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Questions about the Big Bang

  1. Feb 27, 2015 #1
    hey guys, my question about the big bang is this.. we have all this matter "out there" and "maybe" we had a " big bang". now can anyone answer.. where did the " nothingness " or the "emptiness" that the "big bang" expanded out into..or . how was emptiness made or come to be. without the emptiness being there first, the matter would not have any way or place to expand into... does anyone understand what I am tryin to ask or get at???
  2. jcsd
  3. Feb 27, 2015 #2
    ohh.. sorry forgot this.. and you cant just say the "emptiness " was always there. it had to come into "being" so to speak some kinda/sorta way. could it be that GOD just snapped his fingers and everything 'JUST WAS" ...?????
  4. Feb 27, 2015 #3
    Check out this short, lucid article by Drs. Charlie Lineweaver and Tamara Davis originally published in _Scientific American_. (March 2005). It should answer your question pretty completely as well as a few others that I suspect you may have.


    Highly recommended reading all around!

  5. Feb 27, 2015 #4
    thanks diogenesNY
  6. Apr 14, 2015 #5
    Hi all. Another newbee here.

    I didn't want to start a new thread for the same old topic, so I'll just add here and hope it's ok.

    I've read some confusing replies to this question on this forum in other threads, but all those threads are closed. My question is this: It is said that the Big Bang was not an explosion, but an expansion. Question: WHAT is the DIFFERENCE? Every explosion I've been privileged to know involved an expansion. If the B.B. was an "expansion", I'm confused by the term and also by the fact that galaxies are racing away from a central point as you would expect in an explosion. So what is the difference?
  7. Apr 15, 2015 #6


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    (Many thanks to Marcus for assisting me with the following)

    Expansion, in the context used when describing the expansion of the universe, is a way of describing how distances between objects increase based on two factors; current distance between the objects and something known as the Hubble expansion rate or distance growth rate.

    For example, if two objects are 10 meters apart and the growth rate is steady at 2 per minute, that means that the distance between the objects will double every minute. So after one minute the two objects are 20 meters apart. After 2 minutes they are 40 meters apart. At 3 minutes they are 80 meters apart. And so on. Again assuming the expansion rate remains constant and does not decline, the objects' recession speed, the speed at which the distance between them increases, also doubles every minute. A constant growth rate would mean exponential growth of distances.

    Recession speeds can accelerate even if the expansion rate is not constant, but is declining, as long as the decline is gradual enough. The universe currently has a very low expansion rate---about 7% per billion years---but early in the history of the universe the expansion rate was much larger. Thanks to gravity, it was decreasing over time so rapidly that recession speeds actually slowed. But the decline in the expansion rate appears to be leveling out around 6%, it is now so gradual that recession can accelerate. Distance growth can be nearly exponential. That's what we mean when we say that the expansion is 'accelerating'.

    An explosion does not work like this. There is a very fast expansion from an initial point with no increase in recession velocity after the initial explosive force is gone. In space, all motion after the explosion is done is simply inertial motion. This is simply not what we see when we look at the universe.

    Galaxies are not racing away from a central point. Because of the way this particular type of expansion works, every observer will see all other galaxies (that aren't bound to their own through gravity) as receding away from themselves and see themselves as stationary. This holds true no matter what galaxy the observer is in. So galaxies aren't moving away from a central point, they are simply getting further away from all other galaxies over time.

    See the following link: http://www.phinds.com/balloonanalogy/
    Last edited: Apr 15, 2015
  8. Apr 15, 2015 #7


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    The big bang has no 'central' point. There is no evidence of a location in the universe from which all galaxies are receeding. Were this not true the CMB would be preferentially redshifted in that direction - unless, of course, we happen to be at the 'center' of the universe. That is viewed as highly improbable. A similar argument could be made we must also be at the 'center' of time in the universe - an equally improbable proposition. It would be effectively equivalent to the geocentric theory of cosmology. We can safely dismiss that prospect, so we may also safely dismiss any earth as the center of the universe proposition.
  9. Apr 15, 2015 #8
    First, many thanks to Drakkith, Chronos, and any others who responded.

