An artist's impression of SN 2006gyM, one of the brightest supernovas ever recorded. Photo: Weiss/NASA/CXC/Getty
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“Supernova in a bottle” will help create matter from light

The new process could provide a clean way of doing particle physics experiments.

In 1934, two physicists came up with a theory that described how to create matter from pure light. But they dismissed the idea of ever observing such a phenomenon in the laboratory because of the difficulties involved setting up such an experiment.

Now, Oliver Pike of Imperial College London and his colleagues have found a way to achieve this dream, 80 years after US physicists Gregory Breit and John Wheeler explained the theory. This group hopes to use high-energy lasers aimed at a specially designed gold vessel to convert photons into matter-antimatter particle pairs, recreating what happens in some exceptional stellar explosions.

Pike, who led the research published in the journal Nature Photonics, said, “The idea is that light goes in and matter comes out.” To be sure, the matter created won’t be every day-objects; instead the process will produce sub-atomic particles.

“To start with, the matter will consist of electrons and its antimatter equivalent positrons,” Pike said. “But with higher energy input in the lasers, we should be able to create heavier particles.”

Pike concedes this won’t be the first time light has been converted into matter. In 1997, US researchers at the Stanford Linear Accelerator Centre (SLAC) were able to do so, albeit in a different way.

The SLAC experiment used electrons to first create high-energy light particles, which then underwent multiple collisions to produce electrons and positrons, all within same chamber. This is called the multi-photon Breit-Wheeler process, named after the two physicists who came up with the theory in 1934.

“The key difference in the SLAC experiment and the one we propose is that our process will be more straightforward,” Pike said. In the new proposal, the laser beam will still be generated using free electrons, but it will be separated from the electrons.

Why create light using matter and then convert it back? Apart from showing that the Breit-Wheeler process can happen without the multiple photons the SLAC experiment needed, Pike thinks their process provides a clean way of doing particle physics experiments.

Current particle-physics experiments involve smashing sub-atomic particles at great speeds and sorting through the mess of new particles that are created in the explosion. This is how the Higgs boson was found in the Large Hadron Collider.

The new experimental design will be similar. Rather than involving a complicated mix of particles and photons, the laser beam will be sent into a small gold hohlraum (German for “empty room”). There, individual photons can interact with the radiation field that’s generated when the hohlraum is excited by a laser, creating the electron-positron pairs.

“While physicists have excellent methods to sift through such data, our process has the advantage that it will be easier to analyse,” Pike said. “Light will go in from one end of the hohlraum and particles created will come out from the other end.”

Pike and colleagues are now working to secure time on high-energy laser beams to carry out the experiment. The two likely candidates are Aldermaston, Berkshire in the UK or Rochester, New York in the US.

Andrei Seryi at the University of Oxford found the work interesting, but warned it is still too far away from being used in particle-physics experiments. “Theoretically, however, it would be great if we are able to create particles from only light.”

“With such high energy lasers, we may not need to build big particle colliders, such as the Large Hadron Collider, which is a 22km underground tunnel,” Seryi said.

Even if we do manage to create a photon collider, we would only be catching up with the natural world, where a specific type of supernova, called “pair instability,” involves the creation of proton-antiproton pairs. If Pike is able to achieve this phenomenon, he will essentially be creating a supernova in a bottle.

The ConversationThis article was originally published on The Conversation. Read the original article.

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YouTube announces new measures against extremism – but where do they leave the far right?

Videos by alt-right commentators have arguably radicalised many online. Will Google's latest policies do anything to change this?

Within hours of the terrorist attack in Finsbury Park, Tommy Robinson was trending on Twitter. The former leader of the English Defence League accused the Finsbury Park mosque of “creating terrorists” in a series of tweets on his personal account.

More than 17,400 people have now tweeted about the 34-year-old, with many theorising he could have radicalised the attacker who allegedly shouted “I’m going to kill all Muslims” at the scene. At present, there is no evidence that the man arrested by police on suspicion of attempted murder is a fan of Robinson.

