That got the pair thinking: how far away could you see a major city on another world using only existing telescopes? The question percolated for a while, until Loeb happened to mention it to Freeman Dyson, the Institute for Advanced Study physicist famous for spending more time thinking outside the box than in it. (In the early 1960’s, Dyson worked on the idea of a rocket propelled by atom bombs, and has suggested that astronomers look for aliens who might have completely enclosed their stars to trap solar energy.) Dyson was, predictably, intrigued by the question of extraterrestrial cities. “He encouraged us to write it up,” says Loeb.
The city the researchers picked as a reference wasn’t Dubai; it was Tokyo. “I love Tokyo,” Turner admits, but that wasn’t the reason for the choice. Instead, it’s because the loss of the Fukushima nuclear plants in last spring’s tsunami forced major power cutbacks in Japan. As a result, there was a lot of information publicly available about how much electricity Tokyo uses for what purposes, which made its light output easy to calculate.
Unsurprisingly, there’s no way you could see city lights on a planet orbiting another star. Even if the aliens use a whole lot more light than we do, says Turner, the ability to detect it at such vast distances is “two or three generations of telescope away.” But closer to home you might see a glimmer. Tokyo, Turner and Loeb calculated, would be visible at the very edge of our Solar System, 30 times farther out than Pluto — though it would take a long exposure on a telescope like the Hubble to see it. (See slightly altered pictures of the solar system.)
Even if you spotted something suggesting a city in space, you’d still have to figure out whether the light was artificial — alien-made, in other words — or simply reflected back from the sun. One way to do that is with a spectrograph, which breaks light into a rainbow of colors; artificial light makes for a different sort of rainbow from the one sunlight produces. Again, though, that takes a powerful telescope.
But Loeb and Turner realized there was a much simpler way to do things. As Isaac Newton first showed, the intensity of light drops off with the inverse of the square of distance. In plain English, this means that if you move a light source twice as far away, it becomes a fourth as bright. Move it three times as far and it becomes a ninth as bright. Many objects in the Kuiper belt — the ring of comets and other bodies that surround the solar system — are in highly elliptical orbits, meaning they get closer and farther away as they orbit the sun. A Kuiper belt Tokyo would get brighter and dimmer with that motion, and it would do so according to Newton’s inverse-square law.
The nifty thing is, the law applies only if you’re seeing light produced by the orbiting object itself. If all you’re seeing is reflected sunlight it would be much dimmer, since the light first has to travel from the sun, bounce off the object, then bounce again to Earth, which doubles the Newtonian effect: If the object were to move twice as far from Earth, its light would be not four times dimmer, but sixteen.
So all you need to do is watch Pluto and its kin for a while and see which rule their light follows. And while keeping a constant eye on them would ordinarily be a time-consuming chore, a new instrument called the Large Synoptic Survey Telescope (LSST) will be coming on line by the end of the decade. Its only job will be to survey the entire sky every few nights with the world’s most powerful light detectors. Among other things, it will note anything that changes, including stars that pulsate, stars that explode, potentially dangerous near-Earth asteroids — and Kuiper Belt objects that move and, maybe, brighten or dim in unexpected ways. (See pictures of outer space.)
One obvious question Loeb and Turner’s idea raises is that since we always see the Sun-facing, daylight side of Kuiper Belt objects, why would aliens have the lights on? The answer: the Sun is so faint at the edges of the Solar System that any beings that evolved closer-in would feel the need to supplement natural light by a lot, even at high noon. And the aliens would have to have evolved closer in because the emergence of life, as far as we know, requires liquid water. Once they had emerged and evolved, a gravitational encounter with a larger planet would have shotgunned them out to the fringes.
OK, the fact is it’s vanishingly unlikely that there’s some thriving Manhattan or Minneapolis stuck on an ice-ball in the depths of the Kuiper belt. But the same principles of reflected light that would reveal the existence of such a city can also help scientists study the size, rotation and reflectivity of other worlds. And of course, the zillion to one improbability of a Kuiper metropolis is not the same as absolutely ruling it out. “It’s unlikely that there are cities in the Kuiper Belt, but we should not pretend we know this for sure,” Turner says. “If it involves no additional resources, we should definitely [look for it].”
