You know when grown-ups tell you everything's going to be fine, and you think they're probably lying to make you feel better?
Yes.
Everything's going to be fine.
Thursday, July 22
Units Of Measure
Today on Pixy's Science Theatre: Tales of the Very Small!
A micron, or micrometre, is one millionth of a metre, 10-6 m. A typical human hair is about 80 microns thick (the range is rather large, from 18 to 180 microns). A human red blood cell is 6 to 8 microns across; the average bacterium is between 1 and 10 microns. The wavelength of visible light is around half a micron - ranging from 0.38 microns for violet to 0.74 microns for red. The smallest features of today's computer chips are just 0.09 microns wide.
An Ångström is much smaller, one ten-thousandth of a micron, one ten-billionth of a metre, 10-10 m. Atoms are around one Ångström wide - half an Ångström for hydrogen, the smallest of all atoms. X-rays have a wavelength of around an Ångström. The double-helix of DNA is about 20 Ångströms across.
The Fermi is far smaller still, one one-hundred-thousandth of an Ångström, one quadrillionth of a metre, 10-15 m. A proton or neutron is about one Fermi in diameter.
The Planck Length is really ridiculously small: about a tenth of a billionth of a quadrillionth of a Fermi, 1.6 x 10-35 m. According to current theoretical physics, that's as small as you can go: any distance smaller than a Planck Length doesn't actually exist.
62 orders of magnitude in length
83 orders of mangitude in mass
Posted by: Pixy Misa at
01:32 PM
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1
So a half a Planck Length is not physically possible or is it not metaphysically conceivable?
Posted by: Jim at Thursday, July 22 2004 02:32 PM (IOwam)
2
Not physically possible - if the theory is correct.
Posted by: Pixy Misa at Thursday, July 22 2004 08:21 PM (+S1Ft)
3
The (untested) string theory explanation is that since particles are not points, but extended strings, about planck length long, it doesn't make sense to talk about distances or sizes smaller than the strings.
There must be a conventional quantum explanation, but I don't know it. I think it relates to the uncertainty principle, that even with the largest energy uncertainty a particle can have, its position uncertainty is still nonzero, about planck length. You can't locate a particle to within a fraction of a planck length, so distances that small don't matter. Finite sized strings just make more sense to me, though.
I remember reading
somewhere that it's even more weird than that, in that in some weird 11 dimensional way, distances smaller than planck length really aren't smaller. Half a planck length in some sense is the same as two planck lengths. I have enough trouble with 3 dimensions, though. I think 11-dimensional physics will remain forever beyond me.
Posted by: Anonymous Coward at Friday, July 23 2004 02:23 AM (8M5Yp)
4
As I understand it - which is to say, not very well - distance may be quantized just as (say) electrical charge is. And that quantum is the Planck length.
Your explanation also makes some sense. I'm really not comfortable dealing with distances below a picometre or times shorter than an femtosecond, so I'm a bit out of my depth. :)
Posted by: Pixy Misa at Friday, July 23 2004 03:28 AM (kOqZ6)
5
10
35 planks are about a mile. Maybe we can reform the metric system to bring it into line (so to speak) with traditional measurements.
Posted by: David Boxenhorn at Friday, July 23 2004 03:56 AM (Zblwc)
6
At least in all my experience, Angstrom is becoming deprecated. It is 10^-10m, and so isn't one of the standard fractional units. The nanometer (10^-9m, 10 Angstroms) is the preferred SI unit of distances in the former Angstrom range.
Pretty soon we are going to need a shorthand for nanometer like "micron" for micrometer. Nanon? (Picon for picometer?)
In my laser physics classes, we always just called it a nano -- "The laser wavelength is 633 nanos." And yes, we would routinely deal with nanos, especially when dealing with interferometry. We could measure the length (ok, the change in length) of an interferometer or optical fiber to within a few nanos. We had one device which could measure the change in wavelength of a laser to better than 0.1nano.
Now that the chips are getting down to 90 nanos, the nano is becoming an increasingly important unit of distance. The only problem with calling them nanos is that the chip guys probably use nanoseconds at least as often.
Posted by: Anonymous Coward at Friday, July 23 2004 06:20 PM (sCYzS)
7
I don't have notes in front of me, but I'm pretty sure that 10^-15m is the
radius of a proton, not the
diameter.
I'm truely truely sorry for this comment.
;P
Posted by: Tuning Spork at Saturday, July 24 2004 09:18 PM (5TORB)
8
Next time on Pixy Science Theater 3000... Exponential growth, as exemplified by the interval between posts.
Posted by: Anonymous Coward at Tuesday, July 27 2004 11:04 AM (sCYzS)
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Thursday, July 15
Look Ma, No Hands!
Oh look, a new urgent security update!
Really, the difference between open-source software and closed-source software is not the number of bugs, but the manner in which fixes are announced. Err, and the price too.
But this time I managed to completely rebuild MuNu's Apache server with all its attentand modulary without breaking anything! As far as I know...
Update: DOH! Why the hell does the Apache install script in CPanel reset the permissions on everyone's home directory, forcing me to manually correct the settings for 113 users?
Posted by: Pixy Misa at
11:40 AM
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1
Proof that you wuv us. You weally, weally wuv us.
And YOU ARE THE BESTEST!
Posted by: Emma at Thursday, July 15 2004 01:36 PM (NOZuy)
2
Now's your chance to do what makes Open Source great: Find the bug in the install script, fix it, and send the patch in.
