This perpetual motion machine she made today is a joke! It just keeps going faster and faster.
…
Lisa! Get in here. In this house, we obey the laws of thermodynamics! – Homer J Simpson

Perpetual Motion Email Guidelines

Short version: no, it won’t work.

“If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.”
— Arthur Eddington, The Nature of the Physical World (1928)

A Supertask Shows How Particles Can Spontaneously Start Moving

A particle, traveling at a meter per second, knocks into the square. Because the particle’s speed is a meter per second, and the square is a meter wide, within a second, all the motion that was introduced into the square is gone. But there is no particle ejected. The infinite amount of collisions means there is no final particle. The motion just stops.

The problem with thought experiments is that if they lack rigor, it’s easy to argue into something that is contrary to the laws of physics. With a verbal description, you can get something like Zeno’s paradox, which seems like a contradiction until mathematical rigor is applied.

I think the above is such an example. Somebody has taken a liberty with infinities or made a hand-wavy argument somewhere in the middle of all this. The conclusion violates conservation of momentum and energy, so there’s a flaw somewhere. I’d like to hear more about how the motion ceases after one second. There’s a dodgy assumption in there, I’m sure. There may be an infinite number of particles but they are also infinitely small, so how do you determine their cross-section and the resulting collision rate?

The paper isn’t even that subtle.

What happens at t = 1? By that time, every particle Pi has collided with its immediate left-hand neighbor and so is stationary. Therefore, all the particles are stationary.

Um, what? At that point I confess I stopped reading. This sounds like a technicality of math that doesn’t apply to a real system, i.e. there is no “last particle” that’s moving. If you assume something that is physically impossible, you can come to just about any conclusion you want.

The predictability of randomness and the age of Earth

The uranium-lead transition isn’t the only one used. There’s also the rubidium-strontium transition (with a half-life of 49 billion years), the potassium-argon decay (1.3 billion years), and a handful of others. The key in all these cases is to have a rock — meteorite or otherwise — with enough atoms of the given types to perform measurements. One we don’t see in the list is “carbon dating”: carbon-14 has a half-life of about 5,700 years, so it’s useful for archaeology and dating the remains of animals from the relatively recent past, but utterly useless for measuring the age of Earth.

But why is a random process like radioactive decay useful as a clock?

Please Don’t Beam Me Up, Scotty

Visitor: It doesn’t transport. It disassembles your molecules and reassembles them on the other side. It annihilates you, and builds a perfect copy in a new location. It’s not a transporter, it’s a replacer. What results is a facsimile, a reproduction, a brand-new being with borrowed memories. The original creature—its consciousness—its soul—all gone.

This is funny, and mostly right. But there’s one physics error I spotted, and it’s a whopper. As you might guess, it ties in with the details of quantum teleportation. It’s unfortunate, too, because I think much of the story holds together without it.

Visitor: Think about it. It’s not the actual molecules being “transported,” just information about them. You could just as easily transmit that information—and build the new being—while leaving the old one perfectly intact. Couldn’t you? And if the old one persisted, wouldn’t it be obvious that the new copy is a different being altogether?

Spock: His analysis is not incorrect, Captain.

What Spock should have said was that the answer is “no”; i.e. there’s a superfluous “not” in there (a sign error, of sorts). Destruction of the state of the original is a requirement of quantum teleportation, which renders the rest of that section’s argument moot. Perfect copying while retaining the original is cloning and there is something called the no-cloning theorem in quantum mechanics: basically, you can’t make copies of an unknown quantum state (the wikipedia page on this gets technical pretty quickly). You can transfer that information from one particle to another, but the information in the original is destroyed.

The gory details of this bit of theory is tad outside of my wheelhouse, but as I understand it if you could clone, then you could measure the cloned state without disrupting the original. But there are a whole bunch of quantum effects that depend on a state being undetermined, rather than having some underlying reality — there must be more than one possible state in order to see interference. It’s a reason that classical explanations for entanglement fail, because in classical physics you can have an unknown state (a coin you’ve flipped) and then measure it (look at the coin, see it’s “heads”), and you will know that it was heads even before you looked at it. In QM, you don’t know that it was heads until the moment of measurement — it was in a superposition of heads and tails before that, and that superposition will behave differently than a state that was secretly heads (or tails) the whole time.