I'm not sure what it is about the US that makes it impossible to have more than 2 parties, but first past the post isn't it.

For the presidency, the US has a double first-past-the-post system for a single seat. Electing a minor party requires winning a majority of a pluralities: a plurality in enough states to get an electoral college majority. That's a very tough task, somewhat harder than trying to elect a Green party candidate nationwide if all Canadians voted for a single "Prime Minister Seat."

Parliamentary systems like Canada also do more to encourage minority parties at the per-seat level, for a few reasons:

• In a minority government, like Canada has seen for much of the last decade, minority parties like the NDP and BQ really do have legitimate power to shape the national agenda.
• In a majority government, nobody expects the opposition parties -- any of them -- to have much if any influence on the agenda, so to first order it doesn't matter what party you vote for provided it's not for the nationwide winner. Strategic voting does affect this, but it also cuts both ways if a minority party puts out a strong, local showing.
• Party discipline is also much stronger in Canada than the United States, so the parties occupy correspondingly smaller ideological grounds. In the States, a Republican in New York City is not necessarily the same as a Republican in Alabama, and a southern Democrat will still tend to be more conservative than a Northern counterpart -- and this really does influence legislation, to both good and ill. The upshot is that third parties are less likely to get a consistent regional base in the States, since the local duopoloy will incorporate the regional idiosyncrasy.

I am a scientist, but not an E&M specialist. Take this with a grain of salt.

I've read through the New Journal of Physics article. The ``radio vorticity'' means that the phase of the signal goes through a 180 flip across the beam centre, and the zero-point of this phase shift rotates as you move along the beam. The receiving antennas in the experiment were a pair of yagis, used to create a radio interferometer. The math and experimental results behind this appaer sound, but there are a few limitations:

• This is a highly directional effect. Not only would multipath interference destroy the crap out of this signal, but they also needed pairs of antennas on opposite sides of the beam centre to discriminate between mode-0 and mode-1 rotations. Directionally-wide beams will have more interference, and building the interferometer will be more difficult with less than a 180 separation.
• The transmitting antenna was very specialized. The transmitter itself not so much, but the antenna was a parabolic antenna ``mechanically modified'' -- they sliced through the top of it to turn the atenna into one loop of a parabolic spiral. If you have access to the article online, take a look at the picture, it's kind of neat.
• ``In principle an infinite number of channels'' my ass. They're building an interferometer, so they need at least one antenna per mode they wish to discriminate between, and when they used antenna-separation to do the phase filtering for them they saw some significant interference form secondary lobes for intervals where the match wasn't perfect. This was okay for the two-channel experiment (mode 0 and 1), but the receiving antenna design would really start messing with higher channels, where those secondary lobes start seriously interfering themselves.
• As written, the receiving antenna design is highly sensitive. The phase cancellation used required some pretty precise antenna positioning, since they needed a displacement of one half-wavelength in the beam direction for proper interference (to discriminate the mode 1 angular momentum). Trying this in a production environment is going to be pretty tricky -- perhaps they could get somewhere with electronic phase delay.

So for controlled channels -- perhaps even microwave links -- I'm optimistic about engineers being able to build something useful out of this. But the basic math isn't going to generalize to omnidirectional links, and it certainly isn't going to deal well with strong multipath interference. Simply being able to discriminate between modes requires straddling the beam centre, so this absolutely isn't going to work for general consumption.

Also, I don't think that practical antenna design will ever allow more than three or four channels of angular momentum outside of a lab setting. Even that may potentially be a huge win for fixed microwave links, though.

Without reversible computing, there indeed is a fundamental limit to how much energy a computation takes. In short, "erasing" one bit of data adds entropy to a system, so it must dissipate kT ln 2 energy to heat. This is an extremely odd intersection between the information theoretic notion of entropy and the physical notion of entropy.

Since the energy is only required when information is erased, reversible computing can get around this requirement. Aside from basic physics-level problems with building these logic gates, the problem with reversible computing is that it effectively requires keeping each intermediate result. Still, once we get down to anywhere close to the kT ln 2 physical constraint, reversible logic is going to look very attractive.

Yes, I did read the paper. (Disclaimer: I have a PhD, but not in graph theory. Your results may vary.)

In short, the paper repeats analysis and numerical simulations of a simplified 'agreement model'. People are abstracted as nodes on a graph, communication happens between them, and consensus is reached. If a graph is initialized randomly, with nodes 'believing' either A or B, eventually (in log(N) time) the graph reaches consensus with every node 'believing' A xor B.

This paper adds a twist; some fraction of nodes are 'committed' to A, and cannot ever be convinced of B. To quote the paper:

Here, we study the evolution of opinions in the binary agreement model starting from an initial state where all agents adopt a given opinion B, except for a finite fraction p of the total number of agents who are committed agents and have state A. Committed agents, introduced previously in [23], are defined as nodes that can influence other nodes to alter their state through the usual prescribed rules, but which themselves are immune to influence.

Now, if even one node cannot be convinced of B, then no consensus can be reached -- but it doesn't really matter. If the fraction is really small, then you can more or less ignore them.

The interesting part about that paper is their threshold effect -- once p gets to be over 10%, not only does A eventually win, but it does so -quickly-.

The applications to politics still hold, but not on the big, obvious issues. Those issues, like taxes and abortion and health care and anything else that really makes the news, have committed believers on both sides -- they're outside the scope of study. Where this research becomes really interesting is in quieter, uncontroversial issues -- like regulation details, or climage change before Al Gore. There, this research suggests that the influence of sockpuppetry and lobbying is nonlinear -- beyond a critical point, the lobbyists completely win.

Of course, caveats about "the real world isn't an abstract graph" apply.