RECENT EVENTS IN RELATIVITY — ROTHMAN 399 



cube moved a distance Lv/c. Therefore it is really the light from E' 

 which reaches the plate simultaneously with light from B. 



Thus we would expect to see a picture like the one labeled "Non- 

 Relativistic," where we find a square ABCD, followed by the projec- 

 tion of the rear end of the cube, ABEF. Without relativity, we expect 

 to see a distorted, elongated picture of the moving cube. 



How does relativity change the situation ? Relativity says that all 

 lengths are shortened in the direction of motion by the f actorVl — vVc^. 

 The other lengths, at right angles to the direction of motion, are not 

 changed. Therefore, under the relativistic interpretation, we would 

 see the shortened square ABCD^ followed by the rear end of the cube, 

 ABEF^ as shown in the diagram labeled "Relativistic." 



What makes this interesting is illustrated in figure 8&. If we take 

 the same cube, motionless, but simply rotated through an angle 9, 

 whose sine is v/c, its picture will be exactly the same as the one obtained 

 from the moving, relativistic, cube. 



In other words, a person looking at a cube moving rapidly will see 

 that it appears to be rotated through the angle 9, but that it otherwise 

 appears normal. Previously, the relativistic interpretation would 

 have said that the cube appeared shortened — ^now we say that it 

 appears rotated. 



When this argument is applied to a sphere, such as a star or planet, 

 we conclude that the sphere remains spherical in shape, but appears to 

 be rotated. If you were moving fast enough you could see part way 

 around the opposite side of the sphere. 



Professor Weisskopf, in his paper, goes into the details of how a 

 moving object changes its appearance as it comes towards us, passes 

 by, and then recedes. In brief : We first see the front face of the object, 

 strongly Doppler shifted to high frequencies. When the angle of 

 vision reaches a certain value, the color shifts toward lower frequen- 

 cies, the intensity of the light drops, and the object seems to turn. 

 Soon the object has turned all around and we are looking at its trailing 

 face. As Weisskopf says, "It is the picture expected when the object 

 is receding. However, it appears already when the object is moving 

 toward us." 



This description, of course, applies only to objects wliich are moving 

 very nearly at the speed of light. 



As stated originally, none of this invalidates the basic findings of the 

 theory of relativity. It merely emphasizes, as many have found to 

 their chagrin, that we must always be very careful in interpreting the 

 results of the theory. 