In that, Turner echoes the words of Philip Morrison and Giuseppe Cocconi, whose forward-looking paper in 1960 in the journal Nature laid the intellectual foundation for SETI, the search for extraterrestrial intelligence. “The probability of success is difficult to estimate” they wrote. “But if we never search, the chance of success is zero.”
Biggest Jump Ever in Global Warming Gases: The global output of heat-trapping carbon dioxide jumped by the biggest amount on record, the U.S. Department of Energy calculated, a sign of how feeble the world’s efforts are at slowing man-made global warming.
The new figures for 2010 mean that levels of greenhouse gases are higher than the worst case scenario outlined by climate experts just four years ago.
“The more we talk about the need to control emissions, the more they are growing,” said John Reilly, co-director of MIT’s Joint Program on the Science and Policy of Global Change.
The world pumped about 564 million more tons (512 million metric tons) of carbon into the air in 2010 than it did in 2009. That’s an increase of 6 percent. That amount of extra pollution eclipses the individual emissions of all but three countries — China, the United States and India, the world’s top producers of greenhouse gases.
It is a “monster” increase that is unheard of, said Gregg Marland, a professor of geology at Appalachian State University, who has helped calculate Department of Energy figures in the past.
Extra pollution in China and the U.S. account for more than half the increase in emissions last year, Marland said.
“It’s a big jump,” said Tom Boden, director of the Energy Department’s Carbon Dioxide Information Analysis Center at Oak Ridge National Lab. “From an emissions standpoint, the global financial crisis seems to be over.”
Boden said that in 2010 people were traveling, and manufacturing was back up worldwide, spurring the use of fossil fuels, the chief contributor of man-made climate change.
India and China are huge users of coal. Burning coal is the biggest carbon source worldwide and emissions from that jumped nearly 8 percent in 2010.
“The good news is that these economies are growing rapidly so everyone ought to be for that, right?” Reilly said Thursday. “Broader economic improvements in poor countries has been bringing living improvements to people. Doing it with increasing reliance on coal is imperiling the world.”
In 2007, when the Intergovernmental Panel on Climate Change issued its last large report on global warming, it used different scenarios for carbon dioxide pollution and said the rate of warming would be based on the rate of pollution. Boden said the latest figures put global emissions higher than the worst case projections from the climate panel. Those forecast global temperatures rising between 4 and 11 degrees Fahrenheit by the end of the century with the best estimate at 7.5 degrees.
Even though global warming skeptics have attacked the climate change panel as being too alarmist, scientists have generally found their predictions too conservative, Reilly said. He said his university worked on emissions scenarios, their likelihood, and what would happen. The IPCC’s worst case scenario was only about in the middle of what MIT calculated are likely scenarios.
Chris Field of Stanford University, head of one of the IPCC’s working groups, said the panel’s emissions scenarios are intended to be more accurate in the long term and are less so in earlier years. He said the question now among scientists is whether the future is the panel’s worst case scenario “or something more extreme.”
“Really dismaying,” Granger Morgan, head of the engineering and public policy department at Carnegie Mellon University, said of the new figures. “We are building up a horrible legacy for our children and grandchildren.”
But Reilly and University of Victoria climate scientist Andrew Weaver found something good in recent emissions figures. The developed countries that ratified the 1997 Kyoto Protocol greenhouse gas limiting treaty have reduced their emissions overall since then and have achieved their goals of cutting emissions to about 8 percent below 1990 levels. The U.S. did not ratify the agreement.
In 1990, developed countries produced about 60 percent of the world’s greenhouse gases, now it’s probably less than 50 percent, Reilly said.
“We really need to get the developing world because if we don’t, the problem is going to be running away from us,” Weaver said. “And the problem is pretty close from running away from us.”
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