[Telescope](https://www.reddit.com/r/interestingasfuck/comments/ke2p2r/nasa_is_about_to_launch_a_telescope_that_can/?utm_source=share&utm_medium=ios_app&utm_name=iossmf)
In: Technology
Because the speed of light is finite, space radiation, including light, is in a sense, time travel. When you see a star that’s 5 million light years away, you’re seeing that star as it existed 5 million years ago, not as it exists right now. For all we know, that star may have supernovaed out of existence 4 million years ago and doesn’t exist now.
The light they see is billions of years old, therefore when they see a planet they are seeing a billions of years old picture. If we we’re on another plant that far away we would see dinosaurs.
Light takes a very long time to reach us from very far away in deep space. The events that this telescope will show us will have happened billions of years ago but the light to let us see them is only just getting here because they happened billions of light years away.
We can see 13.8 billion years into the past because the universe is expanding.
One way to reason about it is to think about being at the big bang 13.8 billion years ago. Draw a circle around yourself. Anything on the circle line is what happened exactly 13.8 billion years ago. Anything outside the circle is what happened earlier, and anything inside the circle is what happened after.
Because of the expansion of the universe, the circle gets bigger as time goes on.
Light from events outside the circle has already passed us and light from events inside the circle is still coming towards us.
A common misconception is that when we see something, we think it happened right then and there, but this is not the case. It’s more clear with sound, if you have a friend stand let’s say 100 meters away and claps their hands, you will see a noticebal delay between you seeing them clap and hearing it. This is because the sound waves takes time to travel to you.
This is equally true for the light you saw showing them clapping! Light is also a wave like sound and moves at a constant speed. If a star “claps” and you stand 1 light year away. It will take exactly 1 year until you hear it. In this case the clap can be a burst of light, and you hearing it is you seeing/detecting the light.
Because of the huge distances that is the universe, we can see old light from stars. Painting us a picture of how they looked like billions of years ago. These stars might still be alive or be dead when the light reaches us, but we will always see it as it was a long time ago.
We can take another closer example, it is widly said that the light from the sun takes 8 min to reach us and this is true. If you look at the sun you will see a 8 min old picture of it!
But how can it capture ist the Telescope ist still on earth so the Light has to reach the earth?
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