Difference between revisions of "Less Wrong/2008 Articles/Summaries"

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(The American System and Misleading Labels: Added MinibearRex's summary.)
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is not the same as the power to choose which candidates will
 
is not the same as the power to choose which candidates will
 
run) is not the greatest power of the voters. Instead,
 
run) is not the greatest power of the voters. Instead,
voters' main abilities are the threat to change which party
+
voters' main ability is the threat to change which party
controls the government, or extremely rarely, to completely
+
controls the government, or, extremely rarely, to completely
 
dethrone both political parties and replace them with a
 
dethrone both political parties and replace them with a
 
third.
 
third.

Revision as of 00:39, 12 December 2011

Posting on Politics
The Two-Party Swindle

Voters for either political party usually have more in common with each other than they do with the politicians they vote for. And yet, they support their own "team members" with fanatic devotion. Nobody is allowed to criticize their own team's politicians, without their fellow voters accusing them of treason.

The American System and Misleading Labels

The conclusions we draw from analyzing the American political system are often biased by our own previous understanding of it, which we got in elementary school. In fact, the power of voting for a particular candidate (which is not the same as the power to choose which candidates will run) is not the greatest power of the voters. Instead, voters' main ability is the threat to change which party controls the government, or, extremely rarely, to completely dethrone both political parties and replace them with a third.

Stop Voting For Nincompoops
Rational vs. Scientific Ev-Psych
A Failed Just-So Story
But There's Still A Chance, Right?
The Fallacy of Gray
Absolute Authority
Infinite Certainty
0 And 1 Are Not Probabilities
Beautiful Math
Expecting Beauty
Is Reality Ugly?
Beautiful Probability
Trust in Math
Rationality Quotes 1
Rationality Quotes 2
Rationality Quotes 3
The Allais Paradox

(and subsequent followups) - Offered choices between gambles, people make decision-theoretically inconsistent decisions.

Zut Allais!

Offered choices between gambles, people make decision-theoretically inconsistent decisions.

Rationality Quotes 4
Allais Malaise

Offered choices between gambles, people make decision-theoretically inconsistent decisions.

Against Discount Rates
Circular Altruism
Rationality Quotes 5
Rationality Quotes 6
Rationality Quotes 7
Rationality Quotes 8
Rationality Quotes 9
The "Intuitions" Behind "Utilitarianism"
Trust in Bayes
Something to Protect
Newcomb's Problem and Regret of Rationality
OB Meetup: Millbrae, Thu 21 Feb, 7pm
The Parable of the Dagger

A word fails to connect to reality in the first place. Is Socrates a framster? Yes or no?

The Parable of Hemlock

Socrates is a human, and humans, by definition, are mortal. So if you defined humans to not be mortal, would Socrates live forever?

(alternate summary:)

Your argument, if it worked, could coerce reality to go a different way by choosing a different word definition. Socrates is a human, and humans, by definition, are mortal. So if you defined humans to not be mortal, would Socrates live forever?

You try to establish any sort of empirical proposition as being true "by definition". Socrates is a human, and humans, by definition, are mortal. So is it a logical truth if we empirically predict that Socrates should keel over if he drinks hemlock? It seems like there are logically possible, non-self-contradictory worlds where Socrates doesn't keel over - where he's immune to hemlock by a quirk of biochemistry, say. Logical truths are true in all possible worlds, and so never tell you which possible world you live in - and anything you can establish "by definition" is a logical truth.

You unconsciously slap the conventional label on something, without actually using the verbal definition you just gave. You know perfectly well that Bob is "human", even though, on your definition, you can never call Bob "human" without first observing him to be mortal.

Words as Hidden Inferences

The mere presence of words can influence thinking, sometimes misleading it.

(alternate summary:)

The mere presence of words can influence thinking, sometimes misleading it.

The act of labeling something with a word, disguises a challengable inductive inference you are making. If the last 11 egg-shaped objects drawn have been blue, and the last 8 cubes drawn have been red, it is a matter of induction to say this rule will hold in the future. But if you call the blue eggs "bleggs" and the red cubes "rubes", you may reach into the barrel, feel an egg shape, and think "Oh, a blegg."

Extensions and Intensions

You try to define a word using words, in turn defined with ever-more-abstract words, without being able to point to an example.

(alternate summary:)

You try to define a word using words, in turn defined with ever-more-abstract words, without being able to point to an example. "What is red?" "Red is a color." "What's a color?" "It's a property of a thing?" "What's a thing? What's a property?" It never occurs to you to point to a stop sign and an apple.

The extension doesn't match the intension. We aren't consciously aware of our identification of a red light in the sky as "Mars", which will probably happen regardless of your attempt to define "Mars" as "The God of War".

Buy Now Or Forever Hold Your Peace
Similarity Clusters

Your verbal definition doesn't capture more than a tiny fraction of the category's shared characteristics, but you try to reason as if it does.

