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1500 questions
46
votes
2 answers
Introduction to AdS/CFT
AdS/CFT seems like a really hot topic and I'd like to start reading about. I am looking for the best introduction at my level, i.e. I have a background in QFT, CFT and general relativity at the level of a master student in theoretical physics. What…
Just_a_wannabe
- 451
46
votes
5 answers
Does centrifugal force stiffen a rotating blade?
I'm a helicopter pilot with limited physics knowledge (units in BSc and HNCs).
I have recently challenged an assertion that rotating blades are stiffened by centrifugal force. In My mind, stiffness refers to the resistance of a member to bending…
Simon
- 561
46
votes
2 answers
Can anybody provide a simple example of a quantum computer algorithm?
Does anybody give a good textbook description of a quantum computer algorithm and how its different from an ordinary algorithm?
Humble
- 2,194
46
votes
3 answers
How does 'Tear Here' work?
How does 'Tear Here to Open' work? Why is it easier to tear there as opposed to anywhere else? What is its physics?
PhyEnthusiast
- 2,908
46
votes
4 answers
What is the status of Mpemba effect investigations?
There is this puzzling thing that is called Mpemba effect: paradoxically, warm (35°C) water freezes faster than cold (5°C) water. As a physisist, I've been asked about it several times already. And I have no definite answer to that, apart from the…
Kostya
- 19,992
46
votes
11 answers
Why can electric cars recoup energy from braking, but a spaceship cannot?
It is said that in a spaceship, you need to spend as much energy to brake as you spent for accelerating. An electric car, however, charges its batteries while braking, thus it actually recovers energy by braking.
Both facts somehow seem intuitive to…
Jens
- 634
46
votes
3 answers
Lie theory, Representations and particle physics
This is a question that has been posted at many different forums, I thought maybe someone here would have a better or more conceptual answer than I have seen before:
Why do physicists care about representations of Lie groups? For myself, when I…
Sean Tilson
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46
votes
3 answers
Why is Sachdev-Ye-Kitaev (SYK) Model model important?
In the past one or two years, there are a lot of papers about the Sachdev-Ye-Kitaev Model (SYK) model, which I think is an example of $\mathrm{AdS}_2/\mathrm{CFT}_1$ correspondence. Why is this model important?
Nahc
- 2,071
46
votes
7 answers
If the ground's normal force cancels gravity, how does a person keep rotating with the Earth?
When I am on earth, the weight of my body is countered by the reaction of the ground. So, there is no net force acting on me.
But I am spinning with earth. But if there is no centripetal force then why am I spinning? And the equal air pressure on…
Mockingbird
- 1,228
46
votes
4 answers
Why is water evaporated from the ocean not salty?
I am wondering about this. When salty water in the ocean evaporates we are getting the clean distilled water. Why is that?
I was trying to think on this and maybe the comparative size/mass of water molecules to the size of different salts molecules…
46
votes
9 answers
Is it theoretically possible to shield gravitational fields or waves?
Electromagnetic waves can be shielded by a perfect conductor. What about gravitational fields or waves?
netvope
- 563
46
votes
4 answers
How does the light source fire a single photon in the double-slit experiment
All the youtube videos I have seen on the double slit experiment broadly fall into one of the following three categories:
Documentaries and fan made videos heavy on animation which 'admire' the wave-particle duality of light rather than…
user58110
46
votes
6 answers
What are some critiques of Jaynes' approach to statistical mechanics?
Suggested here: What are the justifying foundations of statistical mechanics without appealing to the ergodic hypothesis?
I was wondering about good critiques of Jaynes' approach to statistical mechanics. @Yvan did a good job in pointing out a…
genneth
- 8,669
46
votes
9 answers
Extension of Schrödinger's cat thought experiment
My question is quite simple. In the thought experiment of Schroedinger's cat: When the scientist measures the state of the cat, its wavefunction collapses into either the alive or dead state. But wouldn't then the scientist in turn be in a…
Loreno Heer
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46
votes
6 answers
Can the apparent equal size of sun and moon be explained or is this a coincidence?
Is there a possible explanation for the apparent equal size of sun and moon or is this a coincidence?
(An explanation can involve something like tide-lock effects or the anthropic principle.)
Phira
- 2,072