Category Archives: quantum mechanics

When will the universe end? Not for at least 2.8 billion years

Cosmic doom

We’re safe for now. The way the universe is expanding, it won’t be tearing itself apart for at least a few billion years.

For those of you only now discovering that such an end was a possibility, here’s a little background. Observations of stars and galaxies indicate that the universe is expanding, and at an increasing rate. Assuming that acceleration stays constant, eventually the stars will die out, everything will drift apart, and the universe will cool into an eternal “heat death”.

But that’s not the only possibility. The acceleration is thought to be due to dark energy, mysterious stuff that permeates the entire universe. If the total amount of dark energy is increasing, the acceleration will also increase, eventually to the point where the very fabric of space-time tears itself apart and the cosmos pops out of existence.

One prediction puts this hypothetical “big rip” scenario 22 billion years in the future. But could it happen sooner? To find out, Diego Sáez-Gómez at the University of Lisbon, Portugal, and his colleagues modelled a variety of scenarios and used the latest expansion data to calculate a likely timeline. The data involved nearby galaxies, supernovae andripples in the density of matter known as baryon acoustic oscillations, all of which are used to measure dark energy.

The team found that the earliest a big rip can occur is at 1.2 times the current age of the universe, which works out to be around 2.8 billion years from now. “We’re safe,” says Sáez-Gómez.

Time equals infinity

And when is the latest it could happen? “The upper bound goes to infinity,” he says. That would mean the rip never comes and we end up with the heat death scenario instead.

Given that the sun isn’t expected to burn out for at least another 5 billion years, it would be surprising if the universe ended so early. But pondering our doom could be a worthwhile exercise anyway, Sáez-Gómez says. Scenarios like the big rip result from a lack of understanding of physics in particular our inability to marry quantum mechanics and general relativity, the theory of gravity. Exploring the possibilities could show us a way forward.

“You learn more about a physical theory by looking at the exotic and extreme cases,” says Robert Caldwell of Dartmouth College in New Hampshire, who helped come up with the big rip idea. He thinks Sáez-Gómez’s lower bound is very conservative, however – the universe is likely to last much longer. Even if it doesn’t, at least we’ve got a good run ahead of us. he says.



Researchers have written quantum code on a silicon chip for the first time

For the first time, Australian engineers have demonstrated that they can write and manipulate the quantum version of computer code on a silicon microchip. This was done by entangling two quantum bits with the highest accuracy ever recorded, and it means that we can now start to program for the super-powerful quantum computers of the future.

Engineers code regular computers using traditional bits, which can be in one of two states: 1 or 0. Together, two bits create code words that can be used to program complex instructions. But in quantum computing language there’s also the possibility for bits to be in superposition, which means they can be 1 and 0 at the same time. This opens up a vastly more powerful programming language, but until now researchers haven’t been able to figure out how to write it.

Now engineers from the University of New South Wales (UNSW) in Australia have demonstrated that not only can they do this, but they can do it on silicon microchips very similar to the ones that make up today’s computers, which means the technology will be easy and quick to scale up.

So how exactly do you write quantum code? It all comes down to a phenomenon known as quantum entanglement. When two particles are entangled, it basically means that the measurement of one of them will instantly affect the state of its entangled particle, even if it’s thousands of kilometres away.

“This effect is famous for puzzling some of the deepest thinkers in the field, including Albert Einstein, who called it ‘spooky action at a distance’,” said lead researcher Andrea Morello, from the Centre for Quantum Computation and Communication Technology at UNSW. “Einstein was sceptical about entanglement, because it appears to contradict the principles of ‘locality’, which means that objects cannot be instantly influenced from a distance.”

But entanglement has been demonstrated time and time again through something by something known as Bell’s test, which requires engineers to violate Bell’s Inequality Principle. Basically, Bell’s Inequality Principle sets a limit for the amount of correlation there can be between two classical bits – anything above that must be quantum entangled.

“The key aspect of the Bell test is that it is extremely unforgiving: any imperfection in the preparation, manipulation and read-out protocol will cause the particles to fail the test,” said one of the researchers, Juan Pablo Dehollain. “Nevertheless, we have succeeded in passing the test, and we have done so with the highest ‘score’ ever recorded in an experiment.”

In their experiment, the two entangled particles in question were the electron and the nucleus of a single phosphorous atom, which was placed inside a silicon microchip. By entangling the two particles, they made it so that the state of the electron was entirely dependent on the state of the nucleus.

This meant that they expanded on the four possible digital codes that can be made with two traditional bits (00, 01, 10, or 11) to being able to create a much wider set of code words with two entangled bits, such as 00+11, 00-11, 01+10 or 01-10.

CollageEntangled web

“This is, in some sense, the reason why quantum computers can be so much more powerful,” said team member Stephanie Simmons. “With the same number of bits, they allow us to write a computer code that contains many more words, and we can use those extra words to run a different algorithm that reaches the result in a smaller number of steps.”

The next step is to entangle more particles and create more complex quantum code words, so that the team can begin to program an entire quantum computer. All the other pieces are already in place, in large part thanks to another UNSW team, which just last month built the first logic gate in silicon. The material is important, because it’s something we’re already incredibly familiar with building computers out of.

“Now, we have shown beyond any doubt that we can write this code inside a device that resembles the silicon microchips you have on your laptop or your mobile phone,” said Morello. “It’s a real triumph of electrical engineering.”

The research has been published in Nature Nanotechnology.

Teleportation is no longer science fiction – thanks to quantum mechanics scientists

Teleportation is no longer science fiction – thanks to quantum mechanics scientists can teleport information securely from one place to another. The latest episode of Quantum Around You explains how.

When most people think about teleportation, they think about someone disappearing in one spot and appearing in another instantly, Star Trek style. While that would be extremely useful, so far scientists haven’t found a way to do it.

But what they have managed to do is teleport information, and in some ways that’s even cooler.

Quantum teleportation, as its known, is a crucial area of research because it’s the only way humans can transmit information completely securely, with no risk of interception.

To do this, scientists exploit the special characteristics of quantum entanglement. You may have heard of it before, but the latest episode of  University of New South Wales (UNSW)‘s Quantum Around You does an amazing job of breaking down the physics behind the process.

As Associate Professor Andrea Morello, from the School of Electrical Engineering and Telecommunications at UNSW, explains, quantum entanglement is when two electrons become linked and lose their individuality. This means their state or “spin” – which can either be up or down – is defined only as being the opposite of each other.

If you split up two entangled electrons, the person with one can you’re suddenly able to transmit information from one to the other.

That means you could encode information on a single electron (an up spin could mean one thing while a down could mean another, or more commonly, up could represent a ‘1’ in the binary code, while down represents a ‘0’), and the person with the other entangled electron would be able to access that information by looking at what state their electron is in.

So how is that teleportation? What many people don’t realise is that as soon as that information is transmitted, it disappears from the electron of the sender and instantly reappears on the recipient’s electron. Ta da! This is because the sender has to to use another, non-entangled electron to read the information properly, and as soon as they do this the entanglement is lost.

But even though this is a pure example of teleportation, it doesn’t actually contradict Einstein’s theory of relativity, which states nothing can move faster than the speed of light.

Watch the episode above to find out why, and learn more about how scientists are making information disappear and reappear all over the world.