By: Sophie Gabreldar
Most people won’t be able to find absolute zero on an everyday thermometer. It’s actually minus 273.15 degrees on the Celsius scale, or 0 on the Kelvin scale (an absolute thermodynamic scale). Absolute zero is the coldest temperature possible, but why can’t scientists reach it?
How Can There Be A Lowest Temperature?
The key to deciphering absolute zero is understanding what temperature is. To put it simply, it is a measure of how fast the atoms or molecules within a substance are moving. Temperature is usually referred to as the average kinetic energy of the particles.
The atoms are constantly hitting and bouncing off each other, but it happens on an extremely small scale. The atoms hitting each other are we consider to be temperature. The faster the atoms move, the harder they hit each other, resulting in a higher temperature. When a hot object touches a cold object, the faster, hotter atoms impart some of their velocity to the slower, colder ones. This causes the hot object to cool and the colder object to grow warm.
So now the zero in absolute zero should make more sense. Absolute zero is the temperature at which all the particles in the substance are almost completely motionless. Since there’s no way to slow them down further, they can be no lower temperature. This does not mean that everything stops moving at absolute zero. The atoms won’t be completely still as the protons, neutrons and electrons inside the atom will continue to move.
Why Can’t We Reach It?
This largely due to the third law of thermodynamics. The Third Law of Thermodynamics is mainly concerned with the limiting behavior of systems as the temperature approaches absolute zero. A system generally refers to the portion of the physical universe that scientists have chosen to study the changes within.
The Third Law states, “The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0 K).” For this to be accurate, two things need to work. The first is that in order to achieve absolute zero in a physical system, the system’s entropy (amount of disorder in a system) must also hit zero. The second is the unattainability principle, which states that absolute zero is physically unreachable because no system can reach zero entropy.
After years of debate, physicists have finally offered up mathematical proof of the third law of thermodynamics, which states that a temperature of absolute zero cannot be physically achieved because it’s impossible for the entropy of a system to hit zero.
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