Kaufmann–Bucherer–Neumann experiments
Encyclopedia
The Kaufmann-Bucherer-Neumann experiment
s measured the dependence of the inertial mass of an object on its velocity
. The historical
importance of a series of this experiment performed by various physicist
s between 1901 and 1915 is due to the results being used to test the predictions of special relativity
. Its developing precision and data analysis, and the resulting influence on theoretical physics
, during those years is still a topic of active historical discussion, since the early experimental results at first contradicted Einstein
's then newly published theory, but later versions of this experiment confirmed it. See also Tests of special relativity.
had discovered the radioactive decay
in a variety of chemical element
s. Subsequently, the beta radiation
from these decays was discovered to be the emission of a negatively charged particle
. Later these particles were identified with the electron
, discovered in cathode ray
experiments by J.J. Thomson
in 1897.
This was connected with the theoretical prediction of the electromagnetic mass
by J.J. Thomson in 1881, who showed that the electromagnetic energy contributes to the mass of the body. Thomson in 1893, and George Frederick Charles Searle
(1897) also calculated, that this mass depends on velocity and becomes infinitely great, when the charge moves at the speed of light with respect to the luminiferous aether
. Also Hendrik Antoon Lorentz (1899, 1900) assumed such a velocity-dependence as a consequence of his theory of electrons. At this time, the electromagnetic mass was denoted by these authors as "apparent mass", while the invariable Newtonian mass was denoted as "real mass".Miller (1981), pp. 45-47Pais (1982), pp. 155-159
began to experiment with cathode rays using a device similar to a cathode ray tube
, where the source of the electrons was the decay of radium
that was placed in a vacuated
tube. He applied electric
and magnetic
fields to measure the ratio of the charge
and mass of the particles, and since the charge of the electrons did not change with the speed of the particle, any change of the ratio must be the result of a change of its mass. Kaufmann published a first analysis of his data in 1901 – he actually was able to measure a change in the charge/mass ratio, thus he demonstrated the velocity dependence of mass. Based on Searle's formula, he separated the measured total mass into a mechanical (true) mass and an electromagnetic (apparent) mass, where the mechanical mass was considerably greater than the electromagnetic one. Additionally, he performed a series of experiments with updated and improved experimental techniques in 1902.Miller (1981), pp. 47-54Staley (2009), pp. 223-233
published a theory based on the assumption that the electron was a rigid, perfect sphere
, with its charge being distributed evenly on its surface. He also showed the earlier calculations of Searle are incomplete, since they only give the correct expression for the electron's energy and mass in the direction of motion – the "longitudinale electromagnetic mass". Abraham showed, that the expression for mass is different at right angles to the direction of motion (which was actually measured by Kaufmann), so he introduced the so-called "transverse electromagnetic mass". Consequently he demonstrated that Kaufmann's results are in full agreement with this predictions. Both Kaufmann and Abraham concluded that only electromagnetic mass exists, while the assumption of a constant Newtonian mass isn't necessary any more.Miller (1981), pp. 55-67Staley (1982), pp. 229-233
Also Lorentz (1899, 1904) extended his theory of electrons, and assumed that electrons were spreading their charge throughout their volume and in Kaufmann's experiment their shape would be compressed in the direction of motion and stay unchanged in the transverse directions. To Kaufmann's surprise, Lorentz could show that his model agrees with his experimental data as well. This model was further elaborated and perfected by Henri Poincaré
(1905), so that Lorentz's theory was now in agreement with the principle of relativity
.Miller (1981), pp. 55-67Janssen (2005), pp. 16-25
A similar theory was developed by Alfred Bucherer
and Paul Langevin
in 1904, with the difference that the total volume occupied by the deformed electron was assumed unchanged. It turned out, that this theory's prediction was closer to Abraham's theory than to Lorentz's.Janssen (2005), pp. 16-25
Finally, Albert Einstein
's theory of special relativity
(1905) predicted the change of the point-like
electron's mass due to the properties of the transformation between the rest-frame of the particle and the laboratory frame in which the measurements were performed. Mathematically, this calculation predicts the same dependence between velocity and mass as Lorentz's theory, although it assumes very different physical concepts.Staley (2009), pp. 241-242
Kaufmann assumed, that he had conclusively disproved the formula of Lorentz-Einstein, and therefore also disproved the principle of relativity
. In his view, the only remaining options were the theories of Abraham and Bucherer. Lorentz was perplexed and wrote that he was "at the end of his Latin".Miller (1981), pp. 228-232Staley (2009), pp. 242-244
Shortly after Kaufmann published his results and the conclusions of his analysis, Max Planck
decided to re-analyze the data obtained by the experiment. In 1906 and 1907, Planck published his own conclusion on the behavior of the inertial mass of electrons with high speeds. Using just nine data points from Kaufmann's publication in 1905, he recalculated the exact setup of the fields for each point, and predicted the measurements using the two competing theories. He showed, that Kaufmann's results are not fully decisive and would lead to superluminal velocities. Also Adolf Bestelmeyer
