Questions tagged [physical-constants]

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4answers
493 views

The fine structure constant

I have a question about the really meaning of the fine structure constant. Actually, my doubt is why the physicist look to a meaning for this constant. I understand the difference between this ...
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1answer
37 views

Are there multiple Rydberg constants?

I'm sorry if this is a trivial question, I'm trying to understand the Rydberg formula and unsure if there are different values for the Rydberg constant? According to Wikipedia's articles about ...
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0answers
22 views

What does the derived unit “square coulomb” quantify?

As a square meter (m$^2$) quantifies area and not length, what does a square coulomb (C$^2$) quantify?
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4answers
151 views

Can $G$ (Newton's constant) be thought of as a fundamental parameter of physics? [closed]

Can I think of Newton's Gravitational Constant as a fundamental parameter of nature (based on our current understanding of physics)? I realize that it is very unlikely that $G$ is actually a ...
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1answer
33 views

Is our metrics and/or constants geocentric?

Considering that all our metrics is now based on physical constants as measured here on earth, With earth having both gravity and velocity, as well as the whole solar system having too, and special ...
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1answer
46 views

How to go from one equation to another?

I am starting to studying quantum physics, but this part of the theory catch me, how do we go from the $-e^2/2a_0$ to the next expression? $$ E=\frac{1}{2}\left(\frac{e^2}{a_0}\right)-\frac{e^2}{a_0}=-...
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0answers
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Confusion about the relation between Einstein $A$ and $B$ coefficients

In hyperphysics website it's shown $$\frac{A}{B} = 8πh\frac{\nu^3}{c^3}.$$ But in many famous textbook like Quantum Mechanics: Concepts and Applications Textbook by Nouredine Zettili the formula is ...
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1answer
91 views

Doubt about the constant $\kappa$ of Einstein's field equations

I'm trying to understand each of the terms in this equation intuitively but I'm having a little trouble. I know that we can represent the equation in the following way: $G_{\mu\nu}= \kappa T_{\mu\nu}$ ...
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1answer
104 views

Why is the constant in Coulomb's law written in terms of $\pi$ but not the constant in Gravitation?

What is the significance of writing it as $\frac{1}{4\pi \epsilon _0}$? Why not just name the whole thing $\epsilon _0$? And if there is a significance, why not do the same thing for gravitation? I ...
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2answers
58 views

Measurement of the gravitational constant $G$ in free fall

is there a reason why an accurate measurement of $G$ cannot be performed by measuring the distance and rotation period between 2 orbiting 1 kg masses in free fall? Using a simple estimation for 2 Pt ...
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0answers
38 views

Does gravitational constant $G$ depend on energy of masses?

Just read that strong force coupling force will become weak near Planck energy while weak force coupling constant will become equally strong as strong force. Same will also apply to gravitation and $G$...
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2answers
66 views

Confusion regarding the appearance of $\hbar$ in the eigenfunctions of momentum operator

The two images below are from different books. One has the $\hbar$ in the root below which seems right to me as that gets the dimensions correct but other does not have a $\hbar$. I am confused as to ...
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2answers
82 views

Single Planck $h$ constants

Planck developed his black body radiation theory assuming that atoms treated as simple harmonic oscillators can stay in states of very much defined energy. If normal frequency of such oscillator is $\...
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1answer
76 views

String Theory for beginners: what is a scale?

I'm reading this introduction to string theory by Mariana Grana and Hagen Triendl and I have understanding problems around the method of compactification in string theoretical sense. The ...
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1answer
74 views

How to incorporate HEP into the naive picture of QM?

When I explain QM to non-physicists, I sometimes say that quantum effects are typically noticeable on very small scales. For example, a QM particle in the harmonic potential behaves mostly classically,...
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2answers
42 views

Is there a minimum “Planck” probability analog of the minimum Planck distance? [closed]

I know the Planck distance is real, but is there a Planck probability? I know the wavefunction units is length to the negative 3/2 number of particles. So can we calculate a minimum probability from ...
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0answers
33 views

How exactly do transformations affect constants?

