The Physics Diet


Happy holidays and post-holidays!


This is an “and more” post to help people combat post-holiday funk and guilt about over-eating and drinking during the season.   Many people have New Year’s resolutions which involve losing weight, either weight gained over the holidays or because they feel the general need for weight loss. I’m writing this post and a few others to give some practical advice for those in need, and to look at the science (physics, particularly) of dieting and weight loss. This is going to be the first in three or four posts on the general subjects of dieting, exercise and weight loss, including a literary and philosophical discussion of one’s ideal weight.

I feel that I can write with some authority on this. Between April 2012 and April 2013, I lost 50 lbs, going from an initial weight of 205 lbs to a final weight of 155 lbs. More to the point, I have kept my weight at this level since then. I’ve included a graph of my weight on this blog.  (The blue dots are the actual weight, and the red dots from straight line fits to the data to figure out how fast I was losing weight.  Each dot is my average weight for that particular week – week zero was when I started.)  The shape of the curve is pretty interesting in itself, and I’ll come back to that point in a later post. Other details: I am 5’9” (178 cm) tall, which implies a Body Mass Index of about 23 at my current weight. This is well within the region considered healthy. I have a 32” waist (down from 40”), meaning a waist-height ratio between 0.4 and 0.5, again generally considered to be in the healthy region.  All of my vital stats (blood pressure, trigliceride levels, cholesterol levels, blood sugar, and heart rate) improved when I lost this weight, so I think I can safely say that I am in better health now than when I started.

Before I begin discussing weight loss methods, there are two points I want to make:

  • If you decide to lose weight, please talk to your doctor first and discuss different options, how fast you should lose weight, and what your goal weight should be. The methods I describe here should work for anyone in reasonable health to begin with, but are not good for everyone.
  • There are many fad diets and exercise plans out there. What I am describing are techniques for losing weight rather than a detailed specific plan. In particular, for reasons I will discuss in a later post, I am not going to specify particular foods one should or shouldn’t eat to lose weight.

These techniques are straightforward. This doesn’t mean they are easy! I don’t know why, but there are very few things worth doing in this world which are easy. They are also discussed in varying different forms in other places on the web and elsewhere. What I am discussing uses the same basic underlying ideas as other plans which range from very complicated (The Hacker’s Diet) to the very simple (such as a plan discussed by Tom Murphy). It is also similar to commercial plans such as WeightWatchers. Any and all of these work if you follow them, so don’t just read what I’m saying. In point of fact, the approach I took when I wanted to lose weight was to gather up as much information as possible from different sources and evaluate them. I considered WeightWatchers, but because I am a poor professor and a cheap bastard, I decided to formulate my own plan. (One later post will include instructions on how to effectively exercise at home without paying any money for equipment or a gym membership.)

So: here is the big plan for losing weight. It involves three parts, each equally important:

  1. Exercise more than you currently do;
  2. Eat less than you currently do;
  3. Weigh yourself every day and record the weight, but make plans based on weekly averages of your weight.

Here’s an easy way to remember this: sweat, starve and scribble. (Don’t really starve yourself, of course…) A few points regarding this:

  • Some people are going to read this and think,”well, duh — this is obvious!” Well, maybe, but there are a lot of fad diets or exercise routines out there which attempt to circumvent these rules. IMHO, they may work for the short term, but are probably unsustainable. What I am writing about is sustainable, and based on real science, at least as best I understand it.
  • The type of exercise doesn’t matter much as long as it is hard, aerobic exercise. I started out doing 45 minutes on an exercise bike, three times per week, which seemed like a reasonable way for me to begin. I’ve ramped up the duration, frequency and intensity since then, but again I will discuss this in a later post. I’ve also added other aerobic exercises which don’t require a machine (again, to be discussed in a later post.) Pushups, situps and other types of conditioning exercises won’t work for losing weight, although they’re good for other things.
  • The eating less part is more difficult, as it is pretty hard to count calories accurately. As a rule of thumb, try to go to bed slightly hungry (Not starving! Not with a belly crying out to be filled!) Slightly hungry seems to be a good measure for most people if you want to lose weight.
  • Keeping accurate records of your weight is as important as the other two aspects of the plan! Try to use the same scale each time at the same time of day (just after waking for me), and if possible, weigh yourself nude. (Clothing adds anywhere from about 1 to 5 pounds to your weight.) Some people use their computers or apps for their smartphones; I write my weight in a Monthly Planner book, but use an Excel spreadsheet program to calculate averages.
  • Plan for the long term. Don’t try to lose too much weight too quickly. My doctor and I decided that losing between half a pound to a pound per week was healthy, so that’s what I attempted (and largely succeeded at.) Again, discuss this with a doctor before beginning!

