You work in a patent office. One day this chap walks in with a rather large box and said he has invented antigravity. He places his box on your trusted old spring balance and the reading is 30kg. He then presses a button on a remote control, and series of strange noises are heard coming from the box. Lo and behold, the weight has gone down to 29.5kg!
After about 30 seconds he presses his remote control again, and the reading went back to 30kg.
The box is hermetically sealed and your weighing balance is not compromised in anyway.
You said calmly,"We know that the Laws of Gravitation cannot be defied, and neither can the Law of Conversation of Mass. I know wht's going on in the box."
The Question is: What is going on in the box?