# Tag Info

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This is not really an answer to your question, essentially because there isn't (currently) a question in your post, but it is too long for a comment. Your statement that A co-ordinate transformation is linear map from a vector to itself with a change of basis. is muddled and ultimately incorrect. Take some vector space $V$ and two bases $\beta$ and ...

29

Straight from the horse's mouth: Source: Bureau International des Poids et Mesures (Search for "dimensionless" for all guidelines.) The International Bureau of Weights and Measures (French: Bureau international des poids et mesures), is an international standards organisation, one of three such organisations established to maintain the ...

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The thing is that $\mathrm{dm}$ is a single symbol, not a combination of two symbols. Yes, it can be understood in terms of a prefix and a base indicator, but it is still a single symbol. An analogy to the concatenation of variable is inappropriate. Reference to an authoritative statement: The grouping formed by a prefix symbol attached to a unit ...

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Typically: $\rm d$ denotes the total derivative (sometimes called the exact differential):$$\frac{{\rm d}}{{\rm d}t}f(x,t)=\frac{\partial f}{\partial t}+\frac{\partial f}{\partial x}\frac{{\rm d}x}{{\rm d}t}$$This is also sometimes denoted via $$\frac{Df}{Dt},\,D_tf$$ $\partial$ represents the partial derivative (derivative of $f(x,y)$ with respect to $x$ ...

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The main distinction you want to make is between the Green function and the kernel. (I prefer the terminology "Green function" without the 's. Imagine a different name, say, Feynman. People would definitely say the Feynman function, not the Feynman's function. But I digress...) Start with a differential operator, call it $L$. E.g., in the case of ...

23

The Physiccs work in this field is rigorous enough. Hawking and Ellis is a standard reference, and it is perfectly fine in terms of rigor. Digression on notation If you have a tensor contraction of some sort of moderate complexity, for example: $$K_{rq} = F_{ij}^{kj} G_{prs}^i H^{sp}_{kq}$$ and you try to express it in an index-free notation, usually ...

21

The symbol $\Delta$ refers to a finite variation or change of a quantity – by finite, I mean one that is not infinitely small. The symbols $d,\delta$ refer to infinitesimal variations or numerators and denominators of derivatives. The difference between $d$ and $\delta$ is that $dX$ is only used if $X$ without the $d$ is an actual quantity that may be ...

21

It is an ångström, a unit of length commonly used in chemistry to measure things like atomic radii and bond lengths. Although not an official SI unit, it has a simple relationship to the metric units of length: $$1\:\mathrm{ångström} = 1\:\mathrm{Å} = 10^{−10}\:\mathrm{m} = 0.1\:\mathrm{nm} = 100\:\mathrm{pm}.$$

18

The statement "$A$ happens given that $B$" is equivalent to "If $B$, then $A$", which is symbolically represented as an implication $$B \Rightarrow A$$ or, if you want to preserve the order of $A$ and $B$ in the original statement $$A \Leftarrow B$$

15

Surely there is a story behind the print on Feynman's tee, these are the CM-1/CM-2 T-shirts. Quoting Tamiko Thiel: The geometric boxes and their 'hard' connections represent the 12-dimensional 'cube of cubes' that forms the internal hardware network connecting all processor chips with each other in a maximum of 12 steps. Feynman is the one who suggested ...