In the next several posts I am going to go into detail on how to do this. The next post will introduce the “master equation” for dieting, and discuss its implications.


Why send a person to do a robot’s job?


A few more thoughts on the Rosetta project:  no human being has ever been that far from the Earth, The farthest people have ever been was to the moon, about 234,000 miles away from the center of the Earth, or less than 1/1,000 of the distance which the Rosetta Mission is right now. At the moment, we only send people as far as International Space Station, which is about as far above the surface of the Earth as Washington is from New York.

Sending robot probes out has many advantages over sending people: you don’t have to include life support, you don’t have to get them back, you can build them for a tiny fraction of the cost of a manned mission.  It’s cheaper and safer, and you can send them on ten-year missions without having to worry about boredom or psychological problems.

So:  why didn’t the scientists in the movie Interstellar send out robot probes to explore beyond the wormhole?  Another advantage was made amply clear as the plot advanced: any given robot in that movie was much smarter than all of people in it.

An unrelated thought inspired by my colleague Kevin Emerson:  in the latest episode of the Flash, he grabs Iris and brings her up to the roof.  I won’t do the math again, but the acceleration should clearly kill her: he’d have to accelerate to his high speeds and decelerate from them over a distance comparable to several football fields for her to be safe when he grabs her.  (It strikes me that I’m blogging about the Flash just as much as she does in-show…  I’ll try to find a new topic next time, but the show just keeps on giving.)

Stingless “Scorpion”


I watched the second episode of the new CBS TV show “Scorpion” last night, and was, to put it mildly, underwhelmed. (This isn’t exactly a science fiction topic, and it isn’t exactly a critique of the science in the show, but what the hey… Call it part of the “and more” byline.) I’m not going to discuss the problems which the show’s credibility has had, or the ridiculousness of the plot of episode 1, or the hubris associated with naming the central character after one of the executive producers. There’s enough to bug me about the show without worrying about any of that. (Pun intended, even though I know scorpions are arachnids.)

The show’s premise is that a team of four geniuses go around solving crises relayed to them by their Homeland Security mentor. I can’t remember the names of the characters, nor do I care enough to look them up, so I’ll refer to them by the traits which (in lieu of personality) are used to define them: there is the handsome one (call him “Face”) who is the computer specialist, who supposedly hacked into NASA computers at age 13 and has an IQ of 197; the awkward, shy, mathematically gifted one who has an eidetic memory and counts real well; the token female nerd, who is mechanically gifted; and the con man/psychologist (who, given his personality, no one in their right mind would trust for even an instant). There is also the waitress who is the token normal person, who is Face’s love interest-to-be, and her supposed genius son, who is mostly silent and exists for Face to bond with so he can score points with Mom.

As someone who is not a genius but who has some nerd cred anyhow, the show rings entirely false. The producers rang up central casting and asked for four genius stereotypes without giving much thought to what genius (or, frankly any sort of technical or scientific ability) is really like. The important point when discussing genius is to remember Edison’s adage that it is 1% inspiration and 99% perspiration. For example, in the first episode, it is casually revealed that sonny-boy is playing chess with Math Nerd and beating him, despite M-N being a grandmaster. (They’re playing chess with various condiment bottles on a diner counter without a board.) Anyone who knows anything about serious chess playing realizes that this is ridiculous. Chess grandmasters aren’t born – they’re made. They all spend ridiculous amounts of time studying chess openings, endgames, chess strategy and the like. Bobby Fischer is kind of the ur-example of this: he had enormous innate talent, yes, but also spent most of his free time improving it by playing other talented people and studying, studying, studying! The idea that a random child, no matter how intrinsicly gifted, will beat a grandmaster just with pure talent, is pretty ridiculous. (The idea that M-N is a grandmaster is also pretty hard to believe, as he doesn’t seem to be spending most of his time studying chess either, but we’ll let that pass.)

Then, of course, there is the issue of IQ itself. In the opening credits, Face states that he has an IQ of 197, whereas Einstein’s was 160-something. I’m not sure Einstein ever had his IQ measured, but that’s beside the point. IQ isn’t a measure of intrinsic intelligence (whatver that is anyhow.) This is the MENSA fallacy, that a) the ability to score well on an IQ test means that one is intelligent, and b) that pure intelligence means anything anyhow. Back to Edison again: great people are defined by their actions, not by their potential. What Einstein did with his “meager” IQ was much more important than whatever Face is doing with his humungous one.

