Most Popular
1500 questions
85
votes
4 answers
Why treat complex scalar field and its complex conjugate as two different fields?
I am new to QFT, so I may have some of the terminology incorrect.
Many QFT books provide an example of deriving equations of motion for various free theories. One example is for a complex scalar field:
$$\mathcal{L}_\text{compl…
BMS
- 11,733
85
votes
8 answers
Why does fire make very little sound?
Sound is air particles vibrating (thus hitting each other to make longitudinal waves) and heat is the vibration of air molecules. Because we can only assume that heat made from fire is a higher intensity of vibration than sound (because we don't…
yolo
- 2,724
85
votes
6 answers
If a mass moves close to the speed of light, does it turn into a black hole?
I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever since.
From the show transcript:
Arunus Gidgowdusk…
shopsinc
- 977
85
votes
4 answers
If you are vacuuming your carpet and you wrap the cord around your body do you become a magnet?
If you wrap an active electric cord around your body, do you become an electromagnet?
Shawn Anderson
- 890
85
votes
2 answers
Why don't fluorescent lights produce shadows?
I have watched light sources such as incandescent lamps and other lamp sources; they have always made shadows. But a fluorescent lamp doesn't make any shadow. What is the reason behind the non-appearance of prominent shadow?
natarajan physicist
- 1,007
84
votes
1 answer
Why do chimneys have these spiral "wings"?
While walking around I noticed something very peculiar. Many chimneys had spiral "wings", while others didn't. I came up with two possibilities:
The wind circles around the chimney upwards which pushes whatever gases being released even higher into…
Adi
- 1,628
84
votes
24 answers
List of freely available physics books
I'm trying to amass a list of physics books with open-source licenses, like Creative Commons, GPL, etc. The books can be about a particular field in physics or about physics in general.
What are some freely available great physics books on the…
pcr
- 1,103
84
votes
3 answers
Why is the sky not purple?
I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of Rayleigh scattering goes like $\omega^4$, why is the…
Warrick
- 9,870
84
votes
6 answers
Why does public mains power use 50-60 Hz and 100-240 V?
Is there a physical reason behind the frequency and voltage in the mains electricity? I do not want to know why exactly a certain value was chosen; I am rather interested to know why that range/order of magnitude was selected. I.e., why 50 Hz and…
SuperCiocia
- 25,602
84
votes
8 answers
Why is there no absolute maximum temperature?
If temperature makes particles vibrate faster, and movement is limited by the speed of light, then I would assume that temperature must be limited as well.
Why is there no limit?
serg
- 1,483
84
votes
2 answers
Lev Landau's "Theoretical Minimum"
The great russian physicist Lev Landau developed a famous entry exam to test his students. This "Theoretical Minimum" contained everything he considered elementary for a young theoretical physicist. Despite its name, it was notoriously hard and…
jdm
- 4,277
84
votes
4 answers
Where does the extra kinetic energy come from in a gravitational slingshot?
I read in this answer in this site that the KE a free-falling ball acquires is not originated by the attracting body but that energy was actually stored in the ball when it had been lifted to the height it dropped from.
In this way, it was said,…
Cory Baumer
- 851
83
votes
7 answers
Does Coulomb's Law, with Gauss's Law, imply the existence of only three spatial dimensions?
Coulomb's Law states that the fall-off of the strength of the electrostatic force is inversely proportional to the distance squared of the charges.
Gauss's law implies that the total flux through a surface completely enclosing a charge is…
Justin L.
- 6,090
83
votes
5 answers
What reference clock is an atomic clock measured against?
I looked at a few of the other posts regarding the accuracy of atomic clocks, but I was not able to derive the answer to my question myself.
I've seen it stated that atomic clocks are accurate on the order of $10^{-16}$ seconds per second. However,…
zrbecker
- 987
83
votes
6 answers
Why does a rubber band become a lighter color when stretched?
I was stretching a pink colored rubber band, and I noticed that the longer I stretch it, the lighter the pink becomes.
Why does this happen?
wavion
- 1,266