It does not matter whether or not a person believes in Ki. If you are alive, there is life energy. The next question is whether or not it can be used in a martial setting. I have personally experienced it in both Aikido and in other martial arts.
If you guys in Europe would like to get an opportunity to experience it at a very frightening level, then I would suggest that you set aside the weekend of April 9 &10 in Lyon, France. Kenji Ushiro Sensei will be teaching his first seminar in Europe. He was introduced to the Aikido world at the Aiki Expo. He teaches a style of Bujitsu. A lot of his students have left other "hard" arts in Japan to study under him. Katsumi (Oyama top tournament fighter) is just one example of many. His use of Ki in a fighting context is a real game changer. You have to personally experience it to actually believe it.
I don't see any one really "hitting" him in his demo's...... Why is it when really challenged these people don't or won't face up to it? I have "felt" their so called "ki" and there is nothing there!!!! Other than your own belief in thinking it exists, like those who believe in gods, spirits, spooks and all manner of hocus pocus..... If you believe he can stop you with his "ki" then he has already conned you into thinking it and has therefore "defeated" you already..... That is called psyching out your opponent.....