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1500 questions
42
votes
15 answers
I don't understand what we really mean by voltage drop
This post is my best effort to seek assistance on a topic which is quite vague to me, so that I am struggling to formulate my questions. I hope that someone will be able to figure out what it is I'm trying to articulate.
If we have a circuit with a…
oyvey
- 631
42
votes
7 answers
Bush fires and heat waves, the real mechanics?
Like many others, I have been following the sad development of the bush/forest fires in Australia recently. A claim that gets repeated is that one of the contributors to this blaze is the ongoing >45°C heatwave.
Now I am not really putting this in…
Elmore
- 606
42
votes
3 answers
Is it really possible to break the speed of light by flicking your wrist with a laser pointer?
Minutephysics has a popular YouTube video called "How to break the speed of light". In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the spot of light on the moon will travel 20 times the speed…
miguel.martin
- 551
42
votes
9 answers
What are the strings in string theory made of?
This is a follow-up to an intriguing question last year about tension in string theory.
What are the strings in string theory composed of?
I am serious. Strings made of matter are complex objects that require a highly specific form of long-chain…
Terry Bollinger
- 21,997
42
votes
5 answers
In the double-slit experiment, why is it never shown that particles may hit the space between or outside the slits?
In depictions of the double-slit experiment that model the photon or electron as a particle, i.e. when attempting to measure which slit the particle passes through, it always shows the particle entering one of the two slits. Why is it that the…
Andrew Cheong
- 679
42
votes
5 answers
Is Stephen Wolfram's NKS, an attempt to explain the universe with cellular automata, in conflict with Bell's Theorem?
Stephen Wolfram's A New Kind of Science (NKS) hit the bookstores in 2002 with maximum hype.
His thesis is that the laws of physics can be generated by various cellular automata--simple programs producing complexity. Occasionally (meaning rarely) I…
Gordon
- 4,263
42
votes
3 answers
Why does a mirror reflect visible light but not gamma rays?
Visible light (~500 THz) as well as gamma rays (~100 EHz) are electromagnetic radiation but we can reflect visible light using a glass mirror but not gamma rays. Why is that?
MrV
- 551
42
votes
2 answers
What is the net charge of the Earth?
This question arose in a seminar today about the solar wind...
This is my vagueish understanding of the problem - please correct if you see errors!
The 'classical' picture of atmospheric electricity is that the Earth as a whole is neutral, but that…
Hywel
- 591
42
votes
5 answers
Intuitive explanation of why momentum is the Fourier transform variable of position?
Does anyone have a (semi-)intuitive explanation of why momentum is the Fourier transform variable of position?
(By semi-intuitive I mean, I already have intuition on Fourier transform between time/frequency domains in general, but I don't see why…
user541686
- 4,131
42
votes
3 answers
If I drop a ball in an accelerating rocket, will it bounce? If so, how?
Einstein's equivalence principle says that you cannot distinguish between an accelerating frame or a gravitational field. However, in an gravitational field, if I drop a tennis ball, it will bounce, but I don't think that it will in the accelerated…
user189508
42
votes
3 answers
Not all self-adjoint operators are observables?
The WP article on the density matrix has this remark:
It is now generally accepted that the description of quantum mechanics in which all self-adjoint operators represent observables is untenable.[17][18]
The first footnote is to the appendix in…
user4552
42
votes
2 answers
Periodic vs Open boundary conditions
In condensed matter, people often use periodic boundary conditions to perform calculations about the bulk properties of a material. It's generally argued that in the $N\rightarrow\infty$ limit the boundary conditions don't affect the bulk…
Jahan Claes
- 8,080
42
votes
4 answers
Will the Large Hadron Collider "explode" if the power is turned up too high?
The Large Hadron Collider, at low power, accelerates particles such that much of the total energy provided goes towards increasing their kinetic energy and their masses increase to some extent as well, and so Newton's equations are valid for this…
Michael Lee
- 1,365
42
votes
4 answers
Fourier transform paradox(?) of a wave packet
Assume you have a near perfect monochromatic red laser light. The Fourier transform of the laser light is a delta function peaked at the frequency of the light.
Now assume someone places a shutter on the path of the moving light, cutting off a wave…
Normie
- 1,456
42
votes
4 answers
Why can I see a diamond?
So a diamond has a energy band gap of $\approx 5$eV. If that is too much for visible light $\approx 1.6$eV to be absorbed and then it travels straight through a diamond.
Although, I still see a diamond. I know that when light goes through, there is…
Tsangares
- 712