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Looking back

  1. Nov 4, 2014 #1
    Lately there have been a lot of shows about the Big Bang. They kinda use the same material and say the same thing. In a nut shell they touch on expanding space and everything that exist comes from a space about size of an atom. I wish they would explain how if we look far into space from earth we can look back in time almost to the Big Bang. This blow my mind cause if we came from the starting point of the Big Bang and expanded to our current location How do we see light from Big Bang Seems that if light and Earth dust started at same spot and raced out that the light would be way ahead of us not us looking back at it
    Please help
  2. jcsd
  3. Nov 4, 2014 #2


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    The first thing you need to understand is that the big bang did not occur at a particular point in space. Expansion occurred everywhere at the same time. At about t=0, the point in time that we say the big bang occurred, the observable universe was very small in size. However, there was still much more of the universe than that, possibly an infinite amount of space, where matter was highly compressed and very, very hot. Over time the matter and radiation in the entire universe, both the observable part and the regions beyond, expanded and became cooler and less dense over time.

    The light that we see now did not come from our own section of the universe, but was emitted a very long time ago from regions of space far away from ours. We actually can't see back beyond a point in time about 186,000 years after the big bang. Prior to this point in time, the universe was too hot and dense for light to freely propagate. It was continuously emitted and absorbed, never getting anywhere. Then, about 186,000 years after the big bang, an event called "recombination" occurred where most of the hot plasma finally cooled off enough to turn into neutral gas, which is transparent to light. Once this occurred the very first light was emitted that we can still see today. This light has been redshifted over time and is now in the microwave range. It is known as the Cosmic Microwave Background.

    Note that the nature of expansion means that everything expands away from everything else not bound to it. From our point of view, everything in the universe is expanding away from us. The light we see today from old galaxies was emitted long ago when those galaxies were much closer to us.

    Does that help?
  4. Nov 4, 2014 #3
    Shouldn't Morgan Freeman be forced to explain that "explosion from a point in space" is nonsense?
    It is a 3rd thread about this misconception in last few days.
  5. Nov 4, 2014 #4
    I don’t know if Morgan Freeman actually said “explosion from a point in space”, but until trained cosmologists can present an understandable explanation to the masses, the uninitiated are going to continue to accept that concept because lacking an alternate explanation, it is understandable and seems reasonable.

    Responses to the question over the years on this forum of where the big bang originated usually contain the phrases, “It happened everywhere” and that “the universe was smaller than it is now.” To the untrained reader with a casual curiosity about cosmology, both phrases imply size and location, which naturally leads to….where?

    What should Morgan Freeman say to the masses? Or do we simply cancel his program and say that current scientific thinking regarding the origin of the universe is unknowable to the general public?
  6. Nov 4, 2014 #5
    Morgan Freeman is just a symbol.
    I think it is possible to make 1 hour video "top 10 common misconceptions in physics"

    1. "This is just a theory..."
    2. Physics explains WHY things happen
    3. Big Bang as an explosion
    4. Energy is conserved in the Universe
    5. If someone gets accelerated to light speed, he/she would see...
    6. If object is accelerated fast enough, it becomes heavier and becomes a black hole
    7. Time stops near the horizon.
    8. If you jump into Black hole, you would see the future of the Universe
    9. Copenhagen is not the only interpretation in QM
    10. ...?
  7. Nov 4, 2014 #6
    I read the forums for days before asking my question. Yes I am the general public and I was hoping someone asked this question already and I could just read it. I saw the balloon example and I grasp that. I think my way of thinking about pre Big Bang is wrong. To the average Joe, It sounds like space was infinite but empty. All matter was compressed by Gravity into a space the size of an atom. Infinitely dense. Then it spewed forth all matter growing very fast. And there is where people keep saying point in space. That point was our universe and expanded and still is. 13 billion years ago light left a point in our universe and just now got to our point. my confusion is that 13 billion years ago the universe was still very small compared to current size. and light is the speed limit how did The 13 billion year old light not already pass by us since it was so much closer to 13 billion years ago. using the balloon analogy. The balloon barley expanded at all in when clear light formed the point of origin of light and our point was much closer less distance
  8. Nov 4, 2014 #7
    I knew you'd become heavier, but a black hole? Hadn't heard this one before, care to explain?
  9. Nov 4, 2014 #8
    It is a misconception.
    People ask: when object is accelerated it becomes contracted (TRUE)
    and heavier (aka relativistic mass) - TRUE and FALSE, relativistic mass is not used now + it is not a (single) source of gravity.
    So, people ask, density of relativistic object becomes higher and higher, so it should become a Black Hole (FALSE for many reasons)
  10. Nov 4, 2014 #9
    I am afraid the balloon analogy is misleading too because it suggests that there is a center of the Universe (FALSE)
  11. Nov 4, 2014 #10
    From general public to general public: light is still coming to us and it will keep coming to us until it's so "cold" there is nothing left to detect. There was no matter back then, and it was not infinitely dense. Don't think pre-Big Bang, that's wild speculation for now. Don't think of space, think of things getting apart at different rates for whichever reason we may or may not know, it's a problem of metrics only evident in equations. Trying to reason with it is just never going to work, it simply is that way. The balloon analogy has never worked for me and the sooner you abandon the hopes of explaining things with it, the easier you'll get to accept things the way they are. All those analogies are confusing and make things worse.

    Oh, thanks! I thought I had gotten everything wrong again haha
  12. Nov 4, 2014 #11


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    @nobody special: is this you asking for further clarification, or is this you describing the source of the now-dispelled confusion?
  13. Nov 4, 2014 #12
    thanks everyone tv is misleading thanks for clarification
  14. Nov 4, 2014 #13


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    (Underlining mine)

    The observable universe, the part we can see, was much, much smaller 13 billion years ago. The size of the entire universe is unknown, but if it is infinite now it was infinite in the past.
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