The Universe is expanding at an ever-accelerating rate, and scientists are still grappling with what could be driving this mysterious force.
Could gravity be behaving differently on cosmic scales, or is the vacuum of space creating a form of negative pressure that defies our current understanding?
For now, the term "dark energy" serves as a placeholder for this unknown force, leaving room for all sorts of speculation about what might be lurking in the intergalactic shadows.
Naman Kumar, a PhD student at the Indian Institute of Technology, has offered some intriguing ideas in a pair of recently published papers. One of his proposals suggests that our Universe might not be as isolated as it seems.
If we wind the clock back far enough, we reach a point where all matter was condensed into a hot, dense sea of subatomic particles brimming with potential. But what came before that? This is where quantum physics comes into play, and to truly understand it, we would need a new theory that unifies general relativity with quantum mechanics—or perhaps something even more revolutionary.
Kumar's model begins with the quantum phenomenon of matter generation. Under the right conditions, virtual particles can spontaneously emerge in pairs—one particle of matter and its antimatter counterpart.
This could be a positron and an electron, a charm quark and an anti-charm quark, or, as Kumar proposes, a Universe and an anti-Universe.
The idea of a multiverse isn’t new. It's a useful concept for explaining why our Universe seems so finely tuned for life.
Several years ago, physicists Latham Boyle, Kieran Finn, and Neil Turok from the Perimeter Institute for Theoretical Physics in Canada proposed that our Universe might have a twin that runs backward in time, with mirror-image particles and opposite charges.
Kumar's version draws on a concept from quantum information theory known as relative entropy, which measures differences in probability distributions across asymmetric systems, like two Universes linked at a point in time.
If our Universe was born with a backward-running, charge-flipped, mirror-image twin governed by the same energy conditions as ours, their entanglement could naturally explain the rapid expansion of space—no dark energy required.
But Kumar didn’t stop there. In a second proposal, he explores how varying the tension in hypothetical boundaries between dimensions, known as branes, could cause spacetime to expand at an accelerating rate.
While invoking extra dimensions and mirror Universes to explain the Universe's expansion might seem far-fetched, cosmology may have reached a point where we need to entertain ideas that stretch the limits of our imagination.
Even the most unconventional theories could lead to observations that reveal new particles and forces in the shadowy intersection of general relativity and quantum mechanics, or perhaps uncover previously hidden layers of reality.
"After working on the problems of dark matter and dark energy, I can say that either we accept that general relativity is correct and we live in a dark universe with these elusive and peculiar dark matter particles and dark energy, or we accept that we live in a higher dimensional multiverse," Kumar explains in his ScienceX dialogue.
Discover:
The Allure of the Multiverse:
Extra Dimensions, Other Worlds, and Parallel Universes
“A superb introduction to the concept of the multiverse… the curious will find much to ponder.”―Publishers Weekly