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1500 questions
50
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6 answers
Where do photons go when they are absorbed?
The answer I usually get (and I'm paraphrasing here) is that they disappear and are instead absorbed as heat energy.
But I find it hard to believe that the photon simply "disappears." Common sense tells me it must turn into something or other, not…
user3932000
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50
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6 answers
Difference between spin and polarization of a photon
I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as the oscillations of the E and M field, not…
user929304
- 4,635
50
votes
5 answers
Is the world $C^\infty$?
While it is quite common to use piecewise constant functions to describe reality, e.g. the optical properties of a layered system, or the Fermi–Dirac statistics at (the impossible to reach exactly) $T=0$, I wonder if in a fundamental theory such as…
Tobias Kienzler
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50
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8 answers
Why isn't dark matter just ordinary matter?
There's more gravitational force in our galaxy (and others) than can be explained by counting stars made of ordinary matter. So why not lots of dark planetary systems (i.e., without stars) made of ordinary matter? Why must we assume some…
Andrew Beatty
- 603
49
votes
8 answers
Why does the speed of light in vacuum have no uncertainty?
I could understand that the definition of a second wouldn't have an uncertainty when related to the transition of the Cs atom, so it doesn't have an error because it's an absolute reference and we measure other stuff using the physical definition of…
The Quantum Physicist
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49
votes
7 answers
Explaining UV radiation to a 6 year old
My (just completed) PhD involved a considerable amount of research involved with the detection of solar UV radiation. This generated quite a bit of interest, especially when I was conducting my experiments outside.
A friend's 6 year old was most…
user29350
49
votes
6 answers
Does alternating current (AC) require a complete circuit?
This popular question about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work (ignoring resistance/inductance of the wire)" was recently asked on the Electronics SE.
(Picture edited from the one in…
49
votes
1 answer
Differences between pure/mixed/entangled/separable/superposed states
I am currently trying to establish a clear picture of pure/mixed/entangled/separable/superposed states. In the following I will always assume a basis of $|1\rangle$ and $|0\rangle$ for my quantum systems. This is what I have so far:
superposed: A…
ftiaronsem
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49
votes
5 answers
Could I, within my lifetime, reach any star I wanted if I went fast enough?
Disclamer: I'm not talking about FTL travel here. I'm also not talking about any weird space warping mechanics like wormholes and such.
I've always thought that if a star was 4 light years away, then it would be impossible to reach it with less than…
Augs
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49
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4 answers
Physicists adding 3 decimals to the fine structure constant is a big accomplishment. Why?
Yesterday, a team of physicists from France announced a breakthrough in nailing down a "magic number" by adding three decimals to the the fine-structure constant (news article; technical paper)
$$\alpha^{-1}\approx 137.035\,999\,206(11)$$
To the…
Déjà vu
- 737
49
votes
4 answers
Could I survive at (or near) absolute zero with a very, very, very thick sweater?
Imagine I'm in an infinitely large vacuum and have a special apparatus built into my body that allows me to breath, eat, pee/poo, etc. and never age. The vacuum is similar to deep space and has no heat source or visible light and is therefore quite…
Behacad
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49
votes
3 answers
What is the evidence for 'billions of neutrinos pass through your body every second'?
This statement is repeated so often that it has become somewhat of a cliche: 'billions of neutrinos pass through your body every second'. For example see 1, 2, 3, 4, 5, 6.
What is the evidence for it, especially considering that we have never…
Ritesh Singh
- 1,315
49
votes
8 answers
How is it possible there are UV photos while our eyes cannot detect UV waves?
I know this question sounds dumb, but please bear with me. This question came into my mind while I was looking at the photos in an astronomy book. How is it possible that IR and UV photos of stars and nebulae are taken if our eyes could not detect…
Bored Comedy
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49
votes
6 answers
Because things smell, is everything evaporating?
Everything, in theory, can have a smell, but that is not the whole point of this question.
My main query is, since things do smell, does that mean that everything is slowly evaporating (or, sublimating, I suppose)?
For example, if we perceive metal…
deed02392
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49
votes
10 answers
Is it really better for the environment if I take the stairs as opposed to a lift?
This question is inspired by a sign I saw at a lift, which said something like:
Going up 1 floor or down 2 floors? Take the stairs, it's better for your health and for the environment.
There's no doubt that taking the stairs is better for one's…
Allure
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