The Quantum Gravity

How can Einstein‘s theory of gravity be unified with quantum mechanics? It is a challenge that could give us deep insights into phenomena such as black holes and the birth of the universe. Now, a new article in Nature Communications, written by researchers from Chalmers University of Technology, Sweden, and MIT, U.S., presents results that cast new light on important challenges in understanding quantum gravity.

We strive to understand the laws of nature and the language in which these are written is mathematics. When we seek answers to questions in physics, we are often led to new discoveries in mathematics too. This interaction is particularly prominent in the search for quantum gravity—where it is extremely difficult to perform experiments,” explains Daniel Persson, Professor at the Department of Mathematical Sciences at Chalmers university of technology.

An example of a phenomenon that requires this type of unified description is . A black hole forms when a sufficiently heavy star expands and collapses under its own gravitational force, so that all its mass is concentrated in an extremely small volume. The quantum mechanical description of black holes is still in its infancy but involves spectacular advanced mathematics.

The challenge is to describe how gravity arises as an ’emergent’ phenomenon. Just as everyday phenomena—such as the flow of a liquid—emerge from the chaotic movements of individual droplets, we want to describe how gravity emerges from quantum mechanical system at the microscopic level,” says Robert Berman, Professor at the Department of Mathematical Sciences at Chalmers University of Technology.

In an article recently published in the journal Nature Communications, Daniel Persson and Robert Berman, together with Tristan Collins of MIT in the U.S., showed how gravity emerges from a special quantum mechanical system in a simplified model for quantum gravity called the holographic principle.

Using techniques from the mathematics that I have researched before, we managed to formulate an explanation for how gravity emerges by the holographic principle, in a more precise way than has previously been done,” explains Robert Berman.

The new article may also offer new insight into mysterious dark energy. In Einstein’s general theory of relativity, gravity is described as a geometric phenomenon. Just as a newly made bed curves under a person’s weight, heavy objects can bend the geometric shape of the universe. But according to Einstein’s theory, even the empty space—the “vacuum state” of the universe—has a rich geometric structure. If you could zoom in and look at this vacuum on a microscopic level, you would see quantum mechanical fluctuations or ripples, known as dark energy. It is this mysterious form of energy that, from a larger perspective, is responsible for the accelerated expansion of the universe.

Source: Nature

Worlds Like Earth Common In The Cosmos

A new way of studying planets in other solar systems – by doing sort of an autopsy on planetary wreckage devoured by a type of star called a white dwarf – is showing that rocky worlds with geochemistry similar to Earth may be quite common in the cosmos. Researchers studied six white dwarfs whose strong gravitational pull had sucked in shredded remnants of planets and other rocky bodies that had been in orbit. This material, they found, was very much like that present in rocky planets such as Earth and Mars in our solar system. Given that Earth harbors an abundance of life, the findings offer the latest tantalizing evidence that planets similarly capable of hosting life exist in large numbers beyond our solar system.

The more we find commonalities between planets made in our solar system and those around other stars, the more the odds are enhanced that the Earth is not unusual,” said Edward Young, a geochemistry and cosmochemistry professor at the University of California, Los Angeles (UCLA), who helped lead the study published in the journal Science. “The more Earth-like planets, the greater the odds for life as we understand it.”

The first planets beyond our solar system, called exoplanets, were spotted in the 1990s, but it has been tough for scientists to determine their composition. Studying white dwarfs offered a new avenue.

A white dwarf is the burned-out core of a sun-like star. In its death exoplanets, the star blows off its outer layer and the rest collapses, forming an extremely dense and relatively small entity that represents one of the universe’s densest forms of matter, exceeded only by neutron stars and black holesPlanets and other objects that once orbited it can be ejected into interstellar space. But if they stray near its immense gravitation field, they “will be shredded into dust, and that dust will begin to fall onto the star and sink out of sight,” said study lead author Alexandra Doyle, a UCLA graduate student in geochemistry and astrochemistry.

This is where that ‘autopsy’ idea comes from,” Doyle added, noting that by observing the elements from the massacred planets and other objects inside the white dwarf scientists can understand their composition.


Rotating Black Holes Might Serve As Portals For Hyperspace Travel

Black holes skirt the line between science fiction and science fact. On the one hand, scientists have seen real black holes in action, consuming unsuspecting stars that pass too close. But where reality ends and fiction takes over is at the edge of a black hole — a place called the event horizon, where no spacecraft has ever gone.

So, whatever happens beyond that boundary, inside of a black hole, is anyone’s guess. Scientists agree that if you travel far enough into a black hole, gravity will eventually become so strong that it kills anything in its path. But sci-fi films are more optimistic, depicting black holes as portals through space and time or gateways to other dimensions. And it turns out, some scientists now think the sci-fi buffs may be onto something. Black holes might be suitable for hyperspace travel, after all; it just takes the right kind of black hole. At the center of every black hole is a point of infinite density, called a singularity. It’s what gives black holes their strong gravitational pull. And for decades, scientists thought singularities were all the same, so anything that passed the event horizon would be destroyed the same way: by being stretched and pulled like an infinitely long piece of spaghetti.

But that all changed in the early 1990s when different research teams in Canada and the US discovered a second singularity called a “mass inflation singularity.” It still has a strong gravitational pull, but it would only stretch you by a finite amount, and potentially NOT kill you in the process, meaning, you might survive the trip through a black hole. More specifically, through a large, rotating black hole, which is where these types of singularities exist.

Now, astronomers obviously can’t travel through a black hole yet to test this theory. In fact, the best place to test this is at the supermassive black hole in the center of our home galaxy, the Milky Way, which is 27,000 light years away. Not conveniently close to the least.

Therefore, scientists instead run computer simulations to see what would happen if we did manage to reach an isolated, rotating black hole, and now, for the first time, a team of scientists at UMass Dartmouth and Georgia Gwinnett College has done exactly that.


You would feel a slight increase in temperature, but it would not be a dramatic increase. It’s just that you don’t have enough time to respond to the very strong forces. It would just go through you too quickly,” said Lior Burko from Georgia Gwinnett College.  He added that passing through a weak singularity is like quickly running your finger through a candle flame that’s 1,000 degrees Celsius. If you hold your finger in the flame long enough, you’ll get burned, but pass your finger through quickly, and you’ll barely feel a thing. Similarly, if you pass through a weak singularity with the right speed and momentum, and at the right time, you may not feel much at all.

As for what happens once you get through to the other side, no one really knows, but Burko has his own ideas. He says one possibility is that we’d arrive at some other remote part of our galaxy, potentially light years away from any planets or stars, but a second, and perhaps more intriguing, possibility is that we’d arrive in a different galaxy altogether. That’s if you even make it that far. Scientists say more research is needed before we’re anywhere close to successfully traveling through a black hole. But when we are ready, one of the safest passageways might be the supermassive black hole at the center of our galaxy called Sagittarius A*, and it might just be our ticket out of the Milky Way.