DOC.

319

MARCH

1917 311

319. To Felix Klein

[Berlin,]

26

March

1917

Esteemed

Colleague,

Many

thanks

for

your

papers

and

your friendly

card.[1]

It

is

really astonishing

that

such different

points

of

departure

as

mathematics

and

physics

give

occasion

to

establishing

the

same

thought

structures in

the

end.

I

have

already

read

with

pleasure

the

marked

places

in

your papers;

the

other

will

follow.

As

I

have

never

done non-Euclidean

geometry,

the

more

obvious

elliptic

geometry

had

escaped

me

when

I

was

writing my

last

paper.[2]

Mr.

Freundlich has

already

made

me

aware

of

this

point.[3]

My

observations

are

just

altered

thus,

that

the

space

is

half

as

large;

the

relation between

R

(radius

of

curvature)

and

p (mean density

of

matter) is

retained.

The

new

version of

the

theory means, formally,

a

complication

of

the

foun-

dations

and

will probably

be looked

upon by

almost all

our

colleagues

as an

interesting, though

mischievous and

superfluous

stunt, particularly

since

it

is

un-

likely

that

empirical

support will

be

obtainable

in

the

foreseeable future.

But

I

see

the

matter

as a

necessary addition,

without

which

neither inertia

nor

the

geometry

are

truly

relative.

But

someone

who does

not

find it

disturbing

when

the

existence

of

a

guv-field

can

result from

the

theory

without

field-producing

matter and

when

a single mass (imagined as being

alone in

the

universe) can

have

inertia, cannot

be convinced

of

the

new

step’s

necessity.[4]

I

am

very

much

looking

forward to

seeing Debye

in

the

next

few

days

and

ask

you please

to

inform

me

when

you

are

coming

to Berlin

again

so

that

I

can

visit

you.

It

would

certainly

be desirable

if

between

Göttingen

and

Leyden

there

were

an

exchange

of

papers addressing

the

area

of

general relativity.

In

that

way,

much

intellectual

effort would be

spared.

For

ex.,

a

precise

treatment of

the

point

problem,

as

Hilbert

provides

in his

last

article,[5]

already

exists in

the dissertation

by

the Dutchman

Droste.[6]

Furthermore,

Lorentz has worked

on

many

things.[7]

With

kind

regards, yours truly,

A.

Einstein.

Document

description:

“Einstein

to

Klein.

To

Messrs.

Baade

and

Fréedericksz for

your

o[bliging]

perusal

and

return

on

Saturday.

K[lein].”