IVÁN JIMÉNEZ MONTALVO

In astronomy, when things cannot be seen we must look for indirect evidence. And there is nothing more difficult to see than the origin of the Universe. As science tries to get close to this time, everything becomes opaque. To understand how those first moments were, we have devised complex instruments capable of detecting signals that have been printed faintly in the farthest space and time. This has been the work and the obsession of Lyman Page, a researcher at Princeton University (USA), who has participated in some of the most important experiments (WMAP, experiment ACT) dedicated to the study of the Cosmic Microwave Background (CMB), today the Rosetta Stone of Cosmology. This radiation, a type of fossil light from all directions of the sky, provides a snapshot of the early universe. Currently, Professor Page is dedicated to the measurement of a phenomenon associated with this radiation called "polarization". In particular, he hopes to detect a type of polarized signal - primordial B-modes - to prove the existence of gravitational waves. Supposedly, these waves were caused by a short phase of accelerated expansion that shook the universe in its earliest stages and which scientists call "inflation". However, detection of these modes is very difficult, especially because they are not easily distinguishable from background pollution produced by other sources, such as dust in our galaxy. For this reason, many researchers - Professor Page included-, have doubts about the recent announcement of the discovery by the team of BICEP2, a microwave telescope located at the South Pole. New data, such as those the PLANCK satellite will bring soon, and new observations, such as those with the new Atacama Cosmology Telescope (Adv-ACT), led by the professor Page, or with the QUIJOTE experiment at the Instituto de Astrofísica de Canarias (IAC), may possibly end the controversy.

How and why did you become interested in the CMB as a field of study?

I became interested in the CMB in 1984 at the beginning of my PhD thesis at MIT when I began working on experiments to measure it. At that time the anisotropy [variations in the physical properties of the apparently homogeneous CMB] had not been detected. It seemed intuitively that we could learn very interesting things from studying the afterglow of the Big Bang. At the time we had no idea how much we would learn!

What can we know about our Universe studying the polarization of the CMB?

We can learn a large number of things. At large angular scales we can detect primordial gravitational waves if they are there, and we can learn more about the process of cosmic reionization [the phase in which the Universe started to emit visible light], a process that is not well understood. At all angular scales we can get an independent determination of the cosmological parameters. That is, the primary results of Planck and WMAP thus far can be checked in an independent manner. At smaller angular scales we can determine the sum of neutrino masses. And this is just a start. Essentially, we are in the early stages of developing a new cosmological observable.

What is the role that the WMAP has played in our understanding of the CMB and in validating the current cosmological model?

WMAP gave us the foundation for the standard model of cosmology. The universe is geometrically flat and described by six parameters. While there are many other probes of the cosmos, it was WMAP that pulled it all together and linked the observed universe to fundamental processes in the early universe. Planck has shown that the WMAP model is by and large correct. There are some very minor discrepancies that are still being worked out.

Which goals do you expect to achieve with the new Adv-ACT?

To me, the major goals are to determine the sum of neutrino masses, measure or limit the presence of primordial gravitational waves to r < 0.01 after accounting for foreground emissoin, and to nail down the process of cosmic structure formation.

What role do you think the Quijote experiment will play within the different initiatives that currently study the polarization of the CMB?

QUIJOTE is important because it should get a nice measurement of the sky from 10-30 GHz and possibly higher. This is important for a number of reasons. It will see E-modes and it may observe B-modes if the signal is large. The other aspect is that we really don't know the polarized foreground emission that well. The BICEP result is a recent example. From Planck and WMAP we have pretty good maps but not great ones. QUIJOTE will help here as well. Lastly, it is worth remember that the largest angular scale measurement of the CMB that was done from the ground was done by "Tenerife" experiment in the late 1980s and early 1990s. The QUIJOTE scan strategy may again make that feat possible to duplicate. It is a path finder in many ways as I am not aware of any other CMB experiment using the 360 deg instrument rotation to observe the sky, although a number have proposed it.

What is your opinion about the results of BICEP2? How the controversy about the interpretation of the data can be solved?

At this point the uncertainty in foreground emission is so large that the BICEP team cannot make conclusions about primordial gravitational waves. They now (finally) admit this. They say:  "However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal." Their announcement/claim of a detection of primordial B-modes was uncalled for and premature.

Do you think the way the data was reported is correct? Should the scientific community consider the way we are communicating the discoveries?

By far most groups report data properly and with care. BICEP2 was grandstanding and was way out of line.

Do you think the primordial B-modes of the CMB polarization eventually will be confirmed?

I don't think "confirmed" is the right word here. I'm waiting for an independent measurement by another group. Personally I will have a difficult time believing anything by the BICEP team until they make all of their data public. If r>0.01 then I think primordial B-modes can be measured by other groups.

In case we never got to prove, would the current model of the Big Bang be in trouble? Are there other alternatives to this model?

There are a number of alternatives but I am not an expert in them. I hope the recent kerfuffel spurs theorists to develop more alternative models. It was surprising how many said that finding primordial B-modes "proved" inflation and then when the detection was in doubt said that they were not necessary to inflation. Perhaps inflation is the correct framework but more work needs to be done to be confident.

If the measurement of the primordial B modes is confirmed, what will be the consequences for cosmology and our understanding of the universe?

We will have a whole new handle on the universe. It will be very exciting, and the search is very exciting.