Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

An old theory of quantized gravity is gaining new life

quantamagazine.org

Post reply on HN
Print view View original

61–69 of 69 posts

Re: An old theory of quantized gravity is gaining new life

#61

Post by Florin_Andrei »

ars wrote: post #32
Taniwha wrote: post #28

Earlier quoted context omitted.

Dumb question: how do you exchange gravitons with a black hole?

A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't intera…

> A graviton would have to be both massless and energyless.

However, gravitational waves do carry energy.

Gravitons, whatever they are, must be some very tricky things.

Re: An old theory of quantized gravity is gaining new life

#62

Post by sago »

InternetOfStuff wrote: post #42
jsmthrowaway wrote: post #40

Earlier quoted context omitted.

The weird thing about IPA is that the non-IPA pronunciation you’re replying to seems easier to understand.

Only to you. I feel exactly the opposite way. I wish people would use the IPA instead of their absurd ad-hoc systems. I learned IPA at school, and it has served me well. All the pronunciation systems based on some other language are unreliable and idiosyncratic. And English, with its near-absence of reliable pronunciation/spelling rules, is particularly ill-suited.

The aim is communication. When the aim is very precise communication between knowledgeable parties, a technical language is reasonable. Expecting people to learn that language before they're allowed to have even a basic discussion is a recipe for existing in your own irrelevant bubble.

It is human tendency to think that the things that you know should be known by everyone, and the things you don't know are probably not worth knowing.

On IPA specifically, it can often be overspecified, particularly with regard to vowel sounds and vowel position in the mouth. It isn't clear when a vowel position is determined by accent or by the word, or whether a vowel becoming a shewa is idiomatic. By relating to similar sounding lexemes (or obvious parts thereof), vernacular pronunciation guides have fewer problems in that regard. IPA is easy to learn a little of, but it's a deep deep well to throw people down when all they want is a glass of water.

Re: An old theory of quantized gravity is gaining new life

#63

Post by sago »

gnulinux wrote: post #39
sago wrote: post #27

Earlier quoted context omitted.

Particularly as the pronunciation is strange. Strange place to break syllables, and I'm not sure the second vowel is a 'e' in most pronunciations. /a-sim-TOT-i-klee/

This is how I pronounce it in IPA: /a.sim'to:.ti.kli:/ Why is TOT one syllable?

It isn't. The problem with a vernacular pronunciation guide is that you need to think about ambiguity.

/a-sim-TO-ti-klee/

is a much better syllable break, but /TO/ is likely to be mispronounced /'tu:/. And /TOH/ could be interpreted as /'toʊ/. So /TOT/ splits the difference between syllable break and pronunciation for (imho) maximum clarity.

Re: An old theory of quantized gravity is gaining new life

#64

Post by InternetOfStuff »

sago wrote: post #62
InternetOfStuff wrote: post #42

Earlier quoted context omitted.

Only to you. I feel exactly the opposite way. I wish people would use the IPA instead of their absurd ad-hoc systems. I learned IPA at school, and it has served me well. All the pronunciation systems based on some other language are unreliable and idiosyncratic. And English, with its near-absence of reliable pronunciation/spelling rules, is particularly ill-suited.

The aim is communication. When the aim is very precise communication between knowledgeable parties, a technical language is reasonable. Expecting people to learn that language before they're allowed to have even a basic discussion is a recipe for existing in your own irrelevant bubble. It is human tendency to think that the things that you know should be known by everyone, and the things you don't know are probably n…

> The aim is communication. When the aim is very precise communication between knowledgeable parties, a technical language is reasonable. Expecting people to learn that language before they're allowed to have even a basic discussion is a recipe for existing in your own irrelevant bubble.

> It is human tendency to think that the things that you know should be known by everyone, and the things you don't know are probably not worth knowing.

You're over-interpreting what I said, and being not nice about it by assuming a hostile or superior stance on my part.

I didn't expect anyone to do anything. Parent stated that pseudo-English was better than IPA, and I disagreed. The end.

Re: An old theory of quantized gravity is gaining new life

#65

Post by InternetOfStuff »

freehunter wrote: post #47
InternetOfStuff wrote: post #42

Earlier quoted context omitted.

Only to you. I feel exactly the opposite way. I wish people would use the IPA instead of their absurd ad-hoc systems. I learned IPA at school, and it has served me well. All the pronunciation systems based on some other language are unreliable and idiosyncratic. And English, with its near-absence of reliable pronunciation/spelling rules, is particularly ill-suited.

>I learned IPA at school That's why people use their ad-hoc systems. Because many many many people don't know IPA. It's so far removed from English and uses so many letters that don't occur in English that it's close to being a completely different language. The word "ɪn·tərˈnæʃ·ə·nəl" may make complete sense to someone who knows IPA but to to the many people who don't, it's complete gibberish.

> That's why people use their ad-hoc systems. Because many many many people don't know IPA.

I was disagreeing with parent's claim that ad-hockery was better than IPA. Nothing more, nothing less.

However if ad-hockery is the best someone can do (I say this without snark), then fine. Certainly better than nothing.

