company valuation and future growth

how do you determine the value of a company?

i asked my friend 

he replied: future growth

my response: 

how do you know how much the company will grow in the future?

who can predict the future?

no one that i know

is it a growth industry?

my response: 

how do you know if something is a growth industry?

can you take market share or invent something new to generate growth?

my response: 

two different things

gaining market share is hard

inventing something people will use or buy is hard

the industry drives the innovation to a degree
does the industry have innovation to offer?
can the innovation make a material difference or just a minor contribution?
my response:
i don't know if industry drives innovation
people innovate, not industry
this is an assumption people will disagree about

in most cases industry have some innovation to offer, most of it minor

iPhones do not grow on trees

neither does innovative thinking

future valuation is based on a lot of optimistic assumptions

technology = scale
future growth depends on technology? sounds reasonable to me