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Niels Bohr
1885–1962 · Physicist
A Danish physicist whose 1913 atomic model and later principle of complementarity made major contributions to the development of quantum physics.
“We not only believe the existence of atoms to be proved beyond a doubt, but also we even believe that we have an intimate knowledge of the constituents of the individual atoms.”
Why is this scientist famous?
Developed the Bohr model of the atom and made foundational contributions to quantum mechanics.
Bohr applied early quantum ideas to Rutherford's nuclear atom and proposed that electrons could occupy specific energy states. His model successfully explained important features of the hydrogen spectrum and became a major step in the development of quantum theory. He later developed the principle of complementarity, which became influential in interpreting quantum mechanics.
Niels's story
Early Life
Born in Copenhagen in 1885 to a professor of physiology, Bohr grew up in an academic household. He excelled at football and physics, playing as a goalkeeper for a top Danish club while studying at the University of Copenhagen.
The Bohr Model
In 1913, Bohr proposed a revolutionary model of the atom in which electrons orbit the nucleus in fixed energy levels. When an electron jumps between levels, it emits or absorbs light at specific colours. This explained why elements produce characteristic spectral lines and why the periodic table works.
Quantum Mechanics and the Copenhagen Interpretation
Bohr played a central role in attempts to understand the new quantum mechanics developed in the 1920s. In 1927 he introduced his principle of complementarity: depending on how an experiment is arranged, quantum phenomena may require different descriptions, such as wave-like or particle-like behaviour. These complementary descriptions cannot always be observed simultaneously but are both needed for a fuller account of quantum phenomena. Ideas developed around Bohr's Copenhagen institute later became known collectively as the Copenhagen interpretation.
Nuclear Fission and the Manhattan Project
After nuclear fission was discovered in 1938–39, Bohr helped develop its theoretical explanation. Working with John Archibald Wheeler, he published an influential 1939 theory describing the mechanism of nuclear fission and differences in the behaviour of atomic nuclei. After escaping occupied Denmark in 1943, Bohr travelled through Sweden and Britain to the United States and contributed as a consultant to the Manhattan Project. After the war he advocated international cooperation and openness over nuclear technology.
What did they discover?
The Bohr Model of the Atom
Proposed that electrons orbit the nucleus in discrete energy levels, explaining atomic spectra and the structure of the periodic table.
The Principle of Complementarity
Established that quantum objects can exhibit wave-like or particle-like properties depending on the experiment — both descriptions are complementary and necessary.
Nuclear Fission Research
With John Archibald Wheeler, developed an influential theoretical description of nuclear fission in 1939, helping explain how heavy atomic nuclei can split.
Amazing facts
He won the Nobel Prize in Physics in 1922, the same year his son Aage was born — who also won a Nobel Prize in Physics in 1975.
Bohr enjoyed playing football as a young man; his brother Harald went further and represented Denmark internationally.
The element Bohrium (Bh, atomic number 107) is named after him.
In 1943, Bohr and his family escaped Nazi-occupied Denmark across the Øresund to Sweden before Bohr travelled on to Britain and the United States.
His famous debates with Einstein about quantum mechanics took place at conferences throughout the 1920s and 30s.
He received the Atoms for Peace Award in 1957 for his work on peaceful uses of atomic energy.
Timeline
Born in Copenhagen, Denmark on October 7
Earned his PhD from the University of Copenhagen
Published the Bohr model of the atom, describing electrons in fixed energy levels
Founded the Institute for Theoretical Physics in Copenhagen (later named the Niels Bohr Institute)
Won the Nobel Prize in Physics for his work on atomic structure
Presented his principle of complementarity, which became central to what was later called the Copenhagen interpretation
Worked with John Archibald Wheeler on an influential theoretical description of nuclear fission
Fled Nazi-occupied Denmark, eventually reaching the United States
Returned to Copenhagen after World War II
Died in Copenhagen on November 18, age 77
Awards & honours
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Articles about this scientist
Inside the Atom: How Scientists Discovered Atomic Structure
Follow Dalton, Thomson, Rutherford, Bohr and Chadwick as experiments transformed the atom from a simple idea into the nuclear model taught today.
Einstein and Bohr: The Debate Over Quantum Reality
The equations worked. Einstein still asked what they left out. Bohr argued that the way an experiment is arranged shapes what can be learned from it.
The Quantum Revolution
Physics had been spectacularly successful at explaining the everyday world. Then experiments with light and atoms began producing results that the old rules could not handle. What followed was one of the strangest and most successful revolutions in science.