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1500 questions
79
votes
6 answers
Is the total energy of the universe zero?
In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of the gravitational field".
But I can't find anything…
user1265
79
votes
6 answers
What is information?
We're all familiar with basic tenets such as "information cannot be transmitted faster than light" and ideas such as information conservation in scenarios like Hawking radiation (and in general, obviously). The Holographic Principle says, loosely,…
Mitchell
- 1,025
79
votes
5 answers
Is fire plasma?
Is Fire a Plasma?
If not, what is it then?
If yes why, don't we teach kids this basic example?
UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify the answer.
daniel.sedlacek
- 1,968
79
votes
3 answers
Why do we need to "create our own" Higgs boson in order to see one?
I understand that the LHC found the Higgs boson by pumping so much energy into a tiny space (via near light speed proton-proton collisions) that a Higgs boson appeared momentarily, then instantly decayed. They detected the products of the decay, and…
Max Williams
- 1,321
79
votes
8 answers
Does quantum mechanics play a role in the brain?
I'm interested in whether the scale of processes that occur in the brain is small enough to be affected by quantum mechanics. For instance, we ignore quantum mechanics when we analyze a game of tennis because a tennis ball is much too large to be…
QCD_IS_GOOD
- 7,145
79
votes
11 answers
Why is the charge naming convention wrong?
I recently came to know about the Conventional Current vs. Electron Flow issue.
Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and negative charges.
There is even this little comic…
GetFree
- 1,321
78
votes
7 answers
What is the difference between Newtonian and Lagrangian mechanics in a nutshell?
What is Lagrangian mechanics, and what's the difference compared to Newtonian mechanics? I'm a mathematician/computer scientist, not a physicist, so I'm kind of looking for something like the explanation of the Lagrangian formulation of mechanics…
grautur
- 961
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78
votes
4 answers
If water is incompressible, how can sound propagate underwater?
Since sound travels as longitudinal waves, sound waves should only be able to propagate in a medium through compressions and rarefactions. However, water, as a liquid, is generally treated as an incompressible fluid. Since compression is essential…
Omnitragedy
- 793
78
votes
14 answers
Does throwing a penny at a train stop the train?
If I stand in front of a train and throw a penny at it, the penny will bounce back at me.
For the penny to reverse its direction, at some point its velocity must go to zero. This is the point it hits the train. Two objects in contact have the same…
Whose
- 767
78
votes
7 answers
Is Pauli-repulsion a "force" that is completely separate from the 4 fundamental forces?
You can have two electrons that experience each other's force by the exchange of photons (i.e. the electromagnetic force). Yet if you compress them really strongly, the electromagnetic interaction will no longer be the main force pushing them apart…
Jan M.
- 1,162
78
votes
20 answers
Why doesn't current pass through a resistance if there is another path without resistance?
Why doesn't current pass through a resistance if there is another path without resistance? How does it know there is resistance on that path?
Some clarification:
I understand that some current will flow through the resistance.
A depiction of this…
ten1o
- 1,255
78
votes
9 answers
Why are "degrees" and "bytes" not considered base units?
From Wikipedia:
The SI base units and their physical quantities are the metre for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the candela for luminous intensity,…
Wais Kamal
- 939
78
votes
3 answers
Why do I see a saddle in this picture of a computer screen?
I am not entirely sure this is an appropriate question for PSE, however since many of you have such diverse backgrounds, I'll give it a shot.
I have noticed that when one takes a picture of a computer, TV screen with a phone, you can "see" what…
78
votes
2 answers
Can an atom orbit the Sun?
Is it possible for a molecule or atom to orbit a star (e.g. the Sun)? Or is there always too much outward force imparted by solar radiation compared to the inward force of gravitational attraction?
Nicole Sharp
- 657
78
votes
9 answers
If the speed of light is constant, why can't it escape a black hole?
When speed is the path traveled in a given time and the path is constant, as it is for $c$, why can't light escape a black hole?
It may take a long time to happen but shouldn't there be some light escaping every so often?
I'm guessing that because…
Zaibis
- 1,299