- Email: [email protected]
The universe weighed and found wanting
COMMENTARY
media? The most ready explanation is that a pacifier could be a fomite. Sharing a pacifier has been shown to be a risk factor for the development of meningococcal disease in children in Auckland.5 However, contrary to what might be expected, cultures of 40 recently-used pacifiers were negative for the three major bacterial species commonly associated with acute otitis media.6 Data regarding viral transfer are unavailable. Other potential mechanisms include the facilitated transfer of nasopharyngeal organisms into the middle-ear space via the Eustachian tube, or the transudation of fluid into the middle ear, perhaps by pressure changes associated with long periods of sucking. To further cloud the issue, studies from four countries suggest that pacifier use may reduce the risk of sudden infant-death syndrome (SIDS),7–10 although the results are not conclusive.11 Thus, as with so many issues in clinical medicine, the appropriate guidance to be offered parents about pacifier use is not clear-cut. On the basis of existing information, a reasonable suggestion is that a child can use a pacifier for up to a year of age, both for comfort and as a possible protective factor against SIDS. Since long-term pacifier use is associated with oral candidosis,12 an increased incidence of respiratory and gastrointestinal illness,13 dental caries,14 and dental malocculsions,15 clinicians should encourage parents to reduce pacifier use to transitional situations or periods of stress after age 1 and eliminate use after age 2. However, further studies are needed before otitis can be added to the list of pacifier sins. *J Christopher Post, Mary C Goessier *Department of Paediatric Otolaryngology and Department of Paediatrics, Allegheny General Hospital, Pittsburgh, PA 15212, USA (e-mail: [email protected]) 1
2
3 4
5
6 7
8 9
10
11 12 13 14
15
Niemela M, Uhari M, Hannuksela A. Pacifiers and dental structures as risk factors for otitis media. Int J Pediatr Otorhinolaryngol 1994; 29: 121–27. Niemela M, Uhari M, Mottonen M. A pacifier increases the risk of recurrent acute otitis media in children in day care centers. Pediatrics 1995; 96: 884–88. Jackson JM, Mourino AP. Pacifier use and otitis media in infants twelve months of age or younger. Pediatr Dent 1999; 21: 255–60. Niemela M, Pihakari O, Pokka T, Uhari M, Uhari M. Pacifier as a risk factor for acute otitis media: A randomized, controlled trial of parental counseling. Pediatrics; 106: 483–88. Baker M, McNicholas A, Garrett N, et al. Household crowding a major risk factor for epidemic meningococcal disease in Auckland children. Pediatr Infect Dis J 2000; 19: 983–90. Brook I, Gober AE. Bacterial colonization of pacifiers of infants with acute otitis media. J Laryngol Otol 1997: 111: 614–15. Arnestad M, Andersen M, Rognum TO. Is the use of dummy or carry-cot of importance for sudden infant death? Eur J Pediatr 1997; 156: 968–70. Mitchell EA, Taylor BJ, Ford RP, et al. Dummies and the sudden infant death syndrome. Arch Dis Child 1993; 68: 501–04. L’Hoir MP, Engelberts AC, van Well GT, et al. Dummy use, thumb sucking, mouth breathing and cot death. Eur J Pediatr 1999; 158: 896–901. Fleming PJ, Blair PS, Pollard K, et al. Pacifier use and sudden infant death syndrome: results from the CESDI/SUDI case control study. Arch Dis Child 1999; 81: 112–16. Righard L. Sudden infant death syndrome and pacifiers: a proposed connection could be a bias. Birth 1998; 25: 128–29. Sio JO, Minwalla FK, George RH, Booth IW. Oral candida: is dummy carriage the culprit? Arch Dis Child 1987; 4: 406–08. North K, Golding J, Fleming PJ. Pacifier use and morbidity in the first six months of life. Pediatrics 1999; 103: E34. Ollila P, Niemela M, Uhari M, Larmas M. Prolonged pacifiersucking and use of a nursing bottle at night:possible risk factors for dental caries in children. Acta Odontol Scand 1998; 4: 233–37. Adair SM, Milano M, Lorenzo I, Russell C. Effects of current and former pacifier use on the dentition of 24- to 59-month-old children. Pediatr Dent 1995; 17: 437–44.
