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.

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Why Twitter is dying, in ten tweets

It's ironic that the most heated discussions of the platform's weaknesses are playing out on the platform itself. 

Twitter has been dying since 2009, and commentators have pre-emptively declared it deceased pretty much every year since. To declare that it's on the downturn has become a bit of a cliché. But that doesn't mean that it isn't also, well, true.

Grumbling among users and commentators has grown to a roar over the past few days, thanks in part to a Buzzfeed report (refuted by Jack Dorsey, Twitter's CEO) claiming the service will move away from a chronological timeline and towards an algorithmic one. Users coined the hashtag #RIPTwitter in response, and, tellingly, many of their complaints spanned beyond the apparently erroneous report. 

They join a clutch of other murmurings, bits of data and suggestions that things are not as they should be in the Twitter aviary. 

Below is one response to the threat of the new timeline, aptly showing that for lots of users, the new feed would have been the straw that broke the tweeters' backs:

Twitter first announced it was considering a new 10,000 character limit in January, but it's yet to be introduced. Reactions so far indicate that no one thinks this is a good idea, as the 140 character limit is so central to Twitter's unique appeal. Other, smaller tweaks – like an edit button – would probably sit much more easily within Twitter's current stable of features, and actually improve user experience: 

While Dorsey completely denied that the change would take place, he then followed up with an ominous suggestion that something would be changing:

"It'll be more real-time than a feed playing out in real time!" probably isn't going to placate users who think the existing feed works just fine. It may be hard to make youself heard on the current timeline, but any kind of wizardry that's going to decide what's "timely" or "live" for you is surely going to discriminate against already alienated users.

I've written before about the common complaint that Twitter is lonely for those with smaller networks. Take this man, who predicts that he'll be even more invisible in Twitter's maelstrom if an algorithm deems him irrelevant: 

What's particularly troubling about Twitter's recent actions is the growing sense that it doesn't "get" its users. This was all but confirmed by a recent string of tweets from Brandon Carpenter, a Twitter employee who tweeted this in response to speculation about new features:

...and then was surprised and shocked when he received abuse from other accounts:

This is particularly ironic because Twitter's approach (or non-approach) to troll accounts and online abusers has made it a target for protest and satire (though last year it did begin to tackle the problem). @TrustySupport, a spoof account, earned hundreds of retweets by mocking Twitter's response to abuse:

Meanwhile, users like Milo Yiannopolous, who regularly incites his followers to abuse and troll individuals (often women and trans people, and most famously as part of G*merg*te), has thrived on Twitter's model and currently enjoys the attentions of almost 160,000 followers. He has boasted about the fact that Twitter could monetise his account to pull itself out of its current financial trough:

The proof of any social media empire's decline, though, is in its number and activity of users. Earlier this month, Business Insider reported that, based on a sample of tweets, tweets per user had fallen by almost 50 per cent since last August. Here's the reporter's tweet about it:

Interestingly, numbers of new users remained roughly the same – which implies not that Twitter can't get new customers, but that it can't keep its current ones engaged and tweeting. 

Most tellingly of all, Twitter has stopped reporting these kinds of numbers publicly, which is why Jim Edwards had to rely on data taken from an API. Another publication followed up Edwards' story with reports that users aren't on the platform enough to generate ad revenue:

The missing piece of the puzzle, and perhaps the one thing keeping Twitter alive, is that its replacement hasn't (yet) surfaced. Commentators obsessed with its declining fortunes still take to Twitter to discuss them, or to share their articles claiming the platform is already dead. It's ironic that the most heated discussions of the platform's weaknesses are playing out on the platform itself. 

For all its faults, and for all they might multiply, Twitter's one advantage is that there's currently no other totally open platform where people can throw their thoughts around in plain, public view. Its greatest threat yet will come not from a new, dodgy feature, but from a new platform – one that can actually compete with it.

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.