> It's so far removed from English and uses so many letters that don't occur in English that it's close to being a completely different language.

English is far removed from my native language, so either way I have to learn a pronunciation system (and the English one is... special).

While we're at it, do we use pseudo-American or pseudo-British pronunciation in our ad-hockery? Pseudo-US-East-coast or pseudo-Southern-US?

I think ad-hockery provides a trap in that it gives a false sense of security. You think you know to pronounce something, but if you actually try, chances are your native speaker conversation partner will go ¿que?

> The word "ɪn·tərˈnæʃ·ə·nəl" may make complete sense to someone who knows IPA but to to the many people who don't, it's complete gibberish.

I agree that it looks like gibberish to those who don't know IPA. But I'm honestly not sure "intaneshenel" (or "intönäschänäl", or whatever) is better. For me at least, it's equally confusing.

As an aside: making up pronounciation if it's of little relevance to what you're writing is one thing. What really grinds my gears is language books (or, say, the language section of guide books) that make up their funny ways of writing pronunciation. They might use that same amount of effort to teach the basics of IPA, which is about the same amount of effort, and provides the reader with something lastingly useful.

They even write multi-page explanations, complete with examples, on how to interpret funny charecters in their script. I remember the absurd contortions the Lonely Planet Germany guide went through to explain umlaut sounds to people in terms of English words, and then coming up with ways that weren't the IPA to type those sounds.

Re: An old theory of quantized gravity is gaining new life

#66

Post by auntienomen »

ars wrote: post #32
Taniwha wrote: post #28

Earlier quoted context omitted.

Dumb question: how do you exchange gravitons with a black hole?

A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't intera…

This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way.

Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity.

Gravitons need to be massless. They need not be zero energy. They can indeed be associated with frequency. They do couple to gravitational backgrounds and to other gravitons. You can crate them just like any other field quanta. The barrier to studying gravitons the way we do photons is that they couple very weakly to other systems.

Re: An old theory of quantized gravity is gaining new life

#67

Post by ars »

auntienomen wrote: post #66
ars wrote: post #32

Earlier quoted context omitted.

A graviton would have to be both massless and energyless. Thus it would be unaffected by gravity. It also means it can not have a "frequency" like light does (because lacking any energy there is no frequency to change). It must also always move at the speed of light, and could not exist at any slower speed. (Because to slow down, would imply a change in its energy, which it can not do.) But that means it can't intera…

This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can inde…

> They need not be zero energy.

How would that work exactly? First of all it means they could not escape a black hole, since they would be carrying energy out of it. It also means they would not travel in straight lines, since by carrying energy, they are subject to gravitational force, and boy of boy what a mess that would make of things if the gravity carrier was affected by its own gravity (or even the gravity of the neighbors).

Second when the graviton "landed" it would have to transfer energy. If they only act via gravity, how would you transfer energy to or from them?

And then if they carry energy, then what, energy is constantly streaming out of every particle in the universe? Or are you proposing two kinds of gravitons, those that carry energy and those that don't?

> They can indeed be associated with frequency.

Really? So how would their measured effects vary as their frequency varied?

Are you confusing gravitational waves with gravitons? The two are not the same.

> You can crate them just like any other field quanta.

No you could not because if you did you would be creating gravitational force out of nothing, which is impossible (violates a whole bunch on conservation laws).

Re: An old theory of quantized gravity is gaining new life

#68

Post by auntienomen »

ars wrote: post #67
auntienomen wrote: post #66

Earlier quoted context omitted.

This comment is almost completely wrong. It muddles together classical and quantum reasoning in any incoherent way. Gravitons are best understood as the quanta of the effective qft governed by the Einstein Hilbert action. This mathematical model is the universal low energy approximation to any quantum theory that reduces to general relativity. Gravitons need to be massless. They need not be zero energy. They can inde…

> They need not be zero energy. How would that work exactly? First of all it means they could not escape a black hole, since they would be carrying energy out of it. It also means they would not travel in straight lines, since by carrying energy, they are subject to gravitational force, and boy of boy what a mess that would make of things if the gravity carrier was affected by its own gravity (or even the gravity of…

You need to learn some quantum field theory. You're trying to reason with a popsci level understanding and failing miserably.

Re: An old theory of quantized gravity is gaining new life

#69

Post by effie »

whatshisface wrote: post #56
effie wrote: post #46

Earlier quoted context omitted.

'Exchange of virtual photons' is a metaphorical expression used to describe artifacts of perturbation theory, it is not necessarily a real process. There is no widely accepted model of what really happens on microscopic scales, we only have equations and those are often replaced by simpler perturbation scheme. So, explanations of attractive force are welcome, Le Sage - type models including.

> There is no widely accepted model of what really happens on microscopic scales, There's no experimental reason to come up with one - virtual photons work, which means anything else is at this point a matter of philosophy. That's not to cast off philosophy, of course.

Virtual photons work in a very limited way (metaphorical language describing perturbation theory). Physics outside of applicability of perturbation QED (bound systems of charged particles, gravity) is not a matter of philosophy.
Post reply on HN