(1906) criticized some technical aspects of Kaufmann's measurements. And Einstein remarked in 1907, that although Kaufmann's results are better in agreement with Abraham's and Bucherer's theories than with his own, the foundations of the other theories are not plausible and therefore have only little probability of being correct.Miller (1981), pp. 232-235Staley (2009), pp. 244-250
performed new measurements by using a velocity filter
. Contrary to Kaufmann, he argued that those experiments confirmed the relativity principle and consequently the "relativity theory of Lorentz and Einstein". Bucherer was immediately applauded by Lorentz, Einstein, and Hermann Minkowski
. On the other hand, Adolf Bestelmeyer
published a paper, in which he cast doubt on the validity of Bucherer's result. What followed, was a polemic dispute between those two scholars in a series of publications. Thus, although many physicists accepted Bucherer's result, there still remained some doubts.Miller (1981), pp. 345-350Staley (2009), pp. 250-254
Neumann (1914), Guye and Lavanchy (1915) – again repeated the experiments. Especially the experiments by Neumann were considered as conclusively in favor of special relativity.Pauli (1921), p. 636Miller (1981), pp. 350-351Staley (2009), pp. 254-257
Lorentz summarized these efforts in 1915:Lorentz (1915), p. 339
However, Zahn and Spees showed in 1938, that many assumptions employed in those early experiments as to the nature and the properties of electrons and the experimental setup, were wrong. The Kaufmann–Bucherer–Neumann experiments would only show a qualitative increase of mass, and were incapable of deciding between the competing theories.Miller (1981), pp. 351-352Janssen (2005), pp. 41-43, 57
So, Rogers et. al. (1940) repeated the experiments with improved setup and eventually found a clear agreement with the Lorentz-Einstein-formula.
While those experiments were disputed for a long time, the investigations of the fine structure
of the hydrogen lines
already in 1917 provided a clear confirmation of the Lorentz-Einstein formula, and the refutation of Abraham's theory.Pauli (1921), pp. 636-637
Today, in modern particle-accelerators, the predictions of special relativity are routinely confirmed beyond any doubt.
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
s measured the dependence of the inertial mass of an object on its velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
. The historical
History of science
The history of science is the study of the historical development of human understandings of the natural world and the domains of the social sciences....
importance of a series of this experiment performed by various physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
s between 1901 and 1915 is due to the results being used to test the predictions of special relativity
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
. Its developing precision and data analysis, and the resulting influence on theoretical physics
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, during those years is still a topic of active historical discussion, since the early experimental results at first contradicted Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
's then newly published theory, but later versions of this experiment confirmed it. See also Tests of special relativity.
Historical context
In 1896 Henri BecquerelHenri Becquerel
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...
had discovered the radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
in a variety of chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s. Subsequently, the beta radiation
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
from these decays was discovered to be the emission of a negatively charged particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
. Later these particles were identified with the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
, discovered in cathode ray
Cathode ray
Cathode rays are streams of electrons observed in vacuum tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, the glass opposite of the negative electrode is observed to glow, due to electrons emitted from and travelling perpendicular to the cathode Cathode...
experiments by J.J. Thomson
J. J. Thomson
Sir Joseph John "J. J." Thomson, OM, FRS was a British physicist and Nobel laureate. He is credited for the discovery of the electron and of isotopes, and the invention of the mass spectrometer...
in 1897.
This was connected with the theoretical prediction of the electromagnetic mass
Electromagnetic mass
Electromagnetic mass was initially a concept of classical mechanics, denoting as to how much the electromagnetic field, or the self-energy, is contributing to the mass of charged particles. It was first derived by J. J. Thomson in 1881 and was for some time also considered as a dynamical...
by J.J. Thomson in 1881, who showed that the electromagnetic energy contributes to the mass of the body. Thomson in 1893, and George Frederick Charles Searle
George Frederick Charles Searle
George Frederick Charles Searle was a British physicist and teacher, and a Fellow of the Royal Society.-Biography:Searle was born in Oakington, Cambridgeshire, England....
(1897) also calculated, that this mass depends on velocity and becomes infinitely great, when the charge moves at the speed of light with respect to the luminiferous aether
Luminiferous aether
In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light....