(alternate summary:)

Your verbal definition doesn't capture more than a tiny fraction of the category's shared characteristics, but you try to reason as if it does. When the philosophers of Plato's Academy claimed that the best definition of a human was a "featherless biped", Diogenes the Cynic is said to have exhibited a plucked chicken and declared "Here is Plato's Man." The Platonists promptly changed their definition to "a featherless biped with broad nails".

Typicality and Asymmetrical Similarity

You try to treat category membership as all-or-nothing, ignoring the existence of more and less typical subclusters.

(alternate summary:)

You try to treat category membership as all-or-nothing, ignoring the existence of more and less typical subclusters. Ducks and penguins are less typical birds than robins and pigeons. Interestingly, a between-groups experiment showed that subjects thought a disease was more likely to spread from robins to ducks on an island, than from ducks to robins.

The Cluster Structure of Thingspace

A verbal definition works well enough in practice to point out the intended cluster of similar things, but you nitpick exceptions.

(alternate summary:)

A verbal definition works well enough in practice to point out the intended cluster of similar things, but you nitpick exceptions. Not every human has ten fingers, or wears clothes, or uses language; but if you look for an empirical cluster of things which share these characteristics, you'll get enough information that the occasional nine-fingered human won't fool you.

Disguised Queries

You ask whether something "is" or "is not" a category member but can't name the question you really want answered.

(alternate summary:)

You ask whether something "is" or "is not" a category member but can't name the question you really want answered. What is a "man"? Is Barney the Baby Boy a "man"? The "correct" answer may depend considerably on whether the query you really want answered is "Would hemlock be a good thing to feed Barney?" or "Will Barney make a good husband?"

Neural Categories

You treat intuitively perceived hierarchical categories like the only correct way to parse the world, without realizing that other forms of statistical inference are possible even though your brain doesn't use them.

(alternate summary:)

You treat intuitively perceived hierarchical categories like the only correct way to parse the world, without realizing that other forms of statistical inference are possible even though your brain doesn't use them. It's much easier for a human to notice whether an object is a "blegg" or "rube"; than for a human to notice that red objects never glow in the dark, but red furred objects have all the other characteristics of bleggs. Other statistical algorithms work differently.

How An Algorithm Feels From Inside

You talk about categories as if they are manna fallen from the Platonic Realm, rather than inferences implemented in a real brain.

(alternate summary:)

You talk about categories as if they are manna fallen from the Platonic Realm, rather than inferences implemented in a real brain. The ancient philosophers said "Socrates is a man", not, "My brain perceptually classifies Socrates as a match against the 'human' concept".

You argue about a category membership even after screening off all questions that could possibly depend on a category-based inference. After you observe that an object is blue, egg-shaped, furred, flexible, opaque, luminescent, and palladium-containing, what's left to ask by arguing, "Is it a blegg?" But if your brain's categorizing neural network contains a (metaphorical) central unit corresponding to the inference of blegg-ness, it may still feel like there's a leftover question.

(see also the wiki page)

Disputing Definitions

An example of how the technique helps.

(alternate summary:)

You allow an argument to slide into being about definitions, even though it isn't what you originally wanted to argue about.

(alternate summary:)

You allow an argument to slide into being about definitions, even though it isn't what you originally wanted to argue about. If, before a dispute started about whether a tree falling in a deserted forest makes a "sound", you asked the two soon-to-be arguers whether they thought a "sound" should be defined as "acoustic vibrations" or "auditory experiences", they'd probably tell you to flip a coin. Only after the argument starts does the definition of a word becom

(alternate summary:)

You allow an argument to slide into being about definitions, even though it isn't what you originally wanted to argue about.

(alternate summary:)

You allow an argument to slide into being about definitions, even though it isn't what you originally wanted to argue about. If, before a dispute started about whether a tree falling in a deserted forest makes a "sound", you asked the two soon-to-be arguers whether they thought a "sound" should be defined as "acoustic vibrations" or "auditory experiences", they'd probably tell you to flip a coin. Only after the argument starts does the definition of a word become politically charged.

Feel the Meaning

You think a word has a meaning, as a property of the word itself; rather than there being a label that your brain associates to a particular concept.

(alternate summary:)

You think a word has a meaning, as a property of the word itself; rather than there being a label that your brain associates to a particular concept. When someone shouts, "Yikes! A tiger!", evolution would not favor an organism that thinks, "Hm... I have just heard the syllables 'Tie' and 'Grr' which my fellow tribemembers associate with their internal analogues of my own tiger concept and which aiiieeee CRUNCH CRUNCH GULP." So the brain takes a shortcut, and it seems that the meaning of tigerness is a property of the label itself. People argue about the correct meaning of a label like "sound".

The Argument from Common Usage

You argue over the meanings of a word, even after all sides understand perfectly well what the other sides are trying to say.

(alternate summary:)

You argue over the meanings of a word, even after all sides understand perfectly well what the other sides are trying to say. The human ability to associate labels to concepts is a tool for communication. When people want to communicate, we're hard to stop; if we have no common language, we'll draw pictures in sand. When you each understand what is in the other's mind, you are done.

