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Seeing double could help resolve dispute about how fast the universe is expanding
The question of how quickly the universe is expanding has been bugging astronomers for almost a century. Different studies keep coming up with different answers — which has some researchers wondering if they've overlooked a key mechanism in the machinery that drives the cosmos.
[...] At the heart of the dispute is the Hubble constant, a number that relates distances to the redshifts of galaxies — the amount that light is stretched as it travels to Earth through the expanding universe. Estimates for the Hubble constant range from about 67 to 73 kilometers per second per megaparsec, meaning that two points in space 1 megaparsec apart (the equivalent of 3.26 million light-years) are racing away from each other at a speed between 67 and 73 kilometers per second.
[...] [Scientists] chose one specific subset of quasars — those whose light has been bent by the gravity of an intervening galaxy, which produces two side-by-side images of the quasar on the sky.
Light from the two images takes different routes to Earth. When the quasar's brightness fluctuates, the two images flicker one after another, rather than at the same time. The delay in time between those two flickers, along with information about the meddling galaxy's gravitational field, can be used to trace the light's journey and deduce the distances from Earth to both the quasar and the foreground galaxy. Knowing the redshifts of the quasar and galaxy enabled the scientists to estimate how quickly the universe is expanding.
[...] The UCLA-led team came up with an estimate for the Hubble constant of about 72.5 kilometers per second per megaparsec, a figure in line with what other scientists had determined in research that used distances to supernovas — exploding stars in remote galaxies — as the key measurement. However, both estimates are about 8 percent higher than one that relies on a faint glow from all over the sky called the cosmic microwave background, a relic from 380,000 years after the Big Bang, when light traveled freely through space for the first time.
H0LiCOW - IX. Cosmographic analysis of the doubly imaged quasar SDSS 1206+4332 and a new measurement of the Hubble constant (DOI: 10.1093/mnras/stz200) (DX)
(Score: 2) by inertnet on Wednesday January 23 2019, @03:57PM (1 child)
If you use an average expansion speed of 70 km/s/Mpc and 300,000 km/s for the speed of light, then the edge of the observable universe would be 300,000/70 = 4285.71 Mpc = 13,971 billion light-years away. Anything beyond that distance would be invisible to us. The age of the universe is estimated to be around 13,8 billion years. Is it a coincidence that these figures match so closely, or is my calculation flawed?
(Score: 0) by Anonymous Coward on Friday January 25 2019, @12:53PM
I have the very same problem as you. I think we're both saying that its wrong to say that: AgeOfUniverse == MaxPerceptibleDistance.
The only workaround offering a solution here, seems to be to say "The Big Bang happened everywhere at once in an infinite space". Which of course means that it wasn't a single point event which in its time ran counter to the 2nd law of thermodynamics due to its creation of order out of disorder. Roger Penrose has viable stories where Entropy makes sense and my/our? intuitions are not brutalized.