Perpetual motion machines. Are they pure science fiction? Or could we ever truly build one? 

There have been many claims of such devices in the past and all of them have proved to not be as advertised — to put it mildly. But could our current knowledge of physics and the universe open up actual possibilities of building a perpetual motion device in the future?

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These types of machines move perpetually, meaning, they never stop. If you could create one today, set it moving, and leave it alone it should keep moving until the end of days, aka the "Big Freeze". 

The "Big Freeze" is the theoretical end of everything, when the universe has expanded to such an extent that it reaches a state of zero thermodynamic free energy.

At this point, the cosmos will be unable to sustain motion, and generally, everything will be dead. Space and everything in it will reach absolute zero.

This will be a time of eternal, never-ending, utter darkness. Nice to know, but don't lose sleep over it —  it's only about 100 trillion years or so away. There are a plethora of other theories of the end of everything, but this one is most widely accepted by experts.

Thankfully, our species and all life in the universe will likely be extinct by this point. 

You will likely find many designs out there on the internet claiming to be working prototypes or proofs of perpetual motion. Some of these designs certainly do look convincing on an initial inspection. You could probably develop a design yourself, and if it were possible to engineer it, it could also move for all time.

If a true perpetual motion device could be achieved, it would have enormous implications. They could provide an eternal source of energy for just the cost of building the machine in the first place — not too shabby. 

Sadly, the real world and the fundamental laws of physics have other ideas for perpetual motion machines. They are, by definition, impossible.

At least given our existing knowledge of physics. It could be possible that new fields of knowledge will present themselves in the future and overturn our current understanding of physics, but this looks unlikely.

After all, you can never possibly know what you don't know. 

But, let's just assume that perpetual motion machines aren't impossible and look at some possible examples, and how they could theoretically work. 

We are sure you are familiar with the first law of thermodynamics. This is the law of the conservation of energy.

This states that energy is always conserved and can neither be created nor destroyed, although you can change its form. However, for a machine to keep moving, the energy input into the system must stay within the system without any losses. This fact alone renders the idea of perpetual motion machines moot.

A true perpetual motion machine must obey the following:

1. Friction must be eliminated - There can be no friction between any moving parts. Friction would rob the machine of energy, which would be lost as heat, or if it gets hot enough, light. You could make the surfaces of the parts as smooth as possible, but there would still be microscopic imperfections that would create friction. Whenever two parts rub together heat will be generated. According to the laws of thermodynamics kinetic energy is converted to heat energy and is lost from the system. Not cool, no pun intended, for the proposed perpetual motion machine.

2. The machine must operate inside a vacuum, i.e. no air - Air, like other moving parts, will rub on the moving machine, creating friction, which results in a small but important loss of energy from the machine. Over time, even if this were the only friction, the machine would lose all of its kinetic energy from this friction. This would take a long time, but the machine would grind to a halt long before the end of days.

3. The machine must be silent, absolutely silent - Any sound production is also a loss of energy from the system. This, like the two other points above, would eventually rob the machine of its kinetic energy.

Even with the proposed inability of perpetual motion to break the laws of physics, this hasn't stopped ambitious inventors from attempting to achieve that.

Simanek's online museum unveils some of the first machines designed by Indian mathematician and astronomer Bhaskara in the 12th Century. The design of one machine was such that it supposedly kept spinning indefinitely due to an imbalance created by containers of mercury around its rim. Other examples of attempts at a perpetual motion machine include 16th Century windmills, 17th Century siphons, and some water wheel designs.

It must be noted that some perpetual motion machines have been designed genuinely in the spirit of curiosity and science. Others, on the other hand, were direct attempts at deception for monetary gain.

Probably the most famous hoax being that of Charles Redheffer, from 1812. We'll discuss this in more detail later.

Nineteenth-century America, like many other places, was a prime location for hoaxes of this kind. In his book "Pranksters: Making Mischief in the Modern World," Kimbrew McLeod reveals to us many of the people having a go from the 1600s to the modern-day.

While the more scrupulous sought the truth using the scientific method, for others, the way to make money was through pseudo-science. 

Here we'll look at some of the most interesting examples of proposed perpetual motion machines in history. Some are hoaxes, while others are genuine attempts to create these fantastical machines. 