You pull out a dictionary in the middle of an empirical or moral argument. Dictionary editors are historians of usage, not legislators of language. If the common definition contains a problem - if "Mars" is defined as the God of War, or a "dolphin" is defined as a kind of fish, or "Negroes" are defined as a separate category from humans, the dictionary will reflect the standard mistake.

You pull out a dictionary in the middle of any argument ever. Seriously, what the heck makes you think that dictionary editors are an authority on whether "atheism" is a "religion" or whatever? If you have any substantive issue whatsoever at stake, do you really think dictionary editors have access to ultimate wisdom that settles the argument?

You defy common usage without a reason, making it gratuitously hard for others to understand you. Fast stand up plutonium, with bagels without handle.

Empty Labels

You use complex renamings to create the illusion of inference.

(alternate summary:)

You use complex renamings to create the illusion of inference. Is a "human" defined as a "mortal featherless biped"? Then write: "All [mortal featherless bipeds] are mortal; Socrates is a [mortal featherless biped]; therefore, Socrates is mortal." Looks less impressive that way, doesn't it?

Classic Sichuan in Millbrae, Thu Feb 21, 7pm
Taboo Your Words

When a word poses a problem, the simplest solution is to eliminate the word and its synonyms.

(alternate summary:)

If Albert and Barry aren't allowed to use the word "sound", then Albert will have to say "A tree falling in a deserted forest generates acoustic vibrations", and Barry will say "A tree falling in a deserted forest generates no auditory experiences". When a word poses a problem, the simplest solution is to eliminate the word and its synonyms.

Replace the Symbol with the Substance

Description of the technique.

(alternate summary:)

The existence of a neat little word prevents you from seeing the details of the thing you're trying to think about.

(alternate summary:)

The existence of a neat little word prevents you from seeing the details of the thing you're trying to think about. What actually goes on in schools once you stop calling it "education"? What's a degree, once you stop calling it a "degree"? If a coin lands "heads", what's its radial orientation? What is "truth", if you can't say "accurate" or "correct" or "represent" or "reflect" or "semantic" or "believe" or "knowledge" or "map" or "real" or

(alternate summary:)

The existence of a neat little word prevents you from seeing the details of the thing you're trying to think about.

(alternate summary:)

The existence of a neat little word prevents you from seeing the details of the thing you're trying to think about. What actually goes on in schools once you stop calling it "education"? What's a degree, once you stop calling it a "degree"? If a coin lands "heads", what's its radial orientation? What is "truth", if you can't say "accurate" or "correct" or "represent" or "reflect" or "semantic" or "believe" or "knowledge" or "map" or "real" or any other simple term?

Fallacies of Compression

You have only one word, but there are two or more different things-in-reality, so that all the facts about them get dumped into a single undifferentiated mental bucket.

(alternate summary:)

You have only one word, but there are two or more different things-in-reality, so that all the facts about them get dumped into a single undifferentiated mental bucket. It's part of a detective's ordinary work to observe that Carol wore red last night, or that she has black hair; and it's part of a detective's ordinary work to wonder if maybe Carol dyes her hair. But it takes a subtler detective to wonder if there are two Carols, so that the Carol who wore red is not the same as the Carol who had black hair.

Categorizing Has Consequences

You see patterns where none exist, harvesting other characteristics from your definitions even when there is no similarity along that dimension.

(alternate summary:)

You see patterns where none exist, harvesting other characteristics from your definitions even when there is no similarity along that dimension. In Japan, it is thought that people of blood type A are earnest and creative, blood type Bs are wild and cheerful, blood type Os are agreeable and sociable, and blood type ABs are cool and controlled.

Sneaking in Connotations

You try to sneak in the connotations of a word, by arguing from a definition that doesn't include the connotations.

(alternate summary:)

You try to sneak in the connotations of a word, by arguing from a definition that doesn't include the connotations. A "wiggin" is defined in the dictionary as a person with green eyes and black hair. The word "wiggin" also carries the connotation of someone who commits crimes and launches cute baby squirrels, but that part isn't in the dictionary. So you point to someone and say: "Green eyes? Black hair? See, told you he's a wiggin! Watch, next he's going to steal the silverware."

Arguing "By Definition"

You claim "X, by definition, is a Y!" On such occasions you're almost certainly trying to sneak in a connotation of Y that wasn't in your given definition.

(alternate summary:)

You claim "X, by definition, is a Y!" On such occasions you're almost certainly trying to sneak in a connotation of Y that wasn't in your given definition. You define "human" as a "featherless biped", and point to Socrates and say, "No feathers - two legs - he must be human!" But what you really care about is something else, like mortality. If what was in dispute was Socrates's number of legs, the other fellow would just reply, "Whaddaya mean, Socrates's got two legs? That's what we're arguing about in the first place!"

