Planck thoughts

March 22, 2013

It’s great to see the Planck cosmic background radiation data released, so what is it telling us about the universe? First off the sky map now looks like this

Planck_CMB_565x318

Planck is the third satellite sent into space to look at the CMB and you can see how the resolution has improved in this picture from Wikipedia

PIA16874-CobeWmapPlanckComparison-20130321

Like the LHC, Planck is a European experiment. It was launched back in 2009 on an Ariane 5 rocket along with the Herschel Space Observatory. The US through NASA also contributed though.

The Planck data has given us some new measurements of key cosmological parameters. The universe is made up of  69.2±1.0% dark energy, 25.8±0.4% dark matter, and 4.82±0.05% visible matter. The percentage of dark energy increases as the universe expands while the ratio of dark to visible matter stays constant, so these figures are valid only for the present. Contributions to the total energy of the universe also includes a small amount of electromagnetic radiation (including the CMB itself) and neutrinos. The proportion of these is small and decreases with time.

Using the new Planck data the age of the universe is now 13.82 ± 0.05 billion years old. WMAP gave an answer of 13.77 ± 0.06 billion years. In the usual spirit of bloggers combinations we bravely assume no correlation of errors to get a combined figure of 13.80 ± 0.04 billion years, so we now know the age of the universe to within about 40 million years, less than the time since the dinosaurs died out.

The most important plot that the Planck analysis produced is the multipole analysis of the background anisotropy shown in this graph

Planck_power_spectrum_565w

This is like a fourier analysis done on the surface of a sphere are it is believed that the spectrum comes from quantum fluctuations during the inflationary phase of the big bang. The points follow the predicted curve almost perfectly and certainly within the expected range of cosmic variance given by the grey bounds. A similar plot was produced before by WMAP but Planck has been able to extend it to higher frequencies because of its superior angular resolution.

However, there are some anomalies at the low-frequency end that the analysis team have said are in the range of 2.5 to 3 sigma significance depending on the estimator used. In a particle physics experiment this would not be much but there is no look elsewhere effect to speak of here, any these are not statistical errors that will get better with more data. This is essentially the final result. Is it something to get excited about?

To answer that it is important to understand a little of how the multipole analysis works. The first term in a multipole analysis is the monopole which is just the average value of the radiation. For the CMB this is determined by the temperature and is not shown in this plot. The next multipole is the dipole. This is determined by our motion relative to the local preferred reference frame of the CMB so it is specified by three numbers from the velocity vector. This motion is considered to be a local effect so it is also subtracted off the CMB analysis and not regarded as part of the anisotropy. The first component that does appear is the quadrupole and as can be seen from the first point on the plot. The quadrupole is determined by 5 numbers so it is shown as an everage and a standard deviation.  As you can see it is significantly lower than expected. This was known to be the case already after WMAP but it is good to see it confirmed. This contributes to the 3 sigma anomaly but on its own it is more like a one sigma effect, so nothing too dramatic.

In general there is a multipole for every whole number l starting with l=0 for the monpole, l=1 for the dipole, l=2 for the quadrupole. This number l is labelled along the x-axis of the plot. It does not stop there of course. We have an octupole for l=3, a hexadecapole for l=4, a  dotriacontapole for l=5, a tetrahexacontapole for l=6, a octacosahectapole for l=7 etc. It goes up to l=2500 in this plot. Sadly I can’t write the name for that point. Each multipole is described by 2l+1 numbers. If you are familiar with spin you will recognise this as the number of components that describe a particle of spin l, it’s the same thing.

If you look carefully at the low-l end of the plot you will notice that the even-numbered points are low while the odd-numbered ones are high. This is the case up to l=8. In fact above that point they start to merge a range of l values into each point on the graph so this effect could extend further for all I know. Looking back at the WMAP plot of the same thing it seems that they started merging the points from about l=3 so we never saw this before (but some people did bevause they wrote papers about it). It was hidden, yet it is highly significant and for the Planck data it is responsible for the 3 sigma effect. In fact if they used an estimator that looked at the difference between odd and even points the significance might be higher.

