Wednesday, April 15, 2009

Newcomb's paradox

Wikipedia article
Some website's article.
There are two boxes, labelled A and B . You face a choice between taking just box B or both boxes.
Box A contains 1000$ . If Predictor had predicted that you'll take just the box B, box B contains 1000000$. Else if Predictor has predicted that you'll take both boxes, box B contains nothing.
A million people played this game, and Predictor was never wrong.
Will you take just the box B or will you take both boxes?
(I'm "one-boxer")

I think this paradox is not weird enough and needs to be made weirder. Imagine that boxes are made of glass. In such case, would you still choose one box? Why does it make difference when even with opaque boxes you know that taking both boxes always gives you 1000$ more?
(There is why it makes difference, actually: you could pre-decide to pick box B if it empty, and pick both if B is not empty, making predictor certainly wrong)
Also, what happens if its 50$ vs 100$ ? 99$ vs 100$ ? 0.01$ vs 100$ ?

Thursday, April 2, 2009

Sherlock Holmes and The mystery of Cold Fusion

I think that the first questions that Sherlock Holmes would have asked if he was investigating cold fusion would be...
Who did experiment and where did they bury the body?!

It is very easy to show that if cold fusion with reported excess heat was real, there would have been quite a few fatalities, given the lack of precautions in such experiments.

Human lethal dose is 5..10 Sieverts, equivalent to or 5..10 Grays of gamma radiation, i.e. 5..10 joules per kilogram.
1 Gray = 1 Joule of absorbed ionizing radiation per kilogram = 100 Roentgen.

Neutron radiation does 5..10x more damage than gamma radiation, so lets assume it takes 1 Gray of neutron radiation to kill, or at very least, seriously hurt human. Suppose that experimenter weights 100kg, that'll be 100 joules of absorbed neutron radiation.
Most of the deuterium-tritium fusion energy is released in form of neutron radiation, which is somewhat poorly absorbed by electrolysis cell.

You see where its going. Excess heat output of 1 watt means 3600 joules per hour, which means that there is real risk for experimenter to absorb lethal dose and die, or less dramatically, to get sick. The doses, even for short experiments, would easily exceed yearly allowance for nuclear industry workers. Worse yet, neutron activation would make equipment and walls of building themselves radioactive.

Interestingly, even one milliwatt of fusion power would make regular four-digit geiger counter that you can buy on ebay (and which counts 10 clicks a minute on background) quickly overflow and beep its "run for your life" alarm.

The conclusion is... either there is massive cover up of many deaths, or cold fusion is a hoax.


After hearing about twitter for 10th or 20th time, I thought its about time to register account on it, dmytry, rationalizing it as reserving my name.
Geez. It even got a button to auto-follow a bunch of random people, and a bunch of them will auto-follow you.
Feel free to follow me, I'll auto-follow you, and yes, it is extremely unlikely I'll read what you write, and just as unlikely you'll read what I write.

So bloody useless, even more useless than this blog.

Wednesday, April 1, 2009

Couple compound shell commands

make passwords:
base64 < /dev/urandom
(I know of pwgen, but above line is better for paranoid. You may fear that pwgen has some sort of bug that greatly decreases amount of entropy in passwords, but, surely, you gotta trust /dev/random and /dev/urandom , and base64. if those fails you're screwed anyhow)

print all gcc defines
gcc -dM -E - < /dev/null

access to some sites behind mis-configured switches can be improved with (as root)
ifconfig eth0 mtu 1000
or lower number

reversing order of numbered files
for((i=0;i<720;++i)); do mv file_$(printf "%05d" $i).png file_$(printf "%05d" $((720-i))).png ; done
(replace 720 with number of files)

remove executable privileges recursively without making folders non-browsable:
find ./ -type f -exec chmod -x {} \;