Rail gun engine the future of space travel?

[sevenperforce]

53 minutes ago, Lordmaddog said:

DISCLAIMER 

I realize that this it what is called a reactionless drive and many believe such a thing brakes the laws of physics, however I am a firm believer that we haven't even began to scratch the surface of science and what we THINK we know is often WRONG. I also believe that for every law there is another that counters that law IE: Law of gravity witch for thousands of years was thought impossible to get around yet a few hundred years  ago the law of aerodynamics was discovered for ever changing what we as humans are capable of.

Sigh.

Reactionless drives cannot work. Before I tell you specifically why your modified reactionless drive will not work, let me first attempt to explain in general why reactionless drives cannot work.

All thermodynamic systems are reversible, at least in principle. An electrical motor which uses electrical energy to turn a wheel can be converted into a generator, which uses the motion of a wheel to generate electrical energy. Inward force can be applied to a piston to compress a gas, or a compressed gas can be expanded against a piston to produce outward force. 

This is why reactionless drives cannot work. Let us say you have a reactionless drive in a box. You don't know how it works, necessarily; you just put energy in, and it accelerates you forward. Great!

Now, what happens if you run the cycle in reverse? Well, presumably, you would decelerate, and it would generate energy in response.

But...deceleration is just acceleration in the opposite direction. So what's to stop you from "decelerating" continuously, for as long as you want, generating as much free energy as you want? Heck, I've got a better idea. Just point your reactionless drive in the opposite direction and run it in reverse cycle! You'll accelerate faster and faster in the direction you wanted to go all along, AND you'll generate unlimited energy!

Obviously this is nonsense. And so are reactionless drives.

Now, on to specifics:

54 minutes ago, Lordmaddog said:

At the end of the rail the liquid projectile slams into the splitter (bright red) cutting the projectile in half and sadly reducing the total thrust generated by 20 to 35%.

The divided projectile flies down the redirecting tubes (purple) once again sadly reducing the total thrust generated further by another 15 to 20%. as their momentum and kinetic force are turned 90*.

Once redirected the two projectiles enter the stopping chamber (black) and slamming into the plungers (red) exactly opposite of each other at the exact same time. Thus canceling out each others remaining momentum and kinetic energy and leaving at least 40% of the thrust the engine generated by launching them. 

You may not realize it, but you seem to be assuming through this whole process that kinetic energy and momentum are proportional. They are not. Kinetic energy is a scalar that is proportional to the square of velocity; momentum is a vector which is proportional to the velocity. It is possible to change an object's momentum without changing its kinetic energy.

First of all, where are you getting these numbers? Why would splitting the projectile in half reduce the total thrust by any appreciable amount? The "splitter" need only exert an infinitesimal force on the projectile to split it.

Your second paragraph above is where you run into problems. Whatever force the purple tubes exert on the projectiles to turn them by 90 degrees, the projectiles also exert (in reverse) on the purple tubes...cancelling not 15-20% of their downward momentum, but 100% of their downward momentum.

This seems strange, because the projectiles presumably strikes the plungers with momentum, right? Yes, each projectile has momentum, but the two projectiles together have zero net momentum, because the purple tubes canceled out the net momentum. They did this without eliminating kinetic energy, of course, so net kinetic energy is still present, but there is no net momentum and therefore no thrust.

You have a great mind. Learn more math and invent something that will actually change the world.

[sevenperforce]

46 minutes ago, Hypercosmic said:

Looks like that mad dog made another thread for this railgun bull[censored]...

I tried to be nice about it. I was once like him. When I was, like, 11....

 

[Vanamonde]

Redundant threads have been merged. 

And please don't attack each other over science. It kinda defeats the purpose. 

[YNM]

2 hours ago, Lordmaddog said:

... however I am a firm believer that we haven't even began to scratch the surface of science and what we THINK we know is often WRONG. ...

So, why do you think your idea works then ?

 

Science™ is not something to be scratched from. Science is the scratching action itself.

[Green Baron]

This goes into philosophy, but i find it important.

One cannot make someone understand if he/she does not want to. This is actually a basic insight. As @YNM points out, OP actively rejects basic working principles of nature with the power of belief and this is too strong an "argument" to overcome. It needs a lot of time and education to make someone see that that what science has brought forth in the past 600 years (and before) is actually a quite encompassing collection of models that do work, which is proved every day in the application from theoretic sciences to such things as making cars or buildings, converting energy for use @home or describing processes in nature like climate, weather, plate tectonics, solar systems, clusters, galaxies, ... it works ! Not always perfectly and some in a manner that needs refinement or even redefinition, there is a scientific process to ensure that the development goes in a reasonable way.

