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50
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5answers
9k views

Dimensionless Constants in Physics

Forgive me if this topic is too much in the realm of philosophy. John Baez has an interesting perspective on the relative importance of dimensionless constants, which he calls fundamental like alpha, ...
43
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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 ...
43
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8answers
9k views

Why does the speed of light in vacuum have no uncertainty?

I could understand that the definition of a second wouldn't have an uncertainty when related to the transition of the Cs atom, so it doesn't have an error because it's an absolute reference and we ...
39
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3answers
9k views

Is the Planck length the smallest length that exists in the universe or is it the smallest length that can be observed?

I have heard both that Planck length is the smallest length that there is in the universe (whatever this means) and that it is the smallest thing that can be observed because if we wanted to observe ...
35
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10answers
22k views

Why and how is the speed of light in vacuum constant, i.e., independent of reference frame?

I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them. How and why ...
29
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6answers
4k views

Does the speed of light in vacuum define the universal speed limit?

Is light the thing causing the universal speed limit to be $299\,792\,458\,\mathrm{m/s}$? So the universal speed limit would be different if light travelled faster or slower? Or, is $299\,792\,458\,\...
23
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4answers
5k 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 ...
21
votes
8answers
3k views

What is the proof that the universal constants ($G$, $\hbar$, $\ldots$) are really constant in time and space?

Cavendish measured the gravitation constant $G$, but actually he measured that constant on the Earth. What’s the proof that the value of the gravitation constant if measured on Neptune would remain ...
20
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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 ...
19
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6answers
4k views

How can the speed of light be a dimensionless constant?

This is a quote from the book A first course in general relativity by Schutz: What we shall now do is adopt a new unit for time, the meter. One meter of time is the time it takes light to travel ...
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 ...
16
votes
4answers
859 views

Why isn't it $E \approx 27.642 \times mc^2$?

Sorry for the strange question, but why is it that many of the most important physical equations don't have ugly numbers (i.e., "arbitrary" irrational factors) to line up both sides? Why can so many ...
16
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7answers
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 ...
15
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5answers
621 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 light,...
15
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4answers
2k views

Is the Avogadro's constant equal to one?

Question: Is the Avogadro's constant equal to one? I was tasked with creating a presentation on Avogadro's work, and this is the first time I actually got introduced to the ...
14
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5answers
4k views

Is speed of light and sound rational or irrational in nature?

Just as circumference of circle will remain $\pi$ for unit diameter, no matter what standard unit we take, are the speeds of light and sound irrational or rational in nature ? I'm talking about ...
12
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4answers
2k views

What's keeping us from simply redefining Avogadro's Number / the Mole as a definite integer?

This might be a question to ask in a Chemistry site, but because there is a lot of talk about redefining many units of measurements in terms of Avogadro's Number / the Mole, I was wondering why we don'...
12
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3answers
2k views

Why do universal constants have the values they do?

This is meant to be a generic question of the type that we get repeatedly on this site, in different versions: The origin of the value of speed of light The gravitational constant G theoretically? ...
11
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4answers
534 views

Is the Fine Stucture constant constant?

I have read that the fine structure constant may well not be a constant. Now, if this were to be true, what would be the effect of a higher or lower value? (and why?)
11
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1answer
670 views

Is the fine-structure constant a parameter of the standard model?

According to the wikipedia entry on the fine-structure constant: In fact, α is one of the about 20 empirical parameters in the Standard Model of particle physics, whose value is not determined ...
10
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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 ...
10
votes
2answers
3k views

Has the speed of light changed over time?

Could someone judge my (stoner) hypothesis that the speed of light has changed over time -- ie. as the universe has expanded in volume light has slowed down, perhaps going so far as back to the big ...
10
votes
3answers
327 views

Is it possible to speak about changes in a physical constant which is not dimensionless?

Every so often, one sees on this site* or in the news† or in journal articles‡ a statement of the form "we have measured a change in such-and-such fundamental constant" (or, perhaps more commonly, "we ...
10
votes
1answer
2k views

Gravitational constant in higher dimensions?

From Newton's law of gravitation we know that $$F=G\frac{m_1m_2}{r^2}$$ where $G$ is gravitational constant. We can also see that it has dimensions $$[G]=\frac{[L]^3}{[M][T]^2}$$ and we have a ...
9
votes
5answers
2k views

Is the speed of light in vacuum always the same value?

The escape velocity of different planets and stars vary. If they vary, the velocities of bodies escaping from the respective stars or planets should also vary. Like, if I want a ball to reach 10 ...
9
votes
1answer
749 views

Gravitational Constant in Newtonian Gravity vs. General Relativity

From my understanding, the gravitational constant $G$ is a proportionality constant used by Newton in his law of universal gravitation (which was based around Kepler's Laws), namely in the equation $F ...
9
votes
2answers
635 views

What constant varies in the fine structure constant?

