Suppose someone from the high point of the Han Dynasty was magically transported to Qing Dynasty China under the Kangxi emperor? I am asking because I often read about China having the longest continuous civilization and a lot of narratives that emphasize continuity rather than change in Chinese history. At the same time, it seems inconceivable to me that there wouldn't be massive change over a period of thousands of years, and I was wondering how to better think about this.
Great question! The short answer is that the Han time traveler would be completely bewildered by the social and cultural changes but would probably find the politics to be pretty familiar. For our purposes here, I'll assume we're taking a Chinese man from the Eastern Han reign of Emperor Zhang (75-88) to the Qing reign of Qianlong (1735-1796)- this could arguably be a "peak Han" to "peak Qing" comparison.
The first thing they would notice would likely be the linguistic change- the Hanren would be a speaker of Old Chinese now surrounded by speakers of essentially Modern Chinese, a difference that may be comparable to that between the Latin spoken by Cicero and the French spoken by Voltaire. If he found himself in northern China, he would be especially surprised by the difference in speech, as the Northern dialects had diverged more sharply from Old Chinese than had Southern dialects like Cantonese/Yue. But fortunately for him, he would be able to communicate with Qing elites through writing- in the centuries since the end of Han, influential works of Zhou, Qin and Han writing were taken as the standards for Literary Chinese or wenyanwen, so even while spoken Chinese had drifted freely the written form preserved grammar and usage from Old Chinese. Many staples of Qing-era education, from the Confucian classics to the Daodejing to Sima Qian's Records of the Grand Historian, would have been intimately familiar to a Han reader.
In territorial and demographic terms, the Han visitor would have been astonished by the changes. The Han census of 2 AD recorded some 57 million people, the vast majority of them living in north China's Central Plains, but by the end of Qianlong's reign at the turn of the 19th century, China's population had swollen to 300 million, most of them living south of the Yangzi, outside the traditional heartland of early Chinese culture. A Grand Canal, built in Sui times, linked Beijing to Hangzhou and connected the Yellow and Yangzi river systems. And the borders of China had expanded to take in Manchuria, Mongolia, Dzungaria, Taiwan and Tibet, while former Han territories in Vietnam and Korea were now independent but tribute-paying Confucian monarchies.
Religion would be another shock for the time traveler. Buddhism, which was a little-understood foreign religion just beginning to impact China during the Eastern Han, by Qing times had become a fundamental part of Chinese religious life, alongside a religious Daoism that had only emerged after the Han collapse. The empire also had millions of Muslim subjects, not just among the northwestern steppe peoples but also in Hui communities spread across urban China. Traditional Chinese ancestor worship continued in a form basically familiar to the Hanren, but now alongside Buddhist, Daoist and other rites and customs.
Politically, the general contours were the same but the fine details may have been shocking. The Qianlong Emperor ruled, like the Han emperors, under the title huangdi from a glorious capital that was symbolically at the center of the world. That capital was no longer in a traditional Han royal site- Xi'an or Luoyang- but the new capital at Beijing had the expansive palaces and temple complexes a Han ruler would have expected. Qianlong was served by a professional bureaucracy, educated in the Confucian tradition and selected (hypothetically) on merit, and that bureaucracy collected taxes, administered justice, maintained public works and kept exhaustive records, like the Han bureaucracy. But Qianlong was a Manchu, descended from a foreign conqueror. His dynasty had imposed the distinctive queue hairstyle on the defeated Chinese as a mark of subjugation. The court leaned heavily on Manchu nobles, and the core of the army was made up of Manchu bannermen. With the seismic cultural and demographic shifts in China, the administrative system had also been redrawn, and Chinese foreign policy had also kept pace with the rise of other states since Han times and, more recently, the arrival of Westerners.
This is a very broad question. I would suggest recommend breaking it down by domain.
Examples:
Linguistics: would a Han dynasty scholar be able to have a conversation with an educated Qing gentleman? (No, as pronunciations had changed unintelligibly, but they could communicate in writing, as educated Chinese mastered the classical texts)
Demographics: the Qing dynasty saw a population explosion, partly the result of newly introduced foreign staples like sweet potatoes, maize, and peanuts, with a population tripling to 450 million people by the mid 19th century. The Han dynasty actually conducted a population census in 2 CE and counted slightly under 60 million people. Your Han era man would find the countryside and cities quite densely populated and notice considerable deforestation.
Religion -- Buddhism was only just introduced in China during the Han dynasty and didn't achieve widespread popularity until the Tang. There were huge changes in Buddhist practice over the centuries.
Politics: Your Han individual would be distressed to learn that China had been conquered and was now being ruled by foreigners from the North (the Manchu), but would recognize the basic organizational system of emperor and officials.
Technology: Innovations that we think of as classically Chinese, like gunpowder, paper, blue and white ceramics, and movable type printing, appeared or were popularized after the Han era. (For that matter, even tea drinking didn't become widespread until the Tang).