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Questions tagged [physical-constants]

The tag has no usage guidance.

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Is gravitational constant a rational number? [duplicate]

The question is the title. But I'm quite doubtful if this question is meaningful or not. Since this constant is obtained by experiment, we can never know its exact value, unlike $π$ or $e$. Is it ...
0
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1answer
34 views

Spatial variation in the fine structure constant

An article in Time (I saw it reprinted in Medium), and questions on this site discuss observations that suggest that the fine structure constant might vary spatially in the universe. If true, wouldn't ...
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2answers
42 views

How was the value of vacuum permittivity originally found?

The vacuum permittivity appears originally in Maxwell's equations, used to describe electric fields. The permeability of vacuum was defined using Ampere's force law (itself derived from Biot-Savart ...
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3answers
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How fine of grain size will it take to cover a football field?

There is a claim in health circles that a single Tablespoon of Bentonite clay has enough surface area to cover a football field. Let's assume a heaping tablespoon. If you halve a (roughly spherical) ...
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1answer
52 views

What is a good site to use for finding physical constants at times when NIST web resources are affected by government shutdowns?

There are multiple resources for finding physical constants (say, particle data, atomic spectra, or even special-function identities) which are generally hosted by NIST, and which form essential ...
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0answers
79 views

Why $\kappa = 8 \pi G$ in $D$ dimensional spacetimes?

Probably another question without an answer! ;-) In most books/papers I saw on General Relativity, everybody writes $\kappa = 8 \pi G_D$ in the right part of Einstein's equation, even for spacetimes ...
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0answers
67 views

Natural classification of fundamental constants of Nature

I was wondering about the fundamental constants of Nature since several years, and still pondering on them. Of course, I have read a lot of papers on them, but never found any satisfying ...
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43 views

General question about making differential equations dimensionless

Suppose you have a set of differential equations that you wish to normalize/make dimensionless. From what I've seen, you can usually use dimensional analysis to figure out a good choice of constants ...
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1answer
100 views

How can a Lego version of a Kibble balance measure the Planck constant?

As the picture shows below [][1] in a Kibble balance, one can drop out the measurement uncertainty of $B$ (magnetic flux intensity) and $L$ (length of coil) by the use of two modes, force mode and ...
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2answers
79 views

Can we set cosmological constant equal to one?

People often say that the cosmological constant is too small. $\Lambda=10^{-120}$ in Planck units. Can we set $\Lambda=\hbar=c=1$ ? If so what would this give for $G$, the gravitational constant in ...
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1answer
46 views

Constants of proportionality in Force Equations/ Physics in General

I was in physics class and we were talking about the gravitational constant G (6.67 x 10^-11 Nm^2/Kg^2). The question came up: "Why does $F= (GMm)/r^2$ have a constant of proportionality and not $...
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1answer
58 views

Can a physical quantity be of different dimensions depending of the system of measurement?

When comparing the Wikipedia articles on the International System of Units, the Planck unit system, and the geometrized unit system one question arises: can a physical quantity be of different ...
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1answer
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Is the uncertainty principle a circular argument? [closed]

Uncertainty is due to the measurement techniques humans tend to use requiring photoelectric effect. The Planck constant is due to the photoelectric effect. If the standard deviation of measurement was ...
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3answers
439 views

Why does the fine-structure constant $α$ have the value it does?

This is a follow-up to this great answer. All of the other related questions have answers explaining how units come into play when measuring "universal" constants, like the value of the speed of ...
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1answer
42 views

What does the universal gas constant, $R ,$ represent?

What does universal gas constant represent? My textbook says: it is the energy required to raise a ideal gas by 1K The Mayer formula is $$ C_{\text{p}} = C_{\text{v}}+R \,,$$ so isn't text book ...
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1answer
70 views

In the value of gas constant $R$, what kind of mole is it?

Wikipedia gives $$R=8.3144598(48)\, \rm J\,mol^{−1}\,K^{−1}$$ But I want to ask how is it possible to write $\mathrm{mol}$ without a suffix? I mean, we must determine if we have $1\ \mathrm{mol}$ of ...
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0answers
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How should constants of nature be changed to experience extreme phenomena in everyday situations (like Mr. Tompkins did)?

