EINSTEIN ON

GRAVITATION

AND

RELATIVITY:

THE

COLLABORATION

WITH

MARCEL GROSSMANN

I

Einstein's collaboration

with

Marcel

Grossmann,[1]

which

probably began

in late

sum-

mer

1912

after Einstein's

return

from

Prague

to Zurich, led to two

joint papers:

Ein-

stein and Grossmann

1913

(Doc.

13)

and Einstein and Grossmann 1914b

(Vol. 6,

Doc.

2).

The

first

of these

was

published

before

the

end of June

1913,

the

second

almost

a

year

later, two

months after Einstein's

move

to

Berlin.

The

first

paper

is

modestly

entitled "Entwurf einer

verallgemeinerten

Relativitäts-

theorie und einer Theorie der Gravitation"

("Outline

[or Preliminary Version]

of

a

Generalized

Theory

of

Relativity

and of

a

Theory

of

Gravitation"),

but

it

actually

contains the

first

comprehensive theory

of

gravitation

that

according

to

Einstein also

generalized

the

principle

of

relativity

of classical mechanics

and

of Einstein's

paper

on

the

electrodynamics

of

moving

bodies,

Einstein 1905r

(Vol. 2,

Doc.

23).

Although

the "Entwurf"

theory

of Einstein and Grossmann later turned

out to

be

untenable, it

has

important

characteristics

in

common

with the

final

version of Einstein's

general

theory

of

relativity, published

more

than

two

years

later:[2]

The

gravitational

field is

represented

by a

metrical

tensor; the

mathematical

apparatus

of the

theory

is

based

on

the work of

Riemann, Christoffel, Ricci,

and Levi-Civita

on

differential

covariants;

and the action of

gravity on

other

physical processes

is

represented

by

generally

covar-

iant

equations.

The

major

difference

is

that

the

equations determining

the

gravitational

field in

the "Entwurf"

theory

are

not

generally

covariant.

The restricted covariance of the

theory posed

some

intricate

problems.

At

first it

was

only

certain that the

field

equations

were

covariant for linear coordinate

trans-

formations;

whether

any

other transformations,

for instance

to

accelerated frames of

reference,

were

allowed

was

unknown. Thus Einstein felt unable

to

announce

that the

theory incorporated

a

true

generalization

of the

principle

of

relativity

for uniform

motions.

Initially

Einstein

perceived

this feature

as

a major flaw,

but later

on

he found

two

arguments

that seemed

to

justify

the restricted covariance

and

even

suggested

that

a

meaningful generally

covariant

field

theory

of

gravitation

would be

physically

unac-

ceptable.[3]

In the

spring

of

1914

the

matter

seemed

to be

further clarified when Ein-

stein claimed that certain accelerated

frames of reference exist

in

which the

gravita-

tional

field

equations

of

the "Entwurf"

theory are

valid.[4]

This claim

was published

in

Einstein and Grossmann 1914b.

[1]Marcel Grossmann

(1878-1936) was

Professor of Mathematics

at

the ETH and

a

friend

of Einstein's since their student

days.

See Vol.

1,

Biography,

pp.

381-382.

[2]See

Einstein

1915e.

[3]For

a more

detailed

discussion of these

arguments

and of their

validity,

see sec.

III

below.

[4]See

Einstein

to

Michele

Besso,

ca.

10

March

1914

(Vol. 5,

Doc.

514).