You claim "Ps, by definition, are Qs!" If you see Socrates out in the field with some biologists, gathering herbs that might confer resistance to hemlock, there's no point in arguing "Men, by definition, are mortal!" The main time you feel the need to tighten the vise by insisting that something is true "by definition" is when there's other information that calls the default inference into doubt.

You try to establish membership in an empirical cluster "by definition". You wouldn't feel the need to say, "Hinduism, by definition, is a religion!" because, well, of course Hinduism is a religion. It's not just a religion "by definition", it's, like, an actual religion. Atheism does not resemble the central members of the "religion" cluster, so if it wasn't for the fact that atheism is a religion by definition, you might go around thinking that atheism wasn't a religion. That's why you've got to crush all opposition by pointing out that "Atheism is a religion" is true by definition, because it isn't true any other way.

Where to Draw the Boundary?

Your definition draws a boundary around things that don't really belong together.

(alternate summary:)

Your definition draws a boundary around things that don't really belong together. You can claim, if you like, that you are defining the word "fish" to refer to salmon, guppies, sharks, dolphins, and trout, but not jellyfish or algae. You can claim, if you like, that this is merely a list, and there is no way a list can be "wrong". Or you can stop playing nitwit games and admit that you made a mistake and that dolphins don't belong on the fish list.

Entropy, and Short Codes

Which sounds more plausible, "God did a miracle" or "A supernatural universe-creating entity temporarily suspended the laws of physics"?

(alternate summary:)

You use a short word for something that you won't need to describe often, or a long word for something you'll need to describe often. This can result in inefficient thinking, or even misapplications of Occam's Razor, if your mind thinks that short sentences sound "simpler". Which sounds more plausible, "God did a miracle" or "A supernatural universe-creating entity temporarily suspended the laws of physics"?

Mutual Information, and Density in Thingspace

You draw your boundary around a volume of space where there is no greater-than-usual density, meaning that the associated word does not correspond to any performable Bayesian inferences.

(alternate summary:)

You draw your boundary around a volume of space where there is no greater-than-usual density, meaning that the associated word does not correspond to any performable Bayesian inferences. Since green-eyed people are not more likely to have black hair, or vice versa, and they don't share any other characteristics in common, why have a word for "wiggin"?

Superexponential Conceptspace, and Simple Words

You draw an unsimple boundary without any reason to do so.

(alternate summary:)

You draw an unsimple boundary without any reason to do so. The act of defining a word to refer to all humans, except black people, seems kind of suspicious. If you don't present reasons to draw that particular boundary, trying to create an "arbitrary" word in that location is like a detective saying: "Well, I haven't the slightest shred of support one way or the other for who could've murdered those orphans... but have we considered John Q. Wiffleheim as a suspect?"

Leave a Line of Retreat
The Second Law of Thermodynamics, and Engines of Cognition
Perpetual Motion Beliefs
Searching for Bayes-Structure
Conditional Independence, and Naive Bayes

You use categorization to make inferences about properties that don't have the appropriate empirical structure, namely, conditional independence given knowledge of the class, to be well-approximated by Naive Bayes.

(alternate summary:)

You use categorization to make inferences about properties that don't have the appropriate empirical structure, namely, conditional independence given knowledge of the class, to be well-approximated by Naive Bayes. No way am I trying to summarize this one. Just read the blog post.

Words as Mental Paintbrush Handles

Visualize a "triangular lightbulb". What did you see?

(alternate summary:)

You think that words are like tiny little LISP symbols in your mind, rather than words being labels that act as handles to direct complex mental paintbrushes that can paint detailed pictures in your sensory workspace. Visualize a "triangular lightbulb". What did you see?

Rationality Quotes 10
Rationality Quotes 11
Variable Question Fallacies

"Martin told Bob the building was on his left." But "left" is a function-word that evaluates with a speaker-dependent variable grabbed from the surrounding context. Whose "left" is meant, Bob's or Martin's?

(alternate summary:)

You use a word that has different meanings in different places as though it meant the same thing on each occasion, possibly creating the illusion of something protean and shifting. "Martin told Bob the building was on his left." But "left" is a function-word that evaluates with a speaker-dependent variable grabbed from the surrounding context. Whose "left" is meant, Bob's or Martin's?

37 Ways That Words Can Be Wrong

Contains summaries of the sequence of posts about the proper use of words.

Gary Gygax Annihilated at 69
Dissolving the Question

This is where the "free will" puzzle is explicitly posed, along with criteria for what does and does not constitute a satisfying answer.

(alternate summary:)

this is where the "free will" puzzle is explicitly posed, along with criteria for what does and does not constitute a satisfying answer.

Wrong Questions
Righting a Wrong Question
Mind Projection Fallacy
Probability is in the Mind
The Quotation is not the Referent
Penguicon & Blook
Qualitatively Confused

Using qualitative, binary reasoning may make it easier to confuse belief and reality; if we use probability distributions, the distinction is much clearer.

Reductionism

We build models of the universe that have many different levels of description. But so far as anyone has been able to determine, the universe itself has only the single level of fundamental physics - reality doesn't explicitly compute protons, only quarks.

