R ENDICONTI
del
S EMINARIO M ATEMATICO
della
U NIVERSITÀ DI P ADOVA
V ÁCLAV H LAVATÝ
Report on the recent Einstein unified field theory
Rendiconti del Seminario Matematico della Università di Padova, tome 23 (1954), p. 316-332
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EINSTEIN UNIFIED FIELD THEORY 1)
Memoria
(*)
di VÁCLAVHLAVATÝ
(aBloomington, Indiana)
This short paper is a summary of some main results
( without proofs)
which I obtained intrying
to find aphy-
sical
interpretation
of the new Einstein unified fieldtheory.
The
proofs
aregiven
in the papers[2] - [14]
mentioned atthe end. The paper consists of four sections: I.
Mathematics,
II.
Conjeetures,
III. Restricted case, IV.Applications.
* * *
I. Mathematics.
The
gravitational
field isrepresented
in thefour-space
ofthe
general relativity 2) by
ten components of aquadratic symmetric tensor,
while theelectromagnetic
field is represen- tedby
six components of a skewsymmetric quadratic
tensor.Therefore,
it is understandablewhy Einstein,
in his recentattempt
for unified fieldtheory
started with sixteencomponents
of ageneral quadratic
real tensorThe existence of such a tensor
imposes
analgebraic
struc-ture on the
four-space.
In order to deal with some conse-quences of this
algebraic structure,
we introduce first thesymmetric
part of(*) Pervenuta in Redazione il 29 marzo 1954.
1 ) Prepared under joint contract with the Office of Naval Research and the Army Office of Ordinance Research.
2) The general relativity will always be referred to as pure gravi- tational theory, even if the electromagnetic field is present.
Assume that its
signature
is - - -+,
so that its deter- minant b isnegative,
and use itthroughout
this paper as metric tensor.Moreover,
denoteby k).i1-
the skewsymmetric
part of glp.
and introduce the determinant h of
kÀVo’
which isobviously non-negative.
The determinant g of is assumed to be different from zero andby
reason ofcontinuity
we have toassume g 0. Later on we shall need also the
following
setof scalars ’
3) There are three algebrically different classes
kD ~
0, the first classk _-__ 0,
D ~ 0,
the second class k = 0, D = 0, the third class.The second class splits into two different subclasses. The
case k =1=
0,D = 0 cannot occur for a real tensor
The tensor may be written
where
I7~ , ... ,
are fourmutually perpendicular
unitvectors. In the case of the first and second
class, they
areuniquely
determinedby
in thefollowing
way: the vectorsulc , ull
areuniquely
determined up toordinary
rotationsin the bivector the vectors are
uniquely
determined up to Lorentz rotations in the bivector
In the case of the third
class, only
onenullvector,
say-E- ~ l7~° ,
isuniquely
determined(up
to afactor) by
This classification will be very
handy
later on. It has also aphysical meaning
with which we will deal later on.We mention
here, parenthetically,
also anotherphysical significance
of the existence ofg,, .
It leads in the most natural way tospinor algebra
andspinor analysis [2], [3],
[9].
The connection
r¡p.
of the Einstein unifiedtheory (which replaces
the connection of Christoffelsymbols y
of thepure
gravitational theory
based on is nolonger symmetric
and is defined
by
the set of 64equations
equivalent
to(4)b
Here
D ~
is thesymbol
of covariant derivative withrespect
to the connection
r1p..
Before wetry
to solve(4)
forrvx,,,
let us make the
following
remarks: there are tensors glp.with 9 =1=
0 for which(4)
does not admit any solution]PV 1,L.
There are tensorswith 9 =1=
0 for which(4)
admitsmore than one solution. Unlike in the pure
gravitational theory
where the Christoffel
symbols
are(uniquely)
definedby
thecovariant
constancy
of the metrictensor,
in the unifiedtheory
the connection is not defined
by
the covariantconstancy
of the basic tensor
(cfr. (4)b).
It may beproved
that the re-quirement
of the covariantconstancy
of gÀp. leads to a solu-tion
only
if g = const(which
condition will turn out to be aphysical restriction).
