When we look out at the night sky across vast, cosmic distances using our most sensitive and advanced telescopes, we look back in time. Einstein taught us that light has a finite speed; therefore, it takes light longer to travel to us the further one looks.
Thanks to this, cosmologists have been able to see light dating back to about 14 billion years ago. This light reveals something spectacular and mysterious – the Universe is filled with a sea of energy, waves of tangled electrons and photons in the form of a hot fluid, known as a plasma. We call this plasma the Cosmic Microwave Background (CMB).
We cosmologists have precise theoretical and observational evidence that this plasma underwent gravitational collapse with the aid of an invisible form of matter, called dark matter, forming the first stars and eventually forming the organised superstructure that inhabits the current Universe.
However, a mystery still lurked: the properties of this sea of energy seem to originate from what Einstein called “spooky action-at-a-distance” - objects communicating with each other at instantaneous speeds across ridiculously large distances. This is known as the horizon problem.
In 1981, my colleague, Alan Guth of MIT, proposed an elegant solution to this problem. The idea was to introduce a new player called the inflation field that filled the Universe, and whose energy caused space to expand extremely rapidly. The repulsion that arises due to gravitational effects caused by inflation neatly solves the horizon problem – it makes those regions that we thought to be spookily interacting subject to the weird, but well-confirmed, laws of quantum physics.
The theory of cosmic inflation also provided us with a physical mechanism that answers a question that had long troubled cosmologists: how did the seeds of structure originate in a seemingly featureless primordial Universe over 14 billion years ago?
According to the theory, it was the very tiny quantum vibrations of the inflation field that acted as the seeds of the vibrations we see in the CMB today. Think about it. This means that the vast distribution of galaxies spanning across trillions of kilometres of space emerged from microscopic subatomic quantum fluctuations that occurred at the earliest stages of the Universe.
When I was a younger scientist, I became interested in the field of particle physics and cosmology by what appeared to be a preposterous question: what is the connection between the largest and smallest things in the Universe?
Cosmic inflation gives us a clue to this but two unresolved and apparently unrelated mysteries remain. First, we don’t know the origin and identity of this inflation field. All we know is that it behaves like a particular type of field known as a scalar field and that it permeates the largest distances imaginable.
Another serious problem for inflation is that the very quantum fluctuations that give birth to us can grow without being bound by infinity. And that poses a problem: some theorists would like to get rid of the infinity bathwater and keep the baby of cosmic structure. These contradictions, called ‘instabilities’, have proven difficult to reconcile over the last two decades.
A further mystery, which reigns in the microscopic domain, concerned the origin of mass found in every electron and nuclei on our planet. In the 60s, Peter Higgs, Tom Kibble, François Englert, Robert Brout, Carl Richard Hagen and my professor Gerry Guralnik, predicted that a mysterious particle, now dubbed the Higgs boson, and its corresponding field of energy that pervades the Universe, could interact with massless matter and give it its weight.
This particle was later detected at the Large Hadron Collider at CERN in 2012, and a Nobel Prize awarded to Peter Higgs and François Englert a year later.
But despite these successes, there is a problem with the Higgs - it shares a similar instability with inflation, this time in the very quantum fluctuations of the Higgs that give us our mass.
In recent years, physicists Mikhail Shaposhnikov postulated that perhaps the microscopic Higgs boson could be behind the omniscient, primordial inflation. But how does one reconcile this picture of micro and macro?
The key is to realise that the Higgs is fundamentally a fieldandparticle which, like a fluid, can permeate all of space. It’s the wave-like vibrations of the Higgs fields organising themselves into microscopic, localised quantum fluctuations that are identified as the Higgs particle.
So, could the Higgs field have permeated the early Universe and given rise to the phenomenon of cosmic inflation? If this idea of Higgs-Inflation is correct it would represent a breathtaking cosmic-microscopic unification.
However, there is a serious elephant in the room that continues to plague both ideas. They rely on quantum fluctuations to create cosmic structure and endow mass, respectively. The problem is that these very quantum effects end up rendering the theories problematic by generating infinities in quantities that we measure to be finite.
For now, the solution remains elusive. However, we physicists must courageously, and humbly, continue down the rabbit hole of potential conundrums that lurk in any theory.
Read more about cosmology:
