niels bohr discovery experiment

(1885-1962)

Who Was Niels Bohr?

Niels Bohr was an accomplished physicist who came up with a revolutionary theory on atomic structures and radiation emission. He won the 1922 Nobel Prize in physics for his ideas and years later, after working on the Manhattan Project in the United States, called for responsible and peaceful applications of atomic energy across the world.

Niels Bohr was born on October 7, 1885, in Copenhagen, Denmark, to mother Ellen Adler, who was part of a successful Jewish banking clan, and father Christian Bohr, a celebrated physiology academic. The young Bohr eventually attended Copenhagen University, where he received his master's and doctorate in physics by 1911. During the fall of the same year, Bohr traveled to Cambridge, England, where he was able to follow the Cavendish Laboratory work of scientist J.J. Thomson.

In 1912, Bohr wed Margrethe Nørlund. The couple would have six children; four survived to adulthood and one, Aage, would become a well-known physics scientist as well.

Bohr’s own research led him to theorize in a series of articles that atoms give off electromagnetic radiation as a result of electrons jumping to different orbit levels, departing from a previously held model espoused by Ernest Rutherford. Though Bohr's discovery would eventually be tweaked by other scientists, his ideas formed the basis of future atomic research.

After teaching at Manchester’s Victoria University, Bohr settled again at Copenhagen University in 1916 with a professorship position. Then, in 1920, he founded the university’s Institute of Theoretical Physics, which he would head for the rest of his life.

Wins Nobel Prize

Bohr received the 1922 Nobel Prize in Physics for his work on atomic structures, and he would continue to come up with revolutionary theories. He worked with Werner Heisenberg and other scientists on a new quantum mechanics principle connected to Bohr's concept of complementarity, which was initially presented at an Italian conference in 1927. The concept asserted that physical properties on an atomic level would be viewed differently depending on experimental parameters, hence explaining why light could be seen as both a particle and a wave, though never both at the same time. Bohr would come to apply this idea philosophically as well, with the belief that evolving concepts of physics deeply affected human perspectives. Another physicist, by the name of Albert Einstein, didn’t fully see eye to eye with all of Bohr's assertions, and their talks became renowned in scientific communities.

Bohr went on to work with the group of scientists who were at the forefront of research on nuclear fission during the late 1930s, to which he contributed the liquid droplet theory. Outside of his pioneering ideas, Bohr was known for his wit and warmth, and his humanitarian ethics would inform his later work.

Fleeing Europe

Atoms for peace.

After the end of the war, Bohr returned to Europe and continued to call for peaceful applications of atomic energy. In his "Open Letter to the United Nations," dated June 9, 1950, Bohr envisioned an "open world" mode of existence between countries that abandoned isolationism for true cultural exchange.

He helped to establish CERN, a Europe-based particle physics research facility, in 1954 and put together the Atoms for Peace Conference of 1955. In 1957, Bohr received the Atoms for Peace Award for his trailblazing theories and efforts to use atomic energy responsibly.

Bohr was a prolific writer with more than 100 publications to his name. After having a stroke, he died on November 18, 1962, in Copenhagen. Bohr’s son Aage shared with two others the 1975 Nobel Prize in Physics for his research on motion in atomic nuclei.

QUICK FACTS

• Name: Niels Bohr
• Birth Year: 1885
• Birth date: October 7, 1885
• Birth City: Copenhagen
• Birth Country: Denmark
• Gender: Male
• Best Known For: Niels Bohr was a Nobel Prize-winning physicist and humanitarian whose revolutionary theories on atomic structures helped shape research worldwide.
• Science and Medicine
• Astrological Sign: Libra
• Copenhagen University
• Nacionalities
• Danish (Denmark)
• Death Year: 1962
• Death date: November 18, 1962
• Death City: Copenhagen
• Death Country: Denmark

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CITATION INFORMATION

• Article Title: Niels Bohr Biography
• Author: Biography.com Editors
• Website Name: The Biography.com website
• Url: https://www.biography.com/scientists/niels-bohr
• Access Date:
• Publisher: A&E; Television Networks
• Last Updated: May 20, 2021
• Original Published Date: April 2, 2014
• Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.
• An expert is a man who has made all the mistakes which can be made, in a very narrow field.
• Never express yourself more clearly than you are able to think.

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Atomic flashback: A century of the Bohr model

In July 1913, Niels Bohr published the first of a series of three papers introducing his model of the atom

12 July, 2013

By Kelly Izlar

Niels Bohr, a founding member of CERN, signs the inauguration of the Proton Synchrotron on 5 February 1960. On the right are François de Rose and then Director-General Cornelius Jan Bakker (Image: CERN)

The most instantly recognizable image of an atom resembles a miniature solar system with the concentric electron paths forming the planetary orbits and the nucleus at the centre like the sun. In July of 1913, Danish physicist Niels Bohr published the first of a series of three papers introducing this model of the atom, which became known simply as the Bohr atom.

Bohr, one of the pioneers of quantum theory, had taken the atomic model presented a few years earlier by physicist Ernest Rutherford and given it a quantum twist.

Rutherford had made the startling discovery that most of the atom is empty space. The vast majority of its mass is located in a positively charged central nucleus, which is 10,000 times smaller than the atom itself. The dense nucleus is surrounded by a swarm of tiny, negatively charged electrons.

Bohr, who worked for a key period in 1912 in Rutherford’s laboratory in Manchester in the UK, was worried about a few inconsistencies in this model. According to the rules of classical physics, the electrons would eventually spiral down into the nucleus, causing the atom to collapse. Rutherford’s model didn’t account for the stability of atoms, so Bohr turned to the burgeoning field of quantum physics, which deals with the microscopic scale, for answers.

Bohr suggested that instead of buzzing randomly around the nucleus, electrons inhabit orbits situated at a fixed distance away from the nucleus. In this picture, each orbit is associated with a particular energy, and the electron can change orbit by emitting or absorbing energy in discrete chunks (called quanta). In this way, Bohr was able to explain the spectrum of light emitted (or absorbed) by hydrogen, the simplest of all atoms.

Bohr published these ideas in 1913 and over the next decade developed the theory with others to try to explain more complex atoms. In 1922 he was rewarded with the Nobel prize in physics for his work.

However, the model was misleading in several ways and ultimately destined for failure. The maturing field of quantum mechanics revealed that it was impossible to know an electron’s position and velocity simultaneously. Bohr’s well-defined orbits were replaced with probability “clouds” where an electron is likely to be.

But the model paved the way for many scientific advances. All experiments investigating atomic structure - including some at CERN, like those on antihydrogen and other exotic atoms at the Antiproton Decelerator , and at the On-Line Isotope Mass Separator ( ISOLDE) - can be traced back to the revolution in atomic theory that Rutherford and Bohr began a century ago.

"All of atomic and subatomic physics has built on the legacy of these distinguished gentlemen," says University of Liverpool’s Peter Butler who works on ISOLDE. 

