Questions tagged [history]
History questions are welcome on this site whenever they have any bearing on our modern understanding of physics. However, if a question has only minimal or null bearing on our current understanding, or it specifically requires a historian's skills, toolset, and mindset to answer, then it should be migrated to the History of Science and Maths site. See the FAQ on Meta for more information.
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Everyday relevance of theory of relativity [closed]
I hope my question is not completely off-topic here. I'm looking for arguments in favor of scientific curiosity and I'm struggling to justify theories of relativity. I'm happy that politicians fund ...
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Seeking quote about Georges Lemaître and visualization of 4 dimensions [migrated]
I have been trying for some time to track down a quote about Georges Lemaître, which I recall reading a few years ago. The author was another cosmologist, who met Lemaître at a conference. Lemaître ...
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Kepler's measurements in solar system
I am interested in knowing that does Kepler measured distances in solar system or only relative distances to a astronomical unit which he doesn't know how long is it in our meters.
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Assistance Needed to Identify PhD Advisor of Herbert Joseph Reich [closed]
I am currently working on creating an academic genealogy tree for physicists specializing in electric discharges. As part of this project, I am trying to identify the PhD advisor of Herbert Joseph ...
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Did Einstein himself ever follow up on his theory that light travels with infinite velocity? [closed]
In reading the freely available English translation of "On the electrodynamics of moving bodies" I find on page 10 Einstein himself conducts a critical evaluation of the domain of validity ...
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Who - if anyone - predicted the emission of gamma rays from jetted active galaxies? An historiographical inquiry
We know that the relativistic electrons that produce synchrotron radiation in the jets of active galaxies also produce gamma radiation via the inverse Compton mechanism (in the most simple scenario ...
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Did Einstein say the one-way speed-of-light is "not a fact of nature"? [closed]
If so is there a published paper where he said as much?
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Ideal gas equation: Bernoulli's original derivation
I'm reading through some of Stephen Brush's books and i found Daniel Bernoulli's (1738, Hydrodynamica) original derivation of the Ideal gas law. In particular, this first part refers to the derivation ...
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Historical view of the second law of thermodynamics as a complete differential
My question sort of has two parts. I've been reading about the foundations of thermodynamics and statistical mechanics, older texts name the fact that $\frac{\delta Q}{T}$ is a complete differential ...
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Understanding the field strength tensor $F_{\mu\nu}$ as a commutator
As far as I understand, one way to define the field-strength tensor is by using the commutator of covariant derivatives as follows:
$$-igT^aF^a_{\mu\nu} = [D_\mu, D_\nu]$$
where $T^a$ is a basis for ...
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Why did scientists believe in an eternal universe before Lemaitre, even if the Kelvin paradox was already known since the 19th century?
Why did scientists believe in a static and eternal universe in Einstein times, before Lamaitre showed that the Einstein equations are compatible with a universe which started from a primeval atom, ...
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What is $F$ and what is $P$ in the sentence "$F × dP$ is a total differential"?
The physicist Emilio Segrè, as a student, attended lessons of Calculus given by Francesco Severi and of Analytical Mechanics given by Tullio Levi-Civita. Segrè wrote in his autobiography1
For many ...
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Electromagnetsm, isospin, spin-1/2, and the early years of quantum mechanics question
An electron going around in a circular orbit produces a magnetic field because there is a varying electric field.
But the electric field of the electron itself is a spherically symmetrical field.
...
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How exactly did Harrison's chronometer circumvent the impulse problem of time-keeping on a moving ship?
According to folklore, around the time of the exploration of the New World, there was a quandary regarding how to measure time on the open sea. Time keeping then was based on the pendulum clock, which ...
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About electron radiation frequency in Heisenberg's 1925 paper
In Heisenberg's 1925 article Quantum Theoretical Interpretation of Kinematic and Mechanical Relations, one of the first things he establishes are the form of the frequency functions in (what I assume ...
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How does special relativity lead to anti-particles?
