Serious Scientific Answers to Absurd Hypothetical questions

[DDE]

1 hour ago, p1t1o said:

which one of these would stand out?

That reminds me...

Totally an 80 t geophysics experiment, nothing to see here!

[Slam_Jones]

I've got (̶w̶h̶a̶t̶ ̶I̶ ̶t̶h̶i̶n̶k̶ ̶i̶s̶)̶ ̶a̶ ̶f̶a̶i̶r̶l̶y̶ ̶e̶a̶s̶y̶ one:

If the Earth's rotational speed were to suddenly decrease to half its current speed, would the average global temperature change?

What if the rotation speed doubled?

Edited November 17, 2017 by Slam_Jones
Nothing is ever as easy as I think it is!

[Green Baron]

23 minutes ago, Slam_Jones said:

I've got (what I think is) a fairly easy one:

If the Earth's rotational speed were to suddenly decrease to half its current speed, would the average global temperature change?

Hard to say. Practically it might have an influence on the heat distribution as the landmass (which heats up quicker than the water bodies) is unequally distributed. Cloud cover might change as well, influencing insolation as well as radiation to space at night.

Clear answer: perhaps. But probably not very much.

Quote

What if the rotation speed doubled?

Same as before. But orbit would be much easier to reach ! :-)

 

Edit: "fairly easy" might refer to the fact that the received energy per total area doesn't change, but patterns that hold energy back or allow radiation to space might change, thus actually changing average global temp. Ice can thaw during day and not build at night because of precipitation pattern change, thus changing the albedo, thus warming, or other effects. But again, probably not much.

I have to get hands an a weather model for use @home ... :-)

Edited November 17, 2017 by Green Baron

[Gaarst]

1 hour ago, James Kerman said:

Would quantum communication (if it could be made to work) be detectable from a satellite in orbit?  My limited understanding is that the communication would be unreadable to an outside party but I am unsure if there are (or might be) methods of detection.

Quantum communication is not about sending messages encrypted quantically, contrary to what most people think. The main means of quantum communication (there are other ways to do it) consists in sending messages encrypted traditionally, decypherable using a traditional key that is passed through quantum means.
Basically, instead of sending the key "classically" to your Bob, you use superimposed (or entangled) quantum states to transmit it. If someone is eavesdropping (Eve), it will cause the states to collapse to a single state, and depending on the value of the state Eve measures it can change the value received by Bob. Because a part of it is random, Bob can freely communicate to you the values he measured (because Eve doesn't know what you measured, so she doesn't know if her measurements are identical to yours), and when comparing with what you measured you can tell with certitude if someone is eavesdropping. If not, send your message; if yes, you know that someone is spying on you but you haven't sent any critical information so it's not that bad.

Now this doesn't prevent someone from intercepting your message, and try to crack it the old-fashioned way, but it is a lot easier (and quicker) to try to intercept the key than to decypher the message on your side using your classical algorithms. Another part of quantum communication is creating keys using quantum algorithms which would be virtually impossible for a classical computer to crack. Because people are anticipating that cracking keys will become much quicker with quantum computers, so that classical keys will not be secure once your enemy has access to quantum computers, it creates the need for quantum encryption that would take a quantum computer a long amount of time to crack. This field is called post-quantum cryptography.

Back to your question, quantum communication has nothing to do with sending undetectable messages.

 

1 hour ago, DAL59 said:

Could a sufficiently powerful [something] do [something]?

Usually, the answer is yes.

[Diche Bach]

On 11/13/2017 at 4:40 AM, Zeiss Ikon said:

Just when you thought black holes couldn't get any weirder...

Seem to recall some physicist or another who thinks that black holes "are" the other Universes in the multiverse or something like that.

ADDIT: Okay I've got one that might flop given there are so few biological science types among you, but here goes.

What would happen if human beings cells did not senesce past their prime age? There are a lot of sub-questions that would have to be addressed for that one, but I'll leave it at that and see if it gets any bites.

Edited November 18, 2017 by Diche Bach

[Zeiss Ikon]

9 hours ago, Diche Bach said:

What would happen if human beings cells did not senesce past their prime age? There are a lot of sub-questions that would have to be addressed for that one, but I'll leave it at that and see if it gets any bites.

Presuming you're referring to the Hayflick limit (chromosomes lose a little telomere length with each mitosis; when too short, the cell undergoes apoptosis).

