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Guest post: Amedeo Balbi, “Dark Energy for Beginners” April 2, 2007

Posted by dorigo in astronomy, Blogroll, internet, italian blogs, physics, science.
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Amedeo Balbi is a researcher at the Physics Department of the University of Rome “Tor Vergata” and an associate of INFN. His research interests are in theoretical cosmology, particularly the cosmic microwave background (CMB) radiation and dark energy. In the past he worked in the MAXIMA collaboration , one of the first experiments to observe the high-resolution pattern of the CMB and to measure the geometry of the universe. Currently, he is involved in ESA’s Planck satellite. He just published “La musica del Big Bang”, a popular-science book (in Italian) on cosmology and the CMB. His blog (in Italian) is Keplero.

So let’s hear it from him…

The facts

In the past decade, cosmologists have observed many distant type Ia
supernovae (SN): these are exploding dying stars of a particular
kind, which have a strong correlation between their intrinsic
luminosity and their light curve (this is, essentially, the time it
takes for the peak luminosity reached during the explosion to
decrease of a certain amount): this means that we can accurately know
the real luminosity of a type Ia SN. Then, measuring their apparent
luminosity, we can infer their distance, just as we can estimate the
distance of a 100 W light bulb by measuring its flux. Technically,
what is measured with type Ia SN is a quantity called luminosity
distance
, which is related to another observable quantity, the
redshift of the supernovae (known lines in the spectra of any distant
source in the universe appear systematically shifted to larger
wavelengths – redder light in the visible spectrum – because of the
expansion of the universe). The relation between the luminosity
distance and redshift depends on the cosmological model, and here we
get to the main point: it was first found in 1998 and always
confirmed by subsequent observations that distance vs redshift
relation of the supernovae can only fit the theoretical curve if
one assumes that the universe is accelerating its expansion
.
So, to sum up: 1) type Ia supernovae are “standard candles”, i.e.
objects whose real luminosity can be measured, so we can infer their
distance and plot it as a function of redshift; 2) their apparent
luminosity is always dimmer than expected (i.e. they are more distant
then expected) in a way that suggests that the universe is expanding
at an increasing rate.
Can the dimming of type Ia SN be explained by other physical models?
In principle, yes: for example it might be that some dust is causing
the light to scatter and dim across the line of sight. However, these
alternative explanations are very contrived (they require ad-hoc
hypothesis: for example, dust that continuously replenish itself in
order to compensate for the expansion of the universe) so that they
don’t look very plausible. The simplest explanation right now is that
the expansion rate is increasing.

The hypothesis

What can be the cause of the accelerated expansion? Whatever the
explanation, it must be some really strange thing, since any ordinary
cosmological model predicts that the universe should slow down its
expansion as time goes by. The cumulative gravitational pull of all
the matter in the universe should act as a restraint to the
expansion, rather than as a boost! So, it appears that some repulsive
gravitational phenomenon has to be introduced in the cosmological
model to explain the acceleration. The simplest approach is to
resurrect an old idea by none other than Albert Einstein. In 1917, he
introduced a new term in his general relativity field equations. At
the time he did not know that the universe was in fact expanding, so
the new “repulsive” term, called cosmological constant, was
needed to keep the universe static, preventing it from collapsing.
But if the universe is expanding, as we now know it is, the
effect of introducing a cosmological constant is to accelerate the
expansion. But what is the cosmological constant, really? Basically,
there are two possible interpretations. One is to consider it as a
new constant of nature which modifies the spacetime metric: think of
it as an intrinsic feature of spacetime which does not depend on how
much matter (or energy) exists in the universe. This is close to the
way Einstein himself pictured it. The other interpretation is to
think of the cosmological constant as the energy density of the
vacuum (or of spacetime itself, when you get rid of all matter and
energy). This is the modern interpretation, since it is related to
the concept of zero-point energy of quantum field theory:
roughly speaking, when you sum the contribution of the ground state
energy of all quantum fields, in general you expect a non-null
result. This is usually not observable since we only measure energy
differences in the laboratory, so any contribution from the zero-
point energy is just a common offset, so to speak. However, as we
said, the vacuum energy density is relevant in cosmology, since it
accelerates the expansion of the universe.

