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Imposssible to see light that left a star 13.4 billion yrs ago

  1. Jul 7, 2012 #1
    From the following, can anybody tell me where I am going wrong in my thinking?

    Cosmologists tell us that our telescopes can detect starlight that left a star 13.4 billion years ago. I say that is impossible for the following two reasons:

    1. The Big Bang occurred 13.4 billion years. At that time, there were a lot of sub-atomic particles and emerging gas but no stars. Without the existence of stars 13.4 billion years ago, there could not have been light that left a star at that time and which traveled in that amount of time to reach our telescopes today.

    2. At the time the Big Bank exploded into existence. the "stuff" that eventually coalesced into our earth (let us call that the "Earth Stuff') and a given star (let us label that star "Star X") came into existence at the same time. The light from the "stuff" that made up Star X reached and then flew past the Earth Stuff about 13.4 billion years ago. Thus, today it is impossible for our telescopes to see the birth-light from Star X since that light flew past the Earth Stuff long ago.
     
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  3. Jul 7, 2012 #2
    I think this is one reason to argue inflation...
     
  4. Jul 7, 2012 #3

    marcus

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    I don't know of any astronomer or cosmologist who says that. The oldest light we can see is not STAR light. It is the glow of hot gas from a time long before there were any stars. It comes more or less equally from all directions and is called the CMB.

    That light comes from more than 13.6 billion years ago. Close to the estimated 13.7 billion year age of the expansion itself. But you aren't talking about CMB, you said star light.

    If you are going to say "cosmologists tell us" about STAR light from so long ago then you need to provide a professional source. But I doubt you can provide a source link. Because I doubt that any ordinary working astronomer ever said that.

    The most distant oldest STAR light I've seen reported had a redshift of around z = 10
    To find out how old that light is, google "wright calculator" and put 10 in the box,
    and press the "general" calculate button. You will get something like 13.2 billion years.

    Actually it says 13.184 billion when I do it. Anyway 13.2 is way less than 13.4, by
    200 million years. 200 million years can make a lot of difference, it can, for example allow time for stars to form.
     
    Last edited: Jul 7, 2012
  5. Jul 7, 2012 #4

    marcus

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    @aboro, what you say about "flew past" is wrong.
    The estimated age of expansion is 13.7 and the oldest starlight we know of was emitted about 13.2 billion years ago and is arriving here today with a redshift of about 10.

    The stars that emitted that light, that is now getting here after traveling for 13.2 billion years, were ALREADY QUITE FAR AWAY from our matter (you call "earth stuff") when they formed and emitted the light which we are now receiving.

    Because they were far away their light did not get a chance to arrive here until today. There is no possibility that it got here earlier and "flew past".
     
  6. Jul 7, 2012 #5
    Marcus, you say that "The stars that emitted that light, that is now getting here after traveling for 13.2 billion years, were ALREADY QUITE FAR AWAY from our matter (you call "earth stuff") when they formed and emitted the light which we are now receiving.

    Because they were far away their light did not get a chance to arrive here until today. There is no possibility that it got here earlier and "flew past". "

    Marcus, how is it possible for the stars emitting that light and that is now getting here after traveling 13.2 billion years, were already quite far away from Earth Stuff. It seems to me that 13.2 billion years ago, Earth Stuff and the stuff that made up Star X were close to the origin of the Big Bang just about the time it exploded and were not far away from each other.

    If what I am saying is true then what you have said (quoted above) can not be true.

    P.S.: My understanding from cosmologists is that their telescopes are seeing star light that is 13 billion years old. Nevertheless, as you say, I do need to find a "professional source".
     
  7. Jul 7, 2012 #6
    Marcus, one other point -- you mention in your reply that the light reaching us today has a redshift of about 10.

    I do not understand how the red shift of star light is relevant. Even though the light may have a red shift of 10, it is still traveling the speed of light and it still took (according to cosmologists as i understand it) 13 billion years to reach us.
     
  8. Jul 7, 2012 #7

    marcus

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    It's not part of the logic, it's how I keep track of ages and distances.Redshift is what the astronomer measures. Then you plug that into the model and it tells you the distance now, the distance back then when the light was emitted, the light travel time. Redshift is the basic central handle that everything else relates to.
    Well the usual estimate of the expansion age is 13.7. That differs by half a billion years from the 13.2 figure. A lot can happen in half a billion years. 500 million?

    If you want a professional source, one thing is to google "ned wright". He is a world class cosmologist and as a public service (plus for his students) he has an excellent website.

    I can tell you how far away the Star X was from "earth stuff" by googling "wright calculator".
    the redshift for the oldest starlight I know of is about z = 10. So put 10 in the redshift box and press "general" calculate button. You should learn to do this yourself.

    Star X was NOT close to "earth stuff". The calculator says it was at a distance of
    2.84 BILLION LIGHT YEARS when it emitted the light we are now getting.

