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1500 questions
57
votes
4 answers
What does the Moon's orbit around the Sun look like?
I'm curious as to what the Moon's orbit around the Sun looks like. If there's an answer, what's the intuition for it? Here are some things I'm assuming when trying to tackle this question:
The Moon's orbit must be concave toward the Sun.
The Moon…
Alex
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57
votes
3 answers
Are there exact analytical solutions to the electronic states of the hydrogen molecular ion $\mathrm H_2^+$?
The hydrogen molecular ion (a.k.a. dihydrogen cation) $\mathrm H_2^+$ is the simplest possible molecular system, and as such you'd hope to be able to make some leeway in solving it, but it turns out that it's much harder than you'd hope. As it turns…
Emilio Pisanty
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57
votes
4 answers
Is there an underlying physical reason why the Coriolis force is similar to the magnetic component of the Lorentz force?
I couldn't help but notice that the expression for the magnetic component of the Lorentz force,
$$\mathbf F = q\,\mathbf v \times \mathbf B\,,$$
is very similar in its mathematical form to the Coriolis force,
$$\mathbf F = 2m\mathbf v \times \mathbf…
dahemar
- 2,403
57
votes
8 answers
What are the prerequisites to studying general relativity?
This question recently appeared on Slashdot:
Slashdot posts a fair number of physics stories. Many of us, myself included, don't have the background to understand them. So I'd like to ask the Slashdot math/physics community to construct a…
David Z
- 76,371
57
votes
9 answers
Are we slightly lighter during the day and slightly heavier at night, owing to the force of the Sun's gravity?
Using $g = \frac{Gm}{r^2}$, the force on a point mass located at 1 AU from the Sun ($m = 2 \cdot 10^{30} \text{ kg}$) is about ~0.006 N/kg.
Does that mean that, e.g., a 70 kg person is ~42g lighter during the day, and ~42g heavier at night? That…
John Feminella
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57
votes
7 answers
Is there any proof for the 2nd law of thermodynamics?
Are there any analytical proofs for the 2nd law of thermodynamics?
Or is it based entirely on empirical evidence?
AIB
- 1,364
56
votes
5 answers
Why is it hard to solve the Ising-model in 3D?
The Ising model is a well-known and well-studied model of magnetism. Ising solved the model in one dimension in 1925. In 1944, Onsager obtained the exact free energy of the two-dimensional (2D) model in zero field and, in 1952, Yang presented a…
Marton Trencseni
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56
votes
4 answers
Does anything in an incandescent bulb actually reach its color temperature (say 2700 K)?
This question is inspired by a question about oven lightbulbs over on the DIY stack. It spawned a lengthy comment discussion about whether an incandescent lightbulb with a color temperature of 2500 K actually has a filament at a temperature of 2500…
Bear
- 573
56
votes
8 answers
Proof that the Earth rotates?
What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis?
By basic physics I mean the physics that the early physicists must've used to deduce that it rotates, not relativity.
user8721
- 563
56
votes
5 answers
What is this wavy light coming through my blinds?
On many mornings I get this cool light pattern on my ceiling:
It's light coming in through the blinds, but there is this rippling/wavy/moving effect. Its intensity varies (as can be seen a little in the GIF). I am basically just curious as to…
Tom
- 647
56
votes
4 answers
Why does a supernova explode?
This is really bugging me. When you look up some educational text about stars life, this is what you find out:
Gravity creates the temperature and pressure to start fusion reactions.
The fusion proceeds to heavier and heavier cores ending with…
Tomáš Zato
- 3,088
56
votes
2 answers
Neutrinos vs. Photons: Who wins the race across the galaxy?
Inspired by the wording of this answer, a thought occurred to me. If a photon and a neutrino were to race along a significant stretch of our actual galaxy, which would win the race?
Now, neutrinos had better not be going faster than the speed of…
user10851
56
votes
9 answers
Is a "third quantization" possible?
Classical mechanics: $t\mapsto \vec x(t)$, the world is described by particle trajectories $\vec x(t)$ or $x^\mu(\lambda)$, i.e. the Hilbert vector is the particle coordinate function $\vec x$ (or $x^\mu$), which is then projected into the space…
Tobias Kienzler
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56
votes
9 answers
Is a spontaneous decrease in entropy *impossible* or just extremely unlikely?
I was reading this article from Ethan Siegel and I got some doubts about a sentence about entropy, specifically when Ethan explains the irreversibility of the conditions of the hot-and-cold room, as in this figure:
In his words:
It's like taking a…
Andy4983948
- 765
56
votes
3 answers
How does the Earth's center produce heat?
In my understanding, the center of the Earth is hot because of the weight of the its own matter being crushed in on itself because of gravity. We can use water to collect this heat from the Earth and produce electricity with turbines. However, I'd…
Radvylf Programs
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