These machines are large. The size of mountains. Have not moved in millennia. And now they're awake again. And moving. With every movement, there are quakes as the crust literally buckles under their massive weight.

It is possible that they were used in the original terraforming of the planet millennia ago. Or perhaps they were simply an art form created by the famous eco-poet Deirdre Skye just because she could.

Assuming a vaguely conical shape: $$V=\frac{πr^2h}{3}$$ A height of about 5,000 m;
A radius of about 5,000 m;
And a density similar to that of titanium 4500 $kg/m^3$;
$1.31×10^{11}m^3 \times 4500 kg/m^3 = 5.9\times10^{14} kg$

We get a mass of about 590 billion metric tons.

Is there any way such a machine would still be mobile?

If it is relevant to answering the previous question, feel free to address related topics such as what material it is probably build out of, how much energy it would need to move (fusion reactors?), but this is not mandatory if you can argue for a credible answer without using such estimates.

Edit: Yes, in terms of size and speed I would imagine them to be comparable to (very fast) glaciers.

  • $\begingroup$ I'm open to the possibility that they might be somewhat hollow, or lighter on the inside, it that helps. $\endgroup$ Commented Feb 3, 2016 at 18:55
  • $\begingroup$ Get Young Alice to ask them to move? $\endgroup$
    – Samuel
    Commented Feb 3, 2016 at 19:02
  • $\begingroup$ My immediate response is: "Disassemble it and steal its power-source." This thing is massive enough to warp the Earth's crust. $\endgroup$ Commented Feb 3, 2016 at 19:05
  • $\begingroup$ I'm pretty sure something that heavy would literally cause the land beneath it to simply crumble, and it would sink into the ground. Also, it would be interesting to ask someone with a little more knowledge on the subject if they would affect the planet's orbit. $\endgroup$
    – AndreiROM
    Commented Feb 3, 2016 at 19:37
  • $\begingroup$ @AndreiROM, The mountains don't simply sink in completely. It is heavy yes, but spread over~78 sq. km. $\endgroup$ Commented Feb 3, 2016 at 21:49

9 Answers 9


Let's look at the pressures involved. Given the $5km$ radius and the $5.9*10^{14}kg$ mass, that's an average of $5.9*10^{14}/(\pi 5000^2)\approx 7.5*10^6kg/m^2$ supported by the rocks underneath these machines. This then translates into $7.5*10^6kg/m^2*9.8m/s^2=7.35*10^7N/m^2=735$ bars of pressure. According to Wikipedia, this is not enough pressure to transform the rock into metamorphic rock. I couldn't find a number for how much weight rocks can hold, but not being able to turn into metamorphic rock is a good sign.

Intuitively, this should make sense—titanium is a little less than twice as dense as rock is, and mountains usually don't collapse under their own weight. To be safe, I'd suggest that the machines should not be entirely solid (which is probably more realistic anyway). If it is about 50% hollow, it will have the same density as rock and so you shouldn't have to worry about the rock underneath it collapsing.

Keep in mind that this is if the pressure is evenly distributed across the base. If this isn't the case, it's probably going to crush the rock underneath areas receiving more pressure.

However, you've got another problem to deal with. Rock is strong enough to support them, but the terrain they want to move across likely isn't rock. This means that you've got a lot of dirt, plants, and possibly buildings in the way. Your mountain-machines are going to be swimming in this stuff, so why not design them to swim in it?

Basically, they will "eat" everything above bedrock in front of them, and spit it out behind them. This could also provide some of their fuel for moving, whether it is some form of fusion using some of the hydrogen (and other light elements) they consume, or some form of direct mass-to-energy converter.


According to Wikipedia, titanium (which I have chosen to use, even though it's not a requirement) is diamagnetic but not ferromagnetic. That means that direct diamagnetic levitation is possible.

Diamagnetic levitation will work when $$B\frac{dB}{dz}\geq\mu_0\rho\frac{g}{\chi}$$ where $B$ is the magnetic field, $\mu_0$ is the permeability of free space, and $\chi$ is magnetic susceptibility. According to this, $\chi\approx1.51\times10^{-4}\text{ cm}^3\text{ mol}^{-1}$. Changing the units, we get $1.51\times10^2\text{ m}^3\text{ mol}^{-1}$ The molar mass of titanium is $0.047867\text{ kg mol}^{-1}$, so $\chi\approx3155\text{ m}^3\text{ kg}^{-1}$. This means that diamagnetic levitation will work when $$B\frac{dB}{dz}\geq1.76\times10^{-5}\text{ T}^2/\text{m}$$ This sounds surprisingly easy, so I suspect that I messed up somewhere.

