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1500 questions
120
votes
7 answers
Why are most metals gray/silver?
Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray?
What makes copper and gold have different colors?
What atomic characteristics determine the color?
Ali Abbasinasab
- 1,819
120
votes
3 answers
Differentiating Propagator, Green's function, Correlation function, etc
For the following quantities respectively, could someone write down the common definitions, their meaning, the field of study in which one would typically find these under their actual name, and most foremost the associated abuse of language as well…
Nikolaj-K
- 8,443
119
votes
8 answers
Why is the $S_{z} =0$ state forbidden for photons?
If photons are spin-1 bosons, then doesn't quantum mechanics imply that the allowed values for the z-component of spin (in units of $\hbar$) are -1, 0, and 1?
Why then in practice do we only use the $\pm 1$ states?
I have been told that this is…
Todd R
- 1,776
119
votes
10 answers
Why is quantum entanglement considered to be an active link between particles?
From everything I've read about quantum mechanics and quantum entanglement phenomena, it's not obvious to me why quantum entanglement is considered to be an active link. That is, it's stated every time that measurement of one particle affects the…
Andrey Tatarinov
- 1,371
119
votes
18 answers
How does mass leave the body when you lose weight?
When your body burns calories and you lose weight, obviously mass is leaving your body. In what form does it leave? In other words, what is the physical process by which the body loses weight when it burns its fuel?
Somebody said it leaves the…
exokernel
- 1,355
119
votes
16 answers
Is it possible for information to be transmitted faster than light by using a rigid pole?
Is it possible for information (like 1 and 0s) to be transmitted faster than light?
For instance, take a rigid pole of several AU in length. Now say you have a person on each end, and one of them starts pulling and pushing on his/her end.
The…
Jonathan.
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119
votes
10 answers
How can I stand on the ground? EM or/and Pauli?
There is this famous example about the order difference between gravitational force and EM force. All the gravitational force of Earth is just countered by the electromagnetic force between the electrons on the surface of my feet and the ground.
But…
Kivanc Uyanik
- 1,291
118
votes
7 answers
What's inside a proton?
What constitutes protons? When I see pictures, I can't understand. Protons are made of quarks, but some say that they are made of 99% empty space. Also, in this illustration from Wikipedia, what's between the quarks?
118
votes
12 answers
Why don't we use weights to store energy?
One of the main reasons why we haven't switched to clean energy is the lack of efficient storage methods - But, why aren't we using dead weights to store energy and draw it back later when needed? As an example of what I mean:
Blake Angelo
- 1,151
118
votes
6 answers
What are the justifying foundations of statistical mechanics without appealing to the ergodic hypothesis?
This question was listed as one of the questions in the proposal (see here), and I didn't know the answer. I don't know the ethics on blatantly stealing such a question, so if it should be deleted or be changed to CW then I'll let the mods change…
Logan M
- 4,464
118
votes
13 answers
If all motion is relative, how does light have a finite speed?
I've often heard that Einstein shattered the notion of absolute motion (i.e. all things move relative to one another) and that he established the speed of light as being absolute. That sounds paradoxical to me; I cannot understand how the two…
CircleSquared
- 1,321
118
votes
6 answers
Trace of a commutator is zero - but what about the commutator of $x$ and $p$?
Operators can be cyclically interchanged inside a trace:
$${\rm Tr} (AB)~=~{\rm Tr} (BA).$$
This means the trace of a commutator of any two operators is zero:
$${\rm Tr} ([A,B])~=~0.$$
But what about the commutator of the position and momentum…
Joe
- 3,444
117
votes
2 answers
Is it necessary to consume energy to perform computation?
As far as I know, today most of the computers are made from semiconductor devices, so the energy consumed all turns into the heat emitted into space.
But I wonder, is it necessary to consume energy to perform computation?
If so, is there a…
jiakai
- 1,223
117
votes
18 answers
Can the Heisenberg Uncertainty Principle be explained intuitively?
I have heard several pseudoscientific explanations about the Heisenberg Uncertainty Principle and find them hard to believe.
As a mathematician mainly focusing on functional analysis, I have a considerable interest in this matter. Although I still…
D1X
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116
votes
9 answers
What is the relation between electromagnetic wave and photon?
At the end of this nice video (https://youtu.be/XiHVe8U5PhU?t=10m27s), she says that electromagnetic wave is a chain reaction of electric and magnetic fields creating each other so the chain of wave moves forward.
I wonder where the photon is in…
Xtro
- 1,671