![Image source: physics4me The Problem of Dark Energy Image source: physics4me](http://www.timeone.ca/wp-content/uploads/2013/06/052-dark-energy.jpg)
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The total matter that behaves like mass amounts to only 27% of what the numbers tell them must be there. In other words they’ve lost another 73%. To call this carelessness would be Wildely witty but for cosmologists this is a problem.