Can We See Distant Galaxies at Multiple Points in Time?

  • Context: Graduate 
  • Thread starter Thread starter zewpals
  • Start date Start date
  • Tags Tags
    Time
Click For Summary

Discussion Overview

The discussion revolves around the concept of observing distant galaxies at multiple points in time, exploring the implications of light travel time and the movement of galaxies in the universe. It touches on theoretical aspects of cosmology and the nature of light propagation in relation to the expanding universe.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that if we can look back in time at distant galaxies, we should be able to see them at multiple points in their past and present locations.
  • Another participant argues that for this to occur, a galaxy would need to be moving faster than the speed of light, which raises questions about the feasibility of such observations.
  • A participant expresses confusion about the reasoning behind the speed of light limitation in observing multiple positions of a galaxy over time.
  • Another participant attempts to clarify the concept by using an analogy involving an object moving at the speed of light, explaining that light emitted from an object traveling slower than light would not allow for simultaneous observations of its past and present positions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the feasibility of observing galaxies at multiple points in time, with some agreeing on the limitations imposed by the speed of light while others question the reasoning behind it.

Contextual Notes

The discussion includes assumptions about the nature of the universe and the movement of galaxies, as well as the implications of light travel time, which remain unresolved.

zewpals
Messages
38
Reaction score
0
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.
 
Space news on Phys.org
zewpals said:
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.
 
I don't understand why, though.
 
zewpals said:
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.
 
Last edited:

Similar threads

High School Clarification on how old the Universe is
  • · Replies 11 ·
Replies
11
Views
3K
High School Question regarding light from distant objects
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad How far into the Universe can we theoretically reach?
  • · Replies 34 ·
2
Replies
34
Views
5K
Undergrad Why do we still see the CMB today?
  • · Replies 103 ·
4
Replies
103
Views
13K
Undergrad How do you get to the conclusion that there is accelerating expansion?
  • · Replies 23 ·
Replies
23
Views
4K
Undergrad Why Aren't Galaxies Formed After the Big Bang Referred to as Being Further Away?
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Oldest galaxy to date: UDFy-38135539
  • · Replies 23 ·
Replies
23
Views
3K
High School We see a quasar 13 billion light years away. What does this mean?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad What Is the Cosmic Horizon and Its Relation to Black Holes?
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Imaging galaxies receding at a velocity that exceeds c?
  • · Replies 12 ·
Replies
12
Views
4K