University of California, Davis economics Professor Gregory Clark has declared in an essay published by the Council on Foreign Relations that there is no such thing as the American Dream.

In his essay, The American Dream Is an Illusion, Clark points to "recent evidence" that suggests the rates of social mobility -- "the speed with which the children of families of low or high incomes, wealth, and education approach the average" -- are "extremely low."

He writes:

The evidence shows that immigrant groups tend to retain the social status that they arrive with.

Given current patterns of immigration to the United States, Washington faces an enormous policy challenge… they are often the people who found themselves in such desperate economic circumstances at home that they preferred to live as illegal immigrants in the United States. 

The effects have been dire: there can be no doubt that immigration is widening social inequality in the United States.

But it's not just the immigrants' dreams that are being dashed, it's everyone. Speaking with CBS Sacramento, Clark said:

America has no higher rate of social mobility than medieval England, or pre-industrial Sweden. That’s the most difficult part of talking about social mobility is because it is shattering people's dreams.

The status of your children, your grandchildren, your great grandchildren your great-great grandchildren will be quite closely related to your average status now.

Concluding his essay, Clark writes, "The truth is that the American Dream was always an illusion. Blindly pursuing that dream now will only lead to a future with dire social challenges."