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1500 questions
63
votes
6 answers
What does antimatter look like?
I have seen simulations of antimatter on TV. Has antimatter ever been photographed?
Catzmuze
- 776
63
votes
10 answers
How did Newton discover his second law?
I've always assumed/been told that Newton's 2nd law is an empirical law — it must be discovered by experiment. If this is the case, what experiments did Newton do to discover this? Is it related to his studies of the motion of the moon and earth?…
occam98
- 899
63
votes
4 answers
Why does the sun have to be nearly fully covered to notice any darkening in an eclipse?
I was looking at eclipse footage and I noticed that it doesn't get any noticeably darker until the very end when it suddenly all the light is gone. As the moon blocks out the Sun, I would expect that the brightness would gradually decrease as less…
Giulio Crisanti
- 2,010
63
votes
4 answers
Why does moonlight have a lower color temperature?
Moonlight has a color temperature of 4100K, while sunlight has a higher color temperature of more than 5000K.
But objects illuminated by moonlight don't look yellower to the eye. They look bluer. This holds for indoor scenes (like my hall) and for…
Kartick Vaddadi
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63
votes
3 answers
Why is a second equal to the duration of exactly 9,192,631,770 periods of radiations?
Why is a second equal to the duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom?
Why is the number of periods so complicated?
It could be any…
A. Vats
- 757
63
votes
0 answers
How to apply the Faddeev-Popov method to a simple integral
Some time ago I was reviewing my knowledge on QFT and I came across the question of Faddeev-Popov ghosts. At the time I was studying thеse matters, I used the book of Faddeev and Slavnov, but the explanation there is not very transparent, specially…
Alexander Cska
- 1,210
63
votes
3 answers
Why is the Sun almost perfectly spherical?
Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest and narrow diameters would be much less than the…
user81619
63
votes
3 answers
Do solar systems typically spin in the same direction as their galaxy?
Is the net angular momentum vector of our solar system pointing in roughly the same direction as the Milky Way galaxy's net angular momentum vector? If yes or no, is that common for most stars in the galaxy?
Alex
- 5,973
63
votes
4 answers
Why can't energy be created or destroyed?
My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or false? I apologize for the elementary question, but…
Dustin L.
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63
votes
5 answers
How wrong are the classical Maxwell's equations (as compared to QED)?
Now, I don't really mean to say that Maxwell's equations are wrong. I know Maxwell's equations are very accurate when it comes to predicting physical phenomena, but going through high school and now in college, Maxwell's equations are seen as the…
user28375028
- 905
63
votes
6 answers
What enables protons to give new properties to an atom every time one is added?
How does adding one more particle to the nucleus of an atom give that atom new properties? I can see how it changes it's mass, that's obvious... But how does it give that new atom different properties like color?
A good example would be: start with…
Investor
- 1,093
63
votes
3 answers
Why do the big nuts always remain at top? The Brazil-nut Effect
Most of the time when I mixed different nuts in a bowl, I observed that the big Brazil nuts were always on top while the small peanuts settled near the base. No matter how you take it, if the big nuts are put at the bottom and then the small nuts…
user36790
63
votes
15 answers
Why does dust stick to rotating fan propeller?
Why does dust stick to rotating fan propeller?
Intuitively, most people (including I) think of the dust will not stick to rotating fan propellers.
Display Name
- 2,699
63
votes
6 answers
How exactly does gravity work?
The electromagnetic force and strong and weak forces require particles like photons and gluons. But in case of gravity there is no such particle found.
Every mass bearing object creates a gravitational field around it, and whenever another mass…
Normie
- 1,456
62
votes
7 answers
Fourier transform of the Coulomb potential
When trying to find the Fourier transform of the Coulomb potential
$$V(\mathbf{r})=-\frac{e^2}{r}$$
one is faced with the problem that the resulting integral is divergent. Usually, it is then argued to introduce a screening factor $e^{-\mu r}$ and…
Emerson
- 1,277