00:00We know that the ancient Egyptians were quite talented to build buildings as grandiose as the pyramids,
00:07but were they smart enough to measure the speed of light?
00:12A theory circulating online suggests it.
00:15If you compare these two figures, you will see that they correspond perfectly.
00:19The first is the speed of light in the vacuum of a meter per second,
00:23and the second is the latitude of the Great Pyramid of Giza.
00:27So, was it intentional, or was it just a coincidence?
00:32Fortunately, we can assure you that it is simply a coincidence,
00:36and not another conspiracy theory.
00:39The Great Pyramid is just one of the many places on Earth sharing this latitude.
00:44Moreover, even if the Egyptians had managed to measure the speed of light
00:49and had decided to keep it secret, they would not have used meters to express it.
00:54It was only defined at the end of the 18th century.
00:57The builders of the pyramids used another unit of measurement, called the elbow.
01:02An elbow is equivalent to a foot and a half, or 45 cm.
01:06This unit, based on the length of the forearm from the elbow to the tip of the thumb,
01:11was widespread in Antiquity.
01:13Thus, if they had wanted to amaze everyone by positioning their pyramids
01:17at a latitude corresponding to the speed of light in an elbow,
01:21they would have had to build their emblematic buildings somewhere in Europe.
01:25Moreover, the Danish astronomer Ole Römer,
01:29who measured the speed of light for the first time in 1676,
01:33would have been quite opposed to discovering that someone had done it centuries before him.
01:38Although the Egyptians had been ahead of their time in many respects,
01:42they never measured the speed of light,
01:45nor used latitude and longitude coordinates for their construction.
01:49The base of the Great Pyramid of Giza may seem to be a perfect square,
01:53but it is actually an eight-sided structure, not four.
01:57Each of these four sides has a slight concave indentation
02:01that uniformly divides them from the base at the top.
02:04The official version would be that a British pilot named Groves
02:07was the first to notice it in 1940, when he was flying over the pyramid.
02:12He took a photograph showing the shadows that underlined these indentations.
02:17Some believe that these lines are only visible from the air
02:20and can be best observed at dawn and dusk,
02:23during the equinoxes of spring and autumn.
02:26This led to a strange theory according to which the ancient Egyptians
02:29could have designed these pyramids to communicate with celestial visitors.
02:33The Pyramid of Cheops is one of the only three pyramids
02:36that once had a rotating door.
02:39This door, weighing about 20 tons, could be easily opened from the inside.
02:44Its precise adjustment made it almost invisible from the outside.
02:48Without a latch or visible handle,
02:50only very slight roughness in the outer wall denoted the opening.
02:54The other two pyramids with similar doors
02:56respectively belonged to Cheops' father and grandfather.
03:00The Great Pyramid also contains a hidden void at least 30 meters long,
03:05discovered in 2017.
03:07We still do not know what is inside this space,
03:11its exact function, or if it is the only one of this type.
03:14Researchers have used a technology
03:16to see through the walls of cathedrals,
03:18Mayan pyramids and even volcanoes,
03:21resting on a natural rain of subatomic particles called muons.
03:25These particles pass through empty spaces more easily than solid materials.
03:30By placing several muon detectors around a structure,
03:33scientists can map these solid elements and these empty areas.
03:37A team placed muon detectors inside the Cheops Pyramid,
03:41collecting data over the months.
03:44Scientists have analyzed many times
03:46samples of the mortar used to build the pyramids.
03:50Although we know the composition,
03:52modern technology still cannot reproduce it.
03:56This mortar, mainly composed of treated gypsum,
03:59was not used as the current cement of our bricks,
04:02but was used to support the joints between these massive stones
04:05during their installation.
04:07About half a million tons of this mortar
04:10would have been necessary to build the Great Pyramid of Cheops.
04:14This gypsum mortar is more robust than the stones themselves
04:17and has resisted for millennia.
04:20The four sides of the Pyramid of Cheops are aligned with the cardinal points,
04:25North, South, East and West.
