Ten years later, Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann equations from Albert Einstein's equations of general relativity, showing that the Universe might be expanding in contrast to the static Universe model advocated by Einstein at that time.

Only a few months later, Karl Schwarzschild found a solution to Einstein field equations, which describes the gravitational field of a point mass and a spherical mass.

Louis de Broglie later ( 1924 ) showed in his doctoral dissertation that electrons are in fact much like photons in the respect that they act both as waves and as particles in a dual manner as Einstein had shown earlier for light.

Later, Albert Einstein proposed that the quanta of light might be regarded as real particles, and ( still later ) the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton.

Einstein later declared the cosmological constant the biggest blunder of his life.

In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper Zur Quantentheorie der Strahlung ( On the Quantum Theory of Radiation ); via a re-derivation of Max Planck ’ s law of radiation, conceptually based upon probability coefficients ( Einstein coefficients ) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation ; in 1928, Rudolf W. Ladenburg confirmed the existences of the phenomena of stimulated emission and negative absorption ; in 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify “ short ” waves ; in 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission ; in 1950, Alfred Kastler ( Nobel Prize for Physics 1966 ) proposed the method of optical pumping, experimentally confirmed, two years later, by Brossel, Kastler, and Winter.

Albert Einstein later re-derived the transformation from his postulates of special relativity.

In 1905, Einstein explained certain features of the photoelectric effect by assuming that Planck's energy quanta were actual particles, which were later dubbed photons.

Based upon Max Planck's theory of black-body radiation, Einstein theorized that the energy in each quantum of light was equal to the frequency multiplied by a constant, later called Planck's constant.

" Five years later, Albert Einstein published his paper on special relativity, which challenged the very simple set of rules laid down by Newtonian mechanics, which had been used to describe force and motion for over two hundred years.

When it was found in 1900 by Max Planck that the energy of waves could be described as consisting of small packets or " quanta ", Albert Einstein further developed this idea to show that an electromagnetic wave such as light could be described as a particle ( later called the photon ) with a discrete quantum of energy that was dependent on its frequency.

Then, in 1905, to explain the photoelectric effect ( 1839 ), i. e., that shining light on certain materials can function to eject electrons from the material, Albert Einstein postulated, based on Planck ’ s quantum hypothesis, that light itself consists of individual quantum particles, which later came to be called photons ( 1926 ).

Einstein later famously derided entanglement as " spukhafte Fernwirkung " or " spooky action at a distance ".

A more mathematical statement of the Principle of Relativity made later by Einstein, which introduces the concept of simplicity not mentioned above is:

It was Einstein who later proposed that it is the electromagnetic radiation itself that is quantized, and not the energy of radiating atoms.

Einstein later referred to his failure to predict the expansion of the universe from theory, before it was proven by observation of the cosmological red shift, as the " biggest blunder " of his life.

Some of Mach's criticisms of Newton's position on space and time influenced Einstein, but later Einstein realized that Mach was basically opposed to Newton's philosophy and concluded that his physical criticism was not sound.

Six years later, Einstein would decline the offer of an honorary degree from Brandeis, writing to Brandeis president Abram L. Sachar that " what happened in the stage of preparation of Brandeis University was not at all caused by a misunderstanding and cannot be made good any more.

Giacconi's pioneering research continued in 1978 with the Einstein Observatory, the first fully imaging X-ray telescope put into space, and later with the Chandra X-ray Observatory, which was launched in 1999 and is still in operation.

Phonons are also necessary for understanding the lattice heat capacity of a solid, as in the Einstein model and the later Debye model.

Seconds later, Earth received the wave of radiation, where the powerful output of gamma rays inundated the detectors of three U. S. Department of Defense Vela satellites, the Soviet Prognoz 7 satellite, and the Einstein Observatory.

The inn was a popular stop for farmers going to the city's markets and later it sat near a horse racing track built by Aaron Einstein in 1868.

The debates between Bohr and Einstein essentially concluded in 1935, when Einstein finally expressed what is widely considered his best argument against the completeness of quantum mechanics.

" This is a major departure from the approach of Newton, Einstein and Schrödinger, all of whom expressed their theories in terms of deterministic equations.

These equations may be more succinctly expressed using Einstein notation, in which matched indices imply a sum over those indices and and:

" This is a major departure from the approach of Newton, Einstein and Schrödinger, all of whom expressed their theories in terms of deterministic equations.

