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Astronomers warned: don't assume the universe is flat
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Don’t be so sure that our universe is flat
they took data from WMAP and other cosmology experiments and analysed it using Bayes’s theorem, which can be used to show how the certainty attached to a particular conclusion is affected by different starting assumptions. Using modern astronomers’ assumptions, which presuppose a flat universe, they calculated the probability that the universe
FOR centuries the ancients believed the Earth was flat. Evidence to the contrary was either ignored or effortlessly integrated into the dominant world view. Today we dismiss flatEarthers as ignorant, yet we may be making an almost identical mistake – not about our planet, but about the entire universe. When it comes to the universe, “flatness” refers to the fate of light beams travelling large distances parallel to each other. If the universe is “flat”, the beams will always remain parallel. Matter, energy and dark energy all produce curvature in space-time, however. If the universe’s space-time is positively curved, like the surface
of a sphere, parallel beams would come together. In a negatively curved, saddle-shaped universe, parallel beams would diverge. Thanks in part to the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, which revealed the density of matter and dark energy in the early universe, most “The calculation reveals astronomers are confident that the how strongly astronomers’ universe is flat. But that view is now prejudices can affect their conclusions” being questioned by Joseph Silk at the University of Oxford and was in one of three states: flat, colleagues, who say it’s possible that the WMAP observations have positively curved or negatively curved. This produced a 98 per been misinterpreted. cent probability that the universe In a paper accepted for is indeed flat. When they reran publication in Monthly Notices the calculation starting from a of the Royal Astronomical Society more open-minded position, (www.arxiv.org/abs/0901.3354),
From the start, blood flows from the heart
(DOI: 10.1016/j.cell.2009.04.023). “The answer is that there must be a cue to start making adult blood cells, and that cue is the onset of circulation and blood flow,” he says. The discovery could lead to a source of blood for people with leukaemia who need a transplant but don’t have a matched donor, by exposing stem cells to flowing liquid, says Zon. In a separate study, George Daley of the Children’s Hospital Boston and colleagues found that blood cells form more readily in cultures of embryonic stem cells if they’re exposed to fluids mimicking the usual flow and pressure of blood (Nature, DOI: 10.1038/ nature08073). They also showed the phenomenon in embryonic aortic tissue from mice embryos engineered to have no heartbeat or circulation. Left alone, the aortic tissue made little blood, but blood production soared when Daley exposed the tissue to flowing fluid. “The discovery underscores the critical importance of mechanical forces play in the development of blood and other functional tissue,” says Robert Lanza, chief scientist at Advanced Cell Technology of Worcester, Massachusetts. Andy Coghlan ■
WHEN the embryonic heart begins to beat, it kick-starts the production of blood from cells lining the growing aorta, two independent research teams have shown. As the heart starts pumping a primitive blood-like fluid around the body of an embryo, the change in pressure from the flowing liquid is the cue for cells lining the aorta to change first into blood stem cells, then into all blood-cell types in the body. As they multiply and mature, these rapidly replace the initial embryonic “blood”, which is composed of embryonic red blood cells in a nutrient-rich serum. Leonard Zon of the Howard Hughes Medical Institute in Boston and his colleagues demonstrated that the pressure of the embryonic fluid is what switches on the production of adult blood in zebra fish and mouse embryos. “The finding answers an age-old question as to why the aorta makes blood stem cells at all,” says Zon, whose findings appear in Cell
however, the probability changed to 67 per cent, making a flat universe far less of a certainty than astronomers generally conclude. “It’s a reasonable assumption that the universe isn’t entirely flat,” Silk says, adding that the calculation reveals how strongly astronomers’ prejudices can affect their conclusions. David Spergel of Princeton University, the spokesman for WMAP, agrees. “They’ve developed a statistically rigorous way of examining the question,” he says. Silk says astronomers need to achieve a 99.9999 per cent level of confidence on the flat universe, high enough that the case starts to look compelling no matter what the starting assumptions are. It’s possible, however, that no measurements will ever be able to get to that level of accuracy. Eugenie Samuel Reich ■
