The Big Bang Bamma

Some great questions here I'll get to them as I find the time. Hmmm, I'm glad you appreciate the futility. Not because the theory is unassailable, but because your level of understanding will be based on analogies, and rather stretched analogies at that. The target for your attack will thus be these analogies, and to be honest, I'd be surprised if you didn't find some holes...Be back later...

In the classical Big Bang scenario, time as we think of it, begins AT the Big Bang, i.e. t=0. BUT the way we think of it isn't particluarly relevent. Only in the way that the surface of the Earth "begins" at the South Pole: it's one way of putting it, but it's rather misleading. Possibly but not necessarily Either way, it is irrelevent to the Big Bang scenario. Why does the earth begin at the South Pole? It doesn't. It's just one way of looking at it. Because it did not come to exist. It exists, that's all there is to it. There is no "before" when it did not exist, and there is no "after" when it will not exist. Creating more space... a great way of putting it too. EM and the strong force are far too strong to be affected by the expansion (except in the big-rip hypothesis) See 7 Yes, and in quite a terrifying way!!! See 3.

Yes it could. You are trying to use local concepts to describe a global situation. Simple cons of energy arguments do not work. Or if you do want to talk that way, then the simplistic picture is that your "positive" energy is balanced by the effective "negative" energy of the universe's gravitational potential, giving the universe a total "energy" of zero.

As with my previous comments, this is a local statement. It doesn't actually mean a great deal wrt the universe as an entity. And of course, matter can be created and destroyed... pair creation and pair annihilation are the obvious examples of this: two photons can create an electron/positron pair. "before" there is no matter, only massless photons, and "afterwards" there are two massive objects, the electron and the positron. Energy has been conserved, but matter has not. Matter that falls into a black hole is eventually re-radiated from the black hole in the form of Hawking radiation. In a perpetually expanding universe, all of the black holes will eventually disappear as they radiate themselves to extinction.Destruction is misleading (as is creation). Think instead of there being a maximum to the concept you call time, and that maximum occurs at a point in the universe.BTW, welcome to EvC This message has been edited by cavediver, 11-15-2005 10:26 AM

An electron is not made up of smaller particles in the way that neutrons and protons are made up of quarks. It is the closest example of an actual "point" that we have. In fact it has no size at all at any length scale that we can probe! If you stare at an electron from a decent distance, it can appear to be particle like. But as you zoom in you realise that what appeared to be empty space surrounding the electron is actually a seething sea of activity of photons and other electrons! But you never manage to resolve the central point. So in a sense, what we think of as an electron is made up of other particles: photons and more electrons!!! Confused? The problem is that the everyday particle picture has broken down and you are now observing a quantum field, or actually, two interacting quantum fields: the Dirac field of the elctrons and the Bose field of photons.Pair creation is just one of four identical processes: pair creation, pair annihilation, compton scattering and bremsstrahlung radiation. The only difference in each of these pictures is the direction of time wrt the interaction. Two electrons and two photons undergo an exchange. It can be two photons for two eletcrons (pair creation) two electrons for two photons (pair annihilation), an electron and a photon for an electron and a photon (compton and bremsstrahlung). There's no better demonstration of the simple 4d nature of space-time than the symmetry between these "different" interactions.

\                   /
         \                 /
       e+ \               / e-       Time ^
           \  e_v    ____/
            \____----    ~
            ~             ~
           ~               ~
          ~                 ~
         ~  Ph               ~ Ph
        ~                     ~

Oops, was going to do all four but outta time... sorry!

