
While exploring these fascinating scientific phenomena, we can't help but ask: Are there natural laws and mysteries of the universe hidden in this unreachable temperature limit that we have not yet understood?
