The closest situation I've been in to this would be my best friend who turned out to be a global warming denier. Once I got over the shock and horror, we just made an unspoken agreement never to discuss it, but instead to focus on the things we had in common. I don't know if this would work with your mother, though, especially if you live under the same roof.

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"If you think the LHC will create black holes, you might as well believe Hobbits are at the bottom of your garden."- Dr. Mike Inglis
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song