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Werner Heisenberg's uncertainty principle, published in 1927, says that some pairs of quantities cannot both be known exactly at the same time. The best-known pair is a particle's position and its momentum, which is its mass multiplied by its velocity.

Zeitschrift für Physik, 1927

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The story behind the card

Heisenberg was 25 and working with Niels Bohr in Copenhagen when he wrote the paper. He first explained the limit with an imagined microscope: to see an electron you must hit it with light, and the light knocks it off course. Bohr showed that this explanation was flawed. The deeper reason is that a particle also behaves like a wave. A wave squeezed into a small space has to be made of many different wavelengths, and in quantum physics wavelength sets momentum, so a sharp position means a spread of possible momenta. Later in 1927 the American physicist Earle Kennard wrote down the exact limit, set by Planck's constant, a tiny number. That is why the effect rules the world of atoms but is invisible for a football. Heisenberg received the 1932 Nobel Prize in Physics.

Türkçe oku
Werner Heisenberg'in 1927'de ortaya koyduğu belirsizlik ilkesine göre bazı nicelik çiftleri aynı anda tam kesinlikle bilinemez. Bunların en bilineni, bir parçacığın konumu ile momentumudur; momentum, kütle ile hızın çarpımıdır.
Zeitschrift für Physik, 1927

Heisenberg bu makaleyi yazdığında 25 yaşındaydı ve Kopenhag'da Niels Bohr'un yanında çalışıyordu. İlkeyi önce hayalî bir mikroskopla açıkladı: Bir elektronu görmek için üzerine ışık göndermek gerekir; ışık da elektrona çarpıp onu yolundan saptırır. Bohr bu açıklamanın kusurlu olduğunu gösterdi. Asıl neden, parçacığın aynı zamanda bir dalga gibi davranmasıdır. Küçük bir alana sıkıştırılmış bir dalga, pek çok farklı dalga boyunun birleşiminden oluşur. Kuantum fiziğinde momentumu dalga boyu belirlediği için, konum netleştikçe momentum belirsizleşir. Aynı yıl Amerikalı fizikçi Earle Kennard sınırın tam formülünü yazdı. Bu sınırı Planck sabiti denen son derece küçük bir sayı belirler; bu yüzden etki atomların dünyasında belirleyicidir, ama bir futbol topunda fark edilmez. Heisenberg 1932 Nobel Fizik Ödülü'nü aldı.

Sources and further reading

Background reading: Uncertainty principle
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