Added, 2/12/04


What if the Dark Energy and Dark Matter Essential to Modern Explanations of the Universe Don't Really Exist?

From The Economist print edition Feb 5th 2004


Edited portions of the report appear in quotes. Comments are appended in italics.

"Some people think modern astronomy is based on a kludge similar to Ptolemy's theory of epicycles. At the moment, the received wisdom is that the obvious stuff in the universe - stars, planets, gas clouds and so on - is actually only 4% of its total content. About another quarter is so-called cold, dark matter, which is made of different particles from the familiar sort of matter, and can interact with the latter only via gravity. The remaining 70% is even stranger. It is known as dark energy, and acts to push the universe apart. However, the existence of cold, dark matter and dark energy has to be inferred from their effects on the visible, familiar stuff. If something else is actually causing those effects, the whole theoretical edifice would come crashing down."

"According to a paper just published in the Monthly Notices of the Royal Astronomical Society by Tom Shanks and his colleagues at the University of Durham, in England, that might be about to happen. Many of the inferences about dark matter and dark energy come from detailed observations of the cosmic microwave background (CMB). This is radiation that pervades space, and is the earliest remnant of the Big Bang which is thought to have started it all. Small irregularities in the CMB have been used to deduce what the early universe looked like, and thus how much cold, dark matter and dark energy there is around."

"Dr. Shanks thinks these irregularities may have been misinterpreted. He and his colleagues have been analyzing data on the CMB that were collected by WMAP, a satellite launched in 2001 by NASA, America's space agency. They have compared these data with those from telescopic surveys of galaxy clusters, and have found correlations between the two which, they say, indicate that the clusters are adding to the energy of the CMB by a process called inverse Compton scattering, in which hot gas boosts the energy of the microwaves. That, they say, might be enough to explain the irregularities without resorting to ghostly dark matter and energy."

In other words, the minute fluctuations in the CMB, which are theoretically assumed to be the seeds that caused galaxies and other structure in the universe to form, may be due to an entirely different cause! This would make all of the computational work that models galaxy formation invalid, unless new seeds were found to take their place.

"In a pair of papers published in a December issue of Astronomy and Astrophysics, Sebastien Vauclair of the Astrophysics Laboratory of the Midi-Pyrénées, in Toulouse, and his colleagues also report the use of galaxy clusters to question the existence of dark energy. Cosmological theory says that the relationship between the mass of a galaxy cluster and its age is a test of the value of the 'density parameter Omega' of the universe. The density parameter is, in turn, a measure of just how much normal matter, dark matter and dark energy there is. But because the mass of a cluster is difficult to measure directly, astronomers have to infer it from computer models which tell them how the temperature of the gas in a cluster depends on that cluster's mass."

"That has been done for nearby clusters, but not for distant ones which, because of the time light has taken to travel from them to Earth, provide a snapshot of earlier times. So Dr. Vauclair and his colleagues used XMM-Newton, a European X-ray-observation satellite that was launched in 1999, to measure the X-ray luminosities and the temperatures of eight distant clusters of galaxies. They then compared the results with those from closer (and therefore apparently older) clusters. The upshot was that the relationship between mass and age did not match the predictions of conventional theory. It did, however, match an alternative model with a much higher density of 'ordinary' matter in it."

Previous estimates of Omega have been made assuming that the density of the nearby universe is the same as the density far away, corresponding to the uniformity assumptions of General Relativity. But if the density varies with distance, the Big Bang model must be wrong. These observers are attempting to save the Big Bang by postulating that more ordinary matter would fix the discrepancy. But that doesn't explain why the two observations differ.

"On the other hand, a universe that requires three completely different sorts of stuff to explain its essence does have a whiff of epicycles about it. As Albert Einstein supposedly said, 'Physics should be made as simple as possible, but not simpler.' Put Dr. Shanks's and Dr. Vauclair's observations together, and one cannot help but wonder whether Ptolemy might soon have some company in the annals of convoluted, discarded theories."

The logical consequence of discarding dark matter is to discard the Big Bang model itself!