There is another anomaly called the cold spot in the constellation of Eridanus. This is not on the axis of evil but it is terribly far off. Planck has also verified this spot first seen in the WMAP survey which is 70 µK cooler than the average CMB temperature.

What does it all mean? No idea!

23 Comments | Cosmology, Space | Permalink
Posted by Philip Gibbs

Guest Post by Felix Lev

July 17, 2012
Today viXra log is proud to host a guest post by one of our regular contributors to the viXra.org archive. Felix Lev gained a PhD from the Institute of Theoretical and Experimental Physics (Moscow) and a Dr. Sci. degree from the Institute for High Energy Physics (also known as the Serpukhov Accelerator). In Russia Felix Lev worked at the Joint Institute for Nuclear Research (Dubna). Now he works as a software engineer but continues research as an independent physicist in a range of subjects including quantum theory over Galois fields.

Spreading of Ultrarelativistic Wave Packet and Redshift

In standard cosmology, the red shift of light coming to the Earth from distant objects is usually explained as a consequence of the fact that the Universe is expanding. This explanation has been questioned by many authors and many other explanations have been proposed. One of the examples – a recent paper by Leonardo Rubio “Layer Hubble and the Alleged Expansion of the Universe” in viXra:1206.0068.

A standard explanation implies that photons emitted by distant objects travel in the interstellar medium practically without interaction with interstellar matter and hence they can survive their long (even billions of years) journey to the Earth. I believe that this explanation has the following obvious flaw: it does not take into account a well-known quantum effect of wave-packet spreading and the photons are treated as classical particles (for which wave-packet spreading is negligible). The effect of wave-packet spreading has been known practically since the discovery of quantum mechanics. For classical nonrelativistic particles this effect is negligible since the characteristic time of wave-packet spreading is of the order of ma2/ℏ where m is the mass of the body and a – its typical size. In optics the wave-packet spreading is usually discussed in view of the law of dispersion ω(k) when a wave travels in the medium. But even if a photon travels in empty space, its wave function is a subject of wave-packet spreading.

A simple calculations the details of which can be found in my paper viXra:1206:0074, gives for the characteristic time t* of spreading of the photon wave function a quantity given by the same formula but with m replaced by E/c2 where E is the photon energy. This result can be rewritten as t* = 2πT(a/λ)2 where T is the period of the wave, λ is the wave length and a is a dimension of the photon wave function in the direction perpendicular to the photon momentum. Hence even for optimistic values of a this quantity is typically much less than a second.

If spreading is so fast then a question arises why we can see stars and even planets rather than an almost isotropic background. The only explanation is that the interaction of photons with the interstellar medium cannot be neglected. On quantum level a description of the interaction is rather complicated since several processes should be taken into account. For example, a photon can be absorbed by an atom and reemitted in approximately the same direction. This process is an illustration of the fact that in the medium the speed of propagation is less than c: because after absorbing a photon the atom lives some time in an excited state. This process plays an important role from the point of view of wave-packet spreading. Indeed, the atom emits a photon with a wave packet of a small size. If the photon encounters many atoms on its way, this does not allow the photon wave function to spread significantly.

In view of this qualitative picture it is clear that at least a part of the red shift can be a consequence of the energy loss and the greater the distance to an object is, the greater is the loss. This phenomenon also poses a problem that the density of the interstellar medium might be much greater than usually believed. Among different scenarios discussed in the literature are dark energy, dark matter and others. As shown in my papers (see e.g. viXra:1104.0065 and references therein), the cosmological acceleration can be easily and naturally explained from first principles of quantum theory without involving dark energy, empty space-time background and other artificial notions. However, the other possibilities seem to be more realistic and now they are intensively studied.

44 Comments | Cosmology | Permalink
Posted by Philip Gibbs

How did early supermassive black holes form?

July 2, 2011

It seems like every few weeks that we hear news of a new study of the early universe showing that black holes formed earlier than expected and that structure in the pattern of galaxies extends to larger distances than expected.