Anyway, the point is, we might be able to levitate a mountain made of titanium. Stronger magnetic fields might be needed to lift up the base if I'm wrong in my calculations, but making the machine mainly hollow might do the trick.

The reason this is important is that you need to lift these creatures off the ground to move them forward. This will reduce friction a lot. For propulsion, I would suggest going in the direction of maglev trains. Granted, they use methods other than diamagnetism for levitation, but you could write up some of the same electromagnets for forwards/backwards motion.

  • $\begingroup$ Wouldn't that require laying out a track of magnets? I guess they can be swept up at the rear of the mountain and reused. Also, solar panels could provide energy because nothing can overshadow a thing like that, but dirt, dust and moss can be a problem. $\endgroup$
    – k-l
    Commented Feb 6, 2016 at 0:25
  • $\begingroup$ @KiranLinsuain I would require a track, yes, and solar panels do seem to be a good energy source. $\endgroup$
    – HDE 226868
    Commented Feb 6, 2016 at 16:13

Without some kind of antigravity field it probably could never have been mobile.

Anne McCaffrey had an alien species called the Theks, they were a Silicate based life form that started 'small' the size of a small boulder and grew to immense sizes over millenia. The size of small mountains in some cases. One was discovered to be approximately 100 millions years old and was mistaken as a mountain.

They used fusion for power generation and could fly though space without a ship (once they reached a certain size). But they didn't 'move' as such after they got large, they could 'fly' but they didn't walk, roll or shuffle.

There are issues with moving things that large. First of course is the ground it is resting on. Take airplanes for example. many small airports can't handle large jumbo liners, not because the runways are too short (though that might be another issue) but because the runways can't handle the weight of the plane. they would ruin the runways.

Now take something so much larger. all that weight pushing down, squeezing the reinforced concrete between it's wheels like a warm cow-pie between your toes. That much weight most land would be more liquid and it would be 'sailing' through plowing it's way at some buoyancy point. This would also cause a lot of friction creating a lot of heat. leaving a gouge a couple miles wide and hundreds if not thousands of feet deep.

if it settles down in place it might start making metamorphic rock, using the heat gathered and generated from movement to help.

That is assuming you could get it to move in the first place. Taking into account the Square Cube law I don't think we have any materials that could handle the stresses of moving such a mass without it crushing it into a lump, much less a drive system to handle the torque needed. Not even the largest tracks imaginable would work.

So Actually moving under their own power with conventional mechanics is not happening. And then the power consumption to move 5.9×10^14kg X 2.34 cal (roughly moving 1 kg vertically 1m with minimal friction) is a LOT. Sorry my math classes where years ago.

So anti-gravity and a fusion power-source are minimum requirements to have a chance.


It's not looking good for your machines.

They're currently about $6*10^{14}$ kg. The bomb dropped on Hiroshima released about 60 Terajoules of energy - about $6*10^{13}$ J. Therefore, by definition of what a Joule is, if we were able to harness 100% of the Hiroshima bomb's energy, we could accelerate your machine by 0.1 $m/s^2$ through one meter.

Current worldwide energy consumption per year is about $6*10^{20}$ J. Harness 100% of that and you can accelerate your machine by a million $m/s^2$ through one meter, or one $m/s^2$ through a million meters. But at that point you're using the same energy that the planet uses in a year and you're only moving a thousand kilometers (for those in the US, that's not quite the distance from New York, NY to Knoxville, TN).

Only you wouldn't make it that far, because that doesn't take friction into account. You'll have a lot of friction force due to your large mass, so the acceleration you have won't get you moving very quickly; much of the energy will go to simply fighting friction.

And even that doesn't cover the fact that as you said, they're breaking the Earth's crust every time they move. They'd sink into the Earth a bit just by existing on the surface due to their mass. As such they have to fight against gravity as well as friction. They aren't simply moving along the surface, they have to move upwards too.

And, of course, we can't harness energy with 100% efficiency. Physical impossibility (given what we know blah blah blah).

Best case: make them smaller, particularly in the radius (since there's a square on the radius, cutting it in half cuts the end volume [and therefore mass] in four), and have incredibly efficient incredibly powerful fusion reactors. Otherwise, get used to your new scenery, because they aren't going anywhere.

  • $\begingroup$ Technically they wouldn't need to move upwards, they would need to compress the land in front of them downards. $\endgroup$
    – Tim B
    Commented Feb 3, 2016 at 22:44

OK, let us try to move the machine with a rocket engine, more specifically, the F1, the largest liquid fuel engine ever created. Having a thrust of 6,770,000 N at sea level, we must have 870 million of them in order to make it lift off...

