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2
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3answers
361 views

Are length contractions limited by Planck length?

While we are getting closer to speed of light our length in the direction of the movement is according to Lorentz transformation getting shorter. But we can not (even theoretically) consider length ...
2
votes
1answer
57 views

Deriving (dimensionless) physical constants from theory

The Wikipedia entry on Physical Constants says: With the development of quantum chemistry in the 20th century, however, a vast number of previously inexplicable dimensionless physical constants ...
2
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2answers
88 views

What Planck units are limits?

Some Planck units, like time, length, or temperature, describe a physical maximum or minimum, at least approximately: you can't get hotter than the Planck temperature, measure anything smaller than ...
0
votes
0answers
66 views

How the experimental charge $e=1.60217657 × 10^{-19} C$ has precisely this value?

The coupling constant that we measured in "arbitrarily" low energy is $e=1.60217657 × 10^{-19} C$. How this is presented in Renormalization Group flow in charge coupling space? Why the action of the ...
6
votes
3answers
134 views

Can someone explain Planck's constant simply? [closed]

Can someone explain Planck's constant simply? I know the math, however I don't understand the relevance. To explain what I'm asking, what is the significance of it when doing quantum mechanical ...
1
vote
1answer
72 views

What is the significance of Planck's constant in De Broglie–Bohm theory or Pilot-wave theory?

In standard QM, Planck's constant seems to be a constant that describes the smallest quanta of energy in some way. Does De Broglie–Bohm theory have an alternate interpretation of that constant and ...
0
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0answers
22 views

Is there a Planck uncertainty?

There are theories which place lower limits on length, time and temperature. Is there a corresponding one for the lower limit for uncertainty? Is there a probability so small it cannot exist in this ...
2
votes
1answer
74 views

Why is $\mu_0$ missing in EM formulas in Peskin and Schroeder?

In this post, $\hbar=c=1$ units are used throughout. It is well known that the action of classical electromagnetism is given by $$\mathcal S_{\text{Maxwell}} = \int ...
0
votes
5answers
172 views

Why is the speed of light in vacuum constant? [duplicate]

Are there any proof of the speed of light in vacuum being constant? All I hear is that light in vacuum travels at a constant speed because that's an observation and that it fits in a coherent theory ...
0
votes
1answer
42 views

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 ...
0
votes
4answers
131 views

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 ...
1
vote
2answers
161 views

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 ...
5
votes
1answer
209 views

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? ...
0
votes
2answers
60 views

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 ...
1
vote
2answers
109 views

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?
1
vote
1answer
186 views

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?
0
votes
1answer
90 views

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 ...
-3
votes
1answer
128 views

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 ...
3
votes
1answer
68 views

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, ...
3
votes
1answer
33 views

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 ...
0
votes
1answer
43 views

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 ...
0
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0answers
25 views

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 ...
1
vote
0answers
31 views

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?
1
vote
1answer
36 views

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 ...
3
votes
2answers
64 views

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?
0
votes
1answer
35 views

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 ...
2
votes
2answers
88 views

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 ...
2
votes
2answers
34 views

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 ...
9
votes
3answers
247 views

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? ...
5
votes
5answers
349 views

The gravitational constant $G$ theoretically?

We know all that the gravitational constant is $$G=6.67428±0.00067\times 10^{-11}m^{3} kg^{-1} s^{-2}.$$ But can we calculate it theoretically?
1
vote
0answers
54 views

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 ...
1
vote
4answers
564 views

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? ...
1
vote
0answers
41 views

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 ...
6
votes
2answers
204 views

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 ...
1
vote
3answers
378 views

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: ...
-1
votes
1answer
51 views

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 ...
4
votes
4answers
216 views

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 ...
1
vote
1answer
92 views

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 ...
1
vote
0answers
47 views

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 ...
1
vote
1answer
37 views

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 ...
2
votes
2answers
137 views

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 ...
0
votes
1answer
103 views

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 ...
2
votes
1answer
62 views

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 $\frac{1}{4\pi\varepsilon_0}$?
2
votes
1answer
104 views

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 $10^{-20}$ ...
1
vote
1answer
38 views

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 ...
13
votes
5answers
3k views

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 ...
4
votes
3answers
205 views

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. ...
3
votes
1answer
75 views

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 ...
-3
votes
3answers
85 views

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 ...
2
votes
1answer
258 views

Value of weak force coupling constant

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, ...