## Einstein, Albert (1879–1955)

## Einstein, Albert (1879–1955)

# EINSTEIN, ALBERT

*(1879–1955)*

Albert Einstein was born in Ulm, in the south German kingdom of Württemberg on March 14, 1879. Following his graduation from the Federal Polytechnical Institute (*ETH* ) in Zurich in 1900 he obtained a job as a patent examiner, ("technical expert, third class") in the Swiss patent office in Bern, starting in the summer of 1902. In January 1903 he married his first wife, Mileva Maric, a fellow student of physics at the *ETH* and, with Mileva's support, continued his investigations in physics, earning a PhD from the University of Zürich in 1905.

That was Einstein's "miracle year." In 1905 Einstein published the founding papers of the special theory of relativity, including a version of the famous *E* = *mc* ^{2}. Also in 1905 he developed the light quantum hypothesis to treat the photo-electric effect, a work important in the subsequent development of the quantum theory and the official basis of his 1922 award of the Nobel Prize. There were also two papers on Brownian motion he produced that year, which helped demonstrate the reality of molecules.

Einstein left the patent office in 1909, moving to Berlin in 1914 to assume the directorship of the new Kaiser Wilhelm Institute for Physics. There his marriage quickly dissolved and his wife moved back to Zürich with their two sons, Hans Albert and Eduard. Einstein had been working on extensions of relativity since 1907 and in 1916 he published an account of what he called the "general theory" of relativity, which is essentially the modern theory of gravity. It predicted the bending of light rays around the sun. When that was confirmed during the solar eclipse of 1919, Einstein became a worldwide celebrity overnight, the first scientific superstar.

Einstein's celebrity status made him a target of growing German antiSemitism. His own interest was growing in Zionist and pacifist causes. Amidst this turmoil, in 1917 Einstein became ill and was cared for by his cousin Elsa Einstein Löwenthal, recently divorced and with two daughters, Ilse and Margot. Following his own divorce in 1919, he married Elsa, whose daughters also took the name Einstein.

In the period from 1914 to 1919 Einstein's scientific work continued to flourish. He began investigations into gravitational waves and cosmology, where he reluctantly introduced the cosmological constant, which he subsequently rejected, but which has come back to represent what now appears to be substantial density and pressure associated with empty space. Einstein also worked on statistical aspects of the quantum theory, developing the coefficients of spontaneous and induced emission and absorption that provided the theoretical opening for laser technology.

In the 1920s Einstein traveled extensively in aid of science and of Zionism. His scientific contributions slowed down in this period, although he made some preliminary attempts at tying together the electromagnetic and gravitational fields geometrically in a unified field theory. He made important contributions to the quantum theory of gases, developing Einstein-Bose statistics to treat radiation as a quantum gas of indistinguishable particles. This led to his discovery of the Bose-Einstein condensation, a low temperature phenomenon displaying quantum behavior at nearly macroscopic scale. In the 1927 Solvay conference Einstein began to "debate" with Niels Bohr over the foundations of the emerging quantum mechanics.

Einstein left Germany in 1932 for the Institute for Advanced Study in Princeton. He became a United States citizen in 1940. A year earlier he had signed a letter drafted by Leo Szilard advising President Franklin D. Roosevelt of the military potential of atomic energy. Later he was an advocate for the control of atomic energy and for institutions supporting world peace. He was also a prominent critic of McCarthyism and a defender of civil liberties, as well as an outspoken opponent of racism and a defender of civil rights. Einstein died on April 18, 1955, of complications following a ruptured aortic aneurysm. His last scientific work was on the unfinished project for a unified field theory. His last phrase, written a few days before his death, was in a document with the pungent title, "Political Passions, Aroused Everywhere, Demand Their Victims."

## Philosophy of Physics

Throughout his life Einstein read deeply in philosophy, where he was influenced both by David Hume and Immanuel Kant, as well as by Spinoza. His views in turn influenced the development of neo-positivism, whose more extreme doctrines he rejected in his criticism of the quantum theory. His philosophical reflections on the epistemology of science, as well as on metaphysical issues relating to space, time and causality, constitute an important chapter in twentieth century thought.

### relativity

Einstein was a critic of the spatio-temporal framework of Newtonian physics, following a path marked out by Ernst Mach, who attacked Newton's introduction of "absolute" space and time not as unobservable (a fact advertised by Newton himself) but as unnecessary for doing physics. In Einstein's hands, however, Mach's critical method became a tool for positive theory construction.

