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CP violation and element forging

  1. Sep 6, 2006 #1
    Hi, I just saw the premier of "Birth of the Universe" on Naked Science (National Geographic) and had a couple of questions as a result, which I'm hoping somebody could answer.

    First, they said that the reason we have matter and no evidence of anti-matter is because when energy was converted into matter/anti-matter particles in the early universe (after quark/anti-quark pair production), the amounts were disproportionate. There was more of matter, in the amounts of one part per 10 billion (is that the baryonic number?). Well, fine, but wouldn't that imply that the mass of the observable universe would be dominated by mass in the form of energy from the early annihilation process? If the baryonic number is so small, then matter would be sooo small percentage of the total mass. The popular "mass pie chart" shows, however, that the total mass is about 75% dark energy, 20% dark matter, 5% baryonic matter (luminous and non), less than 1% - radiation. Where is the mass/energy from the annihilation ?!?!

    Secondly, they said the elements heavier than iron were forged by exploding cores of supernovas, which produce enough energy to forge heavy elements. I always thought that fusing heavy elements consumes energy, which would inhibit the process of fusion, as the energy required to produce really heavy nuclei wouldn't be available due to it being consumed by lighter heavy elements. I thought the heavy elements were produced by neutron capturing, some of which would later turn into protons via weak force interactions and decay. I know I couldn't have come up with that stuff on my own, I read about it somewhere.... So, did I read some crackpot or an outdated theory??

    In advance, thanks!

    Pavel.
     
  2. jcsd
  3. Sep 6, 2006 #2

    SpaceTiger

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    Good question, and basically the answer is that it was redshifted (i.e. robbed of energy) by the expansion of the universe. If you wonder how this conserves energy, then see here:

    Is Energy Conserved in GR?

    This happens only to relativistic particles and light, so in the absence of other mysterious components (like dark energy) matter will eventually dominate the energy budget in an expanding universe.


    They are. It turns out that there are quite a lot of neutrons zipping around right after a supernova...and the elements that were created by fusion will be rapidly bombarded by these neutrons. This is called the r process and is one way of generating elements heavier than iron. The other, called the s process, is basically the same, but occurs more gradually in the envelopes of massive stars. The slower rate of neutron capture means that decays occur between captures and a different series of isotopes can be created.
     
  4. Sep 7, 2006 #3

    hellfire

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    Diluted currently in the cosmic microwave background, that contains about 109 photons for each baryon in the universe (this is called "photon-baryon ratio"). After matter antimatter annihilation the universe became actually radiation dominated as you suggest. This means that radiation was indeed the component with the greatest energy density. However, the energy density of radiation scales with the scale factor as [itex]\rho_r \sim 1/a^4[/itex], faster than the energy density of matter that scales as [itex]\rho_m \sim 1/a^3[/itex]. The universe became matter dominated. The energy density of matter, in turn, dilutes faster than the energy density associated to the cosmological constant (whose energy density does not change) and after matter domination the universe became dominated by the cosmological constant.
     
    Last edited: Sep 7, 2006
  5. Sep 7, 2006 #4

    Garth

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    Agreed, hellfire, in the standard model.

    If DE exists and is explained by a CC, that just leaves the question: "If 'after matter domination the universe became dominated by the cosmological constant', why should the present epoch energy density of the CC (~73%) be approximately equal to the present epoch matter density (baryonic + non-baryonic ~ 27%), and not many orders of magnitude greater?"

    Garth
     
    Last edited: Sep 7, 2006
  6. Sep 8, 2006 #5
    Thanks for your responses guys. Here’s something I still don’t get, maybe because I didn’t understand the math in the link, but please let me try to deal with this conceptually. I understand the conservation of energy, scaling, and the reference to the energy density, which means to me it’s a function of some unit of space. In the case of CC, it’d be a constant, per *unit* of space. But what about the total amount? Let me offer you a simple thought experiment which might easily reveal where I make an erroneous assumption.

