lIt’s hard to describe the state of things in the universe when everything was compressed to a size slightly smaller than the period at the end of this sentence – because the concepts of time and space literally didn’t apply yet. But that challenge hasn’t stopped the trailblazing theoretical astrophysicist, dr. Laura Mersini-Houghton, of seeking knowledge at the edge of the known universe and beyond. In her new book Before the big bangMersini-Houghton talks about her early life in communist Albania, her career when she rose to prominence in the male-dominated field of astrophysics, and discusses her research into the multiverse that could fundamentally rewrite our understanding of reality.
taken 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.
Scientific investigations into problems such as the creation 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, as the puzzle pieces begin to fall into place, investigators intuitively sense that the answer is close at hand. This was the feeling I had as Rich and I was trying to figure out how to test our theory about the multiverse. Rationally it seemed a long way, but intuitively it seemed feasible.
Finally a possible solution occurred to me. I realized that the key to testing and validating this theory was hidden in quantum entanglement – because decoherence and entanglement were two sides of the same coin! I was able to rewind the creation story all the way to the roots of the quantum landscape, when our wave universe was entwined with others.
I already knew that the separation – the decoherence – of the branches of the universe wavefunction (which then become individual universes) was caused by their entanglement with the environmental bath of fluctuations. Now I wondered if we could calculate and find traces of this early entanglement imprinted in our skies today.
This may sound like a contradiction. How could our universe still be enmeshed in all the other universes after the Big Bang? Our universe must have been separated from them in its quantum childhood. But as I struggled with these issues, I realized it was possible to have a universe that had long since decomposed, but also kept its infantile “dents” – minor changes in shape caused by the interaction with other surviving universes that had become entangled. in ours during the earliest moments – as identifiable moles. The scars of his initial entanglement should still be discernible in our universe today.
The key was in the timing. Our wave universe was decohering around the same time as the next stage, the particle universe, went through its own cosmic inflation and came into existence. Everything we observe in our sky today arose from the primordial fluctuations produced in those early moments, which take place in the smallest units of measurement of time, much less than a second. In principle, in those moments, when the entanglement was swept away, the signatures on inflation and its fluctuations could have been stamped. There was a chance that the kind of scars I imagined had formed in this short period of time. And if they had, they should be visible in the sky.
Understanding how scars form from entanglement is less complicated than you might think. I started by trying to create a mental image of the scars of the entanglement of our air. I visualized all surviving universes from the branches of the universe’s wave function, including our own, as a bunch of particles dispersed across the quantum multiverse. Since they all contain mass and energy, they interact with each other by gravity, just as Newton’s apple had curved its orbit of motion by interacting with Earth’s mass, guiding it toward the ground. However, the apple was also pulled by the moon, the sun, all the other planets in our solar system, and all the stars in the universe. The Earth’s mass has the strongest force, but that doesn’t mean these other forces don’t exist. The net effect that the entanglement left in our sky is captured by the combined pull of other baby universes on our universe. Like the faint tug of stars on the famous apple, the signs of entanglement in our universe right now are incredibly small compared to the signs of cosmic inflation. But they are still there!
I admit… I was excited just by the thought that I potentially had a way to see beyond our horizon and before the Big Bang! By my proposal to calculate and track entanglement in our sky, I very well, for the very first time, found a way to test the multiverse. What got me most excited about this idea was its potential to make possible what we’d thought impossible for centuries: an observation window to glimpse space and time beyond our universe in the multiverse. Our expanding universe provides the best cosmic laboratory for detecting information about his childhood, because everything we observe on a large scale in our universe today was also present in the beginning. The basic elements of our universe don’t disappear over time; they simply rescale their size with the expansion of the universe.
And this is why I thought to use quantum entanglement as the litmus test for our theory: Quantum theory contains an almost sacred principle known as ‘unitarity’, which states that information about a system can never be lost. Unitarity is a law of information retention. It means that signs of our universe’s earlier quantum entanglement with the other surviving universes must still exist today. Thus, despite decoherence, entanglement can never be erased from our universe’s memory; it is stored in its original DNA. Moreover, these signs have been encoded in our sky since childhood, since the time when the universe began as a wave on the landscape. Traces of this earlier entanglement would simply extend with the expansion of the universe as the universe became a much larger version of its childlike self.
I was concerned that these signatures, which have been stretched by inflation and the expansion of the universe, would be quite weak. But based on unitarity, I believed that as weak as they were, they were preserved somewhere in our sky in the form of local violations or deviations from uniformity and homogeneity predicted by cosmic inflation.
Rich and I decided to calculate the effect of quantum entanglement on our universe to find out if any traces were left behind, then flush them from childhood to the present and derive predictions of what kind of scars we should have. search our skies. If we could identify where to look for them, we could test them by comparing them to actual observations.
Rich and I started this research with the help of a physicist in Tokyo, Tomo Takahashi. I first met Tomo at UNC Chapel Hill in 2004, when we overlapped for a year. He was a postdoc about to take up a faculty position in Japan, and I had just arrived at UNC. We enjoyed the interaction and I saw the high standards Tomo set for his work and his incredible attention to detail. I knew he was familiar with the computer simulation program we needed to compare our theory’s predictions with actual data about 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 start our search was in the CMB – cosmic microwave background, the afterglow of the Big Bang. CMB is the oldest light in the universe, a universal ‘ether’ that permeates the entire cosmos throughout its history. As such, it contains a sort of exclusive record of the first millisecond in the life of the universe. And this silent witness of creation is still all around us, making it an invaluable cosmic laboratory.
The energy of the CMB photons in our current universe is quite low; their frequencies peak around the microwave range (160 gigahertz), much like the photons in your kitchen microwave when you heat up your food. Three large international science 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 to superb precision. We even encounter CMB photons here on Earth. Indeed, seeing and hearing CMB was an everyday experience in the era of old TV sets: when changing channels, the viewer would experience the CMB signal in the form of static electricity – the blurry, buzzing gray and white dots that screen appeared on the TV.
But if our universe started out purely from energy, what can we see in the CMB photons that give us a nascent view of the universe? Here, quantum theory, in particular Heisenberg’s uncertainty principle, offers the answer. According to the uncertainty principle, quantum uncertainty, represented as fluctuations in the initial inflation energy, is inevitable. When the universe stops blowing up, it suddenly fills with waves of quantum fluctuations of the inflaton energy. The whole range of fluctuations, some with mass and some without, are known as density perturbations. The shorter waves in this spectrum, which fit into the universe, become photons or particles, depending on their mass (reflecting the phenomenon of wave-particle duality).
The tiny vibrations in the fabric of the universe that create faint ripples or vibrations in the gravitational field, called primordial gravitational waves, contain information about which particular inflation model has occurred. They are incredibly small, at a fraction of about ten billion of the strength of the CMB spectrum, and are therefore much more difficult to observe. But they are kept in the CMB.
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