New-York tribune., 1920-06-13

imagine two observers, each r;.s
his measuring instruments. m..'.
of subsistence, ETC., in largs ~,
perfectly impervious box vh,.s
forms his "closed system"
The first observer, with his h.
and its contents, alone in space, van
remote from all gravitatins hos.'
and entirely at rest.
The second observer, with hi. h.
and its contents, is, it may be im,s' /
lned, near the earth or the sun :, /
some star and falling freely und., ,
the influence of its gravitation
To be more precise, we jmsr,
him in WHIST is called aunifors
gravitational feld,' where the sr.y,
rational force is exerted on all ob,a..
IN exactly the same direction and !,
not converging toward the center =,
the attracting body, where it is :,
ways of exactly the same amour.
and there is nothing to int.rt.r
with an indefinitely long fall.
This second box and its cont.,..
including the observer, will then AN
under the gravitational force-4h,,
ls' get up an ever-increasing su..d
but at exactly the same rate, 50 that
there Will be no tendency for th,;,
relative positions to be altered
According to Newton's princiu,. f
this will make not the slightest Il. M +
ference in motions Of the phvs,,,,
objects comprising the system o,I
their attractions on one another. ~ I
that no dynamical experiment c,,I
distinguish between the condition MI
the freely falling observer in n. /
second box and the observer AZ -.
in the first.
But once more the question aris.
What could be done by an ontic,l
experiment?
According to the beliefs vb;,.
have been held from the time Of
Maxwell, who first developed The e
electromagnetic theory of light uu. /
til the present, it has generals been
believed that gravitation, however !
powerful, has no effect whatev,,
upon light, and the light would /
therefore travel in a straight line !
through a field of gravitational at.
traction exactly as it would through
empty space.
How Light Travels
Elnstein, on the other hand, a.
sumed, just for the fun of seein, /
what would come of it, that the priu I
clple of relativity still applied in !
this case, so that it would be imposE
sible to distinguish between the con.
ditions of the observers in the two /
boxes by any optical experiment
1t can easily be seen that it fol. l
lows from this new generalized rel.. ,
tlvlty OF Einstein that light csnnot; ;I
travel in a straight line in a grsv.
rational field.
Imagine that the first observerH
sets up three Sits, all in a straisMl|
line, at considerable distances apart
A ray of light which passes throughI
the first and second will obviously
pass exactly through the third.
Suppose the observer in the freely I
falling system attempts the sane
experiment, placing the line Of hi;
three Sits at right angles to @
direction in which he is falling and Y
having them equally spaced. 4
The ray of light which has passed
the first slit must, in order to getn
through the second, move not toward h
the point where that slit was when B
1t emerged from the first, butE
toward the point where the SECOND II
Slit will be when the light reachesi. H
1t will, therefore, be moving nc'E
at right angles to the direction il
which the system is falling. but Ct
a slant, so that during the interwl
IN which it has Travelled lateral!
from the first slit to the second III
will have moved downward by GER
tain fixed amount, namely, by thE
amount through which the system
fell in that interval. =
In moving from the second to th B
third slit, the light will occupy thy
same interval of time, and, II "a
moves in straight line, will ssf
downward by the same amount S5
before. 4
But since the system is falling
ever faster and faster, it will during /
this time interval havs droppa /
further than it did in the precedihsk !
time interval and carried the thru
slit with it. /
Hence, the ray of light will stfN /
above the third slit and fail to 8 1
through it, provided it travel MI
straight line IN space. 4