Anti-particles and spinors pop out of the Dirac equation very naturally, yet the Dirac equation is only a modified version of the Schrödinger equation which includes the relativistic energy-momentum ...
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How did Einstein figure out mass (and hence energy) bends spacetime?
I can understand that once I fix the velocity of light at $c$, there is a relative variation in space-time based on special relativity (inertial frame of reference). It's not clear to me how Einstein ...
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How did J. J. Thomson conclude that the particles present in cathode rays were not ions but are in fact much smaller than the smallest of all atoms?
What evidence did he have to prove that the particles in cathode rays are much smaller than atoms? Did he have the e/m ratio of hydrogen ion in 1897? If yes, where did he get that from?
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Was the "demon core" hot?
The demon core was a sphere of plutonium (Pu-239, not Pu-238 that is known to get hot and is used in RTG) that weighed 6.2 kilograms (14 lb) and was 8.9 centimeters (3.5 in) in diameter. It was made ...
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Gravitational attraction between two bodies
While the gravitational force between two bodies is directly proportional to their masses, and inversely proportional to the distance between them is understandable / seems logical, how did Newton ...
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What are the differences between Navier and Stokes versions of equation?
What are the main differences between Navier(1822) and Stokes(1845) versions of equation?
If I understood correctly, original equations formulated Euler, what did they invent that they deserved to ...
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Matter density estimates in the 1980s
Liddle (2015, p.67) writes: "From the crude estimates that a typical galaxy weighs about $10^{11}M\odot$ and that galaxies are typically about a megaparsec apart, we know that the Universe cannot ...
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What mistake did Einstein make in 1911 when he miscalculated the light deviation?
When Einstein published the general relativity theory in 1911, why was the light deviation not predicted correctly? What was the incompleteness of the theory when he published it in 1911? When and how ...
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How is the wave equation derived or discovered? [duplicate]
I don't really understand where the fundamental or general wave equation $$\frac{\partial^2y}{\partial t^2} = v^2\frac{\partial^2y}{\partial x^2}$$
comes from. I understood the derivation of wave ...
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How were luminous intensity changes for each EM frequency measured in the blackbody experiments of the late 19th c., which led to up to Planck’s Law?
If in today’s parlance it would be either ‘spectral density’ or ‘spectral radiance’ that was in fact measured then as opposed to ‘luminous intensity’ please feel free to clarify.
Kindly note that my ...
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History/motivation: road from wavefunction QM to QFT
I am trying to give concise motivation (to math students) for why we have QFT as the fundamental theory of matter and forces, I may start like this:
Schrodinger's equation (in the sense of ...
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2
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What made Einstein to think time also dilates, along with space, with increasing gravity?
Michelson–Morley experiment showed that speed of the light remains same regardless of speed of observer. Based on it Albert Einstein came up with the proposal of time dilation for object in speed (...
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Fermat principle: how did they know the speed of light in different mediums?
Pierre de Fermat derived his principle of least time by considering the path that light would take when traveling between two points. He postulated that light would follow the path that minimized the ...
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How did G. I. Taylor derive the PDE's in his landmark 1941 paper?
To gain a deeper understanding of the derivation of G. I. Taylor's foundational equation $R= S(γ)t^\frac{2} {5} E^\frac{1}{5} ρ_0^\frac{-1}{5} $, I'd be grateful if you could point me towards the ...
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I want to know about origin of non-Hermitian quantum field theory model having two complex scalar fields $\phi_1$ and $\phi_2$
In the paper Symmetries and conservation laws in non-Hermitian field theories by Jean Alexandre, Peter Millington, and Dries Seynaeve, Phys. Rev. D 96, 065027 the authors use this Lagrangian:
$$ L = ...
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Who wrote $c = λ ν$ for the first time and where can I find it?
I have been surfing for days and still I could not find who wrote the equation $c=λν$ for the first time. Neither I found a name for this equation. A lot about Planck's constant and energy related ...
