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0
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2answers
40 views

Could Charles-Augustin de Coulomb measure the charge in Coulombs?

Did Charles-Augustin de Coulomb know: Coulomb's constant Coulomb (as a unit) if not then what was the first time it was measured?
3
votes
2answers
311 views

Uncertainty of permittivity of vacuum [duplicate]

Question: The value of permittivity of vacuum, $\epsilon_0$, is given with absolutely no uncertainty in NIST Why is this the case? More details: The permeability of vacuum can be given by ...
3
votes
2answers
57 views

Maxwell's Equations: Induction

What is the reason for some writing Faraday's Induction Law as $$ \nabla \times E= -\frac{1}{c}\frac{\partial B}{\partial t} $$ versus $$ \nabla \times E= -\frac{\partial B}{\partial t} ?$$
8
votes
3answers
138 views

Is there a limit to acceleration?

As we all know the speed of light is the limit at which energy/matter can travel through our universe. My question being: is there a similar limit for acceleration? Is there a limit to how quickly ...
0
votes
1answer
128 views

Damping Coefficient for a Hydraulic-Controlled Door

I have to apologize as I am not very good with physics terms, so please treat me as an ignorant. I am trying to calculate damping coefficient dynamically and it is for a hydraulic-controlled door ...
3
votes
2answers
359 views

What is the smallest existing thing in theory and law?

What is the smallest existing thing in theory and law?
2
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2answers
262 views

Newton's Law of Graviation: Why $G$ and not e.g. $\dfrac{1}{4\pi G_0}$?

I've been wondering, in Coulomb's Law, $k_e = \dfrac{1}{4\pi\epsilon_0}$. Therefore, why do we use $G$ in Newton's Law of Gravitation? What if the constant is more like Coulomb's Law, e.g. $G = ...
2
votes
1answer
148 views

Why is Planck mass much larger than the smallest mass that we actually know about?

The three fundamental constants $h$, $c$ and $G$ are manipulated and rearranged in different ways to get the Planck time, Planck mass etc. The Planck time is said to be the smallest time possible and ...
0
votes
1answer
121 views

Is it true that no one, not even Planck himself, knows how Planck's Constant was arrived at?

Planck's Constant is said to be one of the smallest constants used in Physics. Some even say it is one of the imponderables – something that we know exists and is true but cannot be explained yet. I ...
2
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0answers
157 views

What prediction led to the vacuum catastrophe?

The disagreement between predicted and measured energy density of the vacuum is one of the great unsolved problems of science. According to this book the predicted energy density was obtained as ...
3
votes
2answers
187 views

Fundamental Constants in a theory of everything (TOE)

Do physicists ever expect to be able to derive the fundamental constants of nature from theory? For example, if string theory or some other theory unites the four forces, would the theory be ...
1
vote
0answers
31 views

What is the constant appearing in the low energy action?

Usually one finds this expression for the low energy action $$S = \frac{1}{2\kappa_0^2}\int d^D X\; \sqrt{-G}\; \mathrm{e}^{-2\Phi}\,(R-\frac{1}{12}H_{\mu\nu\lambda}H^{\mu\nu\lambda}+4 ...
1
vote
1answer
64 views

Have the values of constants ever changed before?

Example sub-questions: Was the speed of light always that value? Was the acceleration due to gravity always been 9.8m/s/s? Etc By "change" I mean both actual change in the physical world because ...
3
votes
1answer
203 views

If Fine Structure Constant in not uniform in space what would that imply for cosmic background?

Recently J.Webb submitted paper which has extraordinary claim - that Fine Structure Constant is different in different directions in space! He (with others) measured $\alpha$ using quasar spectrum ...
6
votes
1answer
557 views

Why can you remove the gravitational constant from a computer game simulation?

I've seen in a few gravity simulation games (ie. bouncing balls) the equation: force = G * m1 * m2 / distance^2 shortened to this by removing the gravitational ...
10
votes
6answers
5k views

Why and how is the speed of light in vacuum constant, i.e., independent of reference frame?

