Perpetual Motion - is it so damn hard?

Factual Questions
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This belief is so common that it needs to be singled out, stuffed into a leaky submarine, and sunk to the bottom of the ocean, unable forever to return.

Airplanes are probably the best example. At the very moment in history that people were supposedly saying that man was never meant to fly, hot-air balloons had a history of more than a century and the hydrogen dirigible was forecast to be the people mover of the next century. That’s because people understood the problem. Understood it all too well, in fact. Lighter-than-air crafts were known to be possible and powerful. Heavier-than-air crafts were impossible - but solely because there was no known engine that was both sufficiently light enough and powerful enough for the forces necessary. Then the gasoline engine was developed and got better and better.

See how this is a totally different usage of the word impossible? Heavier-than-air flight was an engineering impossibility. The physics was well known, which meant that success would occur as soon as the engineering exceeded the physical constraints.

For perpetual motion, the physics says explicitly that the constraints can never be exceeded. Cannot even ever be matched. You can’t simply improve your engineering sufficiently. There’s no such thing, even by using unobtainium.

Science is filled with almost impossible tasks that are nevertheless theoretically possible. Wormholes could be built with exotic matter that has negative pressure. Don’t ask me to explain that. There probably is no such stuff and if there were there’s probably no way to gather and manipulate and stabilize such stuff. But if there were it becomes an engineering problem. No real scientist would say that’s it’s impossible in theory, because we know the theory.

Perpetual motion is impossible in theory - because we also know that theory. Which says that no amount of engineering will suffice.

If your argument then becomes, but what if we come up with an entirely new theory that encompasses all physics and allows for perpetual motion? Strictly speaking, that argument can’t be refuted. Strictly speaking, I also can’t refute the argument that tomorrow the laws of physics will change and I’ll be able to flap my arms and fly to Betelgeuse. Neither one’s very likely, though, and science can be forgiven for not paying attention to either in the interim.

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The problem is that, as you mention, it needs to encompass everything we currently know. It needs to explain why we are wrong about everything we currently do in science, but wrong in a way that just happens to work as if it’s not wrong.

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A lot of people have an annoying tendency to confuse engineering and technological limitations with limitations of the physical universe itself.

There were once claims that we would never be able to break the sound barrier. However, this doesn’t mean that scientists were stating that this was physically impossible to accomplish, only that they were skeptical of our ability to successfully engineer an aircraft that could hold up under the stresses of supersonic flight.

The laws of physics, on the other hand, are not an option. They’re not a technological barrier. They are an inevitable and inescapable consequence of the physical universe we inhabit. The very existence of this universe is evidence of that.

Some people just can’t seem to deal with the fact that there are simple physical laws upon which our entire existence is contingent. You just can’t wish them away because you want your sci-fi fantasy to come true.

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Right to all. Think about it this way. A 100% efficiency engine is optimistic beyond reason. A wheel that you spin and never stops spinning. Even without knowing the laws of thermodynamics that tell you it is impossible, you can tell it would be a major challenge to isolate this wheel from all possible external influence.

Now imagine that you want that wheel not only to keep spinning from your little initial push but you also want it to do work. You want that wheel to be able to move things you couldn’t have moved with your initial push. You don’t really need to know the formulas to intuit that there is something very wrong with that. You would be, in essence, creating energy. From where?

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While I agree with the basic point of your post (and feel you expressed it well), I’ll take issue with this. By a wide margin the biggest challenge in heavier-than-air flight was devising a reliable system of (3-axis) control. It’s no coincidence that the most successful early experimenters (Lilienthal and the Wrights) confined their early work to unpowered aircraft.

Once the control problem was solved the job of finding an acceptable engine was rather easy. The Wrights wound up building a crude but acceptable version from scratch, in a surprisingly short time. Contrast this with Langley, who had a beautiful, state-of-the-art engine that completely outclassed the Wrights’ - but no system of control: his expensive experiments with manned flight were an abject failure.

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I’m sure we could get into a fascinating discussion of whether even Langley’s last and best engine (which weighed twice as much as the Wrights’, albeit with four times the horsepower) would have powered his craft with better control.

However, that’s irrelevant to what I meant. At the time, obviously, people didn’t know the problem was one of control until after - well after - the Wrights’ success. The reason given for the “impossibility” of heavier-than-air flight was heaviness: the heaviness of any known engine. Once the engines were available, successful flights were made independently by several people who didn’t know about the Wrights. But that was the bottleneck, not the issue of control.

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It did so - after the “Aerodrome” was extensively modified by Glenn Curtiss in 1914.

True of most people. But you can certainly argue that Lilienthal - and those who studied what he’d done - knew this before the Wrights.

It was perceived as a bottleneck - until the Wrights showed otherwise. No flying machine with an advanced engine and poor system of control ever had more than very limited success, whereas the Wrights showed that a crude engine was adequate. They made hour-long flights with engines that were rather ordinary for the time.

Who are you thinking of as an experimenter whose success depended on a state-of-the-art engine?

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If by “extensively modified” you mean “fudged until it had nothing to do with Langley” then I agree. :slight_smile:

But I’m not continuing this hijack. I’m just noting that a rash of flights were made all over the U.S. and Europe all about the same time all using light engines, many of which were not “state-of-the-art” but just not heavy steam engines. (Some used compressed air rather than gas, for example.) It’s undoubtedly true that they also needed proper controls to be stable. Still, I can’t support the notion that throughout the 19th century the cry went up around the world that “man was never meant to fly because of the lack of 3-axis controls!”