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Niels Bohr: Biography & Atomic Theory

Niels Bohr was one of the foremost scientists of modern physics, best known for his substantial contributions to quantum theory and his Nobel Prize -winning research on the structure of atoms.

Born in Copenhagen in 1885 to well-educated parents, Bohr became interested in physics at a young age. He studied the subject throughout his undergraduate and graduate years and earned a doctorate in physics in 1911 from Copenhagen University.

While still a student, Bohr won a contest put on by the Academy of Sciences in Copenhagen for his investigation into the measurements of liquid surface tension using oscillating fluid jets. Working in the laboratory of his father (a renowned physiologist), Bohr conducted several experiments and even made his own glass test tubes. 

Bohr went above and beyond the current theory of liquid surface tension by taking into account the viscosity of the water as well as incorporating finite amplitudes rather than infinitesimal ones. He submitted his essay at the last minute, winning first place and a gold medal. He improved upon these ideas and sent them to the Royal Society in London, who published them in the journal Philosophical Transactions of the Royal Society in 1908, according to Nobelprize.org . 

His subsequent work became increasingly theoretical. It was while conducting research for his doctoral thesis on the electron theory of metals that Bohr first came across Max Planck's early quantum theory, which described energy as tiny particles, or quanta.

In 1912, Bohr was working for the Nobel laureate J.J. Thompson in England when he was introduced to Ernest Rutherford, whose discovery of the nucleus and development of an atomic model had earned him a Nobel Prize in chemistry in 1908. Under Rutherford's tutelage, Bohr began studying the properties of atoms.

Bohr held a lectureship in physics at Copenhagen University from 1913 to 1914 and went on to hold a similar position at Victoria University in Manchester from 1914 to 1916. He went back to Copenhagen University in 1916 to become a professor of theoretical physics. In 1920, he was appointed the head of the Institute for Theoretical Physics.

Combining Rutherford's description of the nucleus and Planck's theory about quanta, Bohr explained what happens inside an atom and developed a picture of atomic structure. This work earned him a Nobel Prize of his own in 1922.

In the same year that he began his studies with Rutherford, Bohr married the love of his life, Margaret Nørlund, with whom he had six sons. Later in life, he became president of the Royal Danish Academy of Sciences, as well as a member of scientific academies all over the world.

When the Nazis invaded Denmark in World War II, Bohr managed to escape to Sweden. He spent the last two years of the war in England and the United States, where he got involved with the Atomic Energy Project. It was important to him, however, to use his skills for good and not violence. He dedicated his work toward the peaceful use of atomic physics and toward solving political problems arising from the development of atomic weapons of destruction. He believed that nations should be completely open with one another and wrote down these views in his Open Letter to the United Nations in 1950.

Atomic model

Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. 

Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

The chemical element bohrium (Bh), No. 107 on the periodic table of elements , is named for him.

Liquid droplet theory

Bohr's theoretical work contributed significantly to scientists' understanding of nuclear fission . According to his liquid droplet theory, a liquid drop provides an accurate representation of an atom's nucleus.

This theory was instrumental in the first attempts to split uranium atoms in the 1930s, an important step in the development of the atomic bomb.

Despite his contributions to the U.S. Atomic Energy Project during World War II, Bohr was an outspoken advocate for the peaceful application of atomic physics.

Quantum theory

Bohr's concept of complementarity, which he wrote about in a number of essays between 1933 and 1962, states that an electron can be viewed in two ways, either as a particle or as a wave, but never both at the same time.

This concept, which forms the basis of early quantum theory, also explains that regardless of how one views an electron, all understanding of its properties must be rooted in empirical measurement. Bohr's theory stresses the point that an experiment's results are deeply affected by the measurement tools used to carry them out.

Bohr's contributions to the study of quantum mechanics are forever memorialized at the Institute for Theoretical Physics at Copenhagen University, which he helped found in 1920 and headed until his death in 1962. It has since been renamed the Niels Bohr Institute in his honor.

Niels Bohr quotations

"Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it."

"Everything we call real is made of things that cannot be regarded as real."

"The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness."

"Never express yourself more clearly than you are able to think."

Additional reporting by Traci Pedersen, Live Science contributor

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Elizabeth is a former Live Science associate editor and current director of audience development at the Chamber of Commerce. She graduated with a bachelor of arts degree from George Washington University. Elizabeth has traveled throughout the Americas, studying political systems and indigenous cultures and teaching English to students of all ages.

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Chemistry archive

Course: chemistry archive   >   unit 1.

• Spectroscopy: Interaction of light and matter
• Photoelectric effect

Bohr's model of hydrogen

• Bohr's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits, around the nucleus.
• Bohr's model calculated the following energies for an electron in the shell, n ‍   :

E ( n ) = − 1 n 2 ⋅ 13.6 eV ‍  

• Bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels, where the photon energy is

h ν = Δ E = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV ‍  

• Bohr's model does not work for systems with more than one electron.

The planetary model of the atom

• Where are the electrons, and what are they doing?
• If the electrons are orbiting the nucleus, why don’t they fall into the nucleus as predicted by classical physics? Why does classical physics predict that? According to classical physics, a negatively charged electron moving around in the positive electric field created by the nucleus should emit electromagnetic energy. The electron would continue to lose energy as it orbited the nucleus until it eventually collapsed into the nucleus. Unfortunately, this reasoning would suggest that all atoms are inherently unstable!
• How is the internal structure of the atom related to the discrete emission lines produced by excited elements?

Quantization and photons

Atomic line spectra, bohr's model of the hydrogen atom: quantization of electronic structure.

Bohr radius = r ( 1 ) = 0.529 × 10 − 10 m ‍  

Absorption and emission

Δ E = E ( n h i g h ) − E ( n l o w ) = ( − 1 n h i g h 2 ⋅ 13.6 eV ) − ( − 1 n l o w 2 ⋅ 13.6 eV ) = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV ‍  

h ν = Δ E = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV                         Set photon energy equal to energy difference ν = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV h                                             Solve for frequency ‍  

c = λ ν                                                                                                                                     Rearrange to solve for  ν . c λ = ν = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV h                             Divide both sides by c to solve for  1 λ . 1 λ = ( 1 n l o w 2 − 1 n h i g h 2 ) ⋅ 13.6 eV h c ‍  

What have we learned since Bohr proposed his model of hydrogen?

• " Bohr's Theory of the Hydrogen Atom " from OpenStax College , CC-BY 4.0
• " Bohr's Hydrogen Atom " from UC Davis ChemWiki, CC-BY-NC-SA 3.0 US

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February 8, 2022

100 Years Ago, a Quantum Experiment Explained Why We Don’t Fall through Our Chairs

The basic concept of quantum spin provides an understanding of a vast range of physical phenomena

By Davide Castelvecchi

Otto Stern.

Alamy Stock Photo

The moment I meet Horst Schmidt-Böcking outside the Bockenheimer Warte subway stop just north of the downtown area of Frankfurt, Germany, I know I have come to the right place. After my “Hi, thank you for meeting me,” his very first words are “I love Otto Stern.”

