# Tagged Questions

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### Fine structure constant definition

The fine structure constant is usually defined using $e$, $h$ ,$c$ ... However, from QED, we know it cannot be derived but only experimentally measured. Does that mean the usual definition we use in ...
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### How confident can we be that the speed of light in a medium is constant?

I have recently found this article http://news.harvard.edu/gazette/1999/02.18/light.html it tells that physicists have been able to slow the speed of light. Is this hokum? If not how is it possible to ...
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### Why is the Luminiferous aether theory wrong? [closed]

I saw on this page about the constant speed of light that there are two ways of interpreting this constant speed: General relativity The Luminiferous aether theory I understand why the theory of ...
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### The fine structure constant - can it genuinely be a random variable?

The question Does it make sense, and are there physical reasons to think about the fine structure constant as a (very concentrated) probability distribution rather than a single real number? ...
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### Can gravitational constant be changed?

In my book(Principles of Physics by Resnick,Halliday,Walker) , the authors write: If $G$ - by some miracle - were suddenly increased by a factor of 10, you would be crushed to the floor by Earth's ...
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### What is the point of the reduced Planck's constant $\hbar$ (h-bar)? - Why don't we just have Planck's Constant $h$?

I know that $ħ$ is $h / 2π$ - and that $h$ is the Planck Constant ($6.62606957 × 10^{-34}$ $Js$). But why don't we just use $h$ - is it that $ħ$ is used in Angular Momentum Calculations?
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### Why is the gravitational force $10^{38}$ times smaller than the strong nuclear force?

Also, why is the weak interaction force $10^7$ times smaller than the strong nuclear force?
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### How can gravity truly be infinite?

From my knowledge, gravity is infinite and extends throughout all of space. It diminishes as distance increases but is still present everywhere. So given enough time, no matter where something is in ...
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### Emission and absorption of photons by electrons [closed]

Two questions occur at a critical review of the two famous experiments devised by Millikan in 1914, respectively Duane, Hunt and others in 1917-1920, which confirmed the action constant calculated by ...
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### From which dimensionful constants does proton mass arise?

It is well known that the most of the proton (or any other hadron with light quarks) mass is not made up from quark masses, but it is dynamically generated by QCD mess inside. I've also heard that, ...
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### Are laws of nature changing?

I am reviewing articles that address whether fundamental laws of nature (physics) are changing. The following letter sums up my research literature and conclusions. "Book Review: The Constants of ...
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### Light speed after the Big Bang

We know that immediately after the Big Bang space was opaque to light. As space expanded, light could travel. However I would think that as space expanded at some de sites the light would be much ...
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### Variable parameters in cosmology

Mainstream theories in cosmology assume that parameters like the speed of light $c$, and the gravitational constant $G$ are time-independent. Is there any evidence suggesting that this assumption is ...
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### Ultimate Planck Frequency [closed]

Is there an upper limit to the Planck Frequency? Does it simply depend upon the inverse of the Planck Time unit?
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### Why is the Fermi coupling constant always expressed in units of $(\hbar c)^3$?

Everywhere I've looked so far (such as NIST) the Fermi coupling constant $G_F$ is always expressed as $$\frac{G_F}{(\hbar c)^3} = 1.166 364(5) \times 10^{-5} \textrm{ GeV}^{-2}$$ never as just ...
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### How is the most accurate value of $G$ measured?

How do modern scientists update the measurement of $G$, the gravitational constant? Is CODATA the authority on this measurement and the experiment?
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### Reference for the value of the axial vector coupling constant, $g_A$

This paper (I don't know if it is available for free or not) defines the axial-vector coupling constant (a constant important in calculations involving the weak interaction) as $g=1.26$. My advisor ...
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### Where is the fine-structure constant in this list?

so John Baez has this nice list of what he enumerates as the 26 Fundamental Universal Physical Constants and they're dimensionless, as they should be to be meaningfully fundamental. one if his grad ...
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### The time interval of fundamental interactions?

I extract the below text snippet from our text book: Strong interaction is charge independent.The time interval of such a strong interaction is about $10^{-23} sec$ and it's range is approximately ...
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### Why do universal constants have the values they do?

This is meant to be a generic question of the type that we get repeatedly on this site, in different versions: The origin of the value of speed of light The gravitational constant G theoretically? ...
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### Can the gravitational constant $G$ be calculated theoretically?

We know all that the gravitational constant is $$G=6.67428±0.00067\times 10^{-11}\mathrm{m^{3} \:kg^{-1} s^{-2}}.$$ But can we calculate it theoretically?
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### Natural units in a parallel universe [closed]

Taking ispiration from this question units and nature . The natural Plank units set the gravitational costant $G$, the planck costant $\hbar$, the speed of light $c$, the Boltzmann costant $k_B$ and ...
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### What's so special about the speed of light? [duplicate]

What's so special about the speed of light? Why do many equations in physics include the speed of light in vacuum $c$? Why do so many thing depend upon it? Why can't it be the speed of sound? ...
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### Geometrised Units

I am curious as to how to express a area units in geometrised ones. I was reading on wikipedia and saw that when angular momentum is converted into geometrised units, it is expressed as a dimension of ...
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### Why is Planck's constant the same for all particles?

This question came to me while reading Where does de Broglie wavelength $\lambda=h/p$ for massive particles come from? This question has a nice answer that explains that wave number has be ...
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### How can we minimize the coefficient of static/kinetic friction?

Static frictional force depends on the coefficient of static friction; kinetic frictional force depends on the coefficient of kinetic friction. To minimize friction, one of two things could happen: ...
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### Can quanta have different energy levels? [closed]

The energy of a wave is h*f. How i imagine this is each cycle consisting of 1 quanta. I sometimes hear people say the energy of a photon is equal to h*f which makes it sound like each cycle has a ...
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### How accurate are constants in cgs units?

