Horizon Problem ?

[Kewell]

<p>I was watching the Science channel and they were talking about the Horizon Problem and how its a big problem for the big bang theory. I dont quite understand the problem or the concept of the "Horizon Problem" I tried reading up on it on the internet but it doesnt really make sense.</p><p>&nbsp;</p><p>Can someone please explain this problem and what is so special about it?? Thanks!&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I was watching the Science channel and they were talking about the Horizon Problem and how its a big problem for the big bang theory. I dont quite understand the problem or the concept of the "Horizon Problem" I tried reading up on it on the internet but it doesnt really make sense.&nbsp;Can someone please explain this problem and what is so special about it?? Thanks!&nbsp; <br /> Posted by Kewell</DIV></p><p>&nbsp;</p><p>http://en.wikipedia.org/wiki/Horizon_problem</p><p>&nbsp;</p><p>It basically states how can the properties of one side of the universe be the same as the other if they were never in contact with each other when light (information) first started making its journey some 300,000 years ago.&nbsp; It's not something you can just write off as coincidence... there must be a reason.</p><p>Maybe we can start with what <font size="1"><strong><em>don't</em></strong></font> you understand about it?&nbsp;</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>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I was watching the Science channel and they were talking about the Horizon Problem and how its a big problem for the big bang theory. I dont quite understand the problem or the concept of the "Horizon Problem" I tried reading up on it on the internet but it doesnt really make sense.&nbsp;Can someone please explain this problem and what is so special about it?? Thanks!&nbsp; <br />Posted by Kewell</DIV></p><p>You might try reading Alan Guth's book <em>The Inflationary Universe.</em></p><p>My personal feeling with regard to questions such as your is to learn about the subject from someone who is close to it.&nbsp; Wikipedia and such are useful, but are not always reliable.&nbsp; Guth is a serious physicist, and he actually invented the theory of inflation.</p> <div class="Discussion_UserSignature"> </div>

 

[derekmcd]

I only used Wiki as it seemed liked the most basic description I could find.&nbsp; Hyperphysics had a nice simple description, too but they referred to the isotropic nature versus the homogenous nature which is more fitting.<br /> <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>

 

[redbert]

<p>please clarify for me:</p><p>Can we "see" 10 light years looking "east" and&nbsp; 10 light years looking west?</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<font color="#666699"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>please clarify for me:Can we "see" 10 light years looking "east" and&nbsp; 10 light years looking west?&nbsp; <br /> Posted by redbert</DIV></font><br />I'm not sure I understand your question, but given a powerful enough telescope and a clear line of sight, we can see 13 billion light years in ANY direction.&nbsp; For example, the Hubble Deep Field image was taken in one direction, chosen to avoid being blocked by Earth, Moon, Milky Way, etc., and saw to about 10.5 billion light years.&nbsp; Hubble has since looked in other directions to make the Hubble Deep Field South image and the Hubble Ultra Deep Field image, in which it saw to 13 billion light years. Hubble could have looked in many different directions and seen for the same distance. <div class="Discussion_UserSignature"> </div>

 

[redbert]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm not sure I understand your question, but given a powerful enough telescope and a clear line of sight, we can see 13 billion light years in ANY direction.&nbsp; For example, the Hubble Deep Field image was taken in one direction, chosen to avoid being blocked by Earth, Moon, Milky Way, etc., and saw to about 10.5 billion light years.&nbsp; Hubble has since looked in other directions to make the Hubble Deep Field South image and the Hubble Ultra Deep Field image, in which it saw to 13 billion light years. Hubble could have looked in many different directions and seen for the same distance. <br />Posted by centsworth_II</DIV></p><p>&nbsp;Sorry: I left the&nbsp; word billion out of my question.</p><p>But you gave the answer&nbsp;to the question that I meant to ask.</p><p>And this is the part I do not understand: If far-east galaxy is 13 billion light years away from us&nbsp;and far-west galaxy is 13 billion light years away from us&nbsp;: are the east and west&nbsp; galaxies 26 billion light years apart from each other?</p><p>If every thing started from a big bang 13 billion years ago ; how can two objects be 26 billion light years apart?</p><p>&nbsp;Surely , we are not in&nbsp;the center.</p><p>Can an object be 26 billion&nbsp;light years &nbsp;from us?</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'><font color="#0000ff">If far-east galaxy is 13 billion light years away from us&nbsp;and far-west galaxy is 13 billion light years away from us&nbsp;: are the east and west&nbsp; galaxies 26 billion light years apart from each other?If every thing started from a big bang 13 billion years ago ; how can two objects be 26 billion light years apart?&nbsp;Surely , we are not in&nbsp;the center.Can an object be 26 billion&nbsp;light years &nbsp;from us?&nbsp;</font> <br /> Posted by redbert</DIV></p><p>Just as those galaxies are at the edge of our <em>observable</em> universe, we are at the edge of theirs. They cannot see each other as 26 billion light years apart - if they look in this direction they see our galaxy (or whatever was here 13 billion years ago) at the edge of their universe. We assume they also see 13 billion light years worth of galaxies on their opposite side relative to our galaxy, they see a different part of the universe that we cannot see, a part that is outside of our observable universe.</p><p>We have no idea just how large the whole universe is, only how large our observable portion of it is and so we don't think we are at the centre of the universe, but by definition we are at the centre of our observable universe. Our <em>view</em> is limited by the speed of light and the age of the universe, but the size of the universe as a whole is not limited by the speed of light.&nbsp; </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[centsworth_II]

