“How could the Universe we see around us be created by an explosion?” This is a question often asked by those puzzled by the scientific consensus, the standard model of cosmology, which tells of our entire Universe bursting forth in a single dramatic event, the Big Bang. Modern thinking suggests that the Big Bang event was not a completely uniform eruption of energy. Immediately after the Big Bang, minute regions of slightly different density flickered across the seething chaos. These tiny irregularies became the foundations of all the structures we see now before a rapid period of cosmic inflation stretched them to significant size. Effectively, these little variations in temperature and density were the seeds of the stars and galaxies of today. A European Space Agency space telescope has now mapped these tiny and ancient fluctuations more accurately than ever before, mostly confirming established theories- but hinting of mysteries.
Acquired by ESA’s Planck space telescope, this the most detailed map ever created of the cosmic microwave background (CMB) imprinted across the Universe when it was a mere 380 000 years old. Back then, the young Universe was filled with a hot dense “soup” of interacting protons, electrons and photons at about 2700ºC. When condition allowed protons and electrons to join together to form hydrogen atoms, the photons were free to travel. As the Universe has expanded, these photons have been stretched out to ever longer wavelengths. Today we see them as microwave wavelengths, equivalent to a temperature of just 2.7 degrees above absolute zero.
This new map of the cosmic microwave background shows tiny variations in temperature corresponding to regions of higher and lower density. These variations gave rise to the structures we see today. Had these little patches of unevenness not existed, then we would not either. A completely uniform Big Bang would have led to an utterly boring Universe, no galaxies, no stars, no planets, no people, empty but for a thin and even mist of cold hydrogen atoms. Understanding these fluctuations is important to researchers investigating the origins of the Universe, mapping the early Universe more accurately than ever before is the Planck observatory’s raison d’etre.
Planck’s new map confirms the standard model of cosmology to a previously undreamed level of accuracy, so the previously accepted values of some of the Universe statistics have been slightly adjusted. Our best measurements before Planck came from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) which operated between 2001 and 2010. According to Planck’s results:
- Age of the Universe 13.82 billion years (previously accepted age: 13.78 billion years). The Universe has just got 40 million years older!
- Normal matter, that is the stuff that makes up you, me and everything else we can see, makes up 4.9% of the material in the Universe compared to the previously accepted value of 4.6%.
- Dark matter, the mysterious invisible and intangible ‘something’ that gravitationally dominates the galaxies, makes up 26.8% of the Universe (it was thought to compose 24.0% of the Universe)
- Dark energy, the even more enigmatic entity which fills space and is accelerating the expansion of the Universe, makes up 68.3% of everything (WMAP: 71.4%). Dark energy’s existence has only been known about since 1998; it is strange to think that we only discovered the vast majority of the Universe less than 20 years ago!
- The Hubble Constant, the Universe’s current rate of expansion has been reduced to 67.15 km/s/Mpc (WMAP: 69.32km/s/Mpc)
The results from Planck, confirming most of the standard model, are a triumph of science but…the precision of Planck’s map is so high, it has uncovered some peculiar features of the Universe that cannot be explained by today’s science:
- The fluctuations in the CMB temperatures are not quite what the standard model predicted.
- The standard model assumes that the Universe should be broadly similar no matter which direction we look. This is called the Cosmological Principle. Planck’s results confirm WMAP findings that the sky is asymmetric. Average temperatures on one hemisphere of the sky are slightly higher than those on the other, apparently consigning the Cosmological Principle to the wastebin of history.
- Stranger still, a large cold spot extends over a patch of sky. Again, the WMAP satellite’s data had suggested this existed but it had been thought to an artefact created by the measurement process. Planck has confirmed this anomaly to really exist.
Astronomers are racing to to explain these anomalies. Perhaps the Universe is in fact not actually the same in all directions, so the light rays from the CMB may have taken a more complicated route through the Universe to us than previously thought, resulting in some of the unusual patterns observed today. Alternatively, maybe dark energy does not act evenly everywhere. Or did cosmic inflation happen evenly across the Universe? The great Isaac Asimov once said “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…'” Thanks to Planck (and the European taxpayers who paid for the mission, the satellite alone cost £515 million ), science has some enormous curiosities to explore.
(Article by Colin Johnston, Science Communicator)