At a cost of €700 million, the European Space Agency (ESA) Planck probe is one of the most sensitive instruments that has been used to analyse the nature of the Universe.
The Planck probe has been in operation for nearly 4 years. Its findings have given us the most detailed picture of the Cosmic Microwave Background Radiation – the residual radiation of the Big Bang – yet.
Designed to measure the Cosmic Microwave Background Radiation (CMBR), the afterglow of the Big Bang, the findings from the probe’s readings - which are significantly more detailed than the previous Wilkinson Microwave Anisotropy Probe (WMAP), challenge some aspects of our model of the Universe.
The probe measures the CMBR - the oldest light in the Universe, which was emitted when it was 380,000 years old. As the Universe expanded, this light has stretched to microwave wavelengths, and is equivalent to a temperature of 2.7 Kelvin, or -271.15 degrees Celsius.
This radiation shows the small temperature fluctuations that occurred during the Big Bang and thus provide cosmologists and astrophysicists with what is essentially a map of the early Universe with fluctuations representing different densities, forming a framework from which the stars and galaxies that populate the Universe were able to form.
Planck’s new detailed map has been able to confirm the standard model of cosmology with a very high degree of accuracy, and has given cosmologists an extremely detailed map of the temperature fluctuations when compared to the previous readings.
The results support the theory of cosmic inflation; the idea that during the first few seconds of the Universe’s existence it expanded at an extremely high rate before slowing down, which helps explain the size of the Universe.
Inflation also predicts that quantum fluctuations occurring during this rapid expansion would be amplified, which are reflected in the temperature fluctuations of the CMBR, and gave rise to the existence of matter. However, the Planck data does challenge a fundamental assumption about our model of the Universe - the cosmological principle.
The cosmological principle is the assumption that the Earth does not occupy a unique or privileged location in the Universe as a whole. By that assumption, on sufficiently large scales the properties of the Universe should be homogenous, and be the same for all observers at any point. This is revealed by the asymmetry of the map.
The opposite hemispheres of the sky have different average temperatures, which indicate that the principle may need to be revised, or new physics must explain the anomaly. Additionally, a cold spot has been detected that occupies a large space in the sky.
A possible way to explain these abnormalities is by doing away with the cosmological principle, and instead proposing that the Universe is not the same in all directions on a larger scale. If this is the case, the photons of the CMB may have traversed a more complex path through the Universe which would have resulted in the asymmetries that have been discovered.
Anomalies aside, the data Planck has gathered thus far confirms most other predictions of the standard model of cosmology. The age of the universe is now estimated to be approximately 13.8 billion years, 100 million years older than previously thought, and the Hubble Constant, that is, the rate of expansion of the Universe, has been redefined to be 67.15 kilometres per megaparsec, a much smaller value than the previously recorded 69.32.
Other revisions were made in terms of the composition of the Universe. The matter, such as that which composes the stars and planets, accounts for only 4.9% of the energy density of the Universe, whereas dark matter, detectable only by its gravity, makes up 26.8%. Dark energy, the ill-understood energy that drives the accelerated expansion of the universe, makes up 68.3%, and is thus the main constituent of the energy density of the Universe.
The data analysed so far is only from the first 15.5 months of the probe’s operation, so there is still plenty more to be released. The team expect that these will be released sometime in early 2014.
It therefore appears that the Planck probe has allowed us to become more confident in many of our assertions about the way the Universe works, but will force us to rethink our positions in some other aspects, or come up with new physics to explain the anomalies that it has now confirmed exist, which were only hinted at by the previous WMAP.
These anomalies only add to the many unresolved questions of cosmology, the most pressing of which is perhaps the nature of dark energy. We know it exists due to observed increase in the rate of expansion of the Universe, however very little about it is currently known or understood.
Likewise, dark matter, another major component of the Universe we have not directly detected, still eludes cosmologists. A nobel prize certainly awaits anyone who discovers more about these two features which make up the majority of the energy density of the Universe.
It was Enrico Fermi, one of the great physicists of the 20th century, that said:
“If the result confirms the hypothesis, then you've made a measurement. If the result is contrary to the hypothesis, then you've made a discovery.”
These anomalies that have contradicted the previous hypothesis may necessitate the revision of the current theory, but that will only lead to an exciting new picture of the laws that govern the Universe in which we live.