Theoretically
it is not difficult to solve 64 linear non-homogeneous equations (4)a
for 64 unknowns Practi-cally, however,
it is almostbeyond
control.Moreover, keeping
in mind our main
goal,
i.e. thephysical interpretation,
wecould need
only
a solution in tensorialform 4).
In order toobtain
it,
we start with the first 40equations (4)b
which
yield
Here are Christoffel
symbols
ofh 11, ,
the tensorSvku
is defined
by (3)
andThe
equation (6)
shows the tensorial form of the solution In order to we take in account the last 24equations (4)b
4) Schrodinger, who deals in [16] with a system of the form (4)a, writes (1. c. p. 166), 4~... it is next to impossible to produce it (the solution) in a survey able tensorial form ». Cf. also [ 1] ; for an (in- complete) -bibliagraphy of non-tensorial solution in some very special ,c,ases, see [11].
Substituting
into(7)b
from(6),
one obtainsfinally
and V
is thesymbol
of covariant derivative withrespect
to the
connection I v i
In order to solve thesystem
of 24linear
non-homogeneous equations (8)a
for 24 unknowswe transcribe it first in the non-holonomic frame
given by U~
With the aid of
(1)
and(2),
thesystem (8)b splits
in 6systems
of fourequations
for four unknows each.Hence,
itis not difficult to solve each of these six
systems (and
there-fore also
(8))
as well as to find a necessary and8ufficient
condition
for
theuniqueness of
the solutionnamely
If this condition is
satisfied,
then there exists aunique
in-verse tensor
Y(Q§
to such thatand
(6) yields
theunique
solution of(4)
in the formDenoting by
the curvature tensors ofivy
( of
we introduce the tensorswhich are related
by
where one has to substitute for from
(9)
and forUf,
from
(7)
and(9).
PutThen it turns out that
In order to obtain the field g;,~, from
r~~, ,
one has toimpose
some conditions on the connection. Einstein proposes
(among
other
conditions)
to use eitherin both cases
coupled
withThe conditions
(13)
may be condensedby
virtue of(12)
and(14)a
towhere
X,
is either anarbitrary gradient (in
the case of(13)a)
or a
suitably
chosen vector(in
the case of(13)b).
The equa- tions(14)
are to be looked upon asgravitational
and electro-magnetic
fieldequations.
Remark. The 84
equations (4)
and(14)
for 84 unknowns g,, and X, constitute acompatible system [11].
Cfr.also
[15].
I I.
Conjectures.
So far we
played
mathematicsonly
and the results of theprevious
sectionmight
be looked upon asdescribing
theelementary geometric properties
of thefour-space
of Einstein’sunified
theory, regardless o f
itsphysical interpretation.
If wewant to find a
physicat interpretation
of thispurely
geome- tricaldescription
of thefour-space,
we have to make severalconjectures
about thephysical significance
of these geome- trical conditions. There arepossibly
manysystems
of suchconjectures.
We will follow here one suchsystem
withoutclaiming
that it is theonly
one which leads tophysical
inter- ¡:pretation.
The
symmetric part
ofI ( 14)b together
withI(11)a
leadsto
where
M~~,
is a suitable function ofSip.
and The form of( 1)
is familiar from the puregravitational theory
andsuggests
the
identification of
withgravitational potentials.
In thepure
gravitational theory,
thegravitational
fieldequation (1)
is a
generalization
of the Poissonequation,
where on the lefthand side we have the second derivative of the
potential
func-tion. This is also true for the left hand term in
(1)
if weagree to look upon
hlp. (and
not on itsderivatives)
asgravi-
tational
potential.
Thisgives
us a hint where to look for theelectromagnetic field,
which has tosatisfy
Maxwell’sequations (at
least in a certainapproximation).
