physics-experiments

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April 10, 2026

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"But the changes of dimension and mass due velocity are not conventions but realities; so I urge, on the basis of the electrical theory of matter. The Fitzgerald-Lorentz hypothesis I have an affection for. I was present at its birth. Indeed, I assisted at its birth for it was in my study... with Fitzgerald in an armchair, and I was enlarging on the difficulty of reconciling the then new Michelson experiment with the theory of astronomical aberration and with other known facts, that he made his brilliant surmise:—"Perhaps the stone slab was affected by the motion." I rejoined that it was a 45° shear that was needed. To which he replied, "Well, that's all right—a simple distortion." And very soon he said, "And I believe it occurs, and that the Michelson experiment demonstrates it." A shortening long-ways, or a lengthening cross-ways would do what was wanted. And is such a hypothesis gratuitous? Not at all: in the light of the electrical theory of matter such an effect ought to occur. The amount required by the experiment, and given by the theory, is equivalent to a shrinkage of the earth's diameter by rather less than three inches, in the line of its orbital motion through the aether of space. An oblate spheroid with the proper eccentricity has all the simple geometrical properties of a stationary sphere; the eccentricity depends in a definite way on speed, and becomes considerable as the velocity of light is approached. All this Profs Lorentz and Larmor very soon after and quite independently perceived..."

- Michelson–Morley experiment

• 0 likes• physics-experiments• 1887•
"We have... to speak of a celebrated experiment made by Michelson in 1881, and repeated by him on a larger scale with the cooperation of Morley in 1887. It was a very bold one, two rays of light having been made to interfere after having travelled over paths of considerable length in directions at right angles to each other. Fig 9. shows the general arrangement of the apparatus. The rays of light coming from the source L are divided by the glass plate P, which is placed at an angle of 45°, into a transmitted part PA and a reflected one PB. After having been reflected by the mirrors A and B, these beams return to the plate P, and now the part of the first that is reflected and the transmitted part of the second produce by their interference a system of bright and dark fringes that is observed in a telescope placed on the line PC. The fundamental idea... is, that, if the ether remains at rest, a translation given to the apparatus must of necessity produce a change in the differences of phase, though one of the second order. Thus, if the translation takes place in the direction of PA or AP, and if the length of PA is denoted by L [denoting speed of light c and earth's speed \left\vert w \right\vert (the absolute value of its velocity w)], a ray of light will take a time \frac{L}{c + \left\vert w \right\vert} for travelling along this path in one direction, and a time \frac{L}{c - \left\vert w \right\vert} for going in the inverse direction. The total time is\frac{2Lc}{c^2 - w^2},or up to quantities of the second order [by multiplying numerator and denominator by \frac{1}{c^2} to obtain \frac{2L}{c}\frac{1}{(1 - \frac{ w^2}{c^2})}, then multiplying this numerator and denominator by (1 + \frac{ w^2}{c^2}) and dropping the resulting denominator's negligibly small fraction \frac{ w^4}{c^4}, giving]\frac{2L}{c}(1 + \frac{ w^2}{c^2}),so that for the rays that have gone forward and back along PA there will be a retardation of phase measured by \frac{2Lw^2}{c^3}.There is a similar retardation, though of smaller amount, for the other beam. ...a ray of this beam, even if it returns, as I shall suppose..., to exactly the same point of the plate P, does not come back to the same point of the ether, the point... having moved with the velocity W of the earth's translation over a certain distance say from P to P' while the light went from P to B and back. If Q is the point in the ether where the ray reaches the mirror B, ...with sufficient approximation...the points P, Q, P' are the angles of an isoscele triangle, whose height is L (since the distances PA and PB in the apparatus were equal) and whose base [the total distance traveled by mirror B resulting from the motion of the earth] is \frac{2L\left\vert w \right\vert}{c} [where \frac{2L}{c} is the time for light to travel distance L twice]. The sum of the sides PQ and QP' is2\sqrt{L^2 + \frac{L^2w^2}{c^2}},so that we may write\frac{2L}{c}(1 + \frac{w^2}{2c^2})for the time required by the second beam. It appears from this that the motion produces a difference of phase between the two beams to the extent of\frac{Lw^2}{c^3},and this may be a sensible fraction of the period of vibration, if L has the length of some metres."

