Monthly Archives: April 2008

Where Experience Confuses Physicists

This post is part of the Quantum Physics Sequence.
Continuation ofWhere Physics Meets Experience

When we last met our heroes, the Ebborians, they were discussing the known phenomenon in which the entire planet of Ebbore and all its people splits down its fourth-dimensional thickness into two sheets, just like an individual Ebborian brain-sheet splitting along its third dimension.

And Po’mi has just asked:

"Why should the subjective probability of finding ourselves in a side of the split world, be exactly proportional to the square of the thickness of that side?"

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Blaming The Unlucky

A recent working paper finds that we call the same decision immoral when it leads to a bad outcome, but moral when it leads to a good outcome: 

Two studies investigated the influence of outcome information on ethical judgment. Participants read a series of vignettes describing ethically-questionable behaviors. We manipulated whether those behaviors were followed by a negative or positive consequence. As hypothesized, participants judged behavior as less ethical when it was followed by a negative consequence. In addition, they judged the behavior as more blameworthy and to be punished more harshly. Participants’ ethical judgments mediated their judgments of both blame and punishment. The results of the second experiment showed again that participants rated behavior as less ethical when it led to undesirable consequences, even if they saw that behavior as acceptable before they knew its consequences. Implications for both research and practice are discussed.   …

We show that outcomes of decisions lead people to see the decisions themselves in a different light, and that this effect does not depend on misremembering their prior state of mind. In other words, people will see it as entirely appropriate to allow a decision’s outcome to determine their assessment of the decision’s quality. … The tendency demonstrated in our studies might lead people to blame others too harshly for making sensible decisions that have unlucky outcomes. … Too often, we let ethically-questionable decisions slide for a long time until they result in negative outcomes, even in cases in which such outcomes are easily predictable. 

This makes morality look more like a social convention for who we can blame for what, rather than a direct guide to decision making. 

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Where Physics Meets Experience

This post is part of the Quantum Physics Sequence.
Followup toDecoherence, Where Philosophy Meets Science

Once upon a time, there was an alien species, whose planet hovered in the void of a universe with laws almost like our own.  They would have been alien to us, but of course they did not think of themselves as alien.  They communicated via rapid flashes of light, rather than sound.  We’ll call them the Ebborians.

Ebborians reproduce by fission, an adult dividing into two new individuals.  They share genetic material, but not through sexual recombination; Ebborian adults swap genetic material with each other.  They have two eyes, four legs, and two hands, letting a fissioned Ebborian survive long enough to regrow.

Human DNA is built in a double helix; unzipping the helix a little at a time produces two stretches of single strands of DNA.  Each single strand attracts complementary bases, producing a new double strand.  At the end of the operation, a DNA double helix has turned into two double helices.  Hence earthly life.

Ebborians fission their brains, as well as their bodies, by a process something like how human DNA divides.

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Early Scientists Chose Influence Over Credit

Last June I wrote:

If what you want is influence, instead of credit, the choice should be easy: you should want people to steal your ideas

A recent Nature illustrates

The popular caricature locates the origins of modern science in the natural philosophies of ancient Greece and the rediscovery of their spirit during the Renaissance and the Enlightenment. It passes decorously over the intervening period, deemed to be a hotbed of superstition. In fact, the notion of a Universe governed by laws accessible to human reason – the precondition for science – emerged in Western Europe largely during the twelfth century, several hundred years earlier than we have come to imagine. …

One of the most active translators, the Englishman Adelard of Bath, was a startlingly original and perceptive thinker. Rueing how difficult it was to get his ideas accepted, he wrote: "Our generation … refuses to accept anything that seems to come from the moderns. Thus when I have a new idea, if I wish to publish it I attribute it to someone else." This is why so many of the works of natural philosophy from antiquity to the Renaissance have apocryphal attribution: a book apparently by Pliny or Aristotle was more likely to be read. The progressive thinkers of the early Middle Ages hid their new wine in old flasks, so that others would take them seriously.

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Which Basis Is More Fundamental?

This post is part of the Quantum Physics Sequence.
Followup toThe So-Called Heisenberg Uncertainty Principle

For decades, quantum physics was vehemently asserted to be nothing but a convenience of calculation.  The equations were not to be interpreted as describing reality, though they made good predictions for reasons that it was mere philosophy to question.  This being the case, any quantity you could define seemed as fundamentally real as any other quantity, which is to say, not real at all.

Physicists have invented, for convenience of calculation, something called a momentum basis of quantum mechanics.  Instead of having a complex amplitude distribution over the positions of particles, you had a complex amplitude distribution over their momenta.

