How pyramids with huge structures of stones were built in Egypt more than 2000 years ago. Some people claim by even today’s engineering, it is impossible to build such massive boulders and stones to be put on such a height. They claim that there should have been non-humans (aliens) involved in the construction. Can you please address this issue in detail.
ANSWER: As far as the physics goes, I can address this simply. For "detail" you really need to go out and find all the resources (there are many, just search for "great pyramid of Giza" or something like it) online about it.
Even the heaviest stones can be easily lifted by today's modern heavy-lift cranes. I helped design a nuclear reactor (not yet built, but modeled on buildings that currently exist and operate) with a 150 ton fuel handling robot. The heavier stones in the Great Pyramid of Giza weighed between 30-70 tons (metric, both cases). So, today we would really have no trouble building such a structure at all, though it would no doubt take a few years. Back then, it's truly impressive that people could've built such a structure out of such large blocks (most of them very much smaller, weighing only a few tons). The structures are vast, estimates of the workforce required number somewhere in the 200,000 range. With such a workforce, organized and motivated, could lift such blocks. It would take about 750 or so people working in concert to quite simply lift both a 30 ton block (just add about 15% mass for riging and cross-beams to lift with and then divide, assuming that a worker could manage to lift 40-50 kg) and whatever rigging it was attached to...rolling them along on logs appears to be a more reasonable method with far fewer people to move them the required distance from a quarry. That estimate is just for the heavier blocks and not for the innumerable smaller blocks. The physics is there, the workforce was there, and the numbers add up. Over a period of 10-20 years, the pyramids could have been built quite handily by humans. No aliens are required, and there's absolutely no evidence that non-humans were involved or even exist.
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QUESTION: Thanks for your reply. It is said that the structure of pyramid shape helps in preservation of mummies from decay. How scientific is this claim?
There is absolutely no science behind this claim. It was even disproven as a wild, unsupportable notion on Mythbusters. To quote one of them (via a cited reference) "I'm still ashamed we ever went near pyramid power as a story to test. All of those mystical things. …We're not going to try to prove a negative. We are always going to look for something that we can actually get our hands on and do tests toward the goal of coming to a conclusion."