Why This Universe? New Calculation Suggests Our Cosmos Is Typical.

The scientists have spent decades trying to understand why our universe is so small. It's smooth and flat as far as we can see, but it's also expanding at an ever-so-slowly increasing pace, when calculations suggest that space should have become crumpled up by gravity and blasted apart by repulsive

Physicists propose that space rapidly inflated like a balloon at the start of the Big bang, ironing out any curves. Some argue that our universe is just one of many less hospitable universes in a giant multiverse.

The conventional thinking about our universe has been changed by two physicists. According to a new calculation published by Stephen and Gary, the plainness of the universe is expected. Our universe is the way it is, according to Neil Turok of the University of Edinburgh, for the same reason that air spreads evenly in a room.

Thomas Hertog is a cosmologist at the Catholic University of Leuven in Belgium.

It gives us a chance to see the structure of space time.

The contribution uses different methods compared to what most people have been doing.

The conclusion is based on a mathematical trick in which you switch to a clock with numbers on it. Turok and Boyle were able to calculate a quantity that appears to correspond to our universe using an imaginary clock. Without a more rigorous method, the meaning of the quantity remains a topic of debate. The road to the fundamental, quantum nature of space and time can be seen as a new guidepost by many physicists.

Gielen said that it was giving them a chance to see the structure of space time.

Imaginary Paths

Turok and Boyle are known for their unconventional ideas about the universe. To study how likely our universe is, they used a technique developed in the 1940s.

A particle can explore all possible routes, including a straight line, a curve, a loop, and ad infinitum. He came up with a way to add all the numbers together. Predicting how a quantum system would most likely behave was made possible by this technique.

Physicists noticed a correlation between the path integral and the science of temperature and energy. Turok and Boyle were able to make their calculation because of the bridge between quantum theory and the physical world.

In order to describe a system of many parts, you need just a few numbers. A rough sense of the room's energy is given by the temperature. The room's overall properties are described as a "macrostate".

The air molecule can be arranged in many different ways to correspond to the same macrostate. The temperature won't budge if you move one oxygen atom to the left. The number of microstates that correspond to a given macrostate determines its entropy.

Physicists use Entropy to compare the odds of different outcomes. There are more ways to arrange air molecule in a room than if they are grouped together in a corner. One expects air to spread out. The self-evident truth that probable outcomes are probable, couched in the language of physics, is known as the second law of thermodynamics.

We used a cheap trick to get the answer.

The resemblance to the path integral was obvious. All possible paths can be added with the path integral. There is a glaring difference between thermodynamics and probabilities, which are positive numbers that are easy to add together. The imaginary number i, the square root of 1, is the number assigned to each path. The wavelike nature of quantum particles allow complex numbers to grow or shrink.

Physicists found a way to take you from one realm to another. To make time imaginary, I enter the path integral that snuffs out the first one and turn imaginary numbers into actual probabilities. You can use the inverse of temperature to replace the time variable.

The discovery of space and time was made at the end of a series of theoretical discoveries.

The Entropy of Space-Time

The force of gravity is the tendency for objects to follow the folds in space-time according to Einstein's general theory of relativity. A black hole can be created if space-time curves steeply enough.

Black holes are not perfect, according to Jacob Bekenstein. The second law of thermodynamics states that the universe should not have any entropy at all. Black holes have to have both temperatures and heat.

Stephen Hawking tried to prove Bekenstein wrong by calculating the behavior of quantum particles in a black hole. In 1974 he discovered that black holes do exist. The point of no return for an infalling object was confirmed by another calculation.

In the years that followed, the British physicists Gibbons and Malcolm Perry, and later Gibbons and Hawking, arrived at the same result from different directions. Adding up all the different ways space-time could bend to make a black hole is what they set up. They rounded the black hole to mark the flow of time with imaginary numbers and looked at its shape. The black hole would periodically return to its initial state. They were able to calculate the black hole's temperature and entropy because of the repetition.

If the answers didn't match those calculated earlier, they wouldn't trust the results. At the end of the decade, their collective work yielded a startling idea: that space-time is made of tiny, rearrangeable pieces. Physicists were able to count their arrangements by looking at a black hole in the future.

Hertog said that the result left a deep impression on him. Is the Wick rotation good for more than just black holes? Hertog said it was irresistible to do the same with the properties of the whole universe.