@Lordmaddog: even if you believe that much of science is wrong, you first must understand how it works before you criticise it. Generalisations and diffuse doubts don't get us nowhere ...

 

[YNM]

1 hour ago, Green Baron said:

... what science has brought forth in the past 600 years (and before) is actually a quite encompassing collection of models that do work, which is proved every day in the application from theoretic sciences to such things as making cars or buildings, converting energy for use at home or describing processes in nature...

There's a "joke" that says what engineers uses today are actually well-studied since hundreds of years ago, and you won't see the use of recent discoveries until a few centuries later.

Anyway, some editor's choice :

7 hours ago, Lordmaddog said:

... The rail speeds the projectile up to impossible speeds ...

Yeah, like when the mule foals...

7 hours ago, Lordmaddog said:

... I also believe that for every law there is another that counters that law IE: Law of gravity witch for thousands of years was thought impossible to get around yet a few hundred years  ago the law of aerodynamics was discovered for ever changing what we as humans are capable of ...

We have kites and fireworks before Galileo was born.

7 hours ago, Lordmaddog said:

Then just shoot (BBs are good)

Wouldn't paintballs makes better comparison ? They also "melt".

[sh1pman]

Seriously though, how is this thread still in "Science" section? OP clearly disregards and disrespects science, it would be fitting to move the thread to "Forum games" or something like that. There is no law in physics that would allow reactionless drives, and "we don't know everything yet" is not an argument. 

[p1t1o]

8 hours ago, Lordmaddog said:

DISCLAIMER 

I realize that this it what is called a reactionless drive and many believe such a thing brakes the laws of physics, however I am a firm believer that we haven't even began to scratch the surface of science and what we THINK we know is often WRONG. I also believe that for every law there is another that counters that law IE: Law of gravity witch for thousands of years was thought impossible to get around yet a few hundred years  ago the law of aerodynamics was discovered for ever changing what we as humans are capable of.

Many a young, aspiring scientist has had thoughts like this. "Feelings" that they are certain ought to pan out in the real world, something that we all learn eventually is that science and the universe care nothing for our feelings. Dial back the skepticism a little bit - skepticism is healthy, but not to the point where you question the entire framework in which you are trying to operate.

Anyway, for what its worth, Im a professional scientist. In my career I have worked in many fields from academic research to commercial research to industrial labwork to industrial deskjob - from electron microscopy, to bio-mineralisation, to wound-healing and now chemical safety, and here is my schpiel:

 

Spoiler

DISCLAIMER 

I realize that this it what is called a reactionless drive and many believe such a thing brakes the laws of physics, however I am a firm believer that we haven't even began to scratch the surface of science and what we THINK we know is often WRONG. I also believe that for every law there is another that counters that law IE: Law of gravity witch for thousands of years was thought impossible to get around yet a few hundred years  ago the law of aerodynamics was discovered for ever changing what we as humans are capable of.

 

Careful, what is written here is essentially a bald-faced insult to anyone who has dedicated a life's work to science.

 

 

7 hours ago, Lordmaddog said:

many believe such a thing brakes the laws of physics

Because they are correct - as written, the "laws" would be broken by this machine, if it worked.

It doesnt fail to work because it breaks the laws - it fails to work, time and again, no matter how you build the machine, then we write hypotheses explaining why they dont, then we test them by making predictions and seeing if they pan out. Then we write the laws based on these piles and piles of evidence.

If there was ever any sign at all, ever, anywhere, even on paper, the laws would say so.

Because so many people have attempted to do this, and every single time, there has been no sign at all (people saying "I swear it works, Im not going to show you, or I cant show you, but I swear it works" does. not. count.) and every time, the same explanations pan out. 

When we have a bunch of paper saying "these machines work" and a bunch of paper saying "they dont", we believe the bunch of paper that ALSO explains everything else, from F=ma to electromagnetism - THAT bunch, we call "the laws of physics"

 

7 hours ago, Lordmaddog said:

I am a firm believer that we haven't even began to scratch the surface of science

Who knows how deep it goes, but there are centuries of scientific advancement behind us. And from the beginning, it only increased in accuracy.