824
The universe weighed and found wanting Only a third of the universe is in the form of matter, according to data based on the velocities of 141 000 galaxies. The rest is believed to be mysterious dark energy, a force first postulated by Einstein. The combined effects of low mass and dark energy could mean that the universe will expand forever because there is too little mass to provide sufficient gravity to rein it in. The expansion of the universe was discovered in 1929 by Edwin Hubble, who measured the velocities and distances of 24 galaxies. This time the expansion was measured by an international team of 28 astronomers led by John Peacock, University of Edinburgh. They used the Anglo-Australian Telescope (AAT) to obtain data on 141 000 galaxies. Hubble spent years getting his data; the AAT measures 400 velocities simultaneously in one night. The detailed three-dimensional maps show the highly irregular distribution of the galaxy, with large voids, long filaments of galaxies strung out for 100 million light-years, and dense clusters of galaxies. About 90% of the galaxies appear spread over the surfaces of enormous bubbles in space to give a sponge-like structure of the cosmos. Calculate the mass of the universe from the velocity data is not easy. Each galaxy’s velocity comes from the expansion speed of the universe at its location plus an extra velocity that it acquires because it is falling towards a local concentration of mass. All the galaxies in a galaxy cluster are drawn towards one another by their mutual gravitational attractions, so in a large survey of galaxy velocities, a smearing of the velocities within a large cluster can be detected statistically, and this is imposed on the universal expansion velocity. The extent of blurring of the speeds is driven by the size of the largest mass concentrations, and a statistical analysis of velocities opens up a way of tracing the mass distribution. The average density of the universe is equivalent to about one atom per cubic metre. What Peacock’s tean found is that visible matter (stars, galaxies) accounts for only 3% of the total mass of the universe. Invisible dark matter, which adds to the gravitational forces of the stars and galaxies is ten times as common, but nothing is known of its properties because it does not emit light. The final 67% of the mass is stranger still, taking the form of a uniformly distributed “dark energy”. Evidence is mounting that dark energy is the driving force of the cosmos. From observations of exploding stars in very remote galaxies, astronomers have concluded that the expansion rate is increasing, an astonishing conclusion that implies that the Big Bang that started the universe can never be reversed. To account for the acceleration, cosmologists have reached for their history books to remind themselves that Einstein invoked an inexplicable force of repulsion to explain why the universe has not collapsed under the weight of its internal gravitational forces. This old proposal essentially creates a new force in physics, named quintessence, which acts as an antigravity. The picture of the standard Big Bang model of the universe is rapidly becoming very bizarre. 97% of the universe is not in the form of planets, stars, and galaxies, but exists as so far undiscovered elementary particles and force fields. Simon Mitton St Edmund's College, University of Cambridge, Cambridge CB3 0BN, UK (e-mail: [email protected]) 1
Peacock JA, Cole S, Norberg P, et al. A measurement of the cosmological mass density from clustering in the 2dF Galaxy Redshift Survey. Nature 2001; 410: 169-73.
THE LANCET • Vol 357 • March 17, 2001
For personal use only. Reproduce with permission from The Lancet Publishing Group.
media? The most ready explanation is that a pacifier could be a fomite. Sharing a pacifier has been shown to be a risk factor for the development of meningococcal disease in children in Auckland.5 However, contrary to what might be expected, cultures of 40 recently-used pacifiers were negative for the three major bacterial species commonly associated with acute otitis media.6 Data regarding viral transfer are unavailable. Other potential mechanisms include the facilitated transfer of nasopharyngeal organisms into the middle-ear space via the Eustachian tube, or the transudation of fluid into the middle ear, perhaps by pressure changes associated with long periods of sucking. To further cloud the issue, studies from four countries suggest that pacifier use may reduce the risk of sudden infant-death syndrome (SIDS),7–10 although the results are not conclusive.11 Thus, as with so many issues in clinical medicine, the appropriate guidance to be offered parents about pacifier use is not clear-cut. On the basis of existing information, a reasonable suggestion is that a child can use a pacifier for up to a year of age, both for comfort and as a possible protective factor against SIDS. Since long-term pacifier use is associated with oral candidosis,12 an increased incidence of respiratory and gastrointestinal illness,13 dental caries,14 and dental malocculsions,15 clinicians should encourage parents to reduce pacifier use to transitional situations or periods of stress after age 1 and eliminate use after age 2. However, further studies are needed before otitis can be added to the list of pacifier sins. *J Christopher Post, Mary C Goessier *Department of Paediatric Otolaryngology and Department of Paediatrics, Allegheny General Hospital, Pittsburgh, PA 15212, USA (e-mail: [email protected]) 1
2
3 4
5
6 7
8 9
10
11 12 13 14
15
