Fire and ice: the Earth may be warming, but the cosmos is headed toward a very big chill

Natural History, Dec, 2005 by Neil deGrasse Tyson

When Cole Porter composed "Too Darn Hot" for his 1948 Broadway musical Kiss Me Kate, the temperature he was bemoaning was surely no higher than the mid-nineties. No harm in taking Porter's lyrics as an authoritative source on the upper temperature limit for comfortable lovemaking. Combine that with what a cold shower does to most people's erotic urges, and you now have a pretty good estimate of how narrow the comfort zone is for the unclothed human body: a range of about thirty degrees Fahrenheit, with room temperature just about in the middle.

The universe is a whole other story. How does a temperature of 100,000, 000,000,000,000,000,000,000,000,000 degrees grab you? That's a hundred thousand billion billion billion degrees. It also happens to be the temperature of the universe a teeny fraction of a second after the big bang--a time when all the energy and matter and space that would turn into planets, petunias, and particle physicists was an expanding fiery ball of quark-gluon plasma. Nothing you'd call a thing could exist until there was a multibillion-fold cooling of the cosmos.

As the laws of thermodynamics decree, within about one second after the big bang, the expanding fireball had cooled to 10 billion degrees and ballooned from something smaller than an atom to a cosmic colossus about a thousand times the size of our solar system. By the time three minutes had passed, the universe was a balmy billion degrees and was already hard at work making the simplest atomic nuclei. Expansion is the handmaiden to cooling, and the two have continued, unabated, ever since.

Today the average temperature of the universe is 2.73 degrees Kelvin. All the temperatures mentioned so far, aside from the ones that involve the human libido, are stated in degrees Kelvin. The Kelvin degree, known simply as the kelvin, was conceived to be the same temperature interval as the Celsius degree, but the Kelvin scale has no negative numbers. Zero is zero, period. In fact, to quash all doubts, zero on the Kelvin scale is dubbed absolute zero.

The Scottish engineer and physicist William Thomson, later and better known as Lord Kelvin, first articulated the idea of a coldest possible temperature in 1848. Laboratory experiments haven't gotten there yet. As a matter of principle, they never will, although they've come awfully close. The unarguably cold temperature of 0.0000000005 K (or 500 picokelvins, as metric mavens would say) was artfully achieved in 2003 in the lab of Wolfgang Ketterle, a physicist at MIT.

Outside the laboratory, cosmic phenomena span a staggering range of temperatures. Among the hottest places in the universe today is the core of a blue supergiant star during the hours of its collapse. Just before it explodes as a supernova, creating drastic neighborhood-warming effects, its temperature hits 100 billion K. Compare that with the Sun's core: a mere 15 million K.

Surfaces are much cooler. The skin of a blue supergiant checks in at about 25,000 K--hot enough, of course, to glow blue. Our Sun registers 6,000 K--hot enough to glow white, and hot enough to melt and then vaporize anything in the periodic table of elements. The surface of Venus is 740 K, hot enough to fry the electronics normally used to drive space probes.

Considerably further down the scale is the freezing point of water, 273.15 K, which looks downright warm compared with the 60 K surface of Neptune, nearly 3 billion miles from the Sun. Colder still is Triton, one of Neptune's moons. Its icy nitrogen surface sinks to 40 K, making it the coldest place in the solar system this side of Pluto.

Where do Earth-beings fit in? The average body temperature of human's (traditionally 98.6 degrees F) registers slightly above 310 on the Kelvin scale. Officially recorded surface temperatures on Earth range from a summer high of 331 K (136 F, at Al 'Aziziyah, Libya, in 1922), to a winter low of 184 K (-129 F, at Base Vostok, Antarctica, in 1983). But people can't survive unassisted at those extremes. We suffer hyperthermia in the Sahara if we don't have shelter from the heat, and hypothermia in the Arctic if we don't have boatloads of clothing and caravans of food. Meanwhile, Earth-dwelling extremophile microorganisms, both thermophilic (heat-loving) and psychrophilic (cold-loving), are variously adapted to temperatures that would fry us or freeze us. Viable yeast, wearing no clothes at all, has been discovered in 3-million-year-old Siberian permafrost. A species of bacterium locked in Alaskan permafrost for 32,000 years woke up and started swimming as soon as its medium melted. And at this very moment, assorted species of archaea and bacteria are living out their lives in boiling mud, bubbling hot springs, and undersea volcanoes.

Even complex organisms can survive in similarly astonishing circumstances. When provoked, the itsy-bitsy invertebrates known as tardigrades can suspend their metabolism. In that state, they can survive temperatures of 424 K (303 degrees F) for several minutes and 73 K (-328 degrees F) for days on end, making them hardy enough to endure being stranded on Neptune. So the next time you need space travelers with the "right stuff," you might want to choose yeast and tardigrades, and leave your astronauts, cosmonauts, and (Chinese) taikonauts at home.