My trip on this prepandemic morning in November 2018 is to visit the place that, precisely a century before February 8, 2022, saw one of the most pivotal events for the nascent quantum physics. Without quite realizing what they were seeing, Stern and his fellow physicist and collaborator Walther Gerlach discovered quantum spin: an eternal rotational motion that is intrinsic to elementary particles and that, when measured, only comes in two possible versions—“up” or “down,” say, or “left” or “right”—with no other options in between.

Before the Roaring Twenties were over, physicists would reveal spin to be the key to understanding an endless range of everyday phenomena, from the structure of the periodic table to the fact that matter is stable—in other words, the fact that we don’t fall through our chair.

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But the reason why I have a personal obsession with the Stern-Gerlach experiment—and why I am here in Frankfurt—is that it provided nothing less than a portal for accessing a hidden layer of reality. As physicist Wolfgang Pauli would explain in 1927, spin is quite unlike other physical concepts such as velocities or electric fields. Like those quantities, the spin of an electron is often portrayed as an arrow, but it is an arrow that does not exist in our three dimensions of space. Instead it is found in a 4-D mathematical entity called a Hilbert space.

Schmidt-Böcking—a semi-retired experimentalist at Goethe University Frankfurt and arguably the world’s foremost expert on Stern’s life and work—is the best guide I could have hoped for. We walk around the block from the station, past the Senckenberg Natural History Museum Frankfurt, to the  Physikalischer Verein , the local physicists’ society, which predates Goethe University Frankfurt’s 1914 founding. In this building, in the wee hours of February 8, 1922, Stern and Gerlach shot a beam of silver atoms through a magnetic field and saw that the beam neatly split into two.

Apparatus used for the Stern-Gerlach experiment in 1922, equipped with modifications made a few years later. The schematic shows a silver beam emerging from an oven (O) and passing through a pinhole (S1) and a rectangular slit (S2). It then enters a magnetic field, whose direction is indicated by the arrow between the two pole pieces (P), and finally reaches a detector plate (A). Credit: “Otto Stern’s Molecular Beam Method and Its Impact on Quantum Physics,” by Bretislav Friedrich and Horst Schmidt-Böcking, in Molecular Beams in Physics and Chemistry . Edited by Bretislav Friedrich and Horst Schmidt-Böcking. Springer, 2021 (CC BY 4.0)

Once we are upstairs in the actual room of the experiment, Schmidt-Böcking explains that the whole experimental setup would have fit on a small desk. A vacuum system , made of custom blown-glass parts and sealed with Ramsay grease, enclosed the contraption. I find it hard to picture that in my mind, though, because the room, now windowless, is taken up by some of the nearby museum’s collections—specifically, cabinets with tiny specimens of bryozoans, invertebrates that form coral-like colonies.

Stern and Gerlach expected the silver atoms in their beam to act like tiny bar magnets and therefore to react to a magnetic field. As the beam shot horizontally, it squeezed through a narrow gap, with one pole of an electromagnet bracketed above and the other below. It exited the magnet and then hit a screen. When the magnetic field was turned off, the beam would just go straight and deposit a faint dot of silver on the screen, directly in line with the exit path of the beam from the magnet. But when the magnet was switched on, each passing atom experienced a vertical force that depended on the angle of its north-south axis. The force would be strongest upward if north pointed straight up, and it would be strongest downward if north pointed down. But the force could also take any value in between, including zero if the atom’s north-south axis was horizontal.

In these circumstances, a magnetic atom that came in at a random angle should have its trajectory deflected by a corresponding random amount, varying along a continuum. As a result, the silver arriving at the screen should have painted a vertical line. At least, that was Stern and Gerlach’s “classical” expectation. But that’s not what happened.

Unlike classical magnets, the atoms were all deflected by the same amount, either upward or downward, thus splitting the beam into two discrete beams rather than spreading it across a vertical line. “When they did the experiment, they must have been shocked,” says Michael Peskin, a theoretical physicist at Stanford University. Like many physicists, Peskin practiced doing the Stern-Gerlach experiment with modern equipment in an undergraduate lab class. “It’s really the most amazing thing,” he recalls. “You turn on the magnet, and you see these two spots appearing.”

Later that day in 2018, I get to see some of the original paraphernalia with my own eyes. Schmidt-Böcking drives me north in Frankfurt to one of the university’s campuses, where he keeps the artifacts inside well-padded boxes in his office. The most impressive piece is a high-vacuum pump— a type invented only a few years before the experiment —that removed stray air molecules using a supersonic jet of heated mercury.

It all looks tremendously fragile, and it is: According to witnesses, when the pieces were used, some glass part or other broke virtually every day. Restarting the experiment then required making repairs and pumping the air out again, which took several days. Unlike in modern experiments, the displacement of the beams was tiny—about 0.2 millimeter—and had to be spotted with a microscope.

At the time, Stern was shocked at the outcome. He had conceived the experiment in 1919 as a challenge to what was then the leading hypothesis for the structure of the atom. Formulated by physicist Niels Bohr and others starting in 1913, it pictured electrons like little planets orbiting the atomic nucleus. Only certain orbits were allowed, and jumping between them seemed to provide an accurate explanation for the quanta of light seen in spectroscopic emissions, at least for the simple case of hydrogen. Stern disliked quanta, and together with his friend Max von Laue, he had pledged that “if this nonsense of Bohr should in the end prove to be right, we will quit physics.”

To test Bohr’s theory, Stern had set about exploring one of its most bizarre predictions, which Bohr himself did not quite believe: that in a magnetic field, atomic orbits can only lie at particular angles. To pursue this experiment, Stern realized that he could look for a magnetic effect of the electron’s orbit. He reasoned that the outermost electron of a silver atom, which according to Bohr is orbiting the nucleus in a circle, is an electric charge in motion, and it should therefore produce magnetism.

In Stern and Gerlach’s experiment, the physicists detected the splitting of the beam, which they saw as confirmation of Bohr’s odd prediction: The atoms got deflected—implying that they were magnetic themselves—and they did so not over a continuum, as in the classical model, but into two separate beams.

It was only after modern quantum mechanics was founded, beginning in 1925, that physicists realized that the silver atom’s magnetism is produced not by the orbit of its outermost electron but by that electron’s intrinsic spin , which makes it act like a tiny bar magnet.Soon after he heard about of Stern and Gerlach’s results, Albert Einstein wrote to the Nobel Foundation to nominate them for a Nobel Prize. But the letter, which Schmidt-Böcking discovered in 2011, was apparently ignored because it nominated other researchers as well, against the foundation’s rules. Stern did not quit the field. Eventually he was one of the most Nobel-nominated physicists in history, and he did get his prize in 1943, while World War II was raging.