    My knowledge of cosmology is limited to what can be found on TV. I took college courses in chemistry and physics but no cosmology. So I have to approach this subject mostly with common logic and any benefit derived from basic physics courses.

    Without researching into the use of terms like “recession” and “expansion” as used in cosmology, the two words would be opposites in meaning with “recession” meaning “contraction”. So the notion of the speed of “recession” increasing at the same time the speed of “expansion” decreases, is, to me, contradictory.

    An expansion rate of 7% per time period means to me that the size of that which is expanding is 7% greater at the end of that time period than it was at the beginning of that time period. If we look at an explosion in a vacuum with no external gravity involved, we can expect that the volume defined by the boundaries of the matter expelled in the explosion would double in the first period of “X” seconds and although the matter distributes at various speeds (some moving faster than others) the explosion progresses a given distance from the source in that “X” time period in which the volume doubles. In the next equal time period the explosion continues to progress at the same speed and covers the same distance, but the percentage increase in the rate of expansion decreases as the explosion propagates even though it propagates at the same speed. Example: let’s say an explosion propagates at a speed of 100 feet per second in a vacuum with no external gravity influencing it. We can be confident that it will continue to propagate at that same speed of 100 fps. But while it expands 100% in the second second, increasing from 100 feet to 200 feet, in the next second it will expand from 200 feet to 300 feet or a “rate” of 50%. In the next second it will expand 33.3%, and then 25%, etc. So while the speed of expansion is constant, the percentage (“rate”) of expansion decreases, and this is just a mathematical fact unrelated to any peculiar quirks in the physics of the explosion.

    This seems to be reflected, or logically could be reflected, in your statement that “early in the history of the universe the expansion rate (percent increase) was much larger”. And since we are dealing with far, far greater quantities of matter and mass than we find in known explosions, we now also are dealing with gravity. And so a slowing of the speed of propagation is to be expected. So I find your statement to be expected, logical, and unremarkable although I have remarked quite a bit. ;^)

    There is that confusing (to me) word “recession” again. I don’t understand what it is saying it seems. But let me modify the next sentence as I understand it. Maybe this will help convey and clarify my confusion: “In space, all motion after the explosion is done is simply inertial motion, and, in a case involving enormous quantities of matter, gravity too.”

    All very logical so far.

    Then cosmological theory that said that the Big Bang began with a singularity, -a tiny point smaller than an atom and expanded from there, -is now abandoned?

    That would also be true of an explosion. And “seeing themselves as stationary” is an error very similar to the error of long ago in which humans saw their world as the center with an orbiting sun.

    It would seem that “A” (“galaxies aren't moving away from a central point”) does not indicate/prove “B” (“they are simply getting further away from all other galaxies over time”). First, since cosmology has in the past said that the B.B. proceeded from a singularity and I do not know of any refutation of that, I do not accept “A” yet. And I showed that “B” is true of explosions.

    Since I have little knowledge of cosmology, I don’t understand many of the acronyms like “CMB”. You’ll have to spell it out for me.

    In an explosion, the distances between matter increase. So I would expect in a hypothetical explosion that is the magnitude of the B.B., with distances increasing at huge speeds, red shift would be expected even if the observer is not at the center of the explosion.

    So far I’m not seeing any meaningful distinctions between explosion and expansion. Don’t give up on me! Let’s keep pursuing this if you will!

  10. Apr 15, 2015 #9
    CMB is Cosmic Microwave Background radiation.
    It is light emitted at a time called 'recombinaton', thought to be around 380,000 years after the initial big bang event.
    The light is red shifted due to the expansion, and now is in the microwave range.