The problem

So, it would seem everything is fine: we observe an acceleration in
the expansion of the universe, and we can easily explain it as due to
a non-null cosmological constant. Unfortunately, things are more
complicated than that. The problem is that any estimate of vacuum
energy from quantum field theory is grossly wrong: from 60 to 120
orders of magnitude (yes: 10 to the 60th or to the 120th!) larger
than the values estimated from the cosmic observations. No one knows
what goes wrong here. Are we missing something fundamental in quantum
field theory? Is there a mechanism which cancels the contribution
from the ground states and makes the vacuum energy almost zero? If
that is the case, then why there is only a partial cancellation, just
enough to make the universe accelerate in a recent epoch? (The moment
when the acceleration starts depends on the value of the cosmological
constant: the observed value implies that the universe started
accelerating just a few billion years ago. For a slightly larger
value, the acceleration would have started earlier, disrupting the
formation of any structure in the universe, including our own
galaxy!) Why the supposed cancellation does not make the cosmological
constant exactly zero? This is what physicists call a fine-tuning
problem: the parameter of a model must lie within a very narrow
range, without any reasonable a priori explanation. The small value
of the vacuum energy might be one of the most profound problems for
modern physics.

Alternatives

Can we get rid of the cosmological constant? (After all, Einstein
called it its “biggest blunder” and for about eighty years no one
really thought that its value should be different from zero.)
Unfortunately, it doesn’t seem so. It’s not just that the universe
accelerates. For example, we know that the universe has a flat
geometry, a fact that was discovered for the first time in 2000 by
the BOOMERANG and MAXIMA experiments, measuring the anisotropy of the
cosmic microwave background. This finding has been confirmed to
exquisite accuracy by the WMAP satellite in 2003. The fact that the
universe is flat means that its overall density has to be very close
to a certain critical value (since Einstein’s general relativity
relates the matter or energy content of the universe to its
geometry). But there simply isn’t enough matter in the universe (even
assuming the existence of unknown dark matter) to make it flat. The
vacuum energy can then provide just enough energy density to reach
the needed critical value. Another reason why cosmologists blessed
the resurrection of the cosmological constant is that it helps
solving a problem with the age of the universe. If the cosmological
constant is zero, then the cosmological model gives a universe which
is slightly younger than the oldest stars we observe in it!
So, there are many different, independent and converging evidences
which force the cosmological constant to be non-zero. But because of
the conceptual problems related to that, theorists are trying to come
up with alternative ideas to fit the cosmological observations. There
are so many that I cannot summarize all of them here, but basically
they can be classified into two kinds: either the theory of gravity
on very large scales has to be modified, or there must be in the
universe some unknown component very similar to a cosmological
constant. The latter alternative includes a large class of models,
falling in the broad category of “dark energy”: a component which has
no (or only a very weak) physical interaction (except gravity) with
anything else and is spread almost uniformly in the universe, so that
does not create any observable “lump”. Most of cosmological research
these days focuses on trying to get an idea of what is the real
nature of dark energy. Currently, however, there is no observation
which clearly indicates that we should abandon the “standard”
cosmological constant in favour of some more sophisticated model. As
the data will get better, in the near future, we would probably be
able to understand more clearly what is going on. However, it may
well be that the progress will come from the theoretical side:
perhaps the cosmological constant problem will be solved when we will
reach a better understanding of the unification of fundamental
interactions.

Comments

1. riqie arneberg - April 2, 2007

Dark energy a “simple explaination”? The universe exhibits “lumpiness” at every scale we have been ablre to observe, so it seems silly to deny structure on a scale beyond the reach of observability. Without knowing the structure it is mere conjecture, but in our own galaxy, for example, our position near the edge is actually a bit anomolous, as much more of the mass is much nearer the center. These theorists are all so in love with their own theories that they seem not to have time to refute the simplest explaination of all!

The missing mass comprises teeth carted away by the tooth faerie, “other socks”, and the reciept for that gadget which is just about to go out of warranty.

