Daily Archives: August 20th, 2007

Boggling Boltzmann Brains

From New Scientist :

POP. What are the chances that an everyday object – a rock, a chair, you name it – could suddenly appear out of thin air? Not zero, surprisingly. In fact, given enough space and time, it is conceivable that a conscious being could arise, even if only for a microsecond.

OK, such an event would be incredibly unlikely, but not impossible – at least in theory. Physicists have dubbed such hypothetical beings “Boltzmann brains”, after the 19th-century Austrian physicist Ludwig Boltzmann, a pioneer in thermodynamics and statistical mechanics. Boltzmann posed the question of whether the universe could have arisen from a thermal fluctuation; his work presaged the idea that a fluctuation could also give rise to a conscious entity that sees the universe. In this regard Boltzmann brains are not necessarily actual brains, but rather are a metaphor for observers of the universe that might appear spontaneously.

The idea sounds absurd, but it is helping cosmologists grapple with models of the universe, and our place in it. Cosmology, indeed most of science, assumes that we humans are typical observers in the grand scheme of things. Ever since the 16th century, when Polish astronomer Nicolaus Copernicus argued that the Earth is just a rock orbiting the sun, we have been dethroned from a unique position in the cosmos. The laws of physics seem to be the same in our neighbourhood as in the rest of the visible universe. So the idea has been enshrined that unless we have reason to think otherwise, we should assume that we are typical. “This assumption is very essential to everything that we do,” says Alex Vilenkin of Tufts University in Massachusetts. “If we don’t assume that our observations are typical of observers, we wouldn’t be able to conclude anything.”

The way I understood quantum mechanics is that since universal particles and their inherent building block particles and their building “strings” all buzz around back and forth in different energy states, thus there always is a small probability, no matter how small, that if you start crossing the road to check your mail (yeah, you might get hit by a truck) you’ll dissolve and rematerialize in another part of the world, or Universe for that matter. This idea posits that the longer the Universe exists, because of increasing random fluctuations in thermal radiation of the expansion, the chances of these “Boltzmann Brains” show up to be dominant observers of the Universe. Ludwig Boltzmann is the father of this concept and you can read his Wikipedia profile here.

Professor Leonard Susskind in 2002 hypothesized that entities could arise from the thermal fluctuations in the Universe:

Spikes in space-time

There is another way to think about why our universe began in a highly
ordered or “low entropy” state. In 2002, a group of physicists led by
Leonard Susskind at Stanford University in California proposed that
entities capable of observing the universe could arise via random
thermal fluctuations, as opposed to the big bang, galaxy formation and
evolution. This idea has been explored by others, including Don Page
at the University of Alberta in Edmonton, Canada. Some researchers
argue that under certain conditions, self-aware entities in the form
of disembodied spikes in space-time – “Boltzmann brains” – are more
likely to emerge than complex life forms. Because they depend on
fluctuations of particles, Boltzmann brains would be more common in
regions of high entropy than low entropy. If the universe had started
out in a state of high entropy, it would be more likely to be
populated by Boltzmann brains than life forms like us, which suggests
that the entropy of our early universe had to be low. As a low-entropy
initial state is unlikely, though, this also implies that there are a
huge number of other universes out there that are unsuitable for us.

More philisophical debating about existance and the Universe, I love it!

Next up, Are We Living In a Computer Simulation?