Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Big Bang Question

  1. Nov 20, 2007 #1
    Ive been told by a few people (note that these people were people who dont know much about science), that the big bang was proven wrong..Well I have two questions. Was it actually proven wrong? Because I remember watching a tv show about a year ago showing how I believe in the 60s? That Steven Hawking discovered leftover radiation from the big bang or something? Correct me if Im wrong.
     
  2. jcsd
  3. Nov 20, 2007 #2

    EL

    User Avatar
    Science Advisor

    Definitely not! The Big Bang is a very successfull description of the evolution of our Universe.

    For more reading, see e.g. here.
     
  4. Nov 20, 2007 #3
    I knew it. The guy (well the one guy who really emphasized that it wasn't real) who told me that it was proven wrong was a really religious person who I suppose doesn't like mention of anything other than God so he probably just said that. Thank you for the link though, that cleared things up for me.
     
  5. Nov 20, 2007 #4
    Arno penzias & Robert wilson are the two astronomers who are also nobel prize leureates detected the backround cosmic radiation,I don't think it was Prof HAWKING
     
  6. Nov 20, 2007 #5

    LURCH

    User Avatar
    Science Advisor

    Right, Hawking discovere an entirely different type of radiation. Your friend nay have been referrign to the relativeyl recent discovery about the universe's rate of expansion. Expansion was calculated to be accelerating, which certainly doesn't fit some BB models. In fact, I have to say that this discovery sort-of disproved BB for Me, but not for most people. it is still the accepted model for origins.
     
  7. Nov 20, 2007 #6

    Chris Hillman

    User Avatar
    Science Advisor

    CMB =/= Hawking radiation

    Hi again, Z,

    Of course not; quite the contrary, the so-called "hot Big Bang theory" continues to form the foundation of modern cosmology. But many persons misunderstand what this theory actually says; for example, cosmologists don't neccessarily believe "the universe began with a strong spacelike curvature singularity", but they do believe that it was once much "denser" and hotter than it is now. The cosmic microwave background radiation (CMB), the existence of properties of which has been very thoroughly verified in great detail over many decades, is a kind of "electromagnetic fossil" of this earlier epoch (to be precise, of the "moment" when the density fell to the point where photons could propagate freely for long distances). See the excellent Cosmology tutorial of Ned Wright (Astronomy, UCLA).

    (Note that I not only gave the link but the fact that this website was created by a astronomy professor at a respectable research university, which means it is far more reliable than any old website, which could well have been put up by someone like your friend who doesn't know much about science!)

    You're confusing the CMB, which is a well verified and carefully measured phenomenon, with Hawking radiation, a completely unrelated theoretical prediction which has never yet been confirmed, although several research groups are trying to lay the theoretical foundations for possible tests of the predicted effect--- which is in a sense more "thermodynamical" than "gravitational"--- in so-called analogs of gravitation, such as optical or sonic effects in suitable materials.

    This doesn't make any sense to me at all, and I'd like to stress that all that is needed to reconcile the "acceleration" with the simplest cosmological models in gtr, the so-called FRW dusts, is to add a "cosmological constant term", nowadays more often called "dark energy".

    In the original FRW dust models, the source of the gravitational field (as represented by the stress-energy tensor standing on the right hand side of the EFE [itex]G^{ab} = 8 \pi \, T^{ab}[/itex]) was the mass of the dust particles, which give a highly idealized model of "uniformly distributed" galaxies. In the modified models, one adds a second term which has a very special form and is attributed to the so-far mysterious "dark energy". The two terms look like this if you're curious:
    [tex]
    T^{ab} = \rho \, \operatorname{diag}(1,0,0,0)
    + \varepsilon \, \operatorname{diag}(1,-1,-1,-1)
    [/tex]
    where [itex]\rho[/itex] is the density of the dust (decreasing with time but taken to be homogeneous "in space") and [itex]\varepsilon[/itex] is a positive constant, which is taken to be the energy density of the "dark energy". Students who know about perfect fluids can see from this that "dark energy" behaves like a perfect fluid whose pressure is constant and the negative of its density. (Ordinary fluids have pressures which are positive and much less than their density.) Both mass-energy densities here are much smaller than the density of ordinary matter, so it's not terribly surprising that possible terrestial effects of "dark energy" haven't been observed.

