Galactic Unit

Discussion in 'Astronomy, Exobiology, & Cosmology' started by davidelkins, Feb 21, 2017.

  1. DaveC426913 Valued Senior Member

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    Well, I wouldn't have put it as strongly as an accusation, but I thought I was pretty explicit in saying that you've invented a problem just so that you could find a solution.

    Perhaps it might have made more sense to start the thread as: 'Do astronomers, cosmologists and laypeople struggle to find a useful measuring unit for galaxies?'

    To which the answers would have been 'No, and here are several reasons why what we have works just fine...'

    And then we would all agree that there is no problem that needs solving here.

    So, maybe I'll ask you the question:

    Which astronomers, cosmologists or laypeople do you think struggle to find a useful measuring unit for galaxies?
     
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  3. exchemist Valued Senior Member

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    Unlike you, I am here to learn as well as to teach.

    And, unlike you, I am not too proud to acknowledge the limits of my knowledge.
     
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  5. Xelasnave.1947 Valued Senior Member

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    Please lets be nice guys.
    And TG run a thread on an alternative to dark matter in the alternative section and see how we go.
    I would for one like to explore reasonable alternatives.
    Alex
     
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  7. exchemist Valued Senior Member

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    Not usually, I think - unless they are obvious cranks, in which case it is true that my innate irritability sometimes gets the better of me (especially if they promote myths about Einstein or Galileo as scientific outcasts

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    ). Generally I don't comment much on cosmology threads - if you have particular instance you take exception to, I may be able to explain why - or withdraw what I said if it seems on further reflection I was out of order. (But in a separate thread, I think - it would be off-topic here).

    I'm not really that preoccupied with cosmology per se, it was more the simple astronomical issue of the dynamics of galaxies that I was querying. But as it happens I've been taught, thanks to James and Janus, about one of the primary pieces of evidence for the dark matter hypothesis. Apparently.
     
    Last edited: Mar 7, 2017
  8. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    Don't you find that when you buy a large item of furniture that it might not always fit through your door? I therefore propose a new unit of measurement: the Door Unit. With this new unit we can more quickly establish whether the object will fit through the door. An object of 0.1 DU will clearly fit, whereas something of 1.1 might appear that it will... but won't.
    It'll only be an approximation, of course, a "convenient yardstick", but just as convenient as the AU, surely?

    Yes, yes, I know you can just as easily measure the height, width, length etc using the far more precise "centimetre" and compare it to the actual size of your door, but wouldn't being sold an item in terms of DU be so much more convenient?
     
  9. Sarkus Hippomonstrosesquippedalo phobe Valued Senior Member

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    This doesn't follow. I can try to coin the phrase "doughnut mug", being a mug not only made in the shape of a doughnut but actually made out of doughnut.
    Woohoo! What a great idea!
    Trying to coin a phrase = Trying to come up with a good idea? Nah.
     
  10. Kristoffer Giant Hyrax Valued Senior Member

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    I use the centiKris system.

    1 Kris = 1.85m so a centiKris is 1.85cm.

    // Edit: I think Sarkus' and your criticism of the OP may have been too subtle. -- The Mod
     
    Last edited by a moderator: Mar 8, 2017
  11. The God Valued Senior Member

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    3,546
    Fair enough.
     
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  12. exchemist Valued Senior Member

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    The God and I have just had a very civil exchange. Please don't spoil the magic!

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  13. exchemist Valued Senior Member

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    My comment was meant in all sincerity, hence the smiley. I am pleased that we were able to have a civil exchange. It would be nice if this could continue.

    As for ignorance, it is to be despised when the ignorant person fails to acknowledge it and will not learn. I try to learn from these exchanges, because I am interested in science. I have learnt a huge amount in my time on this forum - and have been forced to recapitulate a lot of what I know, or used to know when I was at university, which is also very satisfying.

    I try not to claim knowledge when I do not have it: you will find me more assertive on matters of chemistry, physics and (bits of) geology than on astronomy, biology or cosmology.

    But enough about me: this is getting seriously off-topic, is it not?
     