    The singularity you refer to is not a physical something, it refers to time t=0, and we have no math models which can describe this.
    BBT describes the evolution of the Universe AFTER this, and all observations fit with theory, but as for T=0 and what is going on there we just don't know.,

    Although there is much speculation, what really happens at T=0 is unknown at present.
    If we do get to find out, that awkward mathematical singularity will go away and we will have discovered some new physics which explains it.
  11. Apr 15, 2015 #10


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    Most of the energy of the big bang was converted into subatomic particles after things cooled down a bit. They later coalesced to form the elementary particle that comprise atoms [electrons, neutrons and photons], which then combined to form atoms after things cooled down even further. These primordial atoms were still very hot and tightly packed in a state of matter known as a plasma. Plasma is opaque to photons so all photons created before about 400,000 years after the big bang were trapped, bouncing around inside this gigantic plasma cloud until it cooled sufficient to permit them to escape and travel freely across the universe. These photons are what we call the CMB [aka cosmic microwave background radiation] - a faint glow in the microwave spectrum detectable across the entire sky in the modern universe. The big bang is often protrayed as an 'explosion' in popular presentations because it is analagous to an explosion in the sense that everything rushed away from it. It is unlike an explosion in the sense that it had no specific point of origin, it happened everwhere in the universe at the same instant. We do not know how large the universe was in the 'beginning'. It may have even been infinite, but, Eintein's theory suggested a singularity - a dimensionless point in space and time. That view is no longer favored by most mainstream scientists.
    Last edited: Apr 15, 2015
  12. Apr 15, 2015 #11
    Is a black hole a "physical thing"? No math models? We are told that within the event horizon of a black hole, physics fails. Maybe at B.B. t=0 math fails too.

    How do we know it happened everywhere at once?

    I've noticed that everything in all our experience of the universe and solar system and nature happens in cycles. I have trouble believing that ONCE there was a beginning to ONE universe and it is all heading for a time when all helium is used up and all energy is dissipated and the universe just stops. There must be a cycle. I cannot believe that 40 billion, 60 billion, 100 billion, 200 billion years ago there was nothing. But that is another discussion and not germane to this discussion of "expansion vs. explosion".

    BTW, apparently the idea of the B.B. NOT originating from a single point but rather happening everywhere at once, is not accepted by "mainstream cosmologists." (How are links posted?) "www dot space.com/52-the-expanding-universe-from-the-big-bang-to-today dot html"

    Anyway, my understanding of "expansion vs. explosion" has not been challenged: I see nothing that has bee said here yet that potentially clarifies this for me. I've been asked to "believe" unbelievable ideas maybe, but sound explanations seem in short supply.
    I'd love a sound, rational explanation or I just have to keep believing the "expansion" concept is little more than "fancy talk". Sorry. You folks are persuaded. How did you "get there"?
  13. Apr 15, 2015 #12
    A black hole certainly is a physical thing, the 'singularity' is not.
    It is a mathematical artifact, we cannot observe it. By definition it is not physically possible
    We do observe physical phenomena indicating the presence of a black hole though.
    Last edited: Apr 15, 2015
  14. Apr 15, 2015 #13


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    we talk about something "receding in the distance" Receding basically means "getting farther away"
    Recession speed is the speed with which the distance to something is increasing. It may not be increasing because of motion thru space. GR allows for curvature (distances not remaining the same, unless they are between things bound together by gravity or molecular forces etc)

    Recession can have several meanings in English. There is also the *Economics* meaning. Better not try to mix the meanings together.

    Only if the expansion rate remains constant.

    Something can be growing now at a rate of 7% per year (e.g. in the second quarter) but at the end of the year it might not be 7% bigger. A rate is an instantaneous thing, it has to be expressed using some unit of time but there is no implication that it remains constant thru out that time.
    Like speed of motion (a different thing but analogous in being instantaneous) I may be going 40 km per hour now but that does not imply that in one hour I will be 40 km from here.

    So think of "7% per billion years" as meaning the same as 0.007% per million years, just easier to say and to remember. And remember because the rate is instantaneous it is continuously compounded. As long as the rate remains at that level it represents exponential growth.

