“It is undeniable that we are profoundly puzzled, especially when it comes to the first fraction of a second that followed the Big Bang,” wrote theoretical physicist Dan Hooper, author of The Edge of Time in an email to The Daily Galaxy–Great Discoveries Channel. “I have no doubt that these earliest moments hold incredible secrets, but our universe holds its secrets closely. It is up to us to coax those secrets from its grip, transforming them from mystery into discovery.”
The Big Bang Singularity
On Sept 14, 2015 after traveling for more than a hundred million years, the aftershocks from a massive collision in a galaxy far, far away finally reached Earth allowing scientists to detect a long-predicted twist in light from the the state of infinite density called the Big Bang singularity that represent the beginning of time predicted in Einstein’s general theory of relativity and the first image of ripples in the universe called gravitational waves –ripples in the fabric of spacetime, that distort the very geometry of space itself.
These ripples –moving and periodic variations in the curvature of space.–were created when two enormous black holes about twenty-nine and thirty-six times as massive as the Sun crashed into each other and merged about 1.3 billion years ago– tripping alarms at two ultra-sensitive detectors called the LIGO-Virgo collaboration. Since the first discovery, a total of 23 confirmed gravitational-wave detections have been made to date across three observing runs. These LIGO discoveries were the subject of the 2017 Nobel prize in physics.
Epoch of Hyperfast Inflation
Detection of this epic event that permeates the universe as a diffuse, persistent hum, sent text messages flying across the planet. The discovery yielded information needed to make a groundbreaking new measurement of one of the most important numbers in astrophysics: the Hubble constant, which is the rate at which the universe is expanding –the epoch of hyperfast inflation created a background of gravitational waves that still ripple throughout all of space and time today–as well as the possible source of dark matter in the universe. Whatever the dark matter consists of, suggests Hooper , it was almost certainly formed in the first fraction of a second after the Big Bang.
“Although this epoch of inflation lasted only a little longer than a millionth of a billionth of a billionth of a billionth of a second,’ notes Hooper, “it left our universe utterly transformed. In many ways, one can think of the end of inflation as the true beginning of the universe that we live in.”
Fractions of a Second After the Big Bang
The events that lie in the most distant past, and closest to the Big Bang remains hidden from our view, buried beneath as-yet-impenetrable layers of energy, distance, and time. “But reaching even farther back in time—into the first seconds and fractions of a second after the Big Bang—we transition from having incomplete information to having essentially no direct observations on which we can confidently rely, writes Hooper in The Edge of Time. “Our understanding of this period of cosmic history is, in many respects, little more than an informed guess, based on inference and extrapolation. Yet it is clear that these first moments are the key to many of our most urgent and enduring cosmic mysteries. Understanding this era is essential to understanding our universe.”
Physicists think it might be possible to someday see primordial gravitational waves left over from the first fractions of a second after the Big Bang. Such waves would allow researchers to look back further than ever before toward the birth of the universe. “The earliest light that reaches us as observers was emitted when the universe was 380,000 years old,” says Nergis Mavalvala from the Massachusetts Institute of Technology. “Whereas gravitational waves have been streaming to us since the earliest moments after the big bang.” The signatures of such waves should be so incredibly faint that only so-called third-generation gravitational-wave detectors, such as the planned Cosmic Explorer in the U.S. or the Einstein Telescope in Europe, would be capable of detecting them.
“Modern cosmology has been incredibly successful at explaining the expansion and evolution of the universe from just fractions of a second after the Big Bang – but four fundamental puzzles remain,” says Hooper, “the biggest being the twin mysteries of dark matter and dark energy, which have never been directly observed but are thought to make up 95% of all matter and energy in the universe.”
Hooper believes that the answer to these and other mysteries – including the lack of anti-matter in the universe – lies in the very first fractions of a second after the Big Bang “triggering an era of so-called cosmic inflation when the universe expanded much faster than the speed of light – that lasted for a little over one millionth of a billionth of a billionth of a billionth of a second.”
