Visible and dark matter evolved together after the big bang, claims a new study

For centuries, the vastness of the universe has captivated the minds of scientists and philosophers alike. One question that has long puzzled physicists is the existence of dark matter, an invisible substance that seemingly permeates the universe, exerting its gravitational influence on the visible stars and galaxies we observe.

What lies behind the dark side of the universe

Pran Nath, the Matthews Distinguished University Professor of physics at Northeastern University, shares his thoughts on this mysterious phenomenon.

“95% of the universe is dark, is invisible to the eye. However, we know that the dark universe is there by [its] gravitational pull on stars,” Nath explains.

Despite its elusive nature, dark matter’s presence is undeniable, as evidenced by its gravitational effects on the visible universe.

Relationship between dark and visible matter

While the existence of dark matter has been widely accepted, the relationship between the visible and invisible domains, particularly in the early stages of the universe’s formation, remains an open question.

Traditionally, it was assumed that these two sectors evolved independently of each other. However, Nath and his team have challenged this notion, proposing that the visible and hidden sectors may have co-evolved in the aftermath of the Big Bang, with significant implications for the universe’s development.

To test this hypothesis, Nath and Ph.D. candidate Jinzheng Li conducted a series of computer simulations, introducing feeble interactions between the visible and hidden sectors in their models of the Big Bang.

While these interactions were not substantial enough to affect the outcomes of particle accelerator experiments, the researchers sought to understand their impact on the visible sector as a whole, from the moment of the Big Bang to the present day.

Temperature enigma of the hidden sector

The results of their simulations, published in a paper titled “Big Bang Initial Conditions and Self-Interacting Hidden Dark Matter” in Physical Review D, were nothing short of remarkable.

Even with minimal interactions between the two sectors, Nath and Li discovered that dark matter’s influence on visible matter could have a significant impact on observable phenomena, such as the Hubble expansion, which describes the expanding nature of the universe.

One crucial variable in their models was the temperature of the hidden sector during the Big Bang. While the visible sector is believed to have started out extremely hot at the moment of creation, the initial temperature of the hidden sector remained uncertain.

Nath and his team modeled both scenarios — a hot and a cold hidden sector — and found that, despite significant differences between the models, both were consistent with the visible universe we observe today.

Pushing the boundaries of experimental capabilities

Rather than viewing this finding as a limitation of their experiment, Nath emphasizes that it highlights the need for more precise experimental tools.

He mentions the Webb Telescope as an example of the next generation of instruments that will enable researchers to make more accurate observations and shed light on the true nature of the hidden sector’s initial conditions.

Ultimately, the goal of this modeling work is to better understand the universe and our place within it. As Nath eloquently puts it, “What’s the significance of this? Human beings want to find their place in the universe. And more than that, they want to answer the question, why is there a universe? And we are exploring those issues. It is the ultimate quest of human beings.”

How visible and dark matter shaped the universe

In summary, this fascinating research highlights the complex relationship between dark matter and visible matter in the universe.

By challenging the assumption of independent evolution and introducing feeble interactions between the two sectors in their Big Bang models, the scientists have opened up new avenues for understanding the universe’s origins and development.

As experimental capabilities continue to advance, the questions posed by their models will find answers, bringing us closer to unraveling the ultimate mysteries of our cosmic existence.

This pursuit of knowledge represents the fundamental human quest to comprehend our place in the universe and the very reason for its existence.

The full study was published in the journal Physical Review D.

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