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Big Bang Questions

  1. Nov 13, 2008 #1
    Personally, I don't believe in the big bang. But those who do, can you explain this to me please. We all know that the earth is exactly the right mass to orbit the sun, and that the inertia of the earth keeps it from flying into the sun. We also know that the velocity of the earth is exactly the right amount so the inertia is precisely enough to keep the earth from either flying into the sun, or flying into space. I ask you this: How did this come to be, from a random explosion? How did the earth form exactly to the right mass, and exactly the right speed, in order for this to happen? It just seems way too random in my opinion.

    and btw, I am a highschool student to don't critique my physics knowledge too much please :)
     
    Last edited: Nov 13, 2008
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  3. Nov 13, 2008 #2

    tiny-tim

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    Welcome to PF!

    Hi d=vt+1/2at^2! Welcome to PF! :smile:

    The mass cancels out in the equations, so the Earth (always begin your address with a capital letter! :wink:) could be replaced by a body with a completely different mass, and it would still go round the Sun in the same time along the same orbit.

    "Mass cancelling out" happens in lots of fields … for example, the biggest acceleration that something can have without something else sliding off is determined by F = ma and F = µmg, so a = µmg/m = µg, which is the same for any m. :smile:
    The Earth didn't form from an explosion, it formed from material gradually coming together (under gravitational attraction).

    The big bang was way before the Earth formed … after the big bang, the universe had to cool down a bit, then the first stars and galaxies formed, made of only hydrogen and helium, much later a new generation was formed of slightly heavier elements, and eventually really heavy elements were made from supernova explosions, and our generation of galaxies was formed.

    So the Sun and Earth are made of material formed in lots of explosions, but way back in the past, and that material was pretty cold by the time the Earth started.

    Even if there had been an explosion, all the bits would have orbited the Sun anyway (except maybe for about .01% that might escape).

    Just as any mass will do, any speed will do also … though that will of course affect the radius and the eccentricity (circularness) of the orbit. :smile:
     
  4. Nov 13, 2008 #3

    marcus

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    Re: Welcome to PF!

    But would it really? :smile:
    If the Earth had the mass of Jupiter, could it still orbit the sun at the same mean distance with the same 365.25 orbital period?

    Or putting it as you did, if the Earth were replaced by a body with the mass of Jupiter...

    I fancy that Jupiter, put in the Earth's place, would have an orbital period about 1/20 of a percent shorter than our year :wink: Do you agree? Of course such a small difference barely matters.

    The number I'm using is the square root of 1.001---as a back of the envelope approximation.
     
  5. Nov 13, 2008 #4

    tiny-tim

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    Hi marcus! :smile:
    hmm … I suppose technically the Earth orbits not round the centre of the Sun but the centre of mass of the Earth-Sun system, so the larger the mass of the Earth gets, the closer that centre of mass gets to the Earth.

    What equation were you using? :smile:
     
  6. Nov 13, 2008 #5
    I am an engineer and I have no cosmology background, nevertheless, I have always been interested and puzzled about the BB theory and there are things in there that defy reason. Is there a better, or easier way to understand the beginning of the universe? I have dreamed of something and I would like your comments.

    At the beginning it was not a particle of infinite density, as the BB tell us, but rather a huge (but finite) amount of pure energy. Pure energy does not need any space to exist, the space did not exist. The BB started with the creation and the expansion of the space, not an explosion of an infinity density point of matter, it was not a big explosion as it is normally represented. Why the space was created and why it started expanding is before the BB and it is impossible to know.

    As the space expanded, and still continues to expand, the original huge amount of pure energy that filled all the space started condensing into matter, which started appearing all over the expanding space. So the matter was not created in a single point and then exploded, but rather all over the universe. This was not a violent episode, but rather a smooth condensation of energy into elementary particles that then started interacting with each other forming hydrogen. The violent phenomena in the universe began latter when matter started interacting.

    Why is this picture easier to digest to me? Because: 1 The notion infinity density does not sound logical to me (although logic may not apply to the beginnings). 2 If it was really an explosion of a point of matter, it would be a very big hole of empty space in the middle of the universe, of which there is no evidence. 3 The BB assumes that the space was there, pre-existed the BB itself, otherwise the matter could not have expanded. 4 We see all the galaxies in the universe recessing from each other because the space continues to expand and it carries with it all the matter, there are no galaxies "flying" away in the universe, but rather the space is "stretching" in all directions (but not necessarily uniformly)

    I know all this is rather non-conventional and someone may explain why it is not possible. One of the problems may be that we do not have a way to describe (or even imagine) and model an expansion of empty space. I would appreciate your comments.