Explaining vs. Explaining Away

elementary reductionism.

Fake Reductionism

It takes a detailed step-by-step walkthrough.

Savanna Poets
Joy in the Merely Real

If you can't take joy in things that turn out to be explicable, you're going to set yourself up for eternal disappointment. Don't worry if quantum physics turns out to be normal.

Joy in Discovery
Bind Yourself to Reality
If You Demand Magic, Magic Won't Help
New York OB Meetup (ad-hoc) on Monday, Mar 24, @6pm
The Beauty of Settled Science
Amazing Breakthrough Day: April 1st
Is Humanism A Religion-Substitute?
Scarcity
To Spread Science, Keep It Secret
Initiation Ceremony

Brennan is inducted into the Conspiracy

Hand vs. Fingers
Angry Atoms
Heat vs. Motion
Brain Breakthrough! It's Made of Neurons!
Reductive Reference
Zombies! Zombies?

Don't try to put your consciousness or your personal identity outside physics. Whatever makes you say "I think therefore I am", causes your lips to move; it is within the chains of cause and effect that produce our observed universe.

Zombie Responses
The Generalized Anti-Zombie Principle
GAZP vs. GLUT
Belief in the Implied Invisible

That it's impossible even in principle to observe something sometimes isn't enough to conclude that it doesn't exist.

(alternate summary:)

If a spaceship goes over the cosmological horizon relative to us, so that it can no longer communicate with us, should we believe that the spaceship instantly ceases to exist?

Quantum Explanations

Quantum mechanics doesn't deserve its fearsome reputation.

(alternate summary:)

Quantum mechanics doesn't deserve its fearsome reputation. If you tell people something is supposed to be mysterious, they won't understand it. It's human intuitions that are "strange" or "weird"; physics itself is perfectly normal. Talking about historical erroneous concepts like "particles" or "waves" is just asking to confuse people; present the real, unified quantum physics straight out. The series will take a strictly realist perspective - quantum equations describe something that is real and out there. Warning: Although a large faction of physicists agrees with this, it is not universally accepted. Stronger warning: I am not even going to present non-realist viewpoints until later, because I think this is a major source of confusion.

Configurations and Amplitude

A preliminary glimpse at the stuff reality is made of. The classic split-photon experiment with half-silvered mirrors. Alternative pathways the photon can take, can cancel each other out. The mysterious measuring tool that tells us the relative squared moduli.

Joint Configurations

The laws of physics are inherently over mathematical entities, configurations, that involve multiple particles. A basic, ontologically existent entity, according to our current understanding of quantum mechanics, does not look like a photon - it looks like a configuration of the universe with "A photon here, a photon there." Amplitude flows between these configurations can cancel or add; this gives us a way to detect which configurations are distinct. It is an experimentally testable fact that "Photon 1 here, photon 2 there" is the same configuration as "Photon 2 here, photon 1 there".

Distinct Configurations

Since configurations are over the combined state of all the elements in a system, adding a sensor that detects whether a particle went one way or the other, becomes a new element of the system that can make configurations "distinct" instead of "identical". This confused the living daylights out of early quantum experimenters, because it meant that things behaved differently when they tried to "measure" them. But it's not only measuring instruments that do the trick - any sensitive physical element will do - and the distinctness of configurations is a physical fact, not a fact about our knowledge. There is no need to suppose that the universe cares what we think.

Where Philosophy Meets Science

In retrospect, supposing that quantum physics had anything to do with consciousness was a big mistake. Could philosophers have told the physicists so? But we don't usually see philosophers sponsoring major advances in physics; why not?

Can You Prove Two Particles Are Identical?

You wouldn't think that it would be possible to do an experiment that told you that two particles are completely identical - not just to the limit of experimental precision, but perfectly. You could even give a precise-sounding philosophical argument for why it was not possible - but the argument would have a deeply buried assumption. Quantum physics violates this deep assumption, making the experiment easy.

Classical Configuration Spaces

How to visualize the state of a system of two 1-dimensional particles, as a single point in 2-dimensional space. A preliminary step before moving into...

The Quantum Arena

Instead of a system state being associated with a single point in a classical configuration space, the instantaneous real state of a quantum system is a complex amplitude distribution over a quantum configuration space. What creates the illusion of "individual particles", like an electron caught in a trap, is a plaid distribution - one that happens to factor into the product of two parts. It is the whole distribution that evolves when a quantum system evolves. Individual configurations don't have physics; amplitude distributions have physics. Quantum entanglement is the general case; quantum independence is the special case.

Feynman Paths

Instead of thinking that a photon takes a single straight path through space, we can regard it as taking all possible paths through space, and adding the amplitudes for every possible path. Nearly all the paths cancel out - unless we do clever quantum things, so that some paths add instead of canceling out. Then we can make light do funny tricks for us, like reflecting off a mirror in such a way that the angle of incidence doesn't equal the angle of reflection. But ordinarily, nearly all the paths except an extremely narrow band, cancel out - this is one of the keys to recovering the hallucination of classical physics.

