"One might think that, once we know something is computable, how efficiently it can be computed is a practical question with little further philosophical importance. In this essay, I offer a detailed case that one would be wrong. In particular, I argue that computational complexity theory---the field that studies the resources (such as time, space, and randomness) needed to solve computational problems---leads to new perspectives on the nature of mathematical knowledge, the strong AI debate, computationalism, the problem of logical omniscience, Hume's problem of induction, Goodman's grue riddle, the foundations of quantum mechanics, economic rationality, closed timelike curves, and several other topics of philosophical interest. I end by discussing aspects of complexity theory itself that could benefit from philosophical analysis."
posted by cthuljew
on May 5, 2013 -
The Nature of Computation
- Intellects Vast and Warm and Sympathetic
: "I hand you a network or graph, and ask whether there is a path through the network that crosses each edge exactly once, returning to its starting point. (That is, I ask whether there is a 'Eulerian' cycle.) Then I hand you another network, and ask whether there is a path which visits each node exactly once. (That is, I ask whether there is a 'Hamiltonian' cycle.) How hard is it to answer me?" (via
) [more inside]
posted by kliuless
on Dec 1, 2012 -
The 2012 Nobel Prize in Physics has been awarded
to Serge Haroche (France) and David Wineland (US) for discovering ways to measure and manipulate quantum particles, a discovery which many are suggesting may soon allow us to build computers with virtually limitless capabilities
. The Nobel press release provides a layman friendly PDF summary
of the research and its potential applications, as well as a less layman friendly PDF with additional scientific background
information. The press release cites two older Scientific American articles for further reading, and the magazine has made these articles available to read free online for the next 30 days:Monroe, C. R. and Wineland, D. J. (2008) Quantum Computing with Ions, Scientific American, August.Yam, P. (1997) Bringing Schrödinger’s Cat to Life, Scientific American, June.
posted by dgaicun
on Oct 15, 2012 -
Morton and Vicary on the Categorified Heisenberg Algebra
- "In quantum mechanics, position times momentum does not equal momentum times position! This sounds weird, but it's connected to a very simple fact. Suppose you have a box with some balls in it, and you have the magical ability to create and annihilate balls. Then there's one more way to create a ball and then annihilate one, than to annihilate one and then create one. Huh? Yes: if there are, say, 3 balls in the box to start with, there are 4 balls you can choose to annihilate after you've created one but only 3 before you create one..." [more inside]
posted by kliuless
on Jul 21, 2012 -
The trend of mathematics and physics towards unification provides the physicist with a powerful new method of research into the foundations of his subject, a method which has not yet been applied successfully, but which I feel confident will prove its value in the future. The method is to begin by choosing that branch of mathematics which one thinks will form the basis of the new theory. One should be influenced very much in this choice by considerations of mathematical beauty.
 [more inside]
posted by smcg
on Apr 28, 2012 -
"Using four photons, we can actively delay the choice of measurement on two of the photons into the time-like future of the registration of the other two photons. This effectively projects the two already registered photons onto one of two mutually exclusive quantum states in which the photons are either entangled (quantum correlations) or separable (classical correlations). This can also be viewed as ‘quantum steering into the past’."
, Nature Physics
, Ars Technica
posted by jeffburdges
on Apr 25, 2012 -
Previous experiments have hinted at the connection...
Physicists have found the strongest evidence yet of quantum effects fueling photosynthesis.
Multiple experiments in recent years have suggested as much, but it’s been hard to be sure. Quantum effects were clearly present in the light-harvesting antenna proteins of plant cells, but their precise role in processing incoming photons remained unclear.
In an experiment published Dec. 6 in Proceedings of the National Academy of Sciences, a connection between coherence — far-flung molecules interacting as one, separated by space but not time — and energy flow is established.
“There was a smoking gun before,” said study co-author Greg Engel of the University of Chicago. “Here we can watch the relationship between coherence and energy transfer. This is the first paper showing that coherence affects the probability of transport. It really does change the chemical dynamics.”
posted by aleph
on Dec 7, 2011 -
Is our present defined by decisions we make in the future?
And maybe we don't know who killed JFK because the universe hasn't decided yet. A Huffington Post science blogger discusses the nature of history from a quantum perspective. To quote Stephen Hawking, "The histories of the universe depend on what is being measured, contrary to the usual idea that the universe has an objective observer-independent history." [more inside]
posted by GnomeChompsky
on Aug 20, 2010 -
is an Internet resource that brings genuine
random numbers, generated
by a process fundamentally governed by the inherent uncertainty in the quantum mechanical laws of nature, directly to your computer in a variety of forms. HotBits
are generated by timing successive pairs of radioactive decays detected
by a Geiger-Müller tube interfaced to a computer. (Warning: random sounds.)
posted by parudox
on Feb 9, 2009 -
Physicists have 'solved' mystery of levitation
Professor Ulf Leonhardt and Dr Thomas Philbin, from the University of St Andrews in Scotland, have worked out a way of reversing ... the Casimir force
, so that it repels instead of attracts. Their discovery could ultimately lead to frictionless micro-machines with moving parts that levitate. But they say that, in principle at least, the same effect could be used to levitate bigger objects too, even a person.
posted by MythMaker
on Aug 19, 2007 -
Happy Anniversary, Quantum Mechanics!
"On December 14, 1900, Max Planck
presented experimental data at the German Physical Society and said that it could best be explained if energy existed in discrete packets, which he called "quanta
." It was on that day that the field of Quantum Physics was effectively born. I call it QM Day and it's the unofficial start of the Agnostica
posted by mystyk
on Dec 14, 2006 -
The physicist Shariah Afshar has used a beautifully simple experiment
, which no-one seems to have thought of before, to disprove Bohr's principle of complementarity
, something which has been pretty much unchallenged for 80 years. He may also have gone some way towards showing that there is no such thing as a photon, and that Einstein's Nobel prize should be revoked. So, big stuff. What do you physicists think?
posted by Pretty_Generic
on Jul 29, 2004 -