Posts Tagged 'Physics'

A 10-Year-Old Asks about Black Holes

I have a 10-year-old cousin who is very curious about the world, and physics in particular.  When his mother sent me two very interesting questions that he asked about black holes, I had fun coming up with some answers for him.  His questions and my answers are reproduced below. (Yes, some of the language isn’t quite as precise as it should be, but I intentionally glossed over a few details. Hopefully I didn’t say anything wrong as a result.)

If a black hole “sucked in” only photons, would it increase in mass?

Photons “die” when they interact with something, but if they do die, then what are they interacting with in the black hole?

These are two great questions, and I had fun coming up with answers to them. I gave a short answer, but any good physics question brings up a lot of related ideas, so I also put a longer answer that brings up some other ideas.

Short answer:
Yes. Einstein taught us that energy and mass are two aspects of the same thing. Even though the photons are massless on their own, their energy can increase the mass of the black hole when they are absorbed. The event horizon prevents any information from escaping a black hole, so we can’t know exactly what the photon interacts with.

Longer answer: Continue reading ‘A 10-Year-Old Asks about Black Holes’


Unsolicited Advice, Volume I

So you want to be a physicist?  Hey, me too!  While I don’t know everything there is to know about getting there, I might be farther along than you are, and have some wisdom that I’ve accrued along the way that I can impart to you, even though you never asked for it.  Hence, this series of Unsolicited Advice.  (I would be remiss if I didn’t mention the inspiration I got from Cosmic Variance.  Plus I borrowed stole the name.)

Since this is Volume I, we’ll start early: before college.

Nurture Your Interest

If you’re reading this, and you’re not yet in college, then I’m willing to bet that you got interested in physics by reading one of the many popular books on physics.  It’s a great way to get into physics (it’s the way I got into it all those years ago).  You should continue to feed that interest in any way you can: read more books, watch tv specials, and discuss what you’ve learned with anyone who will listen. Continue reading ‘Unsolicited Advice, Volume I’

You’re Like School in the Summer…

No class!

Or at least that’s how the corny old Fat Albert joke goes.  Of course, there’s always summer school… In high school, these were remedial classes that you wanted to avoid.  In college, maybe you’re trying to improve a grade, or maybe stay on track to graduate in four years.  But in grad school, summer schools are something entirely different.

Summertime is a time to focus on your research, without the distractions of tests, homeworks, and (hopefully) teaching duties.  But many grad students, at least in physics, take the summer as an opportunity to attend summer schools, which are short, intense sessions aimed at advanced grad students that are held at various institutions around the country and the world.  These schools bring in lecturers to present short courses on different topics within a certain subfield, often focused on a particular theme for that year.  The purpose is primarily to broaden the students’ exposure to the field, getting them out of the narrow focus that dissertation research requires.

Not everyone has the resources or the ability to attend one of these schools, but, thanks to modern technology, you can still participate by watching the lectures online.  In particular, the Theoretical Advanced Study Institute in Elementary Particle Physics (TASI) is going on now, in Boulder, CO.  You can find the links to lecture videos and notes here.  So far, it looks like they are getting the videos posted the day after the lectures occur, so you can make time to take a course or two that looks interesting (the upcoming lineup of talks is also found on the same site).  I have started the course on Supersymmetry and the MSSM, but I am particularly looking forward to the lectures on the AdS/CFT duality, as that pertains to my summer research project.

Continue reading ‘You’re Like School in the Summer…’

What is a Particle?

For my money, particle physics is just about the coolest thing in the world.  The scientifically curious public evidently thinks it’s pretty cool too, as evidenced by the books and articles aimed at the general public that far outnumber the coverage given to other areas of physics, much to the chagrin of the people who study those fields.

So you’ve probably heard about many concepts about particle physics.  I’m sure you know about atoms, electrons and the nucleus.  Maybe quarks, neutrinos, and the higgs boson sound vaguely familiar.  And the media hype around the LHC startup has been hard to ignore.

In this series of posts, I hope to give you a better understanding of what particle physics is about.  I hope these posts will be of interest to both the novice and the relative expert — anyone who wants to explore the question of just what it is we mean when we talk about a fundamental particle.


Before we talk about particle physics, we have to have a little context.  Let’s start with the universe.

Okay, now let’s zoom in juuust a little bit, down to the level of atoms.  This is where I will begin our discussion of what it means to be a particle.  Atoms were originally posited to be the smallest, “uncuttable” building blocks of all matter, the first candidate for a fundamental particle.  This idea, originally put forth by philosophers such as Democritus, was in opposition to the idea that matter was a continuum that could be divided into smaller pieces ad infinitum.  As chemistry developed and new elements were discovered and isolated, the atomic hypothesis moved from the realm of philosophy and became an essential scientific concept.

However, we’re not all that interested in the development of chemistry.  I want to focus instead on what sort of a mental picture this model gives us.  In other words, just what sort of properties does a “fundamental particle” have in this atomic theory?

Continue reading ‘What is a Particle?’

You Load 16 Tons, and What do You Get?

Another day older, and deeper in debt…  Or so the song goes, but is that realistic?

Man, loading 16 tons of coal in a day sounds like a lot of work… But is it as much work as it seems?

Fortunately, physics gives us a way to calculate the amount of work done.  In this case, we will assume that the only work done is to lift the coal against the force of gravity.  As the direction of motion is parallel to the direction of the force, the formula for work done is simple:

Work = Force x Distance

Continue reading ‘You Load 16 Tons, and What do You Get?’

Hip Hop and Error Analysis

There’s sixteen ounces to a pound, twenty more to a ki

–Mos Def, “Mathematics”

Crack cocaine has long been a scourge of America’s inner cities, and as such, often makes its way into hip hop lyrics.  For whatever reason, drug dealers measure large amounts of cocaine in kilograms (usually abbreviated as a “kilo” or a “ki”), while smaller amounts are measured in ounces (“O’s” or an “O-Z”).  This leads to some pretty unusual unit conversion, as illustrated above.

How close is this conversion?  Well, 36 ounces is 2.25 pounds, while a kilogram is approximately 2.2 pounds.  This is about a 2.3% excess, so somebody’s getting ripped off here.  My hunch is that it’s the user who gets the short shrift.  Maybe we can dub 36 ounces the “drug dealer’s kilo,” along the same lines as a baker’s dozen being equal to 13.

Another example of shady unit conversion:

Continue reading ‘Hip Hop and Error Analysis’

Collection of Traffic-Related Science

In my last post about the 35W bridge and the traffic problems it caused, I promised that I would look for some traffic-related science.  So here’s a collection of links I’ve found, plus some memories of older stuff that I’ve read that I haven’t taken the time to track down.

Continue reading ‘Collection of Traffic-Related Science’