Money is intrinsically worthless, so ultimately, it is worth what you can trade it for. The one thing that the government sets the price of is unskilled labor hours (minimum wage). This means the dollar is backed by is unskilled labor hours. Admitting this ruins the ideology that raising the minimum wage will make people better off, rather than devaluing the dollar.
At a minimum wage of $10 an hour, one dollar is worth .10 unskilled labor hours. If we then raise the minimum wage to $15 an hour, one dollar is worth .07 labor hours. Raising the minimum wage does not increase the value of an hour of unskilled labor, it decreases the value of the dollar, increasing inflation.
Now, the "value" of an hour of unskilled labor is unfortunately also decreasing on it's own, due to automation, the importining of eager cheaper foriegn labor (illegal imigrants) and the ease of exporting jobs to other countries.