Niemela M, Uhari M, Hannuksela A. Pacifiers and dental structures as risk factors for otitis media. Int J Pediatr Otorhinolaryngol 1994; 29: 121–27. Niemela M, Uhari M, Mottonen M. A pacifier increases the risk of recurrent acute otitis media in children in day care centers. Pediatrics 1995; 96: 884–88. Jackson JM, Mourino AP. Pacifier use and otitis media in infants twelve months of age or younger. Pediatr Dent 1999; 21: 255–60. Niemela M, Pihakari O, Pokka T, Uhari M, Uhari M. Pacifier as a risk factor for acute otitis media: A randomized, controlled trial of parental counseling. Pediatrics; 106: 483–88. Baker M, McNicholas A, Garrett N, et al. Household crowding a major risk factor for epidemic meningococcal disease in Auckland children. Pediatr Infect Dis J 2000; 19: 983–90. Brook I, Gober AE. Bacterial colonization of pacifiers of infants with acute otitis media. J Laryngol Otol 1997: 111: 614–15. Arnestad M, Andersen M, Rognum TO. Is the use of dummy or carry-cot of importance for sudden infant death? Eur J Pediatr 1997; 156: 968–70. Mitchell EA, Taylor BJ, Ford RP, et al. Dummies and the sudden infant death syndrome. Arch Dis Child 1993; 68: 501–04. L’Hoir MP, Engelberts AC, van Well GT, et al. Dummy use, thumb sucking, mouth breathing and cot death. Eur J Pediatr 1999; 158: 896–901. Fleming PJ, Blair PS, Pollard K, et al. Pacifier use and sudden infant death syndrome: results from the CESDI/SUDI case control study. Arch Dis Child 1999; 81: 112–16. Righard L. Sudden infant death syndrome and pacifiers: a proposed connection could be a bias. Birth 1998; 25: 128–29. Sio JO, Minwalla FK, George RH, Booth IW. Oral candida: is dummy carriage the culprit? Arch Dis Child 1987; 4: 406–08. North K, Golding J, Fleming PJ. Pacifier use and morbidity in the first six months of life. Pediatrics 1999; 103: E34. Ollila P, Niemela M, Uhari M, Larmas M. Prolonged pacifiersucking and use of a nursing bottle at night:possible risk factors for dental caries in children. Acta Odontol Scand 1998; 4: 233–37. Adair SM, Milano M, Lorenzo I, Russell C. Effects of current and former pacifier use on the dentition of 24- to 59-month-old children. Pediatr Dent 1995; 17: 437–44.
824
The universe weighed and found wanting Only a third of the universe is in the form of matter, according to data based on the velocities of 141 000 galaxies. The rest is believed to be mysterious dark energy, a force first postulated by Einstein. The combined effects of low mass and dark energy could mean that the universe will expand forever because there is too little mass to provide sufficient gravity to rein it in. The expansion of the universe was discovered in 1929 by Edwin Hubble, who measured the velocities and distances of 24 galaxies. This time the expansion was measured by an international team of 28 astronomers led by John Peacock, University of Edinburgh. They used the Anglo-Australian Telescope (AAT) to obtain data on 141 000 galaxies. Hubble spent years getting his data; the AAT measures 400 velocities simultaneously in one night. The detailed three-dimensional maps show the highly irregular distribution of the galaxy, with large voids, long filaments of galaxies strung out for 100 million light-years, and dense clusters of galaxies. About 90% of the galaxies appear spread over the surfaces of enormous bubbles in space to give a sponge-like structure of the cosmos. Calculate the mass of the universe from the velocity data is not easy. Each galaxy’s velocity comes from the expansion speed of the universe at its location plus an extra velocity that it acquires because it is falling towards a local concentration of mass. All the galaxies in a galaxy cluster are drawn towards one another by their mutual gravitational attractions, so in a large survey of galaxy velocities, a smearing of the velocities within a large cluster can be detected statistically, and this is imposed on the universal expansion velocity. The extent of blurring of the speeds is driven by the size of the largest mass concentrations, and a statistical analysis of velocities opens up a way of tracing the mass distribution. The average density of the universe is equivalent to about one atom per cubic metre. What Peacock’s tean found is that visible matter (stars, galaxies) accounts for only 3% of the total mass of the universe. Invisible dark matter, which adds to the gravitational forces of the stars and galaxies is ten times as common, but nothing is known of its properties because it does not emit light. The final 67% of the mass is stranger still, taking the form of a uniformly distributed “dark energy”. Evidence is mounting that dark energy is the driving force of the cosmos. From observations of exploding stars in very remote galaxies, astronomers have concluded that the expansion rate is increasing, an astonishing conclusion that implies that the Big Bang that started the universe can never be reversed. To account for the acceleration, cosmologists have reached for their history books to remind themselves that Einstein invoked an inexplicable force of repulsion to explain why the universe has not collapsed under the weight of its internal gravitational forces. This old proposal essentially creates a new force in physics, named quintessence, which acts as an antigravity. The picture of the standard Big Bang model of the universe is rapidly becoming very bizarre. 97% of the universe is not in the form of planets, stars, and galaxies, but exists as so far undiscovered elementary particles and force fields. Simon Mitton St Edmund's College, University of Cambridge, Cambridge CB3 0BN, UK (e-mail: [email protected]) 1
Peacock JA, Cole S, Norberg P, et al. A measurement of the cosmological mass density from clustering in the 2dF Galaxy Redshift Survey. Nature 2001; 410: 169-73.
THE LANCET • Vol 357 • March 17, 2001
For personal use only. Reproduce with permission from The Lancet Publishing Group.