In the quantum world, objects can exist in a what is called a superposition of states: A hypothetical atomic-level light bulb could simultaneously be both on and off. This strange feature has important ramifications for computing.
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In early July, Google announced that it will expand its commercially available cloud computing services to include quantum computing. A similar service has been available from IBM since May. These aren’t services most regular people will have a lot of reason to use yet.
But making quantum computers more accessible will help government, academic and corporate research groups around the world continue their study of the capabilities of quantum computing.
Understanding how these systems work requires exploring a different area of physics than most people are familiar with.
Quantum mechanics, however, describes the subatomic realm – the behaviour of protons, electrons and photons. The laws of quantum mechanics are very different from those of classical mechanics and can lead to some unexpected and counterintuitive results, such as the idea that an object can have negative mass.
Physicists around the world – in government, academic and corporate research groups – continue to explore real-world deployments of technologies based on quantum mechanics. And computer scientists, including me, are looking to understand how these technologies can be used to advance computing and cryptography.
According to our best understanding of the Universe, if you travel back in time as far as you can, around 13.8 billion years or so, you’ll eventually reach a singularity – a super-dense, hot, and energetic point, where the laws that govern space-time breakdown.
Despite our best attempts, we can’t peer past that singularity to see what triggered the birth of our Universe – but we do know of only one other instance in the history of our Universe where a singularity exists, and that’s inside a black hole. And the two events might have more in common than you’ve ever considered, as physicist Ethan Siegel explains over at Forbes.
It might sound a little crazy, but, as Siegel reports, from a mathematical perspective, at least, there’s no reason that our own Big Bang couldn’t have been the result of a star collapsing into a black hole in an alternate, four-dimensional universe.
In fact, the idea was first proposed by theoretical physicists at the Perimeter Institute and University of Waterloo in Canada back in 2014, and despite physicists’ best attempts, no one has been able to rule it out.
So let’s step back for a second here. What we know about the Big Bang is that, immediately after the singularity, our Universe began expanding. Within a few fractions of a second, it underwent a rapid period of inflation, increasing in size by around 1026, before slowing down again and expanding more gradually.
What we know about black holes, is that, in our three-dimensional Universe, black holes spawn a two-dimensional event horizons – which basically means that they’re wrapped in a two-dimensional boundary that marks the ‘point of no return’ for matter.
Below is an artist’s impression of what that might look like:
What black holes and the Big Bang have in common is that they’re the only two instances of a singularity that we know of in the Universe. (A singularity basically just means a point where the rules that govern our Universe no longer work.)
To the best of our knowledge, our Universe is dictated by two sets of rules: quantum mechanics for all the small stuff like particles; and general relativity for all the bigger stuff, like stars, planets, and you and me.
If you crunch the numbers, black holes defy these rules, because their event horizons are bigger than can be explained by the behaviour of the particles inside it.
“The fact that black holes in our Universe are much more massive than this isn’t a problem,” explains Siegel.
“It simply means that the laws of physics that we know break down at the singularity we calculate at the centre. If we ever want to describe it accurately, it’s going to take a unification of quantum theory with general relativity. It’s going to take a quantum theory of gravity.”
For now, though, we don’t have that ‘theory of everything‘, so our understanding of black holes ends at the singularity – just as our understanding of the Universe does.
Knowing that, three physicists from the Perimeter Institute and University of Waterloo suggested two years ago that the two singularities could be one and the same – maybe our Universe was born out of the singularity of a much larger black hole.
Or, to put that another way, maybe our Universe is the three-dimensional packaging around another universe’s event horizon.
“In this scenario, our Universe burst into being when a star in a four-dimensional universe collapsed into a black hole,” a Perimeter Institute press release explained back in 2014.
Mathematically speaking, this holds up.
While we can’t calculate what happens with a black hole’s singularity, what we can calculate is what happens on the boundary of the event horizon – and it matches up pretty well with what happened at the birth of our Universe, as Siegel explains.
