Most people think of "the Middle Ages" as one, 1000-year period which had nothing but knights, peasants, castles and kings in it in Europe. Can someone make a timeline of MAJOR scientific and social changes during the Middle Ages?

No, I don't think it is really possible. One problem is that the story of the Early Middle Ages is one of very large unites breaking down into smaller ones: the collapse of Roman authority in favor of the Germanic kingdoms, replaced by the Carolingian Empire which, in turn, came apart at the seams fairly quickly. It is possible to give a narrative about, say, the Roman Empire and talk abut Britain and Anatolia at the same time, but you can't really do that with the Middle Ages--if you are talking about the period of, say, 900-1300 you will have completely different narratives depending on whether you look at Germany or France.

That being said, this is the conventional periodization:

Early Middle Ages: about 476-1096, the deposition of the last Western Roman emperor to the First Crusade (the latter event chosen just to give an anchor to the vague Year 1000). However, virtually every survey of this period will start with the death of Constantine because the period of "Late Antiquity" (about 300-700, although definitions vary wildly) is simply too cohesive. You can't understand what is happening in 600 if you don't know about 400. The early Germanic kingdoms were highly "Romanesque" in their rhetoric and regalia and the Eastern Roman Empire loomed large over the landscape. The end of Late Antiquity depends on the focus: it can be the unraveling of Justinian's Empire, the rise of Islam, the creation of the Carolingian Empire, even the Viking attack on Lindisfarne. Each of these points an more make perfect sense depending on what area of the former Roman Empire you are looking at, and perhaps it is best thought of as a period in which the phrase "the former Roman Empire" makes sense. The rest of the period is dominated by the Carolingian Empire, and its unraveling (let's say 987 with the accession of High Capet) is often thought of as the end of the Early Middle Ages, although the first Crusade, Battle of Hastings, death of Cnut the Great and many more are perfectly valid--probably why many like to just say "500-1000" and leave it at that.
High Middle Ages: to the Black Death in 1346. Socially this involves a lot of things that /u/Belisarius1 mentions and it is where we get the stereotypes of the Middle Ages that aren't from later periods. we can talk about feudalism, serfs and knights in 1100 in a way we can't in 700. This is where many romances and troubadours are from, as well as religious orders like the Franciscans (1209), Dominicans (1216) and Cistercians (1098) are from (although the last is a bit complicated. So this is the Middle Ages "proper".
Late Middle Ages: To, hell, whenever you want to to be. I saw a somewhat serious argument that pushed it to the French Revolution, but most are happy with using Columbus (1492) or Luther (1517). This period gets a bit of a bad rap because everything nice from it is called "Renaissance" and all of the less nice things get called "Medieval". This is where all the other stereotypes of the Middle Ages come from--witch burnings, for example, is extremely distinctive to this period and very much not to the other ones.

These categories naturally break down very quickly when subjected to too much pressure because as I mentioned above it becomes very difficult to talk about broad processes. But they are still useful units and generally the best way to dive into Medieval history as a whole. Do you like crazy names like Clotho and Gunnhilde? Early Medieval. Knights? High Medieval. Jousting? Late Medieval. It's not perfect but it is a lot more digestible than looking at an extremely complicated one thousand years as a unit.

And I can't recommend the Great Courses series with Philip Daileader on the Middle Ages enough for this.