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Expanding Universe

  1. Apr 27, 2007 #1
    Hey guys,
    I've been wondering a lot about this Big Bang Theory, as I think it is terribly constructed. Anyways, I realize that cosmologists have observed that the universe is expanding and even accelerating in it's expansion. However, I don't see how this can be possible with the laws of physics. Since F = (G*m1*m2)/r^2, and every mass exerts a gravitational pull on every other mass, shouldn't galaxies, even if expanding outward, be moving somewhat closer together? Also, what started this expansion, and what is causing the acceleration? Since F = (G*m1*m2)/r^2 and F=MA, shouldn't gravity be slowing down the expansion of the universe? Is it due to dark energy at the border of the universe or the intensity of the initial big bang? What's the Big Crunch, the universe is predicted to eventually come together again? I'm not stupid, I just want to know the common perspective of you guys, as I question both theories.
     
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  3. Apr 27, 2007 #2
    the accerlerated expansion is due to the mysterious force of dark matter...
    i personally believe in the big crunch followed by big bang followed by the big crunch...and so on...the big crunch is where the universe comes together to a singularity
     
  4. Apr 27, 2007 #3

    marcus

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    observation trumps laws
    if the laws dont fit, we have to adjust them, don't we?

    actually you quoted two laws both of which were shown to be wrong and replaced by corrected versions long BEFORE astronomers observed expansion effects. So for starters, CG, you should probably chuck out those two laws, the F=MA and the Newton gravity law.

    F=MA was shown to be wrong in 1905 by Einstein and replaced by a slightly different law involving the change in momentum. No big deal the old one is still approximately right in a lot of cases.

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

    the other law you mention is Newtons gravity law F = GM M'/r^2
    and that was shown wrong and replaced by the equation of Gen Rel devised in 1915.
    (which had to be tested by observation in 1919 before acceptance)

    the 1915 gravity law is our NEW gravity law and is more accurate than the Newton one, it has been tested over and over again with different kinds of observational data and checks out to many decimal places.

    it allows for expansion (altho Einstein didnt realize this when he published the law in 1915)

    A catholic priest named Lemaitre was one of several people that found out that expansion was allowed by this new gravity law, if you started out with the right conditions.

    http://en.wikipedia.org/wiki/Georges_Lemaître

    but even though he offered it as one possible solution, in 1927, Lemaitre didn't know that this was really happening.

    Expansion is an OBSERVATION thing, so if Einstein's new gravity law had NOT allowed for that possibility then when Hubble SAW evidence of expansion around 1929 there would probably have been a move to throw the 1915 law out and make a corrected version.

    (Although people could have argued about different causes of the redshift, but those arguments get old pretty fast because the alternatives are so bad)
    ==========

    So I think you have no problem. The gravity law that we have, that fits observations made on solar system bodies and all the other data extremely well, allows for it.

    And it just happens to be observed. So be happy! At least in this department there is no contradiction between the commonsense derived from knowing correct physical law, and the observed facts.
    ========
    BTW you ask about "us guys common perspective"
    and I speak for myself only. I don't know that there is a common perspective here at PF Cosmology forum.

    You are welcome to believe whatever you want. But there is a kind of mainstream consensus at the moment among working professional cosmologists and if you are going to disagree it is a good idea to understand that professional consensus first so you can differ from it intelligently if you so choose.
    Just my 2 cents.
     
    Last edited: Apr 27, 2007
  5. Apr 27, 2007 #4
    Common sense says that the attraction between matter will slow the rate of greater expanse to a lesser degree. Hence the idea of an accelerated expansion of space, should make one somewhat skeptical, rather than make up something like dark energy.
     
  6. Apr 28, 2007 #5

    Garth

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    DE is an entity added to 'save the appearances'; however it may be a necessary 'entity'.

    Garth
     
    Last edited: Apr 28, 2007
  7. Apr 28, 2007 #6
    One might as well placate to God as much as dark energy, as we have not a smidge of proof for either. Perhaps it's Pam Andersons breast? At least we know they exist, and we know they have expanded in an accelerated fashion, this is closer to the truth than dark energy by a long shot.
     
    Last edited: Apr 28, 2007
  8. Apr 29, 2007 #7

    Wallace

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    The kind of evidence we have for the existence of dark energy is the same kind of evidence that we have for the existence of every other particle and force in physics. We don't have as much or as convincing evidence for DE as we have for say electrons, but the evidence is of the same nature, i.e. observations of the physical world and the theoretical conclusions that follow from that observation.
     
  9. Apr 29, 2007 #8

    Chronos

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    The dark energy bandwagon was launched by the Perlmutter supernova study. Debunking that study would be the place to start. Ideas like that always look pretty cranky out of the chute, and are rightfully treated with a healthy dose of skepticism before they gain traction in the scientific community at large. The evidence for DE, or something that mimics the effect, is difficult to avoid in the face of existing observational evidence. Some alternatives have been proposed, but to date, they are not very attractive. Appending the laws of physics is less extreme than rewriting them. If a rewrite is in order, the evidence usually accumulates rapidly when the tweak is put to the test.
     