The Maxwellequations
contain
only
first derivatives of the field. Ledby analogy
with the identification of the basic tensor in the pure
gravitational theory,
werequire
thatin
the unifiedtheory
the Maxwell
equations
beexpressible
in terms of the compo- nents of the basic tensorglp.
and its first derivatives alone.In other words we
require
that theelectromagnetic field
bea
function of
alone.As far as the relativistic Maxwell
equations
for an elec-tromagnetic
field m~~~, = areconcerned,
we may assume them in the «idealized» formLet us concentrate first on
(2)a
alone.According
to ourassumption
about theelectromagnetic
field(expressible by
means of gl.,.
alone)
thisequation
cannot be a consequence ofI ( 14)b. Hence,
it must be a consequence ofI ( 14)a.
Nowthe
following problem
has to be solved next. Is there any skewsymmetric
tensor ml.,. ,expressible by
means ofalone,
such that it satisfiesby
virtue ofI ( 14)a
theequation
(2)a
a)
either in a certainapproximation (for
instance fora weak field
only) 5) ; b)
orexactly?
It turns out
[14]
thatinfinitely
many tensorssatisfy
the
requirement a)
and that there isexactly
one tensor(up
to amultiplicative constant)
which satisfies therequirement b), namely
Therefore
weidenti f y
theelectromagnetic f ield
with thetensor
m~~, given by (3).
If we define the class of in thesame way as we did for
kÀp.,
then the tensors and mÀp.are
o f
the sameTherefore,
there are three classes ofelectromagnetic
fields.s) The exact meaning of the word «approximation» is given in [14].
6) (lva¡! is the covariant tensor density, skew symmetric in all indices whose components in every coordinate system are -[-1, -1, 0.
Moreover, x = - sgn
exvzp kxv
The
general algorithm
may now be described as follovc-s : the skewsymmetric part
ofI (14)b
leads to(2)b,
while thesymmetric part
ofI (14)b
leads to« gravitational »
field equa- tions(1).
The
resulting equations expressed
in terms ofh¡p.
and m~~,are somehow
complicated. Therefore,
we shallapply
in thenext section the
general algorithm
to a restricted case which leads more or tesseasily
to test devices.The pure
gravitational theory applied
to celestial mecha- nics leads toprediction
of threephenomena, namely
the ad-vance of
perihelion
ofMercury,
the deflection oflight,
andthe red shift. The « confirmation >> of these
predictions by
observation tests have been looked upon as
satisfactory.
The-refore we shall
try
in the last section toapply
the unifiedtheory
to the celestial mechanics for thespecial
purpose of ob-taining
thecorresponding predictions
of the mentionedpheno-
mena. We shall carry out the
computation
under the same as-sumption
as used in the puregravitational theory
in the presence of theelectromagnetic
field of the sun : We assume that theelectromagnetic field. of
the sun is a weakf ietd
so thatthe
quadratic (and higher) products of
itscomponents
may beneglected.
Theequation (3)
shows that this ispossible only
if the field 7f¡y is so weak that the
quadratic (and higher) products
of itscomponents
may beneglected.
Therefore thecondition
is
automatically
satisfied. On the otherhand,
theequation (4)
is a necessary and sufficient condition forso that
Therefore,
we shallapply
in the next section thegeneral
al-gorithm
to the restricted case characterizedby (4)
or(5),
without
making
first anyassumption
about the weaknessof the field
mx,,. Then,
of course,(4) (or (5)) represent
astructural condition
imposed
on the field Then in the last section we shallapply
the obtained results to celestialmechanics under the above mentioned
assumption
about theweakness of the field so that
(4) (or (5))
becomes aquantitative
condition rather than a structural one.III. The restricted case.
One of the first consequences of
(4)
and(5)
isMoreover,
we assumeand define
so that we obtain an
identity
and
consequently
On the other hand
II(2)a
isequivalent
towhere niz is a
suitably
chosennon-gradient. Using
nowII ( 3), II(5), 11(6)
as well as theidentity (4),
one sees that7) These conditions are necessary if dealing with charged particles.
In the case of radiation they have to be replaced by
8) is the contravariant tensor density, skew symmetric in all indices whose components in all coordinate systems are -~-1, -1, 0.
the skew
symmetric part
ofI ( I4)b
isequivalent
to six equa- tionsfor twelve unknowns m,, vv,
Xz (while hz,
are looked uponas
auxiliary variables). Assuming
that V" is not agradient,
we substitute the solution Vv of
(7)
into theidentity (4)
andobtain in this way the
equation II ( 2)b. Therefore,
weidentify
ny with the"current vect6r
density.
