Seeing The First Galaxies - A Question

[zeestephen]

I can't get my mind around the idea of "seeing" back in time.<br /><br />It seems like this would depend entirely on my position in the cosmos.<br /><br />For instance, if a man ten feet away shines a flashlight on me for one second, that light passes by me and is "gone" in an instant, correct?<br /><br />I can't turn around, focus a telescope on the receding light, and see it, correct?<br /><br />It seems to me that Earth would have to be in a perfect viewing position.<br /><br />All planets "in front " of us can't see this light because it already passed by.<br /><br />All planets "behind" us can't see this light because it hasn't reached them yet.<br /><br />I go round and round with this idea and never work it out. <br /><br />

 

[derekmcd]

<p>"I can't get my mind around the idea of "seeing" back in time"<br /><br />Light takes time to travel through space. The light beginning at it's source 10 billion light years away will need 10 billion years to reach your eyes. You will view this object as it was 10 billion years ago.<br /><br />"For instance, if a man ten feet away shines a flashlight on me for one second, that light passes by me and is "gone" in an instant, correct?"<br /><br />Not really. The photons created by the flashlight will travel on. You could still see those photons created by the flashlight if they are reflected by another source. <br /><br />"I can't turn around, focus a telescope on the receding light, and see it, correct?"<br /><br />In reference to the previous question, I think you are asking if you can still view the source of the photons as they recede away from you. In this, the answer is no. The source creating or emiting the photons is no longer in your line of sight, but the actual photons can be followed (in a sense) and still be seen. The photons from the sun can be viewed after they pass by you if, for example, the moon is behind you. The light from the moon is nothing more than photons originating in the sun, passing by you, and being reflected back.<br /><br />"All planets "in front " of us can't see this light because it already passed by"<br /><br />They can see this light... They simply see the light before we do. I suppose as the image passes by them, it is gone, but distant galaxies are emitting continuous streams of photons. The image is constantly changing.<br /><br />"All planets "behind" us can't see this light because it hasn't reached them yet."<br /><br />This is exactly correct. As light does take time to travel through space, the image we see will reach our view first then travel on for another duration to reach the planet behind us.<br /><br />Great first question and welcome to SDC. I hope I made some sense.</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[dragon04]

Welcome to SDC!<br /><br />I used to have a hard time with that myself. I think mostly because I only thought in terms of my personal frame of reference rather than the actual system.<br /><br />What got me around that dilemma was simple. If the Sun blew up this very moment, I would not know it for 8 minutes and 30 some odd seconds.<br /><br />That and realizing that Neil Armstrong stepped onto the Moon a full second and a half or so before I heard his famous words. I was indeed observing the past in terms of my presesnt. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[yevaud]

A cogent and well stated explanation. Very good. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[derekmcd]

"<i>That's not even the equivalent of one speck of dust on this planet earth in terms of comparisons."</i><br /><br />The sad thing is, we've barely even investigated that 1 speck of dust. All we've really done is pick it up, handle it briefly and set it back down. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[alkalin]

Good answer to an interesting question that could serve on another related issue, why is there a CMB from the big bang? When this event supposedly happened, this energy simply should have escaped the region of the big bang immediately. Some here might argue that space was and is created along with the big bang, therefore we do have to worry about it. Well, I sure would like to put a chunk of pure space under the microscope and see if I could change it in any way. <br /><br />The only reason energy of this form would not have escaped is if the CMB was and is continuously generated from the big bang. Or am I wrong? But of course inflation fixes that problem, and produces dozens of other problems in the process. <br /><br />Illogic coming from math theory that discards cause is holding us back from actually finding reality, which is a daunting task even without paths that lead nowhere.<br /><br />These questions are important, they can open new ideas to solutions. After all, light, the photon, is known only in what we can measure, which does not tell us why it exists, which is the same for gravity and many other things.<br /><br />

 

[dragon04]

<font color="yellow">The photons from the sun can be viewed after they pass by you if, for example, the moon is behind you. The light from the moon is nothing more than photons originating in the sun, passing by you, and being reflected back.</font><br /><br />You know, I never thought about that before, and I don't know why except that your reply provoked a little thought and for that, I thank you.<br /><br />Sometimes, the full moon is visible in the daytime. In the case of both the Moon and the Sun being in the same field of view, this creates the delicious ability to effectively see not just one, but two "pasts" in reference to the Sun. or perhaps more accurately stated, we get to see two frames of a "motion picture" of the Sun's emission of photons.<br /><br />Not very profound, but really cool. <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[derekmcd]

Indeed it is cool. Even thinking about some of the most very basic ideas and concepts of the cosmos is still awe inspiring. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[tom_hobbes]

I have to admit I took his post to be asking this:<br /><br />if the universe is so old, how come we can see nearly all the way back to the begining of it, shouldn't most of that light have already sped past us long ago? <div class="Discussion_UserSignature"> <p><font size="2" color="#339966"> I wish I could remember<br /> But my selective memory<br /> Won't let me</font><font size="2" color="#99cc00"> </font><font size="3" color="#339966"><font size="2">- </font></font><font size="1" color="#339966">Mark Oliver Everett</font></p><p> </p> </div>