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Landmarks

Fermi Questions Knowledge you can work with...

[A first, crufty draft.]

You build a landmark by making some value memorable. [...incomplete description...]
Another approach is to develop a `hands-on feel' by Scaling the universe to your desktop.

Why create landmarks? To have stepping-stones for thought.
For thought and imagination to move easily, one needs handholds, markers. Bits of easily accessible knowledge scattered across the landscape. Making its shape visible, and providing places to stand.

Why remember landmarks when we have them in books? To carry them with us.
Books can be a source of landmarks, and a place to keep landmarks you don't often use. Also a place to keep more detailed versions of the landmarks you carry around. But when something would be useful, it doesn't help much to know just where you left it, forgotten at home. Either it is ready at hand, or you need to use something else.

Over time we change what we carry with us. Choose knowledge which helps with our interests and current questions about the world (including fermi questions).

The choice of landmarks is often a personal one. Some values are recognized and remembered by many. But many others, like your street corner, or a friend's name, are mainly your own.

A good place to start is with things you are familiar with.
You can use them for comparisons. And some, to measure with. Knowing how big something is, you can get a feel for other things you learn about. If you know the area of, say your parking lot, then you can picture surviving on a 10-acre farm. Or [...]

• How big is big?
  What is the size and volume of your room?
  Of your home? School? Of some local large building? A parking lot?
  How heavy is something you handle each day? (Like your sneakers.)
  
• You can use your body as a ruler.
  How big is your arm, from elbow to finger-tip? That's you personal "cubit", and you can then measure things with your arm.
  How long is your foot? That's your personal "foot", and you can then measure things by slowly walking by them.
  How long is your walking step? [...]
  

Links

Some various landmarks...

Human population	ever 1011 1011, ±×2 Earth 6 billion 6 × 109, +4%, ±1%? US 250 million 2.5 × 108, -6%, ±1%? city 107 big, 106 mid, 105 small
Sphere's area volume	"1/2 that of the box it came in" -5%, ±<1%
pi	3 -5%, ±<1% 3.14 ±<0.1%

History:
 2003-Feb-03   Repaired links - 2 fixed, 1 left (cmu).
 2002-Apr-11   Changed a link (evacuating www.tiac.net).
 1997.Aug.01 - Format upgrade.  Content basically unchanged, still crufty.
 1997.Jun.28 - Upgraded notes into a first draft.

Mumble mumble mumble... [visible_universe page was under construction]
Visible universe: 10¹⁸ s old, 10^~26 m, 10^~50 kg
Universe's galaxies: 10^~11, 10^~49 kg
Milky Way: 10⁴² kg
Speed of light in vacuum (c): 3 × 10⁸ m/s
[should add error, non-vacuum]