“People are saying I’m inciting hate,” said Robinson in a video uploaded to Twitter and YouTube after the attack. “I just tell the facts and the truth and I’m not going to apologise for that…

“If giving you quotes from the Quran that incite murder and war against us is inciting hate, I’m guilty. If telling you all the problematic problems that come from the teachings and scriptures of Islam, I’m guilty. But these are just facts.”

After describing the country as being at “war”, he goes on to say: “Please one person, just one, give me one example of me inciting hate.”

When we talk about radicalisation and terrorism, we are finally to understand that this extends beyond the work of Isis.

Just over a year ago, Labour MP Jo Cox was murdered by a white supremacist. This morning, Harry Potter author JK Rowling used Twitter to accuse columnist Katie Hopkins of contributing to radicalisation. The New Statesman’s own Media Mole notes how right-wing tabloids incite hate.

In particular, it is now evident how the far right radicalises online. In December 2016, a man fired three shots in a Washington DC pizza parlour that the alt-right (on 4Chan and YouTube) had accused of being at the centre of a paedophile ring.

The internet arguably allowed Anders Breivik, the Norwegian far right white supremacist who killed 77 people in 2011, to cultivate his extreme views. Alexandre Bissonnette, the white nationalist who murdered six men at a Québec City mosque in January, was described by many as an “internet troll”.

Earlier this year, a report by the Commons home affairs committee accused social media giants of not doing enough to tackle terrorism online. In response to this – and following a series of high-profile brands pulling their advertising from YouTube after it was featured on or by terrorism-related videos – Google, which owns the video-sharing site, has now announced four steps it is taking to fight online terror. But do these reflect the reality that there are many forms of extremism?

Google’s new guidelines speak of “terrorism” and “extremism” in broad terms. This means that videos glorifying or inciting terrorism will be treated the same whether they are from the far right, far left, or pro-Isis organisations.

Google’s four steps for tackling such videos include: using machine learning to identify videos glorifying violence, using a team of human flaggers to identify problematic videos, and using a "redirect method" to send potential Isis recruits towards anti-terror videos. Each of these steps is concerned with content that either breaks the law or violates YouTube’s policies.

The fourth step (or rather the third, as it is ordered in Google’s blogpost) is focused on non-illegal, non-policy violating content. For example, this could include videos that don’t directly incite terrorism, but arguably incite hate, such as those denying the Holocaust.

According to Kent Walker, Google’s general counsel, these could also be “videos that contain inflammatory religious or supremacist content”. Rather than being removed like the other offending videos, these will be hidden behind a warning, not have adverts on them (therefore preventing their creators from making money), and will not be eligible for comments. Essentially, as Walker writes, “that means these videos will have less engagement and be harder to find”.

It remains to be seen whether – or how – this will apply to the content of Tommy Robinson. YouTube’s steps will be taken on a video-by-video basis, meaning no far right commentator will be banned outright. Instead, YouTube simply won’t promote any offending videos, meaning they will not appear in their subscribers’ recommended feeds and will be difficult to find on the site.

In this way, Google has remained committed to free speech while doing more to tackle extremism on YouTube. Those like Robinson who claim to just “tell the facts” could arguably now be held to account for their actions. Many on the far right are careful to not explicitly advocate violence. Nevertheless, the loaded language used in their videos could arguably incite hate.

Paul Joseph Watson, a right-wing conspiracy theorist YouTuber with nearly one million subscribers, has never advocated terrorism, but has videos entitled “Islam is NOT a Religion of Peace” and “Chuck Johnson: Muslim Migrants Will Cause Collapse of Europe”.

In the past I have argued that allowing Google and YouTube to censor us in the name of “extremism” and “terrorism” is a troubling trend, but with these new promises, the company has walked the delicate line between the law and free speech. By allowing hateful, but not illegal, content to be hosted on its site and yet restricted from a wider audience, YouTube is taking a stand against extremists of all kinds.

Amelia Tait is a technology and digital culture writer at the New Statesman.

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