Ripples in the universe from the Big Bang
A team of US astronomers, after years of working in the Antarctic, say they have found long-awaited evidence for the theory that the Universe underwent a period of rapid “inflation” in the very first moments of its existence. They also provide the most direct evidence for the existence of gravitational waves, and thus gravitons, which were predicted by Albert Einstein almost a century ago.
What is the Big Bang theory?
Dr David Krofcheck is a particle physicist who believes that the Big Bang is how matter came about. In this video, David explains how the universe as we know it came about – the Big Bang produced all of the hydrogen and most of the helium present in the universe. He describes the evidence that supports the Big Bang theory.
Point of interest:
The next time you produce, collect, and ‘pop’ a sample of hydrogen in the lab, realise that it was formed about 14 billion years ago in an instant of time after the Big Bang.
Proof of cosmic inflation
In 1979, cosmologist Professor Alan Guth, then a young physicist at Stanford University, had theorised that immediately following the moment of the Big Bang the Universe underwent a process of inflation – an ultra-rapid expansion that took it from subatomic size to a scale so vast that the human mind can barely conceive the distances involved almost instantaneously. Although widely accepted, for three decades the theory has lacked proof, it was fitting then that the principal investigator of the team, astronomer Professor John Kovac from the Harvard-Smithsonian Center for Astrophysics, would visit Professor Alan Guth as one of the first people outside of the research team to be informed that proof was finally at hand before the news went public.
Professor Kovac led a team of radio astronomers who have been monitoring the skies over the South Pole since 2010 using an ultra-sensitive microwave receiver known as BICEP2.
They were able to detect subtle patterns, a type of light polarization called "B-modes", in the cosmic microwave background – the afterglow of the Big Bang which saturates the universe, which they believe could only be caused by the gravitational waves predicted by Einstein. The waves also provide proof of Professor Guth’s theory of cosmic inflation, and apparently open “a window into the unification of the fundamental forces of nature”.
The existence of gravitons
In an interview with Mike Wall, a Senior Writer at space.com, Professor Kovac said an implication of “seeing gravitational waves at the strength that we've seen them is that, yes, in fact, that is the energy scale of inflation. And another thing that is an important aspect of this that is quite fundamental is that the production of these gravitational waves during the inflationary process relies on the interaction of quantum mechanics and general relativity. It actually relies on there being gravitons, the gravitational field being quantized. And that is something of which we'd had no prior direct evidence.”
B-modes the “smoking gun”
In an interview with the Science Media Centre, Professor Richard Easther, HOD of physics at the University of Auckland, said, "The word is that the BICEP team has discovered B-modes, specific patterns in the polarisation of the microwave background. B-modes are the "smoking gun" of inflation, and their strength is tied to the energy density of the universe during inflation – if the rumours hold up, we could soon know that inflation did happen a trillion, trillion, trillionth of a second after the Big Bang, and at energies a trillion times beyond the reach of the Large Hadron Collider.
"There would still be several steps to nailing it down – not all B-mode signals must come from inflation, and not all inflationary models must produce detectable B-modes. And there's one more thing: the B-mode is sourced by gravitational waves – ripples in the fabric of space – generated during inflation.
"Gravitational waves are a key prediction of Einstein's General Relativity and their existence is still not conclusively confirmed. Even so, gravitational waves are getting second billing to what we will learn about the early universe: we will know that inflation is a compelling answer to cosmology's initial-conditions problems, and humankind will have looked directly into the cosmic dawn.”
After painstakingly checking and rechecking their measurements, the US team made the results public on 17 March 2014 at a press conference at the Harvard-Smithsonian Centre for Astrophysics.
The discovery, if confirmed by other teams of astronomers, is widely-tipped to be worthy of a Nobel Prize. At the very least, being able to observe the signature of gravitational waves from the Big Bang will open a new chapter in astronomy, cosmology and physics.
Nature of science
This is an good illustration of the tentative nature of scientific knowledge, how it is subject to change in the light of new evidence or new interpretation of existing evidence.
Update
In early 2015, after further studies were completed, the combined data from South Pole experiment BICEP2 and Planck probe confirmed that Galactic dust was confounding the signal. It was announced that the signal was actually caused by interstellar dust, likely from the Milky Way. The team of astronomers that had reported evidence for gravitational waves from the early Universe withdrew the claim.
“When we first detected this signal in our data, we relied on models for Galactic dust emission that were available at the time,” said John Kovac, in the January 2015 ESA press release. “These seemed to indicate that the region of the sky chosen for our observations had dust polarisation much lower than the detected signal.”
Further studies need to be undertaken to see if evidence of gravitational waves in the microwave background can be found.
Activity idea
The BICEP (Background Imaging of Cosmic Extragalactic Polarization) 2 is a telescope located near the South Pole. Use the article Light and telescopes to learn more about how telescopes detect different wavelengths of light in space.
Useful links
See this special collection Waves from the Big Bang from Nature News that provides a comprehensive and up-to-date coverage of the breakthrough and its aftermath.
ESA press release from January 2015 Planck: gravitational waves remain elusive.
The 2018 book Losing the Nobel Prize: A Story of Cosmology, Ambition, and the Perils of Science’s Highest Honor by Professor Brian Keating tells the story of BICEP2's detection and the ensuing scientific drama.
Findings that disproved the early announcments: Cowen, Ron (30 January 2015). Gravitational waves discovery now officially dead. Nature. DOI:10.1038/nature.2015.16830 Corpus ID: 124938210. Read more about this from space.com in Evidence for Cosmic Inflation Theory Bites the (Space) Dust.
References
Wall, M. (21 March 2014). Confirming the Big Bang's Inflation: Q&A with Study Leader John Kovac. Retrieved from www.space.com/25162-gravitational-wave-discovery-kovac-interview.html.
