How One Supernova Measured The Universe
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it when explaining gravitational lensing time delays, repeat sightings of a supernova, and the radar-to-Venus test of general relativity.
Recommended by 1 people across 1 different months, 2020 to 2023.
What it is
A Veritasium explainer on SN Refsdal, a supernova whose light was split by a galaxy cluster's gravitational lens into multiple images that arrived at different times. Derek Muller walks through how astronomers predicted its reappearance and how the delays can be used to measure the universe's expansion rate, with side material on the Shapiro delay of light near gravity.
Cited in 1 Wikipedia article, including SN Refsdal.
What people said
Recommends mmesser314 · 2023-07 · Physics Stack Exchange · on “Is it possible to witness supernova events from the past? Do they repeat?”
There is one supernova that has been observed at 5 different times because of gravitational lensing. Light from the supernova was bent into different paths that took different amounts of time to reach us. This was important because it provides a third way to measure the rate of expansion of the universe. Currently the other two disagree with each other. See this Veritasium video for more info - How One Supernova Measured The Universe [this video]
Cites Jesse · 2020-11 · Physics Stack Exchange · on “Can you use this method to measure the speed of light in one direction?”
[this video] in this video they measure the same event at different times does that tell you the speed of light in that direction? Since the event doesn’t appear to happen at the same time instantaneously does that mean that the speed of light isn’t infinite in that direction? Can you measure the speed of light by looking at similar events and in different directions?
Cites mon · 2022-07 · Physics Stack Exchange · on “How can we send radar to Venus and reflect it back on earth?”
Question How is it possible to send laser light to Venus and reflect it back on earth? I believe there is no artificial reflection material e.g. mirror on Venus. Background Veritasium How One Supernova Measured The Universe [this video] talks about light travelling slower in the space curved by gravity and the proof by sending laser to Venus. [LINK] Update The question title was How can we send laser light to Venus and reflect it back on earth? but it was not laser but radar that Derek mentioned in the Veritasium video.