Stern’s prize did not honor his work with Gerlach, however. Instead it was awarded for another tour de force experiment in which Stern and a collaborator measured the magnetism of the proton in 1933—shortly before the Nazi regime drove Stern out of Germany because of his Jewish background. That result was the earliest indication that the proton is not an elementary particle: we now know that it is made of three building blocks called quarks. Gerlach never won a Nobel Prize, perhaps because of his participation in the Nazi regime’s attempt to build an atomic bomb.

Today the concept of quantum spin as a 4-D entity is the foundation for all quantum computers. The quantum version of a computer bit, called the qubit, has the same mathematical form as the spin of an electron—whether or not it is in fact encoded in any spinning object. It often is not.

Even so, to this day, physicists continue to argue about how to interpret the experiment. According to now textbook quantum theory, initially, the silver atom’s outer electron does not know which way it is spinning. Instead it starts out in a “quantum superposition” of both states—as if its spin were up and down at the same time. The electron does not decide which way it is spinning—and therefore which of the two beams its atom travels in—even after it has skimmed through the magnet. When it has left the magnet and is hurtling toward the screen, the atom splits into two different, coexisting personas, as if it were in two places at the same time: one moves in an upward trajectory, and the other heads downward. The electron only picks one state when its atom arrives at the screen: the atom’s position can only be measured when it hits the screen toward the top or bottom—in one of the two spots but not both. Others take what they call a more “realist” approach: the electron knew all along where it was going, and the act of measurement is simply a sorting of the two states that happens at the magnet.

A recent prominent experiment seems to lend added credence to the former interpretation . It suggests that the two personas do coexist when the two spin states are separated. Physicist Ron Folman of Ben-Gurion University of the Negev in Israel and his colleagues re-created the Stern-Gerlach experiment using not individual atoms but a cloud of rubidium atoms. This was cooled to close to absolute zero, which made it act like a single quantum object with its own spin.

The researchers suspended the cloud in a vacuum with a device that can trap atoms and move them around using electric and magnetic fields. Initially, the cloud was in a superposition of spin up and spin down. The team then released it and let it fall by gravity. During its descent, they first applied a magnetic field to separate the atoms into two separate trajectories, according to their spin, just as in the Stern-Gerlach experiment. But unlike in the original experiment, Folman’s team then reversed the process and made the two clouds recombine into one. Their measurements showed that the cloud returned into its initial state. The experiment suggests that the separation was reversible and that quantum superposition persisted after being subject to a magnetic field that separated the two spin orientations.

The experiment goes to the heart of what constitutes a measurement in quantum mechanics. Were the spins in the Stern-Gerlach experiment “measured” by the initial sorting done by the magnet? Or did the measurement occur when the atoms hit the screen—or perhaps when the physicists looked at it? Folman’s work suggests that wherever a measurement happened, the separation was not at the first stage.

The results are unlikely to quell the philosophical diatribes around the meaning of quantum measurement, says David Kaiser, a physicist and historian of science at the Massachusetts Institute of Technology. But the impact of the Stern-Gerlach experiment remains immense. It led physicists to realize “that there was some internal characteristic of a quantum particle that really doesn’t map on to analogies to things like planets and stars,” Kaiser says.

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Bohr Model of the Atom Explained

Planetary Model of the Hydrogen Atom

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The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons. Here's a closer look at this planetary model.

Overview of the Bohr Model

Niels Bohr proposed the Bohr Model of the Atom in 1915. Because the Bohr Model is a modification of the earlier Rutherford Model, some people call Bohr's Model the Rutherford-Bohr Model. The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen .

The Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons.

Main Points of the Bohr Model

• Electrons orbit the nucleus in orbits that have a set size and energy.
• The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
• Radiation is absorbed or emitted when an electron moves from one orbit to another.

Bohr Model of Hydrogen

The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively charged electron orbits a small positively charged nucleus. Electromagnetic energy will be absorbed or emitted if an electron moves from one orbit to another. Only certain electron orbits are permitted. The radius of the possible orbits increases as n 2 , where n is the principal quantum number . The 3 → 2 transition produces the first line of the Balmer series . For hydrogen (Z = 1) this produces a photon having wavelength 656 nm (red light).

Bohr Model for Heavier Atoms

Heavier atoms contain more protons in the nucleus than the hydrogen atom. More electrons were required to cancel out the positive charge of all of the protons. Bohr believed each electron orbit could only hold a set number of electrons. Once the level was full, additional electrons would be bumped up to the next level. Thus, the Bohr model for heavier atoms described electron shells. The model explained some of the atomic properties of heavier atoms, which had never been reproduced before. For example, the shell model explained why atoms got smaller moving across a period (row) of the periodic table, even though they had more protons and electrons. It also explained why the noble gases were inert and why atoms on the left side of the periodic table attract electrons, while those on the right side lose them. However, the model assumed electrons in the shells didn't interact with each other and couldn't explain why electrons seemed to stack irregularly.

Problems With the Bohr Model

• It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit.
• The Bohr Model provides an incorrect value for the ground state orbital angular momentum .
• It makes poor predictions regarding the spectra of larger atoms.
• The Bohr Model does not predict the relative intensities of spectral lines.
• It does not explain fine structure and hyperfine structure in spectral lines.
• The Bohr Model does not explain the Zeeman Effect.

Refinements and Improvements to the Bohr Model

The most prominent refinement to the Bohr model was the Sommerfeld model, which is sometimes called the Bohr-Sommerfeld model. In this model, electrons travel in elliptical orbits around the nucleus rather than in circular orbits. The Sommerfeld model was better at explaining atomic spectral effects, such the Stark effect in spectral line splitting. However, the model couldn't accommodate the magnetic quantum number.

Ultimately, the Bohr model and models based upon it were replaced Wolfgang Pauli's model based on quantum mechanics in 1925. That model was improved to produce the modern model, introduced by Erwin Schrodinger in 1926. Today, the behavior of the hydrogen atom is explained using wave mechanics to describe atomic orbitals.

• Lakhtakia, Akhlesh; Salpeter, Edwin E. (1996). "Models and Modelers of Hydrogen". American Journal of Physics . 65 (9): 933. Bibcode:1997AmJPh..65..933L. doi: 10.1119/1.18691
• Linus Carl Pauling (1970). "Chapter 5-1".  General Chemistry  (3rd ed.). San Francisco: W.H. Freeman & Co. ISBN 0-486-65622-5.
• Niels Bohr (1913). "On the Constitution of Atoms and Molecules, Part I" (PDF). Philosophical Magazine . 26 (151): 1–24. doi: 10.1080/14786441308634955
• Niels Bohr (1914). "The spectra of helium and hydrogen". Nature . 92 (2295): 231–232. doi:10.1038/092231d0
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Mediatheque

Prof. dr. niels henrik david bohr > research profile.