No Individual Particles

One of the chief ways to confuse yourself while thinking about quantum mechanics, is to think as if photons were little billiard balls bouncing around. The appearance of little billiard balls is a special case of a deeper level on which there are only multiparticle configurations and amplitude flows. It is easy to set up physical situations in which there exists no fact of the matter as to which electron was originally which.

Identity Isn't In Specific Atoms
Zombies: The Movie
Three Dialogues on Identity

Given that there's no such thing as "the same atom", whether you are "the same person" from one time to another can't possibly depend on whether you're made out of the same atoms.

Decoherence

A quantum system that factorizes can evolve into a system that doesn't factorize, destroying the illusion of independence. But entangling a quantum system with its environment, can appear to destroy entanglements that are already present. Entanglement with the environment can separate out the pieces of an amplitude distribution, preventing them from interacting with each other. Decoherence is fundamentally symmetric in time, but appears asymmetric because of the second law of thermodynamics.

The So-Called Heisenberg Uncertainty Principle

Unlike classical physics, in quantum physics it is not possible to separate out a particle's "position" from its "momentum".

(alternate summary:)

Unlike classical physics, in quantum physics it is not possible to separate out a particle's "position" from its "momentum". The evolution of the amplitude distribution over time, involves things like taking the second derivative in space and multiplying by i to get the first derivative in time. The end result of this time evolution rule is that blobs of particle-presence appear to race around in physical space. The notion of "an exact particular momentum" or "an exact particular position" is not something that can physically happen, it is a tool for analyzing amplitude distributions by taking them apart into a sum of simpler waves. This uses the assumption and fact of linearity: the evolution of the whole wavefunction seems to always be the additive sum of the evolution of its pieces. Using this tool, we can see that if you take apart the same distribution into a sum of positions and a sum of momenta, they cannot both be sharply concentrated at the same time. When you "observe" a particle's position, that is, decohere its positional distribution by making it interact with a sensor, you take its wave packet apart into two pieces; then the two pieces evolve differently. The Heisenberg Principle definitely does not say that knowing about the particle, or consciously seeing it, will make the universe behave differently.

Which Basis Is More Fundamental?

The position basis can be computed locally in the configuration space; the momentum basis is not local. Why care about locality? Because it is a very deep principle; reality itself seems to favor it in some way.

Where Physics Meets Experience

Meet the Ebborians, who reproduce by fission. The Ebborian brain is like a thick sheet of paper that splits down its thickness. They frequently experience dividing into two minds, and can talk to their other selves. It seems that their unified theory of physics is almost finished, and can answer every question, when one Ebborian asks: When exactly does one Ebborian become two people?

Where Experience Confuses Physicists

It then turns out that the entire planet of Ebbore is splitting along a fourth-dimensional thickness, duplicating all the people within it. But why does the apparent chance of "ending up" in one of those worlds, equal the square of the fourth-dimensional thickness? Many mysterious answers are proposed to this question, and one non-mysterious one.

On Being Decoherent

When a sensor measures a particle whose amplitude distribution stretches over space - perhaps seeing if the particle is to the left or right of some dividing line - then the standard laws of quantum mechanics call for the sensor+particle system to evolve into a state of (particle left, sensor measures LEFT) + (particle right, sensor measures RIGHT). But when we humans look at the sensor, it only seems to say "LEFT" or "RIGHT", never a mixture like "LIGFT". This, of course, is because we ourselves are made of particles, and subject to the standard quantum laws that imply decoherence. Under standard quantum laws, the final state is (particle left, sensor measures LEFT, human sees "LEFT") + (particle right, sensor measures RIGHT, human sees "RIGHT").

The Conscious Sorites Paradox

Decoherence is implicit in quantum physics, not an extra law on top of it. Asking exactly when "one world" splits into "two worlds" may be like asking when, if you keep removing grains of sand from a pile, it stops being a "heap". Even if you're inside the world, there may not be a definite answer. This puzzle does not arise only in quantum physics; the Ebborians could face it in a classical universe, or we could build sentient flat computers that split down their thickness. Is this really a physicist's problem?

Decoherence is Pointless

There is no exact point at which decoherence suddenly happens. All of quantum mechanics is continuous and differentiable, and decoherent processes are no exception to this.

Decoherent Essences

Decoherence is implicit within physics, not an extra law on top of it. You can choose representations that make decoherence harder to see, just like you can choose representations that make apples harder to see, but exactly the same physical process still goes on; the apple doesn't disappear and neither does decoherence. If you could make decoherence magically go away by choosing the right representation, we wouldn't need to shield quantum computers from the environment.

The Born Probabilities

The last serious mysterious question left in quantum physics: When a quantum world splits in two, why do we seem to have a greater probability of ending up in the larger blob, exactly proportional to the integral of the squared modulus? It's an open problem, but non-mysterious answers have been proposed. Try not to go funny in the head about it.

