The beginning of the Universe as an explosion is questioned


Astrophysicists say that cosmic inflation, a point in the infancy of the Universe when space-time expanded exponentially, can in principle be ruled out without assumptions.

A team of universities of Cambridge, Trent and Harvard claims that there is a clear and unequivocal signal in the cosmos that could rule out inflation as a possibility. His article, published in The Astrophysical Journal Lettersargues that this signal, known as cos graviton backgroundmico (CGB), can be feasibly detected, although it will be a great technical and scientific challenge.

“Inflation was theorized to explain various adjustment challenges of the so-called hot Big Bang model,” he said. it’s a statement the paper’s first author, Dr Sunny Vagnozzi, of the Kavli Institute for Cosmology in Cambridge, now at the University of Trento. “He also explains the origin of structure in our Universe as a result of quantum fluctuations.”

“However, the great flexibility shown by potential cosmic inflation models encompassing an unlimited panorama of cosmological outcomes raises concerns that cosmic inflation is not falsifiable, even if individual inflationary models can be ruled out. Is it possible, in principle, to test cosmic inflation in a model-independent way?”

Some scientists raised concerns about cosmic inflation in 2013, when the Planck satellite published its first measurements of the cosmic microwave background (CMB), the oldest light in the universe.

“When the Planck satellite results were announced, they were presented as confirmation of cosmic inflation,” said Prof. Avi Loeb of Harvard University, Vagnozzi’s co-author on the current 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 those who argued that Planck’s results showed that inflation raised more puzzles than it solved, and that it was time to consider new ideas about the beginnings of the universe, which, for example it may have started not with a bang but with a rebound from 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. We cannot see further.

“The actual edge of the observable universe is the distance that any signal could have traveled at the speed of light limit. during the 13.8 billion years since the birth of the Universe”Loeb said. “As a result of the expansion of the universe, this 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 earlier the layer of cosmic history that we discover, all the way back to the Big Bang that represents our ultimate horizon. What lies beyond the horizon is unknown.”

It might be possible to delve further into the early universe by studying nearly weightless particles known as neutrinos, which are the most abundant particles with mass in the universe. The Universe allows neutrinos to travel freely without scattering from about one second after the Big Bang, when the temperature was ten billion degrees. “The current universe must be full of relic neutrinos from that time,” Vagnozzi said.

However, Vagnozzi and Loeb say we can go even further back by tracking gravitons, particles that mediate the force of gravity.

“The Universe was transparent to gravitons from the first instant tracked by known physics, the Planck time: 10 to the power of -43 seconds, when the temperature was the highest conceivable: 10 to the power of 32 degrees,” he said. Loeb. “A proper understanding of what came before requires a predictive theory of quantum gravity, which we do not possess.”

Vagnozzi and Loeb say that once the Universe allowed gravitons to travel freely without scattering, a relic 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 that they are undetectable. This can be turned into a test: if the CGB were detected, clearly this would rule out cosmic inflation, that does not allow its existence.

Vagnozzi and Loeb argue that such a test is possible and, in principle, CGB could be detected in the future. The CGB adds to the cosmic radiation budget, which otherwise includes neutrino and microwave backgrounds. Thus, it affects the cosmic expansion rate of the early Universe to a level that is detectable by next-generation cosmological probes, which could provide the first indirect detection of CGB.

However, to claim a definitive detection of the CGB, the “smoking gun” would be the detection of a background of high-frequency gravitational waves peaking at frequencies around 100 GHz. This would be very difficult to detect and would require tremendous advances. technological advances in the technology of superconducting magnets and gyrotrons. However, the researchers say, this signal may be within our reach in the future.