. Also Hendrik Antoon Lorentz (1899, 1900) assumed such a velocity-dependence as a consequence of his theory of electrons. At this time, the electromagnetic mass was denoted by these authors as "apparent mass", while the invariable Newtonian mass was denoted as "real mass".Miller (1981), pp. 45-47Pais (1982), pp. 155-159
First Experiments
Walter KaufmannWalter Kaufmann (physicist)
Walter Kaufmann was a German physicist. He is most well known for his first experimental proof of the velocity dependence of mass, which was an important contribution to the development of modern physics, including special relativity.-Life:In 1890/91 he studied mechanical engineering at the...
began to experiment with cathode rays using a device similar to a cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
, where the source of the electrons was the decay of radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
that was placed in a vacuated
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
tube. He applied electric
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
and magnetic
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
fields to measure the ratio of the charge
Charge (physics)
In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...
and mass of the particles, and since the charge of the electrons did not change with the speed of the particle, any change of the ratio must be the result of a change of its mass. Kaufmann published a first analysis of his data in 1901 – he actually was able to measure a change in the charge/mass ratio, thus he demonstrated the velocity dependence of mass. Based on Searle's formula, he separated the measured total mass into a mechanical (true) mass and an electromagnetic (apparent) mass, where the mechanical mass was considerably greater than the electromagnetic one. Additionally, he performed a series of experiments with updated and improved experimental techniques in 1902.Miller (1981), pp. 47-54Staley (2009), pp. 223-233
Competing theories
In 1902, Max AbrahamMax Abraham
Max Abraham was a German physicist.Abraham was born in Danzig, Imperial Germany to a family of Jewish merchants. His father was Moritz Abraham and his mother was Selma Moritzsohn. Attending the University of Berlin, he studied under Max Planck. He graduated in 1897...
published a theory based on the assumption that the electron was a rigid, perfect sphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
, with its charge being distributed evenly on its surface. He also showed the earlier calculations of Searle are incomplete, since they only give the correct expression for the electron's energy and mass in the direction of motion – the "longitudinale electromagnetic mass". Abraham showed, that the expression for mass is different at right angles to the direction of motion (which was actually measured by Kaufmann), so he introduced the so-called "transverse electromagnetic mass". Consequently he demonstrated that Kaufmann's results are in full agreement with this predictions. Both Kaufmann and Abraham concluded that only electromagnetic mass exists, while the assumption of a constant Newtonian mass isn't necessary any more.Miller (1981), pp. 55-67Staley (1982), pp. 229-233
Also Lorentz (1899, 1904) extended his theory of electrons, and assumed that electrons were spreading their charge throughout their volume and in Kaufmann's experiment their shape would be compressed in the direction of motion and stay unchanged in the transverse directions. To Kaufmann's surprise, Lorentz could show that his model agrees with his experimental data as well. This model was further elaborated and perfected by Henri Poincaré
Henri Poincaré
Jules Henri Poincaré was a French mathematician, theoretical physicist, engineer, and a philosopher of science...
(1905), so that Lorentz's theory was now in agreement with the principle of relativity
Principle of relativity
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference....
.Miller (1981), pp. 55-67Janssen (2005), pp. 16-25
A similar theory was developed by Alfred Bucherer
Alfred Bucherer
Alfred Heinrich Bucherer was a German physicist, who is known for his experiments on relativistic mass...
and Paul Langevin
Paul Langevin
Paul Langevin was a prominent French physicist who developed Langevin dynamics and the Langevin equation. He was one of the founders of the Comité de vigilance des intellectuels antifascistes, an antifascist organization created in the wake of the 6 February 1934 far right riots...
in 1904, with the difference that the total volume occupied by the deformed electron was assumed unchanged. It turned out, that this theory's prediction was closer to Abraham's theory than to Lorentz's.Janssen (2005), pp. 16-25
Finally, Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...
's theory of special relativity
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
(1905) predicted the change of the point-like
Point (geometry)
In geometry, topology and related branches of mathematics a spatial point is a primitive notion upon which other concepts may be defined. In geometry, points are zero-dimensional; i.e., they do not have volume, area, length, or any other higher-dimensional analogue. In branches of mathematics...
electron's mass due to the properties of the transformation between the rest-frame of the particle and the laboratory frame in which the measurements were performed. Mathematically, this calculation predicts the same dependence between velocity and mass as Lorentz's theory, although it assumes very different physical concepts.Staley (2009), pp. 241-242
Experiments of 1905
To bring a decision between those theories, Kaufmann again performed his experiments with higher precision. With respect to the increase of mass, the predictions of the various theories were:Kaufmann assumed, that he had conclusively disproved the formula of Lorentz-Einstein, and therefore also disproved the principle of relativity
Principle of relativity
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference....
