- How did Leavitt's period-luminosity relation later enable Edwin Hubble to measure the scale of the universe?
Big Bang Theory
The prevailing cosmological model of universe origin and expansion.
- What did Hubble's 1924 distance measurement to Andromeda's Cepheids ultimately prove about the Milky Way?
- Why did confirming a physical pulsation mechanism matter for trusting the period-luminosity relationship as a cosmic distance ladder?
- How did Edwin Hubble use Leavitt's relation to prove the Andromeda nebula lay outside the Milky Way?
- How far did Hubble calculate Andromeda to be, and why did that distance settle the debate?
- What later discoveries about the universe followed from Hubble's proof that other galaxies exist?
- What did Lemaître derive from Einstein's field equations in 1927?
- What relationship between galaxy distance and recession speed did Lemaître work out two years before Hubble?
- What was Lemaître's hypothesis of the primeval atom?
- What relationship did Hubble find between a galaxy's distance and its recession velocity?
- How did Georges Lemaître anticipate Hubble's Law two years earlier, and why did his paper go unnoticed?
- Why does an expanding universe imply that everything was once in the same place?
- What role did the 100-inch Hooker telescope play in making Hubble's measurements possible?
- Why did Gamow add Hans Bethe's name to a paper Bethe hadn't worked on?
- What did the 1948 paper actually explain about the formation of hydrogen and helium?
- What temperature did Alpher and Herman predict for the universe's leftover radiation, and when was it confirmed?
- Who independently proposed the steady-state theory in 1948, and how did their papers differ?
- Where did the term 'Big Bang' actually come from, and was it meant as a compliment?
- What did the 15.8% redshift in 3C 273's spectrum reveal about its distance from Earth?
- How did Maarten Schmidt realize the strange emission lines in 3C 273's spectrum were actually redshifted hydrogen?
- What did the redshift of 3C 273 imply about its distance and energy output?
- How was Robert Dicke's team at Princeton already prepared to explain the exact signal Penzias and Wilson had found?
- How old is the cosmic microwave background radiation, and what does it reveal about the early universe?
- What did Gamow, Alpher, and Herman predict in 1948 about radiation left over from the early universe?
- Why did Gamow never receive a Nobel Prize for a prediction that Penzias and Wilson were awarded one for confirming?
- How does a uniform 2.7 Kelvin glow across the whole sky count as evidence for the Big Bang?
- How did William Fowler's nuclear physics work explain where elements heavier than hydrogen come from?
- Why did the 1983 Physics Prize pair a theory of stellar collapse with a theory of element formation?
- What did the FIRAS instrument's blackbody spectrum measurement confirm about Big Bang cosmology?
- How was Hubble's vision corrected, and what major discoveries followed once it was fixed?
- Why are Type Ia supernovae useful as 'standard candles' for measuring cosmic distances?
- What did both the Supernova Cosmology Project and the High-Z Supernova Search Team find when they measured distant supernovae?
- Why did fainter-than-expected supernovae imply that the universe's expansion is accelerating rather than slowing?
- What did Fred Hoyle's B2FH paper explain about how stars forge the elements heavier than helium?
- Why did Hoyle coin the term 'Big Bang' as an insult rather than a compliment?
- What fringe theories did Hoyle advocate later in his career despite lacking evidence?
- What is the cosmic microwave background, and when was it formed?
- What did COBE's measurements of the cosmic microwave background confirm about the Big Bang?
- How cold is the afterglow of the Big Bang today, and why has it cooled so much?
- How did astronomers use Type Ia supernovae to measure the expansion rate of the universe?
- Why were the discovering teams reluctant to believe their own results?
- What is a kilonova, and what did its spectrum reveal about heavy-element formation?
- How much gold did the neutron-star merger produce, and why is that significant for where gold on Earth originated?