376

THE

RADIATION

PROBLEM

Doc. 57

ON

THE

PRESENT

STATUS OF THE

RADIATION

PROBLEM

by

W.

Ritz

and

A.

Einstein

[Physikalische

Zeitschrift

10

(1909):

323-324]

[1]

To

clarify

the

differences

of

opinion

that

came

to

light

in

our

respective publications1,

we

note

the

following.

In the special

cases

in which

an

electromagnetic

process

remains

restricted

to

a

finite

space,

the

process

can

be

represented in

the

form

f

=

f

1

=

1

x',

y',

z',

t

- -

dx'

dy'

dz'

as

well

as

in

the

form

f

=

f2

1

x'

y' z'

,t

+

-c

dx'

dy' dz'

and

in

other forms.

While

Einstein believes

that

one

could restrict oneself

to

this

case

without substantially

limiting

the

generality of

the consideration, Ritz

considers this restriction

not

to

be permissible

in

principle.

If

one

takes

this

standpoint,

then

experience

compels one

to

consider the

representation

by

means

of

retarded

potentials

as

the

only

one

possible,

if

one

is inclined

to

the

view

that the fact

of

irreversibility

of

radiation

processes must already

find its

expression

in the

fundamental

equations.

Ritz considers the restric-

tion

to

the

form

of retarded potentials

as

one

of

the

roots

of the

second law,

while

Einstein believes

that

irreversibility is

exclusively

due

to

reasons

of

[3] probability.

Zurich,

April

1909.

(Received

on

13

April

1909)

[2]

1W.

Ritz,

Phys.

Zeit.

9

(1908): 903-907,

and

A.

Einstein,

Phys.

Zeit.

10

(1909):

185-193.