by Roberto Lalli

Niels Henrik David Bohr Nobel Prize in Physics 1922 "for his services in the investigation of the structure of atoms and of the radiation emanating from them". Born in Copenhagen on October 7 1885, Niels Bohr was the second of three children of the eminent Danish physiologist Christian Bohr. Since his boyhood, Bohr enjoyed the lively cultural environment surrounding his father’s professional life. Even before becoming a university student, Bohr attended gatherings with important exponents of the Danish intelligentsia, such as the philosopher Harald Høffding, who had a long-lasting influence on the philosophical outlook which Niels Bohr brought to physical problems. He began his studies in physics in 1903 at the University of Copenhagen, then the only university in Denmark. Although Bohr is remembered for his fundamental contributions to theoretical physics, his first work concerned the purely experimental question of measuring the surface tension of a jet of liquid emerging from a cylindrical tube. To deal with this question, Bohr had to deepen both the experimental and theoretical issues concerning such a calculation. The mixture of theoretical ability and physical intuition that Bohr showed in handling this problem remained one the central features of Bohr’s style. Bohr began his epoch-making study of the structure of matter with his master’s thesis on the electron theory of metals - a topic that he further elaborated in his PhD dissertation completed in 1911. The theory on which Bohr based his study was the Lorentz-Drude model, according to which metals were depicted as gases of electrons moving almost freely in a potential generated by positive charged ions fixed in a crystal structure. The Lorentz-Drude theory explained some of the electrical and thermal properties of metals, but several experiments disagreed with the values predicted by the theory. By generalizing the assumptions of the Lorentz-Drude theory, Bohr deduced that it was not possible to derive the diamagnetic and paramagnetic properties of metals from the accepted laws of electromagnetism. This conclusion was fundamental in giving Bohr the conviction that a revision of classic electromagnetism was necessary, in order to deal with atomic phenomena. The problem Bohr underlined in his dissertation was, indeed, resolved only after fundamental developments of quantum theory, such as the formulation of the exclusion principle by Wolfgang Pauli in 1925 and the independent development by Enrico Fermi and Paul Dirac of the statistics of the particles obeying said principle in 1926.

Inside the Atom

The following steps of Bohr’s intellectual life concerned his research in England with two of the most authoritative experimental physicists of the period: J. J. Thomson, who had received the Nobel Prize in Physics in 1906 for his discovery of the electron; and E. Rutherford, who had been awarded the Nobel Prize in Chemistry in 1908 for his studies on radioactivity. Both Thomson and Rutherford had established two flourishing schools of experimental physics housed in two different laboratories. The former succeeded Lord Rayleigh as the third director of the Cavendish Laboratory in Cambridge in 1884, while the latter had instituted his laboratory in Manchester in 1907. They had also formulated two different models of the atom. Thomson had been building the first well-known dynamical model of the atom since 1903. At that time, electrons were the only subatomic particles whose existence was widely accepted because of various experimental observations, culminating in Thomson’s verification of the constancy of the electron charge-mass ratio in 1897. In the Thomson model, the negatively charged electrons were the only corpuscular constituents of the atom, while the electrical neutrality was obtained by hypothesizing a substance that surrounded the electrons and whose positive charge perfectly balanced that of the atomic electrons. Rutherford proposed a different model in 1911 after the result of the Geiger-Marsden experiments performed at the Manchester laboratory had convinced him that all the positive charge was concentrated in the pointlike centre of the atom, which he later called the nucleus. Rutherford hypothesized a planetary model of the atom in which a sphere of negative electrification of charge –Ne (where e is the charge of the electron) surrounded the nucleus of total charge +Ne due to the attraction generated by the Coulomb potential of the nucleus. In his proposal of the nuclear atom, however, Rutherford did not attempt to resolve the theoretical issues concerning the mechanical and electromagnetic stability of the atom. The major outcomes of Rutherford’s proposal were the clarification of the role of the nucleus in the scattering of alpha particles as well as of its contribution to the total atomic mass. In spite of its success in explaining some specific experimental results, the Rutherford atom lacked the mathematical refinements of the Thomson model and was rarely cited by the scientific community in the period 1911-1913.

The main developments of the Rutherford model were due to Bohr who used the study of the structure of the atom to pursue that departure from classical electromagnetism he had envisaged in his dissertation. This research was Bohr’s earliest relevant contribution to the development of quantum physics. Bohr started by underlining the problems affecting the dynamics of the electrons in Rutherford’s nuclear model. Such a system, Bohr maintained, was unstable both electromagnetically and mechanically. The former instability depended on the radiation loss due to the accelerated motion of the electrons, which would eventually lead the electron to fall on the nucleus. The mechanical instability occurred in atoms with more than one electron, because of the repulsive forces between the electrons moving in the same orbit. To overcome these difficulties, Bohr introduced a novel “hypothesis for which there will be no attempt at a mechanical foundation (as it seems hopeless)” - a hypothesis in which the kinetic energies of the electrons rotating around the nucleus were related to the period of rotation through a constant that, in turn, depended on Planck’s quantum of action. In 1913, Bohr published his proposal in three long papers grouped under the same name “On the Constitution of Atoms and Molecules.” The first of the three papers dealt with the constitution of the hydrogen atom and was a milestone in the development of the old quantum theory. The main hypothesis on which Bohr based his model was that the electron in its ground state is stable and is not subject to a radiative loss – an assumption that resolved the problem of the electromagnetic instability affecting the Rutherford model. Moreover, Bohr related this postulate to the observed spectral lines of the hydrogen atom synthesized by the generalized Balmer formula. Bohr postulated that the electron of the hydrogen atom could only occupy stationary states of specific energies. In order to explain the discreteness of atomic spectra, Bohr formulated a second postulate that constituted a deep break with classical electromagnetism: The hydrogen atom emits or absorbs radiation if and only if the electron goes from a stationary state to another by means of a sudden jump: the spectrum is discrete because the allowed stationary states are discrete. The frequency of the radiation emitted was a pure quantum phenomenon and was related to the difference of energies between the states 1 and 2 through the Planck constant h:

With this first formulation of a quantum model of the hydrogen atom, Bohr was able to resolve the theoretical problem of the stability of the atom, while explaining the discreteness of spectra. He also derived the Rydberg constant from the atomic constants and thus was able to explicitly write the generalized Balmer formula for the emission frequencies of the the hydrogen atom:

where m and e are respectively the mass and the charge of the electron.

Bohr’s formula (2) was extremely successful in explaining the observed spectra of the hydrogen-like atoms. Moreover, in 1914 Bohr’s theory of the atom received the most striking confirmation by means of an experiment performed by J. Franck and G. Hertz who observed the behavior of electrons passing through a low pressure gas in dependence of their energy. Franck and Hertz observed that up to a specific energy level the electrons were elastically scattered; however, as soon as the energy of the electrons exceeded this value the scattering became inelastic and a specific spectral line was observed. This observation was soon interpreted as a confirmation of the existence of energy levels within the atoms of the target gas.

