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The miserable near future of Cosmology March 27, 2007

Posted by dorigo in astronomy, Blogroll, news, physics, science.
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I have no energy nor time to discuss yesterday’s talks in any detail, so I decided I’d skip them and pretend they did not happen, and use today’s lunch break for giving some highlights about the things I heard this morning. As previous ones on the same topic, this post is a bit more technical than I would like it to be, so be patient with me. I have a hard time understanding everything myself…

PS: the title of this post comes from the talk of Lawrence Krauss, see below.

  • Shaun Cole talked on “Galaxy and Mass Power Spectra“. He asked himself the question: do uncertainties in modeling non-linearity and galaxy bias compromise constraints on cosmological parameters coming from measurements of the galaxy power spectrum? And he went on to discuss it by analyzing data from 2dF and SDSS, surveys of galaxy distributions in the universe which have small overlap and different sensitivities. Biases come from the Sloan survey’s higher sensitivity to red galaxies, which has to be taken into account, and their non-fixed magnitude limit. It seems that at large distance scales the Sloan survey finds less power in the spectrum, which implies a slightly higher value of the matter fraction of the matter-energy budget of the universe than current best estimates – although within uncertainties things agree. At small scales, blue galaxies are less clustered than red galaxies, but if one takes the color bias away and compares the two surveys, results agree better.

  • Douglas Scott (above) talked about “The Standard Model of Cosmology versus the Other One“. He compared the model of Cosmology to the model of Particle Physics, and tried to gain some insights in what is in store for cosmology. I really hope that the comparison yields no similarities, being fed up with the static nature of theory in my research field, but he seemed more optimistic about it. Douglas pointed out the many successes of the standard cosmology, a string of results which indeed looked impressive from his perspective. He showed that Peebles and Yu back in 1970 had already predicted the acoustic peaks in the microwave background that would be later confirmed by COBE and measured so well by WMAP.

  • Lawrence Krauss (pictured above with his last slide on the background) talked about “Cosmic Ignorance: What We Don’t Know about Dark Energy, and Dark Matter, and Might Never Know“. He discussed how miserable cosmology will be in the short term – he had discussed long-term forecasts at the dinner banquet yesterday (see my last post below). He said that the geometry of the universe is irrelevant for one’s destiny. We actually are in a position to being unable to tell. The only meaningful question for Krauss seems to be, is Dark Energy any distinguishable from a Cosmological Constant, and will it ever be ? Now, since the most reasonable theory predict w=-1, and other alternative models do not depart from that value, measuring it will tell us nothing. And the highest precision we can ever hope to obtain on it is only of about 0.06, which will not shed any light on the matter. As for Dark Matter candidates, he discussed the detection of wimps (weakly-interacting massive particles), but was quite pessimistic about the possibility of resolving the issue in the next few decades, given the fact that one would not just need to detect a few hundred of those particles in the high-noise underground detectors, but also measure their direction. In the Q/A session Richard Lieu called Krauss a pessimist (to which he replied with a surprised “meeee ?“). In his concluding slide, Krauss indeed had a sentence which read “It is not unlikely that we will never empirically determine the nature of dark energy”, and he argued this was not actually too pessimistic. There followed a funny dialogue with Douglas Scott, who was mentioned by Lieu in his question: LK – “I always agree with Doug“. DS (from the audience) – “No you don’t!“. LK – “No I don’t“.

  • John Cowan (see picture above, where he is comparing the abundance of atoms from a particular halo star to the favorite model) gave a enlightening talk on “The age of the oldest stars as a constraint on cosmological models“. He discussed measurements of the abundance of high-Z elements in stars from the outer halo of our galaxy, which are quite old. These stars are the relatives of the first stars in the Universe. Neutron capture is the mechanism by which the heavy elements are created, but there are two: slow capture or fast capture. In the fast capture mechanism, the average time for a capture is much smaller than beta decay of the nucleus. Measuring the abundance of these rare elements (a part in 10^12 with respect to the abundance of Hydrogen) is hard but it has been performed on a few stars from the galactic halo. These spectra – which comprise as many as 57 elements in the case of a particular star – show great agreement with rapid neutron capture models. With these heavy elements one can fit the ratio of abundances, for instance thorium to europium (thorium has a half-life of 14 billion years and is thus a “chronometer” of the age of the Universe). Absorption spectra of Thorium can be fit with various models, and the abundance of this element is measured. At the end of the day, one obtains the age of the universe with a uncertainty of two to three billion years, and the method is quite independent from the particular cosmological model of one’s liking.

  • Finally, Andrew Jaffe (see his blog here) discussed “Constraints on the Topology of the Universe“. He started by explaining the topology of a torus by analogy with the old “Asteroids” game (see picture above). He discussed how the cosmic microwave background can provide hints on the repetitive appearance of the sky, which is a signature for peculiar topological structure of the Universe. He showed that the low-l data could be better fit by models implying some particular topology, but “not much improvement can be done in a fit which is already less than 2-sigma away from the data”.

