A talk for the WSU Physics Five Slide competition.

1. The Physical Properties of Ghosts
• Same size as a person
• More or less transparent
• Can float in the air
• White glare around the ghost
• Made of ectoplasm *
• Can walk through walls **
* Source: “Ghostbusters”
** Source: “Halloween” episode of
“Buffy the Vampire Slayer”

2. Ectoplasm is Made of Boosons
White glare Mie scattering
8
2 R R /2 8 10 m
So for visible light (λ = 500 nm)
2 14 2
booson cross - section boo
R 2 10 m

3. Ghosts: Optically thick or thin?
On the borderline!
Ectoplasm optical depth for thickness
D = 0.24 m (9.5”)
n boo boo
ds n boo boo
D 1
1 14 3
n boo 2 10 m
D
25 3
Quite rarefied! n air 2 . 6 10 m
Most of a ghost’s body is air, not ectoplasm!
(Like most of our bodies are bacteria, not human cells.)

4. What is the mass of a booson?
How can ghosts float in the air?
Consider a rectangular slab ghost made of ectoplasm
• Height H = 5’9” = 1.75 m
• Width W = 1’6” = 0.46 m
• Depth D = 9.5” = 0.24 m
• Volume V = H x W x D = 0.19 m3
N = Vnboo = 4 x 1013 boosons
in a typical ghost
Consider a ghost of mass M traveling with speed v ≈ 1 m/s
Ghost trapped in an
Infinite square well

5. Ghost Tunnelling and Booson Mass
Require ghost wall thickness  0 .12 m
h h h 33
 M 5 . 5 10 kg
p Mv v
ghost mass M = 5.5 x 10-33 kg
booson mass mboo = M/N = 1.4 x 10-46 kg
(tiny, as expected)
Almost all of a ghost’s mass is air, so it is neutrally
buoyant in air. That’s how ghosts can float in the air!
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.
- Mark Twain in Life on the Mississippi