    Probably the least confusing way to express the distance growth rate (the Hubble parameter H) is to simply invert it and state the time T = 1/H

    7% is about 1/14 so we could take this rate 1/14 per billion years, and flip it over and have 14 billion years. It is a convenient handle on the current growth rate. Actually the more precise figure is 14.4 billion years.
    T defines the distance growth rate 1/T = H = 1/14.4 per billion years.
    Last edited: Apr 15, 2015
  15. Apr 15, 2015 #14


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    I'd suggest you find out something about contemporary cosmic modeling, a lot of which involves a contraction and rebound. Get a little exposure to professional research papers (even if you have to skip over the math parts and just read the introduction and conclusion paragraphs where they say it in words.)

    It's a handicap to be completely dependent on (possibly shoddy) journalism in such as "space.com" online magazine. One of the best really recent papers I've seen is one by Edward Wilson-Ewing and Yi-Fu Cai (postdocs at McGill in Canada and Einstein Institute outside Berlin). To find a free online copy just google
    "LambdaCDM bounce" or use this link:


    The key thing they do is study what would happen if a universe like ours were collapsing at the same rates as ours is expanding, according to our best understanding of the physics and a few (reasonable if not proven) general assumptions about what takes over at extremely high energy density.
    (quantum effects :oldbiggrin:, Heisenberg principle, nature does not like to be pinned down)
  16. Apr 15, 2015 #15
    Math may provide some with assurance that what is observed is also "real". But when thousands of whole planets fall into a small/tiny region of space, and evidence of matter orbiting that small region at shockingly high speeds proves an unimaginable gravity, there's little more we need to see to know what it is. Physics, which fails within the event horizon (we are told), would cause us to believe that with such gravity and with so much matter crushed into such a small spot, temperatures would be astronomical. To me, that is equivalent to "seeing a black hole".
  17. Apr 15, 2015 #16
    Various sources addressed to the layman who is not knowledgeable of "contemporary cosmic modeling" (including dictionaries, wikipedia, and other types of journalism) state that the universe did not "explode into being" at the time of the B.B., but expanded. Hence I conclude that many who understand this believe that the common man can also understand it if told about it. So I am asking to be told about it; to have it explained so it makes sense and so I understand it. So far I'm not advancing much at all in my effort to understand. It still looks like "expand rapidly" is a synonym for "explode". I'm really thinking there's no "there" there. But I still search. What more can you tell me to help me?
  18. Apr 16, 2015 #17


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    In my experience discussions along those lines tend to be about the meaning of words. People unpack and compare their associations with "singularity" and "expansion" and "fabric".
    So it is a purely verbal merry-go-round and round it goes.

    Cosmology is quantitative. As a purely verbal discussion it resembles Gertrude Stein's description of Oakland California, "There is no there there." Someone whose questions have merely verbal content and who is not in some way interested in the quantitative measurements being made and used to model, is not there.

    I'm skeptical that a "common man" exists in any Q&A about cosmology. Someone may come in here with a stereotyped idea of the Common Man, and he may pretend to us that he is that Common Man that he imagines, and play that role. But that individual has already exhibited Uncommon behavior and facets.

    In your case you seem to generalize inaccurately about what we think, and questions we're interested in, and current research we are following.
    My suggestion is for you to actually look at some current research, and I have suggested a paper. It is representative of a lively active direction of current research in cosmology. There are a bunch of related papers. I suggest you look at it and then reformulate your questions. Here is the link again:
    A ΛCDM bounce scenario
    Yi-Fu Cai, Edward Wilson-Ewing
    (Submitted on 9 Dec 2014)
    We study a contracting universe composed of cold dark matter and radiation, and with a positive cosmological constant. As is well known from standard cosmological perturbation theory, under the assumption of initial quantum vacuum fluctuations the Fourier modes of the comoving curvature perturbation that exit the (sound) Hubble radius in such a contracting universe at a time of matter-domination will be nearly scale-invariant. Furthermore, the modes that exit the (sound) Hubble radius when the effective equation of state is slightly negative due to the cosmological constant will have a slight red tilt, in agreement with observations. We assume that loop quantum cosmology captures the correct high-curvature dynamics of the space-time, and this ensures that the big-bang singularity is resolved and is replaced by a bounce. We calculate the evolution of the perturbations through the bounce and find that they remain nearly scale-invariant. We also show that the amplitude of the scalar perturbations in this cosmology depends on a combination of the sound speed of cold dark matter, the Hubble rate in the contracting branch at the time of equality of the energy densities of cold dark matter and radiation, and the curvature scale that the loop quantum cosmology bounce occurs at. Importantly, as this scenario predicts a positive running of the scalar index, observations can potentially differentiate between it and inflationary models. Finally, for a small sound speed of cold dark matter, this scenario predicts a small tensor-to-scalar ratio.
    14 pages, 8 figures