    Advanced undergraduate students curious to learn more about the FRW models can consult D'Inverno, Understanding Einstein's Relativity, which offers a clear discussion of all the FRW models. As you will learn there, the FRW dust with the second term added does begin with a strong spacelike curvature singularity. However, gtr is a relativistic classical field theory, whereas Nature adores the quantum, and for various strong theoretical reasons, physicists expect that gtr will break down at very high curvatures. For this reason, many expect that the putative curvature singularity at the beginning of the FRW models in question might turn out to be an artifact of using the simplest possible "classical approximation" to a yet unknown quantum field theory. However, at present it seems fair to say that this expectation is more of a pious hope than a well-supported hunch.

    The second kind of term shows up in many of the simplest solutions to the EFE, including the de Sitter lambdavacuum and the Nariai-dS lambdavacuum (see [thread=195445]this recent thread[/thread] on the latter). It is true that at the moment it is pretty mysterious just what physics underlies this kind of term, but it is important to understand that gtr is a theory of gravitation in which all forms of mass energy gravitate , with physical effects precisely determined by the density and momentum of said mass-energy. Thus, in a sense gtr doesn't care what terms stand on the RHS of the EFE. At the same time, if we allowed just any term there, in another sense, gtr couldn't rule out any gravitational phenomena and would be in danger of being declared unfalsifiable. The sensible mainstream attitude is that if we believe gtr is a good theory --- which we do, for many good reasons--- then we must assume that we have stumbled over something which has a certain kind of energy and momentum and that we will eventually figure out the physics which produces this term. In other words, we don't yet know what dark energy is, but we know it must be there since we have measured its gravitational effects.
     
    Last edited: Nov 20, 2007
  8. Nov 20, 2007 #7

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Well before Big bang was the paradigm, scientists saw the steady state Universe as the ultimate proof that God does not exists, because the Bible and other religous scriptures talks about a creation. The jarong was "we know that the univers has been here for ever, so there cant be any God". And one of the first contributurs to the Big Bang thery was actually a Belgian Priest.. so a person who belives in a God of creation should not be afraid of Big Bang..
     
  9. Nov 20, 2007 #8

    Sorry, what I meant was that he doesn't exactly like to talk about the possibilities of why we are here or how we are here..He thinks that god is the creator and, nothing else should be mentioned about the creation of the universe or the Earth.
     
  10. Nov 20, 2007 #9
    No, Big Bang hasn't been disproven. When religious people say something like that they're trying to seed doubt on the opposition's viewpoint and are banking on the fact that most people who would take their opinion on such a topic seriously aren't the type to look it up for themselves. As much as I wanted to add to the technical side of this discussion, I'd say it's pretty much covered.

    I am reminded when my mother heard the evolution version of this statement. She'd become convinced I was an athiest and as such she was crying herself to sleep at night. Hearing that evolution was being disproven as part of a church sermon she immediately wanted to check. I was beginning my second year of grad school at the time and as such pretty much the only person with any sort of access to the accepted scientific community that she knew. I explained to her that evolutionary theory was not only not being disproved but it was in fact stronger then the gravitational theory that I work with every day until we find a graviton. A little discussion into scientific lexicon and that was the end of that, for a week.

    The preacher at my mom's church apperently liked saying that evolutionary theory was weakening and crumbling down. As a result I'd get a call after lunch on sunday like clockwork as I told her that nothing had changed. Now we just call because we can. Sappy I know.