Ok, quickly for now...Take a closed FRW universe - i.e. normal big bang, with <1. It has curvature. If you measure the circumference of circles that you draw around yourself, you will find they are less than 2piR. However, if there is a period of inflation, the inflated universe's curvature will be much much less. Cosider the curvature of a balloon... you can see it. Blow it up to the size of the Earth and it's no longer so obvious. You measure curvature by quoting the radius of a sphere that would match the curvature. So the curvature of the Earth's surface rather obviously has a radius of curvature of the Earth's radius! So that should explain what they mean when they say the radius of curvature of the universe is so large that it is pretty much flat. Now if >1, you don't have sphere, you have a pseudo-sphere (great fun to visualise ) but the same flattening occurs under inflation. This is how the universe finds itself so finely tuned to flatness... according to inflation anyway. No, there is not. The balloon is the rubber surface, not the space inside. Same with the universe. It is the surface that matters, except that the surface is 3d. This is child's play to a mathematician as one of the first things they learn is that a sphere is a 2d object, not 3d. It is the surface that matters. There is no inside. The sphere can be defined without any reference to a 3d embedding space. The inside does not exist! There is no spoon... From us. And every other point in the universe. Think of the balloon blowing up and all the points on the surface stretching away from each other. Only as much as every other point in the universe is also at the centre. This makes perfect sense from GR. It is GR that dictates this fact to us. There is nothing else that gives a concept of topology to the universe. Good This is not even scratching the surface...This message has been edited by cavediver, 11-15-2005 01:32 PM

Thought I'd add these for completeness...

~                     ~
              ~                   ~
               ~                 ~
             Ph ~               ~ Ph       Time ^
                 ~  e_v    ____~
                  ~____----    \
                  /             \
                 /               \         Pair annihilation
                /                 \
               / e-                \ e+
              /                     \

and

             ~                     /
              ~                   /
               ~                 /
             Ph ~               / e-       Time ^
                 ~  e_v    ____/
                  ~____----    ~
                  /             ~
                 /               ~         Compton scattering
                /                 ~
               / e-                ~ Ph
              /                     ~

Ph photon
e- electron
e+ positron
e_v virtual electronThis message has been edited by cavediver, 11-15-2005 08:25 PMThis message has been edited by cavediver, 11-15-2005 08:40 PM

Then every point is the centre. Every point in space was "born" in the big bang. In a finite closed big bang scenario, all of those points were coincident. You will find that this is true for every point in the universe. Every point thinks it is the centre because everything is moving away from it, with a speed proportional to the distance. Again, you will find this true for every point in the universe!Think of the balloon analogy. Every point on the balloon skin thinks that every other point is moving away radially as the balloon inflates, so concludes that it is the centre of expansion of the balloon. But we can see from our vantage that there is no centre on the balloon surface.

You can think that way but it doesn't really help. It's stretching the analogy a little too far. Instead of a picture of 3d space as a surface, you want to jump to a picture of 4d space-time as a surface. Remember my globe analogy that I use frequently? North pole - big bang, South pole - big crunch. Our balloon has been reduced to a circle, a circle of latitude. The balloon inflating is now the circle of latitude growing as you move south from the north pole. Time is distance along the line of longitude. Again, inside the globe has no meaning.

Yes, I think you are. It is simply measure of how curved something is, it is not a distance in space as such. The bigger the radius of a circle or sphere, the less it is curved. Anything that is curved can have its curvature at a point described as the radius of a circle or sphere that would have the same curvature at that point. Check this out: The piece you were reading was just a little confusing in the way it described the vast length of the radius of curvature as if it lay within the universe. It does not, it was simply making a comparison. Absolutely, or zero curvature if the universe is indeed perfectly flat, or negative curavture... It's easy... it's just the observation that on our balloon, two points move away from each other much more quickly if they are far apart compared to if they are neighbouring.

quote:

---

Any two points which are moving away from the origin

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The mention of origin is a very poor choice. There is no origin. No, it makes no sense to do so. The inside simply does not exist. You cannot point to it. They are electrom and photon interactions. Someone (madeofstarstuff?) was asking a while back about the significance of photon interactions to our understadnign of reality, and I always meant to get back to him. [If you're reading, do you still want to talk about this?]