I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them. How and why ...
2
votes
2answers
81 views

The physical interpretation of Newton's constant $G$

It is well known that the speed of light $c$ can be interpreted as the speed limit for information propagation. Similarly, the Planck's constant $h$ is interpreted as the minimum quantum package of ...
2
votes
2answers
184 views

The famous drop of $c$

In this, in my opinion, intriguing speech, Rupert Sheldrake, tells the story of the drop between the measured valued of $c$ in 1928 and 1945. When he goes to visit the Head of Metrology of the Physics ...
8
votes
1answer
326 views

Gravitational constant in higher dimensions?

From Newton's law of gravitation we know that $$F=G\frac{m_1m_2}{r^2}$$ where $G$ is gravitational constant. We can also see that it has dimensions $$[G]=\frac{[L]^3}{[M][T]^2}$$ and we have a ...
-2
votes
4answers
234 views

Why is the speed of light considered as a fundamental constant if its speed changes with medium resulting in refraction? [duplicate]

I know that the speed of light, the universal constant of gravitation and the Planck's constant are considered to be the three fundamental constants of the universe. But, why is speed of light ...
1
vote
1answer
691 views

What do physicists mean when they say “speed of light”?

Does it make sense to say, "The speed of light varies?" Some may say right off the bat "Yes, it changes as a wave passes through a different medium." However, I'd like to say no, because when I hear ...
4
votes
5answers
717 views

Planck mass is about the mass of one eyebrow hair

Unlike most Planck units named after "Planck" such as Planck length, Planck temperature, etc, the Planck mass seems more closed to daily life. It is about $10^{-5}$g, same order of magnitude of one ...
4
votes
3answers
206 views

What is the opposite of the Planck length?

What "large size" unit of length could be considered at the opposite end of spectrum from Planck's length? Is there a table of smallest and largest value for various physical quantities that can be ...
2
votes
0answers
148 views

Dimensional analysis to estimate order of magnitude of quantities

In the Coursera course From the Big Bang to Dark Energy on several occasions dimensional analysis was used to estimate the scale of quantities. This almost seems like a contradiction in terms to me, ...
16
votes
5answers
2k views

How can the speed of light be a dimensionless constant?

This is a quote from the book A first course in general relativity by Schutz: What we shall now do is adopt a new unit for time, the meter. One meter of time is the time it takes light to travel ...
11
votes
4answers
1k views

What's keeping us from simply redefining Avogadro's Number / the Mole as a definite integer?

This might be a question to ask in a Chemistry site, but because there is a lot of talk about redefining many units of measurements in terms of Avogadro's Number / the Mole, I was wondering why we ...
4
votes
5answers
861 views

Can Planck's constant be derived from Maxwell's equations?

Can mathematics (including statistics, dynamical systems,...) combined with classical electromagnetism (using only the constants appearing in chargefree Maxwell equations) be used to derive the Planck ...
6
votes
1answer
135 views

Why is it meaningless to speak about changes in a dimensional constant?

Every so often,* we get a question about what would happen should there be a change in a physical constant that contains dimensional information, such as $\hbar$, $c$, $G$, or often "the scale of the ...
0
votes
0answers
110 views

Calculating Integrated Precipitable Water using GPS

I'm trying to calculate the Integrated Water Vapor (IWV) using GPS data. I'm following the equations in the following publication: GPS Meteorology: Remote Sensing of Atmospheric Water Vapor ...
4
votes
3answers
169 views

In what subfields and how far can the naive limit $c\rightarrow\infty$ of special relativity be carried?

Even if many interesting similarities between the classical and the quantum mechanical framework have been worked out, e.g. in the subject of deformation quantization, in general, there are some ...
3
votes
3answers
487 views

Why are the classical electron radius, the Bohr radius and the Compton wavelength of an electron related to each other?

Using the definition of the fine-structure constant $\alpha = \frac{4 \pi \epsilon_0 \hbar c}{e^2}$ and the Compton wavelength of an electron $\lambda_c = \frac{h}{m_e c}$ the classical electron ...
1
vote
0answers
47 views

Eddington-Weinberg relation

The numerical coincidence that triggered Dirac to postulate his Large Number Hypothesis can be summarized by expressing the proton-electron gravitational angular momentum in units $\hbar c$: ...
4
votes
1answer
453 views

Additional merits to Wetterich's “Universe without expansion” compared to standard cosmological redshift interpretation?

