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Questions tagged [physical-constants]

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What is the role of $\hbar$ in quantum mechanics? [duplicate]

Planck's constant $\hbar$ appears in the Schrodinger equation: $$i\hbar \frac{d|\psi\rangle}{dt}\ = \hat{H}|\psi\rangle$$ which implies for stationary states, $$|\psi(x,t)\rangle=e^{-iE_n/\hbar}|\...
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98 views

What's going on with the Hubble constant?

I'm doing a small project on LIGO for a third-year project at University. I want to write something about how LIGO can be used to measure $H_0$, which would be useful because the current state of the ...
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1answer
55 views

Are constants derived or calculated?

I am currently writing up a lab report on the determination of Planck's constant using x-ray diffraction and atomic spectra. In my introduction, I am talking about the history of Planck's constant, ...
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How many combinations of physical constants would allow a sustainable/similar universe? [closed]

If physical constants like the gravitational constant, the speed of light, charge/mass/spin of an electron, etc, were to be different, how different could they be while still producing a universe ...
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1answer
65 views

What would the effects be on the world if light slowed down? [duplicate]

It would be really helpful if the effects were just given in a list form so I can research them. The reason why I am asking this is because I to write an essay regarding the effects of a change in a ...
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1answer
114 views

How to derive $c=1/\sqrt{\varepsilon_0\,\mu_0}$ from integral form of Maxwell equations? [closed]

I've read similar questions and answers given thereto but find them unsatisfactory. So please don't mark my question as "duplicate". The question may as well be a duplicate, but it's still waiting for ...
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2answers
119 views

A theoretical limit of accuracy?

Is there an agreed upon/conjectured theoretical limit to our ability to resolve the accuracy of time?
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40 views

Faradays constant determination? [closed]

I am a bit confused on how faraday determined his constant. So I’ve been taught that he realized that if you sent a certain amount of charge (96485 C), then one mole (or some fraction of that based on ...
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1answer
72 views

How do fundamental constants determine the size of material bodies? [duplicate]

The size of an object depends on the size of the molecules and atoms it is made of and these ultimately depend on the value of the fundamental physical constants. The simplest example could be the ...
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1answer
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About the fine structure constant value

In the PARTICLE PHYSICS BOOKLET, Extracted from the Review of Particle Physics, we read that the fine structure constant has a value $\alpha \approx 1/137$ at $Q^2=0$ and $\alpha\approx 1/128$ at $Q^...
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1answer
43 views

How to deal with constants on computer simulations? [closed]

I'm beggining learning about natural simulations on my courses and I had a few questions about time, and especially with the game "Universe Sandox²". I know about the basic Newton's formulas about ...
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4answers
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Is the fine-structure constant related to the size of the observable universe?

The fine-structure constant $\alpha \approx 1/137$. In Planck units, this is also the charge of the electron squared, $e^2 = \alpha$ ($e \approx 0.085$). In Planck units the size of the observable ...
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After the redefinition of the units of fundamental physical quantities in 2019, will an uncertainty incur in the Universal constants values?

I am specifically interested in the following constants because being a student these are some of the most common constants that I face: $R$ (universal gas constant) Stefan constant Permeability of ...
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3answers
85 views

Newtonian gravity equation / Big $G$; not duplicate from search results

EDIT: I apparently need to rewrite this from the RE's, but I'll leave it for continuity sake. Please read my replies for my point/question clarifications. There are several threads regarding big G ...
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1answer
52 views

Van der Waals constant $b$ (real gas) chemical form. only

http://www2.ucdsb.on.ca/tiss/stretton/database/van_der_waals_constants.html I don't understand how to calculate exact constant - b, given only the chemical formula and nothing else. Q: T || F --- ...
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2answers
66 views

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 ...
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1answer
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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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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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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
59 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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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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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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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
124 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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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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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
131 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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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
519 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
46 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
74 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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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
56 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
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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
215 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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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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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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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
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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
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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
273 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
487 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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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
110 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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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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241 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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370 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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683 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 ...