CONJUGATE POINTS ALONG NULL GEODESICS IN A CLASS OF SPACETIMES

The existence and location of conjugate points along null geodesics in Taub's vacuum spacetime is investigated in detail. It is shown that every null geodesic η not confined in a t-z plane contains two pairs of segments (M,M) and (N, N) such that each point p in M(resp.N) has a unique conjugate point p along η that is located in M (resp. N) and vice versa, and what is more interesting, if p and p are conjugate points along η with p∈J⁺(p), then p∈I⁺(p). This presents a realistic example illustrating that there do exist null geodesics emanating from p that can get into I⁺(p) before meeting a point conjugate to p. All results are generalized to a class of spacetimes.     

灯泡会闪亮吗？——对2008年江苏高考物理试题第8小题的探讨

高考历来是中学教学的"指挥棒",因此每年的高考试题也往往成为老师们关注和研究的重点.2008年江苏高考物理试题中有一个关于自感的题目,引起不少老师的关注.