Whenever W2 del=t= 0 ~
we
identify
W with the electriccharge density.
The condition(2) yields B?" =F 0
andbv b"
> 0. Later on we shall use also the vector and the scalarand in the case
w2 ~
0 also the vector(the velocity
four-vector»).
A similar method
applied
to thesymmetric part
ofI ( 14)b yields
Hence,
we have 20equations II(2)b (7) (8)
fortwenty-two
unknowns mx, vv,
Xx, hx,. Therefore,
we may as wellprescribe
at least one condition more
which enables us to define a
(rest)
massdensity by
thefollowing requirements
similar to thecorresponding require-
ments in the pure
gravitational theory : M
is anon-negative
function of I~ such that 0
only
if H = 0 and moreover, it satisfies the(relativistic) continuity equations.
These re-quirements yield
u.here : ~
0 is a function ofposition (to
be foundexperimen- tally)
which is constantalong
thetrajectory
of theparticle
Adopting
this definition we see that0153 ==
0 if andonly
ifthe
particle
moves with thevelocity
oflight (photons).
Mo-reover, we see from
(11)
that has(besides
the samearguments
as the total momentum energy tensor in the puregravitational theory
whenever theelectromagnetic
field is pre- sent.Hence,
weidentify T¡p.
with the total momentum energy tensorof
theuni f ied theory
and moreover,(still
on the basisof
(8))
weidentif y g ~
0 with a constantmultiple of
thegravitational
constant1°).
The ten
equations II ( 2)b
and(7)
may be looked upon asdefining (besides VII)
theelectromagnetic field
in termsof
thegravitational field tc~~, (and Xx).
On the otherhand,
the
equations (8)
may be looked upon asdefining
thegravi-
tational
field h~~,
in termsof
theelectromagnetic field
m~~, .The absence of m¡¡.t. is here excluded
by
theassumption
# 0
while there are cases(as
we shall seelater)
without9) As a matter of fact, we already used this condition for deri- ving (8) and (9).
10) g is constant if and only if This conditions is satisfied here by virtue of II (5) . ap.
gravitational
field. Therefore we look at theelectromagnetic
field as a
primary field,
so that theprevious
statements may be worded as follows: Thegravitational field
as well as ABare built up
from
theelectromagnetic field,. However,
thereare
electromagnetic fields,
which do not create anygravita-
tion.
Thus,
forinstance,
if we aredealing
with radiationonly
so that(2)
has to bereplaced by (2)*
then thesystem
of
equations 11(2), (7), (8), (10) (as
well as(2)*, 11(5))
admits a solution
where
a = a (Z), b = b ( Z)
areperiodic
functions of the argu- ment so thatrepresents
theplane
waveof
the
electromagnetic theory of light. Hence,
this electroma-gnetic field
does not create anygravitation
as it was to beexpected. Incidently,
this casemight
be looked upon as afirst con f irmation of
theunified theory,
at least in this veryspecial
case.The
equations
of motion follow fromwhich is a consequence of
(8)
and of the well know-n Bianchiidentity
forThey
areequivalent
toThe last result
suggests
a-slight change
of thetheory
whichwould result in the law of inertia in the usual form: The skew
symmetric part
ofI ( 14)b
isequivalent
toLet us
replace
thissystem
of fourequations by
another oneof the same number of
equations
Here a is a scalar to be chosen in such a "-ay that
which is
equivalent
to(10).
Then we obtainagain
the Max-well
equations 11(2)
and thegravitational
fieldequations ( 8),
but the
equations
of motion derived from(12)
are nowor in
equivalent
formHence the law of inertia based on
(16)
runs as follows :I f
aparticle
moves in thefield
without externalforces,
thenit describes a
path
which is anautoparallel
lineof
the connec-tion
given by 1(4) (cf.
alsoI ( 10)). Despite
the presenceof
theelectromagnetic field,
thispath
is the same as in thepure
gravitational theory
in the absenceof
theelectromagnetic field, nanzely
ageodesic of
IV.
