110

The maximum height a mountain can have on Earth is a tad more than what Mount Everest is high. This is due to the fact that when you increase the height of the structure, you are also increasing the load. After a certain point you will be adding too much weight for what the material can sustain, and the entire structure will crumble on itself. The potential ...


79

You've already accepted an answer, but aside from the structural issues (and the sheer mindboggling amount of energy it would take to pump all that water up that high), there's another misunderstanding: allow a train running on a train track going up the cone to escape earth's orbit? Getting into orbit isn't simply a matter of getting up really high. ...


74

These aren't long-span bridges, but causeways The current record for a single span is just under 2km long, and any single vehicular span over oh, 100 to 200m long is going to require modern truss or suspension bridge technology. However, it has been possible to span far longer distances over water for much longer periods than that, using only pre-Roman era ...


51

Have a look at Rama's Bridge here. It is 48k long and runs between the southern tip of Tamil Naidu and one of the northern islands of Sri Lanka Investigations suggest that a chain of atolls was connected and brought above the water by manual labour. The entire length was above water until the 15th century. Given the right geomorphology and backstory I see ...


25

Those bridges are built by connecting together floating rafts or pontoons. They are easy to build and maintain: just chop trees and craft the trunks in the proper shape. Assemble them together, place some anchors along the path. A similar technology was used in Japan to build wooden bridges which could withstand typhoons: during a flood the wooden parts ...


19

It may stretch the parameters of your question but I believe a combination of slowing the speed of light and capturing it in a lossless optical fibre system could do this. The speed of light is normally about 186,000 miles per second, or fast enough to go around the world seven times in the wink of eye. Scientists succeeded in slowing it down to 38 ...


16

I think it depends on what orbit it is at. For instance if it is at a low orbit and spun up to create artificial gravity, then once the ring is broken the remaining pieces will fly away by their own momentum. This wouldn't be the case if they are at the right speed for their orbit. Another thing to consider is how the ring is broken. If a large explosive is ...


16

A deposit of pumice, a light-weight volcanic rock, near the bridges could help the construction a lot. It's not necessary the volcano exists anymore, the rock could have formed thousands of years ago. Pumice floats on water for a time, making it easy to move even large rocks into place. It will slowly sink when water seeps into its pores, and it could be ...


15

Let's start off looking at this from a conservation of angular momentum point of view. We can say that angular momentum is definitely conserved here because there is no external torque being applied to the system. I'm not sure that orbital energy is conserved here since it really seems like whatever motors are pulling the cables tighter will need to do ...


15

Consider an ancient civilization. In the middle Ages, some of the biggest architectures (aqueducts and bridges) were Roman-built, like the Alcantara Bridge. So, in the past history of your world, a big and organized empire left some magnificent relics of its past power, like these bridges. Maybe they were built with the aid of some magic, or just following ...


13

L.Dutch has already explained why it won't work, I want to add that if you try to do this in any reasonably short amount of time, you will create a huge turmoil. The amount of energy needed to pump thousands of thousands of cubic kilometers of water 3 km uphill (and that's just in the beginning) is staggering mindboggling. A good part of this energy (+ the ...


10

This lake on which your bridges are built on may have only recently become a lake. What I mean by this is that what if several decades/centuries ago, this lake was only a canyon/crater (and has only fairly recently flooded) and these long bridges, as well as the islands, are the only parts of the canyon which were above sea level? These long bridges could ...


10

It being a lake makes the problem somewhat easier from my opinion - any structure in the water would erode much slower then it would in the river or the sea, due to the slower currents. I've looked at the list of longest bridges and dams of the ancient world, and to my surprise, there were actually structures of 2 kilometers in length in both categories. (...


10

There is a good reason to keep the city on an island in the lake. The reason may be irrational but still good. "This is were the kings or government have been for centuries, it would put their legitimacy into question to move elsewhere" or "this is where the main temple has been since the founding of the state, the god would be angry if we move it." Consider ...


10

I won't dare sticking my finger into the relativistic theory of rotating bodies, I will just go with the approximation of linear motion, which is valid for infinitesimal rotations. We know that, by relativity, the mass of an object moving at velocity v is increased according to Lorentz factor $\gamma=$$1 \over \sqrt{1-v^2/c^2}$. Therefore, the more the ...


