Science › Quantum world
Max Planck
1900· Person
ProvenTested many times; part of working physics.
German physicist (1858–1947) who started quantum physics in 1900 and was for decades a senior figure of German science.
See it on the Science map →How it works
Planck was trying to explain the colors of light given off by hot objects, a practical question for the new electric lighting industry. Every classical formula failed. In late 1900 he found a formula that matched the data perfectly, but only if energy was handed out in fixed small packets. He saw this as a mathematical trick, not real physics. A careful conservative, he reluctantly launched a revolution.
Why it matters
His packets, and the tiny number that sets their size (Planck's constant), became the foundation of all quantum physics. Nobel Prize 1918.
How the work held up
His radiation formula fits measurements of hot-body light precisely; the cosmic microwave background matches it almost perfectly. Einstein (1905) and Bohr (1913) showed the packets were physically real.
Still a mystery
He long hoped the packets could be explained by older physics. They could not, and he never fully embraced the strange picture that followed.
Connections (2)
▸Max Planck discovered Energy comes in packets (quanta)Proven
The relationship
Planck found his formula for oven radiation only worked if the energy of the glowing material's vibrating charges came in chunks, each equal to a constant times the frequency. He introduced that constant, now called Planck's constant, as a counting device. It turned out to set the basic scale of the quantum world.
How the link was found
Max Planck presented it to the German Physical Society in Berlin on December 14, 1900, often called the birthday of quantum theory.
Why it's proven
His formula fit experiments exactly, and his constant appears consistently in every quantum effect since. Since 2019 its fixed value even defines the kilogram.
Open questions and mysteries
Planck later described the step as an act of desperation. Why nature has this constant, with this value, has no deeper explanation.
▸Max Planck defined the natural units of The Planck scale: the smallest meaningful sizeProven
The relationship
In 1899, right after introducing his new constant h, Planck noticed that combining it with the speed of light and Newton's gravitational constant gives units of length, time and mass that depend on nothing human: no meters, seconds or kilograms. He saw them as universal units that any civilization would find. Later physicists recognized they mark where quantum gravity matters.
How the link was found
Max Planck, in a 1899 paper to the Prussian Academy of Sciences; he restated it in 1900 and in his 1906 book on heat radiation.
Why it's proven
The units follow by arithmetic from measured constants. Their deeper meaning, as the scale of quantum gravity, came decades later and is strongly supported by theory, not by experiment.
Open questions and mysteries
Why these particular constant values? Are they fixed, or could they differ elsewhere in a multiverse?