“As the black hole first formed, from a star’s core imploding and collapsing, the event horizon first came to be, then rapidly expanded and continued to grow in area as more and more matter continued to fall in.
If you were to put a coordinate grid down on this two-dimensional wrapping, you would find that it originated where the gridlines were very close together, then expanded rapidly as the black hole formed, and then expanded more and more slowly as matter fell in at a much lower rate. This matches, at least conceptually, what we observe for the expansion rate of our three-dimensional Universe.”
Of course, this whole idea remains an hypothesis until we have some measurable way of merging the laws of quantum mechanics and general relativity, and peering past a singularity.
But, until then, the coolest thing to consider is that, based on this concept, there’s no reason that our own Universe couldn’t be spawning brand new two-dimensional universes every time black holes are born. “As crazy as it sounds, the answer appears to be maybe,” writes Siegel. Oof.
We can’t wait to eventually get that theory of everything so we can begin to test some of these big ideas out.
You can hear more about the black hole birthing our Universe hypothesis in the video below, and read their full paper on arXiv.org.
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Argonne scientists Ivan Sadovskyy (left) and Valerii Vinokur published a paper showing a mathematical construction to a possible local violation of the Second Law of the Thermodynamics. One implication for the research could be a way to one …more
For more than a century and a half of physics, the Second Law of Thermodynamics, which states that entropy always increases, has been as close to inviolable as any law we know. In this universe, chaos reigns supreme.
But researchers with the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory announced recently that they may have discovered a little loophole in this famous maxim.
Their research, published in Scientific Reports, lays out a possible avenue to a situation where the Second Law is violated on the microscopic level.
The Second Law is underpinned by what is called the H-theorem, which says that if you open a door between two rooms, one hot and one cold, they will eventually settle into lukewarm equilibrium; the hot room will never end up hotter.
But even in the twentieth century, as our knowledge of quantum mechanics advanced, we didn’t fully understand the fundamental physical origins of the H-theorem.
Recent advancements in a field called quantum information theory offered a mathematical construction in which entropy increases.
“What we did was formulate how these beautiful abstract mathematical theories could be connected to our crude reality,” said Valerii Vinokur, an Argonne Distinguished Fellow and corresponding author on the study.
The scientists took quantum information theory, which is based on abstract mathematical systems, and applied it to condensed matter physics, a well-explored field with many known laws and experiments.
“This allowed us to formulate the quantum H-theorem as it related to things that could be physically observed,” said Ivan Sadovskyy, a joint appointee with Argonne’s Materials Science Division and the Computation Institute and another author on the paper. “It establishes a connection between well-documented quantum physics processes and the theoretical quantum channels that make up quantum information theory.”
The work predicts certain conditions under which the H-theorem might be violated and entropy—in the short term—might actually decrease.
As far back as 1867, physicist James Clerk Maxwell described a hypothetical way to violate the Second Law: if a small theoretical being sat at the door between the hot and cold rooms and only let through particles traveling at a certain speed. This theoretical imp is called “Maxwell’s demon.”
“Although the violation is only on the local scale, the implications are far-reaching,” Vinokur said. “This provides us a platform for the practical realization of a quantum Maxwell’s demon, which could make possible a local quantum perpetual motion machine.”
For example, he said, the principle could be designed into a “refrigerator” which could be cooled remotely—that is, the energy expended to cool it could take place anywhere.
The authors are planning to work closely with a team of experimentalists to design a proof-of-concept system, they said.
The study, “H-theorem in quantum physics,” was published September 12 in Nature Scientific Reports.
More information: G. B. Lesovik et al, H-theorem in quantum physics, Scientific Reports (2016). DOI: 10.1038/srep32815
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In physics, they are all the same thing. But to you, me, and everyone else, time moves in one direction: from expectation, through experience, and into memory. This linearity is called the arrow of time, and some physicists believe it only progresses that way because humans, and other beings with similar neurological wiring, exist to observe its passing.
