# Tagged Questions

The tag has no usage guidance.

66 views

### What is the difference between a physical constant, a scalar, an invariant, and a conserved quantity?

I don't really know how to properly articulate this question. This question popped into my mind when pondering why the fact that a physical constant like the speed of light doesn't have an associated ...
59 views

727 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 ...
307 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 ...
2k views

### Is there a limit to acceleration? [duplicate]

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 ...
2k 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 ...
609 views

### Can the gravitational constant $G$ be calculated theoretically?

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

The claim is $r_p m_p = 4 L_0 M_0 = 4\hbar/c$, where $r_p$ and $m_p$ are the proton's charge radius and mass, and $L_0$ and $M_0$ are the Planck length and mass. Using the muon measurement $r_p=0.... 1answer 97 views ### When can the constant of proportionality in an eq be set equal to 1 and when not? [duplicate] In$F=kma$,$k=1$but in$F=kx$,$k$is not equal to 1?So what are the conditions for the constant of proportionality to be set 1? 0answers 54 views ### Why Newton's gravitational constant remains unchanged in relativity though gravity is not a force? I know that Einstein described gravity as a curvature of spacetime. So, It is not a "force" but why Einstein had to accept Newton's gravitational force constant? 3answers 102 views ### Are dimensionless physical constants predicted to be rational, irrational, or transcendental numbers? Are dimensionless physical constants predicted to be rational, irrational, or transcendental numbers? Directly measured ones are obviously unknown, but according to Wikipedia many dimensionless ... 1answer 280 views ### Why is the gravitational constant so difficult to measure? The gravitational constant seems to be very low precision. For example, in the Wikipedia article recent measurements are given as having the significands of 6.67 and 6.69, a difference of 2 parts in ... 2answers 60 views ### Proper units for physical quantities when$\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 ... 0answers 40 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 ... 0answers 38 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 ... 1answer 689 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$\alpha_1$. ... 1answer 174 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 ... 1answer 57 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) ... 3answers 333 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 ... 3answers 497 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 itâ€™s a value that doesnâ€™t change, but what is it? Why ... 1answer 106 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 ... 3answers 174 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 ... 0answers 85 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 ... 5answers 171 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? 1answer 69 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 ... 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 ... 3answers 69 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 ... 1answer 71 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? 0answers 35 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 ... 1answer 29 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 "... 1answer 80 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 ...