- Michelson–Morley experiment

• 0 likes• physics-experiments• 1887•
"Relative motion of the aether.—We must therefore consider the aether within dense bodies as somewhat loosely connected with the dense bodies, and we have next to inquire whether, when these dense bodies are in motion through the great ocean of aether, they carry along with them the aether they contain, or whether the aether passes through them as the water of the sea passes through the meshes of a net when it is towed along by a boat. If it were possible to determine the velocity of light by observing the time it takes to travel between one station and another on the earth's surface, we might, by comparing the observed velocities in opposite directions, determine the velocity of the aether with respect to these terrestrial stations. All methods, however, by which it is practicable to determine the velocity of light from terrestrial experiments depend on the measurement of the time required for the double journey from one station to the other and back again, and the increase of this time on account of a relative velocity of the aether equal to that of the earth in its orbit would be only about one hundred millionth part of the whole time of transmission, and would therefore be quite insensible. The theory of the motion of the aether is hardly sufficiently developed to enable us to form a strict mathematical theory of the , taking into account the motion of the aether. Professor Stokes, however, has shown that, on a very probable hypothesis with respect to the motion of the aether, the amount of aberration would not be sensibly affected by that motion. The only practicable method of determining directly the relative velocity of the æther with respect to the solar system is to compare the values of the velocity of light deduced from the observation of the eclipses of Jupiter's satellites when Jupiter is seen from the earth at nearly opposite points of the ecliptic."

- Michelson–Morley experiment

• 0 likes• physics-experiments• 1887•
"If the ether is stationary, as postulated by Fresnel, the optically important phenomenon of aberration is completely explained, but the Michelson Morley experiment appeared to show that this hypothesis was untenable, and left aberration without the shadow of an explanation. ...Fitzgerald... and Lorentz... nearly at the same time made the same suggestion as a possible way out of the difficulty. ...Fitzgerald and Lorentz suggested that the dimensions of the block of sandstone [on which the interferometer mirrors were mounted] were altered by its drift through the ether, that... the stone was shorter... in the direction of the earth's motion in space than when it lay at right angles to this motion. ...All substances might experience such a deformation... but it was conceivable that they might not be all deformed alike, that a soft and yielding substance like wood might suffer a different amount of shortening from that of stone or iron. In 1904 Morley and Miller repeated the experiment of 1887, using a lvery much larger apparatus, the path of each of the interfering beams of light being now 32 metres instead of about 11... The mirrors were separated by rods of pine instead of sandstone... But the effects were the same. No effect could be discovered... to show that the earth drifts or moves through the ether. ...The mathematicians now took the matter up, and under the leadership of Einstein and Minkowski put forward the principle of relativity in all measurements of space and time..."

- Michelson–Morley experiment

• 0 likes• physics-experiments• 1887•
"A few years after writing the preface of that book, Popper fell into an opposite, and equally serious error about an "EPR situation," On this occasion, contrary to the preceding one, there is an over- rather than an underevaluation of the EPR analysis. On p. 27 of the same book, Popper proposes an experiment that constitutes a variant of the EPR argument, asserting that if the the Copenhagen interpretation is correct, the experiment just analyzed would allow for sending signals faster than the speed of light. This work is one of a lengthy series we will discuss later, in which it is maintained that quantum formalism would permit us to use the reduction of the wave packet to violate one of the postulates at the basis of relativity (i.e., that the speed of light cannot be exceeded). Now, despite the peculiarity of the situation addressed by EPR, this conclusion is fundamentally erroneous and arise from an incorrect use of quantum formalism. I recall a spirited discussion I once had with Popper at the International Center for Theoretical Physics at Miramare in 1983. Professor Abdus Salam informed me that on the occasion of Popper's visit (for delivering a lecture on the foundations of quantum mechanics), he would be very pleased if the Center would have on hand some competent person in the field, and asked me to take part in the discussion. I knew Popper's work well and told Professor Salam that my intervention could be critical. Salam's reply was simple: "I have full confidence in you, and if you think you are right, you should explain your position without any fear." Popper presented his thought experiment (a variant of the EPR argument), which, according to him, left us with only two alternatives: either the orthodox interpretation was correct, and it would then be possible to send signals faster than the speed of light, or there would not be any action at a distance and the experiment would constitute a falsification of quantum theory. At the end of the conference I explained to him in simple, but mathematically precise terms, the reasons why his point of departure was erroneous: he had not correctly applied the rules of the theory and in fact, the impossibility of sending superluminal signals would confirm the theory rather than falsify it—the exact opposite of what he maintained. At the end of my intervention he only said that he could not answer my objection since he did not have a mastery of the mathematics of the formalism, but was still convinced that the theory implied the possibility of superluminal signals. This strange, and, as we shall see, fundamentally erroneous idea has been supported by various researchers in various scientific works, and published in prestigious journals."

- Popper's experiment

• 0 likes• quantum-mechanics• physics-experiments• 20th-century-in-science•