There are other bothersome things, of course. M-N supposedly has a photographic memory, and is able to memorize several pages of people taking part in a drug trial under very stressful circumstances. Photographic memory doesn’t really work this way: it takes time to memorize things like this, and most people who can do this have trained their mind using “memory palace” techniques. (These have been showcased on TV recently, in BBC’s Sherlock.) Once again, perspiration rather than innate ability is mostly how this works. The team caught their criminal by blatantly illegal methods, searching an office without a warrant, jurisdiction or vestige of probable cause. Finally, as a young boy, Face is shown in his classroom disputing his teacher over the divisibility by four of several numbers on the board. He (the kid) maintains that all numbers are divisible by four if you include remainders, and that the teacher simply hasn’t defined his terms well enough. As a teacher, I cringed when I saw that: the kid is merely being a know-it-all jerk. The math teacher is clearly using the expression “divisible by four” as a shorthand of saying “divisible by four with remainder zero”: this is one of the standard accepted uses of the term, and young Face is clearly wrong. (And where did his Irish accent go as an adult?) I’m not saying he should get his fingers hit with a ruler for saying this, but he’s not exactly a genius for trying to score a shallow and incorrect point off an authority figure.

I could go on, but I think I’ve made my point. The writers don’t have much idea of how very bright people really interact with the world or with one another. Or of what genius really means. (Or trigonometry. Or legal procedure. Or…) I’ve met geniuses, and you, Face, are no genius.


Matters of Gravity


I was just interviewed on the “Jason Rantz” show on KIRO radio (a Seattle station.)  The interview was much more relaxed than most of them have been – Jason was interested in what I was saying, and seemed a lot more relaxed than most of the other radio talk show hosts I’ve been interviewed by.  The interview will be about ten minutes long, although we talked for about twice as long.  Once there’s a podcast I’ll put a link up for it.

We mostly talked about movies, including the recent movie Gravity.  One thing in the discussion which got me thinking was that Jason was surprised that the chain reaction of satellite destruction which drives the main plot is a real idea.  This got me thinking – most people don’t know about it, so it’s a good idea for a blog.  Three points before I start:

1)    There are spoilers for the movie in this blog, so readers beware!

2)    Neal Degrasse Tyson mentioned this in a tweet about the movie a while ago but I want to treat this in more depth; and

3)    I did like the movie despite what I say below.

As far as the third point goes, I like movies even if they get the science wrong.  I repeat the main point of this blog: thinking about the science adds depth to the movies and enjoyment of them, not detract, at least as far as I’m concerned.  If I had to grade the space science in Gravity, I’d probably give it a B-, which is pretty good as far as movies go.  Here, of course, the gold standard for accuracy in depictions of space travel is 2001: A Space Odyssey, made in 1968.  The depictions of how objects move in space are both highly accurate and beautifully depicted, as one would expect from the pairing of Stanley Kubrick and Arthur C. Clarke.  (If you watch the movie, turn it off once you get to the final 20 minutes and imagine your own ending.)

Gravity wasn’t as good, but it did a better job than a lot of others.  There were no banked turns in space, for example.  I found the final scene hard to believe, and there were a few other points which bothered me.  For example, the parachute seemed to billow when Sandra Bullock was maneuvering the Russian space capsule, which wouldn’t happen in the absence of air.  Also, I think (from a short stint at NASA where I consulted on a project related to it) that fires don’t burn the way they were depicted in the capsule scene.  Fires get fresh oxygen through convection, which doesn’t happen in microgravity situations like on the shuttle or in any free-fall orbit. There’s a Youtube video  which shows how a candle flame extinguishes itself in free fall when dropped down a long shaft – this simulates the same physics as a spacecraft in orbit around a planet.  (The theory behind this is originally due to Albert Einstein!)  However, the movie overall was entertaining and pretty intelligent, even if I was able to guess who was going to die and in which order within five minutes.  (The attractive heroine survives, the senior astronaut played by the big-time movie star dies heroically midway through the movie, and the hapless “red shirt” is killed off asap.  Told you there were spoilers!)

