Any perceived stall may be an illusion for a couple of reasons: 1. Real-world performance is not necessarily linear with technological progress. 2. Landmarks

Any perceived stall may be an illusion for a couple of reasons: 1. Real-world performance is not necessarily linear with technological progress. 2. Landmarks by which we measure progress may be far apart. #1. We frequently compare computer memory to automobile engines and ask why engines have improved so little while memory capacity has skyrocketed. It's an unfair comparison. If we were still using magnetic core-memory, as we were in the 60's, capacities would now be only incrementally larger. The growth of memory capacity has been driven by a succession of novel technologies, while the fundamentals of an automotive engine are essentially the same as they were a century ago. We must ask, "Why is it harder to come up with novel types of engines than novel forms of memory?". Perhaps it's due to complexity. Computer memory is a very simple thing repeated many times. Improving that simple thing yields great benefit with comparatively little effort. An engine is a collection of many different parts that interact in complex ways. Incrementally redesigning individual parts is unlikely to result in novel types of engines with fundamentally different capabilities. To come up with a new type of engine you have to design a very complex system all at once. Expecting memory and engines to improve at the same rate is not realistic. #2. What landmark comes after sending men to the moon? Sending them to Mars? The Apollo missions were tremendously expensive and the scientific value of research conducted on the Moon was small compared to the progress achieved in getting there. That may be why we stopped sending manned missions to the moon. Why it's taken so long to send men to Mars may be because the difficulty is much greater. We need far more thrust to transfer orbits. We need to sustain humans in space for long periods of time without protection from the Earth's magnetosphere. We need to send squishy humans down a gravity well much more significant than the Moon's without much atmosphere for braking. We may have been making steady progress on all of these problems but, until we actually land a human on Mars, the Moon remains the high-tide mark.