December 2, 2004

I've just been victim of a theft. Somebody broke into my car and stole a few euro coins (park meter fodder) and a digital camera that I left carelessly in the glove compartment (top-of-the-line five years ago, a dinosaur today).

The lock on the driver's door has been twisted with a chisel or a screwdriver.

This has been my first theft. The thing that amazes me most is my reaction, of utter indifference: "Oh, somebody stole something from my car". No emotional strings attached - the friend that was with me was more upset than I was.

Considering that I've heard that feelings of violation are not uncommon after such an experience, I can offer the following explanations:

1. I am about to achieve Nirvana, a state where I look down to my mortal belongings as entirely worthless.

2. Money falls out of my ass on daily basis, so the loss of a camera is a small matter.

3. My brain is wired in a strange way, and somebody forgot to put emotions inside along with the rest.

Explanation n. 1 is tempting but unlikely; n. 2 is not worth considering; n. 3 is rather disturbing, therefore I suspect that there is some truth in it.

Right wing morality has very little to do with the ministry of the historical person Jesus of Nazerath. And a lot of Christians are getting pretty tired of people using Jesus's good name to promote hatred, cuts in the income tax, the war in Iraq, and a whole lot of other things besides feeding the hungry, clothing the naked, and doing unto others and we would have done unto ourselves.

My church, the United Church of Christ is one church that is getting sick, and we've decided to do something about it. The debut 30-second commercial features two muscle-bound "bouncers" standing guard outside a symbolic, picturesque church and selecting just who gets to attend Sunday services. Written text interrupts the scene, announcing, "Jesus didn't turn people away. Neither do we." A narrator then proclaims the United Church of Christ's commitment to Jesus' extravagant welcome: "No matter who you are, or where you are on life's journey, you are welcome here."

Apparently this was too much for some networks. According to a written explanation from CBS, the United Church of Christ is being denied network access because its ad implies acceptance of gay and lesbian couples -- among other minority constituencies -- and is, therefore, too "controversial."

NBC has rejected the spot with less comment, but similar reasons

"It's ironic that after a political season awash in commercials based on fear and deception by both parties seen on all the major networks, an ad with a message of welcome and inclusion would be deemed too controversial," says the Rev. John H. Thomas, the UCC's general minister and president. "What's going on here?"

Folks, we can't go on letting people like Jerry Falwell and Ralph Reed define what it means to be a person of faith. I don't want to see networks that aired such blatant liars as the Swift Vote Veterans censor a church for saying everyone is welcome.

The UCC has an online petition you can sign. Please do. It's at:

http://www.ucctakeaction.org/action/

You can also see the ads for yourself and decide at: http://www.stillspeaking.com/

source: official UCC press release

"Oh, there's so much I don't know about astrophysics. I wish I'd read that book by that wheelchair guy."

-- Homer Simpson

Last Tuesday I went to a talk on numerical general relativity. Specifically, it dealt mostly with simulations of two black holes colliding to determine what kinds of gravitational waves are emitted. One of the challenges writing computer programs to do GR is that it's very hard to check them to make sure they're giving sensible answers. Usually, if you're writing a physics simulation, once you debug your code you do several "toy problems", ones you can work out by hand, in order to make sure your program gets the right answer. This gives you some confidence that you haven't made any major errors. The other check that's often done is to solve a problem that someone else has already solved with a different technique (one that the community is pretty confident is correct). The problem is that GR is just very difficult, involving in general 16 coupled, nonlinear, partial differential equations. There are very few problems you can solve by hand, and most of those are of trivial complexity when compared to the problems the code is supposed to solve. Furthermore, the field is young enough that there just aren't that many trusted results to compare against.

At the end of this talk, one of the professors asked (to the best of my recollection), "Couldn't you run the simulation and get the gravitational waves, then start run the simulation backward, starting with the end state black hole and sending the gravitational waves back in? Since GR is time reversal invariant, you should get back the two original black holes at the end of that that you had at the beginning." The speaker said something to the effect of, "Yes, people have talked about doing that off and on for a long time. To the best of my knowledge no one has done it yet," and that was it. It was an unsatisfying answer, since you'd like to know why no one has tried it or if it will be tried in the future.

After the talk, however, this exchange started to bother me. Instead of talking about two black holes colliding, think about one star undergoing gravitational collapse to form a black hole. The same logic would seem to imply that you could take whatever gravitational waves were produced by the collapse and feed them back in, reversing the collapse process and resulting with the star in the state just prior to collapse. That certainly doesn't seem right. Now certainly this ignores the fact that once you're dealing with a star it's a complex, macroscopic object that's properly treated thermodynamically, but still even if you assume your "star" is a sphere made up of an ideal fluid, such a reversal shouldn't be possible. Indeed, some checking in the black bible reminded me that there is a theorem that the surface area of the event horizon of a black hole cannot decrease in classical GR¹. This fact is a vital part of the reason one may equate event horizon surface area to entropy in black hole thermodynamics. So in purely classical GR, such a reversal is not possible. That agrees with my intuition, since an event horizon wouldn't be very meaningful if you could make it go away, and this would allow you to recover the information that went inside.

