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Results tagged with physical-constants
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This tag is for questions relating to physical constants which are any of a set of fundamental invariant quantities observed in nature and appearing in the basic theoretical equations of physics. Accurate evaluation of these constants is essential in order to check the correctness of the theories and to allow useful applications to be made on the basis of those theories.
4
votes
Accepted
Why different versions of the Schwarzschild metric online?
The Schwarzschild radius is $$R= \frac{2GM}{c^2}$$ where $M$ describes the specific black hole we are analyzing and $G$ and $c$ are universal constants.
All of them are dimensionful units, so their va …
- 109k
7
votes
Accepted
Relation between Coulomb's law and Fine-structure constant
We can rearrange the definition of the fine structure constant $$\alpha = \frac{e^2}{4\pi \epsilon_0 \hbar c}$$ to get $$\alpha \frac{4\pi \epsilon_0 \hbar c}{e^2}=1$$ Then we can multiply Coulomb’s l …
- 109k
0
votes
What was defined first and how? The ampere or the vacuum permeability?
Although the historical part of this question does belong on the history of science and mathematics site, there is also a portion of this question that is a question of physics. Specifically, there is …
- 109k
4
votes
What exactly does Einstein's gravitational constant $8\pi G/c^4$ mean?
It is just a conversion factor between stress-energy and curvature in SI units. Usually when doing General Relativity we prefer to use natural units where it is equal to 1. SI units are just not very …
- 109k
1
vote
Are there any significant integer constants that are not unitless?
Are there any significant integer constants that are not unitless?
Values that are not unitless are called “dimensionful”.
Unfortunately, this question is not meaningful. The numerical value of any …
- 109k
8
votes
What physics laws justify Planck's units?
We have, at yet, no specific evidence that any of our current laws of physics collapse at the Planck scale. However, we do expect that at or near the Planck scale quantum gravitational effects will be …
- 109k
1
vote
How does the constant proportionality balance an equation?
1)How do we define a certain value to the proportionality constant?
This is done experimentally. We take many different objects at different sizes and distances and we measure the gravitational forc …
- 109k
4
votes
Is there a explanation to why bodies with higher heat capacity transfer heat to bodies with ...
It is not generally true that heat is transferred from $M_1$ to $M_2$. Suppose, for a counter-example, that both bodies are made of water so $c_1=c_2$ and suppose further that $m_1=2 \text{ kg}$ and $ …
- 109k
3
votes
What is the physical meaning and origin of the gravitational constant $G$?
Is G just a value to fix the units in the equation? Something like a proportionality constant or a coupling constant?
As you say, it is just a value to fix the units in the equation. There is no phy …
- 109k
0
votes
Can the Planck length be altered by relativistic motion?
In standard relativity the Planck length is just another unit. It contracts just as the meter and the mile do.
Perhaps a future theory of quantum gravity will say something different.
- 109k
1
vote
If all fundamental constants changed proportionally would we know?
It is not possible for all constants to change proportionally, due to the various relationships between constants. A good example is the fine structure constant which can be written as: $$\alpha =\fra …
- 109k
2
votes
Using $ct$ axis instead of $t$ axis in special relativity
how can I intuitively think of time in meters or any unit of length
A meter of time is the amount of time that it takes light to travel 1 meter. A foot of time is the amount of time that it takes li …
- 109k
2
votes
What is the exact definition of the Universal Gas Constant $R$? One that gives the reason fo...
The ideal gas constant is not a physical quantity, it is an artifact of your choice of units. In SI units its value is exactly: $R = 8.31446261815324 \text{ J/(K⋅mol)}$. The fact that the value is exa …
- 109k
4
votes
Why can we set $c$ and $\hbar$ to 1 when it changes the result?
If you ask two doctors how much you weigh and one doctor says “you weigh $100\text{ kg}$” and the other doctor says “you weigh $220\text{ lbs}$”, would you claim that they have given you completely di …
- 109k
27
votes
What's exactly the new definition of kilogram, second and meter?
The SI system is now defined entirely by physical constants. There are no more “prototype” artifacts. How it works is thus:
https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-concise-EN.p …
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