Decoherence as Projection

Since quantum evolution is linear and unitary, decoherence can be seen as projecting a wavefunction onto orthogonal subspaces. This can be neatly illustrated using polarized photons and the angle of the polarized sheet that will absorb or transmit them.

Entangled Photons

Using our newly acquired understanding of photon polarizations, we see how to construct a quantum state of two photons in which, when you measure one of them, the person in the same world as you, will always find that the opposite photon has opposite quantum state. This is not because any influence is transmitted; it is just decoherence that takes place in a very symmetrical way, as can readily be observed in our calculations.

Bell's Theorem: No EPR "Reality"

(Note: This post was designed to be read as a stand-alone, if desired.) Originally, the discoverers of quantum physics thought they had discovered an incomplete description of reality - that there was some deeper physical process they were missing, and this was why they couldn't predict exactly the results of quantum experiments. The math of Bell's Theorem is surprisingly simple, and we walk through it. Bell's Theorem rules out being able to locally predict a single, unique outcome of measurements - ruling out a way that Einstein, Podolsky, and Rosen once defined "reality". This shows how deep implicit philosophical assumptions can go. If worlds can split, so that there is no single unique outcome, then Bell's Theorem is no problem. Bell's Theorem does, however, rule out the idea that quantum physics describes our partial knowledge of a deeper physical state that could locally produce single outcomes - any such description will be inconsistent.

Spooky Action at a Distance: The No-Communication Theorem

As Einstein argued long ago, the quantum physics of his era - that is, the single-global-world interpretation of quantum physics, in which experiments have single unique random results - violates Special Relativity; it imposes a preferred space of simultaneity and requires a mysterious influence to be transmitted faster than light; which mysterious influence can never be used to transmit any useful information. Getting rid of the single global world dispels this mystery and puts everything back to normal again.

Decoherence is Simple
Decoherence is Falsifiable and Testable

(Note: Designed to be standalone readable.) An epistle to the physicists. To probability theorists, words like "simple", "falsifiable", and "testable" have exact mathematical meanings, which are there for very strong reasons. The (minority?) faction of physicists who say that many-worlds is "not falsifiable" or that it "violates Occam's Razor" or that it is "untestable", are committing the same kind of mathematical crime as non-physicists who invent their own theories of gravity that go as inverse-cube. This is one of the reasons why I, a non-physicist, dared to talk about physics - because I saw (some!) physicists using probability theory in a way that was simply wrong. Not just criticizable, but outright mathematically wrong: 2 + 2 = 3.

Quantum Non-Realism

"Shut up and calculate" is the best approach you can take when none of your theories are very good. But that is not the same as claiming that "Shut up!" actually is a theory of physics. Saying "I don't know what these equations mean, but they seem to work" is a very different matter from saying: "These equations definitely don't mean anything, they just work!"

Collapse Postulates

Early physicists simply didn't think of the possibility of more than one world - it just didn't occur to them, even though it's the straightforward result of applying the quantum laws at all levels. So they accidentally invented a completely and strictly unnecessary part of quantum theory to ensure there was only one world - a law of physics that says that parts of the wavefunction mysteriously and spontaneously disappear when decoherence prevents us from seeing them any more. If such a law really existed, it would be the only non-linear, non-unitary, non-differentiable, non-local, non-CPT-symmetric, acausal, faster-than-light phenomenon in all of physics.

If Many-Worlds Had Come First

If early physicists had never made the mistake, and thought immediately to apply the quantum laws at all levels to produce macroscopic decoherence, then "collapse postulates" would today seem like a completely crackpot theory. In addition to their other problems, like FTL, the collapse postulate would be the only physical law that was informally specified - often in dualistic (mentalistic) terms - because it was the only fundamental law adopted without precise evidence to nail it down. Here, we get a glimpse at that alternate Earth.

Many Worlds, One Best Guess

Summarizes the arguments that nail down macroscopic decoherence, aka the "many-worlds interpretation". Concludes that many-worlds wins outright given the current state of evidence. The argument should have been over fifty years ago. New physical evidence could reopen it, but we have no particular reason to expect this.

The Failures of Eld Science

Fictional portrayal of a potential rationality dojo.

A short story set in the same world as <a href="/lw/p1/initiation_ceremony/">Initiation Ceremony</a>. Future physics students look back on the cautionary tale of quantum physics.

(alternate summary:)

Jeffreyssai explains that rationalists should be fast.

(alternate summary:)

(prerequisite: Quantum Physics)

(alternate summary:)

Fictional portrayal of a potential rationality dojo.

The Dilemma: Science or Bayes?

The failure of first-half-of-20th-century-physics was not due to straying from the scientific method. Science and rationality - that is, Science and Bayesianism - aren't the same thing, and sometimes they give different answers.

Science Doesn't Trust Your Rationality

The reason Science doesn't always agree with the exact, Bayesian, rational answer, is that Science doesn't trust you to be rational. It wants you to go out and gather overwhelming experimental evidence.

