Can we look back in time and see our galaxy forming? (Intermediate)

If looking far out into the universe allows us to peer "backwards in time", at light from galaxies that left long, long ago - in theory, shouldn't we be able to see our own galaxy forming, as we look towards the "edge" of the universe?

My mind has been trying to grapple with this. It seems that with the fact that the Milky Way moves along with the rest of the universe, and light bends, etc., then at some point in space we should be able to literally see ourselves.

Good question. When we look at an object, you are correct in that we see it as it was when the light left it. It takes time for the light to reach us. We see the Sun as it was just over 8 minutes ago because it is 8 light-minutes away. If it were to explode right now, we wouldn't know for another 8 minutes. (But the Sun won't explode; please see this answer.) Alpha Centauri, which is roughly 4 light-years away, we see as it was 4 years ago.

Now, imagine we could see a star at the other edge of our galaxy, and let's say that is about 100,000 light-years away, which is roughly the size of our galaxy. We see it as it was 100,000 years ago. If we wanted to study what this star was doing 150,000 years ago, we would be unable to do so because the light that left it 150,000 years ago has already long since hit us or passed by us.

Thus, if we wanted to look all the way to the edge of the Universe (which is expanding, but ignore this as the reasoning is still the same), light has been traveling to us for billions of years. Light from our own galaxy billions of years ago has long since left the galaxy and is traveling throughout the distant Universe. Somebody else could see our galaxy as it was billions of years ago, but we could never do so.

This page was last updated January 28, 2019.

About the Author

Michael Lam

Michael Lam is a Cornell University graduate student and a member of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Collaboration. He works on improving the timing precision of an array of millisecond pulsars for the goal of detection and study of gravitational waves. He completed his undergraduate degree at Colgate University in Astronomy-Physics and Computer Science and is originally from New York City.

Most Popular

Our Reddit AMAs

AMA = Ask Me (Us) Anything