Monday, April 28, 2014

Soft Linking

Dear Diary,

I have two folders that I want to access the same information.  Like, let's pretend I have a pdf of something totally swanky that I put into one folder.  For my own filing system, I want to have another folder with a different name that accesses the folder with my swanky pdf.

All I have to do is soft link!  By typing

"ln -s [original directory] [new directory]"

the computer makes a folder that if you go into it, you go to the original folder!  This also works with documents!  I just made one for our journal club tomorrow so I don't have to move all the documents over.  I use them all the time if I see two projects need the same thing:  I soft link both to the relevant whatever!

Our little in-house server has a lot of these.  Many times, students have tried to go wandering around and document the directory tree, but few have made it out!  There's so many soft links everywhere that it's turned into a maze rivalling Crete and only now generates headaches!  But no Minotaur (I think...)!

In fact, the streets of Irvine and many foreign countries such as cities in Spain are set up like this.  The idea is that if you have windy streets, then you can get away from bad guys more easily by running until you're lost yourself.

Wednesday, April 23, 2014

Movers and Shakers

Dear Diary,

It's another office shuffle!

Aurora and Justin moved up to closer to Kieron for motivation and coffee.  The rest of us are left down here enjoying the wide open office atmosphere.

The moves tend to go like this:  The person at the top of the seniority picks a new desk.  Then the next person moves, etc.  I had to wait until the end to get the desk by the window that Aurora had. Aurora even mentioned that a bird enjoys pecking at the glass if the blinds are open.  So cute!
Better yet, a trap desk is now set for the careless of seat.  Once a new member takes my old seat, and sits in my old desk, they'll be me at the bottom of the seniority!  I'll get to gently deliver the line, "It's a trap!"

Now if I a could get a couch placed where that desk used to be, then all the visitors will have cushy supports for their weary legs.  And I'd have an auxiliary chair when I read things...but no naps, diary!  I don't live that far away and need to get some things done. Or risk that Kieron would catch me napping!

Oh no!  House rules say no couches in small offices!  Instead, a bunch of old computers were placed where I used to be.  Maybe it's a signal to work harder or end up like those my old desk!

PS  The Webmaster updated everyone's contact information.  Yay!

Monday, April 21, 2014

What is big?

Dear Diary,

Let's talk about length scales again. Consider the number


This number has a 'scale' of 10^5 since we can rewrite it as 4.14503 x 10^5. Let's look at  it on a graph:

To illustrate my point, I've also plotted the number 4.1 x 10^5.  It's almost the same! You can barely tell the difference!  But trust me!  Now, I only put the y-axis in steps of 10^5 because that's all we care about--it's our scale.

Let's really drive this pedantic point home by adding something way less than our scale--like the number 301 (=3.01 x 10^2).  It's of order 10^2.  The sum of those two numbers is


I've plotted it on our graph.  Again, you can barely tell the difference!  In fact, if you're not pulling any tricks, you can't!  Big numbers don't care about little numbers.  Sometimes, it's a good approximation to just concentrate on big numbers because if you added in smaller numbers, you'd basically get the same answer.

Let's look at the flip side.  10^8 is a huge number--it's on a bigger scale.  Let's add it to our first number:


On our new 10^8 scale, this number basically looks like plain old
10^8 (you couldn't tell the difference between the two on a graph with a scale of 10^8--or realistically, the y-axis are marked by 10^8).  I probably could have just put up a one with eight zeros after it, I certainly wouldn't have checked. This number is basically infinite on our old length scale, it's too big for our puny 10^5-scale to handle!

Lastly, for a real world example, consider you, a person!   Then consider the moon.  You can not handle the moon!   From our analogy above, it's too big a number to add to you without it just appearing that there is only the moon (I'm thinking of it crashing into you, sorry). You + moon = moon!  Only things on the same scale 'matter'...or we need to consider a different scale.

[Editor's note:  Perhaps in a future post, the author will muse on chaos.  This would be an example system where small numbers have big impacts on large ones.  The point remains, find the big numbers in your theory and you'll get a pretty good answer even if you left out some small ones.]