So, I'm in high school and I've just been learning Quantum Mechanics. I'm trying to understand some concepts, since I'm interested in them, and I was having trouble resolving some doubts. Namely, how ...
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1answer
41 views

Are there constants that used to be considered fundamental constants but aren't anymore? Could any today become no longer fundamental?

Are there constants that used to be considered fundamental constants but aren't anymore? Are there efforts to show constants (that we currently consider fundamental) aren't really fundamental or that ...
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1answer
26 views

Has anyone worked out alternative laws of physics assuming different Planck lengths?

This is a purely speculative question and one that is motivated by discrete computational models of space. In particular, I am wondering if there is a worked out mathematical model of physics such ...
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1answer
19 views

How do I obtain the value for the Fermi Coupling Constant?

I have been given an equation, without an explanation on the constant included. The equation is the following: $$\Gamma= \frac{7\pi}{24} G^2_{\text{Fermi}}$$ When looking for a value for the Fermi ...
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0answers
27 views

Confusion regarding variable light speed theories

Einstein and others have thought about VSL theories. But I am unable to understand how VSL theories can be consistent, for the following reasons: Don't we need some mechanism (like Einstein ...
4
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1answer
55 views

What makes a constant of nature fundamental?

I came across a video on youtube in which Alexander Unzicker argues that in order to have a scientific revolution, one of the constants of nature should be eliminated(at 23:00). He gives the example ...
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1answer
61 views

What percentage of the speed of light would an object achieve the Planck energy? [closed]

As energy is proportional to the speed of light at what percentage of the speed of light would an object's energy reach the Planck energy level?
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3answers
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Why is the Planck length considered fundamental, but not the Planck mass?

The planck length is considered by many to be a lower bound of the scale where new physics should appear to account for quantum gravity. The reasoning behind, as far as I understand, is that $l_{P}=\...
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1answer
35 views

How to determine current expansion rate of universe from observing past objects?

How to determine the current expansion rate of the universe from observing past objects? When we look into the light from objects far away, it not only very very far away in the distance it is also ...
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0answers
21 views

Is it possible for physical constant to change in time? [duplicate]

There are many physical constants, like Boltzmann constant, light speed, dielectric constant of vacuum and so on. But is it possible to have physical constant that changes in time, for example it ...
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1answer
69 views

$cGh$-Physics Cube: When Do (General) Relativistic / Quantum Effects Become Relevant?

The $cGh$-cube is a way to visualise todays theoretical physics framework(s). This representation gives the impression $c$, $G$, and $\hbar$ could be viewed as variables between $0$ and $1$. This is ...
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0answers
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Instead of the universe accelerating its expansion, could non-constant constants also explain the phenomena?

The data gathered led physicists and astronomers to the conclusion that the universe is accelerating its expansion and therefore to theories about dark energy. My question is, could certian constants ...
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2answers
69 views

Meaning of the Planck Temperature

I don't understand what makes the Planck Temperature the "absolute hot". To my understanding Temperature is just a measure of the kinetic energy of the particles, so is the Planck ...
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2answers
308 views

How to prove that both $\mu_0$ and $\epsilon_0$ don't depend on any frame of references? [duplicate]

Based on my previous question here, lets us step back a little bit. The speed of light $c=1/\sqrt{\mu_0\epsilon_0}$ is assumed as a value that does not depend on the observer because it is just a ...
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3answers
1k views

Is the Bohr radius deprecated?

The Bohr radius ($a_0$ or $r_{\text{Bohr}}$) is a physical constant, equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state. It is named after ...
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0answers
41 views

How much does $g$ vary according to the position of the moon?

The gravity of the earth or more specifically the gravitational acceleration, $g$, is the acceleration objects with mass experience toward the earth due to gravity. How much does this vary according ...
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1answer
68 views

Derivation of $G=\frac{\hbar c}{m_\rm{P}^2}$

I read that the gravitational constant can be expressed in terms of Planck length. $$G=\frac{\hbar c}{m_\rm{P}^2}$$ What is the derivation of this relationship?
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3answers
90 views

How can vacuum have a permittivity?

I think that it is impossible to have the permittivity in vacuum because of there is no matter. But, in Coulomb's law, the Coulomb constant(1/4πε) have ε which means the permittivity in a vacuum. How ...
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2answers
148 views

Why speed of light in vacuum remains constant over space and time?

