What happened at time t = 0? is still anybody’s guess. At least, earlier observations of Planck’s radiation had suggested the first generation of stars were bursting into life by about 420 million years after the Big Bang. However, scientists from Europe’s Planck satellite mission now say the first stars lit up the Universe later than was previously thought…
The Planck time is the time it would take a photon moving at the speed of light to travel across a distance equal to the Planck length – the scale at which classical ideas about gravity and space-time cease to be valid, and quantum effects dominate; the ‘quantum of length’; the smallest spatial measurement with any meaning, roughly equal to 1.6 x 10-35 m – about 10-20 times the size of a proton.
Anyway, the Planck time is the ‘quantum of time’, the smallest measurement of time that has any meaning, and is equal to t = 10-43 seconds. No smaller division of time has any meaning. Within the framework of the current laws of physics, we can say only that the Universe came into existence when it already had an age of 10-43 seconds.
General Relativity breaks down at the Planck time t = 10-43 s. So, progressing back from that point on to earlier times requires a theory of Quantum Gravity – a field of passionate cutting-edge physical research. Inflation remains without a firm grounding until this very early era is better understood. And however limited progress has been made with quantum cosmology, the new all-encompassing M-theory offers several intriguing lines of enquiry.
What is becoming clear from the Planck investigation/survey is that the simplest models for how the super-rapid expansion of the Universe might have worked may no longer be tenable, suggesting some exotic physics will eventually be needed to explain it.
Professor George Efstathiou and his team of the Planck Science Collaboration have made the most precise map of the “oldest light” in the cosmos.
Planck’s new data now indicates this great ignition was well established by some 560 million years after it all got going.
Although a difference of 140 million years later might not seem very significant in the context of the 13.8-billion-year history of the cosmos, it is actually a very big change in our understanding of how certain key events progressed at the earliest epochs.
The assessment is based on studies of the “afterglow” of the “Big Bang”, the ancient light called the Cosmic Microwave Background (CMB), which has been washing over the Earth since the beginning of the Universe.
Mapping the CMB
The European Space Agency’s (ESA) Planck satellite mapped this “fossil” light between 2009 and 2013. The gathered data contains a wealth of information about the conditions in the early Universe, and can even be used to work out its age, shape and do an inventory of its contents. Scientists can also probe it for very subtle “distortions” that tell them about any interactions the CMB has had on its way to us.
The map was produced using the data from the European Space Agency’s Planck probe-scope positioned at the L2 Earth/Sun Lagrange point – 1.5 million kilometres away in the vast depths of space. Planck scanned the entire sky, and advanced boffinry was used in order to purge its imagery of light emitted by such stuff as distant stars or galaxies.
One of the distortions or anisotropies would have been imprinted when the infant cosmos underwent a major environmental change known as re-ionisation. In the aftermath of the “Big Bang”, when cooling neutral hydrogen gas permeated all space, the Universe was re-energised by the ignition of the first stars.
These hot giants would have burnt brilliant but brief lives, producing the very first heavy elements. At the same time, they would also have “fried” the neutral gas around them, ripping electrons off the hydrogen atoms and leaving protons.
The passage of the CMB through this maze of electrons and protons would have resulted in it picking up a subtle polarisation.
No-one knows the exact timing of the very first individual stars. All Planck’s new timing does is tell us when large numbers of these stars had gathered into galaxies of sufficient strength to alter the cosmic environment.
By definition, this puts the ignition of the “founding stars” well before 560 million years after the Big Bang. Quite how far back in time is uncertain. Perhaps, it was as early as 200 million years. It will be the job of the next generation of observatories like Hubble’s successor – the James Webb Space Telescope – to try to find the answer.
The new Planck result is contained in a host of recent papers posted in the Planck Legacy Archive on the ESA website. These papers accompany the latest data release from the Planck satellite that can now be used by the wider scientific community.
Two years ago, the data dump largely concerned interpretations of the CMB based on its temperature profile. Today, the CMB’s polarisation features takes centre-stage.
Although, the Planck satellite did not find direct evidence in the CMB’s polarisation for inflation – the super-rapid expansion of space that is thought to have occurred a few fractions of a second after the initial event of the “Big Bang”, all the data – temperature and polarisation information – is consistent with that theory, and the precision measurements mean new, tighter constraints have been put on the likely scale of the inflation signal, which other experiments continue to chase.
From that point on, it just looks like the simplest models for inflation are now ruled out…