First published by Einstein in 1915 as a tensor equation, the EFE equate spacetime curvature ( expressed by the Einstein tensor ) with the energy and momentum within that spacetime ( expressed by the stress – energy tensor ).

In later years Einstein expressed his dislike of the idea of " relativistic mass ":

Although the opposition to Einstein was expressed in scientific terms, his theories were also rejected as un-German.

The Bianchi identities can also be easily expressed with the aid of the Einstein tensor:

* Monochromatic electromagnetic plane wave, an example of an important exact plane wave solution to the Einstein field equation in general relativity which is expressed using Mathieu cosine functions.

This allows all three Einstein coefficients to be expressed in terms of the single oscillator strength associated with the particular atomic spectral line:

Quite uncharacteristically, Einstein took this criticism very badly, angrily replying " I see no reason to address the, in any case erroneous, opinion expressed by your referee.

The foundations of quantum mechanics were established during the first half of the 20th century by Max Planck, Niels Bohr, Werner Heisenberg, Louis de Broglie, Arthur Compton, Albert Einstein, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Enrico Fermi, Wolfgang Pauli, David Hilbert, Wilhelm Wien, Satyendra Nath Bose, Arnold Sommerfeld and others.

Research into quantum entanglement was initiated by a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen describing the EPR paradox and several papers by Erwin Schrödinger shortly thereafter.

Following the EPR paper, Erwin Schrödinger wrote a letter ( in German ) to Einstein in which he used the word Verschränkung ( translated by himself as entanglement ) " to describe the correlations between two particles that interact and then separate, as in the EPR experiment ".

From left to right: Top row-Archimedes, Aristotle, Alhazen | Ibn al-Haytham, Leonardo da Vinci, Galileo Galilei, Antonie van Leeuwenhoek ; Second row-Isaac Newton, James Hutton, Antoine Lavoisier, John Dalton, Charles Darwin, Gregor Mendel ; Third row-Louis Pasteur, James Clerk Maxwell, Henri Poincaré, Sigmund Freud, Nikola Tesla, Max Planck ; Fourth row-Ernest Rutherford, Marie Curie, Albert Einstein, Niels Bohr, Erwin Schrödinger, Enrico Fermi ; Bottom row-J. Robert Oppenheimer, Alan Turing, Richard Feynman, E. O. Wilson, Jane Goodall, Stephen Hawking

during a political disaster ", dated 1937-1941, a reader can hear speaking such persons as Erwin Schrödinger, Niels Bohr, Albert Einstein or Max Planck, not only about physics, but also about many other

Finally, some of the originators of quantum theory ( notably Einstein and Schrödinger ) were unhappy with what they thought were the philosophical implications of quantum mechanics.

Like Einstein, Schrödinger was dissatisfied with the concept of entanglement, because it seemed to violate the speed limit on the transmission of information implicit in the theory of relativity.

Schrödinger intended his thought experiment as a discussion of the EPR article — named after its authors Einstein, Podolsky, and Rosen — in 1935.

Schrödinger and Einstein exchanged letters about Einstein's EPR article, in the course of which Einstein pointed out that the state of an unstable keg of gunpowder will, after a while, contain a superposition of both exploded and unexploded states.

The gunpowder had been mentioned in Einstein's original suggestion to Schrödinger 15 years before, and apparently Einstein had carried it forward to the present discussion.

It was supported by Einstein, confirmed by the electron diffraction experiments of Davisson and Germer, and generalized by the work of Schrödinger.

Schrödinger, though, always opposed a statistical or probabilistic approach, with its associated discontinuities — much like Einstein, who believed that quantum mechanics was a statistical approximation to an underlying deterministic theory — and never reconciled with the Copenhagen interpretation.

Born was awarded half of the 1954 Nobel Prize in physics for this understanding, though it was vigorously contested at the time by the original physicists working on the theory, such as Schrödinger and Einstein.

Skepticism from Einstein and published criticisms from other physicists discouraged Schrödinger, and his work in this area has been largely ignored.

Bryce DeWitt first published this equation in 1967 under the name " Einstein – Schrödinger equation "; it was later renamed the " Wheeler – DeWitt equation ".

Bohr publicly introduced the principle of complementarity in a lecture he delivered on 16 September 1927 at the International Physical Congress held in Como, Italy, attended by most of the leading physicists of the era, with the notable exceptions of Einstein, Schrödinger, and Dirac.