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Gary 7

Well, I would agree in principle about this being a form of “soundwave.”

My major question is “varying density of what?” In the analogy about cars, the wave propagates without any direct help from Newton’s laws (which are valid in this regime) because people are judging and mediating the motion of the particles (cars) without a direct mechanical interaction with one another. If a traffic jam wave were the same as a soundwave or water wave, every car would need to be crashed into by the car behind it and in turn crash into the car ahead with no net change in the average position of the car. As such, traffic jam waves proceed with no contact force between the cars. Stars are entering and leaving these structures (mostly) without colliding with one another, which means that this wave is not dependent on mechanical contact in the manner of a soundwave or water wave much the way a traffic jam wave is not dependent on mechanical contact. If these stars were colliding with something, I think we would know it. As such, this is not a transverse wave in water, nor a longitudinal wave in air. The wave is not itself a medium of stars, much like a traffic jam is a wave of human judgement rather than of colliding cars. What is the “varying density” these objects are traveling through? Can is be spacetime? Is there any way to account for this sort of structure without directly invoking general relativity?

I’m not disagreeing with you:-) I am simply focusing my question: can we consider such a structure to be evidence of gravity waves? Is my understanding shortsighted in some manner and requiring a revision of logic?

Simply a gorgious image. I have printed the 8 meg. version and I’m framing it.

Traffic jams often propagate against the flow of traffic, as evidenced on I495 around DC: often you’ll come upon the scene of an earlier accident five miles after the jam you were in breaks up. Sometimes (as other commenters evidence) they actually do stand still and sometimes they move forwards. I’ll revise my earlier statement a little to form a new conjecture: the motion of the density wave is related to the cause — congestion behaves differently from accident behaves differently from fixed road conditions.

You can also see the same phenomenon in water waves. Individual water molecules a ways offshore don’t move much. Try putting a beach ball beyond the breakpoint and you’ll see it just bob up and down, even as waves roll past it. The water itself stays put, and the wave is made up of different molecules every moment until it finally breaks.

So we come back to spirals. Okay I was wrong before, but now there’s the question: how do the arms move, if at all? And what can that tell us about how the spiral formed?

Not to steal Dr. Plait’s line, but I think it’s incredibly cool that we can even know enough to ask that question, and that we might have a shot at answering it.

I’m reading through the movie reviews, and I got to Superman Returns. BA, please say you’ve seen superdickery.com! The movie just drove the point home further! Superman is a Dick!

*goes to dink around Space.com more*

The creationscience.com site is full of lies. Wow. I mean, wow. That astronomy stuff is blatantly wrong, and almost all of it is explainable easily enough. That kind of willful ignorance/lying makes me pretty angry.

Josie: well, wow (but this time in a good way!). Funny- writing these posts makes me want to learn more. Nothing probes your own blank gaps in knowledge like trying to explain something.

I’m actually looking about going back to add a degree now. Not so much because I want to work in the field, but because I want to know. Anyone else get hungry like this, reading the BA posts?

There’s something elegant about the idea of something mundane like traffic jams on Earth applying itself in the same way to something as amazing as this picture.

Tanks.

GAry 7