You may have experienced the feeling on a steamy summer day: Nowhere in the universe could possibly be hotter than this.
Think again. Scientists have used high-tech equipment to generate temperatures in the billions of degrees - that's billions with a "b" - and they can contemplate temperatures that leave that sort of heat in the dust.
But is there a limit to the hot stuff? Is there some maximum possible temperature - kind of the flip side of absolute zero?
That's one of three questions in this edition of "Ask AP," a weekly Q&A column where AP journalists respond to readers' questions about the news.
If you have your own news-related question that you'd like to see answered by an AP reporter or editor, send it to newsquestions@ap.org, with "Ask AP" in the subject line. And please include your full name and hometown so they can be published with your question.
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What was the environmental impact when Saddam Hussein lit hundreds of Kuwaiti oil wells on fire, and dumped millions of gallons of oil into the Persian Gulf, during the Gulf War in the 1990s?
David E. Bergstein
New York
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Retreating Iraqi soldiers set fires in Kuwait's oil fields that burned for about eight months, spreading smoke throughout much of the Persian Gulf region and influencing weather in the area in 1991. Kuwaiti authorities noted an increase in respiratory diseases as a result of the smoke. Oil seeped into the ground water, a resource that largely desert Kuwait does not have in large supply.
However, the most pessimistic forecasts about "nuclear winter" and massive agricultural losses did not come to pass. Vegetation in the contaminated area began to improve after about five years. But the long-term effects of the fire are still not fully understood.
Robert H. Reid
AP Chief of Bureau
Baghdad
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We all know about absolute zero, the lowest temperature possible. Is there such a thing as an absolute in the opposite direction - in other words, hot?
Neil Brown
Spruce Pine, N.C.
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Let's put the question to an expert: Is there some maximum temperature beyond which nothing can be heated?
"That's a very good question, and the answer is: maybe," says University of Chicago physicist Michael Turner. "Honest to goodness, we really don't know."
A few things are clear. First, we're talking hot enough to obliterate any ordinary solid, liquid or gas. So the "thing" to be heated would be a collection of particles.
Secondly, any such temperature would be far beyond anything scientists have cooked up on Earth. In 2006, the Sandia National Laboratories said one of its machines had reached more than 2 billion degrees Celsius, which is about 3.6 billion degrees Fahrenheit. That's pretty toasty, but nothing compared to what a cosmologist like Turner can talk about.
Turner says we can trace the history of the universe back to when its temperature was more than 10 trillion degrees Celsius, or 18 trillion degrees Fahrenheit.
He also cites "the highest temperature we think we can even speculate about." That is a 1 followed by 32 zeros (at this point, the difference between Celsius and Fahrenheit is not worth bothering about). Scientists can't really contemplate higher temperatures without new advances in physics theory.
Some scientists think the maximum possible temperature is lower - about 10,000 trillion degrees, or a 1 followed by 16 zeros, Turner said. "We don't know of any place in the universe today that is that hot," he said.
That lower theoretical maximum might be testable at the Large Hadron Collider, a brand-new facility that straddles the Swiss-French border, he said.
In any case, he notes, while scientists have edged to within about a billionth of a degree of absolute zero, there's still "plenty of room at the top."
Malcolm Ritter
AP Science Writer
New York
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When the EPA rates the mileage of different models of cars, does it account for the various fuel formulations that are used during different times of the year? I have noticed that my small truck's mileage seems to change from 29 mpg in summer to only 24 to 25 in winter, and the change appears to happen suddenly, in October and in March or April.
Les Brooks
Pendleton, Ore.
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Many things can affect your vehicle's fuel economy, so it's difficult to know if the decline in your gas mileage during the winter is directly tied to your fuel. Much of it depends on how you drive, whether your vehicle is properly maintained and where you live.
The Environmental Protection Agency tests all of its vehicles with a consistent "certification fuel" called Indolene, which is 100 percent gasoline. It does not run different tests for seasonal variations of fuels.
An energy bill passed by Congress last year requires 9 billion gallons of ethanol to be blended into gasoline this year. In many metropolitan areas and parts of the Eastern Seaboard and California, fuel providers are required to sell "reformulated," or cleaner, gasoline to meet federal and state clean air requirements.
Reformulated gasoline typically includes ethanol, which has about 25 percent less energy content than conventional gasoline.
Oregon has a requirement to blend 10 percent ethanol with gasoline as a way to promote renewable fuels and reduce gasoline consumption, said Tupper Hull, a spokesman for the Western States Petroleum Association. The requirements in Oregon have been phased in during the last two years, Hull said, so it's possible that the fuel you buy is blended with ethanol.
Many experts told me that a 10 percent ethanol blend would have only a slight impact on fuel economy - perhaps a 2 percent reduction. So based on your description, it would be difficult to attribute the roughly 20 percent fuel economy decline during the winter to your fuel.
Fuel efficiency can be affected by many other factors: your driving habits on the highway and around town, how you maintain the vehicle, aerodynamics and whether you use the air conditioner.
Rapid starts and stops can diminish fuel economy, along with towing extra weight in the truck bed. And as presidential candidates Barack Obama and John McCain noted in exchanges last month over energy policies, keeping your tires properly inflated can improve fuel economy.
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Ken Thomas
Associated Press Writer
Washington
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Have questions of your own? Send them to newsquestions@ap.org.