    I have a helium filled balloon. I have a chamber attached to the balloon. What I’ve got in the chamber is a pen, an anti-matter pen, and annihilator. The mass of the chamber is just (barely) high enough to keep the balloon from taking off – if I removed one of the pens, it’d take off. Now, I turn on the annihilator to destroy the pen. My expectation is the balloon will still be grounded, as I reason that just because I converted the pens into photons, the mass of the chamber doesn’t change. My next step is to expand the chamber. For the sake of the argument, let’s assume the mass of the chamber itself doesn’t change with expansion and there are no other energy effects in the chamber, such as virtual particles, dark energy, etc. Now, as I expand the chamber and rob the photons of their energy by “stretching” them, my expectation is still that the balloon will not take off, because the total amount of that energy is preserved and can be converted back to two pens with equal mass. Isn’t that the case? So, I reason in the same fashion when it comes to the Universe expansion. I have no problem understanding this with CC, because, being the inherent property of space per se, there is no dilution of this energy with expansion, but the totality of it becomes greater and greater. Isn’t it what drives the acceleration of the expansion? But the photons do get diluted; the density decreases but doesn’t the total stay the same?


    I thought it was considered to be one of those interesting coincedences. Can you envoke the anthropic principle and say that when DE is much greater, life (as we know it) is not possible to make the observation of such great value?
     
  7. Sep 8, 2006 #6

    Garth

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    Indeed you can invoke the Anthropic Principle, but would you find that a satisfactory explanation?

    Or could this 'coincidence problem' actually be an indication of some new physics?

    Garth
     
  8. Sep 8, 2006 #7

    wolram

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    Garth, allthough i am in awe of your model, and the standard model, or any model that can describe our universe, i wonder if the building blocks of any model are correct, the very basic questions of (what is mass), (what is energy),(how do they interact), are, so far as i know unansewered, should we not understand these things before building a model universe?
     
    Last edited: Sep 8, 2006
  9. Sep 8, 2006 #8

    Garth

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    Of course we should have the best possible understanding of those basic questions, developed and determined by laboratory experiments and logical conceptual model making, however I would argue that we never will reach the stage of having a complete and final understanding of those basics for there will always be further questions to ask.

    Or at least I very much hope that that is the case! Life would be very boring otherwise!!

    As Popper pointed out if we ever found out the final truth about something we could never be sure it was the final answer!

    However, in the mean time, cosmologists will always build models on the best information available to them. The trick is to find the model requiring the simplest number of 'ad hoc' assumptions to fit the data.

    Astrophysics, and the cosmology developed from that discipline, is the understanding of what goes on 'out there' by understanding what goes on 'down here', in other words it is the application of laboratory physics to the universe at large.

    Very occasionally an astronomical observation is made first that then leads to laboratory confirmation, such as the discovery of helium in the solar spectrum. However, those helium lines might have been some unknown transition lines of a more familiar element. It was necessary for helium to be discovered on Earth before they could be sure that they had actually found a new element.

    Likewise today Inflation, DM and DE may well represent new physics, as the standard model requires, which will be confirmed in the near future by laboratory physics. But until that day comes there must remian a question over that interpretation of the data; best to keep an open mind! :smile:

    And BTW - don't be in awe of my model - objectively criticise it!

    Garth
     
    Last edited: Sep 8, 2006
  10. Sep 8, 2006 #9
    considering the fusion of iron to make elements of higher atomic number, it does require more energy than is gotten out and that is why it can only happen in a supernova on a large scale where immense amounts of energy are released. The iron nuclei use this energy to pay for their fusion into higher elements. The reason why the star goes supernova is because it up most of its easy to fuse hydrogen and higher atomic number atoms are much more likely which give less and less energy per fusion until you reach iron.
     
  11. Sep 8, 2006 #10

    No. Iron atoms do not fuse in a supernova. The temperatures needed for iron fusion are of the same order as the temperature for iron atoms to photo-disintegrate(something like 10^11 K, I forget exactly). See Spacetiger's above post on neutron capture and the r/s-processes.
     
