Talk:Gravitational wave/Archive 2

message: In the sentence "Roughly speaking, they will oscillate in a cruciform manner, orthogonal to the direction of motion. First, east-west separated particles draw together while north-south separated particles draw apart, after which east-west separated particles draw apart while north-south separated particles draw together, and so forth." - what direction does "orthogonal" mean? The images are nice but does the radiation come from the viewpoint of the reader or from left/right/north/south? I think you better need an image in 3D. -- Nichtich 23:48, 3 November 2006 (UTC)
replies: text: In the pictures, the wave is passing directly through the screen, either from behind or in front.  We should try to make this clearer in the rewrite.  I would welcome 3D versions of these pictures, if they didn't complicate things beyond understanding, but I'm not going to spend my time on it.  --MOBle 01:08, 5 November 2006 (UTC)
thread_title:  Which Direction 

message: "Massless" must refer to infitesimal mass rather than no mass since E=M*c^2. Adaptron 11:44, 4 November 2006 (UTC)
replies: text: Well, we don't really have any firm theory for the graviton, but we might by looking at linearized general relativity.  If we assume that it travels at the speed of light (which we linearized gravity says it would), then the formula E=M*c^2 wouldn't apply, just as it doesn't apply to the photon.  --MOBle 00:37, 5 November 2006 (UTC)
thread_title:  massless particle waves 

message: It might be useful to explain the different types (not polarizations) of sources in terms of the different "sounds" their grav. waves would make.  Because grav. waves have an amplitude and frequency, just like sound waves, we can consider what they would sound like if the amplitude were high enough.  (The difference in speeds doesn't really matter.)  If the wave's amplitude were high enough, the output of LIGO could be plugged into a speaker and we could literally hear it.  In fact, in the LIGO control room a speaker that actually is hooked up to the output (though not actually in the expectation that a signal will be heard).
For example, a spinning neutron star -- like what Einstein@Home is looking for -- would have the sound of a pure tone.  It might be nice to play the tone expected from the pulsar in the Crab Nebula, for example.  Merging binaries, however, would have totally different sounds, where the pitch increases to some maximum, and then there's a brief pop, and it's all over.  The difference might be illuminating.
I think this might fit nicely into the article, with a little blurb about comparing grav. waves with sound waves just after the bullet points about amplitude, frequency, etc.  I've put in some commented text about this.  That could then tie into some follow up in the section about sources, where we could link sound files next to the relevant source.
I can make something like the sounds on this page in OGG format, if this would be helpful enough to be worth the trouble.  --MOBle 09:10, 13 November 2006 (UTC)
replies: text: This sounds like a great idea. Unfortunately there's something wrong with my audio and I don't know what the sounds sound like. But I'm sure they sound great. Laymen will love it. Lucretius 09:46, 13 November 2006 (UTC)

text: The intro is crystal clear, excites interest and needs no input from me. I found a split infinitive ('to directly measure') which I corrected by a simple expedient (I deleted 'directly'). Split infinitives are being used more frequently these days, even by quite respectable news agencies, but they are inelegant and just plain wrong. I speak as a school teacher. [:}] Lucretius 10:01, 13 November 2006 (UTC)
thread_title: Sounds

message: :Add any additional comments:
Hi Moble. Do you mean you intend moving sections of the article that deal with waves to a new article 'Gravitational Waves'? If so, yes this would make sense to me. Lucretius 08:04, 20 November 2006 (UTC)
replies: text: Hey Lucretius.  No, I've requested that an admin move the whole thing to "gravitational wave", just so the title is really the main content of the article, and there are fewer redirects.  The "radiation" name refers to energy carried by the waves (in some sources, also to the momentum and angular momentum), whereas the article is clearly mostly about the waves themselves.  This is just some cleanup.  The request is found on this page.  --MOBle 16:04, 20 November 2006 (UTC)

text: The above discussion is preserved as an archive of the debate.  Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.</div>
Thanks for the support, Lucretius.  It was a minor detail, but I think it's good to keep things like that tidy.  --MOBle 19:32, 25 November 2006 (UTC)
thread_title: Discussion

message: Hey Lucretius (and anyone else who's watching).  I've made a bunch of (unfortunately sloppy) changes to the article.  I may have screwed up some formatting (losing em dashes, for instance), and there's a lot more yet to be done.  Overall, though, I think my changes were worthwhile, and have helped us along.  Let me know what you think.  Sorry for any screw-ups.  --MOBle 19:32, 25 November 2006 (UTC)
replies: text: I haven't noticed anything amiss. The point brought up by the other bloke - that g waves cannot be detected locally - and your response - that there has been debate within the scientific community about the existence or detectability of g waves - are news to me. The article should certainly find room for some mention of any such debate, preferably early in the article. I have to admit I don't understand the relevance of Lorentz contractions in the measurement of g waves, nor do I understand in what sense the detectors are assumed to be in freefall. In fact, I assumed this was all specious piffle. Lucretius 12:48, 26 November 2006 (UTC)
replies: text: They're not in free-fall, and Lorentz contractions aren't particularly relevant.  The debate about measurability was in different terms and decades ago, when nobody had really done any analysis.  Specious piffle.  But, I think it's good to point people to the appropriate sources, rather than getting in a debate that probably won't go anywhere.  --MOBle 19:11, 26 November 2006 (UTC)
thread_title: Recent edits

message: Hi Moble! There is a comprehensive list of resources (journal papers, books, websites etc) here . I've now added this to the reference section at the end. I've also added an internal link to Hawking radiation, which has a kind of tangential relevance to grav radiation. Lucretius 11:37, 17 December 2006 (UTC)
replies: text: Nice references.  I didn't know Resource Letters existed.  That's handy.  --MOBle 03:53, 19 December 2006 (UTC)
thread_title:  Resources 

message: Hi Moble. Here is a suggested change to the section 'Power radiated by the Earth-Sun system'. At present, the section sources radiated energy in kinetic energy. I think it could be more coherently sourced in angular momentum. Thus:
'The energy radiated by the Earth-Sun system can be understood to come from angular momentum. Angular momentum is radiated away by gravitational waves according to a formula that is similar to the one above for radiated energy:
:\frac{dL} {dT}=-\frac{32} {\pi}\sqrt{\frac{G (M+m)} {R^3}} \frac{G^3 (Mm)^2} {c^5 R^2}
where the square root factor is the angular velocity of a simple Keplerian system. Angular velocity has the dimension 1/time and here it can be interpreted as the frequency with which angular momentum is radiated. Since angular momentum per unit of time can also be understood to have the dimension energy, the square of the angular velocity returns us to the previous formula for radiated energy or energy per unit of time.
The angular momentum of the Earth-Sun system decreases with decreases in R. The radiated angular momentum however increases. In theory, this loss of angular momentum through radiation should cause the Earth to spiral into the Sun. However, the present angular momentum of the system is approximately 1039 kg.m2/s, whereas the angular momentum radiated over about a year is approximately 1013 kg.m2/s - at this rate, the Sun would use up its supply of fuel long before the Earth could spiral into it. Lucretius 09:28, 4 January 2007 (UTC)
thread_title:  Radiated Power 

message: Someone added 'This is incorrect' in a couple of places in the article. If that someone knows better than others, he/she should justify the changes here, rather than use the article itself to assert superior knowledge. I am assuming from the nature of the 'edit' that that person doesn't even know much about good manners let alone anything about physics. If you haven't learned good manners, you haven't learned anything. Lucretius 08:30, 21 March 2007 (UTC)
thread_title:  Vandal's edits