Isn't there some kind of physics theorem equivalent to "0.9 repeating forever equals one" about things being the same if there's no way to define them as differ

Isn't there some kind of physics theorem equivalent to "0.9 repeating forever equals one" about things being the same if there's no way to define them as different? If a particle can't interact with anything in the universe without having aspect X then isn't saying it doesn't have aspect X before interacting a meaningless statement? Something can't be different without making a difference.