10

This question has actually been well studied throughout the years and is closely related to the Ehrenfest paradox. The answer is no-- it's impossible to spin a giant disk in a way such that its outer rim moves faster than the speed of light. First and foremost, it's a rather basic derivation from the postulates of special relativity to show that no object ...


9

You have several problems here, let's assume the logistical ones are all solved (as they already are for long distance tunnels) and just focus on the engineering ones. You have six problems with a tunnel through the magma: Making the hole Temperature Pressure Leaks Seismic activity Currents Making the hole Actually making the hole is easier in the liquid ...


8

No. Building a fully programmable biosphere and then programming it appropriately for your needs, to replicate an Earthlike environment, could be one Clarketech style method for achieving terraforming, but neither implies the other. If you broaden the definition of "terraforming" to include altering the environment on a planetary body to any particular ...


8

The station's orbit will destabilize. There are several underlying principles to keeping a ring-station in a stable orbit around its parent: Aligned center of mass with parent. Matched rotational spin (specifically the precessional angular speed of the ring to Earth’s rotational angular speed). artificial gravity induced by centripetal acceleration. ...


8

I was once where you are. I wondered if it was possible to create a rotating mirrored propeller capable of spinning fast enough to separate particle pairs in the quantum foam in a manner reminiscent of a Quantum Vacuum plasma thruster. The answer is no. The reason is material stress. Basically the maximum stress on a rotating solid disc (or arm) scales as ...


8

Millisecond pulsars! Gravity waves! Imperial to metric conversions! 60 mile diameter disc. 188 mile circumference. 1000 rotations per second = 188 * 1000 miles / second = 188,000 miles/second Speed of light = 299 792 458 m / s = 186282 miles / second. The edge would be going faster than the speed of light; not allowed. Here is a fine and relevant ...


7

You can have differential rotation among concentric shells over geological times only if the space between the shell is vacuum. Any fluid contained between them would, via shear stress, nullify the differential rotation over the above mentioned geological times. A shear stress, often denoted by $\tau$, is the component of stress coplanar with a material ...


7

Starfish Prime's answer touches on this, but all the answers so far seem to be missing the most significant problem with this question. The question assumes that it is possible to "escape Earth's gravity". This is a very common misconception, based on the observation that people in the space station float around as if there is no gravity. The "as if" is ...


6

A Dyson sphere is only part of what you need A Dyson sphere is a hypothetical method of capturing the power from a star, however if your ship is moving and connected to the Dyson sphere then it needs your 'force field' to stop the sphere crashing into the star. Stars have magnetic fields and so we could generate an opposing field to push against this and ...


6

This question periodically pops up on the Physics SE: Why is Larry Nivens Ringworld Unstable. The summary is, the whole concept of a ring world is not stable; the ring will not stay centered on the star. The concept is similar to trying to balance a pencil on its point: any disturbance will cause the pencil to topple.


6

100% reflective mirrors do not exist in reality. The best we can get is dielectric mirrors, with reflectivity around 99.9% at specific wavelengths. That aside, if you want to trap light, just shape the mirror as a sphere with perfectly reflective surfaces. Any photon inside the sphere will keep bouncing in the sphere. A similar concept is employed in the ...


6

I'm offering this more as storytelling advice than bridge-realism advice, but you can always just leave the origin of these massive bridges a mystery. Tell your players that nobody in the world knows who built the bridges or why. Let them have their theories but never confirm anything either way. Our real world, especially in the time period you mention, was ...


5

A quick word: You want "science-based". I think what I gave you fits this according to what I encounter elsewhere on worldbuilding. I have to say in my defense though: We are dealing with very advanced aliens. What they might be able to build could seem impossible for us. So I'm not going to give you any design specifications. If you want blueprints for ...


5

Only dozens of habitable planets in one solar system, eh? Well, you're thinking small. The work for a solar system with one million Earths has already been done by astrophysicist Sean Raymond. His model, like the one postulated in his question, is centred on a supermassive black hole. Let’s start with a supermassive black hole, like in the Black Hole ...


5

The lake is shallow -- almost a swamp. Three real-world examples of such lakes are the Tulare Lake basin, the Everglades, and the state of Iowa during flood years. Tulare Lake is named for the reed-like plants that grew in much of its area. If San Francisco Bay, the Baltic Sea, and the Persian Gulf were freshwater, they might also be similar lakes. In ...


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