    I make this suggestion, Mr. Eagan, because I have a high opinion of you (based on brief acquaintance), that is, I think you are able to get something out of reading the less technical parts (introduction, conclusion, and whatever else is not too mathy) of this paper.
    Last edited: Apr 16, 2015
  19. Apr 16, 2015 #18


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    Except that an explosion, in the usual sense of the word, simply wouldn't give us the observed properties of the universe. For example, the CMB wouldn't be the same temperature across the entire sky to better than one part in one million or so. In fact, there wouldn't be a CMB at all. Nor does an explosion help explain the fact that the observed redshift of galaxies is equal for all galaxies at any particular distance in any direction to a very high degree of accuracy. There would be a noticeable difference in the direction leading away from the point of the explosion.

    One isn't meant to 'prove' the other. Both are the result of expansion. And no, you haven't shown that B is true, because it is not true. If you haven't already, see how cosmological expansion works in the link I provided in my earlier post.

    We don't 'know'. It's simply the theory that makes the most accurate predictions and has the simplest explanations. All other suggested 'theories' have serious problems in almost every area of cosmology. Many don't make accurate predictions and/or require the breaking of multiple fundamental laws that have never been observed to be broken.

    The vast majority of processes are not cyclic. Radioactive decay, fusion within stars, formation of objects, and many, many more things are not cyclic.

    What would convince you? There are mountains and mountains of evidence supporting the BBT and the expansion of space, and practically none that is explained better by any possible competing model. If you'd like a list of evidence for the BBT then see here: http://www.talkorigins.org/faqs/astronomy/bigbang.html
    You can also find plenty of explanations regarding alternative theories to the BBT and why they aren't considered viable along with very good explanations for each of the listed pieces of evidence supporting the BBT.

    We can't simply explain it to you. It's too complicated to 'simply explain'. That's why so many people have trouble with it. You have to be willing to put in put in the effort to learn things which aren't intuitive and to trust that what we are telling you is accurate and not argue over every little word that you think is contradictory.
  20. Apr 16, 2015 #19
    Let me begin this post by restating why I am here. I am here in the hope of acquiring an understanding of the difference between “expansion” and “explosion”. So far there has been just one concept offered that holds the potential to make this distinction real, and that is the notion of the B.B. not having begun from a point, but that it “happened everywhere at once” and sadly, that is mere theory to be rejected by some I expect. I believe I can explain in logical, familiar terms any other concept/argument that has been posted in this thread as also being true of explosions.

    Now, let’s get on with the discussion.

    Hmmm. Interesting indeed! But as we will see shortly, your linked article seems to disagree.

    Well, consider a bomb full of ball bearings. The ball bearings are quite a bit closer to each other than they are after the bomb is exploded. I think that is easily understood and seen with no further proof being required. Or put some dynamite in a shed loaded with tools and detonate the dynamite. Same thing. This would seem to validate my statement ("B"). Yes?

    Okay. Let’s look at that link, after which I’ll resume a discussion of the remainder of your comments...

    That link says “The expansion has no center, and everything is moving away from everything else, with things farther from each other receding faster from each other than things closer together.”