Posted by: Anonymous Coward at Thursday, July 15 2004 08:33 PM (8+XGc)
3
Unfortunately, the original bug is in an open source package, but the install script isn't open source.
Posted by: Pixy Misa at Thursday, July 15 2004 08:41 PM (+S1Ft)
4
And now that you've done it manually, why can't you do something like this to fix the permissions?
cd /home
find . -type d -exec chmod 700 {} \;
where 700 is whatever the permissions should be. I understand the problem shouldn't happen in the first place, but 'find' does most things I would normally consider doing manually like that.
Posted by: Anonymous Coward at Friday, July 16 2004 04:33 PM (sCYzS)
5
There are some directories in there that will break if I change their permissions from the default. So when I say manually, I mean I wrote a little script but had to carefully edit a list of directories. That's about as manual as I get. ;)
Posted by: Pixy Misa at Friday, July 16 2004 07:07 PM (+S1Ft)
6
Urg. What a mess. I'm sorry. But thank you, Pixy! Thank you very muchly! You *are* the bestest!
Posted by: Linda at Saturday, July 17 2004 05:10 PM (ktJme)
7
I might be a victim of this scourge. Getting this error:
Writing to '/home/nick/www/index.php.new' failed: Opening local file '/home/nick/www/index.php.new' failed: Permission denied
Posted by: Nick Queen at Sunday, July 18 2004 04:33 PM (gBeRV)
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Wednesday, July 14
Again!
The database archive server failed a perfectly good disk out of the RAID-5 set. A quick raidhotremove and a raidhotadd - and a 20-hour resync - and it's back again. It would be better, though, if Linux didn't fail disks out of RAID-5 volumes every time a gnat farts in the computer room.
Posted by: Pixy Misa at
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1
Every time a gnat fats? Surely that should be every time a gnat ext2's ...
Posted by: Rob at Wednesday, July 14 2004 06:16 AM (kXZI6)
2
Just for that, I shall fix my typo and make you look like a very strange person.
Posted by: Pixy Misa at Wednesday, July 14 2004 09:55 AM (+S1Ft)
3
How about every time a gnat fscks?
Ok, I'll duck out now before the throwing of large objects starts.
Posted by: Chris C. at Wednesday, July 14 2004 11:54 AM (yTB+l)
4
I'm linking insect flatulence to platform specific file systems and you really think there's anything you can do to make me look more strange?
Posted by: Rob at Thursday, July 15 2004 03:08 AM (BWDMP)
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Monday, July 12
Shrug
Well, that was weird. No mouse, reboot, no Windows. Boot from CD, chkdsk, reboot, no windows. Put CD back in, reboot... Windows. Eh.
Posted by: Pixy Misa at
11:47 AM
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Meeses To Pieces
My mouse - my shiny 7-button Logitech MX700 cordless optical mouse - no longer mouses. Woe!
Posted by: Pixy Misa at
09:15 AM
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1
What do you use the
7 buttons for?
Posted by: Madfish Willie at Monday, July 12 2004 01:16 PM (yN46R)
2
Well, left and right buttons, and middle button, which opens a link in a new tab in Mozilla. Then I have a button programmed as Back for browsing, two programmed as scroll up and scroll down so I don't need to keep scrolling the scrollwheel, and the last one opens up a Windows Explorer window.
Posted by: Pixy Misa at Monday, July 12 2004 07:51 PM (+S1Ft)
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Saturday, July 10
What Those Physicists Are Really Up To
> Theories are wonderful things. IIRC, there is some speculation that
> the photon possesses a (albeit small) nonzero mass. Also, there is
> the notion that all particles have what is called a "supersymnmetric
> dual", speculatively named the photino, neutralino, and gravitino for
> the photon, neutrino, and graviton respectively.
And squarks, sleptons, ... gluinos and higgsinos. Actually, the
supersymmetric dual of the neutrino is the sneutrino. The neutralino is
a combination of, I think, the Zino, the photino and maybe a Higgsino
that ends up being the lightest supersymmetric particle. In a number of
theories, this particle cannot decay and turns out the be a great
candidate for dark matter.
(Dwight Thieme and Aaron Bergman on rec.arts.sf.science)
Posted by: Pixy Misa at
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Thursday, July 08
Needles And Haystacks Have Nothing On This
I have 86GB of documents here in a hundred different proprietary formats, and I am searching them for the word "pelican".
Posted by: Pixy Misa at
03:38 AM
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1
The pelican, she is a crafty beast. One would be wise to carry a back-up piece when stalking such a creature.
Posted by: Jim at Thursday, July 08 2004 02:19 PM (IOwam)
2
Pixy - stop searching! Here it is: 'Pelican'.
Any other words you want ?
Posted by: Robert Blair at Thursday, July 08 2004 11:53 PM (rN87/)
3
Try Pel*. Then go get some sleep.
Posted by: Ted at Friday, July 09 2004 06:28 AM (blNMI)
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Wednesday, July 07
Inductive Reasoning And All That
The good thing about computers is if you think something is true but you're not 100% sure, you can quickly spot-check a few million examples.
Well, it's useful in my line of work, anyway.
Posted by: Pixy Misa at
03:41 AM
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1
Hi, Pixy,
Came over from Roger Simon, love your site...the name "Ambient Irony" is a killer...so was your July 4 birthday toast. Keep up the good work, we need it!
Buddy Larsen
Posted by: Buddy Larsen at Wednesday, July 07 2004 11:22 AM (n8q+T)
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