Some kinds of cells use telomerase to rebuild the telomeres (non-coding lengths of DNA that compensate for the inability of transcriptase to copy the last X nucleotides in a chain).  Typically, these are single-cell organisms (and embryos of more complex creatures).  Apoptosis and the Hayflick limit seemingly came about in multi-celled animals due to cumulative DNA damage that can make unlimited cell replication an invitation to disaster.

Short answer, in humans and other mammals, and most other macroscopic animals (fish, reptiles, birds, amphibians, even invertebrates), if cells didn't apoptose after some limited number of mitotic cycles, the accumulated DNA damage would lead to descendant cells becoming non-functional, even pathological.  This does happen sometimes; one kind of point mutations that can occur in a cell can turn on telomerase production and hence disable apoptosis.  Now we have damaged cells replicating without limit: we call this cancer.

IFF we could control the process -- restore telomere length without letting damaged cells continue to replicate without limit -- we might be able to prevent aging, or at least repeal the absolute limit on how long the very healthiest animals (and people) can live (currently believed, for humans, to be around 200 years before the Hayflick limit causes death).

[Diche Bach]

6 hours ago, Zeiss Ikon said:

Presuming you're referring to the Hayflick limit (chromosomes lose a little telomere length with each mitosis; when too short, the cell undergoes apoptosis).

Some kinds of cells use telomerase to rebuild the telomeres (non-coding lengths of DNA that compensate for the inability of transcriptase to copy the last X nucleotides in a chain).  Typically, these are single-cell organisms (and embryos of more complex creatures).  Apoptosis and the Hayflick limit seemingly came about in multi-celled animals due to cumulative DNA damage that can make unlimited cell replication an invitation to disaster.

Short answer, in humans and other mammals, and most other macroscopic animals (fish, reptiles, birds, amphibians, even invertebrates), if cells didn't apoptose after some limited number of mitotic cycles, the accumulated DNA damage would lead to descendant cells becoming non-functional, even pathological.  This does happen sometimes; one kind of point mutations that can occur in a cell can turn on telomerase production and hence disable apoptosis.  Now we have damaged cells replicating without limit: we call this cancer.

IFF we could control the process -- restore telomere length without letting damaged cells continue to replicate without limit -- we might be able to prevent aging, or at least repeal the absolute limit on how long the very healthiest animals (and people) can live (currently believed, for humans, to be around 200 years before the Hayflick limit causes death).

Ah yes, had not heard of Hayflicks Limit for over a decade! One interesting thing, the evolutionary biologist are fairly convinced that all of these processes are not merely a reflection of phylogenetic constraint or other inherent limits, but rather are (mostly) all specifically shaped by natural selection. Meaning: the processes by which each tissue type senesce are tuned to the range of life history parameters for the species. For example if you are a rabbit, there is no point allocating "resource" toward longevity, you're going to get predated rather soon anyway. Better to allocate those resources to rapid maturation and earlier fertility and fecundity. The "r vs. K" selection thing figures into it.

So taking your points and extending the absurd question: what if we DID manage to control the process and repeal the absolute limit on how long animals can life?

[raxo2222]

What if nearly indestructible rod (that is as unbreakable as physics allows it) would pass trough super-massive (like in center of Milky Way) black hole?

Lets say rod has 1m diameter and its length is 1 light day.

Its center of mass would be on direct collision course with black hole something like this:

R

R

R ------> BlackHole

R

R

I bet it would be cut in two where it crosses event horizon of black hole.

 

What would happen to rod if I started rotating it and its tip would go into event horizon?

 

------

What if white dwarf crashed into supergiant star at >1% of c?

Could hypothetical alien see star insides in near perfect vacuum while being very close to white dwarf crashing trough star?

Basically it would be using white dwarf as heat shield while aerobraking.

Edited November 18, 2017 by raxo2222

[Delay]

While this is not hypothetical or absurd:

I don't really understand why every orbit is elliptal, but escape trajectories are hyperbolic. For me, it would make sense if it converged to a parabola the greater the speed is, not a straight line.

[Zeiss Ikon]

5 hours ago, Diche Bach said:

Ah yes, had not heard of Hayflicks Limit for over a decade! One interesting thing, the evolutionary biologist are fairly convinced that all of these processes are not merely a reflection of phylogenetic constraint or other inherent limits, but rather are (mostly) all specifically shaped by natural selection. Meaning: the processes by which each tissue type senesce are tuned to the range of life history parameters for the species. For example if you are a rabbit, there is no point allocating "resource" toward longevity, you're going to get predated rather soon anyway. Better to allocate those resources to rapid maturation and earlier fertility and fecundity. The "r vs. K" selection thing figures into it.