    Last edited: Apr 29, 2007
  10. Apr 29, 2007 #9
    If that is true....... then like say for the electron you can say we have an instument that detects dark energy? I don't think so. Dark energy is pure speculation. I have no problem with the speculation as long as it doesn't get in the way of other speculations. :smile:

    Cripe - we don't even have a firm grasp as to what space is, let alone how it expands, if it actually does at all.

    From this perspective - Pam Anderson still looks good and that don't say much for dark energy.
     
  11. Apr 29, 2007 #10

    Wallace

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    We don't have instruments that detect electrons either, not in the way you seem to be demanding of DE. What we have are machines that can give us a certain reading, due to some kind of action, that due to our theory of physics that included electrons we are able to interpret as the effects of electrons.

    This is the same as what we have for dark energy, in that we have observations of the Universe that indicate the action of something on the material we can see. Our theories tell us that this action cannot be caused by the matter that we know about, and since out theories also tell us that there is much more energy in the Universe that we can see in the matter then it seems that the missing energy could be causing that action as evidenced by our observations. This is why we have DE in our theory.

    If dark energy is pure speculation then so is the rest of science. It's a physical theory for this same kind of reasons we have any other physical theory. The evidence is certainly not as strong as the evidence we have for many other theories, but the process is the same.
     
  12. Apr 29, 2007 #11
    I have a question.... from my understanding the strong and weak nuclear forces are what holds atoms together. However, these forces only act under small distances. Obviously when the big bang happened, the subatomic particles were racing out of the singularity's gravitational pull at a speed much faster than the speed of light. When the particles exited the gravitational field, they entered a frictionless environment at incredible speeds. Within a second, all of the subatomic particles would have been too far away for the strong and weak nuclear forces to have any affect on the particles. The end result would simply be an incredible amount of subatomic particles speeding away into nothingness. How then, were atoms formed? Also, the forces seem to just hold together protons and electrons. If the protons and electrons magically got together, wouldn't the neutrons have been far off in space by then?
     
  13. Apr 29, 2007 #12

    Wallace

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    You are thinking of the Big Bang as an explosion that occurred at a finite point within some existing space. This is not what the Big Bang theory suggests.

    Firstly you cannot speak of the 'singularity' as a place or event. The singularity is the point at which our theories break down and we don't know how to describe the physics. Therefore the Big Bang theory starts not at the singularity but at a short time later. At this point what we can say is that the Universe was incredibly dense and hot. The key point however is that the entire Universe was simultaneous in this state, there wasn't a central ball of stuff flowing outwards into a previously empty universe, the whole Universe was in fact incredibly homogeneous (the same everywhere). The Big Bang didn't happen at a single place, it happened everywhere at once.
     
  14. Apr 29, 2007 #13
    Wow, that made pretty much no sense.

    Definition of singularity: A point in space-time at which gravitational forces cause matter to have infinite density and infinitesimal volume, and space and time to become infinitely distorted.

    Definition of a point: A dimensionless geometric object having no properties except location.

    Definition of Location: A place or situation occupied

    The singularity was a point, or small place, the singularity exploded which means the Big Bang happened at the singularity, a finite point.

    Anyway, I often hear the singularity compared to a black hole. Black holes, can't explode because their escape velocity is greater than the speed of light. How then, did the singularity explode, obviously energy magically bursted outward faster than the speed of light. Also, when matter is created by energy in the laboratory, it's antimatter is also created. The energy of the Big Bang would have created equal amounts of antimatter and matter, they would have canceled each other out. "For every action there is any equal but opposite force". Energy turned into matter. Energy converted, and converted is a verb. A verb is an action, so their would have been an opposite created when the matter was created. This is exactly what we find in the lab, whenever energy is converted, so is antimatter. This would have occurred in the Big Bang, and the antimatter would have annihilated the matter, making it the Big Burp.

    Also, you say the universe was homogeneous, therefore, I assume you also believe the Big Bang was homogeneous, meaning equal in dispersion. Why then is the universe unevenly distributed? If the explosion was homogeneous, like all explosions (i.e. fireworks) then how could dark matter be so far out there expanding the universe? And, if this dark matter is so strong that it's expanding the entire universe outward, then why are there colliding galaxies?
     
  15. Apr 29, 2007 #14

    Wallace

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    hmm, maybe it wasn't the best explanation of Big Bang theory that's ever been written down, but the way you are describing the Big Bang in you last two posts bears no resemblance to current cosmological theory, therefore the apparent problems you are finding with it are simply not relevant.

    Perhaps you should try reading a more in depth description of Big Bang theory than I have the time to provide and ability to explain with sufficient clarity. Maybe try "The Big Bang" by Simon Sing (possibile Singh, not sure of the spelling) a very good clear pop science book.
     
  16. Apr 29, 2007 #15

    Chronos

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    Conventional theory, math, logic, etc., ceases to be reliable when you enter the quantum realm that was the mother of all quantum realms - the big bang. Was the big bang an impossibly improbable event that occurred under the most improbable of circumstances - without a doubt. That is what quantum theory demands of any universe. Many apply, but few succeed. We reside in a very bizarre universe.
     
