@ACuriousMind and reviewers: Could one argue to keep it open because of the physics word space-time in the question formulation, cf. this meta discussion?
@Qmechanic I guess one could argue that but the physics question would be why do we use a manifold to model spacetime, not what is a manifold. The answers touch on the former but most seem to interpret the question to be mainly about the latter, which is purely mathematical no matter how you look at it.
We were being given intro to fluid dynamics at our school
So the thing that sparked me up is $ g$ in expression of:
Static pressure of fluid
Bernoulli Principle
I am curious how fluids(especially liquids) will behave when they are near or at strong gravitational fields and when they approach...
The idea here is that of a "web of trust" - if people I trust have signed another user's key, I will be reasonably sure they are who they say they are even if I have never met them.
@JohnRennie The paranoid might say that the gmail encryption is symmetric TLS (right?), so using additional asymmetric RSA protects you against a wider variety of attacks?
I'm trying to upgrade my 1.4.14 GNUPG to 2.0.26 version and the repository has 1.4.14 version... I tryied removing it and building the lastest version from the official GNUPG website downloading its source code (2.0.26), but I can't do it! it is always 1.4.14! and gpg generates this key:
-----B...
I having trouble asking a question on this site without it sounding off topic. I don't want to clutter the site with more attempts to ask off topic questions. Is this a chat room a place to get advice on getting my question ready or at least find out if it's appropriate for this forum?
I'm looking the data that will give me a number will tell me how much technology has subsidized the average person's life in modern society compared to hunter gather days or agrarian.
That question was off topic, so I need help with it.
@JohnRennie For example, once we had to pick our crops, now we have machines do the picking. Energy and technology has subsidized our lives. I'm guessing the work we once used to do can be quantified. That amount is the subsidization.
@JordanEvans in that case about 99%, possibly 99.9%, of current productivity levels are due to technological developments since our hunter gatherer days.
@BernardMeurer that's the way it is. Logic doesn't apply to these things.
@JordanEvans Work, as measured by the physical unit "Joules", is a rather poor measure of "productivity" or progress. How difficult, time-consuming and relevant a task is is almost completely unrelated to how much physical work you have to do to complete it.
We know rotation period of earth (stellar day) is 86164.098 903 691 seconds of mean solar time.
At 0m time is supposed to be more dilated than at 5000m because of gravitational time dilation.
Then hypothetically we count less nanoseconds at 0m relative to 5000m of altitude.
Then assuming this ...
We know rotation period of earth (stellar day) is 86164.098 903 691 seconds of mean solar time.
At 0m time is supposed to be more dilated than at 5000m because of gravitational time dilation.
Then hypothetically we count less nanoseconds at 0m relative to 5000m of altitude.
Then assuming this ...
The paradox in the twin paradox is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible.
There are a thousand explanations out there for why this doesn't happen, but they all end up saying something vague like it's because one tw...
Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for how it happens.
I'm new here, but recently I have been looking around for things on tachyons and black holes. I understand that because, theoretically, tachyons can travel faster than the speed of light, they would be able to escape a black hole due to them possessing a speed faster than a black hole's escape ve...
@JohnRennie I'm rather sure the professionals understand it perfectly fine. They're just, for some unfathomable reason, fond of acting as if it's all a big mystery.
Same as with the virtual particles/quantum fluctuations schtick - they know better, they just act as if they didn't for reasons I don't understand :P
It's a really well written book. Enough maths to be interesting without so much maths it's impenetrable.
@Copernic An observer chooses a coordinate set, and one of the coordinates is $t$. All observers do this. Everything is then measured using the coordinate time $t$.
@Copernic the point is that an observer at some distance $r$ from the centre of the Earth chooses a time coordinate and in that coordinate system the angular velocity of the Earth has some constant (i.e. independent of depth) value.
An observer at a different height $r'$ does the same and because their $t'$ axis doesn't match the other observer's $t$ axis they measure a different, but still constant, angular velocity.
But I think there is some interest in calculating the four acceleration for corotating points inside the Earth to see what the value of $a^\phi$ is and whether it varies with depth.
Bullshit (also bullcrap in the US) is a common English expletive which may be shortened to the euphemism bull or the initialism BS. In British English, "bollocks" is a comparable expletive. It is mostly a slang profanity term meaning "nonsense", especially as a rebuke in response to communication or actions viewed as deceptive, misleading, disingenuous, unfair or false. As with many expletives, the term can be used as an interjection, or as many other parts of speech, and can carry a wide variety of meanings. A person who communicates nonsense on a given subject may be referred to as a "bullshit...
> Bullshit asymmetry principle > Publicly formulated the first time on January 2013 by Alberto Brandolini, an Italian programmer, the Bullshit Asymmetry Principle (also known as Brandolini's law) states that: > > The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it.