The incident driving the plot of the movie is a chain reaction of satellite destruction.  The Russians deliberately destroy an old satellite (presumably so that it won’t endanger other satellites in similar orbits), but this leads to the debris from that satellite destroying others, leading to that debris destroying others, etc.  That is, the Russians create the very situation they were trying to avoid – the planned destruction of one satellite leading to the unplanned destruction of many others.  The consequences include the downing of GPS navigation on Earth and space debris at high velocities coming in to destroy the shuttle the characters are working from.

OK:  two points.  One, the chain reaction is in fact a real concern.  This is known as the “Kessler syndrome” after the space scientist, Donald Kessler, who first predicted it in 1978.  Two, if it does happen, it will not be anything like in the movie.

Issue one:  Low-Earth orbit (LEO), some 160 to 2,000 kilometers above the planet, is filled with debris from older missions.  According to the Union of Concerned Scientists, about half of the thousand or more currently active satellites are in LEO, and there are tens of  thousands of centimeter size or larger fragments of debris from launches or older, inactive satellites.  The potential is that if there is enough material populating these orbits, chain reactions like the one in the movie may start.  Space is big – really big – but there’s a lot of stuff in that particular region of space.  Given enough time, collisions happen.  The collisions take place at very high speed – collisions will take place at relative speeds of something like the orbital speed at that altitude, or 15,000 miles per hour.  It’ll be higher or lower depending on the exact orbital parameters, but whatever it is will be high enough to completely destroy the two colliding objects.

The tricky part is that anything placed into orbit tends to stay there.  It’s not like on Earth, where gravity will cause the debris to fall out of the sky – when two planes collide, the little bits from the collision don’t race off at high speeds to become hazards to other planes for years or centuries to come.  In space, even in a low-Earth orbit, there is barely any atmosphere to cause friction to make the debris fall back down into the atmosphere and burn up there.  The idea behind the Kessler syndrome is that eventually there will be enough junk that the detritus caused by one collision will lead to more, with an ever expanding circle of destruction which will eventually take out most of the satellites at that particular orbital radius.   The mathematics is almost exactly the same as a chain reaction in an above-critical nuclear bomb core:  in that, one neutron’s fission creates more than one neutron, which leads to more fission processes: one leads to two, two create four, four, eight, for example, and eventually there are enough to destroy a city.  It’s harder to do the calculation for space debris, but according to a 2010 paper by Donald Kessler, several regions above 500 km have the potential for a runaway chain reaction.

So that part of the movie reflects real concerns.  However, for dramatic effect, the movie showed the debris ripping through the shuttle, causing mayhem, killing off one of the astronauts, and playing havoc with Earth’s communications satellites and GPS in very short order.  Not going to happen.

First off, most of the satellites are in much higher orbits than LEO.  Much, much higher.  Geosynchronous satellites for satellite TV and communications are at about 35,000 km up.  The GPS satellites, supposedly taken out by the cascade, are up at about 20,000 km.  It takes a whole lot of energy to move a particle from LEO into one of those orbits – most of the particles created by the cascade won’t have enough energy, and the laws of probability dicate that a hit by the small number of the ones which have enough energy is enormously improbable.  So our communications networks are safe.

The bigger problem with the movie is that this is a very slow process.  We think of chain reactions as being fast because of devices like the atomic bomb.  However, space is so sparcely populated that even in a chain reaction situation, the average time between collisions will be months, maybe even years.  The point of the Kessler syndrome isn’t that it’s fast but that one collision will lead to more than one collision afterwards.  The chain reaction wouldn’t have posed a threat to the astronauts up there unless they got incredibly unlucky.  There also wouldn’t have been thousands of these particles just happening to be going in the same direction – the collision would have led to them being spread out in all directions.  (This is not quite true, as the particles would tend to be travelling along the trajectory of the center of mass of the two colliding particles, but it’s close enough.)

I repeat: Gravity was a fun movie.  It’s a good example of the impersonal isolated man or woman against nature film.  If I wasn’t completely bowled over by it, it still made an impact (if you’ll pardon the pun.)


Thoughts on Project Orion


I did an interview a few days ago with Michio Kaku on his radio show “Science Fantastic”. It’ll be broadcast sometime this weekend.   It was a strange conversation, at least from my point of view.  I’d never given a long radio interview before and the whole thing seemed rushed and stressful.  Kaku wanted to emphasize the weirder and more outré aspectes of science fiction; fitting, perhaps, from the program title, but most good science fiction rests on a firm basis of known science.