Lifting it even one meter up requires an amount of energy corresponding to 590,000 tons of bread.

However, this could be used as a vehicle travelling in the opposite direction, down. With that enormous mass, it is going to take quite a while before the magma melts all of it. Even if it melts away at almost half a meter per second, the core of it would stay unaffected for hours. It is one time use though.

A 5 kilometre high conical massive objects is not what I usually call a "machine", I prefer the word "mountain".

After reading your question, I am a little suspicious to what is actually inside all those very conical looking mountains...

Mount Fuji

  • 2
    $\begingroup$ "amount of energy corresponding to 590,000 tons of bread" interesting choice of energy unit. $\endgroup$ Commented Feb 3, 2016 at 20:39
  • $\begingroup$ I prefer bread when dealing with high numbers, 1 kg of bread is very close to 10,000 kJ. $\endgroup$ Commented Feb 3, 2016 at 20:43
  • $\begingroup$ White? Wheat? Rye? And how is the bread converted to energy? $\endgroup$
    – AndyD273
    Commented Feb 3, 2016 at 21:19
  • 1
    $\begingroup$ @AndyD273 That does not actually matter that much, the energy estimates I have found for 1 kg of bread are between 9,200 kJ and 10,400 kJ. I use a "standard bread unit" of 10,000 kJ. The bread is turned into energy by combustion, and leaves out the oxygen from the equation. It is just an everyday unit people are more comfortable with than "Joules" $\endgroup$ Commented Feb 3, 2016 at 21:25

The mountains slide on thin layer of superheated water.

Leaving aside anti-gravity tech, this seems to me the most feasible option, though it will still require fusion reactors.

The mountain collects rain falling on their sides, extracting the deuterium for fusion and storing the rest for when it needs to move. When it wakes up, the fusion reactor generates streams of plasma that on their way to nozzles at the edges and bottom of the cone pass through heat exchange pipes and heat the water to very high temperatures, probably several thousands degrees Celsius. Because of the insane pressure at the flat bottom of the mountain the water remains liquid at those temperatures.

The water is ejected out of the bottom of the mountain much like a steam iron does, where it essentially lubricates the entire bottom surface. Half of the plasma is fired forward from the slightly raised front edge of the mountain where it vaporizes any terrain features that might obstruct the mountain. The other half is injected into the water under the rear of the mountain, where it heats the water beyond the boiling point, generating just enough upward pressure to push the mountain forward.

Note that forward only refers to the current direction of travel. The nozzles would be placed all around so that redirecting the plasma streams will change the direction of travel without having to turn the mountain around.

The major limitation is that this system could not handle more than a tiny upward gradient by itself, as the mountain would simply slide backwards on its own water cushion. However, a more classical solution of giant gear-like wheels (think 100m+ diameter with "teeth" digging 15-20m into the ground )may allow the mountain to push itself forward even uphill.

In retrospect, these ancient devices may be a little less impressive if you think of them as humongous hybrid of steamboat and clothes iron... Fortunately, there's a more awesome solution: Increase the power of the fusion reactors and just vaporize the earth under the machine directly to make it float on a cushion of plasma, leaving a trail of lava behind it!


Float on the Earth's Mantle

Like the Earth's mountains (& crust) do.

enter image description here


Thought I would point out how to visualise the machine's influence on the tectonic plates.

The total weight of a cone is exactly a third that of a cylinder with the same base and height. If titanium is twice as heavy as stone, then the 5km tall solid titanium machine is the same weight as a 3.33km tall stone cylinder. That's pretty much 2 miles tall.

If we assume the pressure at the bottom of the machine is evenly distributed (as is probably best engineering practice) then the rock beneath the machine experiences the same strain as the rock located 2 miles deep into the crust.

Since the crust is solid up to 30 miles (50km) in places we know the weight of the first two miles of crust is not enough to change the composition of the rock. So neither would the presence of the machine cause the crust to change composition.

Worst case scenario is the machine's weight causes the crust to compress by 2 miles. Then the bottom two miles of the crust beneath the machine dissolve into the mantle, but it's still 28-ish miles thick. So you're looking at a new ocean, but an ocean of water as opposed to lava -- as some contributors have suggested.


I think that the machines would bend the crust and the vehicle would sink into the mantle. Possibly it could stay on top of the crust if it was hollow. Best way I can think of to make it move would be to fill it with something like helium so it was light and then spread out the remaining weight with huge treads, with wide enough treads and enough helium it should be able to move along relatively well. It would need a lot of power though. Although obviously using helium would mean you could not go inside it so the machine seems kind of pointless.


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