15

It is, in fact, a double integral! The first notation used $$\varPhi_E = \oint_S \vec{E} \cdot \mathrm{d}\vec{A} = \oint_S \vec{E} \cdot \hat{n} \ \mathrm{d}A$$ is simply a more compact notation. It's much easier to write $\mathrm{d} \vec{A}$ instead of, say, $r \ \mathrm{d}r \ \mathrm{d}\theta$ all the time. Furthermore, it's more general, as $\mathrm{d} ... 13 Bra ket notation has nothing to do with integrals. If I have two vectors in 3D space,$\vec{v}$and$\vec{w}$, I can write them as$|v\rangle$and$|w\rangle$if I want. In that case, I would write their dot product (a.k.a. inner product) as$\langle v | w \rangle$. This dot product has nothing to do with integration. When your vectors are functions then ... 13 If I saw the word "amp" written as such in a paper in my field (astrophysics) it would strike me as a bit informal. I would expect to see the full "ampere" written. That said, it is rare to actually write out the full name of a unit; usually it follows a number and is given its standard abbreviation. When abbreviated to e.g. "$5\ \mathrm{A}$", I would ... 13 I agree with Ron Maimon that Large scale structure of space-time by Hawking and Ellis is actually fairly rigorous mathematically already. If you insist on somehow supplementing that: For the purely differential/pseudo-Riemannian geometric aspects, I recommend Semi-Riemannian geometry by B. O'Neill. For the analytic aspects, especially the initial value ... 12 I've seen "(1)" used. Radians (and steradians) are also "unitless" but they're clearly not appropriate here. 11 It means that only when m and n are equal the value is 1, otherwise it is zero. Check http://en.wikipedia.org/wiki/Kronecker_delta for more information. 11 Technically, apparently, your teacher is correct. BIPM and NIST In the official brochure from the Bureau international des poids et mesures (BIPM, the keepers of SI units) in §5.1 Unit symbols we find: It is not permissible to use abbreviations for unit symbols or unit names, such as sec (for either s or second), sq. mm (for either mm2 or ... 11 It's c for constant or celeritas, which means speed in Latin. Everyone uses it because it's convention. You could use$\xi$or$\zeta$or$\gamma$or any other symbol you wanted, but then you'd have to explain what it meant, and people would have to go through the trouble to remember this every time they read your papers. Better to go with convention and ... 10 Quite often everything inside bra or ket is just a label. In this particular case the meaning of$|λ,m_l⟩$is "a state with the square of the angular momentum being equal to$λ$(in atomic units, where$\hbar=1$) and with the projection of the angular momentum in some direction ($z$-axis conventionally) being equal to$m_l$". That is,$|λ,m_l⟩$state is ... 10 The wedge product has its roots in exterior algebra. Exterior algebra lets you talk about objects like planes or volumes as algebraic elements of their own, separate from ordinary vectors, but still obeying the same notions of being "vectors" in their own vector spaces. The wedge product of two vectors is a bivector, and many concepts you may have been ... 10 Capital$\mathrm{C}$, in upright font, is the symbol for the coulomb. Lowercase$c$, italicized, is the speed of light in vacuum. Thanks to Einstein's equation, we can switch between mass and energy ($\mathrm{MeV}$is a unit of energy) by using factors of$c^2$, and sometimes it's more convenient to know the energy equivalent of a particle's mass rather than ... 10 The notation$\lvert \rangle$is meant to imply that$\lvert \text{anything here you want to put here} \rangle$is a vector in a Hilbert space. If you have got some wavefunction$\psi(x)$, then you often denote the abstract vector (instead of the concrete realisation in a basis like$\psi(x)$) it represents by$\lvert \psi \rangle$. If you have got only a ... 10 Here is a video of the film's science advisor explaining what the equation is and how he came up with it: http://www.youtube.com/watch?v=WjfT6MqTCqQ It is based on the Gompertz equation, which is a model of mortality rates, with some added "mathematical glitter." 9 Are those square brackets standard notation in Physics? Yes. See, for example Sean Carroll notes. At least I can tell you from two other classic references using that notation, "General Relativity" by Wald (1984) and "A First Introducion to General Relativity" by Schutz (2009 for the most recent edition)$ $If I am in a non-curved$\mathbb M$... 9 It's purely notation. Given a real-valued function$f(\mathbf r) = f(x^1, \dots, x^n)$of$n$real variables, one defines the derivative with respect to$\mathbf ras follows: \begin{align} \frac{\partial f}{\partial \mathbf r}(\mathbf r) = \left(\frac{\partial f}{\partial x^1}(\mathbf r), \dots, \frac{\partial f}{\partial x^n}(\mathbf r)\right) ... 9 If you want to make statements over (discrete) time, linear temporal logic may be worth looking at. For instance,\qquad\displaystyle \Box (A \implies B)$means that whenever$A$holds,$B$has to hold at the same time.$\qquad\displaystyle \Box (A \implies \Diamond B)$means that whenever$A$holds,$B$will hold at some point in the future. Or yet ... 9 In physicist jargon, we talk about group representations of$\mathrm{SU}(2)$and$\mathrm{SU}(3)$by denoting an irreducible representation whose representation vector space has dimension$N$by$\mathbf{N}$. Hence, the statement$\mathbf{3} \otimes \bar{\mathbf{3}} = \mathbf{1} \oplus \mathbf{8}$is the statement that the tensor product of the ... 9 They're not used because it's ugly to read such texts with parentheses and it's time-consuming to write it down. A decimeter is indeed a "product" of "deci" and a meter, so the origin is analogous to the product of two real numbers$ab$. But once we define the new derived unit${\rm dm}$, we treat it as a single object, so it really means what you would ... 8 A physicist would write your first equation$x^a = x^\mu e_\mu^a$. The notation$x^a$is invariant in your terminology. The$a$is an abstract index. It is ostensibly not supposed to be thought of as ranging over a set of numerical values, but is just a marker that indicates that$x$is a vector (i.e., rank 1,0 tensor.) Similarly for each$\mu$,$e^a_\mu$is ... 8 The antisymmetric part is defined as $$A_{[a_1 \cdots a_n]} = \frac{1}{n!} \sum\limits_{\sigma \in P(n)} \text{sgn}(\sigma)A_{a_{\sigma(1)} \cdots a_{\sigma(n)}}$$ where$P(n)$is the set of all permutations of the set$\{1,\cdots,n\}$.$\text{sgn}(\sigma)$is called the sign of the permutation and is positive of$\sigma\$ is obtained from the identity ...

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