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Cosmology questions, something that is puzzling me for days!

  1. Apr 27, 2013 #1
    Hello folks

    My name is Mike. I am into Cosmology ever since I was a kid. Throughout the years I strayed away from Cosmology unfortunately but I am very very fond of Cosmology...and thus...call me an amateur Cosmologist :D


    These days couple of questions puzzle me in the Cosmology theory.

    First one is this

    According to the Big Bang theory, and the research that has been carried out, we have recorded the Cosmic Background radiation, but we don't have proof what is beyond that...

    Here is an image from Stephen Hawking's "Universe in a nutshell"
    http://joscalesfineart.files.wordpress.com/2012/02/002.jpg [Broken]

    So according to this diagram, we can only "see" the background radiation and not beyond that, we have no proof of the matter density and I am sure we cannot "see" the Big Bang it self, and I am dying to know WHY we cannot "see" that. According to Einstein theory as we see further (deeper) in the Universe we see the past (millions and billions of years), but we cannot see the beginning of the Universe. Some kind of a hotspot of radiation, matter density of some sort. We only see the remains of that explosion in the form of CBR as I gather.

    Second question

    If the Universe is expanding, the information of this expansion is gathered by the so called redshift effect. The redshift effect is "collected" by objects that are millions and some of them billions of light years away. So actually we are seeing an early expanding Universe. That is no proof that the Universe is expanding now at this very moment. Maybe it has started collapsing by now, and yet we do say "The Universe IS EXPANDING", I think a very courageous gesture.

    Maybe I am wrong, so please enlighten me on these questions.

    Thank you very much

    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Apr 27, 2013 #2
    It depends on what you mean by the word "see".
    After the big bang the universe was a plasma, this state was present until 380,000 years after the big bang. Such a plasma is opaque, you cannot see through it. Like the sun, you cant look at the sun and see into the interior. When the density declined the fog cleared and photons were set free, these photons are what we see when we see the CMB.
    However there are relationships in the CMB which we can observe. Different models of what happened before the CMB make different predictions for these relationships.
    Also there are two things which the CMB does not block us from seeing, these are neutrinos and gravity waves. But these are extrmely difficult to detect. At the moment no neutrino (the cosmic neutrino background) or primordial gravity waves have been detected. To detect these is not going to happen in the near future in my opinion but i sure hope Im wrong. I dont know of any plans to detect the CNB. There are plans to build a space based to detector to observe the gravity waves from the big bang. But they need 12 spacecraft flying in an array. You can bet this is not going to happen any time soon.

    There is some hope that there will be an indirect sign of the gravity waves via their effect on the polarisation of the CMB. Maybe Planck which gives us polarisation data next year will find this. Its pretty unlikely though and most likely will need its own dedicated mission.

    In science I don't think talking about the word "proof" is a good idea. Better to say "the evidence suggests". In this case we have a model called Lambda CDM which tells us the universe is not only expanding it is doing so at accelerating rate. That model fits the data very well. it is possible in this model that the universe was contracting before the big bang but afterwards it is expanding.
  4. Apr 27, 2013 #3
    We estimate the expansion rate by comparing the redshift to the distance of an object. The redshift alone doesn't tell us too much. It is of course true that we can not observe the "present" universe. We only observe our present light cone. So we don't know but assume that the expansion is constant anywhere. If we measure expansion in our vicinity we assume it happens all over even we can only observe it in the future.
    From what we measure it appears that the expansion is slightly accelerating because nearby galaxys have a higher escape velociity/distance than the ones further away (older).
    Anyway we do assume very much and know very little in general but we have to live with that uncertainty.

  5. Apr 27, 2013 #4
    In regards to distance measures this article written by PF members will provide a convenient short cut.

  6. May 20, 2013 #5
    The term Big Bang is a misnomer. There was no explosion merely a rapid expansion of space from a hot dense state of unknown size
    and origins.

    Survival of the fittest is the answer to evolution. We can genetically trace our evolutionary history provided we have sample dna of each evolutionary form. Good luck convincing your friend on that aspect.

    There is no outside the universe even though you stated solar system your beginnings reference implies universe.
    Last edited: May 20, 2013
  7. May 21, 2013 #6
    Hi Mike,

    Going to quote an explanation from Marcus from This Thread Marcus started, post #5 that answers this question pretty well:

    "Notice that today our particle horizon is 46.28 which is the farthest matter is NOW which could have sent us light we'd be receiving today. It is the maximum distance from home a flash of light could have reached in the whole time since start of expansion (through its own efforts aided by expansion).
    But notice that the matter that emitted CMB (the most ancient light we actually do see today) is only at 45.33. That's because light emitted earlier by more distant matter DID NOT GET THRU because the partially ionized gas was effectively opaque. That opacity caused the difference between 45.33 and 46.28.

    Get familiar with the fact that the wavelengths of the ancient light are by now expanded 1090-fold, and the moment the gas became transparent was year 373,000, when distances were 1/1090 of their present-day size."

    Take a look at the table he referencing also, and read over Mordred's response because it explains redshift and what we're seeing when we're observing distant galaxies moving away sometimes faster than the speed of light. (Hence the red shift).
  8. May 21, 2013 #7
    my signature also contains several useful links. The cosmology101 site is one I am developing. It includes the links below as well as Phind's balloon analogy page (with his permission of course).

    I will be adding more material to the site just started construction today on it.

    the other two links contains Jorrie's cosmocalc and lightcone calculator. the main page is the second link the first link is the calculator itself. The light cone generates the table mentioned in Marcus's post
  9. May 23, 2013 #8
    Maybe you are correct...since the universe may be infinite nobody knows for sure what may be going on 'way out there'. But so far, hour after hour, day after day, etc, etc, we keep getting CMBR with the same characteristics.....so it seems a reasonable bet things are still expanding.....

    Our best view so far is that billions of years in the future the universe will be very big, very empty, dark and cold....'dead'....maximum entropy....To date, from the emergence of the CMBR, the temperature has decreased from about 3,000K to about 2.7K.....over about 13.7B years.....and a sudden reversal is not expected especially as expansion appears to be accelerating without any braking mechanism so far known.

    [and you better hope it stays that way, because if things were to start to 'collapse' at some time, and it proceeds as fast as things are likely expanding now, we'd get precious little warning...and even if we did, about all we could do is ever so briefly 'party down'.]
  10. May 23, 2013 #9
    That is a pretty chilling thought. What would happen if everything we see now as red-shifted, was suddenly blue-shifted and moving at us exponentially... How long would it take for us to see the effects, galactic collisions? What would the implications be?
  11. May 23, 2013 #10
    Spourk: relax, dude, our sun will engulf us long before in a massive fireball...and if not, crashing with Andromedia might!!! Just party down!!
  12. May 23, 2013 #11
    Ha, much better. If it involves the life of our sun I know I have plenty of time, and any excuse to party down seems a good one to me, as long as it doesn't end you up in jail or the middle of the antarctic. :tongue:
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