What is the tech difference between the Bronze Age and the Iron Age?
(other than 'bronze' and 'iron', of course).
Being somewhat of a history buff (just a buff, I don't claim any expertise), I had wondered the same, but had not commented due to fear of starting an argument or disrailing this thread. Sorry if my post starts either, not my intention.
In my personal opinion only, I don't think there is a large difference between the two in Traveller 'tech level' terms. An example of each is ancient Greece (bronze) and the Roman Empire (iron). They are two of the most successful civilizaitons of their ages.
Note: If you don't consider ancient Greece old enough, ancient Egypt definitely is and the arguments below can almost word for word be used with Egypt in place of Greece.
If you compare transportation systems, instruments of war, communications, medicine, etc, in my mind I can't think of much of a difference. Both used horses. Both used the phalanx in warfare. Both had scholars of science, possibly Greece more-so (but I think most of these scholars came much later, perhaps not considered the bronze age). Both had water-borne ships of similar abilities. The Roman Empire never developed a true ocean-going vessel that I know of. The only Roman advantages I can think of off the top of my head are architectural (Rome had the arch and aquaducts, I don't think Greece did), and siege engines (Rome's war machine developed several new weapons of war). I think both of these advantages were possible by the early Greek bronze-age technologies and tools. They just never thought of them.
Not a large amount of difference in my opinion. I looked at the detailed technology charts included in MT Referee's Companion (pages 28-29). Of 22 examples listed for TL 1, I could only imagine 2 or 3 of them that were available to the Roman Empire, but not Greece (or ancient Egypt).
Let's compare Stone Age to Bronze/Iron Age. I can think of many things the Stone Age people didn't have: horse-riding, large-scale farming, swords, catapults, sea-going vessels, large settlements, the wheel, etc. Some big technology differences there.
Perhaps this is what was being considered by the game-developers when these tech levels were laid down. While Earth-historians have labeled these ages as vastly different, they were speaking of not just technology, but culture and a time-period.