Humans have been pondering about the inner workings of the Universe for as long as there have been humans. Albeit through different questions, the quest to understand the Universe has been irrevocably entangled with our history and remains an intensely studied topic. This is the field of cosmology.
But how do we map out the history of the Universe from the Big Bang to the present? And what is the future of the cosmos?
The first major tsunami in cosmology in recent times came in 1998 when two international collaborations were attempting to make precise measurements of how fast the Universe is expanding. They did this using a special kind of exploding star called Type 1A supernovae, which acts as a so-called standard candle at various distances.
Since these stars act identically across the Universe we can measure how far away they are moving from us. What these teams found startled the whole community. It turns out that the Universe is not only expanding but accelerating in this expansion.
Up to this point in time, it was fairly universally accepted that the Universe came from an initial Big Bang event that propelled everything in the Universe to move away from each other.
However, given that we always experience gravity to pull things together, it was very unexpected that the Universe would currently be accelerating outward. In fact, both collaborations were awarded the Nobel prize for Physics in 2011.
The fact of the accelerating Universe is called dark energy and has been verified numerous times since this first observation.
To explain this astonishing discovery, scientists used an old idea by Albert Einstein called the cosmological constant. This entails adding a constant to the Einstein equations for the Universe, which he had initially used in 1917 to describe the Universe as being static. He later abandoned the idea when Edwin Hubble in 1929 found that the Universe is expanding. The idea was resuscitated to explain the 1998 observation of an accelerating Universe. This is now called the standard model of cosmology.
The Universe is not only expanding but accelerating in this expansion
Concurrently, scientists have been working on building space-based satellites to make precision measurements of the early Universe to better test this standard model of cosmology.
The first of these missions was called COBE, which confirmed several important features of the Big Bang theory. This was part-led by George Smoot, who won the Nobel prize for these discoveries, and who also opened the Institute of Space Sciences and Astronomy at the University of Malta.
The second mission was also run by Nasa, and called WMap. However, the most recent of these missions, Planck, was run by the European Space Agency. The Planck mission was enormously successful in increasing our certainty in many aspects of cosmology, such as the kinds of particles we see in the Universe and the main stages of the early Universe, as well as a better breakdown of the ingredients that make up the Universe. However, it also found a potential problem with our standard cosmological model.
By making precise measurements of the early Universe and comparing this with the Type 1A supernovae observations we can test whether the theory gives a consistent picture of the rate of accelerating expansion at present. On this point, the Planck mission found a significant tension between these two observations, which would mean that the standard model of cosmology may need to be slightly modified or potentially entirely redrawn.
This observation has led to a reinvigorated examination of Einstein’s theory of gravity and potential alternatives that may better explain the evolution of the Universe, and the role of dark matter in galaxies.
‘Understanding the Universe’ public conference
Leading figures in the cosmology community are meeting in Malta this week to discuss potential paths to reviewing the standard model of cosmology and discuss other issues in current cosmological models.
Given the strong public interest in this work, a public conference entitled ‘Cosmology@Malta 2019: Understanding the Universe’ is being held at the University of Malta’s Valletta campus on Thursday at 7pm.
Two of the speakers, Prof. Mariam Bouhmadi Lopez from the University of Bilbao, Spain, and Prof. Emmanuel Saridakis from the National Technical University of Athens, Greece, will discuss our current understanding of the Universe and outstanding problems that the community is working on.
The event is being held by the University of Malta’s Institute of Space Sciences and Astronomy in collaboration with the Faculty of Science and Malta Café Scientifique.
Admission is free but registration is mandatory as space is limited. To secure a place, register at the link below.
Dr Jackson Levi Said is a lecturer at the University of Malta’s Institute of Space Sciences and Astronomy.