April 18, 2011 | 23
Neutrino beams might create such enigmas, but dare we risk making anything so unpredictable?
In "Too Hard for Science?" I interview scientists about ideas they would love to explore that they don’t think could be investigated. For instance, they might involve machines beyond the realm of possibility, such as particle accelerators as big as the sun, or they might be completely unethical, such as lethal experiments involving people. This feature aims to look at the impossible dreams, the seemingly intractable problems in science. However, the question mark at the end of "Too Hard for Science?" suggests that nothing might be impossible.
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The scientist: Martin Bojowald, associate professor of physics at Pennsylvania State University.
The idea: Among the greatest challenges in physics are areas where our understanding of the known laws of physics break down — infinitely dense points known as singularities. The universe is conjectured to have been born from a singularity, and singularities are thought to exist inside black holes.
To better understand these mysteries, "being able to look at one of them could be highly educational," Bojowald says. "To do so, we could try to make a black hole that is sufficiently long-lived, which requires a large amount of mass to be compressed into a tiny region."
One major problem with such an experiment is that the singularity of a black hole is in principle obscured by an event horizon, a boundary past which nothing can return. This means researchers could not get data back from any probe sent through an event horizon.
However, Bojowald notes that naked singularities could in theory exist, ones not covered by event horizons. Scientists in principle could create such singularities by compressing very light particles such as neutrinos sufficiently quickly. One would want to arrange neutrino emitters spherically, aim them at one central point and ramp up their beam intensity rapidly. Such a singularity would not need to be massive at all — maybe equal in mass to a single electron.
"It would not be naked for long if the mass is small," Bojowald says. Still, "even a brief duration could be quite exciting." If we could look at one, "entirely new observations would become possible, almost like seeing another universe. It would be as though we had always been living in a closed room, and suddenly someone opened the window."
"Once we produce a naked singularity, probing it will be the easy part," Bojowald says. "We point a lot of detectors at the central point looking at whatever comes out. Since we don’t know what happens at the naked singularity, our best chance is to capture as much information as we can get for radiation of all kinds of energies. Some theory of quantum gravity is likely to be relevant to describe a naked singularity, so we should look especially for high-energy particles."
The problem: Directing neutrinos into beams is tricky at best because they only weakly interact with the electromagnetic fields that scientists use to manipulate electrically charged particles. It’s not impossible — neutrinos are produced by decaying particles such as muons that do have an electric charge, "and if the muons form a beam of high velocity, the neutrinos are predominantly emitted in the forward direction. In this way, one obtains a beam," Bojowald says. Still, the intensity of these beams is far below what would be required to generate a naked singularity, "and there would be no way to focus the neutrinos on a single point."
In addition, "general relativity, even though it does allow naked singularities, also indicates that they are unlikely to form," Bojowald says. "We would need very good control of the neutrino beams, making the experiment even more difficult."
A greater concern may be that since our understanding of the known laws of physics break down around singularities, "a naked singularity would be unpredictable according to current theory, so the experiment would be risky," Bojowald says. "We do not know what could come and hit us."
The solution? Instead of attempting to create naked singularities, researchers could try and find them in nature instead. Computer simulations have suggested that black holes could essentially spin fast enough to shed their event horizons and reveal naked singularities, although researchers suggest other factors such as gravitational effects might keep this from happening.
Image of Martin Bojowald from Penn State’s site.
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About the Author: Charles Q. Choi is a frequent contributor to Scientific American. His work has also appeared in The New York Times, Science, Nature, Wired, and LiveScience, among others. In his spare time, he has traveled to all seven continents. Follow him on Twitter @cqchoi.
The views expressed are those of the author and are not necessarily those of Scientific American.