Does dark matter exist?

After 80 years of agreement about the dark stuff, opinions may be changing.

The peasants are revolting. Last night the Flamsteed Astronomical Society met at the National Maritime Museum to hear a debate on the existence (or not) of dark matter. In a vote at the end, the audience decided it probably doesn’t exist.

The idea of dark matter has been around since 1933, when a Swiss astronomer called Fritz Zwicky found that centrifugal forces should have been tearing spinning galaxy clusters apart – but weren’t. The answer, he suggested, was that there was extra stuff in there, whose gravitational pull was holding everything together.
 
Astronomers now believe this stuff makes up around a quarter of the universe, if you take into account all the mass and energy in the cosmos. Ignore the pure energy, and dark matter accounts for 80 per cent of the universe’s mass. Which makes it a little embarrassing that we have never seen any.

Neither do we know what it looks like. We’ve been groping around for dark matter since about 1970. Various predictions have been made: in 1980, astronomer Vera Rubin said it would be found within 10 years. In 1990, astronomer royal Martin Rees said the dark matter mystery would be solved by the turn of the century. In 1999 Rees was aware he had been too hasty, and said we would know what dark matter is by 2004. Last January, CERN theoretical physicist and Gandalf lookalike John Ellis gave the physicists another decade.
 
But patience is starting to wear thin. At last night’s debate, Oxford physicist and co-presenter of The Sky at Night Chris Lintott made the case for dark matter; astronomy writer Stuart Clark argued that a modification to the laws of gravity, which are dictated by Einstein’s general relativity theory, held more promise for explaining the (apparently) missing mass. At the end of the evening, the audience sided with Clark and modifying gravity.
 
That’s not going to have dark matter astronomers quaking in their boots. But it is nonetheless indicative of a change of mood. Take what went on at the Cosmic Variance blog last week. Sean Carroll, the blog’s host, has always been bullishly pro dark matter. But it seems he has started to hedge a bit.
 
In a fascinating post, he published the trialogue he had been conducting with astronomer Stacey McGaugh, the original proponent of the modified gravity idea (it’s called MOND: modified Newtonian Dynamics) and German astrophysicist Rainer Plaga. Right at the top, Carroll concedes that “it may very well turn out that the behavior of gravity on large scales does not precisely match the prediction of ordinary general relativity”. In other words, he is saying, we might well have to modify gravity.
 
It’s worth pointing out a couple more reasons it’s OK to harbour doubts about the dark stuff. Last September, Durham astronomer Carlos Frenk admitted he was “losing sleep” over the results of his own computer simulations. His work had showed that the way simulated dwarf galaxies – mainly composed of dark matter – form in a halo around our own galaxy doesn’t tally with what we observe. His conclusion was that the standard theory of dark matter is almost certainly wrong, adding that searches for the stuff at the LHC in Geneva would therefore prove fruitless.
 
Then last month two groups of astronomers announced that dark matter wasn’t where it should be. The sun is meant to be surrounded by a halo of dark matter, and it isn’t.
 
If there really is no dark matter, that won’t be a mainstream view for decades to come. Once it’s got some momentum, it takes a lot of effort to change direction in science. But it does seem that, after 80 years, someone’s found the handbrake on the dark matter juggernaut.
 

Images of giant galaxy clusters, said to be mainly made up of dark matter. Photograph: Nasa/Getty Images

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

Cleveland police
Show Hide image

Should Facebook face the heat for the Cleveland shooting video?

On Easter Sunday, a man now dubbed the “Facebook killer” shot and killed a grandfather before uploading footage of the murder to the social network. 

A murder suspect has committed suicide after he shot dead a grandfather seemingly at random last Sunday. Steve Stephens (pictured above), 37, was being hunted by police after he was suspected of killing Robert Godwin, 74, in Cleveland, Ohio.

The story has made international headlines not because of the murder in itself – in America, there are 12,000 gun homicides a year – but because a video of the shooting was uploaded to Facebook by the suspected killer, along with, moments later, a live-streamed confession.

