President Barack Obama is proposing a cool solution to help close the gender pay gap , but it doesn't hit at perhaps the biggest problem keeping women from earning what men make.

That problem? Life.

Womens responsibilities outside of work -- mainly looking after children, but also caring for sick and elderly family members -- often keep them from taking on the kinds of jobs that would finally close the distance in pay between the genders.

That doesnt mean that the gender pay gap is the result of some kind of real choice women make, according to Claudia Goldin, one of the leading economists studying the gender pay gap.

Women arent choosing to make less, she told The Huffington Post. Instead, theyre buying the flexibility to handle responsibilities outside of work, said Goldin, who is a professor at Harvard.

U.S. public policy is many years away from grappling with this.