www.BrettDaniel.com

The Halting Problem on Twitter:

Write H(P): true if any program P halts; false otherwise. Write C(P) that halts iff H(P) is false. C(C) halts? Contradiction. Thus, no H(P).

...or as written by Dr. Seuss:

No program can say what another will do.

Now, I won't just assert that, I'll prove it to you:

I will prove that although you might work til you drop,

you can't predict whether a program will stop.

Today I got another PET scan to assess the effectiveness of the previous two chemotherapy treatments. The results look reassuring. I have not yet heard the official word from the radiologist, but it is obvious even to my unprofessional eye that chemo has had an effect. The major tumor in my right lung is no longer visible, and the other smaller tumors have decreased in brightness.

The pictures below show the scans from the initial diagnosis on the left alongside today's scans on the right.

These results mean that I will likely stay with the same set of chemo drugs for one or two more rounds. After that, I will probably get another scan, then switch to some alternate drugs for as long as it takes for the tumors to disappear.

On a private mailing list populated by my computer science friends, Sam asked the following question:

We're going to define the "future" as the first time a real space pirate hijacks a spaceship in space. The question is, how far away are we from the future?

A rousing and deep discussion ensued. Guesses ranged from 50 to 500 years, with an average around 200.

I think we are already in the future and better off not having to worry about space piracy, but that's a separate discussion.

The following is my slightly edited response to a comment about space pirates launching ships from the surface of the Earth (or another planet).

Let's address just the issue of getting into space. There are four ways to escape a planetary gravity well: chemical fuels, atomic energy, a space elevator, and some unknown future technology.

I always find it comical when science fiction writers send a small handful of people into space on top of a rocket. With the earth's dwindling reserves of fossil fuels and the rising environmental costs of burning them, I think one would agree that chemically-powered space travel will be limited in the future and certainly out of the economic reach of a small band of space pirates.

Since the atomic golden age of the 1950s and 60s, we have learned that atomic energy is too dangerous for individual use due to the danger of accidents and atomic weapons. (Aside: Find one of Eisenhower's "civilian atomic energy" videos online. They're hilarious.) I don't see this danger dwindling except by the invention of force shields or other defensive systems. Atomic energy also has the same fuel discovery and transportation issues as chemical rockets.

The deeper problem with both chemical rockets and atomic energy is that the ship must lift both its own weight and the weight of its fuel. This inefficiency makes a space elevator a much more believable method of moving cargo into space. In that case, the energy source remains stationary and must lift only the weight of the payload.

Thus, a space elevator removes the need for surface-to-space ships that space pirates could board and loot. Criminals could certainly infiltrate the elevator "cars" and steal cargo, but as I have explained above, it is unlikely they could get the cargo into space without their own elevator. Furthermore, such a crime stretches the common definition of "piracy" in which criminals hijack an independent vessel in transit.

It is likely that future technologies will provide alternate energy sources or completely new ways of traveling from a planet's surface into space. However, there will always be a lower bound to how much energy is required to lift a certain amount of matter out of a planetary gravity well in a particular amount of time. This is a substantial amount of energy no matter where it comes from.

For these reasons, I don't expect that space pirates will launch from the ground to intercept interplanetary cargo shipments. Instead, if interplanetary commerce ever becomes widespread enough to support piracy, I would expect pirates to stay in space and smuggle stolen cargo through a space elevator or other public transport system.

We have deep discussions like this all the time.

While browsing Flickr, I came across some fascinating photos of Champaign and Urbana in 1975. Several images have then-and-now comparisons in the comments.

The following are my favorites:

• Downtown Champaign – The streets look so open without warning signs, stop lights, or excessive striping.
• Urbana Cinema – Now an art gallery, though I like that the owners have retained the classic sign.
• Kirby's Firestone – Very little change in 33 years.
• The immortal caution sawhorse – The restaurant is gone, but the caution sawhorse remains.
• Walnut Street Tea Company – I buy most of my caffeinated beverages from this store. On one visit, I mentioned that I had found this image from 1975. The proprietor told me she had bought the suite in the early 1980s.

A lot has happened since I last wrote about my most recent cancer diagnosis. I won't go into the grisly details, but a complex sequence of events led to more leg surgery. It was necessary to replace my entire right femur from the knee to the hip. Over half of my right leg is metal now! While lying in the staging room before surgery, I told my surgeon that I hoped this was the last part he'd have to take out of me.

They successfully removed the tumor in my leg. Fortunately, the bony portion was almost completely dead after just one chemo treatment. That makes me confident that the other tumors in my lungs are similarly affected.

Recovery has been difficult but remarkably quick. I am regaining motion and strength every day, can already put my full weight on the leg, and am getting around well with crutches. The downside of a quick recovery is that the doctors were eager to start chemo again. I started the second round of high-dose ifosfamide last week. It hit me pretty hard—I slept through most of the week—but I'm home now and feeling pretty good.