Exploring Time Through Distant Galaxies

[zewpals]

Okay last one for today. promise.

When we look back at distant galaxies, we are looking back into time. If the galaxy is 2 billion light years away, we are looking 2 billion years back in time. But hold on a second. 2 billion years ago it was at that point. But present day it's somewhere else. Most galaxies are spreading apart, but some are headed for collision.

If another galaxy was coming closer to us (not headed directly towards), couldn't we point our telescopes to where it was 2 billion years ago and also to where it was 5 years ago and see it in both places? Why don't we see a blur of the path the galaxies have traveled? If we can look back into time, shouldn't we be able to see that galaxy at every point in time as long as it is within 13.7 billion light years?

This raises another question. Assume the universe is a sphere (I really don't know if it is). If the radius is 13.7 billion light years (the age of the universe), then shouldn't we be able to see further than 13.7 billion light years, since we are not at the center? But how in could we see further than 13.7 billion years ago back into time? Thanks :D.

Since this is all relative it won't really help anyone with anything. I'm just curious.

 

[Chalnoth]

If another galaxy was coming closer to us (not headed directly towards), couldn't we point our telescopes to where it was 2 billion years ago and also to where it was 5 years ago and see it in both places?

The galaxy would have to be moving faster than the speed of light for this to happen.

 

[zewpals]

I don't understand why, though.

 

[Chalnoth]

I don't understand why, though.

Well, think about it. Let's take an object that, ten minutes ago, was ten light minutes away. So we would just now be seeing this object and the light it emitted ten minutes ago.

If we also see the light that it emitted 11 minutes ago, then that would mean 11 minutes ago it was 11 light minutes away, meaning it would have been traveling one light minute per minute, i.e. the speed of light.

For an object traveling slower than the speed of light, it would have been 11 light minutes away before 11 minutes ago, and so the light would have already passed us by.

 

[sardar]

I find this topic incredibly intriguing and thought-provoking. The concept of looking back in time through distant galaxies is a fascinating one, and it highlights the immense scale and complexity of the universe.

To answer your first question, yes, if another galaxy was coming closer to us, we could theoretically point our telescopes to where it was 2 billion years ago and also where it was 5 years ago and see it in both places. However, the light from that galaxy would have traveled a different path to reach us at those different points in time, so we would see slightly different images of the galaxy. And since the universe is constantly expanding, the galaxy would also appear to be moving away from us at a faster rate as we look back in time.

Regarding your second question, the universe is not a perfect sphere and its shape is still a topic of debate among scientists. However, assuming it is a sphere with a radius of 13.7 billion light years, we would indeed be able to see further than 13.7 billion light years, as we are not at the center. This is because the light from objects at the edge of the observable universe would have had more time to reach us, due to the expansion of the universe.

But as you pointed out, this raises the question of how we can see further than 13.7 billion years back in time. This is because the expansion of the universe also affects the speed at which light travels, making it possible for us to see objects that are now further away from us than they were when the light was emitted. This is known as the "inflationary period" and it is a key concept in understanding the expansion of the universe.

While these ideas may seem abstract and difficult to grasp, they are important in helping us understand the universe and its origins. As scientists, we continue to explore and study these concepts in order to gain a better understanding of the mysteries of time and space. Thank you for your thought-provoking questions, and I encourage you to continue exploring and learning about the wonders of our universe.