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Does the prototype BB84 quantum cryptography machine still exist?
According to Wikipedia's timelines, quantum computing may have had some inceptions as early as the late 60's, when Stephen Wiesner invented conjugate coding.
Around the early 80's, Wiesner's ideas inspired Charles Bennett and Gilles Brassard to…
Mark S
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When did linear algebra become the study of vector spaces?
All of the concepts and terminology central to linear algebra were established in the late 19th century.
Following recent comments by user KCd, that in the early 20th century determinants were the “primary language of linear algebra”, I conclude…
nwr
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6
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Historical origin of commas and periods in numbers
I have heard that in Canada and the United States of America, when we write a decimal number, then we use a period, like 1.111. When we write large numbers, then we use a comma, like 1,111. Sometimes we use spaces for large numbers, like 1 111. I…
Arunabh Bhattacharya
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How did Alfréd Rényi die?
Alfréd Rényi was a Hungarian mathematician who survived a lot, including a forced labor camp, and was very active in the fields of probability theory, number theory, graph theory, etc.
Various articles and obituaries on him mention he died early at…
Rohit Pandey
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What did Galileo's "pulsilogon" look like?
Reading how Galileo measured time in the experiment with inclined plane, it says on Wikipedia, that:
Galileo accurately measured these short periods of time by creating a pulsilogon. This was a machine created to measure time using a pendulum.[15]…
pisoir
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6
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What rule or rules did Madelung discover, exactly?
There are two widely used rules of thumb to determine which subshells are filled in a neutral atom in its ground state:
Electrons are assigned to subshells in order of increasing value of $n + \ell$.
For subshells with the same value of $n +…
John Baez
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History of Direct Sums and Direct Products
So I like to get down into the details of how certain mathematical concepts came to be, and purely as a matter of curiosity, I was wondering if anyone know which mathematician first gave the definition of a direct sum?
I’ve always just sort of…
StormyTeacup
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Literary Movements in Math Writing
I am wondering if there is some analog for literary movements in writing (e.g., romanticism/post-modernism) for mathematics or the sciences as a whole. I would think there would be similarly large tonal/structural shifts from decade to decade in how…
Liam Bonds
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What is the origin of "root" as a solution to an equation?
I was curious to know more on the history of the term "root", in the sense of "a value that results in a true statement, when substituted into an equation" (e.g., the roots of $2x^2 + 1= 9$ are $\pm2$).
I saw this question, which is also about the…
Rax Adaam
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Nicollet and the notions of systematic and random errors
I recently read Ken Alder's "The measure of all things" about the first steps of the metric system definition. The project described in the book was the measure the meridian arc between Dunkirk and Barcelona in order to be able to define the meter…
irimias
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What technology was used to determine the shape of the blackbody spectrum at the 19th century?
The shape of the blackbody radiation spectrum was known in the 19th century from experimental measurements, and before the theoretical discovery of Planck's law.
At those times, how did people manage to measure the intensity distribution of the…
Solidification
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Notations for Laplacian: $\nabla^2$ vs. $\Delta$
For a (sufficiently smooth) function $f\colon \Bbb R^n\to\Bbb R$, the Laplacian of $f$ is defined to be $\sum_{j=1}^n \frac{\partial^2 f}{\partial x_j^2}$. There are two notations for the Laplacian that I have seen being commonly used, viz.,…
BigbearZzz
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When were cephalopods assigned to the taxonomic phylum Mollusca?
I am fascinated to read about the evolution of cephalopod intelligence while I understand why cephalopods are mollusks (e.g., https://en.wikipedia.org/wiki/Cephalopod), but I cannot easily find when zoologists finally recognize that cephalopods are…
James Goetz
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Whatever happened to quaternions?
Quaternions were made up by Hamilton. They are an extension of complex numbers. It is said that he first introduced "3d tertions". He was thinking what the relation between $\bf i$ and $\bf j$ had to be (in $t = a + b {\bf i} + c {\bf j}$), walking…
Deschele Schilder
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Who discovered this closed form formula for the n-th prime number?
The following is a formula for the $n$-th prime number ($[\,]$ represents the floor function). Who was the first person to discover it?
$$\newcommand{\lowerbrack}[2]{%
\raise{-#1}{\left[\raise{#1}{#2}\right]}}
p(n) = 1 + \sum_{k=1}^{2^n}…
user776490
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