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Questions tagged [physical-constants]

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Planck's Constant to the Kibble Balance

A tad confused on how the Kibble balance actually relates to the Planck Constant. There's most likely a very simple relationship that I'm missing (I feel this is a stupid question ..) If the Kibble ...
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On existence of other physical constants and the assumption in proof for special theory of relativity? [closed]

The only constant (that exist in the world) is speed of light in vacuum or c which is close to 3X10^8 m/s so 'all other constants should be variables (to some degree) w.r.t. this constant'. If this is ...
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Are all lengths multiples of the Planck length? [duplicate]

If the Planck length is the smallest unit of length that has any physical meaning then is it true to think that all the lengths are multiple of the Planck length?
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What is a free parameter?

Soft question here, but I was wondering just what exactly free parameters are? I have a murky understanding on the concept but I would much appreciate someone shedding some light on the matter. Is ...
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How I can get the numerical factor in the relation between string coupling and YM coupling?

I'm trying to understand some references about Wilson loops being used to test AdS/CFT. Some of them are Nadav Drukker, David J. Gross: An Exact Prediction of N=4 SUSYM Theory for String Theory ...
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Is it a coincidence that the maximum number of protons in a stable nucleus is on the order of $\alpha_s / \alpha_{EM}$?

The equivalent to the fine-structure constant for the strong interaction is about $\alpha_s \approx 0.5$ at the proton rest mass energy (and it runs pretty slowly with energy, so it's on this order ...
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Changes to Planck constant historically [closed]

I looked all over to get the various accepted value of the Planck constant since 1900. But there is never any record about the history of this mysterious number.
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${}$Can the gravitational constant $G$ be calculated theoretically? [duplicate]

In an answer to a previous post of the same question, it was stated that the gravitational constant can not be determined theoretically yet! From my perspective, the reason this is not yet possible ...
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Can a sequence associated with a physical constant lead to natural laws?

I wondered if we know the universal constants (e.g. gravitational constant, etc.) with high enough precision, and try to find a sequence of which it is part of, or a sequence that converges to it, ...
50 views

Physical quantity of energy and it's dimension in the article

I am reading an article about Permutation glass by Mobolaji Williams and not sure about the unit (value/dimension) of energy on Fig.3. If $k_BT_c$ is measured in Joules, then I am not totally sure ...
83 views

Can anyone explain the Planck area?

First of all, I am not an expert. I was reading about the holographic principle and came across the Planck area. It says that Planck area is the square of Planck length and there were some pictures ...
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Is there a way to test whether dimensionless physical constants are rational?

This question is related to a question asked 3 years ago on SE (I was not the OP), but not quite the same. I would like to know if there is a way to test whether a dimensionless physical constant is ...
78 views

If light speed determines the rate of time, could the speed of light be varying over time and we be unaware of it?

Is this a valid implication/alternative explanation of universal red-shift? I thought I'd ask this when I read this question about light clocks. I had speculated this way: If light speed determines ...
105 views

Numerical coincidence with constants

Is there a reason why $$\dfrac{h}{ec}\sim 1.38\cdot 10^{-23} V/(m\cdot s^{-2})$$ ? Dimensionally, the Unruh effect temperature reads $$T_U=\dfrac{\hbar a}{2\pi k_B c}$$ from which the ...
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When using Planck's constant, how do I know when to use electron volts or joules?

Planck's constant may be written as 6.63 x 10^-34 Js or 4.14 x 10^-15 eVs right? But how do I choose which one I should use to figure out an answer to a question?
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Are there known expressions for the running of $\alpha_{em}(Q^2)$ and $\sin^2(\theta_{W})$?

I'm doing some integrations in Hadron physics, involving form factors and the like, and these terms show up often. I can get okay results if I use the values these couplings take at $Q^2=0$, but a ...
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Undoing problems caused by setting $c = 1$ { or “Undoing $c = 1$” }

In the mathematical derivation of equations for physics, and involving wave propagation in particular, the propagation speed at the start of the derivation is often set to one (c = 1). I am working ...
92 views

Does $G$ effectively change in an expanding metric?

Assume that we have a flat FRW metric expressed in conformal time $\eta$ so that the line element is $$ds^2=a^2(\eta)(d\eta^2-dx^2-dy^2-dz^2)\tag{1}$$ where $a=1$ at the present time $\eta=0$ and the ...
79 views

Is the value for the speed of light in vacuum irrelevant? [duplicate]

Does it matter that the speed of light, $c$, is 299,792,458 meters per second in a vacuum? Would the universe be different if $c$ were, for example, 1 meter per second? Or should things be the same, ...
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Fine Tuning of the Universe

I'm an A level student looking into the fine tuning of various constants. Physicists explain the extensive effects that would happen if these constants were to be changed/different and hence, how this ...
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}|\...
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 ...