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1500 questions
36
votes
4 answers
How to imagine WiFi signal propagation?
When thinking about how the WiFi signal propagates through a household, can I use the following thought experiment?
Assume absolute darkness. Place a strong lightbulb where the WiFi access point is. The illumination that reaches various places in…
vektor
- 382
36
votes
4 answers
Why does the moon sometimes appear giant and a orange red color near the horizon?
I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high above the horizon being generally further away than…
logicbird
36
votes
5 answers
How am I able to stand up and walk down the aisle of a flying passenger jet?
The energy of a moving object is $E = mv^2\;.$ That is it increases with velocity squared.
I walk at say 3 miles per hour, or lets round that down to 1 meter per second for a slow walk. I weigh less than $100~\mathrm{kg}\;,$ but lets just round that…
user2800708
- 962
36
votes
4 answers
Why doesn't the solar wind disrupt the planets?
The sun creates this heliosphere by sending a constant flow of particles and a magnetic field out into space at over 670,000 miles per hour, which is also known as solar wind. If the speed of the wind is that great, why doesn't it disrupt the…
Tammy Chong
- 543
36
votes
4 answers
How can we recover the Newtonian gravitational potential from the metric of general relativity?
The Newtonian description of gravity can be formulated in terms of a potential function $\phi$ whose partial derivatives give the acceleration:
$$\frac{d^2\vec{x}}{dt^2}=\vec{g}=-\vec{\nabla}\phi(x)=\left(\frac{\partial\phi}{\partial…
Beyond-formulas
- 1,486
36
votes
3 answers
What is the physical meaning of the partition function in statistical physics?
In many places in statistical physics we use the partition function. To me, the explanations of their use are clear, but I wonder what their physical significance is. Can anyone please explain with a good example without too many mathematical…
albedo
- 1,663
36
votes
5 answers
Why do all the atoms of a radioactive substance not decay at the same time?
Why does the substance decay at a rate which is proportional to the amount of the substance at that moment?
As all atoms are in hurry to become a stable atom and as their decay do not depend on any external things (like pressure, decaying of…
Sanjib Ray
- 409
36
votes
4 answers
Why do we need complex representations in Grand Unified Theories?
EDIT4: I think I was now able to track down where this dogma originally came from. Howard
Georgi wrote in TOWARDS
A
GRAND
UNIFIED
THEORY
OF
FLAVOR
There is a deeper reason to require the fermion
representation to be complex …
jak
- 10,431
36
votes
1 answer
Difference between 1PI effective action and Wilsonian effective action?
What is the simplest way to describe the difference between these two concepts, that often go by the same name?
Newman
- 2,626
36
votes
14 answers
Why does the (relativistic) mass of an object increase when its speed approaches that of light?
I'm reading Nano: The Essentials by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.
However, the equation breaks down when the electron velocity approaches the speed of light as mass…
Kit
- 1,483
36
votes
6 answers
What is the math knowledge necessary for starting Quantum Mechanics?
Could someone experienced in the field tell me what the minimal math knowledge one must obtain in order to grasp the introductory Quantum Mechanics book/course?
I do have math knowledge but I must say, currently, kind of a poor one. I did a basic…
azerIO
- 163
36
votes
5 answers
Why is the nucleus so small and why is the atom 99.999% empty space?
A nucleus consists of protons and neutrons. Both are extremely heavy compared to electrons. Then how come they are contained within an extremely tiny space? And why does the atom consist of 99.999% empty space?
I do not understand the mathematics…
Shades88
- 461
36
votes
4 answers
Why isn't the center of the galaxy "younger" than the outer parts?
I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are slower or further from mass.
So, the illustrative…
Yevgeny Simkin
- 509
36
votes
9 answers
Why do ships lean to the outside, but boats lean to the inside of a turn?
Small vessels generally lean into a turn, whereas big vessels lean out.
Why do ships lean to the outside, but boats lean to the inside of a turn?
For example, a boat leaning into a turn:
Image Source.
And a ship leaning out:
Image source
Philip Seyfi
- 463
36
votes
4 answers
How can area be a vector?
My professor told me recently that Area is a vector. A Google search gave me the following definition for a vector:
Noun: A quantity having direction as well as magnitude, esp. as
determining the position of one point in space relative to…
Green Noob
- 1,025