2. dorigo - April 2, 2007

Hi Riqie,

I think Amedeo can answer better than I can. You are right in observing structure everywhere in the universe, but at the largest distance scales the cosmic microwave background seems to show little of it (but see the discussion in the report of the Conference for March 29).

I hereby invoke Amedeo in answering questions on this column…

Cheers,
T.

3. island - April 2, 2007

What can be the cause of the accelerated expansion? Whatever the explanation, it must be some really strange thing, since any ordinary cosmological model predicts that the universe should slow down its expansion as time goes by.

I have to input that this statement is false per the standard cosmology that I’ve previously discussed here:

https://dorigo.wordpress.com/2007/03/27/the-miserable-near-future-of-cosmology/#comment-31554

The simplest approach is to resurrect an old idea by none other than Albert Einstein. In 1917…

Except that this approach is extremely conditional. It is a fact that Einstein did not know about particle potential in the quantum vacuum or he never would have abandoned this model:

Back to 1917

4. island - April 2, 2007

I want to be as clear as I can about my point as it relates to naturally accelerating expansion in a stable **finite** universe, so I am bringing in the following contents from a post to the research group:

The Second Law of Thermodynamics says “god” doesn’t throw dice…

Begin quote:
” I’d like to talk about what I think is already proven to happen to the gravity of the universe when we make particles from negative-energy states, and the effect that this has on the thermodynamic structuring of our universe.

In quantum field theory, a positron has the same gravitational properties as an electron because the negative energy states are really the positive energy states of antiparticles. That means that pair production makes no difference to the gravity of the universe and even [modern applications of] general relativity support this conclusion if the universe is infinite, since gravity is essentially curvature that caused by the energy that’s contained in a region of space. In this situation, pair production changes this energy from photons to the mass of other particle pairs, but the energy curvature and gravitation of the universe remain the same.

Okay, but what happens to the gravity of the universe if the universe is finite?

Doesn’t this drastically change the effect on the gravity of the universe when… rho+3P/c^2=0 in a finite universe?

You can’t take vaccum energy from a finite universe and then contain the matter energy-density to a finite region of space without increasing negative pressure in proportion to the local increase in positive gravitational curvature, because the graviational acceleraton is zero when the density of the vacuum is -0.5*rho(matter).

You have no choice but to condense this energy in order to attain the
matter density when the negative energy states have negative pressure, because… P=-u=-rho*c2.

So there is no net change on the gravity of the universe, because the effect is two-fold… an increasing antigravitational *effect* is offset by increase in the matter density.

But that means that tension between the vacuum must increase as particle pair creation drives vacuum expansion if the universe is finite, and the offset increase in both, negative pressure, and the matter density, necessarily holds the vaccum flat and stable as it expands at a naturally accelerating rate, so it cannot run-away!

Increasing tension between the vacuum and ordinary matter leads to a self-evident prediction that the integrity of the forces that bind this finite structure will surely eventually be compromised by this process and we will have another big bang.

So the second law of thermodynamics is never violated when the entropy of the universe always increases via the described perpetually inherent thermodynamic structuring, which enables the universe to continuously “evolve” to higher orders of the same basic configuration via this eternally *downhill process*. ”

End quote.

Far from equilibrium dissipative structures that are known or expected to be capable of isolating enough energy to produce these particles include black holes, supernovae, and now us, *cumulatively*.

5. Tony Smith - April 2, 2007

Thanks to Amedeo Balbi for the Dark Energy guest post, saying in part:
“… to fit the cosmological observations …
either the theory of gravity on very large scales has to be modified,
or
there must be in the universe some unknown component very similar to a cosmological constant.

An theoretical example of such an “unknown component” may have been given in gr-qc/9809061 by R. , where they say:
“… a semi-direct product between Lorentz and special conformal transformation groups …[forms]…
the group Q …[which has the]… symmetry of the strong cosmological-constant limit …
in the light of the recent supernovae results … favoring possibly quite large values for the cosmological constant, the above results may acquire a … relevance to Cosmology …”.