04:29According to archaeologist and engineer Glenn Dash,
04:32this alignment is accurate to 4 minutes of arc,
04:35or a 15th of a degree.
04:37Architects have achieved this without modern tools
04:40such as drones or computers.
04:42Many researchers have tried to explain this architecture prodigy.
04:46Could they have used the Polar Star or the Shadow of the Sun?
04:50Dash recently proposed a new and simpler idea.
04:53Egyptians could have used autumn equinoxes to align the pyramids.
04:58This happens twice a year,
05:00when the sun crosses the Earth's equatorial plane,
05:03making the day and the night almost equal in duration.
05:06To prove his theory,
05:08Glenn Dash conducted an experiment on September 22, 2016,
05:12the first day of the autumn equinox.
05:14He used a special rod called gnomon,
05:17which the Egyptians had to project a shadow.
05:21Then he followed the point at regular intervals,
05:24forming a regular curve.
05:26By connecting two points of the curve with a stretched rope,
05:29he created an almost perfect line from East to West.
05:32Dash observed that during the equinox,
05:34the point of the shadow was moving in a straight line,
05:37almost perfectly following the East-West direction,
05:40with a slight deviation in the anti-clockwise direction,
05:43similar to the one observed in the pyramids.
05:45Although the experiment was conducted in Connecticut,
05:48Glenn Dash believes that the same method would work in Egypt.
05:52All the Egyptians needed
05:54was a clear and sunny day.
05:57They could determine the autumn equinox
05:59by counting 91 days from the summer solstice.
06:02However, they left us few clues,
06:05and no engineering document has been found
06:08that explains their method.
06:10So, although they could use shadows to locate themselves,
06:14nothing is less certain.
06:16Scientists have long wondered
06:18how these heavy blocks of stone
06:20were sent to the sites of the pyramids,
06:22and they could finally have the answer.
06:24A team of researchers from the University of North Carolina in Wilmington
06:28discovered that 31 pyramids
06:30had probably been built along an old arm of an island.
06:34This arm is now buried under the desert
06:37and agricultural lands.
06:39For years, archaeologists have thought
06:41that the ancient Egyptians
06:43had to use a waterway nearby
06:45to transport materials, equipment, people,
06:49and everything they needed to build the pyramids.
06:52But until now,
06:53they were not sure of the location,
06:55shape, size,
06:57or proximity of this waterway
06:59to the construction site.
07:01The research team used satellite radar imagery,
07:05historical maps,
07:06geophysical prospection,
07:08and sediment carvings
07:09to map this part of the river.
07:12They think it was buried
07:14following a great drought
07:16and sandstorms thousands of years ago.
07:19The team managed to dive under the sandy surface
07:22and obtain images of certain characteristics
07:25hidden thanks to radar technology.
07:27They discovered hidden rivers
07:29and ancient structures located at the foot of the hills,
07:32where most of the Egyptian pyramids are located.
07:35The discovery of this disappeared riverbed
07:37helps to explain the strong density of pyramids
07:40between Gizeh and Lisht,
07:41in what is now an inhospitable area of the Sahara.
07:45Egypt is not the country with the largest number of pyramids in the world.
07:49This title is due to its southern neighbor,
07:51Sudan,
07:52which has between 200 and 255 pyramids,
07:54compared to the modest 138 pyramids of Egypt.
07:57These Sudanese pyramids
07:59were built by the inhabitants of the Kingdom of Kush,
08:02an ancient civilization that reigned on the lands upstream of the Nile
08:05several centuries ago.
08:07They began to build pyramids
08:09about 500 years after the Egyptians stopped doing so.
08:13Although their pyramids are much smaller than those of Egypt,
08:16from 6 to 30 meters,
08:18compared to 138 meters for those of Cheops,
08:20they were built for similar purposes.
08:23Archaeologists continue to work
08:25to understand how the Sudanese pyramids were built,
08:29how long it took to complete them,
08:31and what happened to this civilization.
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