Try to talk him into taking some philosophy classes. The ability to reason correctly and recognize faulty logic should help a lot. I subscribed to a couple conspiracy theories, not ones like your fathers, but after I took my first philosophy class I saw so many flaws in my reasoning. He has to realize the power of logic and also realize that the universe is full of amazing intriguing things without having to believe in conspiracy theories. Give him The Demon Haunted World by Carl Sagan as a gift. That book may make him reconsider some things.
I gather that your dad pretty much keeps his delusions to himself and the family. As long as he isn't out spreading his nonsense, like in schools or something, what's the harm? If it comforts him in his final years and isn't hurting anybody else, so be it. Hey, my father believed Liberace could only play the piano by having people offstage hold up giant posters of sheet music. It didn't keep him from being a great father.
My problem is getting my dad to stop listening to talk radio... Any ideas? It's impossible to talk politics with him.
When he says, "So you believe whatever scientists tell you," You can reply with ,"So you believe whatever Richard Hoagland/Zacharia Sitchin/David Icke tells you?" Some posters have recommended some lay-science books, and I'll second that. Get him something fascinating & readable, like the Carl Sagan book, or Dawkin's Magic of Reality. If you can get him to see HOW scientists learn things, he might start lending them more credence. Failing that, troll the hell out of him, and maybe he'll wise up if he realizes how much of a willful idiot he's being.
No offense, but I firmly believe anyone who believes this sort of nonsense has other psychological issues that may need to be address first. I am no psychologist, so go ahead of call me out if any disagrees with me, but this is pretty extreme....reptilian race that can shape shift!!!???
The problem with trying to persuade conspiracy theorists is that anything that can be used to convince them that they are wrong becomes part of the conspiracy. Moon landing was a hoax? Well, if you show new photos from the Lunar Reconniassance mission clearly showing an Apollo landing site with abandonedn equipment, then that photo becomes part of the hoax. There is almost nothing you can do to break their beliefs in a conspiracy.
Well, almost. If this bizarre belief system has come on suddenly or has been intensifying in recent years, you may consider the possibility that this is a symptom of a greater problem. Dementia and other mental health concerns would be my first priority in investigating rather than debate on any one issue. If you can talk to a mental health professional about your father's behavior, they might recognize signs of known problem or offer generally helpful advice. Obviously there are some problems when someone becomes that detached from reality and it could prove harmful to themselves or to others if it is not addressed.
It's just a harmless hobby, let him enjoy his crazy loopy science if he wants to
Paranoia and bullshit are far from harmless, it's dangerous and unhealthy.