The question that's been bugging me since then is, "Where is the flaw in the argument?" I can only see two possible flaws: 1) time reversal invariance in GR has an unintuitive meaning that does not imply the sort of "unformation" of the black hole I described above, or 2) GR is not time reversal invariant. The reason I considered 1) is that in GR there are many different time coordinates for the different coordinate systems of different observers, so there's a question of which time you reverse. Do you reverse the coordinate time or proper time? Upon further thought, I think the answer to that question is that it doesn't matter. Since the proper time along any timelike geodesic is monotonically increasing with coordinate time, I believe that reversing time in any valid, physical coordinates is equivalent to reversing time in any other set of coordinates. I'm not sure, though, that this is really what it means to do time reversal in GR. The difficulty is that in GR space-time itself is dynamical, so it seems one is asking a rather strange question like, "Is the behavior of time the same irrespective of time reversal?"

The question of time reversal invariance is always the question of whether you can take a solution of the theory, reverse its time dependence, and have it still be a solution to the theory. So, without getting two bogged down in what the question means, it seems like the simplest way to look at time reversal in GR would be to ask if a Einstein tensor and stress-energy tensor are solutions to Einstein's equation and you reverse the coordinate time, do they still solve Einstein's equation? The answer: a resounding "I don't know"...yet. The problem is that while the time reversal properties of the stress-energy tensor and metric seem pretty simple, deriving the time reversal properties of the Einstein tensor is more involved. In the end, I suspect the answer is that GR is not in general time reversal invariant. I'm sure someone already knows the answer to this, but I haven't run across it yet. Then again, I don't study GR; this question just piqued my interest.

I'm not sure now why I decided this would make a good daylog. Looking at what I've written, I'm not sure that it will be accessible or interesting to anyone. I guess we'll see. :-) Hopefully, I'll find the answer soon and post an update.

[Addendum: There is now an update.]

1. This is violated by black hole evaporation, but that is due to Hawking radiation, which comes from semiclassical physics.

I’m not good at giving speeches, never have been and probably never will be. Maybe it’s because I don’t like the limelight and prefer to remain in the shadows. Maybe it’s because I just don’t have that much to say or that I don’t like the sound of my own voice…

A very dear friend of mine is packing his bags and leaving the friendly confines of Ohio for the sunny skies of Arizona in the next week or so. He had told me about his plans a little over a year ago and it was just one of those thoughts that you put on the back burner until the days grow short and the flame gets hotter. Time is funny that way. It’s been described in more ways than I could possibly count and for me to try and do it again in a way that pertains to me would do it an injustice. Suffice to say that in a world of plenty, there’s just not enough of it.

This Saturday, there’s a party scheduled at our local watering hole to bid him and his wife farewell and to wish them luck on their journey. The kegs will be flowing freely and I’m sure there will be some tears scattered amongst the laughter. They’ll be stories to be told and the raucous atmosphere I’m anticipating will be fun I’m sure. I just can’t see it taking the place of the quiet time when only three or four of us hunched over our drinks and settled our worlds with each other and the bartender. Most of us have little or no family in town and we’ve kind of formed one of our own. It ain’t perfect but it’s all we got.

Anyways, I’m sure at some point in the proceedings there’s gonna be some speeches made. I’ll probably make one up off the top of my head but when all is quiet and we have a moment to ourselves, I’m gonna hand him a note. Here’s what it’s gonna say…

With apologies in advance to Robert Frost….

Over the past couple of days, I’ve pondered long and hard into the night over what to get you as a sort of gift that would be best suited to serve as going away present. Would it be something to put on your mantle or in your book case? Would it be some kind of keepsake that will serve to remind you of the time spent in Ohio or some type of gag gift to mark your arrival Arizona? Would it be an article or trinket that you could carry with you and maybe look back upon when the nights grow long and, at least for the time being, you feel as if you’re surrounded by strangers? Do we get together and share one last meal and tell our stories to each other one last time? Would we take any comfort in that?

No, I decide to leave you with a piece of where our friendship began. With words that are written from the heart and from the soul. Where the kindness doesn’t fade and the memories are kept locked away much like you would keep money in the bank, to be withdrawn on an as needed basis.

If it were up to me, I think the word friendship is tossed around too loosely these days and I don’t use the word too lightly. Many are made too quickly and broken too easily. A really good friendship takes the effort of time and in our rush to make it through the world, I think sometimes that sentiment is forgotten. We have shared time my friend.

When I think of your leaving I sometimes liken it to a chapter in book, with each new one telling another story or building upon the old. The problem with that little analogy, like it or not, is that books come to end whereas friendships, if they are true, do not.

No. I’d more liken a friendship to the twists and turns that the road takes. Unlike Mr. Frost’s road that diverges into two separate paths, I feel compelled to say that while our roads are getting ready to diverge, at some point, they will once again converge. Of this, I am sure. Whether the convergence takes place at another time or some other point doesn’t really matter. Rest assured, it will happen. We’ve shared too much along the way for it not to.

So I leave you with this my friend, we’ve shared our good times and we’ve shared our bad. We’ve tilted many a glass and sat at many at table. We’ve whiled away the hours, more than I can count and although I wish there were more to be had, our time has come. We’ve argued our differences and shared our commonalities. Those two things together should make us stronger. So, in the future, if, in the back of your head, you think you hear the clink of glasses being raised and it whispers in your ear, know that it is me raising a toast and recalling with sincere fondness the time that we’ve been lucky enough to spend together and I shall do the same. I think we’re both better off that way. We each in our own way will strive for greatness for it is on our nature to do so and there is a certain honor in that. Should we fail in our attempt, hopefully we can take some solace in knowing that at least we tried. Godspeed to you and yours as you embark on a new journey. One that I hope takes you far beyond anything you ever expected. Simply, your friend, your brother, Bob