Currently TL is meaningless, as all of you have already told Me. Changing the labels, changes nothing. As I said, call things what you like.
Bleah; ease up on the nihilism. I have not told you that TL are meaningless; just that the current way Traveller defines is inconsistent and not terribly useful. I do not care what 'everyone has told you'; you are having this discussion with me, not them.
How is a selectively bred animal considered higher technology? Does that mean that natural evolution is technology as well? What is your baseline? An ape? A wolf? An ameoba? What is your TL-0?
My base TL-0 is a single, lone naked and unskilled human.
Learning that 'fired clay' is a thing, and that it can be made, and used to do useful things -- that requires advances, insight. Learning that fibers can be spun, woven, knotted -- that requires advances, increased understanding, insight. Leaning to make and use fire for light, heat, and cooking -- that requires a series of acts of invention; more insights. Cooperating as a group, for better hunting, gathering, protection -- that is a discovery, too.
Humans might fairly be described as 'what happens to great apes who become dependent on harnessed fire for cooking', so maybe 'Human' includes use of fire at TL-0. Everything else has to be invented from scratch; and folks who are obsessed with spending every waking moment scrabbling for enough calories to stay alive do not spend very much time innovating. More people working on a problem, the better the odds one of them has an 'Aha!' moment; once a bunch of people have learned that 'Aha!', the chances that it will be lost when a person dies is reduced -- that preserves innovations across time, Inventing language allows better teaching; inventing writing allows learning from those who are dead, or far away.
The more people innovate, the more energy (and better tools) they have available. Domesticating wolves into dogs was an increase in technology -- dogs can use their energy to pull or carry loads, they can extend the awareness and influence of a hunter, they can assist a watchman by paying attention or fighting.... Dogs are tools, and they made more energy available to humans than simply the energy of human muscle. Domesticating cows & oxen was another technological advance; they have greater strength and can provide meat, milk, leather, sinew, and horn -- plus they gather calories stored in grass (nutritionally inaccessible to humans) and convert it into all those useful things.
So 'how is selectively breeding animals a technology' is sort of a naive question; first the animals (or plants! Domestication RADICALLY altered maize and bananas, just as two examples) must be domesticated, and then the rancher must make the effort to select for desirable traits and against undesirable traits. Good examples must be saved and bred instead of killed and eaten -- and people need to have a reason for doing that, which involves the insight that 'offspring tend to be somewhat similar to their parents'. That insight and innovation produces better tools -- better animals.
What is an example of this so that I can understand better?
Throughout history, quality of life has increased in direct correlation with the energy and productivity available to an individual. Productivity is an economic thing, so lets stick with energy.
TL-0 Humans may pick up and move things, but are limited to the energy in human muscle; ~100 W at rest, up to about 400 Watts for sustained periods, and up to 2000 Watts for short bursts.
At TL-1 humans typically have fire from wood; this is about 5kWh per kg. But with just fire, the only useful work is with heat harnessed for cooking, warmth/shelter, and enough dim light to see a few meters from the campfire (maybe a +1, out to 1.2x what can be seen without the fire?-ish -- this is just a constructed example). Tools are not powered by fire; they are powered my human muscle augmented by both cooperation and the simple machines -- levers, axles, inclined planes, etc. This allows maybe five to ten times better use of energy, amplifying human capability; so maybe ~5 kiloWatts for sustained periods, and maybe 10 kiloWatts for short bursts.
Maybe say TL-2 is fire with charcoal; but also domestication of animals. An Oxen can put out more power than any human; subject to various inefficiencies on how they are hitched to the work.
Water wheels (and windmills) also generate useful power, and do not require food.
If we are building an in Game Tech Tree maybe we can say TL-0 is 0.25 'Power' available; TL-1 is 1.25 'Power' available, with up to 3 'Power' with four or five people working together; TL-2 is 6.25 'Power', with up to 12.5 with several beasts harnessed together; TL-3 allows better harnesses, lighter and smoother turning mechanisms, and 31 to 62 'Power'; TL-4 allows 150 to 300 'Power', etc & etc. Maybe folks are harnessing Oxen -- but maybe not; the fluff is unimportant. Maybe it is Donkeys providing the work, or giant riding chickens, or draft horses, or Tortoises Of Unusual Size. The point is that a power-plant outputs (for a given 'unit of power-plant') a specific amount of 'Power' per round, which increases by ~5x per TL. Upper TLs might be Fusion+; 'Cosmic power', anti-matter, or 'Zero-Point Energy', but those are just labels.
Pretty sure that this is already written in the lore, but okay. TLs have always been arbitrary nonsense. They are assigned in-game by some bored scout in a scout ship and out of game based on a terran-centric world view. Actually everything is Traveller is Terran-centric. As you all have pointed out, Traveller is not a simulation, most things do not interact with the rules until the Referee makes up said interaction with how they decide to use a "thing". T5 tried to make thing makers, and that sounds a lot like what you are looking for, but that system is a mess.
Yes, and that can be improved upon. Since the vast majority of Traveller players are Solomani Humans, it is inevitable that more than a few Solomani biases and veiwpoints
are slipp
ed in
by SolSec. But we can extract definitions from first-principles if we care to try; and we can keep the Terran-historical-era illustrations as useful thumbnails for how one world in particular progressed through the various TLs. But those illustrations do not define the TLs they are attached to, they are just labels, examples, descriptions not prescriptions.
The sad reality is this. All defined "Eras" are arbitrary. When was the Bronze Age? The Iron Age? What years exactly? See? All arbitrary. It is just one person deciding that this is what it is and other people agreeing with them.
In North America there were pre-Colombian tribes which worked copper for more than a century, then discarded that knowledge. Using 'era years' to describe their technological progression is unhelpful, and it happened at a wildly different time as the 'copper age' in the fertile cresent. What matteres is the capability, not the 'era'.