    Last edited: Apr 30, 2007
  17. Apr 30, 2007 #16

    Wallace

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    Yes you need quantum gravity theory to go to t=0. But what is so often overlooked is that the cosmological Big Bang theory is only concerned with t>0. We can describe the universe right back until t=some very small number. A singularity is a term for when you equations go infinite and your theory breaks down! This is what the t=0 singularity is.

    Cosmologist don't care about t=0 only t>0 and this is what the Big Bang theory is all about. It's just poorly named really, leading people to think that the point of Big Bang theory is about what happened at the Bang (t=0) when in fact it is entirely concerned with what happened after that.
     
  18. Apr 30, 2007 #17
    Well then, could you please enlighten me (Not sarcastic, it's an honest question, and it's not rhetorical)? Every explanation of the Big bang I've seen has been something like this: Everything in the universe (nothingness) was in a singularity, the singularity was extremely hot (magically), and energy (where'd the energy come from?) exploded outward (magically). Then, the energy magically turned into subatomic particles. The subatomic particles magically started to come together, magically forming gases (hydrogen and helium). Then, the gases magically compressed and somehow magically stopped compressing, forming stars (Gas must be really smart). Then, stars exploded quite frequently, forming heavier elements (magically). Then, after 15 billion years of awesome displays magic, the universe became what it is today. Where'd I go wrong? Honestly....I don't mean to come off as a jerk, it's just that I don't why people believe in this, but not Pinocchio....He was magical....
     
  19. Apr 30, 2007 #18

    marcus

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    You have been looking at unscientific accounts, evidently.
    I've seen websites where they seem to be INTENTIONALLY misrepresenting mainstream cosmology so as to make it ridiculous or needlessly incredible.

    Please understand that Nature is not assumed to have "singularities". A singularity is technically a failure mode in some particular theoretical model.
    A singularity is not assumed to consist of a single point (although the name sounds like that).

    In the normal course of things in the history of science various theories have had singularities and they were "cured" by improving the model so that it would no longer break down in that particular circumstance.

    This is in the process of happening today with General Relativity (which breaks down at the start of expansion)

    If you have a book or a website that tries to persuade you that the cosmological singularity is something real and tries to describe it as having certain properties like temperature----I can only advise to chuck the book or avoid the website.
     
    Last edited: Apr 30, 2007
  20. Apr 30, 2007 #19

    marcus

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    I see this is a test of you, Christian, to see if at heart you really want to understand modern cosmology (classical and quantum) or if you want the satisfaction of thinking you can dismiss it.

    if you cover your ears and repeat loudly that it doesnt make sense and you can't understand we will know what to think of you. the natural universe is a Book that some refuse to read.

    let me explain my difference with Wallace (we differ, but can understand each other much of the time nevertheless)

    the human mind instinctively desires CLOSURE, it connects the dots, it wants to see the pattern and finish the picture (like of a tiger in the grass).

    Part of a scientist's training is to avoid over-interpreting the data, and to restrain himself from jumping to an unfounded closure.

    a scientist like Wallace, working only with CLASSICAL Gen Rel vintage 1915 must practice a kind of ascetic self-denial. As the philosopher said:
    Whereof one cannot speak, thereof one must remain silent
    Because the classical 1915 model only goes back to smaller and smaller t > 0----it never actually gets to t=0.
    It breaks down at t=0, gives meaningless results, and does not achieve closure.

    As a scientist he realizes the model's limitation, and he refuses to speak about where it does not apply.

    A child or untrained person may ask the obvious question what is it supposed to be like at t = 0. And authors of mass-market books have striven to satisfy the demand for an answer to that question by verbal analogies, mythologizing, or whatnot. But the question cannot be honestly answered within the context of classic (pre-quantum vintage 1915) Gen Rel gravity and attempts to do so can lead to commercially motivated doubletalk.
    =======================

    However other mathematical models have arisen since 2001 which DUPLICATE the Gen Rel model as closely as we can determine for all times a few instants after t = 0 and which nevertheless do NOT break down.

    Typically they keep on cranking back into the past, probing a prior contracting phase on the other side of t=0.

    So far we cannot say the new models are RIGHT. We only know that vintage 1915 Gen Rel must be wrong (or have "limited applicability" as they say) because it suffers a singularity and goes off the rails---it stops modeling nature at a certain point.

    The new models must be tested, just as Gen Rel has been tested for the past 89 years. maybe they will be killed by the first test, maybe some of them will survive.

    Again, we have to use a kind of mental asceticism or self-restraint. We must not believe, but instead must look forward to observational tests of the new models.

    And note that this is in the specialty called "quantum cosmology" and ordinary day to day working cosmologists still only do "classical" by and large.
     
    Last edited: May 1, 2007
  21. Apr 30, 2007 #20
    Please then, give me a brief description of the real Big Bang.........Wow, that was sort of paradoxical, real and Big Bang back to back:surprised Just joking, please give me your description....
     
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