Gold particles smashed together at the Large Hadron Collider (LHC) briefly reach 7.2 trillion degrees Fahrenheit—hotter than a supernova explosion—making it the hottest temperature humans have observed, according to the source material. That record sits on Earth, not in deep space.
At the opposite end, atoms stop moving entirely at absolute zero (0 Kelvin, −273°C, or −460°F). The source notes that colder is impossible, comparing it to traveling south from the South Pole. Heat, in this framework, is a measure of how fast atoms and subatomic particles vibrate and move.
Why the Planck Temperature Resists Comprehension
The theoretical ceiling is the Planck temperature: 1032 Kelvin, or 100 million million million million million degrees. The source states that at this point conventional physics breaks down. Gravity becomes as strong as electromagnetism and the strong and weak nuclear forces, and all four merge into one unified force—a phenomenon linked to the sought-after "theory of everything," which remains unexplained.
The Hagedorn Limit and Quark Matter
A more reachable candidate is the Hagedorn temperature, about 2 x 1012 Kelvin, where hadronic matter—all ordinary matter—becomes unstable and breaks down. Some theoretical physicists propose that instead of evaporating, hadronic matter transitions into quark matter, which could then be heated further. However, the source cautions that quark matter is a theoretical phase and its existence is uncertain.
String theorists offer another contender: 1030 Kelvin, slightly cooler than the Hagedorn temperature. Their reasoning is that the universe's most basic constituents are vibrating strings, not familiar particles, and strings have a different Hagedorn temperature than hadrons.
Testing these predictions is impossible, the source states, because the conditions at such extremes cannot be reproduced. As a result, the exact highest temperature remains unknown, though the candidates above represent the best current thinking among physicists.
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