    George
     
  7. Nov 13, 2008 #6

    Janus

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    [tex]T = 2 \pi \sqrt{\frac{r^3}{G(M+m)}}[/tex]
     
  8. Nov 13, 2008 #7

    marcus

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    Exactly! So if r stays the same and M+m increases by a factor of 1.001,
    then T will decrease by a factor of the square root of 1.001.
    Just a rough order of magnitude calculation (real planet masses may vary :smile:)
     
  9. Nov 13, 2008 #8

    tiny-tim

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    Thanks Janus! :smile:

    So since Jupiter's mass is about 1/1000th that of the sun, and Earth's is far smaller, and T is proportional to 1/√(M + m), that makes a difference of a factor of about √(M/(M + m)), or 1 - 0.0005, or as marcus :smile: says, about 1/20 % shorter than our year, or about 4 hours.

    (The centre of mass would be about 93,000 miles from the centre of the Sun, whose diameter is about 430,000 miles)
     
  10. Nov 13, 2008 #9

    marcus

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    Hello George!
    Where did you get your notion of what constitutes the "BB theory"?
    I assume you mean standard mainstream cosmology. The model (with several variants) that professional astronomers almost all use.

    Are you sure you have an accurate idea of the mainstream model?

    I would urge that you get a secure grasp of the standard picture before deviating off on your own. That way you will have a kind of landmark and are less likely to get confused.

    In my sig I have some links that might help. The princeton.edu link is to an article by Lineweaver on popular misconceptions. The einstein_online link is also good.
    What sources have you read about standard cosmology? Can you give me some links, so I can get an idea what you have formed your impressions from?

    What in the standard model defies reason, according to your ideas? I don't know anything that does. The classical model definitely has shortcomings---it breaks down at very high density going back in time and doesn't say anything past a point. That's how physical models are, they all have a limited domain of applicability. (Certain quantized cosmo versions do not break down and do continue on back to a contracting phase, and one can expect observational tests to eventually eliminate some of the alternatives, but that is a fine point.) So the standard model has things about which it does not say anything. And it is also based on some assumptions, like an approximate uniform distribution of matter and the Einstein eqns of GR. On the other hand, the assumptions have been repeatedly scrutinized and seem to be holding up pretty well. I don't know what in standard cosmo could be said to be unreasonable. So I am curious to know what you think is.
     
    Last edited: Nov 13, 2008
  11. Nov 16, 2008 #10
    Honestly, I believe in intelligent design. Where did the particles that made the big bang come from? Where did the law of gravity come from? How did it come to be? Too many questions, too many unknowns, too many coincidences imo for it to be the result of a random explosion. This universe is just way too complex for that.
     
  12. Nov 16, 2008 #11

    cristo

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    Let me get this straight: you ask a few questions, which get answered, but then you come back to the thread and instead of addressing those that have answered your questions, you just state "I believe in intelligent design." Furthermore, you keep quoting this "random explosion." Where does this come from? I urge you to (a) read up on standard cosmology instead of assuming you know it all based on a few readings of popular science, and (b) read the PF rules, which are linked to at the top of the forum, and in my signature, specifically the part regarding speculative claims not backed up by reputable sources.


    Edit: Let me reinforce that point. Intelligent Design is not a science, thus discussion of it is not permitted, at least in the technical forums. If you wish to learn about standard cosmology, then by all means ask questions here and extremely knowledgeable people will be happy to answer, but please do not weight these questions with comments on intelligent design.
     
    Last edited: Nov 16, 2008
  13. Nov 16, 2008 #12

    nicksauce

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    Do you think the big bang model was just thought up randomly and then blindly accepted by everyone? Of course not. There are great amounts of evidence in its favour. It predicts the cosmic microwave background, it predicts the abundance of helium in the universe, Hubble's law strongly supports it, etc. What sort of useful predictive power comes from your intelligent designer?
     
  14. Nov 17, 2008 #13

    tiny-tim

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    Big bang theory doesn't say how it all started.

    Big bang theory (the experimentally- and observationally-based theory) only kicks in just after the start.

    From then on, (ie for the next 13 billion or so years), everything is satisfactorily explained by big bang theory.

    The particles (hydrogen and helium first, then others much later) came from pure energy. No scientist presumes to know where the energy, or the law of gravity, "came from" (though there are "big bounce" theories, without observational support, that postulate that the universe has existed for ever).