Ok, you are getting confused over what we call intrinsic and extrinsic curvature.Take a baked bean can, and cut off the top and bottom. Is it curved?Take a football (sorry, soccer ball :rolleyes Is it curved?Both are extrinsically curved... you can see that. But only one is intrinsically curved.Cut both open and see if you can flatten them out.The can will happily lie flat on the table. No matter how you cut the football, you cannot get any piece of it to lie flat.So which is truely curved?The 2d can was curved by using a higher dimension into which it rolled.The football is by its very nature curved... the extra dimension just enables you to observe that curvature. There are several 2d surfaces that are curved, but 3d is not sufficient for viewing them: the klein bottle and RP2 are the two prototypes of this behaviour. Both are doughnut like surfaces, but with "mobius strip"-like twists. You cannot visualise them in 3d. But only extrinsically. The line can wind its way through a higher dimensional space, but intrinsically it is flat. It cannot posses curvature.I should stress that curvature is a local property. You measure it by noting deficits in the circumference of cirlces or areas of surrounding spheres.Strictly, we do it in mathematics by taking a vector around a little loop in space, keeping it as parallel as possible to its starting direction, and noting how its direction has changed by the time it gets back to its starting point. No change - flat space; change - curved space.Put an arrow on the north pole pointing south (obviosuly ) towards London. Slide it down to the equator along the Greenwich meridian. Now slide it sideways until it is at New York's longitude, but still on the equator. Slide it back up to the pole. It is now pointing towards New York. Conclusion - the Earth's surface is curved. No need to mention a third dimension.

Yes, this is why it is an anology The universe, although 3d spatially, behaves like the 2d skin of the balloon. There is only the surface. There is no "interior". There is no sensible concept of "centre" for the universe unlike the balloon. This is one place the analogy breaks down. Nothing There is no need. This concept is included in the definition of the big bang. The big bang is a prediction of General Relativity, where every point in space IS "born" in the big bang. There is no other theory. You could invent one, but you can't call it a "big bang" 'cos we have the trademark Well, an edge to the universe would be a curious thing, and in fact in these days of immensely speculative M-theory cosmology, such a concept isn't as daft as it was once thought wrt our 3d observable universe (but even then, the embedding space/multiverse/super-universe will not have an edge) HOWEVER, in the standard cosmology, no-one entertains the idea of an edge. It is not possible in General Relativity which is our only current theory of the universe. The universe is either infinite, and so no edge, or finite and topologically some compact object (like a hypersphere), so again no edge. The whole point of the balloon analogy is to take you AWAY from this kind of thinking! The interior is irrelevant. It is the nature of molecules/particles/points on the surface/skin of the balloon that is important. The interior has a centre and an edge, the universe has neither...

To demonstrate that there is no edge and no centre? Yes, it is very compelling. Thanks for bringin it up.Of course, it doesn't discount US being the centre, and the CMBR being some effect OF the edge!!! Hmmm, perhaps I shouldn't have mentioned this possibility...

The point is that apart from the exceptionally small fluctuations (which was our great discovery of the early 90s. I still remember when the COBE team arrived to present us their results. Great times ) the CMBR is identical in all directions (once you have removed the Sun's motion in the Galaxy). This is the same picture we get when we look at the distribution of galaxy velocities. There are two conclusions: either we (our Galaxy) is at the centre of the expansion of the universe, or there is no centre...

Hi CS, glad I'm not just whistling in the wind! You're quite correct, it is a failure of the analogy. There is no "up", there is only the surface of the globe. Each circle of latitude is a 1d analogy of our 3d spatial universe. No, what I am describing is the break-down of our understanding of matter as "things". There is actually no such thing as a single electron, as some sort of individual blob of stuff. It just looks that way when we observe from the intra-atomic scale upwards. If we try to zoom in on the electron, we no longer see "one" electron but rather a seething sea of virtual particles. If you sum over this observed volume, you will regain the charcteristics of the one electron (mass, charge, etc), but there is no one "object".Assuming you are familiar with a little advanced maths... what we deal with at this scale are individual fourier modes of the quantum field. For the electron, the field is fermionic and the individual modes obey a Grassmanian algebra. This is the source of all the exclusion principle weirdness... No, absolutely not. It is the interaction of photons and electrons that give rise to what we call "force". For electrons and photons. the force is called electromagnetism, and the theory is called QED (Quantum ElectroDynamics)Interactions of quarks and gluons give rise to what we call the strong force, and the theory is QCD (Qunatum ChromoDynamics). The quarks and gluons are totally analagous to the electrons and photons. Hwoever, QED is an Abelian gauge theory, where-as QCD is a non-Abelian gauge theory. This is beautiful mathematics, but the upshot is that photons cannot self-interact, whereas gluons can. This is immensely important for our lives, as this is the reason we can see! If photons self-interacted, there could be no vision as photons would be unable to follow free paths from the source to our eyes...