Newton argued that acceleration must be absolute in order to explain inertial effects, such as the way water crawls up the sides of a rotating bucket. From absolute acceleration Newton moved (questionably, it turns out) to absolute space and time. Mach countered that inertial effects, like others, could be seen as purely relational. In particular, if one could rotate large enough masses and leave the bucket alone the same water-crawling effects would occur. This idea came to be known as Mach's Principle, which strongly influenced Einstein's development of the general theory of relativity. Sympathetic to Mach's relational conception of space and time, Einstein criticized an asymmetry built into the Newtonian framework. There space and time affect the behavior of bodies in so far as, in the absence of impressed forces, bodies move inertially, along spatially straight lines with temporally constant speeds. But there is no reciprocity. If space and time are absolute, bodies cannot affect spatio-temporal structure. Once space and time were merged into a unified spacetime, the field equations of general relativity allowed a reciprocal interplay between spacetime and matter.

The introduction of four dimensional spacetime, however, comes from the 1905 special theory of relativity. There Einstein dealt with an apparent conflict between the principle of relativity (any inertial frame is suitable for the representation of electrodynamic as well as mechanical phenomena) and the constancy of the speed of light for inertial observers. In the 1905 paper Einstein approaches this conflict by applying a technique of conceptual analysis that he learned from Mach (and from David Hume). He asks what is time and quickly shifts, epistemologically, to how one tells time in reading a clock. Telling time involves a spatially local judgment of simultaneity (where are the hands, when?); that is, it involves events in more or less the same place. What about events that happen very far apart?

The suggestion is that here one reaches the limit of applicability of the concept of simultaneity. In Mach's hands (or Hume's) one might stop here, with skepticism about the very meaningfulness of assertions of distant simultaneity. But, as Einstein commented later, although he respected Mach's hobbyhorse of seeking the limits of concepts he felt that it does not give rise to anything living. To employ conceptual analysis constructively one needs a theory. In the 1905 paper that theory is grounded on a quasi-operational definition using light signals to determine when distant events happen at the same time. Armed with that definition of simultaneity one can not only reconcile the principle of relativity with the constancy of the velocity of light, one can go on to develop a spacetime framework in which descriptions of events in different inertial frames are tied to one another by Lorentz transformations that leave the so-called spacetime "interval" invariant. Einstein had wanted to refer to this work as a theory of invariants. Ironically, Max Planck coined the term "relativity," and it stuck.

One of the conceptual innovations in special relativity is the variation of relativistic mass with velocity, which no longer appears to be a constant property of matter. This shift in the conception of *mass* prompted Thomas Kuhn and Paul Feyerabend to feature an "incommensurability" between Newtonian and relativistic physics. Einstein was unequivocally against the idea that the so-called "relativistic mass" is a proper notion at all. He rejects it as coordinate dependent and, hence, merely perspectival and thinks "the—unhappily—often mentioned concept of a mass which depends on speed is quite misleading." Instead, in keeping with his emphasis on invariance (as a touchstone for scientific objectivity), Einstein says, "It is better to use the word mass exclusively for rest mass … which is always the same, independent of the speed …" (Earman and Fine 1977, p. 538). It is worth noting that the mass term *m* in *E* = *mc* ^{2} denotes precisely the rest mass.

Einstein was an early supporter of logical empiricism. He was also one of its icons, in part because his positivistic analysis in special relativity seemed evident also in the general theory. In his 1916 account, Einstein defends the relativity of all motion (not just inertial) by requiring that laws of nature be expressed by equations "valid for all coordinate systems." Called general covariance, this requirement, he says, "takes away from space and time the last remnant of physical objectivity." (Einstein 1987, Vol. 6 [1996], p. 287 and 291). In support he appears to offer a straightforwardly verificationist analysis. "All our space-time verifications invariably amount to a determination of space-time coincidences." (Einstein 1987, Vol. 6 [1996], p. 287 and 291). Thus it is only space-time coincidences ("to which all our physical experience can ultimately be reduced"), that is, the coordinate systems, that the laws of nature need respect.

Recent scholarship suggests that this positivist reading is mistaken (Einstein 1987, Vol. 6 (1996), p. 287 and 291). For in these passages Einstein is probably reacting to an earlier argument of his own (called the "hole argument") posing a conflict between general covariance and determinism (Einstein 1987, Vol. 6 (1996), p. 287 and 291). The key to unraveling that argument was his recognition that, by themselves, coordinates (the bare mathematical points) have no physical significance. Significance comes from the fields of the theory, as determined from given sources by the theory's field equations. That's what makes space-time coincidences observable. Einstein later held that, in general, scientific theory determines what one can observe. Thus the positivist reading has things exactly back to front. Whereas in special relativity Einstein follows a positivist line in grounding theoretical notions (simultaneity) in what is observable, here he entheorizes the observable and takes an anti-positivist line in grounding the observable in the theory itself.

### quantum theory

Einstein made fundamental contributions to the early understanding of quantum phenomena and his ideas, which emphasized the problem of wave-particle duality, influenced all subsequent developments. However Einstein became the foremost critic of the quantum mechanics that emerged from 1926 to 1930.