The Correspondence Principle

The next fundamental contribute Bohr made to the quantum theory concerned the formulation of the correspondence principle, which was much more complex and controversial than the one usually exposed in physics textbooks. Bohr did not intend the principle, indeed, as a general agreement between the predictions of quantum and classical theories in the classical limit, but as specific formal correlations between quantum theory and classical mechanics. Already in 1913, Bohr used in the derivation of the Rydberg constant a reasoning that presented some analogies with what he later called the principle of correspondence. With his formula of the radiation emitted by atoms, Bohr had conceptually separated the mechanical frequency of the periodic motion of the electrons (whose harmonics, according to classical electrodynamics, should correspond to the frequencies emitted by the atom), from the radiated frequency that depended only on the energy difference between two stationary states (a pure quantum phenomenon). Bohr contended that, for high quantum numbers, the radiated frequency of the transition between two states n and n-τ was almost equal to the harmonic τ of the mechanical orbital frequency of the initial stationary state. In 1918, Bohr proposed the first systematic generalization of the correspondence principle in the first part of his paper “On the Quantum Theory of Line Spectra,” where he used this generalization to derive the selection rules in the Zeeman and Stark effects and in the fine structure of the hydrogen atom. Bohr extended the principle to multiperiodic systems (physical systems whose dynamics is determined by more than one fundamental frequency) and related the classical electrodynamical derivations of the polarization and intensities of the spectral lines to the probabilities of transition between specific stationary states of the quantum atom.

Although the agreement between quantum probabilities and classical Fourier coefficients was derived only for high quantum numbers, Bohr contended that the amplitude of the harmonic vibrations would “in some way give a measure for the probability of a transition between two states,” also for small quantum numbers. His collaborator Hans Kramers soon utilized the principle to successfully derive the approximate intensities and the polarizations of the lines of the hydrogen spectrum. Only in 1920, however, Bohr eventually exposed a definition of the correspondence principle: "Although the process of radiation cannot be described on the basis of the ordinary theory of electrodynamics, according to which the nature of the radiation emitted by an atom is directly related to the harmonic components occurring in the motion of the system, there is found, nevertheless, to exist a far-reaching correspondence between the various types of possible transitions between the stationary states on the one hand and the various harmonic components of the motion on the other hand. This correspondence is of such a nature, that the present theory of spectra is in a certain sense to be regarded as a rational generalization of the ordinary theory of radiation." After Bohr had explicitly related the quantum theory to the “formal analogy” with classical mechanics and electromagnetism, the principle became a heuristic conceptual device that came to govern the development of the old quantum theory and provided the basis for Heisenberg’s first formulation of matrix mechanics in 1925. The significance of the principle was in turn related to the creation of the school of theoretical physics in Copenhagen directed by Bohr and institutionalized in 1921 with the establishment of the University Institute of Theoretical Physics. During the 1920s, the Institute became one of the major poles of attraction for young theoretical physicists, including Paul Dirac, Pascual Jordan, Werner Heisenberg, Wolfgang Pauli, and John Slater. The Institute generated a community of theoreticians that focused on the same problems and often used a similar approach. The success of this approach was internationally recognized, culminating in the Nobel Prize in physics awarded to Niels Bohr in 1922 "for his services in the investigation of the structure of atoms and of the radiation emanating from them." Bohr himself used the correspondence principle in 1921 to deal with polyelectronic atoms. Having more than one electron, such atoms were assumed not to be multiperiodic. However, the polyelectronic atoms showed experimental properties quite similar to the hydrogen atom. In particular, the atoms all had discrete spectra. This feature led Bohr to apply the correspondence principle in order to define the structure of all the atoms in 1922. In Bohr’s "second atomic theory," as the model was later called, Bohr introduced the idea that in the state of minimum energy, the electrons were in orbits of different quantum numbers - an idea that led Bohr to explain the periodicity of the table of elements. The success of this idea depended also on experimental verifications, including the discovery by Dirk Coster and George de Hevesy of the missing element 72 (Hafnium), following Bohr’s indication that its chemical properties should not resemble those of the rare earths but rather be similar to those of element 40 (Zirconium).

The Road to Quantum Mechanics

Bohr’s influence on the development of quantum theory was not limited to the researches awarded with the Nobel Prize. The correspondence principle continued to guide the researches of various theoretical physicists who were trying to overcome the difficulties of old quantum theory in the explanation of the Helium spectrum and of the anomalous Zeeman effect. By applying the correspondence principle to the derivation of the optical dispersion formula, Kramers introduced a formalism, which was later developed by Heisenberg in a general mathematical scheme in the first formulation of matrix mechanics. In 1924, Bohr himself contributed to the theoretical debate by putting forward a new theory of radiation along with Kramers and Slater, later called the BKS theory. Before the discovery of the Compton effect in 1923, Einstein’s proposal that the radiation itself was quantized was considered too bold because it conflicted with the well-known interference phenomena of the electromagnetic field, and Bohr himself had publicly rejected Einstein’s hypothesis. In 1924, Bohr began looking for a new theory of radiation processes that explained the Compton effect, while maintaining the essential dualism between the discrete nature of matter and the continuous nature of the radiation field. According to the BKS theory, a virtual radiation was directly emitted by the electron in a stationary state. In this new picture, to the harmonic component τ of the nth stationary state corresponded a virtual oscillator, which emitted or absorbed a virtual field governed by the Maxwell equation in free space. The virtuality of oscillations and fields depended on the fact that they were accessible only statistically by observing transitions in a large number of atoms. The deepest feature of the BKS theory was that atoms influence each other only probabilistically. This meant that the classical principle of the energy-momentum conservation was violated. In the BKS theory the total energy-momentum was conserved only statistically, not for individual processes. Related to this failure of the energy-momentum conservation for individual processes was the renunciation of a causal connection between transitions in distant atoms. The BKS theory was eventually proved wrong by the experimental confirmation of the exact conservation of energy-momentum in the scattering between radiation and individual electrons. However, some commentators maintain that the theory had a role in the development of quantum mechanics because it provided a physical picture of the dispersion theory of Kramers and Heisenberg. More conceptually, the BKS theory paved the way to the following developments of the concept of probability in quantum mechanics. In an interview released in 1963, Heisenberg referred to the BKS theory as a “central step,” in the development of quantum mechanics because in such a theory the virtual waves “were a physical reality in the sense that they produced probabilities for decay or emission, and, at the same time [...] were not completely real like the electromagnetic waves.“ For Heisenberg, “such intermediate kind of reality was just the price which one had to pay for understanding quantum theory.”

