Thermodynamic demonology: extracting energy from information

Paul Raven @ 16-11-2010

Here’s a potential plot device for one of Charlie Stross’ Laundry novels or, rather more seriously (though perhaps not as entertainingly), as the hinge for a Greg Egan story; a team of Tokyo researchers reckon they’ve managed to summon up a very tiny version of what physicists call “Maxwell’s demon”. Ars Technica breaks it down:

Maxwell’s demon has haunted thermodynamics for well over a century, since James Clerk Maxwell first suggested that a small demon might be able to selectively allow only hot atoms through a small gate, gradually extracting heat from a gas without expending much in the way of energy. But there’s no such thing as a free lunch, and the demon feeds on information: it needs to know which atoms are hot. Eventually, it was recognized that information was being exchanged for energy, and an equivalence between the two was calculated based on theoretical considerations. Until now, however, nobody has managed to build a demon that could help see how well real-world behavior matched the theory.

[…]

The metaphor the authors use is a spiral staircase. A particle placed on a small staircase will be buffeted by energy, and typically go up or down a stair; on average, it’ll go down more often than up, eventually settling at the bottom of the staircase. The demon stands at the side of the stairs with a barrier. When, by chance, the particle happens to move up to a higher energy state, it inserts the barrier behind it, preventing it from dropping down. Given time, the particle will reach the top of the staircase.

Their real-world implementation involves a bead on a tether that is able to freely rotate around a full 360° axis. Below the bead, the authors set up four electrodes that generated electric fields that were shaped like a sine wave. When the bead was in the trough of the wave, it would be at its lowest energy state. If the bead was jostled anywhere else, it gained potential energy that would eventually be lost again when it fell back down to the trough.

Remember, though, that not even demonologists get a free lunch:

If you ignore the apparatus involved, the authors could directly compare the energy gained against the amount of information required to flip the switches involved. And the results appear to agree very well with the theoretical predications.

As far as thermodynamics is concerned, however, you have to consider the apparatus, since it’s necessary to balance the books in order to avoid thinking that we’re getting energy for free. And, as it turns out, the system for tracking the bead and switching currents is rather elaborate, involving “microscope by constructing a real-time feedback system including video capture, image analysis, potential modulation and data storage.” As an accompanying perspective notes, you’d probably also have to throw in the energetic cost of the grad student who was operating the whole thing, too.

So, no chance of heating my garret with information, then… unless I burn all my books. (Not. Gonna. Happen.)


Is the universe a hologram?

Paul Raven @ 25-10-2010

Wrap your head around this on a Monday morning, if you can: what we think of as the three dimensional universe we inhabit may in fact just be a holographic projection, and Craig Hogan is trying to prove it [via BigThink and Ian Sales].

The idea that spacetime may not be entirely smooth – like a digital image that becomes increasingly pixelated as you zoom in – had been previously proposed by Stephen Hawking and others. Possible evidence for this model appeared last year in the unaccountable “noise” plaguing the GEO600 experiment in Germany, which searches for gravitational waves from black holes. To Hogan, the jitteriness suggested that the experiment had stumbled upon the lower limit of the spacetime pixels’ resolution.

Black hole physics, in which space and time become compressed, provides a basis for math showing that the third dimension may not exist at all. In this two-dimensional cartoon of a universe, what we perceive as a third dimension would actually be a projection of time intertwined with depth. If this is true, the illusion can only be maintained until equipment becomes sensitive enough to find its limits.

“You can’t perceive it because nothing ever travels faster than light,” says Hogan. “This holographic view is how the universe would look if you sat on a photon.”

Coming soon to a Greg Egan short story collection near you…

I just never get tired of these existential cosmology ideas. As I’ve said before, this is the sort of stuff that makes me wish I’d actually paid attention at university and gone on to study hardcore physics… though given how much I sucked at calculus, it’s probably best that I didn’t.


Time is running out

Paul Raven @ 30-09-2010

There’s never enough time in the day, is there? Well, turns out that there may be a finite limit on the number of days, too… though not a limit so hard that it’s going to impact our expected personal life-spans very much.

The prevalent theory among cosmologists and physics heads is that the universe can and should expand indefinitely, meaning that time is essentially infinite and unending, but an apostate little gang of researchers are now suggesting that there’s a 50% chance that the universe – and hence time – will run out in around 3.7 billion years. Given that our own Sun is supposed to last another 5 billion years, that’s something of a curtailment of scope…

Their argument against an infinite universe is simple. In an infinite universe, anything can happen and will happen, no matter how unlikely it is. When there’s an infinite amount of every possible observation occurring, then it becomes impossible to determine probabilities of events, making the laws of physics similarly impossible to determine.

Of course, this makes an important philosophical assumption. Do we need to be able to understand the laws of physics, rather than just observing that they work? If so, then the Universe has to have an end.

I love a bit of epic-scale philosophical wrangling (if only as a layman watching from the sidelines), but it’s a little early in the day for it. My head hurts; I think I’ll go and have a little lay down. If Greg Egan calls, please take a message and tell him I’ll get back to him as soon as I’m able.


