How were megaliths moved?

As to how much energy you could put in, where it would come from, wether it would decrease static and kinetic coeficient of friction and wether it would destroy the rock, I do not know how to estimate that.

Some kind of sonic vibration to move a 500 ton stone?
I don't buy it.
Unless, of course, it's the vibration of 500 slaves moving that stone. Very common in that day, you know.

There is no evidence that the inhabitants of Easter island or the Egyptians used slaves. They had a large work force consisting of free laborers, mainly farmers, during the lapse between harvest and the next planting.
Egyptians and Easter islanders, knew that friction could be reduced by putting the stones (or statues) over sleds made with tree trunks. This is likely the reason why the natives exterminated all trees in the island (see Jared Diamond's "Collapse").

Would it not still require massive slave labor to do this?

Would it not still require massive slave labor to do this?

The second experiment resulted in two quite successful pulls, one of 40 m and another of 70 m. Pulls were limited only by the available rail material laid out on the ground in the direction of travel and/or by rock outcroppings that impeded movement. Between pulls, the rails were repositioned. Coefficient of friction was established at 0.2, which surprised us with its low value, and about half that once sliding commenced. Sliding was greatly enhanced by lubricity of the de-barked eucalyptus.

The third experiment was conducted with the statue face down, base first on the same transport sledge. To support the head and neck, the statue was raised slightly by placing a “triple stack” of lashed logs laterally across the sledge and lashed in place at the statue’s upper torso level (Figs. 4, 5). The slight concavity in the upper torso of the moai was located at exactly the required point and the statue quite naturally accepted this lateral beam. The statue was then pulled 50 m, 30 of which were along a road-path and 20m up an 8% grade ramp to the replica platform where it was to be erected. No rollers were used on the ramp. Instead, individual “rungs” of a “canoe ladder” were spaced up the ramp then lubricated with water/banana stump liquid. The 20 m distance was covered in an astonishing 15 seconds. The statue was then positioned for the raising experiment that followed.

People, Food and Work
Computer modeling suggested that 55-70 people (or 48 average) were required to pull the average statue of 12 m tons over Path 1, and that their collective food requirement would have totaled 201,600 calories per day from agricultural staples such as sweet potatoes and bananas. Our experiment demonstrated that 40 people were fully capable of pulling a 10 m ton statue.

It is estimated that 65% of males and females between the ages of 10 and 65 are available for the average extended family “work force” in contemporary Polynesia. Our hypothesis was that males performed the actual work, while females and children provided support. In fact, however, during the experiment women made up the larger part of the pull crews, while males only were allowed by the Rapa Nui crew chiefs to perform the heavy and far more dangerous tasks of levering in proximity to the statue. The pull crews generated a great deal of excitement, camaraderie and shared purpose during the transport experiment, and this sort of community participation was certainly required and valued in prehistory, part of the euphoria of the statue cult experience.

The wood sledge served as an efficient gantry on which the pukao was neatly balanced and against which workmen levered without damaging the statue. Only 20 expert individuals were required to erect the statue over 3 days. Just as a master carver and apprentice were preferable to a large gang of workmen in the quarry, large crowds of willing workers were neither necessary nor safe while erecting a moai on image ahu. Substantial unskilled labor was required to collect, transport, stack, move and restack large rocks used during raising.

It is fair to say that our manpower estimate remains viable, with an optimum actual task involvement of 55-70 people. Our hypothesis that 5 m of ground would be covered with each discrete pull was low, and a total of 5-7 days for moving the average statue some 15 km over Path 1 is reasonable. The estimated size of the average Rapa Nui chiefdom thus remains at 8.7 extended families or 395 to 435 people. The estimated resources of approximately 50 acres of agricultural crops were required to support this effort, or double the extended family norm for East Polynesia, with supplementary marine resources required as per oral traditions.

Worth of remembering that our current attempts - no matter how educated guesses we did - are probably just a good starting point for fine tuning, which will increase the efficiency. And our ancestors were probably much better at fine tuning with whatever lied around than we are - just a matter of personal experience.