My 30 years old question

[flaurier]

This is my 1st post here,<br />I am an chemical oceanographer and as far as I can remenber the universe and astromy have been fascinating me.<br />I read numerous books and scientific articles and always try to keep myself up to date with the current knowledge.<br />However I have a critical question that is being left un-answered for almost 30 years, something I do not understand and leave me with a long-lasting bitter taste of frustration. <br />The following may appear totally stupid to some of you but I would love to see this question clearly answered.<br />I understand perfectly the concept of constant light speed and that the further you look into space, you further back in time you see.<br />However, if the universe has been expanding since the big-bang, how come we are STILL able to see the universe exactly the way it was billions years ago (e.g. the Hubble ultra deep field)?<br />If you look at a galaxy 10 billions years away, you also look at it the way it was 10 billions years ago, I understand that, HOWEVER, I do not understand why the time it must have taken for<br />the universe expansion to get the galaxy 10 billions light-years away from us does not affect the way it appears to us.<br />Was the original expension of the universe faster than the speed of light?<br /><br />I hope my questions are somewhat clear to some of you.<br /><br />Thank you in advance for any input.

 

[kmarinas86]

http://www.anzwers.org/free/universe/redshift.html<br /><p>Because the universe is expanding, the question of the distance to a very distant galaxy is hard to answer. It all depends on your point of view. </p><br /><div class="caption">This is the problem of defining a distance in an expanding universe: Two galaxies are near to each other when the universe is only 1 billion years old. The first galaxy emits a pulse of light. The second galaxy does not receive the pulse until the universe is 14 billion years old. By this time the galaxies are separated by about 26 billion light years; the pulse of light has been travelling for 13 billion years; and the view the people receive in the second galaxy is an image of the first galaxy when it was only 1 billion years old and when it was only about 2 billion light years away. </div><br /><p>There are four different distance scales commonly found in cosmology:</p><br /><dl><br /><dt><span class="yellow"><font color="#ffff00">(1) Luminosity Distance - D_L</font></span> <br /><dd>In an expanding universe, distant galaxies are much dimmer than you would normally expect because the photons of light become stretched and spread out over a wide area. This is why enormous telescopes are required to see very distant galaxies. The most distant galaxies visible with the Hubble Space Telescope are so dim that they appear as if they are about 350 billion light years away even though they are much closer. <br />Luminosity Distance is not a realistic distance scale but it is useful for determining how faint very distant galaxies appear to us. <br /><br /><dt><span class="cyan"><font color="#00ffff">(2) Angular Diameter Distance - D_A</font></span> <br /><dd>In an expanding universe, we see the galaxies near the edge of the visible universe when they were very young nearly 14 billion years ago because it has taken the light nearly 14 billion years to reach us. How</dd></dt></dd></dt></dl>

 

[harmonicaman]

<i>"Was the original expansion of the universe faster than the speed of light?"</i><br /><br />Here's an explanation for how such a thing may have occurred. <br /><br />

 

[flaurier]

<blockquote><font class="small">In reply to:</font><hr /><p>This is the problem of defining a distance in an expanding universe: Two galaxies are near to each other when the universe is only 1 billion years old. The first galaxy emits a pulse of light. The second galaxy does not receive the pulse until the universe is 14 billion years old. By this time the galaxies are separated by about 26 billion light years; the pulse of light has been travelling for 13 billion years; and the view the people receive in the second galaxy is an image of the first galaxy when it was only 1 billion years old and when it was only about 2 billion light years away.<p><hr /></p></p></blockquote><br /><br />THANK YOU SO MUCH!<br />If I understand correctly, even though the far distant universe was at one time much closer to us, we would onlyl receive its dimmed light/image today? <br />You do not know how happy I am that I finally got such a precise response to my questions!<br />Is there any books that would describe in more details the physics behing such phenomenon?<br /><br />Once again thank you so much<br /> <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><br />It DOES affect it....it red-shifts the wavelengths of light as it rushes away from us. As the universe continues to expand, the farthest objects will be red-shifted into invisibility as they exceed the speed of light, relative to us.<br /><br />Someone correct me if I'm wrong!<p><hr /></p></p></blockquote><br />It is true, but I was not referring to the redshift due to an expanding universe but the fact that we are still able to see a far distant universe the way it was several billions years ago, even though it was at one point closer to us and has spent time "travelling" away from us since then (therefore should have changed).<br /><br />

 

[unlearningthemistakes]

ASTRONOMY: the evolving universe<br />6th edition<br /><br />by MICHAEL ZEILIK<br />ISBN 0-471-53856-6 <div class="Discussion_UserSignature"> <p>pain is inevitable</p><p>suffering is optional </p> </div>

 

[unlearningthemistakes]

more to this, light's speed is also affected by viscosity of space for the void is not really a void. so distances by light speed are affected also. <div class="Discussion_UserSignature"> <p>pain is inevitable</p><p>suffering is optional </p> </div>

 

[unlearningthemistakes]

dust. gas. etc. <div class="Discussion_UserSignature"> <p>pain is inevitable</p><p>suffering is optional </p> </div>

 

[kmarinas86]

The speed of light is constant.<br /><br />The "second" is not.<br /><br />Space-time curvature, and gravitational time dilation alter the "second".<br /><br />The second near dust and gas (i.e. galaxies, suns, blackholes) is longer, hence the statement about "viscosity" which may be a misapplication (or analogy) of the term.

 

[newtonian]

unlearningthemistakes - The IGM is close to a vacuum, but not quite - and the plasma, albeit thin, does effect the spectra of distant objects.<br /><br />It results in what is called the Lyman-alpha forest in spectral analysis - as in a recent Scientific American article.<br /><br />I do not know how such a thin medium would seriously effect the speed of light.<br /><br />However, I do believe the gravity of the universe would effect the speed, or at least direction, of light (compare gravitational lensing).<br /><br />Certainly gravity stops light in a black hole. <br /><br />Some scientists have recently seriously questioned whether the speed of light has been constant since the origin of our universe.