Goodbye, Big Bang?

Paul Raven @ 29-07-2010

Everyone knows about the Big Bang, right? The explosion-into-being of the entire universe, however many billions of years ago? Of course they do. Trouble is, the Big Bang has always been something of a fudged theory… and now Wun-Yi Shu of the National Tsing Hua University in Taiwan has come up with a new theory that fits a lot of observed evidence far more thoroughly… while dumping on some accepted truths.

Shu’s idea is that time and space are not independent entities but can be converted back and forth between each other. In his formulation of the geometry of spacetime, the speed of light is simply the conversion factor between the two. Similarly, mass and length are interchangeable in a relationship in which the conversion factor depends on both the gravitational constant G and the speed of light, neither of which need be constant.

So as the Universe expands, mass and time are converted to length and space and vice versa as it contracts.

This universe has no beginning or end, just alternating periods of expansion and contraction. In fact, Shu shows that singularities cannot exist in this cosmos.

As with all such theories, not everything fits perfectly:

One of the biggest problems he faces is explaining the existence and structure of the cosmic microwave background, something that many astrophysicists believe to be the the strongest evidence that the Big Bang really did happen. The CMB, they say, is the echo of the Big bang.

How it might arise in Shu’s cosmology isn’t yet clear but I imagine he’s working on it.

Even if he finds a way, there will need to be some uncomfortable rethinking before his ideas can gain traction. His approach may well explain the Type-I supernova observations without abandoning conservation of energy but it asks us to give up the notion of the Big Bang, the constancy of the speed of light and to accept a vast new set of potential phenomenon related to the interchangeable relationships between mass, space and time.

So, yeah, bit of a revolutionary idea. Reading stuff like this always makes me wish I’d knuckled down more at college and gotten to grips with the heavy-lifting end of physics; that way I might have ended up making a living from speculating about how the universe works. What could be more fun?

And while we’re talking cosmology, here’s a Fermi Paradox rethink [via SlashDot]:

… a new approach by Igor Bezsudnov and Andrey Snarskii at the National Technical University of Ukraine.

Their approach is to imagine that civilisations form at a certain rate, grow to fill a certain volume of space and then collapse and die. They even go as far as to suggest that civilisations have a characteristic life time, which limits how big they can become.

In certain circumstances, however, when civilisations are close enough together in time and space, they can come into contact and when this happens the cross-fertilisation of ideas and cultures allows them both to flourish in a way that increases their combined lifespan.

[…]

The parameters that govern the evolution of this universe are simple: the probability of a civilisation forming, the usual lifespan of such a civilisation and the extra bonus time civilisations get when they meet.

The result gives a new insight into the Fermi Paradox. Bezsudnov and Snarskii say that for certain values of these parameters, the universe undergoes a phase change from one in which civilisations tend not to meet and spread into one in which the entire universe tends to become civilised as different groups meet and spread.

Bezsudnov and Snarskii even derive an inequality that a universe must satisfy to become civilised. This, they say, is analogous to the famous Drake equation which attempts to quantify the number of other contactable civilisations in the universe right now.

Of course, the only way to prove the theory is to wait until we can get more data… so you might want to read a book or something in the meantime.


Time travel without the paradoxes?

Paul Raven @ 23-07-2010

A new theory based on quantum mechanics promises to do away with the “Grandfather Paradox” that supposedly makes time travel impossible [via BoingBoing]:

Quantum mechanics seems to allow for such simultaneous computations of all possible outcomes theoretically, though actually making it happen is another issue altogether (such quantum computing would blow conventional computing methods out of the water). But combined with quantum teleportation – using quantum entanglement to reproduce a quantum state in space that previously existed at another point in space – MIT’s Seth Lloyd and colleagues say you can theoretically teleport a particle back in time.

This form of theoretical time travel solves two major problems associated with the feat. For one, it doesn’t require the bending of spacetime as most time travel theories do. Considering the conditions necessary to bend the fabric of spacetime might only exist in black holes, that’s a good thing. But further, due to the probabilistic laws of quantum mechanics, anything this method of time travel allows to happen already had a finite chance of happening anyhow. That means a particle can’t really go back and accidentally destroy itself.

Note that this applies to subatomic particles and not people… so we’ll not be letting time-travel stories through the Futurismic fiction selection process just yet. But as soon as we get confirmation that it’s genuinely possible we’ll send someone back to retrospectively amend the guidelines, which will have the knock-on effect of ensuring all time travel stories submitted to us that were otherwise suitable for publication were, in fact, purchased and published. Can’t say fairer than that, can you?

Bonus quantum mechanics news: a recent successful run of a “triple split” experiment has provided evidence to support the theory of quantum mechanics that was originally developed from the double-slit experiment, first performed over a century ago. If you’re hoping that’ll make quantum mechanics make more sense, however, I suspect you’re all out of luck.


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