 Says:  " Mamesh apikorsus & kefira. If a Gadol says it, it is true just by virtue of his saying it. He doesn't have to prove squat to you. He didn't become a recognized Gadol by making up things. He has already earned his authority. If he says day is night, then you daven maariv. The end. "  Actually, there is no one alive today who I would accept such blatant misinformation from. For every Rabbi that tells you day is night, there are others that will tell you it is indeed day. We don't have a Sanhedrin. Any halacha or hashkafa that they didn't decide on is fair game. 