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0
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2answers
57 views

Proper units for physical quantities when $\hbar$=$1$

How to deal with the units of quantities if $\hbar=\tfrac{h}{2\pi}=1$? For example, the energy $E=\hbar\omega$: If I have chosen $\hbar=1$, how do I use the units to properly differentiate between ...
-8
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0answers
50 views

Meaning of constant $c$ [on hold]

I have a puzzlement over Einstein's expression $E = mc^2$. The constant expressed as $c$ is the measured speed at which Light crosses a vacuuum. BUT it is also used to denote the maximum possible ...
1
vote
0answers
30 views

Are there characteristics that distinguish our universe?

Are there any defining characteristics of our universe that could be different for other universes (or "instances of our universe") that operate under the same laws of physics? And which, if any, are ...
1
vote
0answers
29 views

Any method to determine the gravitational constant $G$ from observations in cosmological scale?

By the observations in cosmological scale, I mean observations by astrophysicists like motions of quasars in far distance from us, relative motions of our galaxy to others, etc. I know the famous ...
3
votes
1answer
655 views

What is the most natural definition of the weak hypercharge coupling constant if grand unification is wrong?

A tricky question. Here is the famous graph of the running of the three coupling constants in the standard model: The graph shows, in its top curve, the running of the coupling constant $\alpha_1$. ...
4
votes
5answers
518 views

What is the significance of Planck force?

I have been curious to find what could be the significance of Planck force? It is calculated by the formula $c^4/G = 1.21031359\times 10^{44} \, \mathrm{N}$, where $c$ is the speed of light and $G$ is ...
1
vote
1answer
125 views

Difference between theoretical equations and empirical equations

Some equations are theoretical in the sense that they are derived from an underlying theory. Other equations are empirical in the sense that they were selected only because they fit experimental data ...
3
votes
1answer
41 views

How is a result of no time variation in the gravitational constant $G$ related to a measurement of no local expansion?

In this answer @PhillS linked to the paper Progress in Lunar Laser Ranging Tests of Relativistic Gravity which has given me a great start. While its main focus is on the Equivalence Principle (EP) ...
6
votes
2answers
66 views

Are dimensionless physical constants predicted to be rational, irrational, or transcendental numbers?

Are dimensionless physical constants predicted to be rational, irrational, or transcendental numbers? Directly measured ones are obviously unknown, but according to Wikipedia many dimensionless ...
3
votes
3answers
277 views

Physical Significance of the Planck Density

The Planck density is the Planck mass devided by the Planck volume, approximately 1093 g/cm3. Does this quantity have any known physical relevance? The Planck mass is believed to be the smallest ...
2
votes
3answers
346 views

Why do we need constants? [closed]

This question is driving me crazy because I cannot find a straightforward answer. I want to know what a physical constant exactly is. I know that it’s a value that doesn’t change, but what is it? Why ...
5
votes
1answer
92 views

Proportionality Constant in Einstein Field Equations

The Einstein Field Equations: $$G_{ab}~=~8\pi T_{ab}.$$ I am familiar with how to obtain the $8\pi$ proportionality factor through correspondence with Newtonian gravity, but am wondering if this ...
0
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3answers
151 views

Why did Einstein took speed of light unit or constant in his equation of relativity?

We can find that no object can have speed more than light from Einstein's equation of relativity because if anything have speed more than light then we get -ve value within square root. But why did ...
3
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0answers
74 views

Experiment measuring vacuum permittivity and permeability in high speed

Suppose that we do NOT know anything of constancy of speed of light, to say nothing of special relativity. It is that we acquired a constant speed of light from Maxwell's Equations that we finally ...
1
vote
5answers
150 views

What in nature causes Newton's gravitation constant to have its given value?

Does the value of Newton's universal gravitational constant $G$ remain a mystery? Why does it have the value that it has?
1
vote
1answer
63 views

About Planck tension in strings theory as stated in “The Elegant Universe”

In the book "The Elegant Universe" by Brian B. Greene, on chapter 6 it is stated that there's the so called "Planck tension" in string theory, and it is given a value of $10^{39}$ tons. This value is ...
2
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0answers
26 views

Do time/location-dependent fundamental constant exists? [closed]

Throughout history people have been carrying out experiment after experiment to test many of the known constant, so I like to know if there are any oddities among the known fundamental constants. If ...
0
votes
3answers
67 views

What does the $k_e$ in Coulomb's law and $G$ in Newton's Universal Gravitation Law mean?

I very well understand the proportionality relation that was used to derive these laws like $F$ is proportional to product of masses and inversely to radius squared and hence its proportional to the ...
-1
votes
1answer
51 views

Which was the first Coulomb's constant value? [closed]

Which was the first Coulomb's constant value? I didn't found any info in the Internet. I need the first value of K to compare it with my experiment. Could you please help me?
1
vote
0answers
31 views

Where does the square root of two in the conversion between the Fermi constant and the weak coupling constant come from?

