Shalom, Timtofly.
Actually, if one will take notice, the verse quoted says "the city LIETH foursquare." The Greek phrase is "ἡ πόλις τετράγωνος κεῖται." Transliterated, this is "
hee polis tetragoonos keitai." Translated word-for-word, this is "the city four-angled lies." "Tetragoonos" gives us the word "tetragon" in math terms. It simply means "four angles," and the word refers to the BASE of the city. A regular tetragon is called a "square" on the small scale; however, the sides of this city are said to be TWELVE THOUSAND FURLONGS (STADIA) LONG! This is from the Greek word "stadion," referring to the Roman word "stadium" or "stade" for short. There are literally hundreds of mile markers scattered around Europe and the Middle East from the Roman Empire that give distances all around the old Roman roads.
One can ascertain from
Wikipedia on Roman measurements, that the Roman "stade" was 607.14 feet long. From the other measurements, one can refine this to be 607.142222 feet (2/9ths of a hundredth more). Twelve thousand of these then would be 1,379.868686... miles in length.
This fact throws a HUGE monkeywrench into the calculations for a cube shape to the city! Is the top of the city LONGER than the bottom of the city in length? Anyway one looks at it, the cube has a BIG problem!
However, if one understands that this verse is solely referring to the BASE of the city, then all four walls can be angled in, and by how much wouldn't matter as long as all four sides angle upward to a point, the CAPSTONE of the city. Notice: the city is not said to have a roof nor is it said to be open at the top. And, Yeeshuwa` ("Jesus") is called "the headstone of the corner" or the "capstone!" After all, the children of Israel were in Egypt for 430 years! They knew how a "capstone" appeared.
Gate openings are different than the gates themselves. The gates are said to be single pearls. And, the OPENING in the wall for the gates will be a tunnel through the jasper wall. The other measurement of 144 cubits, or 72 yards, is probably talking about the THICKNESS of the walls at the gates! That's almost 3/4ths of a football field thick! The gates will be almost 460 miles apart from center of gate to center of gate, given that the perimeter of the city will be 4 x 1,379.8686 miles divided by 12 gates. This distance will be 460 miles around the corners, as well. Thus, almost 230 miles from the last gate to the corner of the city.
I don't think that God would allow "God's Tent" to be "just another natural city."
First off, this is not the "third earth age" in Revelation 21.
The earth is made new after the Second Coming, because of the baptism of fire in 2 Peter 3. There was the earth prior to the Flood. That earth was destroyed and perished in the Flood, but why would it change size? All that changed is all, or most of the water above the firmament came back to the surface of the earth and was no longer above the firmament. That was a change to both heaven and earth, due to the concentration of water changing locations. One could say God was creating a new heaven and earth and the former things were no longer remembered. That was a physical change, not a spiritual, mind changing change.
The children of Shem, Ham, and Japheth would have no clue or experience of that prior world, and would have take their father's or Noah's word for such knowledge.
So Peter goes on to say that we have the same heavens and earth until the baptism of fire, which will once again forever change both heaven and earth. Now, neither Peter nor John explicitly states that God creates anything prior to the Day of the Lord. Peter implies:
"Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness."
John implies that life on earth goes on for another thousand years while Satan is bound. Because after the thousand years, people from the four corners of the earth, march across the breadth of the earth to do harm to those around Jerusalem and the camp of the saints. The Day of the Lord is the third earth time frame. It is the third time God put in the effort to create a new and different heaven and earth. In fact we see this new creation in Revelation 6:12-14
"And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood; And the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind. And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places."
This is the baptism of fire per 2 Peter 3:10-13
"But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness, Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat? Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness."
So no one is going to find destruction as mentioned in 2 Peter 3 in Revelation 19, nor 20. Because the 2 Peter 3 moment already happened prior to the 7 Trumpets. Isaiah 65 gives us the detail of Revelation 20.
After the thousand years is when all things are subdued per 1 Corinthians 15:24-28
"Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power. For he must reign, till he hath put all enemies under his feet. The last enemy that shall be destroyed is death. For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him. And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all."
The end is after the Day of the Lord. The baptism of fire is this:
"afterward they that are Christ's at his coming."
So between the Second Coming and the end is the Day of the Lord where Jesus will reign until all things are subdued. This is the new creation of the "third earth age" as you put it. This period is at the minimum a thousand years per Revelation 20.
So even Paul says this current creation returns to God from whence it came. It is not destroyed nor obliterated. Even John does not explicitly say destroyed. John writes they flee away from the presence of God. Paul says they become so that only God remains. So fleeing could resemble what it means to vanish away. The point is that there is not a restoration, but a defined beginning and end to this creation. The NHNE is not an extension of this creation. There is a defined difference between the end of this creation and the beginning of the next creation. I doubt John is implying that the NHNE has to wait until all are cast into the LOF. Nor would those living in the OHOE necessarily notice a change to the NHNE.
Which means that despite the size of the New Jerusalem it will not be affected even if there is curvature to the earth. You are still trying to place the New Jerusalem onto the current earth. And unless you are claiming God built the pyramids and needs a capstone, this city is still a normal city with normal walls all equal in length, depth, and height. Only you are forcing a wall to be slanted. A pyramid is not a city, but would be an interesting building that would comfortably fit inside the New Jerusalem.
But considering the physics aspect if walls were to go up per a curvature a straight line can still go up a thousand miles into the air. You claim they do not go up but go at an angle and meet at the top. There is nothing in this chapter that requires the city to be enclosed. So no city has to have the walls also be the roof. That is the only reason why a pyramid is still considered a building.
Since you have gone into speculation mode, why would there not be future flying modes of transportation? One could assume the gates would also allow for airplanes, as it would be inefficient to fly that high in the air to enter. In your alleged pyramid shape would two gates be at ground level and the third for airplanes, as your slanted walls don't seem to allow 3 gates all at ground level, without loosing height?
For me it just seems a city will look like a city and not an enclosed building. That and this:
"And the city lieth foursquare, and the length is as large as the breadth: and he measured the city with the reed, twelve thousand furlongs. The length and the breadth and the height of it are equal."
I don't see how the height can be equal to both the length and breadth, if a wall is not square. The top would not be equal to the bottom. The height in the center may be, but at a slant, the wall itself would be a different length.
If a is the same length as the length and breadth of the base, then the actual wall will be a different measurement, h. That is what happens when the wall is slanted instead of at a right angle. So your wall is not the same height if it has the same measurement as the base.