    It says the light travel time was 13.2 BILLION YEARS. It couldn't get here sooner because part of that time it was being held back by the very rapid expansion.

    But no, it did not start from somewhere "real close".
    And no, it did not "fly past" a long time ago :biggrin:

    You may be suffering from some common misconceptions*. A lot of people get wrong pictures of expansion cosmology from popular media channels. There is a good Scientific American article you can read that was written expressly to combat these misconceptions. It is the "charley" link in my signature at the end of the post. The first page is blank so scroll down. You should probably give it careful attention. It is by another worldclass cosmologist, an Australian named Charles Lineweaver.

    * like picturing the big bang as an explosion out into empty space from some central point the way they do on Television. Wrong picture. Lineweaver discusses this, among other common misconceptions, and tries to cure them.
     
    Last edited: Jul 7, 2012
  9. Jul 7, 2012 #8
    Thanks Marcus. You have said enough to persuade me that I do have "common misconceptions" about the expansion of the universe. I intend to visit Ned Wright's web page as per your suggestion.
     
  10. Jul 7, 2012 #9

    marcus

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    I hope Wright's tutorial and faq are helpful.
    It might be safer and more gradual to read the Scientific American magazine article first. A lot of people have found that helpful.

    http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

    This is the Charley Lineweaver article. It is called "Misconceptions about the Big Bang" and it is really really basic. Definitely aimed at general audience.
    then after looking that over and making sure you are OK with that, go on to Wright's tutorial (which can get a good bit more technical in places).

    But you'll browse around and find what's right for you :smile:
     
    Last edited: Jul 7, 2012
  11. Jul 8, 2012 #10
    Thanks Marcus. Will do.

    I did have occasion to look at the Ned Wright page and 99% of its contents went light years over my head. no pun intended. Some of it, I was able to follow.

    I will now look at the SA article you mention and see where that gets me (also no pun intended).

    What is still difficult for me to understand - - using the comments you made by way of a specific instance - - is that 500,000 years after the Big Bang, it seems to me that the stuff making up Star X and Earth Stuff, respectively, were also 500,000 from the point of singularity. 13 billion years later these stuffs (which at that time have ripened to become the fully formed Star X and Earth) ought to be in tandem with each other and not 13 billion light years apart. Observers from Earth should no longer be seeing the light that left Star X 13 billion years ago.

    And, BTW, when i say Earth Stuff, I really mean to say the stuff that ultimately formed our star so that we are comparing apples to apples. The stuff that ultimately made up our star and the stuff that ultimately made up Star X were emitted from the Big Bang at the same time about 13 billion years ago. Unless the stuff making up Star X stopped dead in its tracks, it should not be 13 billion light years away from us. But I know that the professionals say it is and that is the concept i am trying to understand as a layman.

    As you said earlier, I suspect my problem lies in the misconceptions I may be having about the expansion of the Universe. Hopefully, i will see the light as you and others do (also no pun intended).
     
  12. Jul 8, 2012 #11

    marcus

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    Some nice use of language in this post. Wright's tutorial was the wrong suggestion on my part. Do have a look at the Lineweaver SA article!
    We should have a clearly posted sign at this forum advising newcomers to check it out--it gets recommended repeatedly, often after a period of confused discussion.

    I just posted about this:
    https://www.physicsforums.com/showthread.php?p=3987625#post3987625

    You know, I think, that what serves today as our Law of Geometry is the GR equation. One of its predictions is an overall pattern of expansion, where the rate that largescale distances increase is not limited by c.

    This does not involve comparatively "small" local structures held together by their own gravity, like the solar system and our Milkyway galaxy. The pattern of increasing distances is different from ordinary MOTION where things change relative position. In ordinary motion somebody gets somewhere, but in overall expansion everything just gets farther apart. There is nothing in physics that puts a limit on the rate.

    It is currently about 1/140 of one percent per million years. It affects the wavelengths of starlight too. If some light is traveling towards us, its wavelengths are increased by 1/140 of one percent for every million years it spends in transit. Lineweaver has a picture about that in his SciAm article.

    I like your verbal image of stuff "ripening" into a star.

    You mention the time period of 500,000 years. that is half a million. You may have meant to write 500,000,000 years, which is half a billion. that is the difference between 13.7 billion and 13.2 billion.

    Star X emitted the light (which we are getting today) when expansion was 0.5 billion years old. At that time the distance between Earth-stuff and Star X was what?

    It certainly was NOT 0.5 billion light years! Because expansion is not limited by c. I will go find out.
    Yeah, when it emitted the light Star X was about 2.8 billion lightyears from Earth-stuff.
    That is called the "proper distance". If you could have stopped expansion at that moment (to have time to measure without things changing) then that's how far. A radar pulse would have taken 2.8 billion years to get from one the the other.
    With expansion stopped, the light itself (from Star X) would have taken only 2.8 billion years to get here. But because of expansion it took longer. We know in fact that it took 13.2 billion years. That was the original premise.
     
