Sputnik 2
Sputnik 2, the satellite that the USSR (or Russia) sent into space carrying a stray dog named Laika, is symbolic of the start of the space race. After the launch of Sputnik, the United States and USSR started to fight for supremacy, often attempting to one up each other and make their respective countries look better.
The Iron Curtain
The Iron Curtain was a symbolic barrier between East (represented by the USSR) and West (represented by the United States). In the West, the dominant ideology was capitalism and democracy; in the East, the dominant ideology was communism and dictatorship. This Iron Curtain likewise represented the ideological divide between East and West.
Tennis
For the novel's main character Kathleen Beckett, tennis is a powerful symbol of the possibilities in her life. In tennis, she has something that, had she not gotten injured, would have enabled her to become wildly successful in life. However, because of her injury, she wasn't able to play tennis, significantly hurting her life.
Kathleen's Red Swimsuit
Kathleen's red swimsuit is symbolic of her youth. Throughout the novel, Kathleen wore her red swimsuit as a way to reconnect with her younger self, which she had forgotten after having kids and a difficult marriage.