    Wouldn’t differences in speed of movement of galaxies away from us result in differences in red shift?

    It also says “There IS no center to the universe.” That can only be true if there is no “edges” or boundary to the universe. If the universe can be defined as so many lightyears this way and so many that way, it defines boundaries, and if it has boundaries the center can be calculated or mathematically approximated. So the statement MUST be saying “there are no boundaries” meaning the universe has no size, -it is infinite. I don’t know that this has ever been established as fact. Hence I am not on board with the notion of “no center”.


    “The fact that all the pennies move away from each other and that ones farther away move away faster and that there is no center.”

    Pardon me, but there certainly is a center to any balloon. Okay, okay, the article states that this objection is not valid because the analogy of a balloon is imperfect. And so to improve the analogy further in that regard we must use imagination. So let’s imagine that there are “pennies” distributed inside the balloon, too. I think it is easy to see that when such a “balloon” is inflated, all pennies including those inside the balloon would move away from each other. And yet there is still a center.

    And it says “That is, things the size of a local cluster of galaxies and smaller (like, the Milky Way, Earth, you, me, atoms, and so forth), do NOT expand.”

    Explosions do that as well. I understand bombs have been built with ball bearings or nails in them.

    Another comment in the caveats below the article: “The universe not only has no center, it has no edge, but that does not imply that it is necessarily infinite, it could be finite but unbounded.”

    This asks me to accept a contradiction on faith, and that stretches its credibility. Maybe there is no “hard edge” i.e. a boundary that can be identified beyond which no matter extends as it advances. i.e. some matter extends far, far beyond other matter or clusters of matter in some areas, but that doesn’t indicate it to be an “expansion” rather than an “explosion” either. It is widely accepted that a shotgun blast sends pellets out in a “sausage-shaped cluster”. But this is not actually true although it is a convenient concept to enable certain discussions of the subject. In reality there are a few pellets that travel much, much faster than the “cluster”, and some that are real slowpokes. This is readily seen by shooting a shotgun at low elevation over a calm, waveless pond. So since the article’s description given for the universe is not specific, I am left having to assume and conclude. Hence, my conclusion is that the universe DOES have a boundary but it is very uneven much like a shotgun blast is. Hence the universe in not infinite; hence the universe does have a “center” which would probably be fairly approximate. Any other explanation I have seen so far would be asking me to accept illogical notions on faith.

    That’s the link. Now to continue with the discussion:

    I don’t follow that. Explosive experts carry out forensic studies of blast sites to determine the point of origin of the blast, and matter does proceed radially from the point of an explosion unless, like a thrown baseball, spin and air friction causes it to curve.

    But I cannot just accept it all on faith and I’m not willing to spend years (I probably don’t have enough left) to acquire a working knowledge of higher mathematics, -not that I think it would be an answer anyway. Thank you all for your time, but so far, every item of evidence that has been presented I can explain as an explosion with the word “expansion” being a synonym and meaning the same thing. My understanding remains where it was. It would be easy for a cosmologist to simply write me off as a person who wants to cling to his views in spite of everything that has been presented, but that would be a case of self-serving failure to grasp why I’m here. I’m open to anything more that can be offered to distinguish explosion from expansion.

    In fact, if it would help you zero-in one what I may need to hear, we can reverse this conversation: I invite you to ask me to explain my view on issues that you think may be key. Then you may have something you can disprove. Just a thought.
  21. Apr 16, 2015 #20
    When we look at galaxies we can deduce their distance from their red shift.
    What we see is that in all directions there are more or less the same amount of galaxies having 'x' amount of redshift.
    There is no particular direction where the redshift is more or it is less.
    Therefore we conclude either that
    A: There is no center from which galaxies are spreading out, they are all just getting further away from each other.
    B: Earth is the center of the Universe, and everything began spreading out from here.

    Which seems more likely to,you?