New discoveries do not decrease the accuracy of what went before. Hypotheses that do require this to work, are not worth very much.

 

7 hours ago, Lordmaddog said:

and what we THINK we know is often WRONG

WRONG. What we think we know is occasionally updated with more accurate models after rigorous scientific treatment.

You would be surprised how little the words "wrong" and "right" appear in science, all we have are best guesses, some of them are even known to not represent reality (hello mister discrete photon, how are you?) and yet we can use the theory as tools to understand the universe around us, because predictions and testing make logically consistent and repeatable results - and what is more, they make sense in conjunction with other theories.

Some areas of science, like say, quantum gravity, are still very difficult to "make sense in conjunction with", more work is required to discover how gravity in some extreme cases, works with our current "laws". Science is not considered a perfect vision of the world, never has been. Rest assured though, that however quantum gravity is resolved, the planets will still swing around the sun in the same manner, and Newtons equations will remain just as accurate.

 

7 hours ago, Lordmaddog said:

I also believe that for every law there is another that counters that law

Thats a rather unusual belief system.

Aerodynamics doesnt "counter" gravity, nor is "aerodynamics" a "law", aerodynamics is a field of science developed by study of many things all in relation to the known laws of physics. The theory of gravitation did not change a single iota during the invention of aerodynamics. Aircraft dont even work without gravity...

 

I mean honestly, as a scientist, why do we get all the stick? Nobody ever argues that dentistry is "ALL WRONG and heres an idea for everlasting teeth", nobody ever argues with their plumber that toilets dont really work like that.

Science is a very old, very wise, experienced lady. One should not presume to challenge her with a mere few years "contemplation" under your belt.

And with that, this thread was done for me. This is a conversation that I have had too many times. 

 

 

 

5 hours ago, YNM said:

Science™ is not something to be scratched from. Science is the scratching action itself.

Dint-ding-ding! THIS ^^

 

 

 

 

[sevenperforce]

37 minutes ago, sh1pman said:

Seriously though, how is this thread still in "Science" section? OP clearly disregards and disrespects science, it would be fitting to move the thread to "Forum games" or something like that. There is no law in physics that would allow reactionless drives, and "we don't know everything yet" is not an argument. 

A discussion of pseudoscience still involves science.

22 minutes ago, p1t1o said:

Many a young, aspiring scientist has had thoughts like this. "Feelings" that they are certain ought to pan out in the real world, something that we all learn eventually is that science and the universe care nothing for our feelings. Dial back the skepticism a little bit - skepticism is healthy, but not to the point where you question the entire framework in which you are trying to operate.

I designed a great many perpetual motion machines at age 11-12, and it was only through the patient (and, at times, exasperated) explanations of my teachers that I was able to slowly get an intuitive grasp for how scientific inquiry works.

I was a hardline creationist for 20 years, and it was only through the dedicated (and at time shouty) persistence of people willing to counter my bad arguments and point me to piece after piece of evidence that it all finally came crashing down.

So I do my best to assume that the @Lordmaddogs of the world are inquisitive, if overly-excitable, minds who simply need to be pointed in the right direction...perhaps more than once.

22 minutes ago, p1t1o said:

There are centuries of scientific advancement behind us. And from the beginning, it only increased in accuracy.

New discoveries do not decrease the accuracy of what went before. Hypotheses that do require this to work, are not worth very much.

What we think we know is occasionally updated with more accurate models after rigorous scientific treatment.

You would be surprised how little the words "wrong" and "right" appear in science, all we have are best guesses, some of them are even known to not represent reality (hello mister discrete photon, how are you?) and yet we can use the theory as tools to understand the universe around us, because predictions and testing make logically consistent and repeatable results - and what is more, they make sense in conjunction with other theories.

Hear, hear.

22 minutes ago, p1t1o said:

Quote

I also believe that for every law there is another that counters that law

Thats a rather unusual belief system.

Aerodynamics doesnt "counter" gravity, nor is "aerodynamics" a "law", aerodynamics is a field of science developed by study of many things all in relation to the known laws of physics. The theory of gravitation did not change a single iota during the invention of aerodynamics. Aircraft dont even work without gravity...

Smells like highly potent homeopathy....