  14. origin Trump is the best argument against a democracy. Valued Senior Member

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    By all means, excuse the intrusion.

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  15. DaveC426913 Valued Senior Member

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    The last seven posts - all today - are due to your initial trolling.

    I may disagree with David Elkins' premise, but I have enough respect from him to not derail his thread with utterly off-topic trolling.

    Try to show at least a scrap of respect for the OP.

    Back on topic now.
     
  16. DaveC426913 Valued Senior Member

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    Criticism is contribution. You haven't made a single on-topic post, troll. Show some respect.

    Reporting for Moderators to clean up all the troll poop.
     
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  17. rpenner Fully Wired Staff Member

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    First show the value, then make sure it generalizes well, then establish the scale. There's more than one galaxy or even type of galaxy.

    Your specious introduction of a new unit of distance seems ignorant of the science of measuring stuff, metrology. The current distance to the Galactic center is estimated with a relative error of 17700 parts per million (which is considered a lot in every field except astronomy and cosmology and experimental determination of Newton's constant) and has no known application to theoretical studies and no methodology for practical studies, while AU, parsec and the (deprecated) light-year have exact definitions which serve actual needs at the bottom end of a calibrated distance scale of cosmology. Ignorance is not a crime, but embrace of the tactics of deflection and ad hominem attack on criticism are considered such in scientific circles.
    https://en.wikipedia.org/wiki/Metrology
    https://www.nist.gov/pml/weights-and-measures/fundamentals-metrology
    http://www.jsmyung.com/Library/Metrology.pdf
    http://pdg.lbl.gov/2016/reviews/rpp2016-rev-astrophysical-constants.pdf
    http://www.astro.ucla.edu/~wright/distance.htm

    Perhaps, but to use it to dismiss a post, rooted in observation, is an ad hominem fallacy.
    This seems like a moot point since noone uses AU for stating interstellar or cosmological distances except in exercises about the definition of parsec.
    Since alternative ideas are strictly frowned upon in the hard science subforums, can you derail a sterile thread topic?
    Discussion of neither was in the OP so it follows that exchemist's post was not uniquely derailing. In fact, while details of dark matter distribution matter little to the fact that a non-point-like mass distribution lead to non-Keplerian relations between distance and speed, the details of the individual galaxy rotation curves would seem to be precisely the type of information davidelkins would need to summarize to give a basis to his intragalactic yardstick.
    First you need a good idea, then a name. Guess who has the burden of demonstrating it's a good idea.
    Criticism, even from students, is NECESSARY in science and teaching in general.

    It is STRONGLY recommended that The God not respond to this post without full consideration of the latest PM.
     
    Last edited: Mar 8, 2017
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  18. The God Valued Senior Member

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    I like your intervention, but expect and hope that you guys (mods) act sooner before it becomes a full blown case.

    I may have a small or big problem, I just cannot tolerate presumptuous posters who are basically ignorant but act as expert. You know them and still you let them post, thats the key issue here. As long as I am here, I may continue to pin point such behavior.

    Did you notice the damage caused by these piranhas? Schmelzer is gone, qreeus has become irregular, you also post very infrequently. Where is the quality discussion? Look hard, my behavior may not have been clear but I feel for this site and expose such posters and in the process you know what I get...marks...banishment score! Wow!!

    I probably scored highest mark against Paddoboy, you know how he bahaved when you took him on. He was at least enthusiastic, he had a desire to learn, he used to do home work. Can you say such positive things about few more resident derailers here? See the bigger picture, dont let them kill this site with catchy one liners. May be you can refer the dictionary meaning of forum piranhas and see who all fit. Expunge them from science section.
     
  19. exchemist Valued Senior Member

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    6,464
    Actually I don't the picture is as black as you paint it. Schmelzer posted 30mins ago and Q-reeus is still very much in evidence (we had another go at zero-point energy only last week). rpenner seems to me to intervene only when something is going badly off track, as he has always done. We've lost Paddo, true, but then he was a mixed blessing, always pursuing vendettas.
     

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