The ruling paradigm says that galaxies formed when hydrogen gas and dark matter slowly clumped together under its gravitational pull. Stars were formed which continued to collapse togther to form galaxies. The early stars which were large would die quickly and form black holes which would coallesque to form supermassive black holes at the centres of galaxies.

The process was seeded by density perturbations in the gas that existed at the time of last light scattering. The effects of these perturbations are seen in the cosmic microwave background and are very familiar to cosmologists. They are believed to be due to fluctuations during the inflationary epoch and they have the right scale invariant spectrum to fit that hypothesis. You can model the formation of galaxies and large scale galactic structure in cold dark matter models using computer simulations. With the right parameters set for the mass of dark matter particles you can get good agreement with observations.

But the agreement is not good enough. It predicts that the black holes form after the stars, yet we see quasars appearing in the early universe containing huge black holes that must have formed much earlier. The latest example is a quasar with a mass of 2 billion suns observed at just 770 million  years after the big bang by ESO’s Very Large Telescope. We have seen proto-galaxies and gamma ray bursts from even earlier.

We also observe structure in the distribution of galaxies that extends out to very large scales. This is not predicted by the cold dark matter theory of structure formation. An example is the Great Sloan Wall, a vast planar structure covering 5% of the size of the observable universe. Up to these scales the distribution of galaxies forms clusters and filaments as well as voids separated by these walls. How could these have formed so soon and so big?

One possible answer is that they did not form through gravitational collapse at all, but instead by a process of caustic focusing of dark matter by gravitational waves. Let me explain.

We know very little about how the inflationary epoch ended. The vacuum state would have changed as the inflationary scalar field dropped into a broken phase. There may have been a phase transition but it may have been a soft second order transition or even a smooth crossover. We don’t even know when it happened. It may have been the elctro-weak transition or something earlier. With new physics from the LHC we may be able to work out how it happened.

It is likely that the transition did not happen simultaneously at all points in space. Fluctuations would mean that inflation continued a little longer in some places than others. This would leave a remnant gravitational wave background in the universe which in time would have cooled and weakened as the universe expanded more slowly. It would be hard to detect directly today because of its very low frequency and weak amplitude, but in the early universe during baryogenesis it would have been stronger.

The effect on baryonic matter would however have been washed out by electromagnetic forces acting more strongly than anything these waves could do. Dark matter on the other hand is uncharged and only interacts weakly. The gravitational waves, if strong enough could have influenced the distribution of dark matter. This is more true if dark matter particles are heavy so that they move more slowly at a given temperature. So what would happen?

In fact heavy particles would follow geodesics through the gravitational waves which would focus them onto caustic surfaces. The process is very similar to the focusing of light through the waves on the surface of the sea of a swimming pool creating familiar patterns of light on the bottom. The caustic lines are replaced with surfaces stretching across the universe just like the ones seen in the Sloan Survey. Where the walls meet even denser concentraions of matter would form.

Caustic light patterns formed by water waves quickly shift to disappear and reform elsewhere, but when enough dark matter is concentrated into one place it will itself gravitate and form dark stars or black holes which lock in the pattern. This could have happened very early in the universe, possibly even before the cosmic radiation background last scattered off hot baryonic matter.

The ordinary stars would form around these structures either by gravitational attraction or due to the pressure of radiation from dark stars and gas falling into the black holes.  Either way the structure in the distribution of galaxies would be largely determined by the caustic patterns provided by the gravitational waves so it can extend much further depending on the spectrum of the waves at large wavelengths. The large black holes that form quasars would originate from concentrations of dark matter at the densest points where the caustic planes meet.

Even as more discoveries appear to contradict the  ΛCDM theory cosmologists stick to the old paradigm because it almost works. Λ, the cosmological constant is there and so is Cold Dark Matter, but that does not mean that they explain the formation of super-massive black holes and large scale structure in the universe. Cosmologists need to wake up to this fact and start exploring alternatives such as the caustic theory outlined here. As usual I will quietly wait while they ignore it and eventually reinvent the idea for themselves. Good luck guys.  :)

23 Comments | Cosmology | Permalink
Posted by Philip Gibbs

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