Hi, I’m Rachel, the Astronomer here at the Space Centre.

What do pigeon droppings and the Big Bang theory have in common? At first glance, it might seem like nothing at all, but these feathery creatures played an important role in advancing the field of physical cosmology. With cosmo- being the Latinized form of the Greek kósmos, meaning world or universe, this branch of astronomy is concerned with the scientific study of the origin and evolution of the universe, and the laws of nature that govern its dynamics. The field has its roots in celestial mechanics, the study of the heavens. It began with Greek philosophers like Aristotle (322 BCE) and Ptolemy (100 CE), moving on to the 16th century ideas of Copernicus, Kepler, and Galileo. In 1917, Einstein published his paper, “Cosmological Considerations of the General Theory of Relativity”,  marking what is generally considered the beginnings of modern scientific cosmology.

From the field equations introduced by Einstein’s paper (written below) came a very important number – the cosmological constant, Λ. This number, depending on its value, said that it was possible for our universe to be an expanding one. Naturally, the idea that our universe could have begun from one “big bang” billions and billions of years ago was postulated by Georges Lemaître in 1927, and confirmed by Edwin Hubble’s observations of receding nearby galaxies just two years later.


However, the strongest evidence we have for the Big Bang model came in 1964, and it all started with pigeon poop. Radio astronomers Arno Penzias and Robert A. Wilson working at Bell Labs were conducting experiments with the Holmdel Horn Antenna, a device used to detect weak radio waves. As the signals they were looking for were so weak, their radio horn had to be extremely sensitive. They did all they could to eliminate any possible sources of noise, running extensive tests on their equipment. Even so, they still detected a strange, buzzing noise that was coming from all parts of the sky, at all times of day and night. Thinking that it must be the pigeons nesting in the horn and interfering with their signal, they put on boots and gloves and cleaned out the pigeon poop. Still, the noise persisted.

At the same time, Robert H. Dicke, Jim Peebles, and David Wilkinson at Princeton University, just 60 km away, were preparing to search for their predicted leftover microwave radiation that would have been produced from the early stages of the universe in the Big Bang model. The microwave signal they were hoping to find is known as the Cosmic Microwave Background (CMB),  and is the oldest form of light that we can detect. It is radiation in the microwave part of the electromagnetic spectrum,  much like how your microwave oven that you use to heat up food operates at these wavelengths (albeit, with a lot more power). If they were successful in detecting this old light, or ‘relic radiation’, then the Big Bang theory would become the best cosmological model we have so far to describe our early universe.

Serendipitously, the radiation that Penzias and Wilson were trying to scrub from their data was a perfect match for what the Princeton researchers had predicted – it was exactly the signal that they were searching for! Thus, from this noisy signal being attributed to pigeon droppings, it is now known as the first measurements of the CMB. You can listen to the CMB noise here,  narrated and interpreted by Robert A. Wilson.

This radiation was emitted almost 14 billion years ago, only a few hundred thousand years after the Big Bang and long before stars or galaxies existed. Imprinted on it are subtle fluctuations in temperature from when the universe was about 370,000 years old, and they represent traces of the seeds which gave rise to the present cosmic web of galaxy clusters (here is an interactive cosmic web model). By studying the properties of the CMB, researchers can learn more about the mysterious components of our universe, such as the elusive dark matter and dark energy. Currently, our interpretation of the Planck data tells us that the universe is 13.8 billion years old, and is composed of 4.9% ordinary matter, 26.6% dark matter, and 68.5% dark energy (here is the universe’s content represented as a pie chart). The universe still has many hidden secrets waiting to be uncovered by cosmologists, whether it be by accident or on purpose.










Arno Penzias and Robert A. Wilson, in front of the Holmdel Horn Antenna at Bell Labs, New Jersey in 1975. Source: https://www.bell-labs.com






The all-sky map of the cosmic microwave background from the Planck cosmology probe, released by the European Space Agency in 2013. Source: http://www.nasa.gov

Astronomers of All Ages - Playlist

The story of how pigeon poop is related to cosmology shows that sometimes even scientists have to do everyday tasks in their scientific questions. Listen to this Ideas podcast, The Relativity Revolution: Albert Einstein and the Making of the Modern World, to find out how his ideas are now part of your everyday life.

Ask yourself: What would your life be like if Einstein had not published his famous equation E=mc2?


Do you have what it takes to be a cosmologist? Try this fun Space Forensics game and see if you can use the process of science to solve the mystery of the origins of the chemical elements in the universe.

Ask yourself: What other mysteries could you solve using the process of science?


Would studying cosmology be easier if you could achieve near-light-speed travel? Watch this fun video to find out the effects of travelling at near the speed of light?

Ask yourself: What other mysteries could you solve using the process of science?


Nothing like the vastness of the universe to inspire your creative side. Have a look at some poetry written by NASA-JPL scientists and engineers here and here. Now it’s your turn—write your own space poetry. To share your poems with us email them to [email protected] with your name and age, and we may feature your work on our social media accounts.

Ask yourself: How has writing a poem inspired by space change the ways you think about space?


You probably have more questions about cosmology. Visit this Cosmology FAQ to see if you can find answers to some of your questions.

Ask yourself: Did you have questions that were not answered on the FAQ page? Do answers to your questions exist? If not, you might need to become a cosmologist to see if you can answer them.


Be a citizen scientist and help analyze data from radio observatories from these two Zooinverse citizen science projects.

Radio Galaxy Zoo: LOFAR

Radio Meteor Zoo

Ask yourself: What do you think some of the challenges radio astronomers might face with collecting and analyzing data?