The special conformal group generators are 4 of the 15 generators of the conformal group SU(2,2) = Spin(2,4) used by Irving Ezra Segal in his conformal cosmology, so the work of Androvandi and Peireira may show how Segal’s work, currently neglected and unfashionable, might be shown to be useful and at least in part correct.

On the experimental side of investigating Dark Energy, the presentation of Christian Beck at the Imperial meeting may have been relevant.

Another possibly relevant experimental result is the work of Martin Tajmar et al. In gr-qc/0603032 and gr-qc/0603033 they say in part:
“… experimental results on the gravitomagnetic London moment … tend to demonstrate that gravitational dipolar type radiation associated with the Einstein-Maxwell equations is real. This implies that Maxwellian gravity is not only an approximation to the complete theory, but may indeed reveal a new aspect of gravitational phenomena associated with a vectorial spin 1 gravitational boson, which we might call the graviphoton. …
we will therefore use the term graviphoton …
if we take the case of no local sources .. the graviphoton mass will be zero … However, in the case of local sources, a spin-1 graviphoton will appear. …
[and]… the graviphoton mass is not zero based on the measurement of the cosmological constant. …
The recent measurement of the cosmological constant /\ = ( 1.29 +/- 0.23 ) x 10^(-52) m^2
by WMAP can be linked to the graviton (graviphoton) mass by a recent result from Novello et al and others
m_g = ( hbar / c ) sqrt( 2 /\ / 3 ) = 3 x 10^(-69) kg …
the … graviphoton …[ mass ] is … a real number which is … confirmed by our experimental results …
The cosmological constant for Einstein’s equation … is the given by
/\ = ( 3 / 2 ) ( 1 / lambda_g^2 ) = ( 3 / 2 ) mu_0g rho_m
…[where]… mu_0g = 4 pi G / c^2 …
The average density of the universe is rho_m = 10^(-26) kg m^(-3) .
This gives a gravi[pho]ton mass of m_g = 3.2 x 10^(-69) kg
and a cosmological constant … of /\ = 1.3 x 10^(-52) m^2 .
Those values are exactly within present experimental observations! …”.

The experimental results of Tajmar et al was described in a 23 March 2006 ESA news web page, which said in part:
“… Tajmar … and colleagues have measured … a gravitomagnetic field … generate[d] …[by]… a moving mass … Their experiment involves a ring of superconducting material rotating up to 6 500 times a minute. … Spinning superconductors produce a weak magnetic field, the so-called London moment. The new experiment tests a conjecture by Tajmar and de Matos that explains the difference between high-precision mass measurements of Cooper-pairs (the current carriers in superconductors) and their prediction via quantum theory. They have discovered that this anomaly could be explained by the appearance of a gravitomagnetic field in the spinning superconductor (This effect has been named the Gravitomagnetic London Moment by analogy with its magnetic counterpart). … Although just 100 millionths of the acceleration due to the Earth’s gravitational field, the measured field is … one hundred million trillion times larger than Einstein’s General Relativity predicts. …”.

It seems to me that the results of Tajmar et al fit together nicely with the theoretical work of Aldrovandi and Peireira, and might also fit with the work described by Christian Beck.
If so, they may give a realistic quantitative “standard model” for Dark Energy.

Selfishly, I will point out that in their paper gr-qc/0603033, Tajmar et al cite as references the work of Gennady Sardanashvily (whose work I have found very interesting) and a couple of papers of my work that were posted on arXiv before I was blacklisted.

Tony Smith

6. riqie arneberg - April 3, 2007

The cosmic bacground data we observe is, by definition, part of the “observable” universe. Structure on a scale an order of magnitude larger can never be “observed”, but it might be inferred, and my suggestion is that it requires less credulity to infer such than some mysterious “dark energy” which we also cannot observe.

I am still waiting for someone to show me why the data is inconsistent with such a model.

7. dorigo - April 3, 2007

Hi Island,

sorry for taking some time to answer your comment, but I just want to say I found it quite interesting to read. I know too little to have an opinion, but what you say makes sense to me… Makes me wish I knew more.