<p><font color="#666699"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>...If far-east galaxy is 13 billion light years away from us&nbsp;and far-west galaxy is 13 billion light years away from us&nbsp;: are the east and west&nbsp; galaxies 26 billion light years apart from each other? --&nbsp; Posted by redbert</DIV></font></p><p>They were 26 billion light years apart 13 billion years ago when the light we see them by left them.&nbsp; Since then they have had 13 billion years to move much further apart.&nbsp;</p>&nbsp;<p><font color="#666699">Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Surely , we are not in&nbsp;the center.</font><font color="#666699"> -- Posted by redbert</DIV></font></p><p>Imagine you are on the mast of a ship at sea and can see 10 miles to the horizon in all directions.&nbsp; You can see other ships out to the ten mile horizon in all directions, provided you have a good enough viewing apparatus.&nbsp; But you cannot see any ships past that ten mile limit no matter how good your viewing apparatus is, even if they are there.&nbsp; An occupant of any other ship on the sea can look around and see out to <strong>their </strong>horizon. They are in the center of their field of view just as we are in the center of ours.&nbsp;&nbsp; </p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<font color="#666699"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Just as those galaxies are at the edge of our observable universe, we are at the edge of theirs....<br /> Posted by SpeedFreek</DIV></font><br />It's fun to imagine that in the farthest, just-forming galaxies that we can see, there are intelligent beings looking to the edge of their observable universe and seeing a very young proto-galaxy which would become our Milky Way.&nbsp; Each of our galaxies looks very young to the other, just being formed. But in actuality, each of our galaxies has matured.&nbsp;&nbsp; <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>They were 26 billion light years apart 13 billion years ago when the light we see them by left them.&nbsp; Since then they have had 13 billion years to move much further apart.</DIV></p><p>Actually they were only 3.3 billion light years distant when they emitted the light we see today, so they were 6.6 billion light years apart at that time. The light took 13 billion years to reach us, during which time they will each have apparently receded to around 30 billion light years away putting them around 60 billion light years apart today. (Light with a redshift of z=8 has been travelling for around 13 billion years). </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[centsworth_II]

<font color="#666699"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Actually they were only 3.3 billion light years distant when they emitted the light we see today... Posted by SpeedFreek</DIV></font><br />It's mind-numbingly difficult to keep track of all this stuff! <div class="Discussion_UserSignature"> </div>

 

[redbert]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> but the size of the universe as a whole is not limited by the speed of light.&nbsp; <br />Posted by SpeedFreek</DIV></p><p>Ok; this all can make sense if the above&nbsp;statement is true. Is it true?</p><p>&nbsp;If we know the age of the universe; does't the speed of light give us the maximum size of the universe?</p><p>Has the universe expanded faster than the speed of light?&nbsp; Or was the speed of light faster in the early moments of the bang?</p><p>So are there objects 30+ billion light years away from us&nbsp; (I agree that that they would be unseen)in a universe that is 13 billion years old?</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[centsworth_II]