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I just want to continue this hijack slightly to point out that “heavier than air flight” was performed over fifty years before the Wright brothers (or most of their competitors) by Joseph Stringfellow, who used a steam engine of his own building, powering a two-propellored monoplane in 1848. His device was unmanned, though. And it had absolutely miserable control (it only worked in relatively still air, ideally in a tent). Why he never put a vertical stabilizer on it is beyond my understanding – it seems such an obvious thing.

But i don’t know of anyone who doubts that his device worked. It’s not in a class with the other claimants like Whitehead – his flights were reported in the Times and his machine exhibited in the Crystal Palace.

http://www.teemings.net/series_1/issue15/calmeacham.html

And six years before him, W.H. Phillips demonstrated a steam-powered helicopter, which was definitely heavier than air. And probably even had less control (and was, of course, unmanned).

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Excellent piece, CalMeacham.

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Very true - which of course does not mean that lightweight engines were the issue, but simply that few people understood what the real problem was.

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Sorry to jump in late…and I admit I haven’t read the whole thread…but I am wondering…

The laws of Newtonian mechanics were also based on that, and ultimately weren’t proved wrong but were shown to be only a close approximation, appearing accurate under certain common but limited conditions.

Has anything been done to show that the current laws of thermodynamics aren’t in a similar situation? Not necessarily changing at high speeds, but maybe under some other condition? Like extremely high temperatures?

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This thread is, in general, an indication of how woeful science education is in the United States that this fundamental understanding of the natural world.

Newtonian mechanics is, as noted above, an approximation of the real world, based primarily upon observation of physical mechanics. Newton (credited, with only minor dissent, to having discovered gravitation) based his eponymous laws on the somewhat nebulous concepts of “inertia” and “gravity”, and while these ideas seem to work, he didn’t fundamentally understand why. When Einstein (and Poincaré, and Hilbert, and others) developed special and general relativity, it was an extension of classical mechanics based upon gravity and inertia being effects that were a result of interactions with an underlying plenum of spacetime. What is spacetime? Nobody really knows; it is essentially a mathematical framework with parameters that work in such a way that it gives results that match to experimental phenomena.

Thermodynamics is a different, and arguably more fundamental type of science entirely. It really underpins all other areas of real world mechanics on every level; rigid body dynamics (both classical and relativistic), continuum mechanics, electrodynamics, chemistry, nuclear reactions, even information theory and quantum field theory. Thermodynamics starts with one essential principle–that energy is neither created nor destroyed–and derives everything else from that principle by mathematical deduction. As it happens, those deductions, as applied in the above listed fields, describe real world phenomena without exception.

Although quantum electrodynamics is often referred to as “The Crown Jewel of Physics” in reference to the extreme precision of prediction verified by experiment, thermodynamics should be considered should be considered “The Great Pyramid of Physics”, occupying the scientific consciousness as the overarching principle of all physical phenomena. In order to invalidate the laws of thermodynamics, you’d have to demonstrate that energy can be created from nothing (or destroyed); and doing so would undermine every field of science in a far more basic way than most people understand.

I could write more words, but the only way you can truly understand the fundamental nature of thermodynamics is to understand the fundamental logic behind it; and that takes about a couple of semesters of study (and unfortunately, it is a topic that is generally poorly taught at the undergraduate level). However, the math isn’t particularly difficult; basic integral calculus is all that is needed to understand the three laws theory, and an understanding of statistical mechanics gives you the means to apply the thermodynamic laws to any real system regardless of size or complexity (though the fidelity of answers will depend on how detailed you model the system in question).

Anyone claiming to have discovered a violation of the laws of thermodynamics is either the greatest genius the world has ever known, or is an imbecilic crackpot. It is left as an exercise for the reader to work out the odds on that.

Stranger

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True - so anything that supplants the laws of thermodynamics has to explain why they seem to work all the time in every context but some yet-to-be-discovered one.

Not sure, but I think if something ever did present a challenge, it would have to be coming out of some high-energy project in a research lab, not from some Fred in a shed with a handful of magnets and overbalanced wheels.

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Of course the ancients knew that heavier than air flying was possible - they just looked up into the sky and watched the birds. They just didn’t know how to do it yet. However, as has been stated, it was a *mechanical *problem not a *conceptual *one as is perpetual motion.

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At the risk of re-opening old wounds:

SOLO-TREC is a heat-harvesting Robotic buoy that can repeatedly ascend and descend 500m with no additional energy input. Fiendishly clever, but it does not violate any rules of thermodynamics (none of Maxwells demons here). Using heated wax to pressurise oil seems pretty cool to me.

Si

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**

**“Natch!” since it is a ‘bootstrap’ design, lifting itself and going nowhere.

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Oh, oh, let me work it out! First, we count how many ways there are to be a genius. Next, we count how many ways there are to be an imbecilic crackpot. Then, we divide the first by the second, and that gives us the a priori likelihood ratio that the claimant is a genius rather than a crackpot. Hmm, I know which way I’d bet. :smiley:

Same system I linked to earlier. :slight_smile:

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You know, every week someone wins the lottery.

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You know in the world we live in, the first thing a person would do, having actually built a perpetual motion machine, would be to begin selling the product of that machine’s work. There is no chance that the person would publish on the internet a simple explanation of how the machine worked. If the work was no more than turning an advertising sign without using power, still, the financial reward would become a permanent source of income, which could be used to produce even more machines. It would not just be a perpetual motion machine, it would be a perpetual money machine. You would not need investors, or publicists, just hire a few mechanics, and start building.

And if it could be done, it would be being done.

Tris