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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Tetris and sleep deprivation: how we can help emergency workers cope with trauma

First responders are at serious risk of developing PTSD during events like the Paris attacks. 

Some people seem able to deal with anything. They save a stranger from bleeding out in a bombed restaurant, protect passers-by from heavily armed gunmen, pull dead and dying people out of collapsed buildings, and they keep going because it is their job. These people are first responders.

When trauma goes on for days, as it has recently in Paris, however, the odds of them bouncing back from the violence, death and injury they are witnessing rapidly diminishes. They are at greater risk of developing a severe stress reaction known as post-traumatic stress disorder (PTSD). One study found that the worldwide rate of PTSD among first responders is 10 per cent, much higher than the 3.5 per cent rate among those not involved in rescue work.

Tetris to the rescue

So how best to address the problem? Research is in its infancy, but there are some promising studies. Emily Holmes’ group at the University of Cambridge has been looking at the benefits of playing Tetris, a video game, after a traumatic experience. The idea is that this could block the consolidation of traumatic memories so they don’t “flash back” later on.

For the study, her team first traumatised people by showing them distressing footage from public safety videos. The next day they invited them back into the lab to reactivate the memories with still images taken from the videos. One group then played Tetris for 12 minutes while the other sat quietly. Over the following week, the group who played Tetris had about 50 per cent fewer unwanted memories from the films compared to the group who didn’t.

The team concluded that playing Tetris helped individuals because it soaks up their visual processing capacity, making it harder for the brain to consolidate the visual parts of a traumatic memory.

Since it takes about six hours for the brain to cement a memory, the key is to play the game soon after trauma or within six hours of re-activating the traumatic memory. How long the helpful effects of playing Tetris will last and whether it will translate into helping people after real-life trauma is still unknown.

Talking it through

Other techniques, such as “updating”, taken from a highly-effective talking treatment for PTSD, may be more practical and easier to implement.

Like a detective, updating is a technique that focuses on finding new information and linking it to the case, the past memory. This is necessary because when the brain and body are in survival mode during trauma, the mind finds it difficult to encode all the relevant facts. Often key pieces of information that could make the memory less traumatic are lost. Updating links new information to someone’s memory of their trauma to make it less upsetting.

But can updating help to reduce unwanted memories after trauma?

We carried out a study, published in PLOS ONE, in which we traumatised people by showing them terrifying films of humans and animals in distress. We then divided our participants into three groups. One group watched the films again but were given new information about how long people suffered and whether or not they lived or died – essentially, they were updated. The second group watched the same films again but without the new information. And the third group watched films of humans and animals who were not in distress. The updated group had fewer traumatic memories and PTSD symptoms than the other two groups.

Updating is now being used by some UK emergency services. First responders will gather after critical incidents and update their memories of what happened before they go home.

Sleep deprivation

There are other techniques that may be helpful. One study found that depriving people of sleep may be useful in the aftermath of trauma.

But the same study found that a week after the trauma, people who had been deprived of sleep had the same number of unwanted memories as people who had slept well afterwards. Consequently, it remains unclear whether there would be any long-lasting benefits using this method. There are, however, certainly health risks linked to lack of sleep.

Still looking for a solution

To develop preventative interventions, we need to study newly-recruited emergency workers who haven’t yet suffered on-the-job trauma and follow them over time, spotting which “coping styles”, present before trauma, may predict their reactions afterwards.

For example, some people naturally react to stressful life events by dwelling on them, thinking about why they happened for hours on end. This strategy, called rumination, has been linked to PTSD in people who survived car crashes.

If rumination predicts PTSD in first responders, then preventative interventions could train people to spot when they are dwelling on an event and refocus their attention to the task at hand.

When we have identified which factors heighten emergency workers’ risk of developing PTSD, programmes can be developed to target those vulnerabilities. Only then can an intervention, directed at first responders most at risk of developing PTSD, properly protect them in their line of work.

The Conversation

Jennifer Wild is a Senior Research Fellow in Clinical Psychology at the University of Oxford

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