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Anti-Dark Energy?

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  1. Apr 22, 2012 #1
    I have no formal training in physics beyond the basics, so if my questions make no sense, feel free to ignore them.

    Dark Matter is described as a gravitational force that either helped form the galaxies or perhaps less likely was drawn in by the formation of galaxies. Personally I prefer the former as I believe the fluctuations in CMB are easier to explain.

    Dark Energy to me is described as a sort of negative force pushing galaxies further apart (not the galaxies or matter itself - this is important) and DE is accelerating over time.

    Is it possible that the amounts of DM and DE also change over time?
    Perhaps the ratio was different in the past?

    Now my real questions:

    Could something be described as Anti-DM (not to be confused with Dark Anti-matter) and what would this stuff be like? Would it have the opposite effect of DM and instead of gravitationally helping galaxies stay together could it then be described as pushing things apart?

    Could something be described as Anti-DE and what would this stuff be like? (i use stuff as E=MC^2) Would it have the opposite effect of DE and instead of pushing galaxies further apart could it then be described as drawing things together?

    Interaction between the 3 types of Energy/Matter of the universe seem to not be able to interact with each other very well in our baryonic perception. This makes me think that Dark Energy and Dark Matter are sort of flip-sides of the same coin. This also makes me think that DE and DM would not be found in large amounts on the scale of say the solar system.
    (ie too much DM the solar system collapses, too much DE and it flies apart)

    Is it possible that those 3 types are somewhat (or completely) mutually exclusive? What I mean is that of the 3 only one can occupy the same space. This brings me further along in my thoughts as baryonic matter excludes DM though DM is needed to give the galaxies the gravity they need to form and continue, DE is also excluded as then particles would fly apart. (though i see now that the electromagnetic force is far stronger than DE, you can still see my point) So in my mind I see galaxies surrounded by DM surrounded by DE. Is this even close? To extrapolate further - I see DE as a pool in between galaxies with the 'shore' of sorts) being DM and the land being well... land heh (baryons). Any info you can give me would be great, also don't be afraid to point out my logical fallicies or just plain bad physics and thank you for reading...
     
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  3. Apr 22, 2012 #2

    Nabeshin

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    It's possible, but let's think about this for a moment.

    If the DM amount is to change over time, it has to either decay into something or something decays into it. So far, we've never seen anything decay into a DM particle on the timescales we're interested in, so that's probably out. So we're left with the DM particle decaying into something else. This obviously must proceed quite slowly, otherwise the observed DM abundance would not occur. But what will the DM decay into? If it decays into standard model particles, these are observable and we don't see anything like this. Beyond observationally, it's theoretically enticing to have DM be a stable particle.

    As far as DE, we really don't know. Again, it cannot have changed too much without messing up what we observe. The thought that DE is somehow a function of time gives rise to 'big rip' scenarios, which I'm sure you've heard about.

    Nothing that I know of could be described that way. Just throwing the prefix anti- onto something is extraordinarily ambiguous, what exactly is anti about it? Do you want it to have opposite spin? charge? mass? etc. The Anti- in Anti-matter is precisely defined within particle physics. At any rate, no such thing is discussed.

    The same issue here, what do you mean? The natural thing to do is to assume that the 'weird' thing about DE (the fact that it has negative pressure) is reversed, in which case such a thing would have w=1, consistent with a scalar field. Such a thing makes sense to discuss theoretically, but is not thought to exist (at least in any large quantities) in our universe.
    Not really. If DE is indeed Einstein's cosmological constant, then it is a property of spacetime itself, so by its nature it exists everywhere. If DM is simply a WIMP particle (and it certainly seems to be), then it can be anywhere normal particles can be, the same as normal matter. There's no reason (other than perhaps an exclusion principle owing to the fact that the WIMP might be a fermion) to suppose that the two cannot intermingle.

    The fact that the D in DE and DM are both dark is a bit unfortunate, really, because it gives people the idea that they might be somehow connected. Realistically, I know of no decent proposal which says that they are. The Dark in Dark Matter means 'non-interacting electromagnetically', while the Dark in Dark Energy means, 'I really have no idea what this stuff is'.
     
    Last edited: Apr 22, 2012
  4. Apr 22, 2012 #3
    Yes. This is called baryonic matter.
     