22 minutes ago, p1t1o said:

I mean honestly, as a scientist, why do we get all the stick? Nobody ever argues that dentistry is "ALL WRONG and heres an idea for everlasting teeth", nobody ever argues with their plumber that toilets dont really work like that.

Is there a Rule 34 for conspiracies? Because dentistry is a conspiracy....

22 minutes ago, p1t1o said:

6 hours ago, YNM said:

Science™ is not something to be scratched from. Science is the scratching action itself.

Dint-ding-ding! THIS ^^

And see, this is what happens when I waste all my likes on discussions of 1.4.

[Green Baron]

1 hour ago, sh1pman said:

Seriously though, how is this thread still in "Science" section? OP clearly disregards and disrespects science, it would be fitting to move the thread to "Forum games" or something like that. There is no law in physics that would allow reactionless drives, and "we don't know everything yet" is not an argument. 

While i in principle support that, a forum like this (a game forum) must also leave room for free discussions between different views. It is a game forum, not a pre print server :-)

As a game "Build a reactionless drive" one probably would have less of a chance to convince OP that his idea is faulty ...

Just a few cents more from my side :-)

[sh1pman]

1 hour ago, Green Baron said:

While i in principle support that, a forum like this (a game forum) must also leave room for free discussions between different views. It is a game forum, not a pre print server :-)

As a game "Build a reactionless drive" one probably would have less of a chance to convince OP that his idea is faulty ...

Just a few cents more from my side :-)

Yeah, maybe you're right. I was just doing some actual scientific experiments in my lab and trying to figure out why they didn't work, feeling embarrassed about it a little bit. And then I saw this nonsense about science being "wrong". Hit a nerve, so to speak. 

[Zeiss Ikon]

20 hours ago, Lordmaddog said:

At the end of the rail the liquid projectile slams into the splitter (bright red) cutting the projectile in half and sadly reducing the total thrust generated by 20 to 35%.

The divided projectile flies down the redirecting tubes (purple) once again sadly reducing the total thrust generated further by another 15 to 20%. as their momentum and kinetic force are turned 90*.

Once redirected the two projectiles enter the stopping chamber (black) and slamming into the plungers (red) exactly opposite of each other at the exact same time. Thus canceling out each others remaining momentum and kinetic energy and leaving at least 40% of the thrust the engine generated by launching them.

Your math or measurements are wrong.  By the time the halves of the molten projectile have been redirected to 90 degrees from their original vector, 100% of their "driving" momentum has been reabsorbed by the structure of the "thruster".  Of course, this thing will disassemble itself when the first pair of projectile half, traveling "unbelievable" velocity, slam into the plungers.

The wasted energy that goes into heating the slug is, well, wasted.  Not to mention that if the divider and redirection tubes aren't just as hot (more wasted energy) as the melted projectile, the metal will solidify in the tube, leading to even more spectacular failure modes (if, perchance, the primary one, of the plungers blowing out of the sides of the housing, hasn't yet taken place).

This device is good for nothing other than separating backers from their money.  If it ever gets built (very unlikely, because either the "inventor" is a scam artist who knows it can't work, or sufficiently incompetent in science and engineering as to be completely unaware how to build it in a "functional" form), it'll destroy itself instantly, or "mysteriously" fail to operate at all when it's time for testing.  Much more likely, anyone who offered up a dime toward "construction costs" will eventually figure out that the "inventor" has vanished, along with their nest egg.

[mikegarrison]

On 3/11/2018 at 7:23 PM, Lordmaddog said:

I realize that this it what is called a reactionless drive and many believe such a thing brakes the laws of physics, however I am a firm believer that we haven't even began to scratch the surface of science and what we THINK we know is often WRONG. I also believe that for every law there is another that counters that law IE: Law of gravity witch for thousands of years was thought impossible to get around yet a few hundred years  ago the law of aerodynamics was discovered for ever changing what we as humans are capable of.

Science has a tried-and-true method for dealing with this. If you actually build it, test it, and show that it works, then the laws of physics will have to bow to the data. Until then, however, you aren't going to get anybody who knows physics to take you seriously.

[mikegarrison]

23 hours ago, sevenperforce said:

All thermodynamic systems are reversible, at least in principle. An electrical motor which uses electrical energy to turn a wheel can be converted into a generator, which uses the motion of a wheel to generate electrical energy. Inward force can be applied to a piston to compress a gas, or a compressed gas can be expanded against a piston to produce outward force.