Counting All Possible Universes

One of the simplest universes had nothing but dark energy built into space itself. A horizon beyond which space expands so quickly that no signal from there will ever reach an observer in the center of the space is called a de Sitter space-time. The de Sitter universe has an entropy equal to one-fourth of its horizon's area. Space-time seemed to have many microstates.

The question of the actual universe's entropy was still unanswered. The universe is filled with light and dark matter. The expansion of space was driven by light and the attraction of matter. The dark energy seems to have taken over. Hertog said that the expansion history was a rough ride. It's difficult to get an explicit solution.

The explicit solution was built over the last year or so. They noticed that adding radiation to de Sitter space-time didn't affect the simplicity of the universe.

They discovered over the summer that the technique would hold up. The world of thermodynamics remained accessible despite the mathematical curve describing the more complicated expansion history. Guilherme Leite Pimentel is a cosmologist at the Scuola Normale Superiore in Pisa, Italy. They were able to locate it.

By rotating the roller-coaster expansion history of a more realistic class of universes, they got a more versatile equation for Cosmic Entitlement. The formula spits out the number of corresponding microstates for a wide range of Cosmic macrostates defined by radiation, matter, and dark energy density. They posted their results online.

The result was applauded by experts. The conclusion that was drawn from their equation was unconventional. Hertog said that it becomes more interesting and controversial at that point.

The equation is believed to conduct a census of all conceivable history. They suspect that their entropy counts all the ways that one might rearrange the atoms of space-time and still end up with a universe with a dark energy density.

The process is similar to surveying a huge sack of marbles. Those with a negative curve might be green. People with a lot of dark energy might be cats. According to their census, the majority of the marbles are blue and correspond to one type of universe: one broadly like our own. It's rare to find weirder types of cosmos. The features of our universe that have motivated theorizing about inflation and the multiverse may be normal.

Hertog said it was a very interesting result. There are more questions than it answers.

Counting Confusion

They calculated an equation that counted universes. They observed that universes like ours seem to account for the lion's share of the possibilities. There is no certainty at that point.

They don't try to explain what quantum theory of gravity and cosmology might mean. How our universe came into being is not explained by them. They see their calculation as a clue to which kind of universes are preferred over a full theory. Turok said that the trick they used to get the answer was a cheap one.

The question of what exactly are the microstates that the cheap trick is counting has gone unanswered since Gibbons and Hawking first kicked off the business.

Henry Maxfield is a physicist who studies quantum theories of gravity.

It's at its core that entropy is a representation of ignorantness. Physicists know the average speed of particles, but they don't know what they are doing in a gas made of molecule.

Physicists are coming to a similar conclusion about black holes. Researchers still don't know what the microstates are, and they include configurations of the particles called gravitons or the strings of string theory.

Physicists don't feel confident about where their knowledge lies when it comes to the universe's structure.

Two theorists tried to put a mathematical footing on the theory. A physicist at the University of Maryland and his graduate student defined the entropy of the universe. The observer's perspective was adopted by them. The Gibbons and Hawking answer was recovered when they used a technique that involved adding a fake surface between the horizon and the central observer. They came to the conclusion that the de Sitter entropy counts all the possible micro states inside the horizon.

The same calculation is made for an empty universe by Turok and the others. In their new calculation, the number of microstates is proportional to volume and not area. Faced with this apparent clash, they theorize that the different entropies answer different questions: The smaller de Sitter entropy counts microstates of pure space-time bound by a horizon, while they theorize their larger de Sitter entropy counts all the microstates of a space-time filled with matter and Turok said it was the entire shebang.

A more explicit mathematical definition of the ensemble of microstates will be required in order to settle the question of what is counted. The answer to a question that is yet to be fully understood is what she sees as the result of the calculation.

Inflation and the multiverse are not dead despite the fact that there are more established answers to the question. Inflation theory has solved more than just the universe's smoothness and flatness. Many of its predictions match the observations of the sky. The entropic argument has passed a notable first test, but it will have to nail other, more detailed data to compete with inflation.

Mysteries that are based on randomness have served as indicators of unknown physics before. The existence of atoms was confirmed in the late 1800s thanks to a precise understanding of entropy. The hope is that if the researchers can figure out what questions they are asking in different ways, those numbers will lead them to a similar understanding of how Lego bricks of time and space pile up to create the universe that surrounds us.

Turok said that the calculation provided extra motivation for people trying to build theories of quantum gravity. The theory will explain the large-scale geometry of the universe