At times, I have thought about trying to explain the modern world to someone from 1920. "Well, we've got automobiles, but they're much faster and require less maintenance, and we have better roads for them. And we've got airplanes, but they're much bigger, and they crash far less often. And we've got better machines for farming, and better medicines..." You could explain television. You could explain transistors - they had vacuum tubes. Computers would be harder - they had mechanical adding machines, but the many-order-of-magnitude-faster computers is a qualitative change that makes them not "like" anything that existed in 1920.
But when I think about trying to explain to someone from 1820, you can't explain anything. They were 40 years before Maxwell's Equations, so no electricity, no radio, no telegraph, no telephone. They were before the first common-carrier railroad. The first internal combustion powered automobile was 1808, but they were not yet practical in any sense. The precursors aren't there. (Yes, the industrial revolution is starting. The products of the industrial revolution that will change how we live aren't there yet, though.)
Most modern tech I can explain in terms of what it does, what it's like to live with. I think this is how I'd explain TV to someone from 1920, but it would be just as easy as explaining it to someone from 1820:
"It's a sheet of glass, and moving pictures with sounds appear on it."
"How does it work?"
"I don't know. It involves several dozen separate inventions, of which I understand perhaps three individual ones well enough to discuss."
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Of course, to really blow the minds of people from 1920, you can either show them anything related to space travel (especially the Apollo missions, but also GPS); or tell them about basically any organ transplant; or show them a 3D printer (you know Bakelite? We found better plastics, and we made a machine that can, without ongoing intervention, use that make any shaped structure we ask it to… and those machines can also do metal, and yes that includes the engines of those spaceships we showed you earlier. Also houses).
But when I think about trying to explain to someone from 1820, you can't explain anything. They were 40 years before Maxwell's Equations, so no electricity, no radio, no telegraph, no telephone. They were before the first common-carrier railroad. The first internal combustion powered automobile was 1808, but they were not yet practical in any sense. The precursors aren't there. (Yes, the industrial revolution is starting. The products of the industrial revolution that will change how we live aren't there yet, though.)