Applications.
Let us now
apply
theprevious
results to celestial mecha- nics under theassumption
that theelectromagnetic
fieldof the sun is weak so that the
quadratic products
of its com-ponents
may beneglected (and consequently 11(5)
is auto-matically satisfied).
Under this
assumption,
theequation III { 8)
reduces toFrom now on we denote
by hx,
the Schwarzschild solution of(1).
Moreoverapplying (as
in the puregravitational theory)
the method of successive
approximation (i.e. neglecting.
inIII ( 12) only
cubic andhigher products
ofmlJJo)’
we obtainthe
equations
of motion in the formIII ( 13)
where nowVp.
refersto the Schwarzschild solution If we assume for the time
being
that we know theelectromagnetic
field of the sunand substitute it into
III ( 131,
then the solution wy of111(13) gives
rise in the usual way to thepath
of aparticle.
Thispath
has to be identified either with an orbit of a
planet (if 0)
or with the
path
of aphoton (for iv
=0). Hence,
we are able(at
leasttheoretically)
topredict
the threephenomena
dealtwith in the pure
gravitational theory:
The advance ofperi-
helion of
Mercury,
the deflection oflight
as well as thered shift. However this
prediction
is based orc theknowledge of
theelectromagnetic field of
the which is ac solutionof II I ( 7)
and11(2).
The situation is much
simpler
in thechanged theory
basedon
111(14).
We obtainagain (1)
fromIII(8),
and denoteby
h¡p.
its Schwarzschild solution. Then theequations III(16)b
define the
geodesics
of so that we do not need the know-ledge
of theelectromagnetic
field of the sun to define them.Identifying
thesegeodesics
either with orbits ofplanets (for
w # 0)
or withpaths
ofphotons (w ‘ 0)
we obtainexactly
the same
predictions for
the three above mentionedpheno-
viena as in the pure
gravitational theory.
. However the
equations III ( 16)b
are a consequence ofequivalent
toIII ( 14). Consequently,
the crucial testfor
thistheory (at
least as far as the three above mentionedpheno.-
mena are
concerned)
will consist znchecking
whether theelectromagnetic field of
the sunsatisfies (2).
Here the last wordbelongs
to theastrophysicist.
11) Here wv is a known solution of III(16)b and has to satisfy II(2)b.
This statement
might
be looked upon from anotherangle (which
leads to the sameresults):
The confirmation of the(pure gravitational)
relativisticpredictions
of the threepheno-
mena has been looked upon as a sufficient
proof
for the puregravitational
relativistictheory (in
these threecases).
We haveobtained the same
predictions
in the unifiedtheory. Hence, adopting
the samejudgement
we may claim that the unifiedtheory
has beenproved (in
these threecases).
Then(2)
has tobe looked upon as a
predictions f or
teelectromagnetic field of
the sun. Here
again
the last wordbelongs
to theastrophy-
sicists.
BIBLIOGRAPHY
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[3] HLAVATY V., « Spinor Space and Line Geometry II », Journal of Rational Mechanics and Analysis, Vol. 1, No. 2, April 1952,
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[9] HLAVATY V., «The Spinor Connection in the Unified Einstein Theory of Relativity», Proceedings of the National Academy of Sciences, Vol. 39, No. 6, pp. 501-506, June 1953.
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[11] HLAVATY V. and SÁENZ A. W., « Uniqueness Theorems in the Uni- fied Theory of Relativity », Journal of Rational Mechanics and Analysis, Vol. 2, No. 3, July 1953, pp. 523-536.
[12] HLAVATY V., «The Elementary Basic Principles of the Unified Theory of Relativity C1: Introduction », Journal of Rational Me- chanics and Analysis, Vol. 3, No. 1, January 1954, pp. 103-1446.
[13] HLAVATY V., «The Elementary Basic Principles of the Unified Theory of Relativity C2: Application », Journal of Rational Me- chanics and Analysis, Vol. 3, No. 2, March 1954, pp. 147-179.
[14] HLAVATY V., «Maxwell’s Field in the Einstein Unified Field Theory », to appear soon in Niew Archief for Wiskunde.
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