24 January 2009: Chilly Thoughts

Workout notes 10 mile run on the treadmill: 1:37:55: 57:28 (6 miles), 1:52 water break, 38:34 last 4 miles. Varied the incline.

Then yoga: I lead the class. There were some groans.

Science I was pointed to these articles by 3-quarks daily.

Here is an interview with an applied mathematician; mostly it is about his books and what he reads.

Here is an article about naked singularities in cosmology. Very roughly speaking, naked singularities are black-hole like objects that don’t have an event horizon; you can exchange information with the center.

Modern science has introduced the world to plenty of strange ideas, but surely one of the strangest is the fate of a massive star that has reached the end of its life. Having exhausted the fuel that sustained it for millions of years, the star is no longer able to hold itself up under its own weight, and it starts collapsing catastrophically. Modest stars like the sun also collapse, but they stabilize again at a smaller size. Whereas if a star is massive enough, its gravity overwhelms all the forces that might halt the collapse. From a size of millions of kilometers across, the star crumples to a pinprick smaller than the dot on an “i.”

Most physicists and astronomers think the result is a black hole, a body with such intense gravity that nothing can escape from its immediate vicinity. A black hole has two parts. At its core is a singularity, the infinitesimal point into which all the matter of the star gets crushed. Surrounding the singularity is the region of space from which escape is impossible, the perimeter of which is called the event horizon. Once something enters the event horizon, it loses all hope of exiting. Whatever light the falling body gives off is trapped, too, so an outside observer never sees it again. It ultimately crashes into the singularity.

But is this picture really true? The known laws of physics are clear that a singularity forms, but they are hazy about the event horizon. Most physicists operate under the assumption that a horizon must indeed form, if only because the horizon is very appealing as a scientific fig leaf. Physicists have yet to figure out what exactly happens at a singularity: matter is crushed, but what becomes of it then? The event horizon, by hiding the singularity, isolates this gap in our knowledge. All kinds of processes unknown to science may occur at the singularity, yet they have no effect on the outside world. Astronomers plotting the orbits of planets and stars can safely ignore the uncertainties introduced by singularities and apply the standard laws of physics with confidence. Whatever happens in a black hole stays in a black hole.

Yet a growing body of research calls this working assumption into question. Researchers have found a wide variety of stellar collapse scenarios in which an event horizon does not in fact form, so that the singularity remains exposed to our view. Physicists call it a naked singularity. Matter and radiation can both fall in and come out. Whereas visiting the singularity inside a black hole would be a one-way trip, you could in principle come as close as you like to a naked singularity and return to tell the tale.

If naked singularities exist, the implications would be enormous and would touch on nearly every aspect of astrophysics and fundamental physics. The lack of horizons could mean that mysterious processes occurring near the singularities would impinge on the outside world. Naked singularities might account for unexplained high-energy phenomena that astronomers have seen, and they might offer a laboratory to explore the fabric of spacetime on its finest scales.

Event horizons were supposed to have been the easy part about black holes. Singularities are clearly mysterious. They are places where the strength of gravity becomes infinite and the known laws of physics break down. According to physicists’ current understanding of gravity, encapsulated in Einstein’s general theory of relativity, singularities inevitably arise during the collapse of a giant star. General relativity does not account for the quantum effects that become important for microscopic objects, and those effects presumably intervene to prevent the strength of gravity from becoming truly infinite. But physicists are still struggling to develop the quantum theory of gravity they need to explain singularities. [...]

Follow the link to read the rest of the article (6 short pages) and see the slides.

Sandwalk: Professor Moran gives a list of those he thinks are good science writers.

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