Images in light years and traveling in light years…


The Hubble telescope captured an image 230 million light years away. It was an image of two galaxies colliding 230 million years ago.

If I had a space ship that contained FTL technology and traveled 230 million light years into that direction, my understanding is that it would look completely different from the image that was captured by Hubble.

**I guess my question is… how do we get that image from 230 MILLION years ago only just now? My brain wants to view it as a physical photo that flew over here because I just can’t wrap my head around how an old image could reach us.**

** FYI: I read through [this ELI5 thread on light years]( and I still don’t really get it. Maybe I’m just stupid :/

In: Physics

Light takes time to reach us. The light that is getting to us today is old, in this case 230 millions of years old.

You kind of answered your question already.

The speed of light is 2,999*10^6 m/s or something like that, so that is the speed it travels. Always when you see light it is from the past time. Coz it is bound by the speed of light.

Same for the speed of sound 300ish m/s, when you hear it the aggregator for the sound already happened a relatively long time before your perception of it.

The image that we see is 230 million years old, if we move in the opposite direction from the light coming from the collision at exactly same speed, the image will stay constant and never change. However, if we look at the collision after travelling 20 million light years in the direction of the collision at the speed of light, the image that we see will be 210 million years old and not 250.

Feel free to correct me as I’m not a 100% sure.

Throw a rock in a pond. Ripples radiate out from the point the rock hit the water.

When the first ripple hits you, you see a representation of what the water looked like when the ripple first left the starting point. Jump straight to the source and you see the water actually looks quite different. So much time has passed it may not even be making ripples anymore.

We look at an image of a star 100,000 light years away. Then we hop on a ship with FTL. When we arrive at the star we may instead find a black hole or a supernova or a white dwarf, indicating the star died.

> how do we get that image from 230 MILLION years ago only just now?

Light moves at a finite speed, so it takes time to arrive.

Maybe you have already seen fireworks or lighting from far away (like a few miles). You might have noticed that you hear the bang some time after you see it. That’s because sound is slower than light. If you were blind, you would perceive the bang only a few second late.
The same thing happens with light, except that we are observing stuff that is ridiculously far (trillion trillions miles), so it takes millions of years for light to reach us.