OK, here is where I am going to disagree with you. You are ignoring entropy.

If you take a liter of oxygen and a liter of nitrogen and mix them together, it takes a heck of a lot more work to separate them than it did to mix them. Mixing is not a reversible process.

And try pumping exhaust gasses into a car engine and creating fuel and air. Good luck with that. Yes, you can synthesize hydrocarbons from CO2 and H2O, but not by "reverse burning" them.

Bottom line is that reversibility is at best an approximation and at worse a very bad approximation, because entropy always has a look in.

[PB666]

On 3/8/2018 at 3:06 AM, Green Baron said:

But there is loss through friction, the force from the propeller would be greater than the pressure on the sail, so maybe it'll move slowly in the direction the propeller pulls it.

Of course, i'll throw the mechanical stuff overboard and go sailing :-)

Well you guys have completely forgot about the inevitable consequences of the Murphy's law propulsion system a predecessor to the infinite improbability drive. The point is that although the system will not move over after returning to the start state, if the cycle is repeated often enough it will heat up, increasing the odds the 'Anything that can go wrong will eventually go wrong' the metal projectile (in the OP) will strike the end plate, which will break free causing propulsion and soon there after partial disintegration of the system.

You could use a fan to propel a boat (these are rather common around here if you hunt ducks or gig flounder), even with a sail, it just needs to point the other direction, and placing a sail up defeats the purpose.

To the OP, you should read the archives on the Cannae drive here, we deal with the reaction mass issue, the bottom line is that the proof of the pudding is in the eating, tell us how well it propels after you launch it into space.

For an electric propulsion system N  = 2 * Power * eff/ [velocity of mass] in the exhaust. Thats the way it works, if its electrically propelled, the force is a measure of what you have expelled.

 

 

[PB666]

2 hours ago, mikegarrison said:

Science has a tried-and-true method for dealing with this. If you actually build it, test it, and show that it works, then the laws of physics will have to bow to the data. Until then, however, you aren't going to get anybody who knows physics to take you seriously.

It wont work, the particle in question is a macroscopic system in which momentum and position can be simultaneously measured, it must obey classical mechanics. Only on the quantum scale can physics be broken that way and get away with. What is that equation δX*δp = h/4π. If you get to the point where you cannot simultaneously measure the momentum and position of a particle, if and only if a particle is produced whose position can be measured, then at that moment its momentum is uncertain. But in that case since its momentum is uncertain, it cannot be used to create thrust since there are no velocity vectors associated with an unmeasurable system. (I think we call it the zero vector, because it can point in any direction).

I should point out that the exception (Cannae drive) is a question in play and that we all pretty much gave up discussing it until it got tested in some spacecraft, but again this at some-point will have a reaction mass identifying it has been the problem, the mechanism is not known. The Cannae drive is a macroscopic system, but the particles (electrons) are one of the smallest quanta of stable matter (electron neutrinos being the smallest, but they have no measurable rest mass).

There is one overriding conservation in Physics that is always true at every level. Energy is always conserved, there are efficient ways to propel spacecraft and inefficient ways (like rail guns or machine guns). The most mass efficient ways require substantial input of energy, likewise the most energy conservative methods require substantial outflow of mass.

The other point is that pretty much any argument that begins with 'needs a fusion reactor, or [handwaving big] fission reactor is a generally sophomoric solution to current space problems and having a system that is going to generate alot of waste heat (even if it did work) could never be used in space because of the excess mass required to keep it cool. We have rather efficient electric mass accelerators, these are called ION drives with up to 80% power efficiency. And we can if we so desire to produce machines with ISP of 100,000. But we don't have a power supply to run those machines.

 

[sh1pman]

4 hours ago, PB666 said:

There is one overriding conservation in Physics that is always true at every level. Energy is always conserved

Not at every level it's not. Dark energy is not conserved. It's density stays constant in an expanding universe.

[Green Baron]

21 minutes ago, sh1pman said:

Not at every level it's not. Dark energy is not conserved. It's density stays constant in an expanding universe.

Uhhh, not sure if the first part is correct. There seems to be a dispute about that. But i am no physicist !

I expect a wall of text here soon describing ... what exactly ?

