Saturday, July 26, 2008


1. I stumbled upon some show on some channel where they were showing some stuff and then blurring some other stuff "for security reasons" or something like that. Good thing I don't remember. If the stuff they were blurring out was in fact real and not some "reconstruction", they'd have made a terrible mistake. Blurring doesn't "delete" any information, it just "scrambles" it. Furthermore, it's a poor scramble. Blurring does what's called a convolution, which is basically adding pixels to their neighbors. They can be easily subtracted - the frame can be deconvolved, revealing the original image. It's being used to enhance pictures that come out defocused or otherwise distorted (by analog convolution versus the digital blurring you do in the GIMP). So I hope those sequences were bogus.
2. News are getting dumber by the day. Besides the presenter obsesivelly calling some kids who pretended to sell stuff on some websites, without actually sending the items, hackers, which is insulting to all hackers on many levels, some other dude was reporting on the way cool "thousands of decibels" at some concert the actual TV station was organizing. Yeah, i'd have liked having a few thousand dB SPL there... any increase in news quality is welcome; though anything above a mere 200 dB isn't physically sound anymore, it's a blast shockwave, a concept similar to the one discussed near the end of the previous (relevant) post.
2000 dB SPL (the smallest that could count as "thousands") equals about 2*10^95 pascals (notably, almost one googol, or "ten duotrigintillion":), of them). Normal air pressure is about 10^5 Pa, or 2{90 zeros} times less.
Having failed to find what the pressure is inside a neutron star, the densest object known, let's calculate a very rough estimate. The average density of such an object is thought to be about 10^17 kg/m^3, although it varies from the surface to the center in a way I don't know, so this limits the accuracy of my calculation. Anyway, the pressure dp contributed by a layer of thickness dx at distance x from the center is dp(x) = rho(x)g(x)dx. The gravitational acceleration g(x) = Gm(x)/x^2, where m(x) is the mass contained in the sphere of radius x. Assuming a constant rho(x) for simplicity and lazyness to search for data, dp(x) = G*rho^2*(4/3)pi*x*dx. Integrating over x from 0 to R we get the pressure in the center of a homogenous sphere of density rho and radius R: p = 2/3 pi G rho^2 R^2. In terms of its mass, that would be p = 3/8pi G M^2/R^4 (the smaller, the more crushing). Doing the numbers, I get around 1.4*10^32 Pa, which is of course much, much, much less than 2*10^95; any other more accurate model would still give a result that's much, much, much less than 2*10^95. So on second thought, I wouldn't like having "thousands of decibels" anywhere, if that were possible.

1 comment:

etor said...

I do believe that this idiocy comes from the lack of interest in physics classes in highschool (not to speak of the fact that the aforementioned classes have been recently reduced in frequency and total number) and from the fact that the relation between in-book physics and actual reality is not well exposed and explored in the aforementioned classes. School should be better. More physics.