What if the Big Bang wasn’t what we’ve been told?

An essential part of the current cosmological model, the one that postulates that the Universe arose from a Big Bang, is the concept of cosmic inflation, a brief period of exponential growth without which the Universe simply could not exist in the way that it does. we see. The idea of ​​inflation was proposed by the physicist Alan Guth in 1981, and came to solve, among others, the so-called ‘horizon problem’: wherever we look, we see a uniform and homogeneous Universe, the same everywhere, and that uniformity It implies that, at some point, all these parts had to be in contact. But how is that possible if nothing can move faster than light and the Universe is huge? How were the most distant regions of the Universe able to ‘communicate’ so that they all look the same? And yet they did, because otherwise these regions separated by enormous distances would have had to evolve independently, giving rise to a very inhomogeneous Universe, and not the uniform Universe that we see today. And that’s where cosmic inflation comes in. During the first moments of its existence, the Universe expanded exponentially, so that all parts of that nascent Universe were ‘tuned’ in the same way. Later, as it got bigger and bigger, that original ‘imprint’ remained and they all evolved in the same way. However, not everyone agrees with this image of the Cosmos. And now, a team of astrophysicists from the universities of Cambridge, Trento and Harvard say there could be a ‘clear and unequivocal’ signal in the Universe that would, in fact, eliminate the need for cosmic inflation. In a paper published in The Astrophysical Journal Letters, the researchers argue that such a signal, known as the cosmic graviton background (CGB), can be feasibly detected, although doing so will be technically and scientifically challenging. “Inflation was theorized to explain various tuning challenges of the so-called hot Big Bang model,” says Sunny Vagnozzi, first author of the paper. And it also explains the origin of structure in our Universe as a result of quantum fluctuations. However, the great flexibility shown by the different models of cosmic inflation, which cover an unlimited range of possible cosmological outcomes, raises the concern that cosmic inflation could be falsified. But is it possible, in principle, to test cosmic inflation in a model-independent way?« And if there was no inflation? Some scientists raised concerns about cosmic inflation as early as 2013, when the Planck satellite published its first measurements of the cosmic microwave background (CMB), the oldest light in the Universe, which began traveling toward us shortly after the Big Bang. “When the Planck satellite results were announced, they were presented as confirmation of cosmic inflation,” says Avi Loeb, co-author of this week’s paper. However, some of us argue that the results could be showing the opposite.” Along with Anna Ijjas and Paul Steinhardt, Loeb was one of the first researchers to argue that Planck’s results showed that inflation posed more puzzles than it solved, and that it was time to consider new ideas about the early Universe. Like for example that it might have started not with a burst but with the ‘rebound’ of a previously contracting Cosmos. Planck’s published maps of the CMB represent the earliest time in the universe that we can ‘see’, 100 million years before the first stars formed. It is not possible to see further because photons did not begin to travel through space until, about 380,000 years after the Big Bang, the Universe became transparent to light. “The real edge of the observable universe is the distance that any signal could have traveled at the limit of the speed of light during the 13.8 billion years that have elapsed since the birth of the Universe,” explains Loeb. But, since the Universe is expanding, that edge is currently 46.5 billion light-years away. The spherical volume within this boundary is like an archaeological dig centered on us: the deeper we probe it, the older the layer of cosmic history we uncover, with the Big Bang as our latest horizon. What lies beyond the horizon is unknown« . Further back in time However, it is possible to delve further into the early Universe by studying nearly weightless particles known as neutrinos, among the most abundant in existence. Unlike what happens with light, the Universe allows neutrinos to travel freely and without scattering from about one second after the Big Bang, when the temperature was ten billion degrees. “The current universe – says Vagnozzi – must be full of relic neutrinos from that time”. But that is not all. In fact, in his paper the researchers say we could go even further back if we track down gravitons, the particles that mediate the force of gravity. «In fact -continues Loeb-, the Universe was transparent to gravitons from the first instant that known physics allows us to track, the Planck time: 10 raised to -43 seconds, when the temperature was the highest conceivable: 10 raised to 32 degrees. A proper understanding of what came before requires a predictive theory of quantum gravity, which we do not possess.” According to Vagnozzi and Loeb, once the Universe allowed gravitons to travel freely without scattering, a background of gravitational thermal radiation with a temperature of just under a degree above absolute zero should have been generated: the cosmic graviton background (CGB). ). However, the Big Bang theory does not allow for the existence of the CGB, as it suggests that the exponential inflation of the newborn universe diluted relics like the CGB to the point of making them undetectable. Although that, according to the article, could become a test: if the CGB were detected, cosmic inflation, which does not allow its existence, would be ruled out. In search of the cosmic graviton background Surprisingly, the two scientists argue that such a test is possible and that, in principle, the CGB could be detected in the future. The cosmic graviton background would thus be added to other forms of cosmic radiation, such as the microwave background and the neutrino background. And like them, the CGB would also affect the cosmic expansion rate of the early Universe to a level that will be detectable by next-generation cosmological probes, potentially providing the first indirect detection of the CGB. MORE INFORMATION Noticias No Spain will lead its first European space mission Noticias No Our radio telescopes are detecting mysterious signals from distant galaxies: what is the origin of FRBs? However, in order to claim a definitive detection of the CGB, the ‘smoking gun’ would be the detection of a background of high-frequency gravitational waves. This would be very difficult to detect and would require tremendous technological advances in superconducting magnet and gyrotron technology. Although, say the researchers, this signal could become within our reach in the future.