 

But OP describes a closed system, so there is little chance for energy to escape :-)

 

5 hours ago, PB666 said:

Well you guys have completely forgot about the inevitable consequences of the Murphy's law propulsion system a predecessor to the infinite improbability drive. The point is that although the system will not move over after returning to the start state, if the cycle is repeated often enough it will heat up, increasing the odds the 'Anything that can go wrong will eventually go wrong' the metal projectile (in the OP) will strike the end plate, which will break free causing propulsion and soon there after partial disintegration of the system.

Hehe. That's why i want to get rid of the suspicious mechanical stuff asap and go sailing. I have much more control over the sails than an engine ! Turnsweatheredfacetowardssunandwaitsforwindtoblowbaldhead

[YNM]

For full pedanticity anyway :

The device isn't entirely free-energy, but it doesn't direct the energy in any remarkable direction.

[PB666]

2 hours ago, Green Baron said:

Hehe. That's why i want to get rid of the suspicious mechanical stuff asap and go sailing. I have much more control over the sails than an engine ! Turnsweatheredfacetowardssunandwaitsforwindtoblowbaldhead

Until you hit a poor unsuspecting sunfish and your mainsail snaps off, then you need that 'last ditch' radio and hope the authorities find you before the pirates.
[wall of text]

 

 

[sevenperforce]

8 minutes ago, YNM said:

For full pedanticity anyway :

The device isn't entirely free-energy, but it doesn't direct the energy in any remarkable direction.

However, any thermodynamically consistent reactionless drive can be used to produce infinite energy. Just like any Maxwell's demon or Brownian ratchet capable of creating work from waste heat (without a heat sink) can also be used to produce infinite energy.

2 hours ago, sh1pman said:

Not at every level it's not. Dark energy is not conserved. It's density stays constant in an expanding universe.

The metric of spacetime balances this out, so conservation of energy is preserved. A lay explanation: https://www.quora.com/Does-dark-energy-violate-the-law-of-conservation-of-energy-mass

9 hours ago, mikegarrison said:

On 3/11/2018 at 11:15 PM, sevenperforce said:

All thermodynamic systems are reversible, at least in principle. An electrical motor which uses electrical energy to turn a wheel can be converted into a generator, which uses the motion of a wheel to generate electrical energy. Inward force can be applied to a piston to compress a gas, or a compressed gas can be expanded against a piston to produce outward force. 

OK, here is where I am going to disagree with you. You are ignoring entropy.

If you take a liter of oxygen and a liter of nitrogen and mix them together, it takes a heck of a lot more work to separate them than it did to mix them. Mixing is not a reversible process.

And try pumping exhaust gasses into a car engine and creating fuel and air. Good luck with that. Yes, you can synthesize hydrocarbons from CO2 and H2O, but not by "reverse burning" them.

Bottom line is that reversibility is at best an approximation and at worse a very bad approximation, because entropy always has a look in.

Yes, I was ignoring entropy, because I was talking about systems which work.

Using work in its formal sense, of course: the product of force and distance. Apply a force of 10 Newtons to an object across a distance of 5 meters, and you have performed 50 Newton-meters of work. A Newton-meter is, of course, a Joule, and if you measure the change in kinetic energy of the object, you will find it has gained 50 Joules of kinetic energy.

This is a reversible thermodynamic process, because there has been no increase in entropy and you can extract 100% of those 50 Joules of kinetic energy by allowing the object to impinge upon a spring or other energy storage mechanism. All thermodynamic processes which actually perform a net amount of work are reversible with respect to the work they perform. So even though entropy always has its lukewarm fingers in every pie, you can separate the positive-entropy component of a process from the work-producing component of a process. The former is irreversible; the latter is reversible.

So if you have a process which actually produces any work, then there's a reversible cycle in there somewhere.

Note that this is true even for something like a rocket engine, which seems like an example of a completely irreversible process. Is it really reversible? Well, yes, if you look only at where work is actually being performed. To start with, the turbopumps perform work by applying force to the propellants across the distance of the turbopump feed lines (we'll assume a separately-powered pump, like the one on the Rutherford, to avoid questions of combustion cycle). Then the propellants combust. Contrary to expectations, the combustion of propellants performs zero work. What performs work is the expansion of the exhaust against the bell nozzle of the engine. A perfectly-efficient nozzle would be infinitely long and all the exhaust would (very gradually) expand to zero degrees Kelvin and zero pressure. If this were the case, then your exhaust stream would be a perfectly-aligned flow of gas molecules, all moving in parallel. This would be reversible, because you could shut down the engines and fire retrorockets to arrest and reverse the direction of the rocket. The infinitely-long rocket bell would then collect all the molecules, forcing back into the combustion chamber and then through the turbopump feed lines. In fact, you could even use this to recharge your batteries, if you have a battery-operated turbopump.