    Last edited: Jul 8, 2012
  13. Jul 8, 2012 #12
    Marcus, you are correct in assuming that what I meant to say was .5 billion light years, not 500,000 years.

    I refer to your reply where you say "Yeah, when it emitted the light Star X was about 2.8 billion lightyears from Earth-stuff. That is called the "proper distance". If you could have stopped expansion at that moment (to have time to measure without things changing) then that's how far. A radar pulse would have taken 2.8 billion years to get from one the the other. With expansion stopped, the light itself (from Star X) would have taken only 2.8 billion years to get here. But because of expansion it took longer. We know in fact that it took 13.2 billion years. That was the original premise."

    Am I understanding you correctly to say that when light was emitted from Star X (an emission that occurred about .5 billion light years from the time of the Big Bang under our hypothetical), the euclidean distance between Star X and Earth Stuff was 2.8 billion light years but that because of the "expansion" phenomenon, it nevertheless took 13.2 light years for the light from Star X to reach earth today?

    If it is not a difficult task for you to do (and of course assuming that I have a proper understanding of your replies to my post), do you have a non-mathematical explanation for your premiss that the proper distance between Star X and Earth Stuff was 2.8 billion light years at the point in time when the expansion was .5 billion light years from the Big Bang? It seems to me that at the time of the explosion. the stuff that ultimately became Star X and the Earth Stuff were essentially adjacent to each other and were both propelled from the point of the Big bang at the same time and at the same rate. If what I am saying is right, how did it come to be that when the expansion was .5 billion light years old, Star X and Earth Stuff all of a sudden became separated by 2.8 billion light years? The only logical explanation i can think of is that the stuff making up Star X and Earth Stuff were emitted from the Big Bang in opposite directions. but if that were so, the proper distance between Star X and Earth Stuff should be 1 billion light years.
     
  14. Jul 8, 2012 #13

    phinds

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    I think you can only reach the conclusion you reached if you assume the big bang started from a single point. It isn't known how big the universe was at the time of the big bang but it may well have been infinite, in which case there were things just after t=0 that were MUCH further away from the "earth stuff" than that. We don't know how big it was but it is NOT believed to have been a single point.

    "Singularity" means "unusual" not "point-like" and in any case is an unfortunate choice of words because of that confusion. In physics, "singularity" is used to mean "the place where our models break down and we don't have a clue what was going on"

    EDIT: here's a good thing to look at and there are some good links at the bottom (including the ones Marcus mentioned):

    www.phinds.com/balloonanalogy
     
  15. Jul 8, 2012 #14
    Marcus, I just finished reading the SA article. It was outstanding in the way it was able to convey difficult concepts in non-mathematical terms to a layman such as me.

    Interestingly enough, it seems that I had a good layman's sense of the recession of the galaxies. Lineweaver uses the "ant walking inside a balloon as it searches for aphid" analogy to convey an understanding of the expansion of space to a laymen. Several years ago, someone described the recession of galaxies observed by Hubble to the baking of raisin bread. Initially, raisins are present everywhere in the uncooked dough. As the dough begins to bake, each raisin moves away from all other raisins. A mythical person sitting atop a particular raisin would swear that all other raisins are receding away from him at a rate proportional to the distance between him and the raisin he is observing. Meanwhile, an observer on the raisin being tracked would swear that all other raisins are receding away from him in a manner that is identical to what the first observer is witnessing as he sits on his raisin. Both observers would be correct.
     
  16. Jul 8, 2012 #15
    Marcus and Phinds,

    Many years ago Einstein wrote a book to explain to a layman in non-mathematical terms his law of special relativity. In it, he said that physics can be taught to a barmaid.

    I say this to the both of you because I have come to realize - - after reading your replies - - the scarcity of book, articles etc. that are written for the specific purpose of explaining difficult concepts like the laws of special and general relativity and the Big Bang to a layman using non-mathematical terms. Lineweaver is one professional in the field who understands the difficulty layman have in understanding what are today the tenets of his profession and uses plain words to explaining some of the fundamentals of those tenants in a way that a reader of ordinary intelligence can understand.

    Marcus and Phinds, the both of you have been very helpful in re-directing me to better understand the breath-taking notions of the Big Bang and the Edge of the Universe. Thanks!!!!!!!!!!!!!!!!!!!!
     
  17. Jul 8, 2012 #16

    marcus

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    For my part you are cordially welcome, Aboro. I hope you continue cultivating your reason and curiosity about all kinds of science (not restricted to cosmology :smile:). Have fun.
     