Using the renormalization group approach, coupling constants are "running". If we apply this to the fine structure (coupling) constant, we do know that, e.g., at energies around the Z mass, $$\alpha \...
8
votes
4answers
2k views

Can Planck's constant be derived from Maxwell's equations?

Can mathematics (including statistics, dynamical systems,...) combined with classical electromagnetism (using only the constants appearing in chargefree Maxwell equations) be used to derive the Planck ...
8
votes
4answers
1k views

Can the accuracy in Planck's constant ever be increased?

I guess I am having some confusion about the history of calculating Planck's constant. I see the mass of the electron may come into the equation here but isn't the measurement of mass based mostly ...
8
votes
3answers
408 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 ...
8
votes
5answers
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 ...
7
votes
1answer
914 views

Why can you remove the gravitational constant from a computer game simulation?

I've seen in a few gravity simulation games (ie. bouncing balls) the equation: force = G * m1 * m2 / distance^2 shortened to this by removing the gravitational ...
7
votes
4answers
448 views

Cases of any known fundamental physical constants changing within our locality?

Has there been any cases where the only explanation has been that at least one of the physical constants must have changed to explain an experiment/event/obervation? I am not intrested in large scale ...
7
votes
3answers
330 views

Can someone explain Planck's constant simply? [closed]

Can someone explain Planck's constant simply? I know the math, however I don't understand the relevance. To explain what I'm asking, what is the significance of it when doing quantum mechanical ...
7
votes
3answers
356 views

why there is no accuracy of the measured value of $G$?

With the advancement of Modern Technology still there is no accuracy of the measured value of $G$ Gravitational Constant, why!?
7
votes
3answers
101 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 ...
7
votes
0answers
222 views

Why is the Planck length the shortest measurable length? [duplicate]

I quote from the Wikipedia article on Planck length: According to the generalized uncertainty principle, the Planck length is in principle, within a factor of order unity, the shortest ...
6
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3answers
3k views

Have I discovered how to calculate the proton's mass using only integers?

Could it be possible that the mass of the proton can be calculated by a series of integer sequences? Or is this just a curiosity? $$\sum_{m=1}^{\infty } \frac{1}{10^{26}(m^2+1)_{2m}}=$$ ...
6
votes
7answers
13k views

Do we take gravity = 9.8 m/s² for all heights when solving problems? Why or why not?

Do we take gravity = 9.8 m/s² for all heights when solving problems?
6
votes
4answers
608 views

Can the gravitational constant $G$ be calculated theoretically?

We know all that the gravitational constant is $$G=6.67428±0.00067\times 10^{-11}\mathrm{m^{3} \:kg^{-1} s^{-2}}.$$ But can we calculate it theoretically?
6
votes
1answer
505 views

Deriving or justifying fundamental constants

Is there a fundamental way to look at the universal constants ? can their orders of magnitude be explained from a general points of view like stability, causality, information theory, uncertainty? ...
6
votes
1answer
279 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 ...
6
votes
3answers
372 views

Is there a simple way to compute some physical constant from Feynman diagram statistics?

I've been playing around writing some software to generate Feynman diagrams for QED, respecting the vertex "rules" described here, and avoiding creating isomorphic duplicates. So from a starter ...
6
votes
1answer
248 views

From which dimensionful constants does proton mass arise?

It is well known that the most of the proton (or any other hadron with light quarks) mass is not made up from quark masses, but it is dynamically generated by QCD mess inside. I've also heard that, ...
6
votes
1answer
169 views

Is $4 \pi G$ the true most fundamental gravitational constant? [closed]

Newton's law of gravitation is: $$F = G m_1 m_2 \frac{1}{r^2}$$ It looks simple and natural. But that's only in 3 dimensions. Let's look what happens in $n$ dimensions: $$n=2 : F = 2 G m_1 m_2 \...
6
votes
1answer
790 views

Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?

I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...
6
votes
3answers
197 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 ...
5
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2answers
899 views

How can I explain the scientific basis of the constant speed of light to a $c$-decay proponent?

This Phys.SE question asks why and how the speed of light is constant. I would like to ask a related, almost converse question: Given that the speed of light is constant, how could I explain to a ...
5
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3answers
239 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 ...
5
votes
1answer
636 views

How is “little $h$” measured in cosmology? The dimensionless parameter from the Hubble constant, $H_0$

Hubble's law has been well-know for close to a century now. It is written as $v = H_0 d$ where the Hubble constant $H_0$ is the constant of proportionality between recession speed $v$ and distance $...