So taking your points and extending the absurd question: what if we DID manage to control the process and repeal the absolute limit on how long animals can life?

Rabbits, mice, etc., on the other hand, never get anywhere close to the Hayflick limit.  Humans might be the only species who do -- we live something like four times as long as any other mammal species, if you measure in a reasonable increment related to "how fast a creature lives" -- heartbeats.  Asimov wrote about this almost fifty years ago.  And even among humans, the only cells that normally get close to the Hayflick limit during a human lifetime (actual telomere depletion) are skin and blood precursors.

If we could repeal the Hayflick limit and avoid giving a green light to dozens of different kinds of cancers, the most obvious result would be a rapid drop in the stock price of vendors of skin care products -- especially those linked to making skin "look younger".  If your skin stayed "18 years old" for centuries, why would you buy Oil of Olay?  Given that accident and lifestyle diseases account for the top five or so causes of death other than age-related disorders, we'd then begin to see the oldest members of society get older and older, while the average age at death barely creeps up, if it moves at all.  As in Larry Niven's World of Ptavvs, in which the Struldbrugs' Club raises minimum age for membership by one year for every two years that pass -- and members appear less and less old because of constantly improving antiagathic therapies (Struldbrugs' Club was disbanded after the introduction of boosterspice, which, as long as you could afford to keep taking it, completely halted and even turned back aging) -- but most people don't live much longer than they did in the latter part of the 20th century.

In reality, though, there is still a limit -- neurons don't seem to replace themselves efficiently, even long before Hayflick gets into the picture.  The 200 year limit I mentioned before mainly has to do with the length of time the brain can last before the ongoing damage inherent with the passage of time puts too many holes in the neural networks.  Cognition, memory, learning would all fade away over enough time.  The very healthiest centenarians seem alert and mentally quick -- but they're still slower than they were eighty years earlier.  Come back in another eighty years, and they'll show still more of that effect, because reproduction of neurons isn't directly limited by telomere length.

[Findthepin1]

What if the Earth was made of Barack Obama 

[Bill Phil]

On ‎11‎/‎18‎/‎2017 at 4:13 PM, Delay said:

While this is not hypothetical or absurd:

I don't really understand why every orbit is elliptal, but escape trajectories are hyperbolic. For me, it would make sense if it converged to a parabola the greater the speed is, not a straight line.

Every orbit is a conic section in the two body problem. This includes escape orbits. Conic sections include circles, ellipses, parabolas, and hyperbolas. This can be observed by starting with a velocity vector and integrating gravity over time. Gravity curves the trajectory, and it ends up looking like a conic section. This allows us to describe an orbit's shape with eccentricity. An eccentricity of zero is a circle, an eccentricity between 0 and 1 is an ellipse, an eccentricity of 1 is a parabola, and an eccentricity greater than 1 is a hyperbola.

Or, rather, we can use Newton's laws. Things in motion tend to stay in motion unless acted upon by an outside force. In this case, the outside force is gravity, curving the otherwise straight line trajectory into a conic section. However, gravity has a finite value. This means that the higher the velocity, the less gravity curves the trajectory, meaning that as velocity increases, the trajectory converges to a straight line.

[kerbiloid]

On 19.11.2017 at 1:13 AM, Delay said:

I don't really understand why every orbit is elliptal, but escape trajectories are hyperbolic. For me, it would make sense if it converged to a parabola the greater the speed is, not a straight line.

Hyperbola is a compromise between a circle and a straight line.

[MatterBeam]

Ramjets.
In reverse.

We all know that ramjets work by compressing incoming air, which heats it up, then injecting fuel and burning it, so it heats up even more, and then expanding it through a nozzle. The net energy gain from the fuel burning is translated into warmer gasses exiting the nozzle at a velocity faster than at the intake, at roughly the same pressure as the exterior. 

The ramjet is therefore a heat engine.

Could we run a ramjet in reverse, turning it into a heat pump? A heat pump takes heat from a cold source, and moves into a warm sink. It expends energy to move heat against the temperature gradient. 

Let us consider a ramjet that is meant to move heat from a cold source (cold gas) into a heat sink. The reverse-ramjet would accept the cold gas at the intake. It compresses it, raising the temperature. The temperature gradient between the gas and heat sink is reversed, allowing heat to flow out of the gas. Then, the gas re-expands in the nozzle. If it is expanded to the same pressure as the inlet, it ends up being colder, as it has lost heat in the compressor. 

