An answer to Chief Justice Roberts: Why Diversity is Important in Physics Classes


In the hearing for Fisher v. University of Texas — the affirmative action case heard by the Supreme Court yesterday — Chief Justice Roberts asked “What unique perspective does a minority student bring to a physics class?” and mused later, “I’m just wondering what the benefits of diversity are in that situation.” (I am quoting from the Huffington Post article on the case.)  This may have been a rhetorical question – I don’t know – but as a physics professor with 20 years of experience, I think I am qualified to answer it. 

        First of all, from the perspective of the professor, it’s vital that physics classes are as diverse as possible.  This is for one simple reason: EVERYONE needs to know physics.  Many of the major problems facing the world today, such as resource depletion, global climate change, alternate energy sources, and the like, can’t be understood without knowing some Physics.  Whether or not someone becomes a Physicist, they need to understand it on some level if they are to be an educated, well-informed citizen who is capable of dealing with the future.  A lot of people think that Physics is some weird esoteric subject studied by geniuses in lab coats.  But it isn’t — it’s a vital, exciting, challenging, interesting subject with big consequences.

        Secondly, Physics as a profession can’t do without diversity.  Even ignoring all of the other advantages which diversity gives us, it comes down to a numbers game. From the mid-1990’s through the mid-2000’s, the numbers of students graduating with Ph. D.’s in Physics was in decline; this trend was reversed in the mid-2000’s, almost entirely due to an increase in people from non-traditionally represented groups entering the field. This was mostly due to women getting Ph. D.’s, but there has also been an increase in the numbers of African American and Hispanic students receiving doctorates over the past few years.   The American Institute of Physics recognizes the need for diversity;  it sponsors many programs to increase it among physics students and faculty.   We need people from all backgrounds if the field is to thrive.  

        Finally, Justice Roberts is ignoring one of the most important findings in Physics education research in the last twenty years.  Our students learn much more when their teachers have them work with each other than if we simply lecture to them.  This is also how scientific research is really done: the interchange of ideas between people working on a common problem.  If we want the classroom to prepare for real research, indeed for any problem solving in the real world, we want everyone to take part in this.  We need for people to learn how to work with others, no matter how different their backgrounds are.  I’ve seen students from vastly different ethnic, cultural and economic backgrounds work together; learning how to teach each other across such divides is one of the most important skills an education can give.  This is the perspective which minority students bring to Physics classes.


How long can you tread water?


The new blockbuster disaster movie Noah looks like it might be harmless, if simple-minded, fun.  I want to see it, if for no other reasons than watching Russell Crowe and Anthony Hopkins ham it up, and to see if Emma Watson, a one-time student at my alma mater, can make it big past Hogwarts.  I had to explain to my kids why I kept on yelling “Voopa-voopa-voopa… DING!” and “You want a hint? How long… can you tread… water? Hah hah hah hah hah,” every time I saw the trailer.  (My wife has ordered them to poke me if I try to do this when we see it.)

Why bring this up here? There’s a teaching point which can be applied to any disaster movie:  How reasonable is it from the standpoint of basic science?  The science fiction writer Isaac Asimov already observed that the rainfall rate would been enough to swamp an aircraft carrier, let alone a smallish ship (by today’s standards).  However, it’s fun to think about.

I want to talk about an aspect of such a disaster which Asimov didn’t cover:  where’d the water come from?  And how much energy is involved in putting it where it needs to go?  We can make some simple estimates using energy methods.

Maybe the water came from the oceans.  According to NOAA (no relation) the average depth of the ocean is about 14,000 feet (roughly 4,000 meters.)  Since there is three times as much ocean area as land, we can imagine (somehow) emptying the oceans to cover the land to a depth of three times as much, or some 50,000 feet – more than enough to do the job.  It would take a heck of a lot of energy to do this, however.  This is a very large volume of water: under some reasonable assumptions it’s something like a million trillion cubic meters.  The mass of that much water is a billion trillion kilograms, or a million trillion tons.

