Were not quite sure, but thats because nobodys ever directly observed dark matter.
We assume it exists because we can see objects and events wecanobserve reacting tosomethingmysterious.
But theres a problem.
There seems to be far too much dark matter in the universe.
Residual dark matter from the Big Bang or whatever doesnt quite explain how the stuff seems to be everywhere.
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But theres a catch!Our universe is expanding.
Quick take:The theory sounds pretty cool.
Read the whole fascinating paperhere on APS Physics.
