The Standard Model stands as one of the most remarkable achievements of modern physics, encapsulating our current understanding of matter’s most fundamental constituents and interactions. This theoretical framework elegantly describes a symphony of 17 particles and 4 forces that shape our physical reality.
And yet, like any scientific theory, the Standard Model is incomplete. As we delve further into matter’s fundamental workings, great puzzles emerge that are beyond the Standard Model’s scope. Tantalising concerns regarding antimatter, dark matter, quantum gravity, and the origins of cosmic structure entice scientists to venture into unexplored theoretical area.
The answers to these mysteries have the potential to revolutionise our understanding of the quantum realm and the cosmos in general. Let us look at some of the most difficult puzzles that researchers are attempting to answer.
Where Has All the Antimatter Gone?
Of all the mysteries about our cosmic origins, the striking disappearance of antimatter ranks among the most confounding. In the infant moments of the Big Bang, matter and antimatter emerged in perfect symmetry, only to later fall radically out of balance.
Why does our universe, as we observe it today, appear to be dominated by matter while antimatter seems to have all but vanished?
Today, antimatter is extremely rare, accounting for just tiny amounts of natural radiation. However, the unbalanced leftover matter went on to build everything we see in the universe, including stars, galaxies, and life itself. Identifying the mechanism that shattered the original symmetry could provide fundamental insights into the evolution of cosmic structure.
Physics says that matter and antimatter should have annihilated each other in equal ratio in the early universe, leaving only energy. Yet here we are, constituted entirely of stuff. Experiments like CERN’s ALPHA collaboration, which catches and investigates elusive antimatter particles known as antihydrogen, are motivated by the need to understand why nature exhibits such severe asymmetry.
To solve the antimatter puzzle, the Standard Model may need to be expanded to include additional processes that could have shifted the balance in favour of matter after the Big Bang. Discovering the source of this asymmetry is one of the most pressing questions at the junction of cosmology and particle physics.
What Makes up 95% of the Universe?
Beyond the ordinary matter of the Standard Model lies an even more perplexing puzzle, the true identity of dark matter and dark energy. Together, these invisible components make up a staggering 95% of the universe’s total mass and energy.
The existence of dark matter is inferred through its gravitational pull on galaxies and clusters, which proves there is far more mass than we can see. Directly detecting dark matter particles has continued to confound scientists for decades. Leading hypotheses suggest axions or WIMPs may account for this missing mass, but these candidates remain unproven.
Even more mysteriously, dark energy appears to drive the accelerating expansion of the cosmos through an unknown mechanism. Unravelling the nature of these two giant unknowns would transform our comprehension of cosmic evolution and the role of matter and energy at the largest scales.
Experiments such as XENON, LUX-ZEPLIN, and SuperCDMS lie at the cutting edge of the hunt for dark matter, while projects like DESI map galaxies to better understand dark energy. We may need to extend physics beyond the Standard Model into new theoretical territory to make sense of these enormous cosmic puzzles.
How does Gravity Exactly Work?
Of the four fundamental forces, only gravity remains aloof from the Standard Model, refusing to reconcile with the quantum rules governing particles. Developing a quantum theory of gravity ranks among the holy grails of modern physics.
The hypothesised graviton particle would neatly align gravity with the other forces by acting as a mediator of gravitational interactions. While not yet observed, gravitational waves – ripples in spacetime from violent cosmic events – provide evidence that gravitons likely exist.
The hypothesis of the graviton received a resounding endorsement with the groundbreaking discovery of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO). These ripples in the fabric of spacetime caused by cataclysmic cosmic events offered firsthand evidence of gravitational waves’ existence and strengthened the graviton’s theoretical basis.
Incorporating gravity into the quantum fold could also aid in explaining events such as the singularity at the centre of a black hole. Formulating a full theory of quantum gravity would represent a significant advance in our understanding.
What Happened Just After The Big Bang?
Perhaps the greatest mystery of all lies at the origin of our universe. The Standard Model falls silent when confronted with the question: what sparked the Big Bang? Researchers are left to speculate about the precursor to our cosmic genesis.
Leading explanations imply that our observable world arose from a quantum fluctuation in an everlasting inflationary multiverse, a realm that extends endlessly beyond what we can perceive. Other radical hypotheses claim that our universe grows and contracts in “Big Bounce” cycles. Perhaps the Big Bang was not a beginning at all, but rather the emergence of a previously collapsed state.
What comes after the Standard Model?
In their endeavour to answer the ultimate question mark, theorists have plenty of ingenuity but little data. Our current physics theories just cannot investigate the severe conditions around the Big Bang’s initial singularity. Before we can understand the early moments of genesis, we must wait for further breakthroughs, which could come from string theory or quantum loop gravity.
