Hitting the Books: How to uncover the true nature of the multiverse

IIt is difficult to describe the state of the universe when it was compressed to a size slightly smaller than the dot at the end of this sentence – since the concepts of time and space literally did not yet apply. But that challenge was met by pioneering theoretical astrophysicist Dr. Laura Mersini-Houghton has not stopped searching for knowledge at the fringes of the known universe and beyond. In her new book Before the Big BangMersini-Houghton recounts her early life in communist Albania, her career as she rose to prominence in the male-dominated field of astrophysics, and discusses her research into the multiverse that could fundamentally reshape our understanding of reality.

excerpt from Before the Big Bang: The Origin of the Universe and What Lies Beyond by Laura Mersini Houghton. Published by Mariner Books. Copyright © 2022 by Laura Mersini Houghton. All rights reserved.

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Scientific investigations of problems such as the origin of the universe, which we cannot observe, reproduce and test in a laboratory, are similar to detective work in that they rely on both intuition and evidence. Like a detective, researchers can intuitively sense that the answer is near as the pieces of the puzzle come together. That’s how I felt when I was Rich, and I was trying to figure out how we could test our theory about the multiverse. Rationally it seemed a long way, but intuitively it seemed achievable.

Finally a possible solution hit me. I realized that the key to testing and validating this theory lay in quantum entanglement – because decoherence and entanglement were two sides of the same coin! I could rewind the creation story to its roots in the quantum landscape when our wave universe was entangled with others.

I already knew that the separation – the decoherence – of the branches of the universe wave function (which then become individual universes) was triggered by their entanglement with the environmental bath of fluctuations. Now I was wondering if we could calculate and find any traces of this early entanglement imprinted in our skies today.

That may sound like a contradiction. All these eons after the Big Bang, how could our universe possibly still be entangled with all the other universes? Our universe must have separated from them in its quantum infancy. But as I wrestled with these issues, I realized that it was possible to have a universe that had long since decoupled but also retained its infantile “dents” — minor shape changes caused by interaction with other surviving universes , with which it was entangled in our earliest moments – as identifiable birthmarks. The scars of his initial involvement should still be visible in our universe today.

The key was in the timing. Our wave universe dissolved at about the same time as the next stage, the particle universe, underwent its own cosmic inflation and came into existence. Everything we observe in our sky today was seeded from the original fluctuations created in those first moments, which take place in the smallest measurable unit of time, far less than a second. In principle, at those moments when the entanglement was erased, their signatures could have been stamped on inflation and its volatility. There was a chance that the kind of scars I had envisioned had formed in that short time. And if so, they should be visible in the sky.

Understanding how entanglement scars form is less complicated than you might think. I began by trying to mentally picture the scarring of our skies from entanglement. I envisioned all surviving universes from the branches of the universe’s wave function, including ours, as a bunch of particles spreading out around the quantum multiverse. Since they all contain mass and energy, they interact (pull) gravitationally with each other, just as Newton’s apple had its trajectory curved by interacting with the Earth’s mass, thus guiding it to the ground. However, the apple was also attracted to the moon, the sun, all the other planets in our solar system and all the stars in the universe. The Earth’s mass is the strongest force, but that doesn’t mean these other forces don’t exist. The net effect entanglement left on our sky is captured by the combined pull of other infant universes on our universe. Much like stars faintly tugging at the famous apple, the signs of entanglement in our universe are incredibly small compared to the signs of cosmic inflation right now. But they are still there!

I’ll admit it… I was thrilled at the mere thought that I might have had a chance to see beyond our horizon and before the Big Bang! By proposing to calculate and track the entanglement in our skies, I have found, for the very first time, a way to test the multiverse. What excited me most about this idea was its potential to make possible what for centuries we thought was impossible—an observation window to peer into space and time, beyond our universe, into the multiverse. Our expanding universe offers the best cosmic laboratory for finding information about its beginnings, for everything we observe in our universe on a large scale today was there at the beginning. The basic elements of our universe do not disappear over time; they simply rescale their size as the universe expands.

And that’s why I thought of using quantum entanglement as a litmus test for our theory: Quantum theory contains an almost sacred principle known as “unity” which states that no information about a system can ever be lost. Uniformity is a law of information preservation. It means that traces of our universe’s earlier quantum entanglement with the other surviving universes must still exist today. Therefore, despite decoherence, entanglement can never be erased from the memory of our universe; it is stored in its original DNA. Furthermore, these signs have been encoded in our skies since its inception, since the universe began as a ripple on the landscape. Traces of this earlier entanglement would simply expand with the expansion of the universe as the universe became a much larger version of its infant self.

I was concerned that these signatures, being stretched by inflation and universe expansion, would be quite faint. But on the basis of uniformity, I believed that faint as they were, they persisted somewhere in our skies in the form of local violations or departures from the uniformity and homogeneity predicted by cosmic inflation.

Rich and I decided to calculate the effects of quantum entanglement on our universe to see if any marks were left behind, then fast-forward them from infancy to the present and derive predictions about what kind of scars we should be looking for in our skies . If we could identify where to look for them, we could test them by comparing them to actual observations.

Rich and I began this investigation with the help of a physicist in Tokyo, Tomo Takahashi. I first met Tomo at UNC Chapel Hill in 2004 when we overlapped by a year. He was a postdoc about to accept a faculty position in Japan, and I had just arrived at UNC. We enjoyed the interaction and I saw the high standards Tomo had for his work and his incredible attention to detail. I knew he was familiar with the computer simulation program we needed to compare the predictions based on our theory with actual data on matter and radiation signatures in the universe. In 2005 I called Tomo and he agreed to work with us.

Rich, Tomo and I decided the best place to begin our search was the CMB – the cosmic microwave background, the afterglow of the Big Bang. CMB is the oldest light in the universe, a universal “ether” that has permeated the entire cosmos throughout its history. As such, it contains a sort of exclusive record of the first millisecond of the life of the universe. And this silent witness of creation still surrounds us today, making it an invaluable cosmic laboratory.

The energy of the CMB photons in our current Universe is quite low; Their frequencies peak in the microwave range (160 gigahertz), much like the photons in your kitchen microwave when you heat your food. Three major international scientific experiments – the COBE, WMAP and Planck satellites (with a fourth on the way) dating from the 1990s to the present – have measured the CMB and its much fainter fluctuations with exquisite precision. We even encounter CMB photons here on Earth. In fact, in the era of old TVs, seeing and hearing CMB was a commonplace experience: when switching channels, the viewer experienced the CMB signal in the form of noise — the blurry, buzzing gray and white spots that appeared on the TV screen.

But if our universe came into being from nothing but energy, then what can we see in the CMB photons that give us an evolving picture of the universe? Here the quantum theory, in particular the Heisenberg uncertainty principle, provides the answer. According to the uncertainty principle, quantum uncertainty, which manifests itself in fluctuations in the initial energy of inflation, is inevitable. When the universe stops inflating, it is suddenly filled with waves of quantum inflation energy fluctuations. The full range of fluctuations, some with mass and some without, are called density perturbations. The shorter waves in this spectrum that fit into the universe become photons or particles depending on their mass (reflecting the phenomenon of wave-particle duality).

The tiny tremors in the fabric of the universe that produce faint waves or vibrations in the gravitational field, called primordial gravitational waves, contain information about what particular model of inflation took place. They are incredibly small, about 1/10 billionth of the power of the CMB spectrum, and therefore much more difficult to observe. But they are kept in the CMB.