Maybe some more knowledgeable reader can post his objections or comments to Island’s comment ?

Cheers,
T.

8. dorigo - April 3, 2007

Hi Tony,

thank you for mentioning those preprints. I would love to have a look but that will have to wait, I am currently quite busy with a new idea I am developing for the correction of biases to the muon momentum scale in CMS… Ordinary stuff, but it’s my job. Reading and learning about the cosmos isn’t, unfortunately!

Cheers,
T.

9. dorigo - April 3, 2007

Hi Riqie,

you are right if you say we cannot see past the CMB radiation… By definition, in a sense. But distance scales larger than those that the CMB anisotropies could show are not something I understand easily.
However you are right if you say we understand little anyway…

Cheers,
T.

10. island - April 3, 2007

Thanks Tomasso, It turns out that this mechanism is essentially the same as the one that gets used when rapid inflation creates mass at a great expense to negative pressure, but there is a every indication that Dirac could have unified GR and QM in this model, (as he had done with SR and QM), since negative mass-energy absurdities don’t arise.

It is no coincidence that the model very simply and self-evidentally resolves all of the following, and more:

http://zebu.uoregon.edu/~imamura/209/mar31/anthropic.html

11. island - April 3, 2007

… and I am terribly sorry for what I did to your name, Tommaso.

12. Fred - April 3, 2007

Hello Tommaso,

A couple of side-bars to your:
“… a new idea I am developing for the correction of biases to the muon momentum scale in CMS… Ordinary stuff, but it’s my job. Reading and learning about the cosmos isn’t, unfortunately!”

1. That is the sad thing about human life. There simply aren’t enough years to appreciate the attention we would love to devote to our interests. I think the Gods underestimated our thirst for life. The balance. I will go to my grave with a golf club in my hands but I’ll never be able to play enough.

2. What have you been reading recently that isn’t field related? Any fiction?

13. dorigo - April 4, 2007

Island, do not worry about my name, you just joined a long list of misspellers, only to leave it a moment afterwards…
I am now going to give a look at the link you mention above.

Cheers,
T.

14. dorigo - April 4, 2007

Hi Fred,

I agree with 1), I in fact maintain that we would need a second life to use for recreative activities (such as chess!). You are lucky you can bring a golf club with you, how can I bring my large dobsonian scope ?

Hmmm, reading ? Let me think… I am halfway through “the singularity is near” by Ray Kurzweil. Been there for a while now tho. I am also at a third of “Meteor showers and their parent comets”, by Jenniskens. I am also picking up every once in a while “My great predecessors – part V” by Kasparov (when he mostly deals with Karpov). The latter require a fresh brain, since I am too lazy to set up the chessboard and I have to analyze the game positions by heart by looking at the chess diagrams, and that is not light work. About fiction, I can’t recall reading much of it in a long time.

Cheers,
T.

15. Louise - April 4, 2007

The simplest solution to the “dark energy” probem has been left completely out of this essay.

16. dorigo - April 4, 2007

Hi Louise,

you cannot blame other researchers for having a point of view… Everybody have their own, especially on such a controversial topic as dark energy. I would be happy if Amedeo visited your site and commented there, but I cannot of course twist his arm – he’s been kind enough to produce the post above.

Ciao,
T.

17. Fred - April 4, 2007

If you’re going to be buried outside, I would plant that scope right on top of your headstone positioned towards the stars. That way, people would have another reason to visit you, yet at night.

18. Amedeo - April 5, 2007

Hi all,
thanks for all the comments. I just want to say that I have been reading all of them, but simply have not enough time these days to get deeper into them or to answer in detail. I see that the dark energy problem stirs a lot of controversy, which is something we should always welcome in science (of course, as long as there is some evidence to support different points of view). As you may have imagined, I stick with the mainstream, but I follow the discussion with great interest. Only future will tell!

19. island - April 5, 2007

Let’s just need to get that collider working…

Tommaso, read this if you get time:

http://evolutionarydesign.blogspot.com/2006/05/once-upon-spacetime.html

20. dorigo - April 5, 2007

Hi Island,

nice account of the story – and I followed the link to Baez’s site, which I also found quite clear and didactic.