When Science Can't Help

If you have an idea, Science tells you to test it experimentally. If you spend 10 years testing the idea and the result comes out negative, Science slaps you on the back and says, "Better luck next time." If you want to spend 10 years testing a hypothesis that will actually turn out to be right, you'll have to try to do the thing that Science doesn't trust you to do: think rationally, and figure out the answer before you get clubbed over the head with it.

Science Isn't Strict Enough

Science lets you believe any damn stupid idea that hasn't been refuted by experiment. Bayesianism says there is always an exactly rational degree of belief given your current evidence, and this does not shift a nanometer to the left or to the right depending on your whims. Science is a social freedom - we let people test whatever hypotheses they like, because we don't trust the village elders to decide in advance - but you shouldn't confuse that with an individual standard of rationality.

Do Scientists Already Know This Stuff?

No. Maybe someday it will be part of standard scientific training, but for now, it's not, and the absence is visible.

No Safe Defense, Not Even Science

Why am I trying to break your trust in Science? Because you can't think and trust at the same time. The social rules of Science are verbal rather than quantitative; it is possible to believe you are following them. With Bayesianism, it is never possible to do an exact calculation and get the exact rational answer that you know exists. You are visibly less than perfect, and so you will not be tempted to trust yourself.

Changing the Definition of Science

Many of these ideas are surprisingly conventional, and being floated around by other thinkers. I'm a good deal less of a lonely iconoclast than I seem; maybe it's just the way I talk.

Conference on Global Catastrophic Risks
Faster Than Science

Is it really possible to arrive at the truth faster than Science does? Not only is it possible, but the social process of science relies on scientists doing so - when they choose which hypotheses to test. In many answer spaces it's not possible to find the true hypothesis by accident. Science leaves it up to experiment to socially declare who was right, but if there weren't some people who could get it right in the absence of overwhelming experimental proof, science would be stuck.

Einstein's Speed

Albert was unusually good at finding the right theory in the presence of only a small amount of experimental evidence. Even more unusually, he admitted it - he claimed to know the theory was right, even in advance of the public proof. It's possible to arrive at the truth by thinking great high-minded thoughts of the sort that Science does not trust you to think, but it's a lot harder than arriving at the truth in the presence of overwhelming evidence.

That Alien Message

Einstein used evidence more efficiently than other physicists, but he was still extremely inefficient in an absolute sense. If a huge team of cryptographers and physicists were examining a interstellar transmission, going over it bit by bit, we could deduce principles on the order of Galilean gravity just from seeing one or two frames of a picture. As if the very first human to see an apple fall, had, on the instant, realized that its position went as the square of the time and that this implied constant acceleration.

My Childhood Role Model

I looked up to the ideal of a Bayesian superintelligence, not Einstein.

Mach's Principle: Anti-Epiphenomenal Physics

Could you tell if the whole universe were shifted an inch to the left? Could you tell if the whole universe was traveling left at ten miles per hour? Could you tell if the whole universe was accelerating left at ten miles per hour? Could you tell if the whole universe was rotating?

A Broken Koan
Relative Configuration Space

Maybe the reason why we can't observe absolute speeds, absolute positions, absolute accelerations, or absolute rotations, is that particles don't have absolute positions - only positions relative to each other. That is, maybe quantum physics takes place in a relative configuration space.

Timeless Physics

What time is it? How do you know? The question "What time is it right now?" may make around as much sense as asking "Where is the universe?" Not only that, our physics equations may not need a t in them!

Timeless Beauty

To get rid of time you must reduce it to nontime. In timeless physics, everything that exists is perfectly global or perfectly local. The laws of physics are perfectly global; the configuration space is perfectly local. Every fundamentally existent ontological entity has a unique identity and a unique value. This beauty makes ugly theories much more visibly ugly; a collapse postulate becomes a visible scar on the perfection.

Timeless Causality

Using the modern, Bayesian formulation of causality, we can define causality without talking about time - define it purely in terms of relations. The river of time never flows, but it has a direction.

Einstein's Superpowers

There's an unfortunate tendency to talk as if Einstein had superpowers - as if, even before Einstein was famous, he had an inherent disposition to be Einstein - a potential as rare as his fame and as magical as his deeds. Yet the way you acquire superpowers is not by being born with them, but by seeing, with a sudden shock, that they are perfectly normal.

Class Project

From the world of Initiation Ceremony. Brennan and the others are faced with their midterm exams.

(alternate summary:)

The students are given one month to develop a theory of quantum gravity.

A Premature Word on AI
The Rhythm of Disagreement
Principles of Disagreement
Timeless Identity

How can you be the same person tomorrow as today, in the river that never flows, when not a drop of water is shared between one time and another? Having used physics to completely trash all naive theories of identity, we reassemble a conception of persons and experiences from what is left. With a surprising practical application...

Why Quantum?

Why do a series on quantum mechanics? Some of the many morals that are best illustrated by the tale of quantum mechanics and its misinterpretation.