<p><font color="#666699"><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>...Has the universe expanded faster than the speed of light?<br /> Posted by redbert</DIV></font><br />That's what the inflation theory is all about.&nbsp; </p><p>From "Cosmic Jackpot" by Paul Davies (p 83):</p><p><font color="#333333"><strong>"The basic structure of the universe is nicely explained by the theory called inflation, which postulates that in the first split-second of its existence, the universe leapt in size by an enormous factor, caused by an&nbsp; intense pulse of antigravity. When inflation ceased, space was essentially empty. The energy of expansion was converted to heat, which brought about the creation of matter."</strong></font></p><p>So the size of the universe is far, far greater than if it had been limited by the speed of light. (I can't remember why the inflation of space in the first moments of creation was not bound to the speed of light limit according to the theory.)</p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>That's what the inflation theory is all about.&nbsp; From "Cosmic Jackpot" by Paul Davies (p 83):"The basic structure of the universe is nicely explained by the theory called inflation, which postulates that in the first split-second of its existence, the universe leapt in size by an enormous factor, caused by an&nbsp; intense pulse of antigravity. When inflation ceased, space was essentially empty. The energy of expansion was converted to heat, which brought about the creation of matter."So the size of the universe is far, far greater than if it had been limited by the speed of light. (I can't remember why the inflation of space in the first moments of creation was not bound to the speed of light limit according to the theory.) <br />Posted by centsworth_II</DIV></p><p>The proscription on exceeding the speed of light is a proscription on anything traveling faster than c in local coordinates.&nbsp; But the expansion of the universe is, essentially, an expansion of the coordinates themselves and general relativity places no limit on how fast that can occur.&nbsp; You actually don't need inflation to handle that particular point.&nbsp; But it does do a nice job of explaining how the universe got to be as big as it is.</p><p>For a good explanation of inflation for a general audience, I recommend Alan Guth's book <em>The Inflationary Universe.</em>&nbsp; Guth is pretty familiar with the inflationary model -- he invented it.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

<p>Exactly.</p><p>Inflation has a solution to the horizon problem and is a good illustration of how the whole universe might be <em>any amount</em> larger than our observable portion of it, but inflation is not required to understand how coordinates in space can separate at apparent superluminal speeds.</p><p>A grossly simplified model:</p><p>Imagine a volume of space. You dont need to worry about any edges to that volume, they are too far away to see. Now visualise a 3 dimensional grid of lines suspended within that volume of space. Where each line crosses, we put a coordinate point, and these points are all 1 meter apart along each axis. So wherever you put yourself in this volume of space, whatever point you choose to sit on, whichever axis you look along you see points at 1,2,3,4,5 etc meters away from you.</p><p>Now lets expand that volume of space over a given period of time. For simplicity let's say the volume doubles in size in 1 second and <em>the grid expands with the volume</em>.</p><p>What is the view, after that expansion? Well whichever axis you look along you now see points at 2,4,6,8,10 etc meters away from you. Each meter has doubled in size. This means the nearest point has moved from 1 to 2 meters away in 1 second - it has receded at 1 meter per second. The fifth point however, has moved from 5 to 10 meters away in 1 second so it has receded at 5 meters per second. The further away you look, the faster a point is apparently receding from you. And the view would be the same whichever point you choose as your viewpoint.</p><p>But none of the points have changed their relationship to the volume of space as a whole, the grid simply expanded with the volume. None of those points is moving <em>through</em> space, the space has simply increased around those points.</p><p>In this simplified model, any point that was originally 300,000,000 meters away from another point will have receded&nbsp; from that point by 300,000,000 meters per second, the speed of light, and any point originally more distant will have receded at a speed apparently faster than light.&nbsp;</p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[majornature]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I was watching the Science channel and they were talking about the Horizon Problem and how its a big problem for the big bang theory. I dont quite understand the problem or the concept of the "Horizon Problem" I tried reading up on it on the internet but it doesnt really make sense.&nbsp;Can someone please explain this problem and what is so special about it?? Thanks!&nbsp; <br />Posted by Kewell</DIV></p><p>&nbsp;</p><p>Damn it!&nbsp; I missed it!&nbsp; Did it come on Tuesday?</p><p>Would it be rapid expansion in the early universe that caused this problem?</p> <div class="Discussion_UserSignature"> <font size="2" color="#14ea50"><strong><font size="1">We are born.  We live.  We experiment.  We rot.  We die.  and the whole process starts all over again!  Imagine That!</font><br /><br /><br /><img id="6e5c6b4c-0657-47dd-9476-1fbb47938264" style="width:176px;height:247px" src="http://sitelife.space.com/ver1.0/Content/images/store/14/4/6e5c6b4c-0657-47dd-9476-1fbb47938264.Large.jpg" alt="blog post photo" width="276" height="440" /><br /></strong></font> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Damn it!&nbsp; I missed it!&nbsp; Did it come on Tuesday?Would it be rapid expansion in the early universe that caused this problem? <br />Posted by majornature</DIV></p><p>No, it would be rapid expansion in the early universe that solves the problem.<br /></p> <div class="Discussion_UserSignature"> </div>