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Origins of the quantum theory

- Sabina Chiriotti
- IFAE Thursday meeting, March 26th 2009

The old quantum theory

To know the Revolutionary impact of quantum

physics one need first to look at pre-quantum

physics

Max Planck

- 1900 Max Plank introduced the concept of energy

radiated in discrete quanta. - Found ? relationship between the radiation

emited by a blackbody and its temperature. - Eh? quanta of energy is proportional to the

frequency with which the blackbody radiate

assuming that energies of the vibrating

electrons that radiate the light are quantized ?

obtain an expression that agreed with experiment.

he recognized that the theory was physically

absurd, he described as "an act of desperation" .

Albert Einstein

- The photoelectric effect
- Not explained by Maxwell's theory since the rate

of electrons not depended on the intensity of

light, but in the frequency. - 1905 Einstein applied the idea of Plank's

constant to the problem of the photoelectric

effect ? light consists of individual quantum

particles, which later came to be called photons

(1926). - Electrons are released from certain materials

only when particular frequencies are reached

corresponding to multiples of Plank's constant

.

Niels Bohr

- 1913 Bohr quantized energy ? explain how

electrons orbit a nucleus. - Electrons orbit with momenta, and energies

quantized. - Electrons do not loose energy as they orbit the

nucleus, only change their energy by "jumping"

between the stationary states emitting light

whose wavelength depends on the energy

difference. - Explained the Rydberg formula (1888), which

correctly modeled the light emission spectra of

atomic hydrogen - Although Bohr's theory was full of

contradictions, it provided a quantitative

description of the spectrum of the hydrogen atom

Two theorist, Niels Bohr and Max Planck, at the

blackboard.

By the late 1910s

- 1916 Arnold Sommerfeld
- - To account for the Zeeman effect (1896)

atomic absorption or emission spectral lines

change when the light is first shinned through a

magnetic field, - - he suggested elliptical orbits in atoms

in addition to spherical orbits. - In 1924, Louis de Broglie
- - theory of matter waves
- - particles can exhibit wave

characteristics and vice versa, in analogy to

photons. - 1924, another precursor Satyendra N. Bose
- - new way to explain the Planck radiation law.
- - He treated light as if it were a gas of

massless particles (now called photons).

Scientific revolution 1925 to January 1928

- Wolfang Pauli the exclusion principle
- Werner Heisemberg, with Max Born and Pascual

Jordan, - - discovered matrix mechanics ?first

version of quantum mechanics. - Erwin Schrödinger
- - invented wave mechanics, a second form

of quantum mechanics in which the state of a

system is described by a wave function, - Electrons were shown to obey a new type of

statistical law, Fermi- Dirac statistics - Heisenberg Uncertainty Principle.
- Dirac contributions to quantum mechanics

and quantum electrodynamics

Many physicists have also contributed to the

quantum theory

- Max Planck Light quanta
- Einstein photon photoelectric
- Louis de Broglie Matter waves
- Erwin Schrödinger waves equations
- Max Born probability waves
- Heisenberg uncertainty
- Paul Dirac Spin electron equation
- Niels Bohr Copenhagen
- Feynman Quantum-electrodynamics
- John Bell EPR Inequality locality
- David Bohm Pilot wave (de Broglie)
- ...

Paul Dirac and Werner Heisemberg in Cambrige,1930.

The first Solvay Congress in 1911 assembled the

pioneers of quantum theory.

Old faces and new at 1927 Solvay Congress

Scientific revolution Heisenberg the

uncertainty principle

Werner Karl Heisenberg Brief chronology

- 1901 - 5Dec He was born in Würzburg, Germany
- 1914 Outbreak of World War I.
- 1920 he entered at the University of Munich
- ? Arnold Sommerfeld admitted

him to his advanced seminar. - 1925. 29 June Receipt of Heisenberg's paper

providing breakthrough to quantum mechanics - 1927. 23 Mar. Receipt of Heisenberg's paper on

the uncertainty principle. - 1932. 7 June Receipt of his first paper on the

neutron-proton model of nuclei. - 1933 .11 Dec. Heisenberg receives Nobel Prize for

Physics (for 1932). - 1976. 1 Feb. Dies because of cancer at his home

in Munich.