The last great fundamental contribution of Niels Bohr to quantum mechanics was the enunciation of the principle of complementarity that, along with Heisenberg’s principle of indeterminacy, constituted the core of the Copenhagen interpretation of quantum mechanics, which remained the main interpretative approach to quantum mechanics for several decades. The two principles followed a development of the theory in which the competing pictures of Heisenberg’s matrix mechanics and Schrodinger’s wave mechanics had been proved to be formally identical, the statistical interpretation of the wave function proposed by Max Born in 1925 had gained momentum within the community of theorists, and the Dirac-Jordan transformation theory had provided the necessary formal generalization that unified the diverse approaches in a coherent conceptual apparatus. The new formalism, however, lacked a clear physical picture for all the mathematical symbols employed in the calculations. As Heisenberg recognized, the conceptual problems surrounding quantum mechanics in 1926 stemmed from the impossibility of applying ordinary conceptual schemes to describe atomic processes. In particular, the space-time descriptions as well as the possibility to conceive casual connections of physical phenomena were prevented by some specific features of the quantum-mechanical formalism, such as the employment of non-commutative quantities and the use of abstract multi-dimensional spaces. While Heisenberg took the decisive step to define the mathematical relationship that limited the precision with which the values of position and linear momentum could be simultaneously known, Bohr tried to formulate a coherent physical view of quantum mechanics through the principle of complementarity. Bohr was trying to resolve the conceptual problems concerning the particle-wave duality of light. According to many, this contradiction was inextricably associated with the De Broglie formulas for the corpuscular energy and momentum, which were based on the wave concepts of frequency and wave number. This contradiction had led Bohr to discard Einstein’s proposal of the photon and to propose the alternative BKS theory. After the Compton effect was confirmed for individual processes, Bohr began looking for a resolution of the contradiction inherent in wave-particle duality. Starting from these considerations, Bohr matured the idea that both features of the phenomena were essential, although mutually exclusive. In this view, the uncertainty relation calculated by Heisenberg became the measure of the impossibility that a physical situation could show simultaneously the two complementary aspects of the phenomena.

In his first exposition of the principle, Bohr stated “[t]he very nature of quantum theory […] forces us to regard the space-time coordination and the claim of causality, the union of which characterizes the classical theories, as complementary but exclusive features of the description, symbolizing the idealization of observation and definition respectively.” In Bohr’s views, the apparent contradiction of the wave-particle duality stemmed from the “impossibility of any sharp separation between the behavior of atomic objects and the interaction with the measuring instruments which serve to define the conditions under which the phenomena appear.” Several physicists regarded the complementary principle as an interpretation of quantum phenomena that allowed the consistent application of classical concepts and that clarified the relationships between these concepts and the experimental conditions, which entered within the formal structure of the quantum theory. With time, the Copenhagen interpretation became the orthodox interpretation of quantum mechanics and influenced several generations of physics. However, it is not possible to briefly summarize the conceptual meaning of the principle: Bohr himself continued to struggle for a coherent and complete definition of the principle and its interpretation has led to several philosophical and physical controversies.

Inside the Nucleus

The last major contributions of Niels Bohr to physics appeared in the 1930s in the field of nuclear physics. In 1913, Bohr had already touched on this topic by arguing that, according to his atomic theory, the β-decay had necessarily to be a nuclear phenomenon. He had reached this conclusion through a comparison between the chemical properties of the isotopes and the spectrum of their β-decay. While isotopes of the same elements had identical chemical properties, and, consequently, the same electronic configurations, they emitted β electrons with different velocities. Consequently, Bohr concluded, these emissions had nothing to do with the orbital electrons.

From the 1910s to the early 1930s, the models of the nucleus were based on the idea that its constituents were only the protons and the electrons. The discovery of the neutron by the English physicist James Chadwick in 1932, allowed a reconfiguration of the theoretical models that simplified the theoretical explanation of some experimental features of the atoms, such as the relationship between the atomic mass and the atomic number of the elements, the statistics followed by the nuclei, and their observed spin. The discovery of the neutron did not have momentous consequences only from a theoretical perspective, but it also produced deep transformations in the experimental practice. From 1932 onward, it was possible to use neutrons in order to penetrate the nuclei, because neutrons carry no charge and, consequently, are much more penetrating than, for example, alpha particles. Bohr was the first theoretical physicist to propose a reliable model that aimed at explaining the scattering observed after the nuclei had been bombarded by neutrons. In 1935, Bohr proposed that nuclear reactions should be interpreted as a two-stage process. In the first stage, the projectile amalgamates with the nucleus and forms what Bohr later called the “compound nucleus,” subject to quantum mechanical fluctuations. The second stage occurs after a certain lapse of time and could lead to three different outcomes: 1) the compound nucleus disintegrates into the particles which originally formed it, with the nucleus maintaining its initial energetic configuration; 2) the compound nucleus breaks up into the original particles, but the original nucleus has gone to one of its excited energy status; 3) the compound nucleus separates into particles different from the initial ones. Along with the Danish physicist Fritz Kalckar, Bohr developed his nuclear model and proposed a parallel between the nucleus and a drop of liquid - a parallel already proposed in 1928 by George Gamow. Bohr’s liquid drop model considered the nucleus as a collection of nucleons in which the repulsive electromagnetic forces between protons were counter-balanced by strong short-range attractive forces. The nucleus, when excited by, for example, an incoming neutron, produces different kind of vibrations, similar to the surface and volume vibrations of a drop of liquid. For small energies of the incoming neutrons, Bohr and Kalckar calculated that nuclear excitations corresponded to quantized surface vibrations of the compound nucleus described by the nuclear spectrum. This model dominated the theoretical researches on the behavior of the nucleus up to the early 1950s, when it was substituted by the shell nuclear model developed independently by several physicists, including Eugene Wigner, Maria Goeppert-Mayer, and J. Hans D. Jensen, who shared the Nobel Prize in Physics in 1963.

In 1938, Otto R. Frish and Lise Meitner employed the liquid drop model to explain the surprising discovery made by Otto Hahn and Fritz Strassmann that uranium seemed to have split into two lighter elements after neutron bombardment. Meitner and Frisch's analysis marked the beginning of the theoretical studies on nuclear fission. Bohr soon agreed with their approach and improved the application of the liquid-drop model by producing, along with John A. Wheeler, the first detailed quantitative study of the mechanism of the fission processes in 1939. One of the main successes of their theoretical model was the prediction that the rare isotope of Uranium U-235 was fissile by slow neutrons, while the more common isotope U-238 tended to absorb the incoming neutron for small velocities. Bohr’s papers on nuclear fission were the last great contributions of one the most influent theoretical physicists of the 20th century. He had a groundbreaking impact on theoretical atomic and nuclear physics. Quantum mechanics (one of the two pillars on which current theoretical physics is based, along with relativity theory) was strongly related to his research and to the school of theoretical physics he built in Copenhagen. The exact role of the various actors and the influence of the underlying philosophy is still the object of heated controversy in both history and philosophy of science. In any case, Niels Bohr was without a doubt one of the leading actors in the deep transformations from classic to quantum physics, occurring in the first half of the 20th century.

Bibliography

Crockcroft J. D. (1963) Niels Hendrik David Bohr, 1885-1962. Biographical Memoirs of Fellows of the Royal Society 9: 36-53. Darrigol O. (1992) From c-numbers to q-numbers. University of California Press, Berkely. Heilbron J. L. and Kuhn, T. S. (1969). The Genesis of the Bohr Atom. Historical Studies in the Physical Sciences 1: 211-290. Jammer M. (1966) The Conceptual Development of Quantum Mechanics. McGrow-Hill Book, New York. Pais A. (1991) Niels Bohr’s Times: In Physics, Philosophy, Polity. Clarendon Press, Oxford. Rosenfeld L. (2008) Bohr Niels Hendrik David, Complete Dictionary of Scientific Biography Vol. 2. Charles Scribner’s Son, Detroit: 239-254

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What was Niels Bohr’s most important discovery?

