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-8
votes
0answers
54 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 ...
0
votes
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 ...
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
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) ...
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 ...
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 ...
2
votes
3answers
347 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
votes
3answers
152 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 ...
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
votes
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 ...
-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 ...
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
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 ...
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 ...
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 ...
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') ...
1
vote
5answers
151 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?
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, $$ ...
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 ...
-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 ...
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 ...
1
vote
2answers
124 views

Why is the speed of light a limit? and why is it just $3×10^8\,\text{m/s}$? [duplicate]

Why does light travel with speed $3×10^8\,\text{m/s}$? and why not more?
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 ...
0
votes
2answers
38 views

What are the roles of physical constants in a relation expression?

To describe the properties of a system for which we have designed mathematical symbols and in relating these properties in an expression, we often introduce some proportionality constant. What is the ...
0
votes
0answers
38 views

Speed of light in vacuum - definition and Constancy [duplicate]

This question has been nagging me for sometimes now, and even after studying all those relativity still cannot find an appreciable answer. The speed of light is $c$ defined and measured as constant ...
0
votes
1answer
83 views

Gravity Relative to Mass?

Why is it that, in basic physics, it is taught that the acceleration of gravity is the same for objects of any mass (at a constant distance from earth)? Why then is the acceleration of gravity ...
-1
votes
2answers
849 views

Dimensional or dimensionless constant

While deriving new equations , how do theoretical physicists know whether the proportionality constant in their equation will be dimensional or dimensionless? I mean, say for example, we consider ...
-2
votes
1answer
67 views

What does the kilogram-hertz relationship stand for?

The value of the kilogram-hertz relationship [$(1kg)c^2/h]$ physics constant is 1.356 392 608 $\times 10^{50}\,\mathrm{Hz}$. What does this constant stand for?
3
votes
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 ...
3
votes
1answer
98 views

Would a Theory of Everything allow us to calculate the constants of physics?

I have heard several times in the past that a Theory of Everything would allow us to calculate (as opposed to measure) the fundamental dimensionless physical constants. What I mean is, e.g., the fine ...
-1
votes
2answers
108 views

Can anyone tell me the name of this constant?

I was watching a TV program about cosmology (I can't remember which or how old it was). In it, it mentioned a fundamental number (which I'm assuming is a constant, but that's not necessarily true). ...
-3
votes
3answers
185 views

Given the Newton constant $G$, the speed of light $c$ and the Planck constant $h$, construct an energy of the system [closed]

How do I use dimensional analysis to construct an energy for the system given the Newton constant $G$, the speed of light $c$ and the Planck constant $h$? I don't know of any energy formulas ...
0
votes
0answers
37 views

What are some ways to measure variations in the speed of light in vacuum?

To avoid confusion, I am not talking about measuring differences in the speed of light in vacuum as a result of a particular Lorentz boost. What I mean is, suppose the "constant speed of light" were ...
-2
votes
2answers
458 views

Why is the speed of light limited to (only) 299.792.458 m/s? [closed]

The speed of light (in a vacuum) is limited to 299.792.458 m/s. This sounds very fast, and it is on a global scale. But if you look at the Universe on a larger scale than it sounds quite slow, For ...
2
votes
3answers
110 views

Does the accelerated rate of expansion of the Universe have any effect on the speed of light in vacuum?

So I was just wondering about this as I finished reading about Michelson-Morley's experiment which disproved the ether theory. My question is since the Universe is constantly expanding and that too ...
2
votes
1answer
63 views

Do we regularly measure and update our physical constants (By using the LHC)?

This question is motivated by sheer curiosity. I certainly do not expect that the free parameters we use in the standard model have changed in value since we started measuring them with a "modern" ...
1
vote
1answer
187 views

Question about Planck's constant

How did Dirac or whoever came up with it know that the momentum operator in quantum mechanics is $-i\hbar\frac{d}{dx}$? How did he know the $\hbar$ was in there? How did all these physicists know ...
5
votes
3answers
216 views

Is the speed of light in vacuum constant or does the math just happen to work out?

My apologies if my question is really idiotic, but I ask sincerely because I want to learn. Based on this question and lots of other places on the web, this topic seems to be really confusing. Let's ...