In George Gamow's Mr. Tompkins books, Mr. Tompkins ends up, first in a world where the speed of light is so small that time dilation and Lorentz contraction are dominantly present when he rides a ...
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1answer
39 views

How are constants derived? [closed]

With little to no background in mathematics and physics respectively, I hope that I might still receive a somewhat elaborate response, but understandable for a layman. I am curious how constants such ...
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1answer
42 views

If the Higgs field was densified a little more, can the physical constants such as Planck Values be changed?

According to theory, the Higgs field is at everywhere in the space. So that, the mass is existing by interaction of energy (in some way) with this field. And according to this the space vacuum has an ...
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3answers
197 views

Is the speed of light in vacuum $3\times 10^8\ \rm m/s$?

I saw another question which says the speed of light is "$3\times 10^8 \:\rm m/s$", and I know that the speed of light is $299,792,458\ \rm m/s$. My chemistry teacher taught me that $3.0$ means $3.0 \...
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2answers
218 views

Statistical mechanics and Planck constant universality

In questions that ask about Planck's constant entering into statistical mechanics, a common and accepted answer is that Planck's constant is an arbitrary normalization that falls out when calculating ...
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2answers
91 views

Is the speed of light in the Universe always $c$?

Every one here knows that $c=(ε'×μ')^{-1/2}$. But what if ε' and μ' are different values in other parts of the visible universe. Maybe near the center of a Quasar galaxy or even a Neutron star?
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Analogue of $\varepsilon_0$ for gravitational mass? [duplicate]

In electric fields, we usually define the dielectric constant in vacuum as: $$K_C=\dfrac{1}{4\pi\varepsilon_0}$$ Why don't we define the gravitational analogue, "digravitational" constant: $$\Delta_0=...
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0answers
28 views

Running of gravitational constant versus. other coupling constants, GUT and TOE

Is there any theory that proves convincingly that the gravitational constant runs with energy AND it is like the other coupling constants and converge at a single point at a given energy? Or is that a ...
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2answers
39 views

Inverse proportionality intuition

Often in physics we model something using proportionality constants. When we can intuitively say that some quantity grows as another quantity grows, we might assume that the relationship is linear and ...
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4answers
82 views

Hypothetical mass-energy equivalence

2 questions: Hypothetically, if in an imaginary universe, the speed of light squared were 90% or 110% of what is is in our universe...would the math require another constant such as 1.1 or .9 next ...
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2answers
52 views

Energy mass equivalence

Regarding $E=mc^2$, in a hypothetical parallel universe. If in that universe the speed of light squared were let’s say 10% slower, would everything still work but just slightly different? Or would an ...
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1answer
206 views

Electric force much stronger than gravitational force? [duplicate]

It is commonly said that the electric force is much stronger than the gravitational force. Indeed, Coulomb's constant $k_e$ is much larger than the gravitational constant $G$ but they are measured in ...
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3answers
444 views

Derivation question of WKB method

Quantum Mechanics (2nd Edition) by Bransden and Joachain contains the following passage: Substituting (8.176) into (8.171), we obtain for $S(x)$ the equation $$-\frac{i\hbar}{2m}\frac{\mathrm{d}^...
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0answers
52 views

Why are the Planck charge and Planck mass values so much larger than observed particles? [duplicate]

The Planck charge and mass values seem rather unusual. Is this an indicator that there is a lack of understanding in current theory, or is there a logical explanation for the magnitude of these two ...
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1answer
105 views

Does $ℏ$ play a role in the 1PI effective action?

In most cases, people discuss the effective action or the effective potential in the convention $\hbar=1$. Occasionally, we see the expression at the 1-loop order as $$\Gamma[\phi]=S[\phi]+\frac{i\...
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10answers
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Why do scientists think that all the laws of physics that apply in our galaxy apply in other galaxies?

I like watching different videos about space. I keep seeing all these videos saying scientists found so and so at 200 billion light years away or this happened 13 billion years ago. My question is ...
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1answer
235 views

Why are there a bunch of cosmological coincidences?

There are several cosmological parameters that are more or less of the same order $10^{-60}$ (in Planck unit), namely, inverse of the age of the universe $$ \frac{1}{t_0}, $$ Hubble constant $$ H_0, $...
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3answers
358 views

Do we need Planck’s constant for second quantization?