The question of time’s arrow is an old one. And to be clear, it’s not whether time exists, but what direction it moves. Many physicists believe it emerges when enough tiny particles—individually governed by the weird rules of quantum mechanics— interact, and start displaying behavior that can be explained using classical physics. But two scientists argue, in a paper published today in Annalen der physik—the same journal that published Einstein’s seminal articles on special and general relativity—that gravity isn’t strong enough to force every object in the universe to follow the same past»present»future direction. Instead, time’s arrow emerges from observers.
This all goes back to one of the biggest problems in physics, knitting together quantum and classical mechanics. In quantum mechanics, particles can have superposition. That is, one electron might exist in either of two places, and nobody can say for sure which until it is observed. Where that electron might be is represented by probability. Experimentally, this checks out.
However, the rules change when electrons start interacting with many objects—like a bunch of air molecules—or decohere into things like dust particles, airplanes, and baseballs. Classical mechanics take over, and gravity becomes important. “The position of electron, each atom, is governed by a probability,” says Yasunori Nomura, a physicist at UC Berkeley. But once they interact with larger objects, or become things like baseballs, those individual probabilities combine, and the odds of all those collective electrons having superposition decreases. That’s why you never see a baseball simultaneously disappear into the left fielder’s mitt while also soaring into the upper deck.
That moment when particle physics merge with classical mechanics is called decoherence. In terms of physics, it is when time’s direction becomes mathematically important. And so, most physicists believe time’s arrow emerges from decoherence.
The most prominent theory explaining decoherence is the Wheeler-DeWitt equation. It dates to 1965, when a physicist named John Wheeler had a layover at an airport in North Carolina. To pass the time, he asked his colleague Bryce DeWitt to meet him. They did what physicists do: talk theory and play with numbers. The two came up with an equation that, to Wheeler, erased the seams between quantum and classical mechanics (DeWitt was more ambivalent).
The theory isn’t perfect. But it is important, and most physicists agree that it is an important tool for understanding the weirdness underlying decoherence and so-called quantum gravity.
Here’s where it gets a bit weirder. Although the equation doesn’t include a variable for time (which isn’t all that weird. Time is something that can’t be measured in terms of itself, in physics it is measured as correlations between an object’s location … over time … anyway, it’s weird). But, it provides a framework for knitting the universe together.
However, the two scientists who penned this recent paper say that, in the Wheeler-DeWitt equation, gravity’s effects kick in too slowly to account for a universal arrow of time. “If you look at examples and do the math, the equation doesn’t explain how time’s direction emerges,” says Robert Lanza, a biologist, polymath, and co-author of the paper. (Lanza is the founder of biocentrism, a theory that space and time are constructs of biological sensory limitations.) In other words, those nimble quantum particles ought to be able to keep their property of superposition before gravity grabs hold. And if, say, gravity is too weak to hold an interaction between to molecules as they decohere into something larger, then there’s no way it can force them to move in the same direction, time-wise.
If that math doesn’t check out, that leaves the observer: Us. Time moves as it does because humans are biologically, neurologically, philosophically hardwired to experience it that way. It’s like a macro-scale version of Schrödinger’s cat. A faraway corner of the universe might be moving future to past. But the moment humans point a telescope in that direction, time conforms to the past-future flow. “”In his papers on relativity, Einstein showed that time was relative to the observer,” says Lanza. “Our paper takes this one step further, arguing that the observer actually creates it.”
This is not necessarily a new theory. Italian physicist Carlo Rovelli wrote about it in a paper published last year on ArXiv, an open physics website. Nor is it uncontroversial. Nomura says one flaw is figuring out how to measure whether this notion of “observer time” is real. “The answer depends on whether the concept of time can be defined mathematically without including observers in the system,” he says. The authors argue that there is no way to subtract the observer from any equation, since equations are by default performed and analyzed by people.
Nomura says the authors also fail to account for the fact that the entire universe exists in a medium called spacetime, “So when you talk about spacetime, you already talking about a decohered system.” He doesn’t go so far as to say the authors are wrong—physics remains an incomplete science—but he disagrees with the conclusions they draw from their math. And like time, interpretations of physics are all relative.
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