I am just curious that if constants in cgs units change the answer of an equation. For example, Coulomb's constant, in SI units it equals to $8.98...\times 10^9 \,\mathrm{N\,m^2\,C^{-2}}$. However in ...
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### Expansion in Quantum Fluctuations of the Path Integral

In this post: Dimensionless Constants in Physics there is a discussion about dimensionful vs. dimensionless constants in physics. In the context of this discussion, I'm wondering about the ...
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### Planck time, time or time interval? [duplicate]

Planck time is really a weird topic, if we try to find out that is it time or time interval. It is the time taken by light to travel a Planck LENGTH so it must be time interval. But we also know that ...
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### How you call the constant $\alpha$ within the heat equation in general and in terms of electromagnetism?

The heat equation or diffusion equation does contain a constant $\alpha$. $$\frac{\partial u}{\partial t} - \alpha \nabla^2 u=0$$ How is it called? I'm interested in a general name which can be ...
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### How “unnatural” is the universe? [closed]

Looking to read up on the impact the discovery of Higgs boson has on the String Theory I came upon these two paragraphs in an article about the Higgs boson Nobel Prize: One possibility has been ...
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### In general, could any ad-hoc relationship of constants be useful?

In general; if one creates an ad-hoc relationship of constants, can we use it to solve equations OR is it just an abstract/artificial math construct? I'm a grad student and as we all know, these ad-...
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### Why do we take the value of the constant in Coulomb's law as $\frac{1}{4\pi\varepsilon_0}$? [duplicate]

Why do we take the value of the constant in Coulomb's law as $\frac{1}{4\pi\varepsilon_0}$?
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### Why do we say that the electric forces are stronger than gravitational forces? [duplicate]

May be I am asking a stupid question but I am very confused...I understand both forces are inversely proportional to the distances squared, and that the gravitational constant is roughly $10^{-20}$ ...
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### Which experiment would be able to detect change in the speed of light? [duplicate]

Since the unit of distance is defined in terms of speed of light in vacuum, if the speed of light in vacuum were to change by "magic", what experiment would be able to detect that? Is there a theory ...
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### Is speed of light and sound rational or irrational in nature?

Just as circumference of circle will remain $\pi$ for unit diameter, no matter what standard unit we take, are the speeds of light and sound irrational or rational in nature ? I'm talking about ...
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### why are the anthropometric units (which are about as big as we are) as large as they are relative to their corresponding Planck units? [duplicate]

so this might have some duplicated inquiry that this question or this question had, and while i think i have some of my own opinion about it, i would like to ask the community here for more opinions. ...
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### How do I choose my constants?

When solutions to Einstein's equations are found (in coordinates $t,r,\theta,\phi$), such as Schwarzschild, Kerr etc. the way they are found seems to be by starting with a generalised metric in terms ...
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### Is there a unit system, where all physical laws looks nice?

And by nice looking law I mean with no constants. I mean, what would we need to set, so all laws would without those nasty constants in front of them? (I mean all of them, also $\pi$!) What would it ...
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I'm trying to get my head around the weak force coupling constant $\alpha_w$ but getting confused by different resources. Hyperphysics suggests it is tiny compared with the strong force coupling, ~$10^... 2answers 95 views ### Significance of mc/h constant in Klein-Gordon equaiton The are several ways, in which one can write the Klein-Gordon equation, the most straightforward being probably the following: $$\hbar^2 \partial_t^2 \psi(x) = (\hbar^2 c^2 \Delta + m^2c^4) \psi(x) ... 1answer 746 views ### Gravitational Constant in Newtonian Gravity vs. General Relativity From my understanding, the gravitational constant G is a proportionality constant used by Newton in his law of universal gravitation (which was based around Kepler's Laws), namely in the equation F ... 3answers 197 views ### Can all laws of physics derived by a single or lists of more general laws? (This is actually my first question - please understand my lack of knowledge and bad English..) I have always been curious about deriving thousands of laws from more general ones.. Can general laws ... 6answers 2k views ### Is there any relation between Planck constant and Gravitational constant? Why is the Gravitational constant about 10^{23} times of the Planck constant in SI-units? Is there any relation between them? I mean Planck constant is about 6.6\times 10^{-34} Js and ... 1answer 169 views ### Is 4 \pi G the true most fundamental gravitational constant? [closed] Newton's law of gravitation is:$$F = G m_1 m_2 \frac{1}{r^2}$$It looks simple and natural. But that's only in 3 dimensions. Let's look what happens in n dimensions:$$n=2 : F = 2 G m_1 m_2 \... 4answers 858 views ### Why isn't it$E \approx 27.642 \times mc^2$? Sorry for the strange question, but why is it that many of the most important physical equations don't have ugly numbers (i.e., "arbitrary" irrational factors) to line up both sides? Why can so many ... 2answers 158 views ### Which is the most fundamental constant between the Planck constant$h$and the reduced Planck constant$\hbar\$?

This question is related to Planck units (also called natural units, absolute units or God's units). I'm wondering which constant is the most fundamental and should be normalized to 1. I would like as ...
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### Why didn't we replace our SI units with a better system? [closed]

Intro It seems to me that the SI units we use today are nothing but the result of a historical 'coincidence'. I recently began researching about natural (absolute) systems of units, which are ...
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### What is a proportionality constant? (Planck's constant)

I understand that Planck's constant is essentially the ratio between the energy of a photon and its frequency. There are 2 things that im trying to verify: isn't the number that Planck's constant ...