Re: Einstein's answer:
If you begin your argument with "Everyone knows...", please back it up with scientific measurement. The reality is, we "know" very little about our universe (about 5% of it to be honest). Without making these measurements, we will never know the properties of antimatter nor be able to unravel the mystery of where it has all gone.
Antimatter behaves like matter going backward in time. Most properties are the same, but the charge is opposite. Other properties, like mass, are expected to be exactly the same. The idea of anti-matter falling up only belongs to journalists (or more likely their editors) trying to come up with catchy headlines. Don't blame them. Blame us readers for being attracted by those headlines!