Can we see the earth in the past ?

  • Context: Graduate 
  • Thread starter Thread starter HossamCFD
  • Start date Start date
  • Tags Tags
    Earth
Click For Summary

Discussion Overview

The discussion revolves around the concept of observing Earth in the past through the lens of cosmological expansion and the nature of light propagation in an expanding universe. Participants explore theoretical scenarios involving the speed of light, the implications of universe expansion, and speculative ideas about technology and instrumentation.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Speculative

Main Points Raised

  • One participant questions whether the expansion of the universe, if exceeding the speed of light, would allow for the possibility of observing Earth in the past if the expansion were to decelerate.
  • Another participant asserts that the expansion of the universe does not enable us to catch up to light already emitted from Earth, regardless of any future contraction.
  • A participant seeks clarification on whether the expansion results in any relative movement from a previous location, suggesting that they may remain stationary relative to emitted light.
  • Speculative ideas are introduced about using a large mirror to reflect light from Earth, with humorous commentary on the practicality and implications of such an endeavor.
  • One participant proposes a hypothetical technology that could collect and process light from an Earth-like planet, suggesting a potential investment opportunity.
  • Another participant raises a question about whether Earth leaves a detectable wake in space-time as it moves, and if such a wake could be measured and reproduced.

Areas of Agreement / Disagreement

Participants express differing views on the implications of cosmic expansion and the possibility of observing past events. While some agree on the limitations imposed by the speed of light and cosmic expansion, others introduce speculative ideas without reaching a consensus.

Contextual Notes

Participants acknowledge the complexities of light propagation in an expanding universe and the speculative nature of ideas presented, such as the use of mirrors or future technology to observe past events.

Who May Find This Useful

This discussion may be of interest to those exploring concepts in cosmology, the nature of light, and speculative technologies related to observational astronomy.

HossamCFD
Messages
63
Reaction score
181
Hi everyone, I am not very knowledgeable in cosmology but I hope you would be patient enough to clarify this issue for me.

I understand that nothing can move through space with speeds higher than the speed of light, however space itself can expand with higher speed. Now I have this, probably silly, idea that i am asking clarification for. If we assume that the current expansion of the universe exceeds the speed of light, that will mean that we are moving from our current place faster than light, right ? If so, then if for any reason the expansion speed decelerates so that light from our previous place reaches us, would we be able to look at the Earth in the past ?

In other words, would the expansion of the universe mean that we are moving relative to any observable frame of reference ? or are our coordinates fixed during this expansion (neglecting the movement of Earth through space) ?
 
Space news on Phys.org
Expansion of the universe does not imply we will catch up to the light already emitted from earth: even if the expansion turns to contraction, that light will always be moving away from us.
 
If I understand you correctly, then this will mean that the expansion of the universe does not result in any movement from our previous location (relative to any sensible reference frame) so that we will always look stationary to the emitted beam of light. am I getting this correctly ?
 
Thanks
 
Wait. That's it??

The OP asks a question, it gets answered, and the OP is enlightened?

There's got to be a trick here. If this is allowed to continue, PF may just explode.
 
DaveC426913 said:
Wait. That's it??

The OP asks a question, it gets answered, and the OP is enlightened?

There's got to be a trick here. If this is allowed to continue, PF may just explode.

LOL. I can see why you get the best humor award :)

The thing is, the answer showed me clearly that I had the wrong understanding of the universe expansion, which I already felt. That's why I was "enlightened" so quickly.

Don't worry, that won't happen again :)
 
You would be absolutely amazed how rarely that happens here.
 
Ya know, if you had a really big mirror way out there, oriented just right, with a little concave parabolic curvature, you really COULD see Earth in the past.

Ya think it would make us look fat?
 
  • #10
It would take a very, very, very long time to view our 'reflection'.
 
  • #11
Chronos said:
It would take a very, very, very long time to view our 'reflection'.

Indeed, if we make such a mirror, let's say, in Andromeda to see the Earth two million years ago, we will have to wait another two million years to see our reflection.
Also if we make it much closer so that we don't wait so much, let's say ten light years away from us, we will only see the Earth ten years ago. Which is not interesting at all !
 
  • #12
Okay, so we are moving at (faster than light) that means that we will never see ourselves because there is no force to slow us down?
 
  • #13
Well - it may not be necessary to make a mirror and place it in space - if we assume our future technology might be able to collect and process scattered photos reflected from an earthlike planet with a large water reflecting surface. If anyone is interested in investing in the development I would be willing to sell a 90% interst in the project for about 20 cents.
 
  • #14
Here is a thought that I had similar to yours. If the Earth moves through space-time does it leave a wake behind it? If it does can an instrument detect that modulated space-time and reproduce whatever modulated it?
 

Similar threads

High School Can the "creation" of space in the Universe affect the speed of light?
  • · Replies 7 ·
Replies
7
Views
4K
Undergrad What if the Universe expands faster than the speed of light?
  • · Replies 19 ·
Replies
19
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
Graduate Black hole thermodynamics and accelerated expansion
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad Receding movement of a stopped object in an accelerating universe?
  • · Replies 23 ·
Replies
23
Views
2K
High School Clarification on how old the Universe is
  • · Replies 11 ·
Replies
11
Views
3K
High School How did expansion take 380,000 years to let light travel freely?
  • · Replies 13 ·
Replies
13
Views
3K
High School Is it possible to see the history of space if it expands faster than light?
  • · Replies 4 ·
Replies
4
Views
2K
High School Size of universe - rewinding big bang versus "flat" universe
  • · Replies 54 ·
2
Replies
54
Views
6K