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DOC.

25

SOLVAY

DISCUSSION REMARKS

earlier

analysis

and in

contrast to Einstein,

Planck

applied

the

quantum hypothesis as

well

as

statistical methods

only

to matter

that

interacts with radiation and

not

directly

to

radiation itself. In

the

discussion this

controversial

point

was

first taken

up by Jeans,

and

subsequently

commented

upon by

Einstein in his second

remark,

referring

to

Lorentz's

analysis

of radiation

(Lorentz 1912).

In his

lecture,

Planck also

presented

his

second attempt

at a theory explaining

the

black-body

radiation formula

(for a

historical

discussion, see

Kuhn

1978, pp. 235ff). According

to

Planck's "second

theory,"

the

quantum hypothesis plays a

role

only

for

the

emission of

radiation,

while Maxwell's

equations

are supposed

to

be valid for

absorption as

well

as

for radiation

in matter-free

space.

In his last remark

during

the

discussion,

Einstein

argues

that it

is

not

possible

to

introduce

any

form of the

quantum hypothesis

for

the

emission

by an oscillator,

but

he

upholds

classical

electrodynamics

in

the

space surrounding

it. His reference

to

Planck's

original theory

is

probably a

reference

to Planck's

attempts

at

an analysis

of

black-body

radiation

prior

to

the

introduction

of

the

quantum hypothesis

(see

Planck

1900a).

No.

51

(Planck

et al.

1914,

p. 95;

Planck

et al.

1912,

p.

115)

1)

What

I find

strange

about the

way

Mr.

Planck

applies

Boltzmann's

equation is

that he introduces

a

state

probability

W without

giving

this

quantity

a physical

definition.

If

one

proceeds

in such

a way,

then,

to

begin with,

Boltzmann's

equation

does not have

any

physical meaning.

The circumstance that

W

is equated

to

the number of

complexions

belonging

to

a

state

does

not

change anything

here;

for there

is

no

indication of

what

is supposed

to

be

meant

by

the

statement

that

two

complexions are

equally

probable.

Even

if it

were possible

to

define the

complexions

in such

a

manner

that the

S

obtained from Boltzmann's

equation

agrees

with

experience,

it

seems

to

me

that

with this

conception

of Boltzmann's

principle

it

is

not

possible

to draw

any

conclusions

about the

admissibility

of

any

fundamental

theory

whatsoever

on

the

basis

of the

empirically

known

thermodynamic properties

of

a

system.

No.[53] (Planck

et al.

1914a,

p. 98;

Planck

et al.

1912,

p. 119)

2)

Objections

have

often been raised

against

the

application

of

statistical

methods

to

radiation. But

I do not

see any reason why

these methods should be

excluded

here

(cf.

Lorentz's

report, §6-§13).

3)

Omit!

No.

100

(Planck

et al. 1914a,

p.

106;

Planck

et al. 1912,

p. 129)

4)

If

an

oscillator

is

to emit

radiation in

a manner

different

from

that assumed

in Mr.

Planck's

original theory,

then

this

means a

renunciation of the

validity

of

Maxwell's

equations

in the

vicinity

of the

oscillator.

For

according

to Maxwell's

equations,

the

quasi-static

field

of

the

oscillating

dipole

necessarily

results in

the release of

energy

in

the

form of

spherical waves.