Fingers of God

This blog post is written by Grzegorz Karwasz, director of ECLAS Central Europe and Professor of Experimental Physics at Nicolaus Copernicus University, Toruń, Poland.

“Fingers of God” was the title of an article that appeared on Wikipedia in about 2011. (Since then the article has been renamed, rather less romantically, to “Redshift-space distortion”, and it describes the distribution of filaments of galaxies over the whole Universe.)

In that year, the Nobel prize in physics was awarded for the discovery of the accelerating expansion of the Universe. The prize recipients Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess had for years studied explosions of stars in remote galaxies. Saul Perlmutter said they wanted to verify if “the Universe was infinite, or that it was finite and going to come to an end”. Instead, they encountered something “greater than great”: a mysterious force was making the Universe expand faster and faster.

One might expect the initial force of the Big Bang to have faded over 13 billion or so years. But Saul Perlmutter and his colleagues were surprised by what they observed of the Universe: “Its expansion rate used to be slowing, but has been speeding up for the last half of its history, and presumably could speed up forever.”

There is still much that we do not know about the Big Bang. We know that the Universe expanded over billions of years from an initial size roughly equivalent to our galaxy (some 100 thousand light-years in diameter) to its current size (with a radius of 13.8 billion light-years). And before that? Scientists hypothesise that the Universe started from the size of an orange – and that its rapid explosion, in a billionth part of a billionth part of a second, violates all known laws of physics.

The history of our expanding Universe is usually shown as a tulip flower, with “an inflation” at the starting point. Here we show a lamp from a restaurant in Trentino, Italy (photo GK).

Albert Einstein was the first to understand that there must be some force counteracting gravity, otherwise the Universe would have had collapsed in on itself just after the Big Bang. He introduced an additive constant to the equation of General Relativity. Later he considered this the biggest mistake of his life, but in truth it was his greatest discovery.

Nowadays, cosmologists explain the expansion of the Universe by a mysterious dark energy that outnumbers another unknown part of the Universe, dark matter, by a factor of four. Dark matter, in turn, exceeds the physical matter known to us by another factor of four. In other words, 300 years after Newton published his Principia, we know (or better: we can merely imagine) only 5% of the material universe.

Let’s quote Saul Perlmutter again: “it’s amazing how big a mystery has opened up as a result, and how much we still have left to discover.”

What is the conclusion of all these mysteries? Personally, I find the picture of Fingers of God that shape the entire Universe really inspiring.

Main image shows redshift effect (left) on galaxies compared to real space (right). Image credit: M.U. SubbaRao et al., New J. Phys. 10 (2008) 125015, via IOPscience.