I read a news article stating that the scientists detected radio waves that reached earth after 8 billion years.
https://www.moneycontrol.com/science/mysterious-deep-space-radio-signal-reaches-earth-after-8-billion-years-leaving-scientists-puzzled-article-12823408.html/amp
My question is how did we figure out that this wave travelled for 8 billion years ?
In: Physics
The speed of light is fixed. Measure the distance to an object in space (because it had to come from SOMETHING, and we can see which direction it came from), and divide that distance by the speed of light. At astronomical distances, you also have to account for the inflation of the universe stretching that distance, but we’ve worked that out too.
As for making that measurement? That’s a bit trickier at those distances, using techniques like standard candles (objects with a precisely known brightness) to roughly work out how far an object is by comparing it to known objects nearby.
We are not sure what process produced it how, but we know the galaxy it’s from. We can measure starlight from that galaxy and determine how much the universe expanded since the light was emitted, which tells us how long the light had to travel. The radio signal has the same speed.
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