Tolman surface brightness test (original) (raw)
The Tolman surface brightness test is one out of six that were conceived in the 1930s to check the viability of and compare new cosmological models. Tolman's test compares the surface brightness of galaxies as a function of their redshift (measured as z). Such a comparison was first proposed in 1930 by Richard C. Tolman as a test of whether the universe is expanding or static. "We show that this is precisely the range expected from the evolutionary models of Bruzual & Charlot. We conclude that the Tolman surface brightness test is consistent with the reality of the expansion."
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| dbo:abstract | The Tolman surface brightness test is one out of six that were conceived in the 1930s to check the viability of and compare new cosmological models. Tolman's test compares the surface brightness of galaxies as a function of their redshift (measured as z). Such a comparison was first proposed in 1930 by Richard C. Tolman as a test of whether the universe is expanding or static. In a simple (static and flat) universe, the light received from an object drops proportional to the square of its distance and the apparent area of the object also drops proportional to the square of the distance, so the surface brightness (light received per surface area) would be constant, independent of the distance. In an expanding universe, however, there are two effects that change this relation. First, the rate at which photons are received is reduced because each photon has to travel a little farther than the one before. Second, the energy of each photon observed is reduced by the redshift. At the same time, distant objects appear larger than they really are because the photons observed were emitted at a time when the object was closer. Adding these effects together, the surface brightness in a simple expanding universe (flat geometry and uniform expansion over the range of redshifts observed) should decrease with the fourth power of 1+z. To date, the best investigation of the relationship between surface brightness and redshift was carried out using the 10 m Keck telescope to measure nearly a thousand galaxies' redshifts and the 2.4 m Hubble Space Telescope to measure those galaxies' surface brightness. The exponent found is not 4 as expected in the simplest expanding model, but 2.6 or 3.4, depending on the frequency band. The authors summarize: "We show that this is precisely the range expected from the evolutionary models of Bruzual & Charlot. We conclude that the Tolman surface brightness test is consistent with the reality of the expansion." (en) Tolman Surface Brightness Test är ett av ett halvdussin test som utformades på 1930-talet för att kontrollera livskraft hos och jämföra nya kosmologiska modeller. Tolmans test jämför galaxers ytljusstyrka som en funktion av deras rödförskjutning (mätt som z). En sådan jämförelse presenterades första gången 1930 av Richard C. Tolman som ett prov på om universum expanderar eller är statiskt. Olika fysiker har hävdat att resultaten stöder skilda modeller. I ett enkelt statiskt universum är ett objekts ytljusstyrka oberoende av avståndet, eftersom såväl det mottagna ljuset som objektets skenbara area avtar med kvadraten på avståndet. I ett expanderande universum adderas dock två olika effekter från avlägsna föremål, så att den uppmätta ytljusstyrkan reduceras med fjärde potensen av (1+z). Till dags dato rapporterades 2001 den bästa undersökningen av sambandet mellan ytljusstyrka och rödförskjutning utförd med 400 tums Keck teleskopet för att mäta nästan ett tusen galaxers rödförskjutningar och med 94 tums Rymdteleskopet Hubble för att mäta dessa galaxers ytljusstyrka. (sv) |
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| rdfs:comment | The Tolman surface brightness test is one out of six that were conceived in the 1930s to check the viability of and compare new cosmological models. Tolman's test compares the surface brightness of galaxies as a function of their redshift (measured as z). Such a comparison was first proposed in 1930 by Richard C. Tolman as a test of whether the universe is expanding or static. "We show that this is precisely the range expected from the evolutionary models of Bruzual & Charlot. We conclude that the Tolman surface brightness test is consistent with the reality of the expansion." (en) Tolman Surface Brightness Test är ett av ett halvdussin test som utformades på 1930-talet för att kontrollera livskraft hos och jämföra nya kosmologiska modeller. Tolmans test jämför galaxers ytljusstyrka som en funktion av deras rödförskjutning (mätt som z). En sådan jämförelse presenterades första gången 1930 av Richard C. Tolman som ett prov på om universum expanderar eller är statiskt. Olika fysiker har hävdat att resultaten stöder skilda modeller. (sv) |
| rdfs:label | Tolman surface brightness test (en) Tolman Surface Brightness Test (sv) |
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