Enter Dark Matter
According to Hooper ,”our knowledge of dark matter is akin to our knowledge of air in the 1850s – we knew it was there but we didn’t know what it was made of. Similarly, astronomers can infer the existence of dark matter based upon its gravitational influence on objects we can see. But dark matter does not interact with light – hence the “dark” – and we do not yet know what it is.”
Dark energy is even more mysterious but it could help explain one of the biggest mysteries of modern cosmology: the accelerating expansion of the universe.”
Enigma of Dark Energy
“What we really do know for sure is that our universe is expanding faster today than it was in the past. And that’s something we can’t explain using Einstein’s Theory of Relativity if the universe was full of only things like ordinary matter, or light,” said Hooper. “To make a universe or a piece of space to grow faster as time progresses you really need something else, a form of energy that occupies space and doesn’t get diluted as space expands.”
“Finding out that the universe is going faster over time is just as surprising as you throwing up a baseball and you watching it rocket off and speeding up away from the Earth,” said Hooper about the phenomenon the scientist believe to be dark energy. “That requires some extra thing to be pushing that baseball upward. And in the case of our universe it requires some extra thing, namely dark energy, whatever that is, to make our universe grow faster.”
“There are things that we see about our universe that we can only explain – at least for the moment – if we postulate that there was an era very, very early in our universe’s history where space expanded extremely dramatically in a giant, sudden burst,” said Hooper. “These are bigger numbers than you can ever wrap your head around but you can just think of the universe growing almost instantly to a vast, vast volume from a tiny little space. If that’s true, and a lot of cosmologists think it is very likely to be true, then the Big Bang didn’t just happen once, but this inflating space in a sense pops off these kind of bubble universes one after the other.”
Ancient Black Holes Would Give Access to Hidden Physics
Primordial black holes (PBHs) are never before seen objects that are considered a dark horse candidate for dark matter—the invisible, unidentified something that makes up most of the matter in the universe. the mass discrepancy identified in the recent LIGO observations, between the measured mass of the merging objects observed by LIGO and masses of black holes observed in conventional means in the Milky Way galaxy and other nearby galaxies.
“Ancient black holes would give us access to physics we would never otherwise be able to do,” wrote Hooper, in an email to The Daily Galaxy. “If primordial black holes are real, they’d have potential to solve a whole host of the biggest problems in cosmology, not the least being the mystery of dark matter, considered to be the backbone to the structure of the universe.
Somehow, more matter than antimatter must have been created in the first fraction of a second of our universe’s history, writes Hooper. “We don’t know how or when this came to pass, or what mechanism was responsible. But somehow, something about the conditions of the early universe made it possible for the seeds of atoms—and all of chemistry, including life—to survive the heat of the Big Bang.”
Stephen Hawking’s Primordial Black Holes
Almost a half-century ago, cosmologist Stephen Hawking proposed that PBHs could have sprung fully formed from regions of the infant universe that were especially dense with matter. “The average density of primordial black holes in the universe must be less than about two hundred per cubic light-year”, suggested Hawking in Black Holes and Baby Universes. “The local density in our galaxy could be a million times higher than this figure if primordial black holes were concentrated in the “halo” of galaxies—the thin cloud of rapidly moving stars in which each galaxy is embedded—rather than being uniformly distributed throughout the universe. This would imply that the primordial black hole closest to the earth is probably at least as far away as the planet Pluto.”
Density Fluctuations in the Very Early Universe
Since Hawking’s proposal, the idea’s popularity among astrophysicists and cosmologists has wildly waxed and waned. Today, in the absence of direct evidence for their existence, reports Nola Taylor Redd for Scientific American — these ancient black holes theorized to have formed from density fluctuations in the very early universe, could still exist today and could explain the mass discrepancy identified in the recent LIGO observations–are seen by many researchers as a hypothesis of last resort, only to be considered when no other scenario readily fits observations. The possibility that PBHs are real and widespread throughout the universe cannot yet be dismissed, however—especially as searches for other dark matter candidates come up empty.
Image credit: LIGO Observatory