One good thing did come from the program.  Kaku and I were discussing starships.  I, perhaps unwisely, told him that my personal favorite idea for a starship was Project Orion, the truly audacious suggestion that we could propel spacecraft using nuclear bombs as propellants.   Dr. Kaku raised a very good objection to this, which is what I want to write about here. (As an aside, there is a new NASA program to develop a crewed rocket propelled by conventional engines called “Orion” – don’t get the two confused!)

Before I go on with this topic, let’s discuss nuclear rockets in general:  spaceflight enthusiasts have always wanted rocket fuels which have higher energy density than chemical propellants.  This is because it takes a lot of energy to get a rocket moving at the high speeds it needs (25,000 mph or more) to reach destinations like the moon or farther.  Chemical propellants like combinations of liquid hydrogen and oxygen work, but just barely. From the 1950’s through the 1970’s nuclear energy was seen as a viable fuel alternative – the Nobel laureate physicist Richard Feynman may have been the first person to realize this, but a number of science fiction writers including Robert Heinlein also came to this conclusion.

The problem is that harnessing the large amounts of energy, millions of times higher per kilogram than chemical energy, is difficult.  The simplest way to do it is to take a gas (usually hydrogen) and heat it to very high temperatures and pressures using the reactor.  The gas escapes through a nozzle and the spaceship is pushed forward.  However, materials science limits this.  If the temperature gets too high, you start melting the nuclear fuel itself.  This limits the fuel ejection speed to about twice what chemical propellants can do.

Project Orion wanted to get around this by building a big spaceship with a “pusher plate” separating the crew from the engines.  Nuclear bombs would be ejected behind the ship and blown up.  The resulting explosion propelled the ship forward.  It seems daft, but a team led by two very good scientists, Ted Taylor and Freeman Dyson, worked out many of the practical details.  The effective fuel ejection speeds which you could get were five or six times, maybe even more, than you could get from conventional chemical fuels.  It also seems that you could keep the crew safe from radiation, and keep the explosions from destroying the ship.

You can’t build a spacecraft based on this principle today.  Trying to make it work would probably violate the 1963 treaty banning above-ground nuclear testing.  Dr. Kaku made the very good point that Ted Taylor himself stopped working on bomb design because the small hydrogen bombs which the ship would use would make very good terrorist weapons.  This caused me to stop and think things over.

I’m of two minds about Orion.  On the one hand, I am very worried about the prospects of nuclear terrorism.  I grew up in the DC suburbs, and was terrified as a teenager by the prospect of nuclear war with the Soviet Union.  Today isn’t much less scary, as smaller nations have gotten the bomb, and mounting pressures due to the world economy and the environment seem to make war and terrorist acts more and more likely.  Developing small nuclear weapons seems foolish in this light.

On the other hand, the Orion idea is the only feasible method using current technology to move a payload at very high speeds – perhaps at speeds of up to a few percent of the speed of light.  People have discussed other methods of powering starships, for example fusion reactors and matter-antimatter annihilation. (Yes, people have studied this seriously – it’s not just from Star Trek!)  However, neither could be done now: antimatter has an equivalent cost of  several trillion dollars a pound, and can only be produced in microscopic quantities today.  No one knows how to make a fusion reactor on Earth, let alone put one in a spacecraft, although recent developments may be promising.

If humanity wanted to send a space probe to the Alpha Centauri system, four light years away, the only conceivable means to do it using today’s technology would be something like Orion.  It wouldn’t be easy or cheap, and it wouldn’t happen any time soon.  It might not be possible, but this method would be the one with the best chance of success.  It would also take decades for the spacecraft to reach the system; any government funding a project like this would need to be farsighted in a way which most aren’t today.  Whether it would be worth doing is something which our society, or perhaps our society fifty years from now, would have to decide for itself.

The issue here is that any propulsion system for any spacecraft is a weapon in disguise.  Conventional rockets are made from highly explosive materials, as we saw in the Challenger disaster.  The higher the energy density, the worse it gets: in the extreme case, if you somehow could make a rocket propelled by antimatter, simply turning the engine on too close to Earth could sterilize it!   You can’t deweaponize a starship.

The best science fiction investigates the problems created or issues raised by new discoveries or new technologies.  I’ve never read a story or seen a movie or TV show which really looks at the societal problems which would be caused by the development of the Orion concept into a truly workable spacecraft.  Perhaps it’s time to write one.

PS  If you like what I write, or even don’t, please leave a comment!