The widely circulated folklore surrounding Planck’s constant $\hbar$ lends it an aura of importance. But could $\hbar$ be a constant of human convention which is dispensable? Is the unorthodox view in ...
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1answer
521 views

What things are smaller than the Planck length?

I recently read Is the Planck length the smallest length that exists in the universe or is it the smallest length that can be observed? The general agreement is that the idea that the Planck length ...
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2answers
71 views

Why does the Hubble constant have a subscript zero?

The title says it all. Why is the Hubble constant written $H_0$ and not just $H$? What is the purpose of that subscript $_0$?
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1answer
161 views

Why does $\frac{1}{4\pi}$ appear in many formulas? [duplicate]

Why do most of the physical equations have $\frac{1}{4\pi}$ as constants? I have seen that many equations have $\frac{1}{4\pi}$ as constants like Coulomb, pendulum problems, etc. Can anyone tell me ...
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1answer
145 views

How much bigger is $a$ than $b$ when we write $a \gg b$?

When a condition of some physical quantity $a$ and $b$ is presented, say $a \gg b$, how much bigger do we say $a$ has to be than $b$? $10$ times? $1000$ times? $10^6$ times? Some context: I am ...
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1answer
81 views

Rewriting Schroedinger's equation with $\hbar c$?

I am solving a special case of the radial component of Schroedinger's equation numerically. The equation looks like this: $$ u''(r) = \frac{2\mu}{\hbar^2}(V(r) - E)u(r). $$ $V(r)$ is a potential and $...
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1answer
117 views

Why does light have a universal speed limit? [duplicate]

$c$, the speed of light constant, is valued at 3x108 meters per second. But why this figure and not, for example, 4x1020 m/s? Is it a random digit pulled out of a bag of numbers when a new universe ...
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0answers
24 views

How do we know the standard of units of measurements do not change? [duplicate]

Throughout human history we have used various scales to represent things like distance (length of someones foot, yard), time duration (time rotation of earth on it's axis for a day etc). When ...
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2answers
105 views

Could there be some system of units such that all fundamental constants are 1? [closed]

The fundamental constants in physics have extremely low values because of our scale compared to fundamental particles. Could there be such a system of units such that all fundamental constants are 1?
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1answer
39 views

Converting units of $G$ [closed]

I want to convert $G$ from $\rm m^3 \:kg^{-1} \:s^{-2}$ to the units $\rm km^3 \: kg^{-1} min^{-2}$. How can this be done? I want to know what $6.67\times 10^{-11} \:\rm m^3 \:kg^{-1} \:s^{-2}$ is ...
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1answer
33 views

How to refute the claim that action at a distance force can be a polynomial function of $r$?

Suppose that we have a body $B$ exerting action at a distance force on body $A$. Now if someone says that the dependence of force on distance between the bodies ($r$) is: $f(r)=\dfrac{1}{r^2}+\dfrac{...
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0answers
54 views

How did Maxwell knew that the square root of two constants equal $c$? [duplicate]

I was watching a documentary on James Clerk Maxwell but the entire film is based on his life and the impact his work brings to the world, not a single mention how he knew how that the electric ...
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2answers
67 views

Formal Term for an invariant constant to all observers

I was thinking of the speed of light and realized I don't know how to quickly name the concept of "physical quantity that is measured to be the same in all reference frames". Are there examples of ...
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Why is there a constant in the ideal gas law?

Why do we have constants? Consider, for example, the ideal gas law, $$PV = nRT \, . \tag{ideal gas law}$$ Sometimes I believe that the constant is there in order to make the equation work (make the ...
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1answer
108 views

Enrico Fermi's photo and the wrong fine structure constant

This photo about the Italian supreme physicist Enrico Fermi is rather famous. Yet nobody ever questioned, as far as I know, the wrongness of the fine structure constant written on it. So I ...
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2answers
147 views

Can Boltzmann's Constant be Calculated from Fundamental Constants?

Boltzmann's constant is not "fundamental" in the same sense as $c$ or $G$. Rather, it is an artifact of measuring temperature in units of kelvins rather than joules. Other non-fundamental constants ...
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0answers
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Is Boltzmann's constant $k_{B}$ the same throughout the universe? [duplicate]

By Boltzmann's constant, I mean $k_{B}$.The question requires special preference since the thermodynamics predictions would vary if $k_{B}$ has a spatial variation