# Is absolute zero Possible?

Absolute zero, or 0 Kelvin (-273.15°C), is the theoretical lowest temperature limit that can possibly be achieved. This is the temperature at which the particles of matter have the lowest possible energy. But is it actually possible to reach this limit in reality? Let’s explore the science behind absolute zero and whether or not we can actually achieve it.

## What is Absolute Zero?

Absolute zero is defined as 0 Kelvin or -273.15°C. This is equivalent to -459.67°F. At this temperature, the particles that make up matter would have the lowest possible energy. This means they would stop moving altogether, achieving zero point energy.

To understand absolute zero, we need to first understand temperature. Temperature is a measure of the average kinetic energy or movement of particles in matter. The more energy the particles have, the faster they vibrate and move, and the higher the temperature.

As you remove heat energy from matter, the kinetic energy decreases and particles slow down. Absolute zero is the point at which there is no more kinetic energy left to be removed – particle motion comes to a standstill.

This lack of particle motion corresponds to zero entropy, which is the measure of molecular disorder in thermodynamics. Absolute zero is the baseline reference point for the thermodynamic temperature scale and all thermodynamic calculations.

## Theoretical Limits

Absolute zero is not actually possible to achieve based on the laws of thermodynamics. The third law of thermodynamics states that absolute zero cannot be reached in a finite number of steps.

As you get closer to absolute zero, residual energy gets frozen into the matter and cannot be removed. There will always be some degree of molecular vibration that cannot be eliminated fully.

In quantum mechanics as well, the uncertainty principle sets fundamental limits on how precisely you can know a particle’s position and momentum simultaneously, meaning there will always be some uncertainty or motion at the quantum level.

Theoretically, to achieve absolute zero, you would need to remove all thermal energy from matter until all particle motion ceases. But the laws of physics do not permit the complete removal of thermal energy.

Still, although absolute zero cannot be reached, we can get exponentially close to it. Scientists have achieved phenomenally low temperatures just billionths of a degree above absolute zero in the laboratory.

## Record Cold Temperatures

Here are some of the coldest temperatures ever achieved in scientific experiments, getting ever closer to absolute zero:

Year Temperature Experiment
1911 14 K (-259.1°C) Helium gas liquefaction
1926 0.9 K (-272.25°C) Magnetic cooling
1938 0.7 K (-272.45°C) Helium-3 cooling
1950 0.002 K (-273.148°C) Nuclear adiabatic demagnetization
1958 0.001 K (-273.149°C) Magnetic refrigeration
2003 0.000 000 1 K (-273.149 999 9°C) Bose-Einstein condensate

As you can see, we have gotten closer and closer to absolute zero over the past century. The current record is just 0.000 000 1 Kelvin above absolute zero. That’s just a billionth of a degree above! This was achieved using laser cooling of a Bose-Einstein condensate.

## Methods to Reach Extreme Cold

Scientists have devised ingenious methods to achieve increasingly colder temperatures in the lab. Here are some of the main techniques used:

### Gas Expansion

Gases cool when allowed to rapidly expand. Releasing high pressure gas into vacuum can cool it down significantly. This is used to liquefy gases like oxygen, nitrogen, methane, etc.

### Laser Cooling

Lasers can be used to slow down atoms and cool them to near absolute zero. The photons from the laser remove momentum from the atoms, reducing their motion.

### Magnetic Cooling

Magnetic cooling uses magnetic fields to align the spins of atoms and molecules. As the field is removed, the spins randomize, which absorbs heat and cools the material.

### Nuclear Demagnetization

Nuclear demagnetization uses the quantum properties of atomic nuclei to remove heat from a sample. The entropy is transferred to the nuclear spins which can be manipulated to continue cooling.

### Doppler Cooling

This technique uses laser light to slow down (cool) atoms. The laser is tuned to a frequency slightly below a transition in the atoms. When the atoms move towards the laser, the Doppler effect brings them to resonance, causing them to absorb photons and slow down.

### Resistive Cooling

Passing a current through a resistive material converts electrical energy to heat which is dissipated to the environment, cooling the material. Low temperature baths enhance heat dissipation.

### Optical Refrigeration

A material is cooled by laser light tuned to a frequency just above a transition in the material. Heat is removed as atoms absorb the slightly higher energy photons.

### Evaporative Cooling

More energetic atoms escape from the surface of a liquid or gas, leaving the remaining atoms with lower average energy, thereby cooling the remaining material.

## Applications of Extreme Cold

Reaching such ultracold temperatures has enabled many scientific breakthroughs and technological applications, including:

• Studying quantum mechanical effects and exotic states of matter not observable at higher temperatures.
• Increasing sensor sensitivity for applications like imaging and navigation.
• Low-loss cryogenic cables that can transmit signals over longer distances.
• Enabling the operation of superconducting materials that have zero electrical resistance at low temperatures.
• New computing architectures like quantum computing require ultracold conditions.
• Precise tests of fundamental physics theories like quantum electrodynamics.
• New vacuum technologies like cryopumps for industrial applications.

The quest for cold has unlocked many insights into quantum physics and led to revolutionary technologies. While absolute zero remains elusive, ultracold research continues to push new frontiers in science.

## Conclusion

In summary, absolute zero is impossible to reach due to fundamental limits set by quantum mechanics and thermodynamics. The lowest possible temperature can only be approximated, but never truly achieved. However, through ingenious methods like laser cooling, magnetic refrigeration, and nuclear demagnetization, scientists have gotten exponentially close to absolute zero.

The lowest temperature ever achieved is just 0.000 000 1 Kelvin above absolute zero. Although the goal remains out of reach, striving towards absolute zero has led to major scientific breakthroughs like Bose-Einstein condensates, tests of quantum theory, and applications like quantum computing. The quest continues to find new physics and technology in the ultracold regime.