. In his view, the only remaining options were the theories of Abraham and Bucherer. Lorentz was perplexed and wrote that he was "at the end of his Latin".Miller (1981), pp. 228-232Staley (2009), pp. 242-244
Shortly after Kaufmann published his results and the conclusions of his analysis, Max Planck
Max Planck
Max Karl Ernst Ludwig Planck, ForMemRS, was a German physicist who actualized the quantum physics, initiating a revolution in natural science and philosophy. He is regarded as the founder of the quantum theory, for which he received the Nobel Prize in Physics in 1918.-Life and career:Planck came...
decided to re-analyze the data obtained by the experiment. In 1906 and 1907, Planck published his own conclusion on the behavior of the inertial mass of electrons with high speeds. Using just nine data points from Kaufmann's publication in 1905, he recalculated the exact setup of the fields for each point, and predicted the measurements using the two competing theories. He showed, that Kaufmann's results are not fully decisive and would lead to superluminal velocities. Also Adolf Bestelmeyer
Adolf Bestelmeyer
Adolf Bestelmeyer was a German experimental physicist.-Life and work:...
(1906) criticized some technical aspects of Kaufmann's measurements. And Einstein remarked in 1907, that although Kaufmann's results are better in agreement with Abraham's and Bucherer's theories than with his own, the foundations of the other theories are not plausible and therefore have only little probability of being correct.Miller (1981), pp. 232-235Staley (2009), pp. 244-250
Bucherer's experiments
In 1908, Alfred BuchererAlfred Bucherer
Alfred Heinrich Bucherer was a German physicist, who is known for his experiments on relativistic mass...
performed new measurements by using a velocity filter
Wien filter
A Wien filter is a device consisting of perpendicular electric and magnetic fields that can be used as a velocity filter for charged particles, for example in electron microscopes and spectrometers. It is named for Wilhelm Wien who developed it in 1898 for the study of anode rays. It can be...
. Contrary to Kaufmann, he argued that those experiments confirmed the relativity principle and consequently the "relativity theory of Lorentz and Einstein". Bucherer was immediately applauded by Lorentz, Einstein, and Hermann Minkowski
Hermann Minkowski
Hermann Minkowski was a German mathematician of Ashkenazi Jewish descent, who created and developed the geometry of numbers and who used geometrical methods to solve difficult problems in number theory, mathematical physics, and the theory of relativity.- Life and work :Hermann Minkowski was born...
. On the other hand, Adolf Bestelmeyer
Adolf Bestelmeyer
Adolf Bestelmeyer was a German experimental physicist.-Life and work:...
published a paper, in which he cast doubt on the validity of Bucherer's result. What followed, was a polemic dispute between those two scholars in a series of publications. Thus, although many physicists accepted Bucherer's result, there still remained some doubts.Miller (1981), pp. 345-350Staley (2009), pp. 250-254
Further development
Using similar techniques, but improving their setup and analysis steps, others – Hupka (1910),Neumann (1914), Guye and Lavanchy (1915) – again repeated the experiments. Especially the experiments by Neumann were considered as conclusively in favor of special relativity.Pauli (1921), p. 636Miller (1981), pp. 350-351Staley (2009), pp. 254-257
Lorentz summarized these efforts in 1915:Lorentz (1915), p. 339
- Later experiments [..] have confirmed the formula [..] for the transverse electromagnetic mass, so that, in all probability, the only objection that could be raised against the hypothesis of the deformable electron and the principle of relativity has now been removed.
However, Zahn and Spees showed in 1938, that many assumptions employed in those early experiments as to the nature and the properties of electrons and the experimental setup, were wrong. The Kaufmann–Bucherer–Neumann experiments would only show a qualitative increase of mass, and were incapable of deciding between the competing theories.Miller (1981), pp. 351-352Janssen (2005), pp. 41-43, 57
So, Rogers et. al. (1940) repeated the experiments with improved setup and eventually found a clear agreement with the Lorentz-Einstein-formula.
While those experiments were disputed for a long time, the investigations of the fine structure
Fine structure
In atomic physics, the fine structure describes the splitting of the spectral lines of atoms due to first order relativistic corrections.The gross structure of line spectra is the line spectra predicted by non-relativistic electrons with no spin. For a hydrogenic atom, the gross structure energy...
of the hydrogen lines
Balmer series
The Balmer series or Balmer lines in atomic physics, is the designation of one of a set of six different named series describing the spectral line emissions of the hydrogen atom....
already in 1917 provided a clear confirmation of the Lorentz-Einstein formula, and the refutation of Abraham's theory.Pauli (1921), pp. 636-637
Today, in modern particle-accelerators, the predictions of special relativity are routinely confirmed beyond any doubt.
External links
- Presentation on Kaufmann experiment (PowerPoint)
- List of SR tests