His dissatisfaction is often portrayed as a last ditch longing for determinism or causality ("God does not throw dice"), as against the essentially probabilistic character of quantum physics. To be sure, although Einstein was a master at statistical physics, he was certainly troubled by a science where probability occurs fundamentally. Nevertheless his problem with the quantum theory was not about determinism alone, nor even primarily about determinism at all. In a 1930s letter to his old friend and translator, Maurice Solovine, Einstein expresses his concerns this way. "I am working with my young people on an extremely interesting theory with which I hope to defeat modern proponents of probability-mysticism and their aversion to the notion of reality in the domain of physics" (Solovine 1987, p. 91). This is a typical linkage in Einstein's thought. In almost every context in which Einstein expresses reservations about quantum indeterminism he couples it with reservations about the irrealism of the theory; that is, giving up the ideal of treating individual events, or what he referred to as real states of affairs.

As usually understood, the quantum theory does not treat real states of affairs at all, not even probabilistically. It does not tell us whether an electron is likely (even) to be here or there, spinning up or down. Quantum theory only gives the probability for finding the electron here, or finding it spinning up, if one actually measures it for that particular property. This is the irrealism that Einstein found so disturbing. That there could be laws, even probabilistic laws, for finding things if one looks, but no laws of any sort for how things are independently of whether one looks, was mysticism, a "mindless" (1987, p. 119) form of empiricism.

Einstein responded with a program just as in the development of relativity. First he set out to establish the limitations of the concepts used in the quantum domain and then he explored the possibility of transcending those limitations with a positive theory. He began by challenging the uncertainty formulas. He accepted that they limit the simultaneous, precise measurement of conjugate quantities (like position and linear momentum) but he questioned the ontological reading in which they limit what is simultaneously real. He went on to examine the rationale offered, especially by Bohr, both for the statistical character of the quantum theory and for its irrealism.

Bohr postulated an uncontrollable interaction introduced in every act of measurement that, he argued, made a statistical treatment necessary and also prevented states of affairs being defined independently of the measurement. In a series of thought experiments Einstein developed the concept of indirect measurement as a challenge to Bohr's postulate. This culminated in a 1935 paper, co-authored with his research assistants Boris Podolsky and Nathan Rosen, and composed by Podolsky. Usually referred to as *EPR* this paper involved the idea that Schrödinger dubbed "entanglement" (*Verschränkung* ).

Entanglement occurs when, after quantum systems interact, certain quantities become linked among the systems. In the *EPR* case, for a pair *A, B* of previously interacting particles—now far apart—both position and momentum are so linked that determining the position of one automatically determines the position of the other, and similarly for momentum. By directly measuring, say, the position of *A* one can determine *B* 's position and apparently without any "uncontrollable interaction" or disturbance of *B*, contra Bohr's postulate. Moreover by assuming a principle of local action according to which, provided the systems are sufficiently far apart, the "reality" at *B* is not affected by the measurement carried out at *A*, it follows that the position determined for *B* must have been *B* 's all along. Thus, contrary to Bohr, one can define a coordinate of position for *B* that is independent of measurement or observation there – a real state of affairs. Unfortunately, in *EPR* it is difficult to track these considerations clearly. It appears that Einstein never saw Podolsky's text before publication. When he did he expressed misgivings that it obscured his central concerns.

*EPR* has been seen as suggesting the possibility of a "hidden variables" account of quantum theory, an account that would introduce simultaneous values for both position and momentum, along with other quantities, and still, somehow, respect the uncertainty relations. But Einstein, who had toyed with and abandoned a hidden variables approach in 1927, was never again interested in such an account. In the context of *EPR*, he told Schrödinger explicitly that he "couldn't care less" about simultaneous values for position and momentum (Fine 1996, p. 38). In fact Einstein thought these point-particle concepts were not appropriate for the quantum domain. He hoped to introduce different concepts and explored how they would emerge from a unified field theory. Einstein pursued that quest unsuccessfully for many years. In the end he questioned whether even a field theory would do the job and speculated about the need for a purely algebraic kind of physics, one not based on a spatio-temporal continuum. He sometimes despaired, however, that this was like trying to breathe in empty space.

## General Philosophy of Science

Einstein's attempt to develop new concepts for the quantum domain accords with his anti-inductivist principle that ideas (or concepts) are free creations. By "free" he meant both that concepts are not innate and also that they are neither given in nor logically derived from experience. The only test for scientific concepts is whether they can be organized in a logically simple system that finds fruitful empirical applications. This highlights logical simplicity as a paramount factor in theory choice. It also represents a holistic attitude to theories, gleaned perhaps from Pierre Duhem. Holism is apparent in Einstein's acute analysis of the testability of geometry where, while rejecting Henri Poincaré's conventionalist defense of Euclidean physical geometry, he ultimately agrees with Poincaré that only the whole system of physics plus geometry is testable.