Senesco semper multa addiscens…

Cheers,
T.

21. island - April 5, 2007

You cannot beat John Baez when it comes to clear and concise explanations. It was one of his negative mass puzzles that made me realize that the cosmological constant has the exact same “counter-orthodox” properties as a negative mass particle, except that the antigravitational effect is just negative pressure that is present whenerver its energy density is below the matter density.

It becomes obvious that a “positron” isn’t going to have negative mass once you condense or gravitationally compress vacuum energy down enough to attain the matter density, (before feynman takes over), and this process will necessarily increase the vacuum if it is finite, because you can’t rip out a huge volumous chunk of its energy without leaving a real hole in it!

It isn’t fair to say:

“The simplest approach is to resurrect an old idea by none other than Albert Einstein. In 1917, he introduced a new term in his general relativity field equations.”

… without considering the finite cosmological model for which it was intended, which was dismissed only becauses it was thought to be unstable, (which it is obviously not, if what I said above has any merrit whatsoever).

If Einstein doesn’t conceed this point, then he wins in Copenhagen, because this model is strictly deterministic, and General Relativity is a much, MUCH stronger theory which naturally demands closure of the geometry in space as a boundary condition on the initial value equations if they are to yield a well determined and unique 4-geometry.

He also recognized “higher” structuring in nature.

What a crackpot…

22. dorigo - April 7, 2007

Hi Island,

“what a crackpot” -> lol…

The issue was not mature to be resolved back then… It in fact is not mature even now. Maybe in 10 years. I only hope I will have understood all the details when that happens🙂

Cheers,
T.

23. Smoky - April 8, 2007

When you find my alternate universe, where all of my lost things are, let me know. Until then, keep up the great posts.

Thanks,

Smoky

24. Thai - April 9, 2007

How great and wonderful the universe is. It is so large in my eyes, yet so small in God’s eyes.

25. island - April 11, 2007

The issue was not mature to be resolved back then… It in fact is not mature even now.

I’ve been kicking this around, Tommaso, and I think that might be incorrect, since it can be argued that the near-perfect balanced structure of the observed universe maximizes work via the uniform dissemination of energy that this “low-entropy” configuration produces.

That’s an energy conservation law if the quantum oscillator is finite, since energy gets wasted in any other configuration and energy can’t be conserved if work isn’t maximized.

That’s fine-tuning from FIRST PRINCIPLES!

26. dorigo - April 11, 2007

Thank you Smoky, I will let you know…

T.

27. dorigo - April 11, 2007

Hi Island,

I love first principles, but, as Groucho used to say,

“Those are my principles, and if you don’t like them… Well, I have others!”.

Meaning that, nothing wrong in using the principle of minimum action to try and justify the structure of the Universe, by making a few assumptions (such as your questionable claim that a uniform universe corresponds to low entropy).

However, one might object that by starting off with a different first principle, plus a different set of additional assumptions, one would get another model consistent with the data… Groucho rulez.

Cheers,
T.

28. dorigo - April 11, 2007

… However, I would not like you to think I am not taking what you posted above seriously, Island. It is just that I find myself ill-at-ease arguing on these matters, because I am basically an ignorant in cosmology, only a well-learned one.

But that should not stop you from discussing your ideas here, of course – I trust this blog attracts more knowledgeable readers than myself.

Cheers,
T.

29. island - April 11, 2007

No, you’re right, I still have to rely on Einstein’s physics to make the point… oh, shucks…😉

30. island - April 12, 2007

Wait just a minute here… the answer to the riddle of the near-flat expanding universe, (as well as the rest of the anthropic coincidences), is/was expected to be revealed by models depicting the normal evolution of the universe within the observed constraints… per least action principle.

