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Looking Backward In Time

  1. Jan 15, 2008 #1
    Warning! You're reading a question from a person who belongs in a home for the confused.

    I'd like to share a thread of thought and follow with a question.

    We can look backward in time by viewing through powerful telescopes. The logical extension of this is that with a powerful enough telescope we could see back to the Big Bang. But we know this is not possible, since we'd be witnessing something of which we were a part.

    On the other hand, how far back should we be expected to see? Perhaps we can only see "sideways," that is, see other pieces of the Big Bang radiating from the origin point.

    But if that's true, then if we swing our all-powerful telescope around to the origin point of the Big Bang, then we should see empty sky---all the "stuff" has exploded away.

    There is an empty space in the sky. Do you suppose? ...
     
  2. jcsd
  3. Jan 15, 2008 #2
    if you are confused than so am i

    you do make a point but i think not

    and you could see your self but you could not change it its just a pic or a presevation of the past

    forgive my spelling i am dislecsic
     
  4. Jan 15, 2008 #3

    marcus

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    you have a misconception of the normal idea of Big Bang. there is a standard picture that professional cosmologists use

    the big bang was not an explosion of stuff outwards into empty space, like a bomb.\
    if yu have a book that says this, throw the book away.

    the big bang (professional version) did not occur at a single point that we could find in our space----so forget about pointing a telescope at the "place" where it happened.

    the Big Bang name was given by a man who did not understand or believe the idea, Fred Hoyle, he believed in a steadystate non-expanding picture----naturally the words give the wrong idea.

    what we call the B.B. is just the beginning of the expansion of space.
    As we look back in time we actually see stuff that was closer to our stuff (which formed us) but seems farether away because space has expanded.

    The farthest we can see is the stuff that produced the Microwave Background which is now some 45 billion LY from us but when it radiated the waves we now see it was only about 40 MILLION LY from the stuff that became us

    the only reason we cant see further is that the cloud of stuff becomes a glowing plasma and is opaque

    if we could see waves that penetrate that fog, then we could see further back in time and we would see stuff that was EVEN NEARER to us when it radiated the signals, even nearer than 40 million LY.

    I have to go, don't have time to clarify, but this is a start. maybe ask some more questions and get people to respond more
     
  5. Jan 15, 2008 #4

    marcus

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    the idea of space expanding (the difficult idea here) is that things sitting still in the space around them can get farther apart

    that's what space expanding means

    it means the distances between stationary objects increase

    this doesnt happen within our Milkyway Galaxy, or even in our local group of galaxies which make a gravitationally bound set of a dozen or so, but it is a necessary consequence of the Einstein theory of gravity (Gen. Rel.) that it can happen and DOES happen at sufficiently large scale.

    near the beginning of the expansion, when the universe was much more dense, this expansion was much more rapid, enormously more rapid. But it was not an explosion. Distance itself was increasing.

    So think of the glowing crud, the hot fog like the surface of a star, that filled the universe when it was 380,000 years old. That filled ALL SPACE. We are now SEEING that crud in the form of the microwave background
    the crud we are now seeing was 40 million LY away from the similar hot crud that become us. think of that as a SMALL distance.

    we and it were shining with 3000 kelvin light (like a 100 watt bulb or the gassy surface of a secondrate star----a bit orange compared with the sun)

    space expanded and put that crud A THOUSAND TIMES FARTHER AWAY from what became us
    and it also stretched out the wavelengths of the light so the 3000 kelvin light is now 3 kelvin light-----that is what microwaves are.
    the wavelengths of that old old light have been stretched thousandfold.

    so as we look farther and farther away, after a certain point we are looking so far back in the past that we are looking at stuff which USED TO BE CLOSER
    After a certain point, paradoxically, the farther and farther you look, what you see used to be closer and closer to you (or the crud that condensed to form you)

    it is just that the very swift increase in distances, or expansion of space, has pushed it very far away.

    the only reason we cant see back BEFORE year 380,000 is because the opaque wall of that hot fog. No light got thru because the glowing plasma of that time scattered the light. All we see is the light from that hot fog plasma wall------stretched out into microwaves.

    someday there may be neutrino telescopes that can see back further, because neutrinos penetrate that kind of fog----they can even go thru stars as if they arent there. I think it is very likely that there will be such telescopes. so then we will see back further in time, and see stuff that was even CLOSER to us, when it radiated what we now see.


    in a sense you don't have to POINT your telescope to see the big bang (the beginning of the expansion, or the early days)
    you can aim your telescope in ANY DIRECTION. every direction is the direction to the big bang, if you look far enough

    hope that helps
     
  6. Jan 15, 2008 #5

    marcus

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    Don P. the other issue is empirical verification

    the expanding space cosmology I'm describing came first of all from Gen. Rel. and then it was found to match the data (the redshifts of galaxies, the microwave background...)
    so even though there are places we cannot look and some things we cannot check the picture as a whole rests on remarkably firm evidence

    1. there is no better theory of gravity for predicting orbits and time-delays, and lightbending, and pulsar star behavior etc.
    Gen Rel is the best theory of gravity we have. it checks out to many decimal places

    2. Gen. Rel. will not work unless distances between stationary objects can increase or decrease.
    That's what spacetime curvature is about. It has to change our basic idea of distance.
    Mentally that is tough on us, but it has no competition as a theory of how the solar system works etc etc.If you want an accurate theory of local gravity, you have to pay the price. You have to adopt a different understanding of distance from what applies common sense on the earth's surface.

    3. So then Gen. Rel. gets applied to the universe as a whole and we eventually get the socall LCDM model, which has the expanding space feature (and what a man who hated the idea called the "big bang" because there has to be a beginning of expansion).
    And what happens is that the LCDM turns out to fit a WEALTH OF OBSERVATION amazingly well----all kinds of statistics on all kinds of wavelengths from all different kinds of objects at every range of distance!

    So that is the evidence. It doesnt prove it's right because no mathematical model is ever proven right only that it is provisionally the best so far. It has these curious features of dark matter and dark energy, which are clues hopefully leading to future discovery. It has unsolved puzzles in other words. But oh boy is it the best so far.
    even tho we can't check everything, and even tho it will probably be improved on, it rests on fairly firm foundations
     
    Last edited: Jan 15, 2008
  7. Jan 16, 2008 #6

    Chronos

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    'Recombination', as marcus noted, forbids us from seeing more than 13.7 billion light years into the past [z~1100] in any direction.
     
  8. Jan 16, 2008 #7
    Thanks to all of you who replied. There's lots for me to chew on!

    Don P.
     
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