The energy to run the ramjet comes from accelerating the cold gas, probably from a fan.

[Zeiss Ikon]

7 hours ago, MatterBeam said:

Ramjets.
In reverse.

We all know that ramjets work by compressing incoming air, which heats it up, then injecting fuel and burning it, so it heats up even more, and then expanding it through a nozzle. The net energy gain from the fuel burning is translated into warmer gasses exiting the nozzle at a velocity faster than at the intake, at roughly the same pressure as the exterior. 

The ramjet is therefore a heat engine.

Could we run a ramjet in reverse, turning it into a heat pump? A heat pump takes heat from a cold source, and moves into a warm sink. It expends energy to move heat against the temperature gradient. 

Let us consider a ramjet that is meant to move heat from a cold source (cold gas) into a heat sink. The reverse-ramjet would accept the cold gas at the intake. It compresses it, raising the temperature. The temperature gradient between the gas and heat sink is reversed, allowing heat to flow out of the gas. Then, the gas re-expands in the nozzle. If it is expanded to the same pressure as the inlet, it ends up being colder, as it has lost heat in the compressor. 

The energy to run the ramjet comes from accelerating the cold gas, probably from a fan.

This would, for instance, allow cabin heat in a sailplane, if you could extract enough energy.  Problem is, the drag -- compressing a high velocity gas stream takes a tremendous amount of energy, and gas compression is a notoriously non-reversible process (precisely because of the mechanism this is based on -- the hot compressed gas loses heat into the pipe and core body).  Using this to heat the cabin in a sailplane, then, would greatly reduce the performance of the plane, if in fact you could get enough compression to even make this work at under 100 kt (where most sailplanes spend most of their flying time).

In faster aircraft, you've got a reliable source of heat -- the engines -- and don't even need to draw heat from their combusions if the cabin is pressurized; the compression of air to pressurize the cabin will warm it (by the same value as metorological lapse rate, roughly around 3 degrees F per 1000 feet, or 5 degrees C per 1000 m).  If you actually need a little more heat than that, just run a heat exchanger to extract heat from excess pressurizing air, and then dump the extra air (after all, a compressor bleed from a jet engine, even a turbocharger bleed for a piston engine, can provide tens of times the air volume needed for cabin pressure without affecting engine performance noticeably).

IOW, this is a solution in search of a problem, and it brought several problems of its own.  Pumping heat without a phase change is terribly inefficient (there's a good reason air was dropped as a working fluid for refrigeration in the 19th century, as soon as ammonia systems became available).  Moving the volume of air needed, at the velocity needed, for this device would require a huge amount of power, even without the device sapping still more energy from the stream.

tl;dr: yes, this is themodynamically possible, but far from practical due to poor efficiency and high power requirements.

[MatterBeam]

15 minutes ago, Zeiss Ikon said:

This would, for instance, allow cabin heat in a sailplane, if you could extract enough energy.  Problem is, the drag -- compressing a high velocity gas stream takes a tremendous amount of energy, and gas compression is a notoriously non-reversible process (precisely because of the mechanism this is based on -- the hot compressed gas loses heat into the pipe and core body).  Using this to heat the cabin in a sailplane, then, would greatly reduce the performance of the plane, if in fact you could get enough compression to even make this work at under 100 kt (where most sailplanes spend most of their flying time).

In faster aircraft, you've got a reliable source of heat -- the engines -- and don't even need to draw heat from their combusions if the cabin is pressurized; the compression of air to pressurize the cabin will warm it (by the same value as metorological lapse rate, roughly around 3 degrees F per 1000 feet, or 5 degrees C per 1000 m).  If you actually need a little more heat than that, just run a heat exchanger to extract heat from excess pressurizing air, and then dump the extra air (after all, a compressor bleed from a jet engine, even a turbocharger bleed for a piston engine, can provide tens of times the air volume needed for cabin pressure without affecting engine performance noticeably).

IOW, this is a solution in search of a problem, and it brought several problems of its own.  Pumping heat without a phase change is terribly inefficient (there's a good reason air was dropped as a working fluid for refrigeration in the 19th century, as soon as ammonia systems became available).  Moving the volume of air needed, at the velocity needed, for this device would require a huge amount of power, even without the device sapping still more energy from the stream.

tl;dr: yes, this is themodynamically possible, but far from practical due to poor efficiency and high power requirements.

