Why is the Universe's Expansion Accelerating? Astronomers to Build "Dark Energy" Telescope At the South Pole

Mo Xinhai

PureInsight | September 9, 2002

According to a report from The Chicago Tribune, astronomers from the University of Chicago and four other institutions plan to build a telescope at the South Pole to figure out the biggest mystery in cosmology: Why is the universe's expansion speeding up? The project has been funded by a $16.6 million National Science Foundation grant and the team expects to have the telescope running at the South Pole in four years.

Its mission is to explore the "dark energy" which is believed to be responsible for the accelerating expansion of the universe. The cosmologists believe that the universe began in a "Big Bang", which leads to the expansion of the universe. It was once widely believed among cosmologists that speed of the expansion should be either constant, or decelerating because of the gravity attraction among the galaxies.

However, it seems that our universe is making a cosmic joke on cosmologists. They are stunned by two independent research results in 1998 and 2002 that confirmed the expansion is speeding up.

An accelerating expansion universe means all stars, galaxies and other matter will spread apart so fast and become so diluted that over billions of years the universe would be nothing but a void. Of course, many leading scientists do not believe the story. For example, Professor Leonard Susskind et. al. published an article in a recent issue of Nature and pointed out that the reason behind such conclusion is that modern cosmology is probably neglecting some fundamental factors that are responsible for both the origin and the evolution of our universe.

What it comes down to is that scientists know very little about gravity. It is an interaction that scientists began to study very early on. It used to be clear that gravity was an attraction between bodies, and that, on Earth, makes an apple fall to the ground. But cosmologists now suspect that, on the scale of the universe, gravity, propelled by something they call dark energy, behaves just the opposite.

'We do have antigravity now, but only on this enormous scale,' said Bruce Winstein, director of the U. of C.'s Center for Cosmological Studies, where the dark energy telescope was conceived and developed.

One of the most bizarre features is that as the universe expands, it creates more dark energy that pushes the expansion to warp speeds. 'If dark energy really is 70 percent of the whole universe and it behaves the way current theory predicts, then it really is beginning to dominate everything about the universe,' said Tony Stark of the Harvard-Smithsonian Center for Astrophysics. 'It will actually turn off the formation of galaxies. From now on there will be very many fewer galaxy clusters formed.' However, the observable facts did not say so. After so many years, the forming of new galaxies is still very active.

Antarctica was selected as the site for the telescope because the temperature is always cold, which limits the amount of water vapor in the atmosphere. Water vapor absorbs the microwave radiation coming from space. The telescope, which will be 26.4 feet in diameter, will be able to measure differences in temperature in ancient space. The instrument will be able to detect tiny variations-- as little as 10 millionths of a degree--in the Big Bang's leftover heat, which scientists call the cosmic microwave background. A variation in the temperature in a specific area signifies the presence of a galaxy cluster. That will allow astronomers to count the galaxy clusters in the field. The fewer the number, the greater the evidence that dark energy is at work.

Astronomers will use the telescope to do a census of galaxy clusters that are 5 to 7 billion light years from Earth, when the universe was one-third of its present size and galaxies were rapidly forming clusters. As the microwave radiation travels through these clusters, their dust slightly changes the wavelength of the radiation. The telescope will be sensitive enough to detect these changes, which will tell astronomers how many galaxy clusters inhabited a given amount of the universe at that early time.

Dark energy is different from another cosmological mystery, dark matter. Dark matter refers to the unseen matter that exerts enough gravity to keep spinning galaxies from flying apart. By studying the spinning of the galaxy, scientist discovered that in order for those stars in the galaxy to remain on their tracks and not fly apart, the gravity among the stars by itself can not do the job. So scientists proposed that there is another type of matter, "dark matter," mysterious, invisible, but with much larger mass than the mass of those stars we can observe, that exerts attraction to those stars. The "dark matter" has about 20%, dark energy has about 70% and the ordinary matter we can see has about 10% of the total share of the mass of the universe, according to most scientists.

The spinning of the galaxies has been a cosmological mystery for scientists for a long time, and the accelerating expansion of the universe found recently makes the problem even more complex. To stabilize a spinning galaxy, we need the "dark matter" to exert additional attraction. To maintain an universe with accelerating expansion, we need "dark energy" to defeat the gravity between the galaxies. The embarrassing situation is very likely caused by the limitations on the knowledge about gravity and the movement of celestial bodies scientists currently hold. The law of gravity was proposed by British scientist Newton based on the movement of the planets in the solar system. Later, it was re-described in the framework of general relativity by physicist Einstein. Although the theory of gravity successfully describes the motions of celestial bodies inside the solar system, but it has never been tested in the cosmic scale. For many years, the scientists in NASA had discovered that the spaceships they launched to outside solar system were slower than one expected from the gravity theory and deviated from the calculated trajectory. Gravity is also the interaction that has disturbed scientists the most for so many years, because many of its properties differ greatly from those of other interactions. Compared to the size of the universe, the solar system is far too small. Whether it is correct to extrapolate results obtained from our solar system to the entire universe probably needs to be answered with a question mark. Probably this is the reason behind this dilemma. If we supposed that Newton knew about the motion of galaxies before he knew about the motion of the planets inside the solar system, he probably would not proposed his theory of gravity, or would have given the theory an entirely different form. The information from the "dark energy" telescope probably can shed some light on this problem.

1. http://www.chicagotribune.com/news/nationworld/chi-0208300266aug30.story?coll=chi%2Dnewsnationworld%2Dhed
2. http://www.nature.com/nsu/020812/020812-2.html
3. The Monthly Notices of the Royal Astronomical Society, Volume 330, No. 2, 21 February 2002.
4. NASA News Release: http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2001/01-199.html
5. http://www3.cosmiverse.com/news/space/0702/space07170203image1.html

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