  5. Apr 22, 2012 #4
    Well, if by stable you mean stable on time scales we are interested in, as even protons will decay (as does everything) and your right I wasn't clear, my intention was to suggest that DM does indeed decay... into DE and not because both have dark in the name but rather to suggest a mechanism for the amounts to change, my thought of course is that it happens unseen as we can't see either dark.

    Again, my intention was to suggest that perhaps DE also decays into more space as to me it's not enough that DE causes more space without decay but rather that more space is created by the decay of DE. All that's left is to explain how more DM could be created.

    Yes yes yes, I know I just threw anti in front to mean opposite and indeed it is ambiguous as DM and DE are so exotic and we know really very little I was just interested if the concepts of the opposition to DM and DE whatever the heck that might be, might be... So I was actually thinking just the opposite of DM or DE. Opposition of all its constituent parts like a Massively non-interactive gravity-less non-particle? (Now that I've written it down it makes me laugh)


    I added a NOT in italics above I hope this is what you meant, otherwise it makes less sense.
    see above as I sort of gave this a go there... (makin me laugh again)

    Ah, so DE happens everywhere but matter can counteract this effect? Is that more to the thinking?
     
  6. Apr 22, 2012 #5

    Nabeshin

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    Where did you hear that protons will decay? This is a theoretical possibility, but has not been observed by any experiment performed to date. At least the most naive prediction from a GUT model with proton decay is very wrong, so either they don't decay or it's something much more exotic.


    Thanks :)


    Yes, this is more in line with the current thoughts on the matter. Note DE is not thought of as a particle at all (if it were, it would not behave as it does with regard to gravity). Whether or not it's Einstein's cosmological constant or something more exotic is a more open question.
     
  7. Apr 23, 2012 #6
    no evidence as noted that DE decays...what apparently happens is that expanding space retains the same dark energy density...that's why it's called the cosmological CONSTANT [energy density] so our universe is moving from a matter dominated to an energy dominated phase with increasing accelered expansion. The idea is that negative pressure [or dark energy] means that something acquires energy when it expands.
     
  8. Apr 24, 2012 #7
    Now I'm really confused, the cosmological CONSTANT does indeed seem to change ie inflation, expansion, accelerated expansion. I would posit that the universe started as energy dominated and matter at 4.6% (give or take) doesn't seem to dominate at all either now or in the past. The last comment does make some sense to me, and explains the acceleration we see today, since expansion doesn't happen within our locality ie your body, earth, solar system, galaxy, local group of galaxies, so expansion seems to happen in empty space and if you create more (empty) space then there is more space in which to create more space which would keep happening faster. (again, in my minds eye, though my mind and I don't always get along)

    Ok, so my use of Anti was a mistake though my intention I thought was clear, I simply wanted to discuss what the opposite of Dark energy might be for no other reason than I want to know. And the same with dark matter, is it even possible to discuss the opposites? I mean it only follows (to me) if matter has an opposite, then why can't dark matter and energy also have opposites and what would they be like and is it possible to discuss them even though there is no evidence for them. (and before you warn me about speculation: CC discovered the 'new' world (at least for those that didn't already live there) by going against conventional wisdom.)
     
  9. Apr 24, 2012 #8
    No, the cosmological constant is a constant expansion of space due to a quality of space itself. It is not the primary reason for expansion, but it could be a candidate for dark energy to explain acceleration
     
  10. Apr 24, 2012 #9

    George Jones

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    Run time backwards, i.e., towards the Big Bang, so that the scale factor of the universe shrinks. The density of matter is inversely proportional to the cube of the scale factor, so the density of matter increases fairly rapidly. Think of particles contained in a cube. As the cube shrinks, the particle density (particles per unit volume) increases. The density of dark energy remains constant. At some time in the past, matter density was greater than dark energy density.
     
  11. Apr 24, 2012 #10

    Nabeshin

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    Just a note on inflation. While it's true that the expansion experienced during inflation and the current epoch of dark energy domination are both quasi de-Sitter (fancy language to say exponential expansion), they seem to be fundamentally different. The period of inflation is driven by some high-energy physics which create a particle, the 'inflaton', which drives a period of exponential inflation. But, this particle then decays away and the accelerated expansion abruptly stops and the universe continues on its way. This is in contrast to the cosmological constant, which is something that is hard-wired into the geometry of the universe.
     
  12. Apr 24, 2012 #11

    Chronos

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    It is conceivable DE is the remains of the original inflationary field.
     
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