Perhaps the depth of love can be calibrated by the number of different selves that are actively involved in a given relationship.

Love lasts about seven years. That's how long it takes for the cells of the body to totally replace themselves.

She had studied the universe all her life, but had overlooked its clearest message: For small creatures such as we the vastness is bearable only through love.

Every one of us is, in the cosmic perspective, precious. If a human disagrees with you, let him live. In a hundred billion galaxies, you will not find another.

In the vastness of space and the immensity of time, it is my joy to share a planet and an epoch with Annie.

[Dedication to Sagan's wife, Ann Druyan, in Cosmos]

To live in the hearts we leave behind is to live forever.