I'm just thinking of alternatives to Stirling heat pumps for moving the heat from a cold gas coolant into a heat exchanger that leads into a radiator. 
Currently, it is very difficult to design a system that wants to run cold and handle a lot of power in space. Examples include particle accelerators, laser generators, ion engines, ect. They run below room temperature, down to 100K or less when superconductors are involved. And yet, kilowatts to megawatts of waste heat are generated by their operation.

Dealing with that waste heat passively means using a set of radiators at even cooler temperatures. Due to the low radiation per square meter, the radiators would have to be massive. Not something a spacecraft can afford!

An ideal option would be increase the radiator's operating temperature. For this to happen, you need heat pumps to move cool heat up a temperature gradient - you need heat pumps. 

The problem is, current heat pumps have poor efficiency and horrendous power density. The mass you save on radiators, you'll lose it with the pumps!

Brayton-cycle turbines can combine high power density and high efficiency. If they can be run in reverse as heat pumps, then you can solve some of the problems involved with running high-energy cold systems in space.

Here's a 1MW example:

An VASIMR engine needs to be kept at 273K temperature for its magnets to operate at peak efficiency. It is 60% efficient and has a power density of 1kW/kg. To handle 1MW, it needs to mass 1 ton. This engine produces 400kW of waste heat. 

A passive heating solution would be use radiators that run at 273K. The Stefan-Boltzman equation says that even very black radiators (emissivity 0.9) would emit only 283W/m^2. You'd need an area of at least 1413m^2. Even if the radiators are radiators are relatively lightweight and double-sided, you'd need to dedicate 3.5 to 7 tons just for radiators. 

Let's introduce an existing heat pump. A stirling-cycle heat pump has an efficiency of up to 35% and a power density of 0.1kW/kg. We will use it to increase the temperature to 600K, so its thermal performance will be 83%. Combined with the pump's own efficiency, you need 3.4W of input to move heat up that temperature gradient. It would allows for the radiators to be 23.3 times smaller and mass only 150 to 300kg. However, to handle all of the waste heat, you need heat pumps that consume 1360kW of power and mass 13.6 tons! Not only are you losing all the gains from the smaller radiator, but you are also more than doubling your energy budget!

How does it go differently if we used a heat pump based on the Brayton cycle and built like a modern turbine?
It could be up to 80% efficient and have a power density of 10kW/kg. It only needs 1.5W of input per 1W of heat moved, and it will mass only 60kg. Quite a difference!

That is the solution that this 'reverse ramjet' is for. 

[Zeiss Ikon]

9 hours ago, MatterBeam said:

How does it go differently if we used a heat pump based on the Brayton cycle and built like a modern turbine?

It could be up to 80% efficient and have a power density of 10kW/kg. It only needs 1.5W of input per 1W of heat moved, and it will mass only 60kg. Quite a difference!

That is the solution that this 'reverse ramjet' is for. 

I'm afraid you'll find that the reverse ramjet makes a common heat pump look like the model of efficiency in comparison.  The phase change in a conventional heat pump reduces the volumetric pumping requirements by orders of magnitude -- when air was the working fluid, a refrigeration system (to chill brine, which was used to make ice) with a "one ton" rating (makes one ton of ice per day, though that's now used to represent a set number of BTU/hr -- convertible to kilowatts of heat transfer) was about fifteen times the size of a modern unit that can make five times as much ice.  It used tens of times as much energy per ton, as well.

On a thermodynamic basis, I think it's unlikely you'll find a heat pump cycle significantly more efficient than a phase change system based on the Rankine cycle.  Might want to look into the power handling capability of Peltier junctions.

[mikegarrison]

On 11/20/2017 at 3:48 PM, Zeiss Ikon said:

In faster aircraft, you've got a reliable source of heat -- the engines -- and don't even need to draw heat from their combusions if the cabin is pressurized; the compression of air to pressurize the cabin will warm it (by the same value as metorological lapse rate, roughly around 3 degrees F per 1000 feet, or 5 degrees C per 1000 m).

Besides that, there is no way you would draw air into the cabin from the engine after you had already used it for combustion, because it is engine exhaust!

The problem tends to be that the air is much too hot to be fed into the cabin, not that it is too cold. That's why some of it needs to go through an air cycle machine that cools it down. Then the cold pressurized air can be mixed with the hot pressurized air in order to get the desired temperature pressurized air.