Monday, April 14, 2014

What is a Phase Transition?

Dear Diary,

I recently was wandering the woods and thought of a good analogy for a coherence length.  Condensed matter is rife with coherence lengths while something like particle physics deals with energy scales.  Really, these two things are the same since there's a relation like

Energy ~ 1 / Length

Consider a big stick stuck in the ground with the sun shining on.  This setup can only be in two phases:  day or night, but without looking at anything else, we can determine if it is day or night (or how much day there is) by looking at the stick's shadow. The length of the shadow is the coherence length for "day phase".

Now, consider what happens as set-up goes from day to night.  The shadow grows and grows and grows until there is a point where the shadow has infinite length but just for one instant.  You blink and you miss it.  What do you miss if you blink?  You missed the phase transition from day to night!  The coherence length went off to infinity.

Now, this happens all the time in physics when there's a phase transition.  So, the coherence length for solids goes to infinity when we transition to a liquid and so on.

Monday, April 7, 2014

A New Focus

Dear Diary,

Ok, this month we're going to get back to basics.  No more publishing fiascos,* funding nightmares,** or other distractions;*** I'm taking charge of my time here and going to tell you all about physics.  This April, it will be the physics information month between us.

Buckle your seat belts.

[Editor's Notes:
*-Ok, well, there'll probably be more of those
**-Well, that's a constant worry.
***-Yeah...sure. ]

Wednesday, April 2, 2014

Let them eat cake

Dear Diary,

Here's a bit of retro-posting for you.  I'm going to tell you about one of the all-time legendary computers games that probably influenced me to become a physicist.

I'm talking about the original Half-life.

The game opens on a scientist going to work in a secret, private corporation's complex by tram past, among other things, a radioactive pit.  The subtitles inform you that you are Gordon Freeman, a theoretical physicist from MIT.  Now, as a nine year old, that theoretical physics thing sounds super dope because no one who is nine years old knows what physics is, so it must be something completely wicked.

That first subtitle holds up well and good until you start thinking about what kind of work Dr. Freeman actually has considering his background in theory.  His job is to be blithely ignorant to all things going on in the facility and push samples into laser beams.  He does this excellently.  But, why did they hire a theoretical physicist to do this?  Is it that an experimental physicist would know too much about pushing samples into laser beams and the work is hyper-classified?  If their goal was to find someone who would definitely never figure out why their experimental appartus was a bad idea, they picked the right guy.  Rather, the game should be focused around you sitting at a desk and pushing math around on a piece of paper.

When Dr. Freeman activates a resonance cascade opening a trans-dimensional portal to allow aliens into our world (almost the first thing you do), he immediately becomes the "hunky, studly" sort of life saving scientist (a la Tony Stark/Ironman, but without any dialog or attitude) and you start to wonder how he knows how to deal with headcrabs (class at MIT? PHYS 301: Monster Management? PHYS 302: How to Save the World from your Research?).

What are the teaching people at MIT, anyway?  How did he get through MIT if he doesn't know what a resonance cascade is?  Does the physics department there also include courses on how to use weapons in case your physics research opens trans-dimensional portals...or is that something he learned at his first postdoc?  Maybe it's a product of the Manhattan project?  Could Dr. Freeman not get a regular postdoc and so had to settle for causing an alien invasion?  I know the job market is bad, but whoa...

Let this be a lesson to all of us:  theorists cause the alien apocalypse working in a theoretical job.  This game is really a lesson in hiring people with the proper job training...and not getting too over-invested so you get impatient waiting for Half-Life 3 to come out.

Tuesday, April 1, 2014

March Meeting: Reimbursement

Dear Diary,

Today, I filled out my reimbursement.  I won a travel award from the university, so that helped to cut down the total cost.  Saving money from Kieron's resources is a good way to stay employed.

Jenny was really nice and helpful.  I got all my paperwork filled out quickly and turned in so I can get the money back.

Now, I should get back to work so I'll have something to present the next time I go to a meeting.