Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
    Re: An Embarrassing Conundrum
    From: Frank Reed
    Date: 2018 Oct 6, 11:01 -0700

    David, you wrote:
    "What had I forgotten from my school geometry, and what fraction of the 28mm Neptune should I have taken to make a 14mm Neptune?"

    Only one-eighth of the original. And it really is hard to believe, for anyone, until you start messing around with lumps of clay. Geometry is surprising for our monkey brains. 

    But we can make our little, linear primate brains happier if we switch to general relativity instead of clay (not often you get to say that!). If you take two black holes, each a mile across, and you merge them (ignoring radiative losses), you will get a black hole that is two miles across. And if you take that two-mile black hole and merge a one-mile black hole with it, you get a three-mile black hole. And so it goes... If you have a million-mile wide black hole at the center of a galaxy and add a one-mile wide black hole to it, the resulting black hole adds one mile to its diameter. Isn't that nice!

    Nice? Well, up to a point. This is why you should be careful about tossing little black holes into big black holes -- the volume of space within event horizons (inside black holes) increases far more rapidly than the rate for fixed-density objects. If you're not careful, you can end up with your whole galactic neighborhood inside a black hole. 

    Frank Reed

    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site