[Zeiss Ikon]

2 hours ago, mikegarrison said:

Besides that, there is no way you would draw air into the cabin from the engine after you had already used it for combustion, because it is engine exhaust!

The problem tends to be that the air is much too hot to be fed into the cabin, not that it is too cold. That's why some of it needs to go through an air cycle machine that cools it down. Then the cold pressurized air can be mixed with the hot pressurized air in order to get the desired temperature pressurized air.

Drawing heat from the exhaust is how cabin heat is done on virtually all unpressurized piston engine aircraft.  A heat exchanger on the exhaust gives heat any time the engine is running.  Air cooled Volkswagens used to use exhaust heat as well -- they'd have heat for the passenger compartment in fifteen seconds after starting, while liquid cooled vehicles take several minutes to heat the cooling jacket.

Compressor bleed air is cooled with passive heat exchangers, not with heat pump cooling systems.  Outside air at altitudes where pressurization is needed is frigid, even in summer over the Sahara.

[MatterBeam]

23 hours ago, Zeiss Ikon said:

I'm afraid you'll find that the reverse ramjet makes a common heat pump look like the model of efficiency in comparison.  The phase change in a conventional heat pump reduces the volumetric pumping requirements by orders of magnitude -- when air was the working fluid, a refrigeration system (to chill brine, which was used to make ice) with a "one ton" rating (makes one ton of ice per day, though that's now used to represent a set number of BTU/hr -- convertible to kilowatts of heat transfer) was about fifteen times the size of a modern unit that can make five times as much ice.  It used tens of times as much energy per ton, as well.

On a thermodynamic basis, I think it's unlikely you'll find a heat pump cycle significantly more efficient than a phase change system based on the Rankine cycle.  Might want to look into the power handling capability of Peltier junctions.

The thermal conductivity of gasses is about five to ten times lower than for liquids, but that only increases the size of the heat exchanger, not the overall efficiency. Peltier junctions have 10-15% the maximum efficiency of a heat pump, while the Rankine systems you mention can achieve 40-60%...  

3 hours ago, mikegarrison said:

Besides that, there is no way you would draw air into the cabin from the engine after you had already used it for combustion, because it is engine exhaust!

The problem tends to be that the air is much too hot to be fed into the cabin, not that it is too cold. That's why some of it needs to go through an air cycle machine that cools it down. Then the cold pressurized air can be mixed with the hot pressurized air in order to get the desired temperature pressurized air.

You can always run the hot exhaust over a heat exchanger and carry only the heat inside. 

[mikegarrison]

5 hours ago, Zeiss Ikon said:

Drawing heat from the exhaust is how cabin heat is done on virtually all unpressurized piston engine aircraft.  A heat exchanger on the exhaust gives heat any time the engine is running.  Air cooled Volkswagens used to use exhaust heat as well -- they'd have heat for the passenger compartment in fifteen seconds after starting, while liquid cooled vehicles take several minutes to heat the cooling jacket.

Compressor bleed air is cooled with passive heat exchangers, not with heat pump cooling systems.  Outside air at altitudes where pressurization is needed is frigid, even in summer over the Sahara.

Yeah, OK, there could be a heat exchanger. This is true. But there is no need in a turbine engine because compression supplies all the heat you want.

[ARS]

Could we use the gun's recoil as an impromptu EVA thruster in space by firing a gun in space? (Like WALL-E with fire extinguisher)

[shynung]

4 hours ago, ARS said:

Could we use the gun's recoil as an impromptu EVA thruster in space by firing a gun in space? (Like WALL-E with fire extinguisher)

Yes, we can. This is the principle behind mass drivers - throw a bucket of dirt really fast with a railgun/coilgun setup, and the setup would go in the opposite direction of where the barrel was pointing.

[kerbiloid]

This works in KSP, I've tried with a pack of BDArmory guns.

(Though, a projectile speed is 1..1.5 km/s, while the engine exhaust speed is 3..4 km/s, so this doesn't make a practical sense.)

Edited November 23, 2017 by kerbiloid

[shynung]

22 minutes ago, kerbiloid said:

This works in KSP, I've tried with a pack of BDArmory guns.

(Though, a projectile speed is 1..1.5 km/s, while the engine exhaust speed is 3..4 km/s, so this doesn't make a practical sense.)

Current-tech railguns being researched by US Navy can achieve muzzle velocities in the range of 2-3 km/s. That's close to storable liquid rockets and solid rockets.