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1500 questions
99
votes
9 answers
What is a manifold?
For complete dummies when it comes to space-time, what is a manifold and how can space-time be modelled using these concepts?
Richard971
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98
votes
3 answers
First and second order phase transitions
Recently I've been puzzling over the definitions of first and second order phase transitions. The Wikipedia article starts by explaining that Ehrenfest's original definition was that a first-order transition exhibits a discontinuity in the first…
N. Virgo
- 35,274
98
votes
10 answers
Quantum Entanglement - What's the big deal?
Bearing in mind I am a layman - with no background in physics - please could someone explain what the "big deal" is with quantum entanglement?
I used to think I understood it - that 2 particles, say a light-year apart spatially, could affect each…
Pete Oakey
- 1,574
98
votes
4 answers
Seeing something from only one angle means you have only seen (what?)% of its surface area at most?
Is there a logical/mathematical way to derive what the very maximum percentage of surface area you can see from one angle of any physical object?
For instance, if I look at the broad side of a piece of paper, I know I have only seen 50% of its…
BarrettNashville
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98
votes
3 answers
Where is the flaw in this machine that decreases the entropy of a closed system?
I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some thinking, I can't figure out why it wouldn't work, other…
QuantumFool
- 1,274
98
votes
6 answers
What is more fundamental, fields or particles?
My confusion about quantum theory is twofold:
I lack an adequate understanding of how the mathematics of quantum theory is supposed to correspond to phenomena in the physical world
I still have an incomplete picture in my mind of how cause and…
jpbrooks-user153707
- 1,171
96
votes
12 answers
Why are radiators always placed under windows?
I don't know if anyone else has noticed this but in most buildings and most rooms, radiators are predominantly placed under a window.
Now, in my eyes, that is the worst place to put them; hot air rises, reaches the window (which no matter how well…
turnip
- 3,768
96
votes
10 answers
Why bother buying efficient lights if you are already heating your house?
Assume I live in a location where at any time of day and any time of year, I need to heat my house. Assume further that I have a room with no windows. In this case, does it make sense for me to buy efficient light bulbs, considering that any…
Mathew
- 1,153
96
votes
4 answers
Why does the shower curtain move towards me when I am taking a hot shower?
When I am taking a shower, the shower curtain slowly moves towards my legs.
Also, it seems that the hotter the water, the faster it gets to my skin.
Why is that?
Gohu
- 925
96
votes
3 answers
Why was carbon-12 chosen for the atomic mass unit?
The atomic mass unit is defined as 1/12th the mass of a carbon-12 atom. Was there any physical reason for such a definition? Were they trying to include electrons in the atomic mass unit?
Why not define the amu as the mass of one proton or neutron…
Dieblitzen
- 1,687
96
votes
4 answers
Why don't miners get boiled to death at $4$ km deep?
The Mponeng Gold Mine is nearly $4$ km deep. It has the largest elevators in the world and is considered one of the most dangerous mines in the world.
The geothermal gradient is $25$ degrees Celsius per kilometer, which would be $100$ degrees.…
Ambrose Swasey
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96
votes
4 answers
If Earth had rings?
If Earth had rings, would they center on the equator like Saturn's rings do on its equator?
Muze
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96
votes
9 answers
Are matrices and second rank tensors the same thing?
Tensors are mathematical objects that are needed in physics to define certain quantities. I have a couple of questions regarding them that need to be clarified:
Are matrices and second rank tensors the same thing?
If the answer to 1 is yes, then…
Revo
- 17,504
96
votes
9 answers
Why is there a controversy on whether mass increases with speed?
Some people say that mass increases with speed while others say that the mass of an object is independent of its speed.
I understand how some (though not many) things in physics are a matter of interpretation based on one's definitions. But I can't…
User 17670
- 1,306
95
votes
10 answers
What is a complete book for introductory quantum field theory?
There's a fairly standard two or three-semester curriculum for introductory quantum field theory, which covers topics such as:
classical field theory background
canonical quantization, path integrals
the Dirac field
quantum…
Andy Bale
- 2,017