It’s possible that the universe isn’t uniform past what we can see, and conditions are wildly different from place to place, says Caltech astrophysicist Sean Carroll. “That possibility is the cosmological multiverse. We don’t know if there is a multiverse in this sense, but since we can’t actually see one way or another, it’s wise to keep an open mind.”
“We didn’t have birds in the very early universe; we have birds later on. We didn’t have time in the early universe, but we have time later on,” said Stephen Hawking’s colleague, physicist James Hartle, at the University of California, Santa Barbara about what came before the Big Bang.
“While it is certainly possible that axions — a hypothetical elementary particle predicted to be among the lightest particles in the universe–make up dark matter, they also may make up a source of “dark radiation” in our universe which we refer to as the Cosmic Axion Background (CaB), analogous to the observed Standard Model radiation, known as the Cosmic Microwave Background,” Jeff Dror, with the Santa Cruz Institute for Particle Physics, told The Daily Galaxy. “Furthermore,” adds Dror, “experiments designed to search for axion dark matter can be repurposed to search for the CaB and potentially lead to the discovery of the axion, which would also teach us a great deal about the history of our universe.”
“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” explained Christian Smorra, member of the BASE collaboration at the CERN research center. “An asymmetry must exist here somewhere but we simply do not understand where the difference is. What is the source of the symmetry break?”
“For all we know, if galactic radiation-emitting civilizations exist, they could be located anywhere in the Milky Way. A signal reaching Earth could thus be as old as about 90,000 years, that is the time it takes for electromagnetic waves to cover the distance between us and the opposite edge of our galaxy, and this time span becomes even larger if we take into account signals from other galaxies. It is thus not unreasonable to think that, at the time we receive a signal, the emitting civilization no longer exist,” wrote Claudio Grimaldi, guest scientist at the Laboratory of Statistical Biophysics (LBS), Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland in an email to The Daily Galaxy.
“The fate of black holes in a quantum theory of gravity is, in my view, the most important problem in theoretical physics,” said Jorge Pullin, the Horace Hearne professor of theoretical physics at LSU.