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B Age of the universe: observable or entire universe?

  1. Aug 16, 2017 #41

    PeterDonis

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    This is off topic for this thread. The observable universe is defined as a region of spacetime, it doesn't involve any considerations of what kinds of brains might or might not exist.
     
  2. Aug 16, 2017 #42
    Is there any genuine proof of the 'Big Bang Theory' or are we dealing with, as the name says, merely a theory? Is there anything to prove what was here before the BBT? I keep thinking of hypothesis through the ages, ie; the world was flat, the earth was the center of the universe, etc., etc., etc. These previous theories were made by the smartest minds of the day, now they're obsolete. What makes today's theories any different?
     
  3. Aug 16, 2017 #43

    Grinkle

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    Off topic, but ....

    Nothing. Science is a sceptic's pursuit. Nothing brings more fame to a scientist than to find evidence that dis-proves or shows previously unknown limitations to a widely accepted theory.

    In general, experiments don't prove theories, they either give results consistent with the theory or they show the theory is incorrect / makes false predictions.

    The cosmic background radiation is strong evidence to support expansion (Big Bang) but it doesn't prove expansion occurred in the way that one can prove a mathematical theorem from a given set of axioms. If you Google cosmic background radiation you will find articles explaining why its existance supports expansion theories.
     
  4. Aug 16, 2017 #44

    PeterDonis

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    There are several lines of evidence that support the standard hot Big Bang model of cosmology and rule out the main alternative models that have been proposed. The key ones are: the detailed relationship between redshift, brightness, and angular size for distant galaxies, the cosmic microwave background radiation (including the "wrinkles", i.e., small variations in temperature, observed in it), and the relative abundances of light elements (hydrogen, deuterium, helium, and lithium).

    The current best model we have is that the hot Big Bang (by which is meant the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good observational evidence) was preceded by an era of inflation. But cosmologists have not settled on a single standard model of inflation, nor do we currently have a good understanding of what preceded inflation.

    Only the fact that we have a lot more detailed, quantitative evidence, so that the possible theories that are consistent with everything we know are more constrained.

    This classic article by Isaac Asimov might be relevant:

    http://chem.tufts.edu/answersinscience/relativityofwrong.htm
     
  5. Aug 16, 2017 #45

    jbriggs444

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    Asimov had something to say on the notion that the previous theories are obsolete. http://chem.tufts.edu/answersinscience/relativityofwrong.htm

    Edit: *blush*, beaten to the punch.
     
    Last edited: Aug 16, 2017
  6. Aug 16, 2017 #46

    PeterDonis

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    Indeed--see my post #44 before yours. :wink:
     
  7. Aug 16, 2017 #47
    The point I made refers to _any_ device which may effect observer retina (more accurately if it may change the state of observer). Whatever this device measures, whatever inputs it takes is totally irrelevant and the nature of device is irrelevant as well; it may be neutrino detector or it may be brain of another observer who writes the article I may read, both changed my state... for example: the set of observables for some researcher/observer/brain makes sense only if he does not need to postulate the wave function collapse so we have Everett relative sate or Linde came up with idea of eternal inflation or Susskind's landscape idea etc... they used observables inputs and their brain interpreted it, very similar as neutrino detector interprets some observables but in a way more complex manner... such generalization implies that the universe of observer is the function of observer's complexity; figuratively speaking, infusoria's universe is quite different from universe of homo erectus...
     
    Last edited: Aug 16, 2017
  8. Aug 17, 2017 #48

    Bandersnatch

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    You're pushing some solipsist philosophy here, which in no way addresses your assertion that the observable universe is somehow underdefined.

    If I want to know how long is an elephant, I grab a yardstick and measure the distance between its head and its rump, because that's how it's defined. If somebody then asks me what is the length of the elephant, I'll tell them it's as much as the yardstick shows - and they'll agree because they use the same yardstick and have the same elephant.
    The size of the elephant doesn't change just because somebody looks at it and imagines it to be larger, or can't comprehend the yardstick like infusoria. Andrew Linde may have come and argued that the elephant we have was once a single cell that grew very fast, and that there exist herds of elephants out there, but that doesn't change the size of our elephant we live with.

    If somebody asks what is the size of the observable universe, I then grab a yardstick (consisting of a telescope and a model of the universe) and measure the distance to the farthest light, because that's how it's defined. It doesn't matter what anybody imagines it to be - they take the yardstick and measure the same thing.
     
  9. Aug 17, 2017 #49

    PeterDonis

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    It implies that the model of the universe in the observer's brain (or whatever it thinks with) is a function of the complexity of the brain. It does not imply anything about the observable universe as that term is used in this thread.

    Further posts along these lines will be deleted and will receive a warning. Please keep the thread on topic.
     
  10. Aug 17, 2017 #50
    You are right, my apology, I pushed a little too far off topic along the line witch up to some point still remains within the scope of the subject; once we extend the notion of observable universe from pure electromagnetic spectrum to neutrino/gravitational-wave detectors or/and interpreting the patterns upon a higher resolution background radiation map etc... I see no logical reason to stop there and do not look at a more general picture; evidently, there are plenty non logical reasons though ;o)
     
  11. Aug 17, 2017 #51

    PeterDonis

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    As I said before, the definition of the observable universe already does include "a more general picture". Even though the definition is usually stated in terms of EM radiation, it actually covers any detectable thing whatsoever, since any detectable thing can travel no faster than light. So the region of spacetime from which EM radiation is in principle observable is also the region from which any detectable thing whatsoever is in principle observable.
     
  12. Aug 20, 2017 #52
    One on the surface of the earth, but the Gravitational time dilation is minimal there so it's not much different than one far away from all gravitations.
     
  13. Aug 20, 2017 #53

    phinds

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    Have you not been paying attention to this thread? That is NOT what we use. As has been pointed out, we use the clock of a co-moving observer. The Earth is not a co-moving observer
     
  14. Aug 20, 2017 #54
    Seems like you forgot to mention my personal favorite, finite and bounded :cool:
     
  15. Aug 21, 2017 #55
    I try not to pay attention to whims and opinions when I see some replies that are radically wrong. So does YOUR clock co-move with the observable universe or the entire universe? How much different is it from the one I spoke of?
     
  16. Aug 21, 2017 #56

    PeterDonis

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    @phinds reply was not "radically wrong"; in fact it was not wrong at all, it was correct. Your post, that he responded to, was incorrect; the "age of the universe" quoted by cosmologists is the age according to a comoving observer--not a clock on the Earth's surface. You are correct that the difference between the two is small, but the fact remains that you gave an incorrect reply to @facenian and @phinds corrected it, so your attitude displayed here is not appropriate.
     
  17. Aug 21, 2017 #57

    PeterDonis

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    This thread has run its course and is now closed.
     
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