    There are some galaxies which are not 'spreading out', such as in the case of our own galaxy is on a collision course with our neighboring Andromeda galaxy, but that is due to gravitational binding on a local scale. It isn't significant on a cosmological scale.
    Last edited: Apr 16, 2015
  22. Apr 16, 2015 #21


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  23. Apr 16, 2015 #22


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    No, it does not. Your ball bearings do get further apart, but only in the axis perpendicular to their motion. If two ball bearings are heading along the same direction, one closer to the point of the explosion than the other, the two do not necessarily get further apart. They might, if the conditions of the explosion accelerate one more than the other, but this type of 'recession' (the increase in distance between the two) does not follow the observed motion of galaxies in space. Namely that the velocity doesn't increase as the distance between the ball bearings increases.

    Also, in an explosion you can think of the ball bearings as being on the surface of an expanding sphere, but in the middle of the sphere, and on the outside, you have a large void where there are little or no ball bearings at all. We don't see this when we look at galaxies. We see a clumpy, but continuous distribution of galaxies in all directions at all distances. If they were moving away from an explosion there would be a huge number of galaxies with very high redshift (the galaxies on the opposite side of this expanding sphere from us) and then a sudden and severe gap in redshift due to the void. This is not what we observe. The redshift is continuous in all directions, exactly what we'd expect if expansion works the way we are telling you it works.

    Expansion, as we are explaining it, is fully compatible with there being a geometric center of the universe. We don't, in fact, even know if there is a center to the universe or not. That doesn't change the fact that if you rewind time and look at what is happening (I'm speaking in terms of looking at a model that describes the evolution of the universe, not physically rewinding time) there is never a time where you can point and say "There's the center of the universe". The singularity happens when we take the scale factor of the universe to zero, which doesn't have any physical meaning. There are plenty of other singularities in physics too. For example, coloumb's law becomes singular when the radius becomes zero and predicts and infinite force. Not only does this not make sense mathematically (because you're dividing by zero), this also doesn't happen in real life. It turns out that coloumb's law is an approximation, and quantum physics provides a better and more accurate description of physics at that scale that avoids a singularity altogether. It is believed that a similar situation is occurring in cosmology and that a future theory will be able to avoid a singularity.

    I caution you on misusing an analogy and trying to make it fit what you believe. As the website explains, and which you yourself pointed out, the analogy assumes that there is no center of the balloon. In other words, in order for the analogy to work you must consider only the surface of the balloon. Considering the inside of the balloon breaks the analogy because that isn't how the expansion of space works. It would be like me saying an electrical circuit should spew electrons out into space when there is an open in the circuit because in the common hydraulic analogy (current as water flow and voltage as water pressure) that's exactly what would happen. It's just an analogy.

    But, even if we do consider that there are pennies inside the balloon:

    Well, no, the pennies inside don't recede from each other. They just sit there. You can try this at home. Now, if you were to embed the pennies inside something that is expanding, say a loaf of bread that is being baked, then the pennies would recede from each other. And you'd also have another common analogy of how expansion works: http://www-personal.umich.edu/~huterer/EPO/analogies.pdf (page 36)
    But again, this is just an analogy, and since the loaf of bread is a real object it has both a boundary and a center. But that's why it's just an analogy and not a full, comprehensive description of expansion supported by proper math and observational evidence.
  24. Apr 16, 2015 #23
    Really? I was under the impression that red shift indicated speed they are moving away from us.

    I can imagine that if we could examine an explosion in space and track a particle that after some time we would find something similar happening. There would be differences though because an explosion of the sort I'm imagining would involve essentially nothing in the manner of gravitational forces. So I'm not ready to declare that this proves it is an expansion and not an explosion in the beginning of all things.
  25. Apr 16, 2015 #24
    The more distant they are, the faster they are receding, so it amounts to the same thing.
    This is as far as I know based on irreffutable evidence rather than a theory.
  26. Apr 16, 2015 #25


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    It's a theoretical model, but it has one big advantage over an "explosion" theoretical model: it explains our observed data. So it isn't a "mere" theory; it's a theory that has observational support.
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