A recent news item in Nature promotes Wetterich's preprint "A Universe without expansion". All sounds very exciting but hard to judge for non-experts. As I understand from the Nature's article, the ...
7
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3answers
301 views

why there is no accuracy of the measured value of $G$?

With the advancement of Modern Technology still there is no accuracy of the measured value of $G$ Gravitational Constant, why!?
1
vote
3answers
468 views

The vacuum light speed: Is it really constant, i.e., independent of location in space-time?

I am by no means an expert in this field, however something puzzles me about the speed of light and the relativity of time and space (space-time). Is is universally acknowledged that the speed of ...
7
votes
2answers
2k views

Has the speed of light changed over time?

Could someone judge my (stoner) hypothesis that the speed of light has changed over time -- ie. as the universe has expanded in volume light has slowed down, perhaps going so far as back to the big ...
5
votes
1answer
292 views

Variable speed of light in cosmology

In this paper, D. H. Coule argues that warp drive metrics, like the one proposed by Alcubierre, require the exotic matter to be laid beforehand on the travel path by conventional travel. At section 5 ...
5
votes
2answers
480 views

How can I explain the scientific basis of the constant speed of light to a $c$-decay proponent?

This Phys.SE question asks why and how the speed of light is constant. I would like to ask a related, almost converse question: Given that the speed of light is constant, how could I explain to a ...
4
votes
0answers
110 views

Physics of Anathem

Disclaimer: I am not asking whether or not the events that occur in Anathem are possible. I understand that this book is a work of speculative science fiction and this site has no interest in it as ...
9
votes
1answer
243 views

Is the fine-structure constant a parameter of the standard model?

According to the wikipedia entry on the fine-structure constant: In fact, α is one of the about 20 empirical parameters in the Standard Model of particle physics, whose value is not determined ...
1
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0answers
48 views

Contact electricity and photoelectric effect

Most universities provide an experiment about the photoelectric effect to determine $h$ by measuring the stop voltage against the light frequency and calculating the slope $h/e$. But mostly they also ...
0
votes
1answer
122 views

Why Planck scale is so important?

I know that Planck scale is the scale where both, gravity and quantum effects are relevant simultaneously. Are there more reasons?
-5
votes
1answer
101 views

Describing physical constants in alternate wording; c = there can only be 671million miles of space for every second of time [closed]

This spawns from part of an answer to a question I asked. All sorts of things go to 0 and/or ∞ if you start boosting at c, and so you cannot boost into and out of a photon's frame. It ...
0
votes
1answer
101 views

Zero uncertainty constant and a unit change

So, we know the speed of light with zero uncertainty. We also know that values of $\epsilon_0$ (electric constant) and $\mu_0$ (magnetic constant) are known with zero uncertainty. My questions are ...
0
votes
0answers
77 views

Why there can't be infinitely small existing?

Why there can't be infinitely small existing? I am not suggesting it can or cannot. I am asking can there be an absolute or reasonable answer to that question.
6
votes
2answers
259 views

What constant varies in the fine structure constant?

Using the renormalization group approach, coupling constants are "running". If we apply this to the fine structure (coupling) constant, we do know that, e.g., at energies around the Z mass, $$\alpha ...
1
vote
1answer
56 views

measure higher frequencies then half of Planck-frequency?

The maximum frequency is defined by the Planck frequency $\omega_P$. Also there is the Shannon theorem which tells us that to lossless capture a signal, you have to sample it with minimum of the ...
11
votes
5answers
2k views

How to get Planck length

I know that what Planck length equals to. The first question is, how do you get the formula $$\ell_P~=~\sqrt\frac{\hbar G}{c^3}$$ that describes the Planck length? The second question is, will any ...
7
votes
0answers
125 views

Why is the Planck length the shortest measurable length? [duplicate]

I quote from the Wikipedia article on Planck length: According to the generalized uncertainty principle, the Planck length is in principle, within a factor of order unity, the shortest ...
6
votes
1answer
314 views

Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?

I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...