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1500 questions
68
votes
5 answers
Can space expand with unlimited speed?
According to this article on the European Space Agency web site just after the Big Bang and before inflation the currently observable universe was the size of a coin. One millionth of a second later the universe was the size of the Solar System,…
cziko
- 783
68
votes
12 answers
Is it possible that there is a color our human eye can't see?
Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it.
If there is, is it possible to detect/identify it?
MegaNairda
- 839
68
votes
6 answers
How does light combine to make new colours?
In computer science, we reference colours using the RGB system and TVs have pixels which consist of groups of red, green and blue lines which turn on and off to create colours.
But how does this work? Why would certain amounts of red, blue and green…
Isky Mathews
- 1,935
68
votes
11 answers
Why is torque not measured in Joules?
Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$.
This means the units of torque are Newton meters. Work & Energy are also measured in Newton meters which are Joules.
However, torque isn't a measure…
General Stubbs
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68
votes
5 answers
Why do grapes in a microwave oven produce plasma?
Some of you may know this experiment (Grape + Microwave oven = Plasma video link):
take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each half-part.
put that in a microwave oven, and few…
JBE
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68
votes
9 answers
What is the difference between the magnetic $H$-field and $B$-field?
From Wikipedia:
"The term (Magnetic Field) is used for two distinct but closely related fields denoted by the symbols $B$ and $H$, where $H$ is measured in units of amperes per meter in the SI. $B$ is measured in teslas in the SI."
So, the two are…
Sergei Gorbikov
- 1,095
68
votes
1 answer
On the Coulomb branch of ${\cal N}=2$ supersymmetric gauge theory
The chiral ring of the Coulomb branch of a 4D ${\cal N}=2$ supersymmetric gauge theory is given by the Casimirs of the vector multiplet scalars, and they don't have non-trivial relations; the Casimirs are always independent.
Also in Gaiotto's class…
Yuji
- 3,602
68
votes
5 answers
Why do archery arrows tilt downwards in their descent?
In the movies, arrows shot into the air rotate so that during the descent, the arrow head hits ground first. What is the source of this angular momentum? It would seem that the bow string exerts a force directly in line with the arrow.
lamplamp
- 1,528
68
votes
9 answers
What are the next generation physics experiments?
The LHC and LIGO are two recent examples of hugely ambitious experiments in fundamental physics, both of which took decades to develop.
What are the next major experiments currently being planned and developed? What will they measure? What impact…
lemon
- 13,220
68
votes
6 answers
Laplace operator's interpretation
What is your interpretation of Laplace operator? When evaluating Laplacian of some scalar field at a given point one can get a value. What does this value tell us about the field or it's behaviour in the given spot?
I can grasp the meaning of…
Džuris
- 3,207
68
votes
5 answers
What challenges needed to be overcome to create (blue) LEDs?
In light of today's announcement of the 2014 Nobel laureates, and because of a discussion among colleagues about the physical significance of these devices, let me ask:
What is the physical significance of blue LEDs, which challenges had to be…
Martin
- 15,550
68
votes
9 answers
Does electricity flow on the surface of a wire or in the interior?
I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that electricity travels on the surface while they…
N. Owad
- 783
67
votes
5 answers
Would touching a black hole of a small mass (the mass of an apple) cause you to spiral in and get dead?
I know that a typical stellar black hole would spaghettify someone who crosses its event horizon.
Is this also true for a hypothetical tiny black hole with a small mass (the mass of an apple)? Would someone touching such a black hole spiral into it…
user9343456
- 1,212
67
votes
8 answers
Can 1 kilogram of radioactive material with half life of 5 years just decay in the next minute?
I wondered this since my teacher told us about half life of radioactive materials back in school. It seems intuitive to me to think this way, but I wonder if there's a deeper explanation which proves me wrong.
When many atoms are involved, half life…
uylmz
- 805
67
votes
8 answers
What are the various physical mechanisms for energy transfer to the photon during blackbody emission?
By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium is a statement of the mean behaviour of the…
Douglas B. Staple
- 1,526