Why can't absolute zero be reached?

Why can't absolute zero be reached?

• A. It would require cooling beyond the universe's possible temperatures.
• B. A substance cooler than absolute zero is needed, which does not exist.
• C. It would violate the second law of thermodynamics.
• D. It would require infinite energy to remove all motion.

Answer: (D)

Absolute zero is the temperature at which particles would have no kinetic energy. As you try to remove heat, each cooling step becomes less effective the closer you get to that limit, because the system and its surroundings approach the same temperature. The last bit of motion would require removing an ever-smaller amount of energy, which, in the limit, would need infinite energy (and time) to achieve. Quantum mechanics also imposes zero-point motion that cannot be eliminated, so the true zero cannot be reached. That’s why reaching absolute zero would require infinite energy to remove all motion.

Absolute zero is the temperature at which particles would have no kinetic energy. As you try to remove heat, each cooling step becomes less effective the closer you get to that limit, because the system and its surroundings approach the same temperature. The last bit of motion would require removing an ever-smaller amount of energy, which, in the limit, would need infinite energy (and time) to achieve. Quantum mechanics also imposes zero-point motion that cannot be eliminated, so the true zero cannot be reached. That’s why reaching absolute zero would require infinite energy to remove all motion.