This list is far from exhaustive and is in no particular order. 

Philadelphia and New York were enthralled by Mr. Redheffer's perpetual motion machine when it was unveiled in 1812. His demonstration shows earned him thousands of dollars, a vast sum of money at the time. The story is covered in great detail in W.J.D Ord-Hume's book "Perpetual Motion: The History of an Obsession".

According to Ord-Hume, historians know very little of Redheffer's history prior to the hoax. He first appeared on the scene in 1812, opening a house near Schuylkill River to show off his miracle machine. Redheffer claimed the machine's "gubbins" could keep moving forever without ever being touched or aided.

The machine allegedly worked through the "assumed principle of perpetual motion through continuous downward force on an inclined plane". This would produce a continuous horizontal force component. Redheffer, according to Ord-Hume, constructed a machine that operated through a gravity-driven pendulum with a large horizontal gear at the bottom.

This interlocked with another smaller gear. These twin gears and the associated shaft rotated separately. Two ramps were placed on the larger gear and on the ramps were also weights. These weights pushed the large gear away from the shaft. The resultant friction would cause the gear and shaft to spin.

This spinning gear would power the smaller gear if the weights were removed the machine would grind to a halt. Redheffer was so pleased with his machine that he lobbied the state of Pennsylvania to build a larger one. The state, rather wisely as it turned out, sent two inspectors to investigate the potential investment.

This is where Redheffer's plot began to unravel.

When the inspectors arrived, they found the machine in a locked room, only visible through a window. One of the inspectors, Nathan Seller, had also brought his son along. 

The inspector's son noticed that the gears in the machine were not working exactly as declared. The cogs and gears appeared to be worn on the wrong side. This would mean that the shaft, weights, and gear were not powering the smaller gear to the side. It seemed, in fact, that the opposite was true.

Nathan believed his son and determined the machine was a hoax. Instead of going public with his hunch, he hired Isaiah Lukens, a local engineer, to build his own version of the machine. The remit was for it to look and "work" as Redheffer's was supposed to. Lukens successfully constructed a similar device with a seemingly solid base and a square piece of glass at the top. The device had four wooden finials that were supposed to be decorative on top of the glass attached to wooden posts.

Lukens placed a clockwork motor at the base. One of these finials, was in fact, a winding device. It could provide power for the motor all day long. This motor would turn the shaft and thus, power the gears. Lukens showed Redheffer the replica machine, who was so overwhelmed with the sight of it working, offered money to know how it worked. Sellers and Lukens let the news of the hoax spread rather than confront Redheffer on the spot.

The machine was debunked a second time after which the crowd smelled blood. Realizing this, the crowd went ballistic and destroyed Redheffer's work. Redheffer understandably made a quick exit, never to be seen again. Here is a model in action, though it is modified slightly from the original design. This machine, and Redheffer's fate, is a warning from history over making false claims of creating a perpetual motion machine.

Bishop John Wilkins, a founder and the first secretary of the British Royal Society, compiled a book on "Mathematical Magick". His work coincided with the period in history where "magical arts" were being replaced by the scientific method during the Age of Enlightenment. An age we could barely understand now as mythology was replaced by reason.

Early in 1600, William Gilbert's book "De Magnete" was released. Readers were offered a fascinating account of Gilbert's experiments with magnetic lodestones and an introduction to the new field of magnetism.

This sparked great enthusiasm and interest in experimentation in this emerging field. However, many misunderstood this mysterious phenomenon. Johannes Kepler attempted to apply the theory to explain the motion of planets, only later to disregard it.

Kepler played with the idea that the Sun was a huge magnet whose fields affected the planet's orbits, but he later dismissed this notion. Anton Mesmer thought that perhaps magnets influenced the human body, thinking that they might create a magnetic influence within people. It is speculated that Anton's work coined the phrases "animal magnetism" and "mesmerism."

Wilkins discussed the difficulty of achieving perpetual motion. He considered a device often attributed by Schott to Johannes Taisnierus. This device consisted of two tilted ramps, an iron ball and a magnetic lodestone stuck on the top. The lodestone was a large chunk of natural stone encased in an iron ball.

The ball was pulled up the ramp towards the lodestone, where it later fell through a hole towards a lower ramp. From here, it rolled down through another hole back to the straight ramp where it was pulled up again. This basic concept obviously needed further work and refinement.

