Precision Cosmology

Which discoveries and technologies helped cosmology to become data-driven and precise? Which parameters do we have to put in the standard cosmology model to achieve agreement with observations? Professor of Physics at Massachusetts Institute of Technology Max Tegmark tells how cosmological inflation explains the beginning of our Universe.

The way we start is by looking at the cosmic microwave background radiation and looking at exactly how the universe was clumpy and clustered 400 000 years after the Big Bang, these 10^-5 level fluctuations. The sky is 10^-5 times hotter in some places, colder in other places. Then we can put this information into really big computers and try to predict how clumpy our Universe will be later, when the first galaxies will form and what sort of patterns they will cluster in. Then we can compare this with all we actually see when we make these three-dimensional galaxy maps with our telescopes. And the result of this has been really quite remarkably successful.

One of the numbers is the density of atoms, another one tells you how much dark matter there is, another parameter tells you how much dark energy there is, another parameter tells you how clumpy the early Universe was, another parameter tells you the ratio of large to small clumps. It’s quite remarkable that we’ve been able to take many many many gigabytes of data and fit them all perfectly with just these six numbers. It’s the greatest triumph for precision cosmology so far, and this is the reason why we now can say with some confidence that we know that there is dark matter and there is dark energy and we know how much of it there is.

Heisenberg uncertainty principle of quantum mechanics says you cannot have the Universe which is completely uniform, there must be little fluctuations. But those fluctuations are on tiny scales, much smaller than atoms, so what do they possibly have to do with galaxies? Well, the beautiful idea is that inflation kept on doubling this space, so these short short distances where you have the quantum fluctuations get stretched out eventually to being larger than galaxies. And also what this theory predicts is that the fluctuations that ultimately led to the formation of the galaxies, and us, and everything else ultimately came from quantum mechanics, from the microworld, and it’s a beautiful connection between these very smallest scales of our Universe and the largest scales of our Universe.