So, first principle physics that accomplishes that which others rely on multiverses to accomplish, necessarily takes theoretical precedence per the scientific method for choosing the preferred theory, while strongly supporting the assertion that the universe is about 13.7 years finite.

http://arxiv.org/abs/hep-th/0512148

The only thing that Sean Carroll ever did for me…😉

31. island - April 14, 2007

Tommasso, I was going to send an email to you, but I’m not positive that I had the right one, and I’m perfectly willing to be held accountable for my claims, so I’m just going to say this here:

Thank you for encouraging me to express my views and for your repeated requests that a theorist might comment.. As I briefly explained in this older posting, that doesn’t happen. It’s kind of hard for anybody to shoot down the physics, since they should already know that this mechanism is valid in inflationary models, not to mention how simple it is (study this), to understand this physics.

The problem is that nobody wants to hear it, and that’s the bottom line until the bottom falls out of particle theory as has been predicted will happen if you guys don’t find the higgs or new physics, so that’s why finding nothig is equally valuable, as far as I’m concerned, even thought that is understably not the hope of so many that have worked so hard, and I am sorry about that.

I could say more, but I am so frustrated by all of this that I probably wouldn’t be comprehensible, so I’m just going to say that I’ve never been in a position before where I can win every battle, yet still lose the war, due only to completely non-scientific willful denial. I know what it’s like, and how to recognize when I’ve been shot down, (which is the difference between a crackpot and an honest scientist, if you ask me), but that hasn’t happened since I stumbled onto all this crap that has caused me to hate the people that I used to respect the most for exactly that reason!

What kills me is the fact that there is obviously an theory of quantum gravity that’s embeded in this physics, which nobody likes because the background changes every time that you take more mass-energy out of the vacuum to make real, massive particles with, but that’s also why Dirac’s ideas about large natural numbers weren’t just “numerology”.

With all the flack flying on both sides about how wrong “either side” is, you’d think that the observation that maybe they’re both hopelessly lost wouldn’t be such a great heresy to their world-view. Ha!

Thanks again, Tomasso, very much, and I’ll try not to hijack another thread in my futile attempts rattle somebody into sanity.

32. Guest post: Fabio Zandanel, “Dark Matter and the MAGIC telescope” « A Quantum Diaries Survivor - July 12, 2007

[…] 73% of the Universe density is accounted for by  dark energy, a bizarre form of energy or matter that is, in effect, gravitationally repulsive. The dark energy […]

33. Dan Browne - July 13, 2007

Let me take a guess here based on a few base assumptions.

1. The acceleration expansion “appeared out of nowhere” some billions of years ago.
2. The Tajmar results show that a strong gravitomagnetic effect is observed in spinning superconductors – orders of magnitude larger than current quantum models suggest.
3. Neutron stars are hypothesized to take billions of years to form.
4. Neutron stars are hypothesized to contain superconducting layers.
5. Neutron stars spin really fast.

Putting all of this together I’d take a stab at a hypothesis and say that perhaps the cosmological constant is *caused* by the accumulation of spinning neutron stars at some point after the big bang.

34. dorigo - July 13, 2007

Wow Dan, my compliments for your boldness. It seems quite a shot in the dark to me, but I’m willing to say we know so little about dark energy that anything goes as a tentative working hypothesis. Only criticism I find compelling with my limited CPU available is: we are talking about a HUGE effect here, and neutron stars not that common in the universe.

Cheers,
T.

35. Maxim - October 9, 2007

The Iraqi government says guards from US security firm Blackwater killed more people than previously thought.

36. Generic Cialis - November 24, 2007
37. Fine tuning and numerical coincidences « A Quantum Diaries Survivor - July 1, 2008

[…] similar coincidence -and actually an even more striking one- happens with dark energy in Cosmology. Dark energy has a density which is orders and orders of magnitude smaller than what […]

38. Pretty Ignorant - October 18, 2008

Hi guys,
I and pretty ignorant about cosmology, but I have been shocked by this recent post:

Axiomatic approach to the cosmological constant
Authors: Christian Beck
arXiv:0810.0752v1 [gr-qc]

He claims to get the actual value of the cosmological constant within error bars. How importat do you feel this finding is?

thanks,

P.I.

39. sandrar - September 10, 2009

Hi! I was surfing and found your blog post… nice! I love your blog. 🙂 Cheers! Sandra. R.

40. grafff098 - December 17, 2009

!!!


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