As in the title, where does the square root of two in the conversion $$ G_{F}=\frac{\sqrt{2}g^{2}}{8m_{W}^{2}} $$ between the Fermi constant and the weak coupling constant come from? I was able to ...
1
vote
1answer
25 views

How are the constants in hydraulics calculated? [closed]

I would like to know (out of sheer morbid curiosity) how constants in hydraulics are calculated. The constants are, for good ol' 'Merican units; 63025, 5252,and 231. These constants came out of ...
1
vote
1answer
76 views

Can the value of $c$ be calculated from Relativity? [duplicate]

I have three related questions about what theories or equations can calculate and what is an input parameter/constant to the theories. This question is not about parameter units (as another similar ...
4
votes
3answers
123 views

String models of particle physics

What general features of particle physics are derived/replicated by constructing string models of particle models? How do such models address the fixing of free parameters like the masses and the ...
3
votes
2answers
71 views

Does the speed of light change? [duplicate]

I know that there is a similar questions, but I think mine is a bit different. I wonder if with the expansion of the universe the speed of light changes. It seems that the speed of light is very ...
2
votes
2answers
94 views

Why is the speed of light exactly $299,792.458$ m/s and not faster or slower? [duplicate]

Why is the speed of light $299,792,458$ metres per second, and not faster or slower. Why not $500$ trillion kilometers per second or $120$ miles per hour? This has been 'bothering' me for a while. ...
2
votes
1answer
50 views

Why are physical “constants” constant?

I am really sorry if this question is inappropriate or wrong. But this is something that I can never perfectly agree with, it just keeps on striking my mind when I am studying something new in ...
15
votes
5answers
519 views

Is the Boltzmann constant really that important?

I read a book in which one chapter gave a speech about the fundamental constants of the Universe, and I remember it stated this: If the mass of an electron, the Planck constant, the speed of ...
-2
votes
1answer
73 views

Constancy of speed of light in vacuum? [closed]

Have scientists tried their best to calculate speed of light in vacuum? It seems very absurd to me that light of all frequencies have same velocity in space. Can someone find in future if this speed ...
0
votes
2answers
1k 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 ...
1
vote
0answers
50 views

What's the unit of fine-structure constant? [closed]

What's the unit of fine-structure constant? I mean in SI units.
2
votes
0answers
43 views

Can we alter/engineer natural “constants”? [closed]

There are numerous constants that define the physical universe, from the fine structure constant to Planck to the speed of light etc. Can any of these be altered locally? For example, it seems that ...
1
vote
2answers
124 views

Is there an equivalent of the Planck length for time?

Is there an equivalent of the Planck length for time? I'd just like a term I may use (high-level) for a similar "unit of time"? I am not looking for a debate on how discrete time might be, but if ...
1
vote
2answers
280 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 ...
6
votes
3answers
189 views

Can all laws of physics derived by a single or lists of more general laws?

(This is actually my first question - please understand my lack of knowledge and bad English..) I have always been curious about deriving thousands of laws from more general ones.. Can general laws ...
1
vote
1answer
74 views

if there is Ideal Gas constant, then do we have real gas constant?

We have Ideal gas constant for ideal gases. But ideal gas is very hard to make or to be found. So we have real gases in nature. Now there is 'real gas equation' (also called 'Van Der Waal's equation') ...
20
votes
5answers
7k 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 ...
1
vote
3answers
314 views

Why do we obtain classical physics by taking the limit of Planck's constant to zero?

Why if we specifically set Planck's constant equal to zero (the limit of it) do we sometimes get classical physics? I mean, what does it mean physically to set the constant equal to zero? Or to say it ...
22
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4answers
4k views

What is so special about speed of light in vacuum?

I will try to be as explanatory as possible with my question. Please also note that I have done my share of googling and I am looking for simple language preferable with some example so that I can get ...
-3
votes
1answer
212 views

Gravitational constant, $G$, What if it is not Constant?

The question is on title; What if Gravitational Constant, $G$, is not constant? Let's skip all the local consequences if it would suddenly change, like asked here; Can gravitational constant be ...
0
votes
0answers
74 views

Does rest mass increase in the FRW metric?

The flat FRW metric can be written in conformal co-ordinates: $$ds^2=a^2(\eta)(d\eta^2-dx^2-dy^2-dz^2)$$ where $\eta$ is conformal time. Let us assume that $a(\eta_0)=1$ when $\eta_0$ is the present ...
2
votes
1answer
336 views

Is there a relationship between the Cosmological constant and the Hubble constant?

I looked around to see if this precise question was asked before and it appears not to be. So is it just me or has anyone else noticed that, no matter what consistent set of units you use, $$ ...
0
votes
4answers
180 views

Why is the speed of light in vacuum what it is?

Three-pronged question on the speed of light. One: simply, do we know why the speed of light in a vacuum is what it is and why nothing is allowed to go faster? Two: if we knew why the speed of ...
8
votes
3answers
403 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 ...
44
votes
3answers
6k views

Why should the Planck constant be a constant throughout all space?

Our value for the Planck constant $h$ can be found on experiments on Earth, but how do we know that the Planck constant doesn't change throughout space, for instance it depends weakly upon the ...
3
votes
5answers
747 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 ...
4
votes
4answers
1k 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 ...
17
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7answers
6k views

Why does the speed of light $c$ have the value it does? [duplicate]

Why does light have the speed it does? why is it not considerably faster or slower than it is? I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed ...
2
votes
2answers
1k 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 ...
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17answers
3k views

The origin of the value of speed of light in vacuum

Meaning, why is it the exact number that it is? Why not 2x10^8 m/s instead of 3? Does it have something to do with the mass, size or behavior of a photon? To be clear, I'm not asking "how we ...