Let’s say we evaporate the oceans so that it rises into the sky and falls as rain onto the land.  This doesn’t happen under ordinary circumstances – the Earth  isn’t hot enough to make this happen.    The energy needed to evaporate all of the oceans is about the same as the amount of energy which would be used by our world civilization in 9 million years.  Another way to put this: it rained for forty days and forty nights.  Therefore, the total rate at which this energy would need to be put into Earth’s climate system is some one billion trillion watts – about seven thousand times the total power which the Earth gets from the sun!  A power input that large would destroy all life on Earth by boiling everything alive.

If the water came from elsewhere, say a rain of comets, which are largely water, the problem gets worse.  The comet impact speed would be about the same as the speed of Earth in its orbit around the sun (30 kilometers per second, or 67,000 mph.)  It’s a hefty speed.  The speed is so high because the comets would be traveling around the sun in about the same way in which the Earth does. It could be somewhat higher or lower depending on exactly how the collision happens.  The total impact energy is given by (1/2) x (the mass) x (impact speed ) x (impact speed), or about seven hundred thousand trillion trillion joules. (Yes, I wrote that right – trillion trillion.) The comet or asteroid which struck Earth 65 million years ago killing the dinosaurs had an impact energy about one million times less than this.  With a series of impacts like this, the flooding would be the least of Noah’s problems.  He’d have to worry about mile-high waves each time one of the comets struck, the fact that Earth’s atmosphere would be more water than air after the impacts, the complete and utter darkness shrouding the land due to kicked up dust…  And how do we get rid of the water afterwards?  You need about the same amount of energy to push it back up into space.

Amazingly enough, real disasters like this have befallen the Earth, luckily before any life existed on it.  The best theory scientists have on how the Moon formed was due to an impact over four billion years ago by an object about the size of Mars.  The impactor had a mass a few hundred times that of all of the oceans on Earth, but the impact would have “only” been ten times more energetic that our hypothetical cometary scenario because the collision was a “slow” one (about 4,000 meters per second, or 8,900 mph).  Luckily, there are no more objects that size in the solar system which could collide with Earth.

Two points: 1) Always start with the energy involved if you’re trying to decide if movie “science” is reasonable;  2)  I’m still looking forward to the movie.  Expect a review if it violates still more basic science.

Why “Star Trek: Into Darkness” Isn’t Good Science Fiction, part 1


The hallmark of good science fiction isn’t necessarily good science.  If it were completely scientifically accurate, it wouldn’t be science fiction; it would be a NOVA special.  I would claim that the hallmark of good science fiction is self-consistency.  You break the laws of Physics? OK, but you still need to play fair with your readers or your watchers.  That is, if you hypothesize some grand new technology or scientific breakthrough, don’t ignore the implications when it’s inconvenient…

By this criterion, the second of the Star Trek reboot movies, Star Trek: Into Darkness, fails utterly.  Here are only a few of the problems; I’m not even going to discuss issues involving acting and the plot. Be aware that BIG spoilers follow.

The transwarp, part 1:  In an early scene, Sherlock Hol… I mean, Smau… I mean, Khan/John Harrison, “transwarps” from Earth to the main planet of the Klingon Empire.  The transwarp was Scotty’s invention from the first movie, a combination (somehow) of the transporter with the Warp Drive.  Well, stars are many light years, meaning at least trillions of miles apart.  Even if the Klingon empire is located in the next-nearest star system, it’s a distance of about 65 trillion miles.  He has to transwarp there with an accuracy of a few feet in order to avoid falling off the big cliff he appears on top of.  This is an accuracy of about 1 part in 50 quadrillion (a quadrillion is a thousand trillion.)  To put this into context, if we knew the Earth’s diameter to that accuracy, we would know it to the size of one atom…

The transwarp drive, part 2:  OK, let’s assume we have this phenomenal accuracy.  A large part of the plot is the Federation’s anxiety over going to war with the Klingons. If you have the transwarp and the Klingons don’t, why worry?  Just transwarp an antimatter bomb on them if they make too much trouble.  (If they have transwarp as well, then everyone is in trouble…)  More things suggest themselves: with transwarp, why have starships?  Transwarp is faster, really accurate, and portable.  Maybe it’s not cheap, but starships aren’t either.  (My book estimates antimatter production costs starting at billions of dollars…)

These are only a few of the problems with the movie – stay tuned for more!