    I heard that later a now former family friend had launched a campaign to get me disowned by my family for being a "liberal athiest homosexual queer", mostly because of the location of my apartment. I'm told she just started laughing, then flipped him off and told him to leave. I wish I was there to see that.
     
  11. Nov 20, 2007 #10
    You know, I think personally that religious people dont like to see science or the knowledge we get from science and mathematics increasing so fast because everyday it provides more and more evidence against the existance of god. However, I am not at all against anybody with a religion, even Albert Einstein was religious, from what I read...
     
  12. Nov 21, 2007 #11

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Now proving or disproing the existence of God is a task for philosophers. You should probably go some courses in philosophy.. Also study more science of natural science.
    And the religious ones you are refering to are the very very small group that often are beeing seen in media or make noise of themselves. Einstein was not religous in the manner we think today, he was deist. And he also said something like "Science without religion is lame, religion without science is blind", he was very skilled in philosophy too and couldbe honest both to himself and others. Persons like R Dawkins should try to read more philisophy then just digging deeper and deeper into their molecules and so on.
     
  13. Nov 21, 2007 #12
    Nah, I dont think that philosophy would be very interesting to me...Even if I had all the knowledge in the wide world I wouldn't try to disprove or prove a divine being. I just think, and this is my personal opinion, that religion is a way to escape from reality perhaps. I for one don't believe the least bit that an everlasting god is watching me every minute knowing exactly what I'm going to do next or when I'm going to die or what my future is, as well as I don't believe that there is an almighty creator who created everything. I am not against religion, but I simply don't believe in it.
     
  14. Nov 21, 2007 #13

    Evo

    User Avatar

    Staff: Mentor

    No, he was agnostic.
     
  15. Nov 21, 2007 #14

    Chris Hillman

    User Avatar
    Science Advisor

    Please avoid glib "quotations" having dubious attribution or murky context

    Ditto Evo, Z; Einstein's views on many issues in physics, politics, and religion were complex, personal, largely private; his public pronouncements are often misquoted, and are almost never quoted in their proper context; consequently, they are generally misunderstood, often very badly misunderstood. In addition, his views often evolved very rapidly, particularly on topics in physics, which is one reason why quotations out of context are almost invariably misleading, particularly when it comes to quoting Einstein. And many "quotations" popularly attributed to Einstein appear to be fabrications (or misattributions). But can we move all "religious"/"historical" discussion to other threads, please?

    Z, your are a newbie, so you might not yet realize that the PF rules state
     
    Last edited: Nov 21, 2007
  16. Nov 21, 2007 #15

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Just to emphasize Chris' point, belief in religion, or lack thereof, are not valid topics for this forum. Please return to discussion of the science ONLY.
     
  17. Nov 21, 2007 #16
    Yeah, well its my fault. Im the one who brought up religion, sorry. Dont worry, wont happen again.
     
  18. Nov 21, 2007 #17
    guys, let me say one thing: chris Hillman knows his sh!t. period.
     
  19. Dec 6, 2009 #18
    Where did we end up?

    Can anyone tell me where we are on the big universe map? Is our Galaxy "out front"? ...or, as I've heard "near the middle"? And, what is in front of us? Anyone know how many light-years can be seen in front of us? ...and what's in them? I know there are more Galaxies, but do they "thin out"? Please bear with me here; no laughing; these are important questions to me. :approve:
     
  20. Dec 6, 2009 #19

    marcus

    User Avatar
    Science Advisor
    Gold Member
    2015 Award
    Dearly Missed

    Re: Where did we end up?

    Beth Ann,

    I think you may be under the mistaken impression that due to the expansion of distances our galaxy is "going somewhere".

    Expansion shouldn't be imagined as the galaxies all heading out into empty space, leaving from some point of departure.

    If that were the case then there would be some definite direction our galaxy is going (as part of the expansion) and there would be a meaningful idea of what is "in front" of us.