Influences

- Studied with three of the worlds leading atomic

theorists Sommerfeld, Max Born and Niels Bohr. - In 3 of the worlds leading centres for

theoretical atomic physics Munich, Göttingen and

Copenhagen. - -

Max Born

From Sommerfeld I learn optimism, from the

Göttigen people mathematics and from Bohr

physics Heisemberg

Arnold Sommerfeld (left) and Niels Bohr

Wolfgang Pauli

- In Munich he began a life-long friendship with

Wolfgang Pauli.

During 1920

- Heisenbergs travels and teachers during help him

to become one of the leading physicists of his

time. - Goal fortune of entering in the world atomic

physics just in the right moment for

breakthrough. - Found that properties of the atoms predicted from

the calculations did not agree with existing

experimental data. - The old quantum theory, worked well in simple

cases, but experimental and theoretical study was

revealing many problems ? crisis in quantum

theory. - The old quantum theory had failed but Heisenberg

and his colleagues saw exactly where it failed.

Quantum mechanics 1925-1927

- The leading theory of the atom when Heisenberg

entered at University was quantum theory of Bohr. - Although it had been highly successful, three

areas of research indicated that this theory was

inadequate - light emitted and absorbed by atoms
- the predicted properties of atoms and molecules
- The nature of light, did it act like waves or

like a stream of particles? - 1924 physicists were agreed old quantum theory

had to be replaced by quantum mechanics.

The breakthrough to quantum mechanics

- Heisenberg set the task of finding the new
- quantum mechanics
- Since the electron orbits in atoms could not be

observed, he tried to develop a quantum mechanics

without them. - By 1925 he had an answer, but the mathematics was

so unfamiliar that he was not sure if it made any

sense. - ? These unfamiliar mathematics contain arrays of

numbers known as matrix. - Born sent Heisenbergs paper off for publication.

All of my meagre efforts go toward killing off

and suitably replacing the concept of the orbital

path which cannot observe Heisemberg, letter to

Pauli 1925

The first page of Heisenberg's break-through

paper on quantum mechanics, published in the

Zeitschrift für Physik, 33 (1925),

The present paper seeks to establish a basis for

theoretical quantum mechanics founded exclusively

upon relationships between quantities which in

principle are observable. Heisemberg, summary

abstract of his first paper on quantum mechanics

The wave-function formulation

1926 Erwin Schrödinger proposed another quantum

mechanics, wave mechanics. Appealed to many

physicists because it seemed to do everything

that matrix mechanics could do but much more

easily and seemingly without giving up the

visualization of orbits within the atom.

I knew of Heisemberg theory, of course, but I

felt discouraged, not to say repelled, by the

methods of transcendental algebra, which appeared

difficult to me, and by the lack of

visualizability.- Schrödinger in 1926.

The Uncertainty Principle

1926 The rout to uncertainty relations lies in

a debate between alternative versions of quantum

mechanics - Heisenberg and his closest

colleagues who espoused the matrix

form of quantum mechanics - Schrödinger and

his colleagues who espoused the new

wave mechanics .

May 1926, Matrix mechanics and wave mechanics,

apparently incompatible ? proof that gave

equivalent results.

The more I think about the physical portion of

Schrödingers theory, the more repulsive I find

it.. What Schrödinger writes about the

visualizability of his theory is not quite right,

in other words its crap Heisenberg, writing to

Pauli, 1926

- In 1927 the intensive work led to Heisenbergs

uncertainty principle and the Copenhagen

Interpretation - The more precisely the position is determined,

the less precisely the momentum is known in this

instant, and vice versa Heisenberg, uncertainty

paper, 1927 - After that, Born presented a statistical

interpretation of the wave function, Jordan in

Göttingen and Dirac in Cambridge, created unified

equations known as transformation theory. The

basis of what is now regarded as quantum

mechanics. - The uncertainty principle was not accepted by

everyone. Its most outspoken opponent was

Einstein.

.

Conclusion

- The history of Quantum mechanics its not easy,

many events pass simultaneously ? difficult

period. - Quantum mechanics was created to describe an

abstract atomic world far removed from daily

experience, its impact on our daily lives has

become very important. - Spectacular advances in chemistry, biology, and

medicine - Quantum information
- The creation of quantum physics has transformed

our world, bringing with it all the benefitsand

the risksof a scientific revolution.

Bibliography

- http//www.aip.org/history/heisenberg/p08.htm
- http//www.4physics.com/phy_demo/QM_Article/articl

e.html - http//www.vcpc.univie.ac.at/ian/hotlist/qc/qm.sh

tml - http//www.slac.stanford.edu/pubs/beamline/30/2/30

-2-carson.pdf