Niels Bohr proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus. This atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus. Bohr used his model to explain the spectral lines of hydrogen .

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Testing spooky action at a distance

A quantum computing research collaboration connects mit with the university of copenhagen..

Researchers at MIT recently signed a four-year collaboration agreement with the Novo Nordisk Foundation Quantum Computing Programme (NQCP) at Niels Bohr Institute, University of Copenhagen (UCPH), focused on accelerating quantum computing hardware research.

The agreement means that both universities will set up identical quantum laboratories at their respective campuses in Copenhagen and Cambridge, Massachusetts, facilitating seamless cooperation as well as shared knowledge and student exchange.

“To realize the promise of quantum computing, we must learn how to build systems that are robust, reproducible, and extensible. This unique program enables us to innovate faster by exchanging personnel and ideas, running parallel experiments, and comparing results. Even better, we get to continue working with Professor Morten Kjaergaard, a rising star in the field, and his team in Copenhagen,” says William Oliver , the Henry Ellis Warren (1894) Professor within the MIT Department of Electrical Engineering and Computer Science (EECS), professor of physics, associate director of the Research Laboratory of Electronics, and the head of the Center for Quantum Engineering at MIT.

Oliver’s team will supervise the funded research, which will focus specifically on the development of fault-tolerant quantum computing hardware and quantum algorithms that solve life-science relevant chemical and biological problems. The agreement provides 18 million Danish kroner (approximately $2.55 million) from the Novo Nordisk Foundation Quantum Computing Program to support MIT’s part in the research.

“A forefront objective in quantum computing is the development of state-of-the-art hardware with consistent operation,” says Maria Zuber, MIT’s presidential advisor for science and technology policy, who helped facilitate the relationship between MIT and the Danish university. “The goal of this collaboration is to demonstrate this system behavior, which will be an important step in the path to practical application.”

“Fostering collaborations between MIT and other universities is truly essential as we look to accelerate the pace of discovery and research in fast-growing fields such as quantum computing,” adds Anantha Chandrakasan, chief innovation and strategy officer, dean of engineering, and the Vannevar Bush Professor of EECS. “The support from the Novo Nordisk Foundation Quantum Computing Programme will ensure the world’s leading experts can focus on advancing research and developing solutions that have real-world impact.”

“This is an important recognition of our work at UCPH and NQCP. Professor Oliver’s team at MIT is part of the international top echelon of quantum computing research,” says Morten Kjaergaard, associate professor of quantum information physics and research group leader at the Niels Bohr Institute at UCPH. “This project enables Danish research in quantum computing hardware to learn from the best as we collaborate on developing hardware for next-generation fault-tolerant quantum computing. I have previously had the pleasure of working closely with Professor Oliver, and with this ambitious collaboration as part of our the Novo Nordisk Foundation Quantum Computing Programme, we are able to push our joint research to a new level.”

Peter Krogstrup, CEO of NQCP and professor at Niels Bohr Institute, follows up, “We are excited to work with Will Oliver and his innovative team at MIT. It aligns very well with our strategic focus on identifying a path with potential to enable quantum computing for life sciences. The support aims to strengthen the already strong collaboration between Will and Morten’s team, a collaboration we hope to make an important part of the NQCP pathfinder phase over the coming years.”

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Testing spooky action at a distance

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Researchers at MIT recently signed a four-year collaboration agreement with the Novo Nordisk Foundation Quantum Computing Programme (NQCP) at Niels Bohr Institute, University of Copenhagen (UCPH), focused on accelerating quantum computing hardware research.

The agreement means that both universities will set up identical quantum laboratories at their respective campuses in Copenhagen and Cambridge, Massachusetts, facilitating seamless cooperation as well as shared knowledge and student exchange.

“To realize the promise of quantum computing, we must learn how to build systems that are robust, reproducible, and extensible. This unique program enables us to innovate faster by exchanging personnel and ideas, running parallel experiments, and comparing results. Even better, we get to continue working with Professor Morten Kjaergaard, a rising star in the field, and his team in Copenhagen,” says William Oliver, the Henry Ellis Warren (1894) Professor within the MIT Department of Electrical Engineering and Computer Science (EECS), professor of physics, associate director of the Research Laboratory of Electronics, and the head of the Center for Quantum Engineering at MIT.

Oliver’s team will supervise the funded research, which will focus specifically on the development of fault-tolerant quantum computing hardware and quantum algorithms that solve life-science relevant chemical and biological problems. The agreement provides 18 million Danish kroner (approximately $2.55 million) from the Novo Nordisk Foundation Quantum Computing Program to support MIT’s part in the research.

“A forefront objective in quantum computing is the development of state-of-the-art hardware with consistent operation,” says Maria Zuber, MIT’s presidential advisor for science and technology policy, who helped facilitate the relationship between MIT and the Danish university. “The goal of this collaboration is to demonstrate this system behavior, which will be an important step in the path to practical application.”

“Fostering collaborations between MIT and other universities is truly essential as we look to accelerate the pace of discovery and research in fast-growing fields such as quantum computing,” adds Anantha Chandrakasan, chief innovation and strategy officer, dean of engineering, and the Vannevar Bush Professor of EECS. “The support from the Novo Nordisk Foundation Quantum Computing Programme will ensure the world’s leading experts can focus on advancing research and developing solutions that have real-world impact.”

“This is an important recognition of our work at UCPH and NQCP. Professor Oliver’s team at MIT is part of the international top echelon of quantum computing research,” says Morten Kjaergaard, associate professor of quantum information physics and research group leader at the Niels Bohr Institute at UCPH. “This project enables Danish research in quantum computing hardware to learn from the best as we collaborate on developing hardware for next-generation fault-tolerant quantum computing. I have previously had the pleasure of working closely with Professor Oliver, and with this ambitious collaboration as part of our the Novo Nordisk Foundation Quantum Computing Programme, we are able to push our joint research to a new level.”

Peter Krogstrup, CEO of NQCP and professor at Niels Bohr Institute, follows up, “We are excited to work with Will Oliver and his innovative team at MIT. It aligns very well with our strategic focus on identifying a path with potential to enable quantum computing for life sciences. The support aims to strengthen the already strong collaboration between Will and Morten’s team, a collaboration we hope to make an important part of the NQCP pathfinder phase over the coming years.”

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• Center for Quantum Engineering
• Research Laboratory of Electronics
• Department of Electrical Engineering and Computer Science
• Department of Physics
• Niehls Bohr Institute at the University of Copenhagen

Related Topics

• Collaboration
• Quantum computing
• Mathematics
• International initiatives
• Electrical Engineering & Computer Science (eecs)

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