How do you stop the ball being held in place on the ramp by the magnet for instance? It would be difficult for us today to understand why this device was taken seriously at the time. Even today, this basic concept is still considered for contemporary perpetual motion solutions, so-called magnetic motors.

Wilkins considered the device and offered detailed discussion and practical difficulties of the device. His discussion considered a major difficulty being that the ball wouldn't fall all the way down to the lower ramp but be held in place by the magnet. Perhaps it would even ascend from the lower ramp.

Wilkin's machine is a good example of how we should be aware that some proposals could be warning us of the futility of this quest.

"Drinking Birds" or "Sipping Birds" or "Insatiable Birds",  whatever you want to call them, are pretty interesting devices. At first, this may seem to be a good contender, with its different design than most perpetual motion "engines".

These cheeky little party tricks have a bird-shaped lever which "takes" a drink and then returns to a vertical position and so on. But how?

The basic design of these toys involves two glass bulbs joined by a length of glass tubing. Just over half of the space inside the glass bulbs and the tube is filled with fluid, which is usually colored, in a vacuum. This liquid is typically dichloromethane or methylene chloride, which has a very low boiling point.

The head is usually covered in felt, which absorbs water as it "drinks". Evaporation of this water lowers the temperature of the head, causing dichloromethane to condense in the head section.

This creates a pressure drop in that section of the apparatus, following the ideal gas law. The higher pressure in the tail end pushes the liquid up the neck, which makes the head section top-heavy. The "Drinking Bird" then pivots and the head touches the liquid. As this happens, the tail section rises above the surface of the liquid.

Pressure equalizes as a bubble of "warm" vapor rises from the head to the tail, displacing liquid as it goes. This increases the weight of the tail and the bird returns to its vertical position, ready for the whole process to start all over again.

Pretty neat, but is this a type of perpetual motion machine? After all, where is the energy coming from?

The answer is the surrounding ambient air temperature. Therefore this is not a perpetual motion machine as it is entirely dependant on external energy sources to work. 

This example teaches us to always look for the energy source if not immediately obvious.

Invented sometime in the 17th-century by the famous chemist Robert Boyle, this device is a very interesting concept. The idea was that when a liquid is poured into the cup, it flows through a winding tube up through the handle and back into the main receptacle. 

In doing so the cup should continue to empty and refill ad infinitum.

The principle behind the cup is actually quite simple: the weight of the liquid in the vessel is significantly higher than the weight of the liquid contained in the neck of the vessel, which results in a pressure difference that causes the water to rise up the neck of the vessel.

This should force the liquid to  flow in order to compensate for the difference in weights (aka. hydrostatic pressures). If this compensation is sufficient to raise the liquid from the neck to the upper zone where the tube ends, the system acquires a continuous behavior to compensate for pressure differences.

Sadly for Mr. Boyle, the theoretical foundation is wrong because it confounds weight with pressure, and therefore this would never work.  Back to the drawing board sir!

Another interesting proposal for a perpetual motion device as the "Crookes Radiometer". This device consisted of a small windmill-looking device contained within an airtight chamber held in a  near-vacuum that actually appeared to move under its own power.

It was claimed by its creator that this little windmill wasn't one at all, but a prototype "light mill". Developed by another chemist called William Crookes, the phenomenon was discovered by accident and he postulated that light photons were pushing the mill's vanes via radiation pressure (as predicted by Maxwell's theory of electromagnetism).

He built the first working prototype in 1873 much to the amazement of his peers.

Sadly, Crooke's conclusion was incorrect. 

A more sensible explanation came a few years later when Osborne Reynolds discovered that light photons warm gas molecules on the black sides of the vanes, which then creep to the edges and flow into the cooler gas molecules on the silversides of the vanes, thus turning them. 

"The net movement of the vane due to the tangential forces around the edges is away from the warmer gas and towards the cooler gas, with the gas passing around the edge in the opposite direction," UC-Riverside's  Phil Gibbs explained.

Close, but no cigar. 

So, could we ever build a true perpetual motion machine? It seems, at least for now, that it is highly unlikely. But we are confident this will not stop many budding inventors in the future from at least trying. 

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