Planck’s data is extraordinary, but will it teach us anything new?

Credit: ESA

The recent results from the Planck satellite have garnered considerable interest among both scientists and the media. But from the discussions that have followed, I am learning at least as much about the nature of science as the origins of the universe.

But first, the science. (If you have heard all you want to about the cosmic microwave background, you may want to skip the next paragraph or two.)

Planck is designed to map and measure the cosmic microwave background (CMB) at higher resolution and over a wider range of frequencies than ever seen before. The CMB itself is a sea of photons left over from the astonishingly high temperature ‘fireball’ of the big bang. As the universe expands after the initial ‘kick’, it cools. When the CMB was formed, the universe was 380 000 years old. Its temperature was 2700C (at this point the universe would have glowed a red colour similar to an electric fire). In the billions of years since then, the expansion and cooling has continued, giving a temperature now of -270C (just 3 degrees above absolute zero) and a glow of microwaves. This glow is the CMB.

The CMB is important as it is the earliest light that it is possible for us to see. Before the CMB was created the universe was effectively opaque. However, imprinted on the map of the microwave sky is information about the universe. Not just at the time the CMB was formed, but much earlier – even well into the first second after the big bang. It is these echoes that Planck is studying. So, what has been discovered in this first data release? The headline numbers are impressive:

  •  Our basic model of the big bang and subsequent evolution of the universe fits well, with no need (or indeed much room) for any strange tweaks in the early stages.
  • The universe is 13.8 billion years old – slightly older than the previous best estimates (though within the uncertainties).
  • The universe appears to be made up of 5% ‘normal’ matter (the stuff of stars, planets and us); 26% mysterious, though much sought-after, dark matter; and 69% dark energy which nobody really has a good handle on at all.
  • There is an odd, albeit slight, north-south asymmetry and an unexplained cold spot in the south.

So, there is no question that Planck is working very well and the data quality is superb. However, none of these results are actually new. The precision is a significant improvement over previous measurements from the Cobe and WMAP satellites, but it could be argued that, while our understanding is more precise, it is no deeper.

It should be stressed that these are early days for Planck and much more analysis and calibration needs to be done before all the implications can be understood. However, it is important to face the question: Is Planck going to lead to any new science?

There is a useful comparison here with one of the biggest science stories of recent years: the discovery of a new particle at the Large Hadron Collider (LHC). Here, like Planck, a new area of ‘parameter space’ was set to be explored by better, more sensitive instrumentation. Also like Planck, aspects of the current best-bet theory would be tested to new limits and values of important parameters refined. However, arguably unlike Planck, there were also some specific new fundamental theories with clear predictions that could be tested. Some of these remain to be tested in future years, some have been relegated to history and some, such as the Higgs boson theory, are well on their way to passing their tests. Could the same be said for Planck?

Of course, the comparison is not a perfect one. Both the scale and scope (and cost) of the LHC are far larger than Planck. On one side, we have an unprecedented instrument that carries a significant fraction of the entire field of particle physics on its 27km shoulders. On the other side, a single telescope chipping away at a corner of astrophysics. Nevertheless, there are disgruntled mutterings that perhaps the resources that went into Planck could have been better spent on other, perhaps more risky or speculative missions.

This sort of discontent is natural when difficult decisions have been made in the allocation of limited resources, and hindsight provides an excellent fuel for it. Nevertheless, the balance between speculative science with a small chance of an enormous return, and the steady improvement of knowledge and understanding through incremental advances is a difficult one to strike, and some will always be unhappy.

Naturally, it is good to get such excellent confirmation that we are on the right track; that the work of the last decades has been well spent and we are moving steadily forward. Nevertheless there are many, myself included, who were hoping for something more. We were hoping that Planck would, at least, show new holes in our knowledge, new questions we should be asking. And, at the most, perhaps even show a crack in our basic understanding – the first hint that somewhere ahead of us is a major leap in our understanding.

Maybe these results are just around the corner and the further analysis from Planck will soon lead to just the sort of major result that I would like to see, but that is unlikely and I will probably remain disappointed for now.

However, that does not mean that I consider Planck in any way a failure. The quality of the data is extraordinary, the work of the science team in analysing it superb (and on time), and the improvements in the values of some fundamental properties are significant. The important thing now is not to ask what could have been done differently, but to see what we can do now. Maybe the results themselves do not (yet!) show anything unexpected, but they may be the first step towards it. And as the Chinese have known for many years:

“It is better to take many small steps in the right direction than to make a great leap forward only to stumble backward.”

Image: Planck’s baby picture of the universe. Credit: ESA


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