16 May 2009 | NewScientist | 15
Don’t be so sure that our universe is flat
they took data from WMAP and other cosmology experiments and analysed it using Bayes’s theorem, which can be used to show how the certainty attached to a particular conclusion is affected by different starting assumptions. Using modern astronomers’ assumptions, which presuppose a flat universe, they calculated the probability that the universe
FOR centuries the ancients believed the Earth was flat. Evidence to the contrary was either ignored or effortlessly integrated into the dominant world view. Today we dismiss flatEarthers as ignorant, yet we may be making an almost identical mistake – not about our planet, but about the entire universe. When it comes to the universe, “flatness” refers to the fate of light beams travelling large distances parallel to each other. If the universe is “flat”, the beams will always remain parallel. Matter, energy and dark energy all produce curvature in space-time, however. If the universe’s space-time is positively curved, like the surface
of a sphere, parallel beams would come together. In a negatively curved, saddle-shaped universe, parallel beams would diverge. Thanks in part to the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, which revealed the density of matter and dark energy in the early universe, most “The calculation reveals astronomers are confident that the how strongly astronomers’ universe is flat. But that view is now prejudices can affect their conclusions” being questioned by Joseph Silk at the University of Oxford and was in one of three states: flat, colleagues, who say it’s possible that the WMAP observations have positively curved or negatively curved. This produced a 98 per been misinterpreted. cent probability that the universe In a paper accepted for is indeed flat. When they reran publication in Monthly Notices the calculation starting from a of the Royal Astronomical Society more open-minded position, (www.arxiv.org/abs/0901.3354),
From the start, blood flows from the heart
(DOI: 10.1016/j.cell.2009.04.023). “The answer is that there must be a cue to start making adult blood cells, and that cue is the onset of circulation and blood flow,” he says. The discovery could lead to a source of blood for people with leukaemia who need a transplant but don’t have a matched donor, by exposing stem cells to flowing liquid, says Zon. In a separate study, George Daley of the Children’s Hospital Boston and colleagues found that blood cells form more readily in cultures of embryonic stem cells if they’re exposed to fluids mimicking the usual flow and pressure of blood (Nature, DOI: 10.1038/ nature08073). They also showed the phenomenon in embryonic aortic tissue from mice embryos engineered to have no heartbeat or circulation. Left alone, the aortic tissue made little blood, but blood production soared when Daley exposed the tissue to flowing fluid. “The discovery underscores the critical importance of mechanical forces play in the development of blood and other functional tissue,” says Robert Lanza, chief scientist at Advanced Cell Technology of Worcester, Massachusetts. Andy Coghlan ■
WHEN the embryonic heart begins to beat, it kick-starts the production of blood from cells lining the growing aorta, two independent research teams have shown. As the heart starts pumping a primitive blood-like fluid around the body of an embryo, the change in pressure from the flowing liquid is the cue for cells lining the aorta to change first into blood stem cells, then into all blood-cell types in the body. As they multiply and mature, these rapidly replace the initial embryonic “blood”, which is composed of embryonic red blood cells in a nutrient-rich serum. Leonard Zon of the Howard Hughes Medical Institute in Boston and his colleagues demonstrated that the pressure of the embryonic fluid is what switches on the production of adult blood in zebra fish and mouse embryos. “The finding answers an age-old question as to why the aorta makes blood stem cells at all,” says Zon, whose findings appear in Cell
however, the probability changed to 67 per cent, making a flat universe far less of a certainty than astronomers generally conclude. “It’s a reasonable assumption that the universe isn’t entirely flat,” Silk says, adding that the calculation reveals how strongly astronomers’ prejudices can affect their conclusions. David Spergel of Princeton University, the spokesman for WMAP, agrees. “They’ve developed a statistically rigorous way of examining the question,” he says. Silk says astronomers need to achieve a 99.9999 per cent level of confidence on the flat universe, high enough that the case starts to look compelling no matter what the starting assumptions are. It’s possible, however, that no measurements will ever be able to get to that level of accuracy. Eugenie Samuel Reich ■
16 May 2009 | NewScientist | 15