Einstein's work in relativity and his project for a unified treatment of gravity and quantum phenomena shows unification as central to his scientific outlook. His study of Baruch Spinoza, whom he read and re-read over the years may have influenced this attitude (or reinforced it). Certainly realism was another central feature. This is evident in his introduction of the light quantum and in his use of the kinetic-molecular picture in treating Brownian motion. It is evident as well in his worries over the instrumentalist understanding of the quantum theory. Nevertheless he ridiculed "assertions" of realism as meaningless, like chiming "cock-a-doodle-doo." For Einstein realism was not a doctrine but rather a motivational program. The program was to develop scientific theories that describe individual events themselves, without reference to conditions of observation. That is what he believed science had always done, and with great success. It was motivational because, at the personal level, he thought individuals would have no motivation to pursue science unless they felt that in doing so they were unlocking the secrets of nature. Clearly this program conflicts with the enormously successful but irrealist quantum theory, which is why Einstein struggled to make room for the possibility, at least, of a realist reinterpretation.

Determinism (or causality—he hardly draws a distinction) is another important item in Einstein's outlook. Here, again, he did not advocate a doctrine like, "The world is deterministic." Characteristically, he favored a program to entheorize determinism; that is, to build deterministic theories. His reaction to the dilemma between determinism and general covariance posed by the hole argument shows this concern, as does his sense that the probabilistic quantum theory involves a retreat into statistics. Nevertheless, in reluctantly accepting that one might have to move to an algebraic physics, he did acknowledge that science might abandon the ideal of representing events in spacetime altogether, and hence move beyond causality (or determinism).

Einstein's views are sometimes described in terms of the philosophical "isms": holism, realism, determinism and so forth. While there can be some truth to these descriptions (provided one entheorizes them), he generally regarded philosophical positions pragmatically. He saw them as tools that may be useful at certain moments for building better scientific theories, judged by the criterion of empirical success. His sometimes strong statements for or against one of the "isms" are best be seen in the terms of the dialogism described by Mara Beller in her *Quantum Dialogue*, a dialectical view that highlights the creative role of scientific disagreement in shifting contexts. Einstein himself described it this way:

I do not feel comfortable and at home in any of the "isms." It always seems to me as though such an ism were strong only so long as it nourishes itself on the weakness of its counter-ism; but if the latter is struck dead, and it is alone on an open field, then it also turns out to be unsteady on its feet.

So, away with the squabbling.

howard 1993, p. 225

** See also ** Quantum Logic and Probability; Relativity Theory; Space; Space in Physical Theories; Time.

## Bibliography

### works by albert einstein

"Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?" With Boris Podolsky and Nathan Rosen. *Physical Review* 47 (1935): 777–780.

*The Evolution of Physics*. With L. Infeld. New York: Simon & Schuster, 1938.

*Relativity: The Special and General Theory*. 15th ed. London: Methuen, 1938.

*Ideas and Opinions*. New York: Bonanza Books, 1954.

*The Collected Papers of Albert Einstein*. Princeton, NJ: Princeton University Press, 1987. Ongoing project that will include most of Einstein's writing and correspondence.

*Letters to Solovine*. Translated by Wade Baskin. New York: Philosophical Library, 1987.

*Out of My Later Years*. New York: Bonanza Books, 1990.

### works about albert einstein

Beller, Mara. *Quantum Dialogue: The Making of a Revolution*. Chicago: University of Chicago Press, 1999.

Earman, John, and Arthur Fine. "Against Indeterminacy." *Journal of Philosophy* LXXIV (1977): 535–538.

Einstein Archives Online. Available from http://www.alberteinstein.info/.

Fine, Arthur. *The Shaky Game: Einstein, Realism and the Quantum Theory*. 2nd ed. Chicago: University of Chicago Press, 1996.

Howard, Don A. "Was Einstein Really a Realist?" *Perspectives on Science* 1 (1993): 204–251.

Norton, John D. "General Covariance and the Foundations of General Relativity: Eight Decades of Dispute." *Reports on Progress in Physics* 56 (1993): 791–858.

Pais, Abraham. *Subtle Is the Lord: The Science and the Life of Albert Einstein*. New York: Oxford University Press, 1982.

Ryckman, Thomas. *The Reign of Relativity: Philosophy in Physics 1915–1925*. Oxford, U.K.: Oxford University Press, 2005.

Schilpp, Paul Arthur, ed. *Albert Einstein: Philosopher-Scientist*. La Salle, IL: Open Court, 1949.

*Arthur Fine (2005)*

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