That’s all folks!

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Comments

1. Bee - March 27, 2007

Will the slides of the talks be online available?

2. dorigo - March 27, 2007

Hi Bee,

dunno. I will check with the organizers…
Cheers,
T.

3. Guess Who - March 27, 2007

There is a recurring theme here (and elsewhere): we are already close to having collected all the cosmological data which it’s meaningful to collect. After Planck, the CMB will have been mined dry. Supernova surveys are unlikely to provide much more insight into the equation of state. Maybe neutrinos or cosmic rays can still give us something new to work with, but those are really hard to work with. Depressing! :(

4. dorigo - March 27, 2007

Hi GW,

I unfortunately think you are right. But that does not mean there is no way out… We just need new ideas. And I listened to one such thing this afternoon… I’ll report about it tomorrow.

Cheers,
T.

5. Tony Smith - March 27, 2007

Tommaso posted:
“… Douglas Scott … talked about “The Standard Model of Cosmology versus the Other One“.
He compared the model of Cosmology to the model of Particle Physics,
and tried to gain some insights in what is in store for cosmology. …
Douglas pointed out the many successes of the standard cosmology,
a string of results which indeed looked impressive …”.

Guess Who said “… we are already close to having collected all the cosmological data which it’s meaningful to collect.
After Planck, the CMB will have been mined dry.
Supernova surveys are unlikely to provide much more insight into the equation of state.
Maybe neutrinos or cosmic rays can still give us something new to work with, but those are really hard to work with. …”.

Based on the above,it does look as though
particle physics had a major breakthrough around the 1970s with the development of the Standard Model of Particle Physics, which has only been confirmed by experiments so far,
and
cosmology had a major breakthrough around the 2000s with the development of the Standard Model of Cosmology, which also has only been confirmed by obersvations so far.

If so,
we are looking at fundamental physics being made up of two well-established models:

Standard Model of Particle Physics for electromagnetism, the weak force, and the color force;

and

Standard Model of Cosmology for gravity and cosmology.

Further,
these two Standard Models seem to be able to coexist independently, with not a lot of experimental/observational results that point the way to unification a la electricity and magnetism.

Some experimental/observational results that MIGHT help seem to me to be:

1 – Josephson junction experiments of Warburton et al at University College London, which might be discussed by Christian Beck on Wednesday at 14:15 – 14:30;

2 – the Pioneer anomaly, in which it seems that gravitational acceleration changes at the orbit of Uranus (maybe there is some sort of phase transition that might be related to the unusual tilt of the rotation spin axis of Uranus?);

3 – the relationship between magnetic moment of celestial bodies and their angular momenta
( on a log-log chart, a nice straight line for all our planets up through our sun and larger stars,
as shown on Figure 2 of a paper by Vasiliev at astro-ph/0002048 ).

This list is not intended to be exhastive, but only to indicate that there are some puzzles out there,
and
to express hope that mabye at least one of them, if investigated in detail by people with no ideological/theoretical axe to grind, might be as productive as was the Planck’s study of blackbody radiation that led to quantum theory.

Tony Smith

PS – Since I do have a theoretical axe to grind (my physics model that seems to me to explain such things), I do not think that I would be a good person to be directly working on such experiments/observations, because people who don’t like me or my work would attack the results thereof as being self-serving on my part.
However, I do hope that somebody will do experiments/observations investigating such puzzles.

6. dorigo - March 28, 2007

Hello Tony,

indeed, you summarized the question well. We are in the rather uneasy position of having two good models which seem to explain most of our data quite well, little prospects to have new data coming which could cause a revolution (many hope that the LHC will do so, I doubt it), and a few inconsistencies to understand. What is worse is that we all know these models are no answer to all our questions…

I think what we really need is a paradigm shift in our theoretical understanding of reality. That is, something leading us to a really new level. Unfortunately, the only one I see around is string theory, which does not seem to be promising for several reasons…

Cheers,
T.

7. island - March 28, 2007

I’ve got one, whose first premise makes it straight to John Baez crackpot list, even though neither, he, nor any other theorist that I’ve ever pressed has been able to dispute my points:

1) Einstein wasn’t wrong.
2) Dirac’s hole theory is valid in this model when negative mass is simply rarefied mass-energy that has positive matter density, but negative pressure, therefore, producing an antigravitational effect. The cosmological constant.

Four, extremely short, but to the point postings to the research group: Back to 1917

http://www.lns.cornell.edu/spr/2005-06/msg0069755.html

Dirac’s cosmology then changes so his large numbers hypothesis becomes valid when it is repaired by the above, uh, “new” light.

1) Einstein was right.
2) Dirac was correct, (in context).
3) Robert Dicke was correct.
4) Brandon Carter was correct.

And science lost it’s freaking mind when it lost touch with the kind of natural rigor that Einstein unsuccessfully attempted to defend his cosmology with in Copenhagen.

