The definition tag is used in situations where the question is either about how some term or concept is define or where the validity of an answer depends on a subtle definition of some term or concept used in the question.

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5
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3answers
541 views

Can temperature be defined as propensity to transmit thermal energy?

I was recently surprised to learn that defining temperature isn't easy. For a long time, it was defined operationally: how much does a thermometer expand. Also surprising, temperature isn't a ...
4
votes
1answer
61 views

Vesta dwarf planet status

Now that we have close-up photos of Vesta, which the IAU had previously said was a candidate dwarf planet, when is the IAU going to decide the issue? Personally, Vesta doesn't look round enough to me. ...
2
votes
1answer
249 views

What examples are there of fuzzy concepts in astronomy?

What examples are there of fuzzy concepts in astronomy? In particular, how fuzzy are the boundaries between different types of stars? As an example of a fuzzy concept I'm thinking of the planet/brown ...
9
votes
4answers
645 views

Two planets in same orbit - not planets?

Let us pretend for a moment that there are two identical planets that are exactly opposite their star from each other and are the same distance from said star. (This would make them, at all times, ...
11
votes
5answers
7k views

What is an asterism compared to a constellation?

I'm doing an astronomy exam tomorrow and in the practice paper it asks for the difference between constellation and asterism. It seems asterism is a group of recognizable stars; however I thought that ...
12
votes
7answers
2k views

What is the current status of Pluto?

Pluto has been designated a planet in our solar system for years (ever since it was discovered in the last century), but a couple of years ago it was demoted. What caused this decision? And is there ...
2
votes
1answer
315 views

Are inductance and self-inductance synonyms?

Wikipedia mentions that the word self in the word "self-inductance" is to differentiate it from "mutual inductance". But it does not state whether the two things are the same thing. So do the both ...
6
votes
4answers
527 views

What exactly is $F$ in $W = \int_{a}^{b} F dx$?

I am trying to teach myself some basic physics, here is something I do not really understand about the definition of work: When moving from $a$ to $b$ (in one dimension), the work done is defined to ...
3
votes
2answers
1k views

what is meant by “crossover phenomena”?

In many articles I read the term "crossover phenomena" and a lot of methodology discussed according to it, with little or no description about what is meant by it. Sometimes there is a connection to ...
14
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1answer
2k views

What is the definition of how to count degrees of freedom?

This question resulted, rather as by-product, the discussion on how to count degrees of freedom (DOF). I extend that question here: Are necessary1 derivatives such as velocities counted as ...
7
votes
3answers
1k views

Definitions and usage of Covariant, Form-invariant, Invariant?

Just wondering about the definitions and usage of these three terms. To my understanding so far, "covariant" and "form-invariant" are used when referring to physical laws, and these words are ...
7
votes
6answers
9k views

Simple explanation of quantum mechanics

Can you please describe quantum mechanics in simple words? When ever I read this word (quantum computers, quantum mechanics, quantum physics, quantum gravity etc) I feel like fantasy, myth and ...
-1
votes
3answers
379 views

Are we crystals?

Can we say that we are crystals because just like crystals we are made up of very small unit (cell) making up almost the same shape (our body) everywhere.
17
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5answers
4k views

What does it mean for a Hamiltonian or system to be gapped or gapless?

I've read some papers recently that talk about gapped Hamiltonians or gapless systems, but what does it mean? Edit: Is an XX spin chain in a magnetic field gapped? Why or why not?
2
votes
3answers
825 views

What is the definition of physically meaningful?

I asked a question recently where I wanted to know whether it was physically meaningful to talk about the arrow of time in other universes. Although many people apparently have an intuitive notion of ...
4
votes
2answers
554 views

Potential functions

Can someone please explain what a potential is? Example. velocity potential in ideal flows, acoustic potential (gradient of which gives the particle velocity in a sound wave). Whenever I see potential ...
12
votes
3answers
2k views

Why are quark types known as flavors?

There are six types of quarks, known as flavors. Why where these types called flavors? Why do the flavors have such odd names (up, down, charm, strange, top, and bottom)?
13
votes
7answers
3k views

What is a general definition of impedance?

Impedance is a concept that shows up in any area of physics concerning waves. In transmission lines, impedance is the ratio of voltage to current. In optics, index of refraction plays a role similar ...
9
votes
4answers
11k views

What is sound and how is it produced?

I've been using the term "sound" all my life, but I really have no clue as to what sound exactly is or how it is created. What is sound? How is it produced? Can it be measured?