    And you could ask how far "in front" of us we can see.
    ==============

    In fact the galaxies do have small individual random motions but they are slow and not a part of the general expansion of distances. For a first approximation we can neglect these individual drift speeds. Our Milkyway galaxy and its sister the Andromeda galaxy are both drifting towards a point in the southern hemisphere, at slightly different speeds. But that doesn't matter. It is not part of the overall expansion we are talking about.
    ================

    There is no "thinning out" in any direction that we can point a telescope. There are small random density fluctuations but they don't amount to much.
    ================

    You might have a look at the balloon model sticky thread in the cosmology forum.

    It has some links to some animations that are often helpful in getting a picture of the universe with its overall expanding distances between galaxies.

    Cosmology is the field where they study the overall picture of the universe, and model it. So this thread, since it is about the Big Bang, should really be in Cosmology. But somehow it got started here.

    Here is a link to the balloon model sticky thread.
    https://www.physicsforums.com/showthread.php?t=261161

    And that thread may be too long and wordy for you, so I will summarize.

    We usually tell people not to imagine the expanding universe as an explosion from some initial point out into empty space. One picture we give people is yeasty raisin-bread dough (with no boundaries, extending everywhere) that is rising by yeast action. So each raisin thinks it is sitting still and the other raisins are getting farther away. And the farther away a raisin is, the faster the distance from you to it is growing. But that raisin doesn't think he is moving either. There is no point of origin so nothing to measure absolute motion against. And the dough extends indefinitely. That is one image people give to newcomers.

    But that image has problems because what if the universe is FINITE. You wonder where the edge of the dough is. Where is the part going to be the crust. And wouldn't the dough have a center? So people get puzzled by the rising bread dough picture.

    What works better for some people, many in fact, is the balloon analogy. You suppose space is 2D instead of 3D, so it is easier to picture---a kind of toy model. All existence is concentrated on the 2D surface of a balloon. There is no inside of the balloon or outside of the balloon. That 2D surface is all there is and we are flat 2D amoeba creatures slithering around in that 2D surface.

    If you want to point your flat amoeba finger in some direction, you can only point it in some direction along the surface of the balloon. You can't point in towards the center of the balloon (that is, like, in the past) or outwards into the surrounding room (that is maybe the future). Inside and outside don't exist. All that exists is in this 2D surface.

    And the surface is expanding, so distances between points are constantly increasing. But each of the points is stationary in the sense of longitude and latitude on the round balloon surface. So in the appropriate coordinates, things all stand still but the distances between them grow.

    At this point it is a good idea to watch this short computer animation of galaxies on a balloon surface
    Google "wright balloon model" to get it, or go here
    http://www.astro.ucla.edu/~wright/Balloon2.html

    Once you have watched that short animation a few times you will understand clearly that nobody and no galaxy could be "in front" of the expansion. Nobody can be on the "leading edge" of the expansion. Because on the balloon all the galaxies are equal. They are more or less evenly distributed over the whole spherical surface.

    Each sees the distances to its various neighbors growing. No galaxy is more central than any other, nobody is "in the middle". And nobody is nearer the edge than anybody else, or "in front".

    I think these are the things you were asking about. Please let me know if I understood your question correctly, and do ask if you have further questions!
     
    Last edited: Dec 6, 2009
  21. Dec 7, 2009 #20
    Thanks for this. This helps but I thought the red shift proved we were moving away from other objects including the farthest objects. With the 2D balloon model I can see that the distance to all the farthest objects are at the same. But I find it hard to think that we are not moving through the universe. I guess the universe by its expansion, is the thing that is moving. I’m still confused. I feel like the distance between us and an object 10 billion LY’s away was shorter 10B LY’s ago, meaning we are all moving away from one another. I’m still trying to figure out how the age of the universe, and therefore the distance to the farthest objects, can be determined if galaxies have never moved in relationship to the farthest one.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Big Bang Question
  1. Big bang question (Replies: 6)

  2. Big bang question (Replies: 27)

Loading...