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Did Newton know that light has no inertia? [closed]
Newton studied a lot about optics and gravitation. Did he realize to some extent that light is a massless particle? How does his theory explain the bending of light due to a gravitational field?
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Size of an atom
This may be a naive question, but today, while reading about the Rutherford experiment in my high school chemistry textbook, I came across the following sentence:
"Calculations by Rutherford ...
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1
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How was the tau lepton predicted?
I know the tau lepton has been predicted before it was discovered – unlike the muon. But how does our theory (SM/electroweak theory) predict the existence of a third lepton generation?
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1
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How did Newton determine the average density of Earth is twice the density of the surface rocks? [closed]
I've read that Newton determined the average density of Earth is twice the density of the surface rocks, but I can't find his computation anywhere. I presume he used the differential calculus in some ...
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What exactly is weird about waves propagating without a medium? What does it violate? [closed]
I can not seem to grasp, why exactly does light travelling through space without the need of any medium was baffling for the scientists of 1800's.
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Has there been a big change in 1983 when the definition of the metre changed?
The metre was defined at the end of the $18^{th}$ century as the ten-millionth part of the quarter of the meridian (from the north pole to equator). Then, from $1983$ the definition changed for the ...
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QED impact on Unified Field Theory [closed]
how did the development of quantum electrodynamics impact the development of modern unified field theories?
and did any other theories have more significant impact?
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Why representations? [duplicate]
I've been studying Talagrand's What is a Quantum Field Theory? lately and I have some questions regarding the scheme he presents.
Essentially the state of affairs as of where I am in the book is that ...
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What means Alan Guth's Free Lunch Principle for the universe?
Alan Guth calls the universe the ultimate free lunch. What does he mean by this?
Does he mean that the total energy of the universe is zero? So the total energy of all particles is the negative of the ...
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1
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Relationship between Hamilton's principle and covariant derivative
The first time I was introduced to the covariant derivative I didn't even realise that was another "kind" of derivative.
Following Hamilton's principle taking an action such that: $$ S=\int ...
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Why did Einstein include reflection of light from a moving mirror in his paper? [closed]
Einstein, in his 1905 relativity paper, allocates a section to the issue of reflection of light from a moving mirror and derives three formulas (angle, frequency, energy). What was his reason or ...
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How close was Maxwell to general relativity? [closed]
In a recent paper by Accolierastro's recent video, she goes back to Maxwells seminal paper on electromagnetism, and the section on gravity. In Maxwells paper, he notes the similarity between the lines ...
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What was defined first and how? The ampere or the vacuum permeability?
I've been looking up the history and evolution of the seven base units and am currently checking out the ampere. What I've found is that 1A is defined as the current in a wire which would experience a ...
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How is negative mass related to string theory according to Eric Weinstein?
Eric Weinstein suggest in his interview that string theory comes from Hermann Bondi's famous paper related to negative mass in 1957 Chapel Hill Conference and that gravitoelectromagnetism and string ...
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2
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How does sweeping out equal areas in equal times show that the orbit is not a circle?
In many popular accounts, Kepler is said to have discovered that the planets move in an ellipse and not a circle after discovering that the planets sweep out equal areas in equal times. For example, a ...
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Carl Anderson's discovery of positron
The picture below is a photograph taken by Carl Anderson in 1932.
It shows for the first time the existence of an anti-electron.
https://www.aps.org/publications/apsnews/200408/history.cfm
The ...
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Apparatus to measure one ampere
The following definition of the Ampere was codified in 1948 at the 9th CGPM (Conference Général des Poids et Mésures)
The ampere is that constant current which, if maintained in two straight parallel ...
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How did Schrödinger do quantum mechanics with his wave functions?
On my way to learn about the very beginning of quantum mechanics and its different formulations, starting with Heisenberg infinite matrices and Schrödinger's wave functions, I can really not find till ...
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Andromeda Galaxy and Hubble
When Hubble determined the distance to Andromeda he based his estimation on Cepheids. However, the result was less than half the current value. What was the cause of this error and could another ...
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