  12. Sep 8, 2006 #11

    Hurkyl

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    First off, the photons are irrelevant -- it will rise because expanding the balloon has made it more bouyant.

    Secondly, the photons are transferring their momentum-energy to the balloon particles -- the energy doesn't just "vanish".

    If it helps your intuition, the same thing happens to gases -- they cool as they expand.
     
  13. Sep 8, 2006 #12
    i thought iron does. do any heavy nuclei fuse in it? I remember in the "Runaway Universe" that it said that heavy nuclei were created in supernova due to the huge amount of energy released.
     
  14. Sep 8, 2006 #13

    Created by neutron capture in the supernova explosion. Not by fusion. I suppose its not entirely impossible that some iron nuclei fuse (since statistically speaking, there is a distribution of kinetic energies at any temperature), but compared to r-process neutron capture its not just insignificant, it might as well not be happening.
     
  15. Sep 9, 2006 #14

    SpaceTiger

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    By the cosmological principle, the universe is uniform on large scales and we are only concerned about the energy density of the various components (mass, radiation, CC, etc.) as a function of time. Since mass and radiation both dilute with time, this means that a CC, if present, would eventually dominate the dynamics of the expansion.


    How can the energy in the universe be the same if all of the photons have redshifted? Unlike in the classical expansion of a gas there are no walls upon which they can do work. That's my point -- total energy is lost in the universe.
     
  16. Sep 9, 2006 #15

    Garth

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    Agreed ST, if I may add, as I have pointed out before, energy is a frame dependent measurement and in general in GR energy is not conserved, instead it is the frame-independent energy-momentum that is conserved.

    A similar situation is simple gravitational red shift such as in the Pound-Rebka experiment. The rising photons lose energy but where has it gone to? According to GR no gravitational force acts upon the photons extracting 'work' from them, they travel on null-geodesics and only suffer the effect of space-time curvature.

    Garth
     
    Last edited: Sep 9, 2006
  17. Sep 12, 2006 #16
    Thank you for the clarification. I see your point (I think :smile: ). It seems I'm stuck with the traditional notion of mass, such as there is an object and then there's mass on top of it. Instead, I need to approach it by defining it in terms of time and other GR notions, for which I have no intuition. If you have a good reference link to something like "GR for amateurs", i.e. without tensors in it, I'd greatly appreciate it. I mean, I know the basics of the theory, but I have no grasp of their implications.

    Thanks,

    Pavel
     
  18. Sep 13, 2006 #17
    Also, please, if you can refer me to a well written source detailing how a photon climbining out of the gravitational well loses energy, which vanishes into thin air, I'd greatly appreciate it. I checked the Pound-Rebka experiment, null-geodesics, and some other articles, but they don't focus on explaining what happens to the energy. They just say the photons get redshifted. The best article so far was a reference by SpaceTiger earlier, but the section "Very Massive Objects Emitting Light" was too short to explain what's going on. To me, If energy = mass, and mass gains potential energy climbing out of the gravitational well, why should I not expect the same potential energry gain from the energy/mass in the form of a photon? What is so special about the photon that prevents it from aquiring potential energy which can be harnessed when the photon will dive back into the well? If energy simply gets lost, wouldn't it imply I can simply vanish a bottle in a "kitchen sink" by introducing a gravitational well in there? (obviously by converting the bottle into photons first). In advance, thank you for your explanation and sources.


    Pavel.
     
  19. Sep 13, 2006 #18

    Garth

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    Hi Pavel!

    First don't mix up classical and relativistic (GR) concepts when analysing this problem.

    In GR the photon does not feel any force, it does not gain potential energy - no work is being done on or by the photon, it simply traverses a curved space-time.

    When analysed in such a space-time the definition of a unit of energy changes because of the effect of time dilation. GR interprets red shift as the a time dilation effect, and because of that energy is not generally conserved.

    If you want to locally conserve energy then you have to re-write GR. In which case you may find the following thread on Self Creation Cosmology interesting.

    Garth
     
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