After it emerged that Facebook took two hours to remove the footage of the shooting, the social network has come under fire and has promised to “do better” to make the site a “safe environment”. The site has launched a review of how it deals with violent content.

It’s hard to poke holes in Facebook’s official response – written by Justin Osofsky, its vice president of global operations – which at once acknowledges how difficult it would have been to do more, whilst simultaneously promising to do more anyway. In a timeline of events, Osofsky notes that the shooting video was not reported to Facebook until one hour and 45 minutes after it had been uploaded. A further 23 minutes after this, the suspect’s profile was disabled and the videos were no longer visible.

Despite this, the site has been condemned by many, with Reuters calling its response “bungled” and the two-hour response time prompting multiple headlines. Yet solutions are not as readily offered. Currently, the social network largely relies on its users to report offensive content, which is reviewed and removed by a team of humans – at present, artificial intelligence only generates around a third of reports that reach this team. The network is constantly working on implementing new algorithms and artificially intelligent solutions that can uphold its community standards, but at present there is simply no existing AI that can comb through Facebook’s one billion active users to immediately identify and remove a video of a murder.

The only solution, then, would be for Facebook to watch every second of every video – 100 million hours of which are watched every day on the site – before it goes live, a task daunting not only for its team, but for anyone concerned about global censorship. Of course Facebook should act as quickly as possible to remove harmful content (and of course Facebook shouldn’t call murder videos “content” in the first place) but does the site really deserve this much blame for the Cleveland killer?

To remove the blame from Facebook is not to deny that it is incredibly psychologically damaging to watch an auto-playing video of a murder. Nor should we lose sight of the fact that the act, as well as the name “Facebook killer” itself, could arguably inspire copycats. But we have to acknowledge the limits on what technology can do. Even if Facebook removed the video in three seconds, it is apparent that for thousands of users, the first impulse is to download and re-upload upsetting content rather than report it. This is evident in the fact that the victim’s grandson, Ryan, took to a different social network – Twitter – to ask people to stop sharing the video. It took nearly two hours for anyone to report the video to Facebook - it took seconds for people to download a copy for themselves and share it on.  

When we ignore these realities and beg Facebook to act, we embolden the moral crusade of surveillance. The UK government has a pattern of using tragedy to justify invasions into our privacy and security, most recently when home secretary Amber Rudd suggested that Whatsapp should remove its encryption after it emerged the Westminster attacker used the service. We cannot at once bemoan Facebook’s power in the world and simultaneously beg it to take total control. When you ask Facebook to review all of the content of all of its billions of users, you are asking for a God.

This is particularly undesirable in light of the good that shocking Facebook videos can do – however gruesome. Invaluable evidence is often provided in these clips, be they filmed by criminals themselves or their victims. When Philando Castile’s girlfriend Facebook live-streamed the aftermath of his shooting by a police officer during a traffic stop, it shed international light on police brutality in America and aided the charging of the officer in question. This clip would never have been seen if Facebook had total control of the videos uploaded to its site.  

We need to stop blaming Facebook for things it can’t yet change, when we should focus on things it can. In 2016, the site was criticised for: allowing racial discrimination via its targeted advertising; invading privacy with its facial-scanning; banning breast cancer-awareness videos; avoiding billions of dollars in tax; and tracking non-users activity across the web. Facebook should be under scrutiny for its repeated violations of its users’ privacy, not for hosting violent content – a criticism that will just give the site an excuse to violate people's privacy even further.

No one blames cars for the recent spate of vehicular terrorist attacks in Europe, and no one should blame Facebook for the Cleveland killer. Ultimately, we should accept that the social network is just a vehicle. The one to blame is the person driving.

If you have accidentally viewed upsetting and/or violent footage on social media that has affected you, call the Samaritans helpline on  116 123 or email jo@samaritans.org

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

0800 7318496