An average person would not be overly useful, but a skilled and knowledgeable individual would have much to offer. A chemist can make nylon, gunpowder, matches, or plastic from relatively easily obtained chemicals even in ancient times, for example. There are also lots of other little tricks that are just as or more valuable. Things like germ theory, medicine, cooking, electricity, etc. In roman times it would have been possible to build telegraphs, without much difficulty, imagine how that would have changed the world.
Science is older than you think. Science is making experiments, recording results, and trying to figure out what is going on.
The oldest clearest example of science is alchemy. Today we know it's impossible, but back then they reacted a tremendous number of compounds and carefully recorded the results.
The course of human history would be a lot different if the simple idea "Look for reasons why you are wrong, not reasons why you are right" could spread earlier and farther. Experimentation has occurred for the whole of human history, but I think that little tidbit is what was missing, distilled down to a single sentence, but one from which everything else can pretty much be derived once you accept it.
Come to think of it, the course of the human present would be pretty different too.
Is finding a way to turn dross into gold or purchase eternal life really science? Taoist alchemy may have been more philosophical in nature, but western alchemy was pretty goal oriented without much mindfulness about science as a higher level process. They weren't trying to understand how nature works, they were trying to enrich themselves. Very different.
You have a "Hollywood" view of alchemy. Most of the people who did it did not realistically expect to succeed. But they continued anyway.
History is full of people who did all sorts of experiments to try to understand how the world works.
It is not necessary to have a goal "understand this" in order to do science, it's enough to have a goal "what happens if I do this". If I do an experiment and find an interesting result, and I publish it, that's still science - even if I have no idea why what I did works.
I'll ignore your undignified cheap shot. Without understanding this as a conscious goal then a directed systematic inquiry that becomes highly integrated into culture and the economic system will not develop. Inventing the printing press, for example, without a sufficiently rich ecosystem in which it can nurture and grow prevented any catalytic effects that might have otherwise formed.
- Better Bread? Historically bakers had extremely short lives because without mixers they had to breathe in the flour dust all day. And the bread would have been extremely unevenly cooked (no temperature-regulated ovens), as well as being extremely salty (no preservatives).
- Pasta? Pasta is absolutely amazing. It is an extremely dense source of calories, which doesn't rot, is super-compact, and only requires water and heat to cook. Great for armies on the march.
- Coffee? Coffee's been around a long time, but high-pressure espresso is relatively new.
Other fairly basic staples are newer than you might think, like Potatoes (16th Cent.), Or Tomatoes (17th Cent.)
Actually that's a terrible idea. You want lemons, not limes. Really.
See http://idlewords.com/2010/03/scott_and_scurvy.htm for a discussion of where the myth to the contrary came from, and for the complex history of how the proper prevention of scurvy was discovered, forgotten, proved false, and only later rediscovered again. It also discusses why you really don't want to use limes.
Pasta is an amazing invention. It's functionally similar to hard tack except it can be prepared to an edible state very quickly with merely boiling water and also tastes much better.
Could you please clarify why whole grain flour pasta would not have nutrients? Unless you meant white flour pasta. And here is how to make it from scratch:
Some of these things would be helpful but you'd need to have them on you if you were dumped in the past. If you landed (now) in the Roman Empire how would you bring them potatoes? ("Just sail across the ocean, then go up the mountains on the other side of that continent and eat those root things there. Easy!")
Sorry, but you're wrong, and I think your racism is showing. Potatoes have been eaten for 7000 years, and tomatoes for 2500 years. They were introduced into Europe in the sixteenth century (and tomatoes weren't eaten there at first), but here in America, we've been eating them since well before medieval times.
Making sure to eat sources of vitamin C to prevent scurvy, having women who intend to get pregnant eat more folate to help their babies' brains...(Not to mention not drinking alcohol while pregnant!)
These might be practically difficult to realize just on brainpower alone.
For example: how do you avoid drinking alcohol if your only sources of drinking water are contaminated? You can boil the water — but you don't know a priori whether the pathogens or toxins in the water can be destroyed by boiling, or how much boiling is needed. If the toxins are things like arsenic, boiling the water will concentrate them, while various kinds of biological processing may filter them out.
And where do you get vitamin C? Tomatoes are a great source of vitamin C, but you can't just go around eating random local tomato-like plants; almost all of them are deadly. Plants like rhubarb have lots of vitamin C, but also lots of oxalic acid. Raw meat is also a good source of vitamin C, but raw meat can harbor many different pathogens. Are you going to build a microscope, synthesize some stains, and inspect a bunch of meat samples to see which ones bear pathogenic bacteria?
And once a couple of your human-subjects experiments go wrong, or just have coincidental unrelated deaths, you're a candidate for a witch-burning.
(Even in the best cases, modern hygiene is not without its drawbacks; the poliomyelitis epidemic is one example.)
