By MATT SEDENSKYCHICAGO (AP) a¿¿ It's an assertion that has been accepted as fact by droves of the unemployed: Older people remaining on the job later in life are stealing jobs from young people. One problem, many economists say: It isn't supported by a wisp of fact. "We all cannot believe that we have been fighting this theory for more than 150 years," said April Yanyuan Wu, a research economist at the Center for Retirement Research at Boston College, who co-authored a paper last year on the subject. The commonly accepted vision of a surge of workers looks like this: A young post-doctoral student dreams of a full-time teaching job at their university, but there are no openings. An 80-something professor who has remained on the job long past what's considered "normal" retirement is blamed, The problem with that vision is that there are probably full-time teaching positions available elsewhere, or the person blocking the young grad student from the job is only 40 years old, economists say. Further, the veteran professor's decision to stay employed and productive may stir other job growth. He may bring research grants to his university allowing for other hiring, may take on assistants, and may be able to dine out and shop and fuel the economy more than if he weren't on the job. None of that would have happened had he retired. The theory Wu and other economists are fighting is known as "lump of labor," and it has maintained traction in the U.S., particularly in a climate of high unemployment. The theory dates to 1851 and says if a group enters the labor market a¿¿ or in this case, remains in it beyond their normal retirement date a¿¿ others will be unable to gain employment or will have their hours cut. It's a line of thinking that has been used in the U.S. immigration debate and in Europe to validate early retirement programs, and it relies on a simple premise: That there are a fixed number of jobs available. In fact, most economists dispute this. When women entered the workforce, there weren't fewer jobs for men. The economy simply expanded.