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1500 questions
47
votes
5 answers
Why are protons, rather than electrons, the nucleus in atoms?
I have been wondering why only electrons revolve around protons instead of protons other way around. They have electrostatic force and I think mass factor has nothing to do here. Then why?
Cyberax
- 717
47
votes
6 answers
Why do rotten eggs float in water?
My mom told me that one can check whether an egg is rotten by sinking it in a glass of water. If it floats, then it is rotten.
I didn't find any explanation for this phenomenon. If anyone knows one, please answer.
prAnjal
- 593
47
votes
5 answers
Why does pitch increase when you blow harder into a whistle?
When you play recorder or whistle, the pitch depends on how hard you blow into the tube. E.g. when you blow a whistle, initially the pitch is slightly lower when there is less air flow. This seems counter intuitive since the airflow should only…
47
votes
3 answers
Doesn't the speed of light limit imply the same electron can be annihilated twice?
If I understand correctly, there is a small probability the same electron to be found anywhere in the universe.
Suppose that an anti-electron collides with an electron, annihilating it and producing two photons. Assuming the speed of light limit is…
user237040
47
votes
2 answers
Dumbed-down explanation how scientists know the number of atoms in the universe?
It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$.
How do scientists determine this number?
And how accurate is it (how strong is the supporting evidences for it)?
Is it more likely (logically >50% chance) that…
Pacerier
- 893
47
votes
2 answers
Rigged Hilbert space and QM
Are there any comprehensive texts that discuss QM using the notion of rigged Hilbert spaces? It would be nice if there were a text that went through the standard QM examples using this structure.
jimi hendrix
- 103
47
votes
4 answers
Why are line spectra only seen in gases?
This might be a stupid question but I could not find the answer in my textbook or on the internet with a few searches.
So I believe when an atomic electron moves down to a lower energy level it emits radiation in the process. However since the…
IK-_-IK
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47
votes
10 answers
Without the Michelson-Morley experiment, is there any other reason to think speed of light is the universal speed limit?
If the Michelson-Morley experiment hadn't been conducted, are there any other reasons to think, from the experimental evidence available at that time, that Einstein could think of the Special Theory of Relativity?
Is there any other way to think why…
47
votes
9 answers
How does a heatsink on top of a CPU, which is hot, cool down your CPU?
A heatsink can be stuck on your CPU to cool it down. That heatsink feels cold when the system is not turned on. However when the CPU is turned on the heatsink is extremely hot. Isn't that contradictory to a certain extent? I expect a heatsink to…
LandonZeKepitelOfGreytBritn
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47
votes
5 answers
Why don't helicopters use reaction wheels to counter the main rotor?
As the main title says. I'm finding myself wondering about helicopters. The tail rotor is a vulnerable and key piece of equipment, especially on military helicopters. I know some helicopters instead use two main rotors (for example the KA-50).
Why…
Scuba Steve
- 572
47
votes
8 answers
Does a "capacitor" for light exist, which could filter out flickering?
If I have a light that is flickering at a frequency low enough to be perceived by the human eye, is there any type of material that exists that will smooth out the appearance of flickering? Similar to how a capacitor smooths the output of a…
salfasano
- 565
47
votes
2 answers
Is there a time operator in quantum mechanics?
The question in the title has been asked many times on this site before, of course. Here's what I found:
Time as a Hermitian operator in QM? in 2011. Answer states time is a parameter.
Is there an observable of time? in 2012. Answer by Arnold…
ziggurism
- 698
47
votes
6 answers
Do photons gain mass when they travel through glass?
Please correct me if I'm wrong, but I believe that photons slow down when travelling through glass. Does this mean they gain mass? Otherwise, what happens to extra kinetic energy?
I understand now that the apparent slowing down is due to electron…
dan_waterworth
- 1,238
47
votes
5 answers
Why is the prospective new kilogram standard a sphere?
I can understand the choice of material, silicon 28, but why is it a sphere rather than (say) a cube? Article here
I would have thought that a sphere would have been the hardest shape to machine accurately.
user56903
47
votes
2 answers
How can airplanes fly upside down?
I've read many times, including here on this very site that the commonly known explanation of flight is wrong, and that airplanes can fly because the shape of their wings deflects air down. This makes sense, but as far as I can tell it doesn't…
Javier
- 28,106