@0celo7 Ah, those are the two point correlation functions of the power spectrum that help define the comoving curvature perturbation. You have to read the corresponding part of the main body, otherwise it'll make no sense
@0celo7 Define lose information. If you're asking if global functions on the sphere are more constrained than global functions on the complex plane, then yes.
I'm ashamed to admit it, but I don't think I've ever been able to genuinely motivate the definition of a topological space in an undergraduate course. Clearly, the definition distills the essence of many examples, but it's never been obvious to me how it came about, compared, for example, to the ...
@0celo7 Compact means that every cover has a finite subcover. The plane is not compact because the cover of successively larger disks centered at the origin has no finite subcover
@glance you asked me if I saw your last proof. Just now I looked again. But, you prove an anti-commutation rule in base of another anti-commutation rule. I repeat, it's not what the user needs. Not in whatever calculi he/she will have to do in the future, he/she will stay to check if there is some anti-commutator offended. This is why he/she wanted to know where is something wrong in his calculus, without altering with starting from vacuum. So, I repeat, Mark gave the solution.
@ACuriousMind He was French though, always lived there and finally acquired the nationality after waiting for a long time (he was nationless for many years)
@ACuriousMind where you wander? Do you want a minus from me (which I would dislike). Why do you post an answer without reading the question? The question was in essence how can the e.m. waves travel without a supporting medium, i.e. which are the carriers. Stop wandering in 50 places at once.
@Sofia EM waves have no carriers. Waves don't need carriers. They are solutions to a wave equation, nothing else, I stand by what I have written.
To ask "how can they travel without a medium" is to commit the fallacy of the aether. They can travel without a carrier because there is no reason they should need one.
@ACuriousMind what you say? Water waves have carriers the molecules of water. The energy is transmitted from molecule to molecule. Did you ever hear sound waves in vacuum?
I am not actually a friend of lies-for-children. I hate them with a passion, and I believe it is better to tell someone something they do not understand than to tell them something which will later turn out to be nonsense or false.
@Sofia I want to answer the question correctly. And the answer to the question "Why are EM waves called waves?" is *"Because they are solutions to a wave equation". The other stuff is all based on widely spread misconceptions, and I will not perpetuate them.
@Sofia: Are you saying I should accept your position that my approach to answering "beginner's questions", as you call them, is wrong/bad because you are olden than me?
@Sofia That doesn't mean he doesn't explain things to children. Just that he doesn't simplify to the point of telling them things that are wrong. A risky strategy but maybe it works for him
@ACuriousMind Pleeease! Never feel offended by my words. I am just saying that you do your best, give an answer, and the answer may pass by them with no help for them.
@Sofia Not true, he could volunteer as a social worker, a teacher, or some other kind of people-oriented duty in his spare time. It's entirely possible he could have more experience than every one of us in dealing with children
@0celo7 Hah, with "harsh" answers I mean those that simply retreat to definitions and facts without trying to be "intuitive". I don't tell stories, mostly.
@JimdalftheGrey , @ACuriousMind I saw once a movie (Ingrid Bergman, Liv Ulmann) if I recall correctly "The autumn sonata" (I am not sure). Bottom line, the daughter was coming with heavy accusations to her mother, e.g. "you gave me to read books that I didn't understand".
I'm playing Devil's advocate. You've been making assumptions that aren't supported by available evidence. I'm just trying to point out how what you propose may not be the case. Not that it actually isn't the case
@Sofia "You gave me books I did not understand" is not an accusation in my world. The realisation that there are many things I do not understand is very important
@ACuriousMind I recall that someone told you "you are telling me that I am an idiot", and you replied "I should have been more compassionate". But again, we just talk, nobody should accept someone else's approach if the former doesn't subscribe to it.
@ACuriousMind beware! Could it be that you heard of the (beautiful) movie "La beaute du diable?" (with Gerard Philippe). A daemon, or a devil, or whatever such thing, may be angelically beautiful.
In modern physics, a quantity is said to behave like a wave if it satisfies a wave equation. With some quick googling, it is quite simple to find out in what context the wave equation was first derived and applied (e.g. here).
Furthermore, it is known that throughout the 18th and 19th century, ...
@Sofia My profile picture is a figure from a setting called Dungeons&Dragons, where all sorts of mystical creatures are real. In that universe, there are various creatures form worlds that are like hell, and they are the demons and devils. The devils are the rule-following sort, while the demons are rather free spirits
My profile picture is a creature from a demon world, hence my saying: "I'm a demon, not a devil"
It really gets even less funny when I explain it :D
@ACuriousMind I wonder, do you do other things too than physics? Do you go to parties with friends, to movies, theatre, concertos, opera? (If you find my question too intrusive I withdraw it).
What is a tachyon? Most physicists think that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. Are they right?
In modern physics, a quantity is said to behave like a wave if it satisfies a wave equation. With some quick googling, it is quite simple to find out in what context the wave equation was first derived and applied (e.g. here).
Furthermore, it is known that throughout the 18th and 19th century, ...
What is a tachyon? Most physicists think that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. Are they right?
