ALBERT MICHELSON (1852-1931) EDWARD MORLEY (1838-1923)

1887 – USA

‘The aim of the experiment was to measure the effect of the Earth’s motion on the speed of light’

This celebrated experiment found no evidence of there being an effect.

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ALEXANDER GRAHAM BELL (1847-1922)

1875 – USA

‘The inventor of the telephone, Bell devoted much of his life to working with the deaf’

After emigrating to Canada from Scotland in 1870, Bell met Thomas Watson, who would help Bell’s theoretical ideas become physical reality. Bell believed that if the right apparatus could be devised, sound waves from the mouth could be converted into electric current, which could then be sent down a wire relatively simply and converted into sound at the other end using a suitable device. Bell’s telephone was patented in 1876.

Bell used the money brought in from his invention to found his company AT & T and the Bell Laboratories.

Just as THOMAS EDISON improved the viability of Bell’s telephone, so Bell enhanced Edison’s phonograph.

Bell spent some time educating Helen Keller and was instrumental in founding the journal ‘Science‘.

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THOMAS ALVA EDISON (1847-1931)

1875 – USA

‘We don’t know one millionth of one percent of anything’

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THOMAS ALVA EDISON

‘Genius is one percent inspiration and ninety-nine percent perspiration’
Scorning high-minded theoretical and mathematical methods was the basis of Edison’s trial and error approach to scientific enquiry and the root of his genius.

1877 – Patents the carbon button transmitter, still used in telephones today.
1877 – Invents the phonograph.
1879 – Invents the first commercial incandescent light after more than 6000 attempts at finding the right filament and finally settling on carbonized bamboo fibre.

Edison held 1093 patents either jointly or singularly and was responsible for inventing the Kinetograph and the Kinetoscope (available from 1894) the Dictaphone, the mimeograph, the electronic vote-recording machine and the stock ticker.

His laboratory was established at Menlo Park in 1876, establishing dedicated research and development centres full of inventors, engineers and scientists. In 1882 he set up a commercial heat, light and power company in Lower Manhattan, which became the company General Electric.

Experimenting with light bulbs, in 1883 one of his technicians found that in a vacuüm, electrons flow from a heated element – such as an incandescent lamp filament – to a cooler metal plate.
The electrons can flow only from the hot element to the cool plate, but never the other way. When English physicist JOHN AMBROSE FLEMING heard of this ‘Edison effect’ he used the phenomenon to convert an alternating electric current into a direct current, calling his device a valve. Although the valve has been replaced by diodes, the principle is still used today.

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WERNER HEISENBERG (1901- 76)

1927 – Germany

‘It is impossible to determine exactly both the position and momentum of a particle (such as an electron) simultaneously’

The principle excludes the existence of a particle that is stationary.

To measure both the position and momentum ( momentum = mass × velocity ) of a particle simultaneously requires two measurements: the act of performing the first measurement will disturb a particle and so create uncertainty in the second measurement.
Thus the more accurately a position is known; the less accurately can the momentum be determined.

The disturbance is so small it can be ignored in the macroscopic world, but is quite dramatic for particles in the microscopic world.
MAX BORN’S ‘probabilistic’ interpretation, expressed at about the same time, concerning the likelihood of finding a particle at any point through probability defined by the amplitude of its associated wave, led to similar conclusions.

The uncertainty principle also applies to energy and time. A particle’s kinetic energy cannot be measured with complete precision either.

Heisenberg suggested the model of the proton and neutron being held together in the nucleus of the atom after the work of JAMES CHADWICK who discovered the neutron in 1932.

Heisenberg decided to try to develop a new model of the atom, more fundamentally based on quantum theory that worked for all atoms. He believed the approach of trying to visualise a physical model of the atom was destined to fail because of the paradoxical wave-particle nature of electrons.

Every particle has an associated wave. The position of a particle can be precisely located where the wave’s undulations are most intense. But where the wave’s undulations are most intense, the wavelength is also at its most ill-defined, and the velocity of the associated particle is impossible to determine. Similarly, a particle with a well-defined wavelength has a precise velocity but a very ill-defined position.

Since the orbits of electrons could not be observed, he decided to ignore them and focus instead on what could be observed and measured; namely the energy they emitted and absorbed, as shown in the spectral lines. He tried to devise a mathematical way of representing the orbits of electrons, and to use this as a way of predicting the atomic features shown up in the spectral lines.
He showed that matrix mechanics could account for many of the properties of atoms, including those with more than one electron.

Together with PAUL DIRAC, Pascual Jordan created a new set of equations based on the rival theories of Schrödinger and Heisenberg, which they called ‘transformation theory’. Whilst studying these equations, Heisenberg noticed the paradox that measurements of position and velocity (speed and direction) of particles taken at the same time gave imprecise results. He believed that this uncertainty was a part of the nature of the sub-atomic world. The act of measuring the velocity of a subatomic particle will change it, making the simultaneous measurement of its position invalid.

An unobserved object is both a particle and a wave. If an experimenter chooses to measure the object’s velocity, the object will transform itself into a wave. If an experimenter chooses to measure its position, it will become a particle. By choosing to observe either one thing or the other, the observer is actually affecting the form the object takes.
The practical implication of this is that one can never predict where an electron will be at a precise moment, one can only predict the probability of its being there.

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PAUL DIRAC (1902- 84)

1928 – UK

‘Every fundamental particle has an antiparticle – a mirror twin with the same mass but opposite charge’

English Physicist Paul Dirac, who developed a wave equation for the electron. --- Image ©

PAUL DIRAC

‘It appears that the simplest Hamiltonian for a point-charge electron satisfying the requirements of both relativity and the general transformation theory leads to an explanation of all duplexity phenomena without further assumption’

1931 – UK

‘A magnetic monopole is analogous to electric charge’

A magnetic monopole is a hypothetical particle that carries a basic magnetic charge – in effect, a single north or south magnetic pole acting as a free particle.

Until recently no one has observed a monopole.

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GEORGE FITZGERALD (1851-1901) HENDRICK LORENTZ (1853-1928)

1890 – Ireland
1904 – Holland

‘A moving object appears to contract’

The contraction is negligible unless the object’s speed is close to the speed of light.

In 1890 Fitzgerald suggested that an object moving through space would shrink slightly in its direction of travel by an amount dependent on its speed.

In 1904 Lorentz independently studied this problem from an atomic point of view and derived a set of equations to explain it. A year later, Einstein derived Lorentz’s equations independently from his special theory of relativity.

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WILLIAM HENRY BRAGG (1862-1942) WILLIAM LAWRENCE BRAGG (1890-1971)

1912 – England

X-rays scattered from a crystal will show constructive interference provided their wavelength ( λ ) fits the equation

2d sin θ = n λ 

where d is the spacing between atoms of the crystal, θ the angle through which the rays have scattered and n is any whole number

This is the cornerstone of the science of X-ray crystallography.

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X-RAY DIFFRACTIONX-RAY DIFFRACTION

Symmetrically spaced atoms cause re-radiated X...

Symmetrically spaced atoms cause re-radiated X-rays to reinforce each other in the specific directions where their path-length difference, 2d sin θ, equals an integer multiple of the wavelength λ (Photo credit: Wikipedia)