Also, there could be a lot of cpu power on Mars as well. So, the New York vending machine shouldn't accept a Mars coin within several hours.
My point is that if there is a lot less cpu power on Mars, then the Mars nodes will ALWAYS lose the "create the longest block chain" race. So the New York nodes will ALWAYS have the advantage.And it is nice to say the New York vending machine "shouldn't accept a Mars coin within several hours," but, in my experience, "shouldn't" doesn't cut it. If the New York candy machine CAN make the sale and keep the coins, it WILL.