Only one universe to observe

by May 16, 2013
Photo by Nuno Serrão (2011)

Photo by Nuno Serrão (2011)

Theoretical cosmologist Roberto Trotta talks to SCOPE about the anthropic principle, slow data, and his science’s happy similarity to art

Dr. Roberto Trotta is a science communicator, statistical consultant, and a senior lecturer in astrophysics at Imperial College London.

SCOPE > Let’s start with the anthropic principle. What is it and how has it evolved since it was first proposed?

RT > The anthropic principle is the notion that in considering our place in the Universe we must take into account that certain physical conditions must be fulfilled for us to exist in the first place. Early applications of this idea were highly successful: for example, the astronomer Fred Hoyle argued in the ’50s that the atomic structure of the carbon atom should have specific properties — properties that had not been observed at the time — for carbon-based life forms such as ourselves to be possible. A few years later, detailed nuclear measurements verified Hoyle’s prediction.

In the last two decades or so, however, the anthropic principle has acquired something of a bad press, as cosmologists have used it to try and explain the mystery of dark energy. Cosmological observations show that our Universe is dominated by a strange form of energy with repulsive behaviour that is making the Universe’s expansion accelerate with time. However, the strength of the dark energy component is extremely small compared with all other known physical scales. The question then arises: why does dark energy have the strength that it does in our Universe? And the puzzle deepens when you realise that life as we know it could not exist if dark energy was only a tiny bit different from what it is.

The anthropic principle often gets invoked today when postulating a large collection of parallel Universes, all with different laws of physics — a theoretical construction called the Multiverse. Necessarily, goes the argument, we must find ourselves in a corner of the Multiverse where the laws of physics, and in particular the strength of dark energy, are compatible with our existence. This conclusion, however, remains highly speculative, and is very controversial from the point of view of statistics. Some doubt that the anthropic principle as applied to the Multiverse can even be defined as “scientific” at all.

Speaking of statistics, you’ve argued that cosmologists should consider releasing their data “slowly”. Why is that?

The point is to avoid a fundamental statistical problem: given any set of data, if you look for “strange things” in those data for long enough, you are guaranteed to find some. For example, I could present you with the outcomes of a sequence of 1000 flips of a perfectly fair coin. But if you stared at the sequence long enough, you might notice a strange string of 10 tails in a row, for example. If you took this string in isolation, you would wrongly conclude that the coin is not fair — and would be grossly misled by your selection of a what is, in fact, a perfectly normal statistical fluctuation in your data.

The resolution of such problems can only come from a fresh set of data that you can use to test whether or not the strange anomaly found in the original data is actually real, or just a statistical artifact. However, in cosmology we don’t have the luxury of having fresh data for certain problems: we only have one Universe to observe (which is rather like having only a single flip of a coin). So my collaborators and I urged observers to be careful in the way their release their data: drip feeding them to the community would avoid the problem of running out of fresh data to test anomalies identified in current sets.

What future role will probability play in cosmology?

Probability and statistics will continue to play a leading role in understanding and interpreting the huge volume of data we will gather about our Universe. Within our lifetimes, new instruments such as the Square Kilometer Array (a continent-sized radio telescope with base stations scattered across Australia and South Africa) will map out the entire visible Universe — all 50 billion galaxies in it! After that effort, astronomy as we have know it will be effectively over: we will have seen all there is to see in the Universe. Our ability to improve our knowledge about the cosmos will be limited by the way we analyse in a statistical fashion this data deluge.

Physicist Ernest Rutherford famously said at the beginning of the twentieth century that “if you need statistics you have done the wrong experiment”. In twenty-first-century astronomy, by contrast, we can confidently say that you have done the wrong experiment if you don’t need statistics!

What’s the connection between art and cosmology? Are they merely metaphors for each other or do they share something tangible?

I believe that art and cosmology have much more in common than just a metaphorical link. In very different ways, they are both pursuits of a new, deeper vision of the reality around us and of our place in it. Artists and cosmologists share a passion for novel, creative ideas. And the fundamental raison d’être of both disciplines is not so different: blue-sky research, like art, is about pushing our boundaries and enjoying the thrill of the quest without necessarily having a final goal in mind. In both cases, the result is a deeper understanding of our role and place in the cosmos. Both contribute to making our lives fuller, more interesting, and worth living.



In the past 12 months, what’s the best…

Book you’ve read?  Marry me by John Updike. An insightful and subtle exploration of the intricacies of love, passion and betrayal.

Band you’ve listened to?  Cat Power — always refreshing.

Artist or photographer you’ve viewed?  Tino Sehgal’s installation at Tate Modern. It really got under my skin. (Read The Guardian‘s recap of Sehgal’s work here)

Film you’ve watched?  “Cloud Atlas” — an excellent interpretation of the book.