The "momentum basis" contains all the information that is in the "position basis", and the "position basis" contains all the information that is in the "momentum basis".  Physicists use the word "basis" for both, suggesting that they are on the same footing: that positions are no better than momenta, or vice versa.

But, in my humble opinion, the two representations are not on an equal footing when it comes to being "fundamental".

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A Model Disagreement

We have often pondered the question: when you find that you and someone else disagree, how much weight should you give to your and their opinions in forming your new opinion?  To explore this, I’ve worked out a simple math model of disagreement between two "Bayesian wannabes", i.e., agents who are trying to act like Bayesians, but know that they make mistakes, and try to adjust for this fact. 

Consider two agents, A and B, having a conversation about a truth t = x1 + x2 + x3 + …  First A sees clue x1, and reports r1, his estimate of truth t.   Next B sees report r1, and also clue x2, and then reports r2, his estimate of truth t.  A now sees report r2, a new clue x3 and reports r3.  The two of them could go back and forth like this for a long time. 

If A and B were perfect Bayesians (and if each xi were independently and normally distributed with zero mean and a known variance Vi), then we would have ri = xi + ri-1.  When combining their last two expressed opinions, each agent puts zero weight on his own last report, and just adds his new clue to the other agent’s last report!

OK, but what about imperfect agents?  I assume:

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The So-Called Heisenberg Uncertainty Principle

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This post is part of the Quantum Physics Sequence.
Previously in seriesDecoherence

As touched upon earlier, Heisenberg’s “Uncertainty Principle” is horribly misnamed.

Amplitude distributions in configuration space evolve over time.  When you specify an amplitude distribution over joint positions, you are also necessarily specifying how the distribution will evolve.  If there are blobs of position, you know where the blobs are going.

In classical physics, where a particle is, is a separate fact from how fast it is going.  In quantum physics this is not true.  If you perfectly know the amplitude distribution on position, you necessarily know the evolution of any blobs of position over time.

So there is a theorem which should have been called the Heisenberg Certainty Principle, or the Heisenberg Necessary Determination Principle; but what does this theorem actually say?

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Caplan Pulls Along Ropes

Last May I wrote:

The space of all policies … is huge – with thousands or millions of dimensions. … The policy world can thought of as consisting of a few Tug-O-War "ropes" set up in this high dimensional policy space.  If you want to find a comfortable place in this world, where the people around you are reassured that you are "one of them," you need to continually and clearly telegraph your loyalty by treating each policy issue as another opportunity to find more supporting arguments for your side of the key dimensions.  That is, pick a rope and pull on it.   If, however, you actually want to improve policy … then prefer to pull policy ropes sideways.

Bryan Caplan prefers to pull along the ropes:

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Decoherence

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This post is part of the Quantum Physics Sequence.
Previously in seriesFeynman Paths

To understand the quantum process called “decoherence”, we first need to look at how the special case of quantum independence can be destroyed – how the evolution of a quantum system can produce entanglement where there was formerly independence.

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Paternalism Parable

My newly published parable, saying we should be clearer on what justifies our paternalism, or be less paternalistic:

Imagine finding yourself near someone about to walk off a cliff. If he seems distracted enough to not notice a crucial bend in the cliff edge, you might feel quite justified in grabbing his arm, to stop him from falling. You might even expect his gratitude.

But what if he seems well aware of the cliff before him? Well, if he seems crazy, either permanently insane or temporarily drugged, you might still grab him. You might also grab him if you knew his family would miss him terribly. In such cases you might at least expect gratitude from his family, his caretaker, or his future sober self. And if you were morally outraged enough by the very idea of walking off a cliff, you might grab him no matter who was grateful or offended.

But what if, aside from the whole cliff thing, he seems no crazier or immoral than most? What if his action mainly affected only him? What if the cliff was only five feet tall, or 20 feet tall over deep water, or if he walked near the cliff at what he considered a close but safe distance? You might still think of grabbing his arm, if you thought you understood something important that he did not. Perhaps you know the wind is unusually gusty, or the ground is unusually slippery. Perhaps there is no time to explain, or he doesn’t understand your language.

But what if he does understand you, and there is time enough to say "Watch out! That cliff is dangerous." If he dismisses your concern and does not back away, would that justify your intervention? Well we can’t very well allow anyone to intervene in anyone else’s life anytime they feel like it. So if you persist in grabbing we might let him sue you for assault.

But what if you were not alone? What if a great many of you also thought him careless? What if you lived in a democracy and could get enough voters to pass a law banning cliff-walking? Perhaps your law requires tall fences, or threatens to jail those who approach cliffs. Are you justified now?  Even in this situation, you are arrogant if you do not at least consider the possibility the cliff-walker knows what he is doing. …

Read the whole thing here.

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