Before the outstanding modern physicist Stephen Hawking left this world, he managed to leave his last scientific work – his latest theory about the nature of the universe, which he co-wrote with his Belgian counterpart Thomas Hertog from the Catholic University of Leuven. The work was finally published in the scientific journal Journal of High Energy Physics, and more details can be found in the online library arXiv.org.
Thomas Hertog, who co-wrote the work with Hawking, said that their goal was ” transform the idea of the multiverse into a verifiable scientific basis. ” And the material published in the Journal of High Energy Physics says that the universe is much less complex than modern multiverse theory suggests.
The paper is based around the concept of infinite inflation of the universe, first introduced in 1979 and published in 1981.  After the Big Bang, the universe experienced a period of exponential inflation (rapid expansion). Then this expansion slowed, and the energy of the universe passed into matter and cosmic radiation. However, according to the theory of infinite inflation, in the universe there were bubbles of space that completely ceased to expand or headed for a complete stop of this expansion, thus forming fractal dead ends of static space. At the same time, in other spatial bubbles, due to quantum effects, inflation did not stop, which in turn led to the formation of an infinite number of multiverse. According to the theory, everything that we see inside the universe we observe is enclosed in only one of these bubbles. Inflation stopped, allowing stars and galaxies to appear.
Visualization of an expanding multiverse
“The familiar theory of infinite inflation predicts that on a general scale our universe looks like an endless fractal, with a mosaic of various pocket universes separated by an expanding ocean” , Explains Hawking.
“Local laws of physics and chemistry can differ from one pocket universe to another, which together form a multiverse. However, I was never a fan of the multiverse theory. If the scale of different universes within the multiverse is too large or even infinite, then the theory will be impossible to verify. “
In recent years, the model of infinite inflation of the universe has been seriously criticized. For example, Paul Steinhardt, a physicist at Princeton University, made a statement that initially the theory, which took on the task of universally explaining all that we see in the universe, simply changed the model.
In a new paper, Hawking and Hertog say that the model of infinite inflation is incorrect, since the laws of the General Theory of Relativity of Einstein break up at the quantum level, becoming useless.
“The problem with the familiar model of infinite inflation is related to the fact that it presupposes the existence of a background universe that evolves in accordance with the General Theory of Relativity of Einstein and considers quantum effects only as minor fluctuations,” explains Hertog.
“However, the dynamics Infinite inflation erases the division between classical and quantum physics. As a consequence, Einstein's theory breaks down in infinite inflation. “
The new theory takes the string theory – one of the models that tries to link the General Theory of Relativity to quantum theory, replacing the smallest particles from particle physics with tiny oscillating one-dimensional strings.  According to the holographic principle in string theory, the volume of space can be described by its boundaries. In other words, in a sense our universe is similar to a hologram in which a physically real three-dimensional space can be mathematically reduced to a 2D projection on its surface.
Scientists have proposed a variation of the holographic principle that projects a time dimension in infinite inflation, Concept without the need to rely on the General Theory of Relativity. This in turn allowed researchers to mathematically reduce the infinite inflation to an infinite state on the spatial surface from the beginning of the universe – the hologram of infinite inflation.
“When we tracked the evolution of our universe back in time, at some point we reached the threshold of infinite inflation, where our familiar concept of time ceases to have any significance, “notes Hertog.
In 1983, Hawking, along with physicist James Hartl, proposed the concept of an unlimited theory of the universe. In it, scientists said that at the time of the Big Bang in the universe there was only space, but there was no time and no boundaries. The concept of Hawking and Hartle allowed the existence of parallel worlds, for which a single wave function is defined. In this variety of universes, human reality is only one of the possible.
According to the new theory, the early universe had boundaries, and this allowed Hawking and Hertog to get more reliable predictions of its structure.
“We predict that our universe in The general scale is sufficiently smooth and has boundaries. It does not represent a fractal structure, “Hawking said.
The findings of this paper do not disprove the idea of the multiverse, but they reduce them to a much smaller range. In other words, the theory of the multiverse in the future can be checked if, of course, the conclusions of Hawking and Hertog succeed in repeating and confirming by other physicists.
Hertog himself would like to test his conclusions with Hawking through observations of gravitational waves that could be created by endless inflation . These waves are too huge for them to be determined with the LIGO interferometer, but future gravitational wave interferometers, such as ground LISA, and subsequent observations of background cosmic radiation, could identify them, the researcher believes.