Dirac’s hole theory in Einstein’s model is correct, so it isn’t gravity that varies over time, it is the electric force, so Dirac simply went the wrong way with it.

In his very short 1961 paper, Dicke refers to three dimensionless constants that are related to values of the order of 10^40 (What a coincidence, weren’t we just talking about this large number?) :

Paul Dirac said:
Take an atomic unit of time, express the age of the universe in this atomic unit, and you again get a number of about ten to the thirty-nine, roughly the same as the previous number.

Now, you might say, this is a remarkable coincidence. But it is rather hard to believe that. One feels that there must be some connection between these very large numbers, a connection which we cannot explain at present but which we shall be able to explain in the future when we have a better knowledge both of atomic theory and of cosmology.

Let us assume that these two numbers are connected. Now one of these numbers is not a constant. The age of the universe, of course, gets bigger and bigger as the universe gets older. So the other one must be increasing also in the same proportion. That means that the electric force compared with the gravitational force is not a constant, but is increasing proportionally to the age of the universe.

The most convenient way of describing this is to use atomic units, which make the electric force constant; then, referred to these atomic units, the gravitational force will be decreasing. The gravitational constant, usually denoted by G, when expressed in atomic units, is thus not a constant any more, but is decreasing inversely proportional to the age of the universe.

When you apply the above described “new” physics, then it becomes clear that it is the electric force that increases with matter generation, with the age of the universe, so when Dicke’s coincidence related the large numbers coincidence to biological features of the observed universe, he was actually working from the physics for the anthropic principle, which is about a thermodynamic constraint of the natural units that enables the universe to maximize work in order that it be as uniformly “spread-out” as possible when growing tension between the vaccum and ordinary matter inevitably compromises the integrity of the forces causing the universe to “leap/bang” to a higher order of entropic… ***EFFICIENCY***.

Anticentrist dogma is the only thing that kills this theory… to date.

8. island - March 28, 2007

I’m sorry, Dirac should have been quoted through four paragraphs ending with:

The gravitational constant, usually denoted by G, when expressed in atomic units, is thus not a constant any more, but is decreasing inversely proportional to the age of the universe.

9. island - March 28, 2007

One other thing:

When I said that it makes it straight to Baez crackpot list, I meant that any claim that Einstein was right automatically gets you there, not that anybody has shown me why that would be true in this case.

After all, I’m not going to simply admit that I’m a nut until I see a valid argument proving it… ;)

10. island - March 28, 2007

I’m very sorry for rambling, but when thinking back I realized that I didn’t say this right:

2) Dirac’s hole theory is valid in this model when negative mass is simply rarefied mass-energy that has positive matter density, but negative pressure, therefore, producing an antigravitational effect.

That should have read:
…when negative mass is simply rarefied mass-energy that has
positive ENERGY density, but negative pressure, therefore, producing an antigravitational effect.

In General Relativity’s most natural universe, the vacuum has negative density when, P=-u=-rho*c^2.

In this static state, pressure is proportional to -rho, but pressure is negative in an expanding universe, and so energy density is positive.

The vacuum energy density is less than the matter energy density, but it is still positive, so positive matter density can be obtained *locally* if you condense energy from this negative pressure vacuum into a fininte region of space, until the energy density over this region equals that of the matter density. This will, in-turn, cause negative pressure to increase, via the rarefaction of Einstein’s vacuum energy, so this expanding universe does not run-away, (meaning that there was no reason for him to abandon it), because the increase in the matter density is offset by the increase in negative pressure that results when you make particles from Einstein’s vacuum.

In Einstein’s static model, G=0 when there is no matter. The cosmological constant came about because we do have matter, so in order to get rho>0 out of Einstein’s matter-less model, you have to condense the matter density from the existing structure, and in doing so the pressure of the vacuum necessarily becomes less than zero, P

11. dorigo - March 29, 2007

Hi Island,

don’t worry about reposting comments here – as long as there are electrons there is a chance for you to write bytes of information here.

And thank you for your quotes of Dirac and your discussion of the cosmological constant. I do not feel qualified enough to comment, but maybe others will.

By the way, I have the feeling your last comment was cut, because of the use of the “less than” sign. That is a quite unfortunate effect of this lousy interface. Apologies, and if you want to post the rest of your discussion above, be my guest.

Cheers,
T.

12. Not Even Wrong » Blog Archive » Quick Links - March 29, 2007

[...] out that cosmology has a “miserable future”, since everything is receding from us. His main conference talk was evidently not very optimisitic about near-term prospects for learning more about dark energy or [...]

13. Thomas Dent - April 4, 2007

Hmm, no use for weak lensing and 21cm and Ly alpha and star/galaxy kinematics and lots of other observational stuff in the future then? I hope that isn’t so.

Dirac large numbers hypothesis has already been ruled out observationally, I think it’s incompatible with the evolution of stars.

14. Jane Howard - June 20, 2007

cosmology is the paradise of dictatorship, money, selfish, fame-seeking, politics because science does not have a mechanism of democracy.


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