    If you want to postulate that an "intelligent designer" kick-started it, there's no experimental or observational evidence to contradict you, provided that you accept that it was running on its own after the first 10-20ish of a second, and has been ever since. :smile:
     
  15. Nov 17, 2008 #14
    You believe!? The only thing you should believe here (and in any scientific forum) is the scientific theory and the assumptions and foundations of science. Regarding any other thing, in this forum, you do not say that you believe in, but you accept it. Since a theory (like the "Big Bang" theory) is the best way we can describe the universe, so we accept it, not believe in, since it is not a religion to believe or disbelieve in.
    So the word "believe" should not be used at all here, because even if you want to discuss the foundation of science, this is not the right place for that (go to a philosophy forum).
     
  16. Nov 17, 2008 #15

    nicksauce

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    To the OP I would recommend, going here http://www.astronomycast.com/archive/
    and listening to episodes 5 and 6, titled "The Big Bang and Cosmic Microwave Background" and "More Evidence for the Big Bang" respectively. They do a nice job of summarizing the lines of evidence for the big bang in language everyone can understand, and should get you up to speed.

    Afterward, come back and discuss why you don't feel these lines of evidence are convincing, if indeed you still feel that way. Try to use phrases like "I did not find this line of evidence convincing because the data could also be interpreted as so and so" or, "I do not quite understand this line of evidence, can you please further describe so and so", instead of phrases like "Too many questions, too many unknowns, too many coincidences imo for it to be the result of a random explosion.".

    Or disregard this suggestion and continue to live in a cloud of religious bliss. Whatever suits you best.
     
  17. Nov 18, 2008 #16
    What you are really saying is that it seems to you improbable that some random events could produce an Earth with a stable orbit. but there's also 8 more planets in this solar system with stable orbits and lots of other solar systems with planets in stable orbits. Personally I dont have a problem reconciling religious beliefs with science. And I don't see why so many others do, even Einstein believed in a God afterall. but unfortunately there is no proof of one so that's not science. Another fallacy that I have heard in this regard is that someone said (don;t remember who where or when) that the fact that the moon is in just the right orbit to give us solar eclipses is evidence of a higher power, to which I would say, so what if it's in just the right place to give us an eclipse? so what? and besides, it's not. sometimes it's total and sometimes annular. The human mind is remarkably adept at finding patterns where there are none. I'm tempted to say one more thing but that may be crossing a fine line and get my post booted :P
     
  18. Nov 18, 2008 #17
    So what???(maybe I did not get all your points). But anyway, I noticed that you have a small mistake, this is a cosmology forums (accurately: a physical cosmology forums), so please post your comment in a religion forum!
     
  19. Nov 18, 2008 #18
    I was merely pointing out the fallacy of attempting to use probabilities or improbabilities as a justification for intelligent design or any other sentient origin of the universe. So you are correct. You didn't get my point, or else I didn't state them simply enough.
     
  20. Dec 1, 2008 #19
    My very limited understanding of cosmology and astronomy comes from TV programs such as 'The Universe'. But, I'm curious about what existed before the Big Bang. Obviously, something - matter, energy, atomic particles - had to be present to cause the Big Bang. Has matter always existed ? Was there ever a time when nothing existed in space ?
     
  21. Dec 1, 2008 #20

    marcus

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    That's a topic of current research.
    For general audience outreach treatment I'd suggest Einstein-Online. A link is in my sig.
    For scholar-level treatment by a world-recognized expert I'd suggest an article that just came out today
    and is posted online. To download a copy, go to this url and click on "PDF":

    http://arxiv.org/abs/0812.0177
    Loop Quantum Cosmology: An Overview
    Abhay Ashtekar
    To appear in the Proceedings of the Bad Honef Workshop entitled Quantum Gravity: Challenges and Perspectives, dedicated to the memory of John A. Wheeler
    (Submitted on 30 Nov 2008)

    "A brief overview of loop quantum cosmology of homogeneous isotropic models is presented with emphasis on the origin of and subtleties associated with the resolution of big bang and big crunch singularities. These results bear out the remarkable intuition that John Wheeler had. Discussion is organized at two levels. The main text provides a bird's eye view of the subject that should be accessible to non-experts. Appendices address conceptual and technical issues that are often raised by experts in loop quantum gravity and string theory."

    ===============

    If you opt for the wide audience stuff at Einstein-online, the link in my sig will get you the Cosmology index page where there are many topics to chose from. A good choice, if you want to know current ideas about the Bang, is the piece called A Tale of Two Big Bangs. That essay helps to sort out a confusion of terminology and helps get the issues clear. Makes understanding easier.
    But Einstein-online has several things related to Bang and early universe cosmology that you might want to look at.
     
    Last edited: Dec 1, 2008
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