These are the most frequently used words in this book.
appear
atoms
away
bang
beginning
between
big
black
body
boundary
called
cannot
case
collapse
different
direction
distance
does
down
early
earth
effect
electrons
end
energy
even
event
expanding
expansion
fact
fig
first
force
form
galaxies
general
get
gravitational
gravity
histories
hole
however
idea
increase
know
large
laws
light
mass
matter
may
means
might
million
model
moving
must
new
now
number
observer
orbits
particles
past
point
position
possible
principle
quantum
quarks
rate
rather
real
regions
relativity
science
second
see
seems
set
should
singularity
small
space
speed
star
state
still
string
sun
theory
therefore
thousand
thus
time
travel
two
universe
waves
years