Imagine a Pulse of light traveling through space at $c$, coming towards an observer on Earth, while at the same time, Space-time fabric (metric) is continuously changing (expanding), then why is the ...
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1answer
29 views

Plastic permittivity compared to vacuum permittivity?

I'm studying electromagnetism and I have found that vacuum permittivity is equal to: \begin{equation} 8.854 × 10^{-12} C m^{-1} V^{-1} \end{equation} and the relative permittivity of plastic is ...
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3answers
4k views

Is Planck's Constant Really a Constant?

I am going through Groenewold's theorem and in his book: On The Principles of Elementary Quantum Mechanics, page 8, eq. 1.30: $$[\mathbf{p}, \mathbf{q}]=1\left(\text { i.e. } \mathbf{p q}-\mathbf{...
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1answer
50 views

What is gravitational constant in this context? [closed]

I've been reading an article and it gives me the following formula: $\vec{v}_B(t) = \vec{v}_0 - \mu_sgt \hat u_0$ It governs the velocity of a ball. In its explanation, it says: The ...
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6answers
403 views

Is my friend right about omitting $c^2$ in world famous tiny equation?

I know $E = mc^2$ says that inertial mass of a system is equal to the total energy content of a system in its rest frame. My friend told me the $c^2$ can be omitted from this equation because that's ...
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2answers
91 views

About the physical definition of the Planck's constant

In Quantum Mechanics (QM), the Planck's constant has the S.I. units of (energy) x (time). So, how should one interpret that?! How should I understand the physical meaning of the following relations? ...
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2answers
66 views

Is there a link between $G$ and speed of light? [closed]

I tried to resolve $G$ from natural units (like Planck), and found that $$ G = (K \times c / r_0)^3 $$ where $ G = 6.67430 \times 10^{-11} $ is gravitational constant, $ K = 1.66053906660 \times ...
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1answer
57 views

Dimensionless quantity using fundamental constants [closed]

Is this quantity dimensionless and a unique construction? $$\frac{c^7\hbar\varepsilon_0^2}{Ge^4}$$ I used the speed of light, the reduced Planck constant, vacuum permittivity, the gravitational ...
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1answer
58 views

Is the process of universe creation a chaotic system?

The anthropic principle says that: The laws of nature and parameters of the universe take on values that are consistent with conditions for life as we know it rather than a set of values that ...
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0answers
50 views

Is there someone how knows the proof of the dimensionless ratio of General Relativity $GM/(R c^{2} )$?

As we know all, the GR discuss the gravity problem and to see these relativistic effects the following ratio must be comparable to 1 $$ GM/(R c^{2}) $$ where $G$ Newton's constant, $M$ the mass of the ...
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2answers
94 views

What is the value of $\pi$ if the diameter of the circle is one Planck length?

We can consider the value of π as being roughly $3.1415927$, but π is defined as the ratio of the circumference of a circle to its diameter. However, if the diameter is one Planck length, does it ...
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4answers
94 views

Why is permeability of free space (in calculation of magnetic field) a non zero number?

I've been reading in Khan academy about the formula for calculating magnetic field lines (Ampere's law). Some materials have the ability to concentrate magnetic fields, which is described by those ...
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2answers
44 views

Regarding the units of a proportionality constant

I got a general query regarding variation of two physical quantities. If we have two physical quantities say $A$ & $B$ such that $A$ is directly proportional to $B$. There exists a proportionally ...
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11answers
5k views

How can any speed be defined as a constant? [duplicate]

We know that the speed of light is a constant, and can therefore be used to calculate many other relative values, but I'm having difficulty understanding how speed can be a constant, seeing as it's ...
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1answer
114 views

Coulomb's Constant

We know that Coulomb discovered experimentally that the electrical force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance, all ...
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1answer
82 views

In quantum field theory, is there a coupling constant for each field? (I.e. an equivalent to the fine structure constant for the EM fields.)

Given that the fine structure constant is a dimensionless ratio quantifying the strength of the coupling between a charged particle and the electromagnetic field, is there a symmetric set of such ...

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