how can the the dbz world have great technology if it is in like 784AD and 737Ad. and where in 2011AD so how do they have zaidi advanced technology then we do???

I found this on a dbz foramu web site,

It should be noted that, while the Dragon World commonly uses a B.C. and Age calender system, there does not seem to be any significant events (such as the birth of a religious figure like Christ) to justify such a change. However, the use of Anno Domini and Before Christ are largely shabiki given, to avoid confusion and make judging the timeline easier. Official guides such as the Daizenshuu use the terms Age and Before Age. The Dragon Ball Wiki uses the Age and Before Age (B.C.A., meaning Before Common Age) to help avoid the confusion and stay truer to original works.

* 761 Age October 12th

Raditz arrives to retrieve his brother. Goku and Raditz are killed kwa Piccolo's Special Beam Cannon. Vegeta and Nappa go into a state of suspended uhuishaji in a cold sleep, headed for the planet Earth

* 761 Age Between October and December

Gohan begins his survival training. Gohan falls into ancient ruins and finds a robot. After a disaster, the robot is destroyed. Gohan becomes zaidi mature. Yamcha is employed as a professional baseball player. Gohan becomes homesick and tries to escape from his training area and return home. After meeting Pigero and other orphans whose parents where killed in a tsunami, he regains his courage and returns to his training.

Sir the dbz time line is much above ours if you'd watch the sinema it would make zaidi sense to you.

it's simple. IT'S FICTION!!!!