  18. Jul 9, 2012 #17
    Phinds, I went to your web -site where you give the "balloon analogy." More of that type of writing needs to be done. I thought I had a reasonable layman's handle about the Big Bang but it now appears I was off base by about 1000 light years.

    I continue to believe that what Einstein once said ("physics can be taught to a barmaid") is both doable and vital. To achieve Einstein's dream, we need more writers like you and Marcus.

    At the risk of asking too personal a question, how old are you and what do you do for a living?? It would be depressing for me to know that you are just a sophomore in high school yet, at such a young age, has managed to understand the origins of our Universe in the way you do and to be able to explain some of its incredibly difficult but extraordinary and wondrous concepts that show our species to have no more consequence to the Universe than the rats who drowned when the Titanic sank.

    Do mankind a favor: write more.
     
  19. Jul 9, 2012 #18

    phinds

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    Glad you found it useful. I had a lot of help by several people here on the forum. This is a very helpful place.

    I'm in my late 60's and learned all of my cosmology in the last 2 years by reading a lot of popularizations (light on math, although I'm an EE by training and could have handled a little more but I'm lazy) and then getting the folks here to straighten me out where the popularizations are just silly. Marcus was one of the ones who was a big help and continues to be. He, and several others here, are just amazingly dedicated to helping newbies (such as me last year and you this year) to learn. They are also staggeringly patient with people that I would probably strangle if I could get my hands on them (I'm a cranky old fart) because those people just PERSIST in not listening to what is explained to them (unlike you, for example).

    Because of all the help I got here, I try to explain some of the more simple things to newbies so as to take some of the load off of folks like Marcus, although my impatience with willful stupidity sometimes keeps me from being as helpful as Marcus and some of the others.

    Paul
     
  20. Jul 10, 2012 #19
    Paul

    As an attorney in my early 60s, I use Einstein’s maxim about the teachability of physics to a barmaid as I try to have my clients understand the application of legal jurisprudence to issues affecting them. By doing that, I find that the client is then able to make a choice among various alternatives available to them and in a manner that allows the client to resolve a problem which required the client to seek legal assistance in the first place. As for my clients and me, it seems that Einstein's impact goes beyond theoretical physics.

    Anyway, part of me is relieved to know that you (and I presume Marcus) are older than what I thought you could have been. It would have been rather irksome and somewhat depressing for me to discover that, as a kid in high school, you understand much of the present day frontiers of cosmological thought, appreciate that the minds of laymen (like me) are burdened by a myriad of cosmological based red-herrings which prevent them from ever (or better) understanding the absolute drop-dead wonder of our Universe, AND, at the same time, has the patience and ability to explain difficult scientific concepts about the cosmos to a laymen and in a manner that is accurate and in plain-English and enables the laymen to recognize, if not get rid of, the many misconceptions the layman has about the Universe and mankind’s place in it.

    As much as you and Marcus have redirected my thinking and resolution of the problem that I outlined in my initial post, what you and he have already said gives rise to even more questions and wonderment. I remain convinced that these difficult cosmological concepts and discoveries are capable of being understood by a layman in non-mathematical terms.

    You may not be a Marcus but like him you are an effective bridge between the cosmologists who speak to each other in a language that they understand but nevertheless is alien to the person on the street who looks up and sees nothing but stars and wonders what is going on above his head.
     
  21. Jul 10, 2012 #20
    Marcus and Paul,

    I hope you get this and are able to respond.

    From what you have said regarding my misconceptions about the Big Bang, the origins of the Universe and Singularity, I accept (but do not fully understand) your telling me that the Big Bang did not come into being in the form of an explosion (as that term is understood in its classic sense) marking the beginning of when the Universe started to inflate and expand . I also accept and understand your telling me that the Universe never had a center or was at one time an extremely dense dot in space. I also understand your telling me that the Big Bang is not located at the center of the Universe , although that concept is easier for me to understand (perhaps wrongly) because non-concentric or oval shaped circles do not have a center.

    With these understandings in mind and applying them to the hypothetical I outlined in my initial post (and assuming I correctly have understood what you have said thus far), can you explain to me on what basis cosmologists are able a) to locate Star X at the point in time when it became 500 million light years distant from the Big Bang and b) to say that Star X and Earth Stuff were 2.4 billion light years from each other?

    In addition, prior to my having the good fortune of stumbling upon this web site and having benefited by each of your comments, I analogized the inflation/expansion of the Universe not in the context of an inflating balloon but as a ball of dough containing a lot of randomly disbursed raisins. As the dough is being baked, an observer sitting on top of each raisin would see the other raisins receding from each other. The raisins further away would be receding at a faster rate relative to the observer in much the same way Hubble observed the distant galaxy recede from the Milky Way. Is not my analogy better than the balloon analogy because it gives a 3-D sense of space/time in describing the speed, location and direction of the galaxies as they are observed receding from our Galaxy?

    Anton
     
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