Of course no exhaust bell is 100% efficient, and so entropy would very quickly put a stop to this approach. But you can still identify the component of the process which performs work and is therefore reversible.

[PB666]

2 hours ago, sh1pman said:

Not at every level it's not. Dark energy is not conserved. It's density stays constant in an expanding universe.

When we talk about energy in a classical sense we can talk about energy as an object on a table or within a box, in this context we can talk about energy flow within a constant view of space-time that is subcomposed of quantum space-time. For example your box is at the surface of the earth, or inside the ISS, or its a sphere about the earth were energy flows in and out of the system. In that context you can think about a fixed space in space-time as an energy isoquant in which quantum space-time flows in and out of that state at the speed of light (in fact it determines the speed of light), but in a dynamic equilibrium with minute differences that are indetectably smalle. For example in a cube of say 1 cubic meter, the resolution of fine grain space is 2 x10¹⁰⁴ units, if wecould (you cant) measure all the cells you would find the actual number varied greatly from time point to time point. in that system we cannot measure the precise energy of the box or the table even if the components with the space were perfectly known. There is the basically is a presumed function of space thus the only the boxes potential is concerned not the box itself. We don't ask the question say in a completely shielded and empty box at Pluto's orbit how much energy is in space-time itself (in fact its generally concluded we don't know all the particles that consist of vacuum space itself) that we, with great effort could change. Ligo basically shows just how difficult it is to measure changes in the box itself. I should point out that several attempts have been made to measure the gravitational constant past 6 digits and each experiment has given a slightly different result, at least the constant may not be as constant as we assume and probably not the same across the expanse of space. In fact at the beginning of the universe space-time does not exist, because time does not exist. Even more wierd is that it does not suddenly appears but evolves as time evolves and energy becomes a measurable quantity. When you talk about dark energy your are talking about energy flow in or out of the foundations of the system not between the foundation and components or between components, changes in the table or box which in any previously defined space-time isoquant in a comoving reference frame we assume to be constant. The energy is only measurable at the universal scale because it something that is occurring in a 'different' kind of box. 

IN that context, we cannot see the universe, we make assumptions based on what we can see. For example we conclude all the universe is made of normal matter because our portion of the universe is made of normal matter (dark swan argument). We assume that its expanding in all directions based on what we see in  our visible universe, we assume that gravity is universal, despite not being able to measure it as precisely as other constants. And when we seek to measure gravity in distance space, we tend to only focus on space (galaxies and star systems) that our similar to our own. SO the conclusion that dark energy is not being conserved only applies to our visible universe, you cannot rigorously argue that energy is conserved in the whole universe or not, since on the whole universal scale energy may be flowing from one place, or the universe may always be adding energy at a constant rate, we just could not see it. What is the universe, its all space and all time, all space-time, since space-time existed until it exists no more.

 

[sh1pman]

34 minutes ago, sevenperforce said:

The metric of spacetime balances this out, so conservation of energy is preserved. A lay explanation: https://www.quora.com/Does-dark-energy-violate-the-law-of-conservation-of-energy-mass

Well, it doesn't really balance it out, it just says that the expansion is not a time-symmetric process, so the usual rules don't apply.

[YNM]

13 minutes ago, sh1pman said:

Well, it doesn't really balance it out, it just says that the expansion is not a time-symmetric process, so the usual rules don't apply.

CPT-violation ?

51 minutes ago, sevenperforce said:

However, any thermodynamically consistent reactionless drive can be used to produce infinite energy.

True that.

I'm just saying that the effectiveness of the device OP is explaining is about as effective as The Sun's radiation in moving itself around.

[sh1pman]

16 minutes ago, YNM said:

CPT-violation ?

Well, a PhD in theoretical cosmology claims that

Quote

The law of conservation of energy is not applicable to cosmology, because the principle only holds when the background is time-translation invariant, which is clearly not the case in a Big Bang universe.  You can write down a form of energy conservation at a given point in the universe, since space is locally Minkowskian and therefore time-translation invariant, but you can't integrate it up.

 

Edited March 13, 2018 by sh1pman