354 DOC.

364

JULY

1917

of

1914

about

Friedrich Adler’s

idea,

to

which he himself attached

such

great

significance.

The

former did

not

find it

noteworthy,

and

so

I

did not

concern

myself

with it

further.

I

am

not

a physicist,

rather

a

philosopher,

but

frequently

study

physical

problems. Upon

discussing

this

with Professor

Frank,

he

now con-

firmed to

me

that

my proposal

of

that

time

coincides with Adler’s

idea,

which

I

am

familiar with

only

through

newpaper reports; yet,

he

continues

as

before not

to consider

the

matter worth

notice.[2] I

would

like

to

present

in

the

following

my

current

conception

of

that

idea,

which

I

have

now

taken

up again

and

which

in

my

view contradicts

neither

the

special

nor

the

general principle

of

relativity,

since different issues

are

involved here. The

principle

of

relativity is

concerned

with the

formulation of

differential equations

through

which the natural

laws

are

expressed;

the latter

observations of

mine,

on

the

other

hand,

concern

the

description

of real

processes

in

nature.

In

describing

these

processes

with the

given

constants,

obviously

not

all

possible systems are equally suited;

certain

ones

portray

the

phenomena

more simply.

The

general principle

of

relativity,

in

particular,

compels

us

to

give

due consideration

to

this

drawback in

general

relativity

as

well.

Although

the

general principle

of

relativity

allows

the

depic-

tion of the

phenomena

in

the

Ptolemaic

system

as well,

there

is

no

doubt that

despite

the

general

covariance of

the

differential

equations,

the

real

phenomena,

which

are

described

by doubly

integrated

equations,

are

presented

more

simply

in the

Copernican system

than

in

a

system

in

which

the

geometry

deviates

so

enormously

from

the

Euclidean and in which

the

light

ray

of

a

star

comes

to

us

along

a

spiral

path

that

revolves

around the Earth

in

24

hours.[3]

I

often

try to

imagine

as

intuitively

as

possible

the Ptolemaic

system according

to

the

general

theory

of

relativity,

with all

the

peculiarities

that

result from it.

How

ought

one

to

imagine a

world

system

in

which

a

billiard

ball, brought

into

rotation

through

an

eccentrical

stroke,

is

viewed

as

at

rest? In

general,

it

can

be said

(if

all

sys-

tems, moving uniformly

and in

a

straight

line with reference

to

one

another,

are

initially regarded

as one

system)

that the

phenomena

are

most

simply

described

in

a

system

whose

geometry

is most

nearly

Euclidean. After

having

chosen

the

three

spatial

axes

in accordance with these

aspects,

we

must

now

determine

the

time

axis,

that

is,

the

spatial

coordinate

system’s

state of motion.

First

of

all,

concerning

the

relative rotation, could

the

most

simple system

not

be defined

by

having

its total

angular

momentum

equal

to zero? If

we

place

the coordinate

system’s origin

at

the Earth’s

center,

this would most

closely

approximate

the

Copernican

system

(with an

infinitesimal rotation

of

this

system).

This

system

would

probably

also be

one

in which Foucault’s

pendulum

is

at rest.

I

state these

considerations

only

with

reservations,

since

I cannot

judge

whether,

after

more

precise calculation,

they

can

still be

seen

as

correct.

Concerning

its

rotation,

the