Dark skies: a view of the milky way during a meteor shower, Myanmar. Photo: Getty
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Dark energy vs dark matter: a battle of two cosmic monsters

Michael Brooks’s Science Column.

It might be the most prestigious journal in physics, but the Physical Review Letters is no good at teasers. Early in November it published a paper entitled: Indications of a Late-Time Interaction in the Dark Sector. Hardly a great headline for what should have been, in the style of Alien v Predator, “Dark Matter v Dark Energy” – a story of two cosmic monsters locked in eternal conflict.

We believe these monsters exist, but we haven’t seen either of them and we know very little about them. We have suspected the existence of dark matter since 1933, when a Swiss astronomer noticed something odd about the way galaxy clusters spin. They looked like they were being held together by the gravitational pull of invisible matter, which he duly named dark matter. We have been trying to see the stuff ever since, to no avail.

Dark energy is a more recent idea. It, too, comes from astronomical observations, this time of supernovae. A 1998 analysis of the light from these stellar explosions suggested that not only is the universe expanding, but this expansion is getting faster all the time. That can only happen with the help of energy from some unknown source – hence dark energy.

Together, dark energy and dark matter make up 96 per cent of the universe. Now, it turns out, dark energy may be consuming the dark matter.

The discovery came from more observations: this time, of the rate at which cosmic structures form. Dark matter seeds galaxy formation, but galaxies aren’t forming as fast as we would expect. This would make sense if dark matter were disappearing from the universe, but various straightforward explanations for why that might occur have failed to correspond with the observed facts. Now a team of British and Italian researchers has created a computer model that does match the observations. Critical to its success is the idea that dark matter is slowly being converted to dark energy.

According to the simulation, the ingestion of dark matter would be a relatively recent phenomenon, beginning roughly eight billion years ago. If it is really happening, it is important to understand, because our attempts to chart the history of the universe depend on dark matter’s role in forming cosmic structures.

Working from observations of the cosmic microwave background radiation, which came into being roughly 300,000 years after the Big Bang, researchers have shown that the radiation’s distribution through the universe would have seeded long filaments of dark matter. The gravitational pull of these filaments attracted the first atoms of normal matter, gradually creating stars and galaxies in long strings. This is the kind of structure we see now.

Yet if dark energy is slowly taking over from dark matter our previous calculations of cosmic history will have to be corrected. And intriguingly (spoiler alert), it will change our predictions. If dark energy is consuming dark matter, the universe will become dominated by dark energy more quickly than previously thought. That will precipitate an inglorious finale in which dark energy’s repulsive power pushes everything interesting away from us.

Eventually, all the other galaxies will be so far away, and receding so fast, that their light will never reach what remains of our Milky Way. Nearby stars will burn out. Our sun is expected to end its life as a huge single crystal of carbon: a dark diamond in the sky, with no surrounding starlight to make it sparkle.

Afterwards, all the atoms will drift apart and then the fundamental particles of matter will slowly decay to nothing. It’s not a Hollywood ending, but don’t complain that you weren’t warned. 

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.

This article first appeared in the 27 November 2014 issue of the New Statesman, The rise of the insurgents

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Apple-cervix ears and spinach-vein hearts: Will humans soon be “biohacked”?

Leafy greens could save your life – and not just if you eat them.

You are what you eat, and now bioengineers are repurposing culinary staples as “ghost bodies” – scaffolding on which human tissues can be grown. Nicknamed “biohacking”, this manipulation of vegetation has potentially meaty consequences for both regenerative medicine and cosmetic body modification.

A recent study, published in Biomaterials journal, details the innovative use of spinach leaves as vascular scaffolds. The branching network of plant vasculature is similar to our human system for transporting blood, and now this resemblance has been put to likely life-saving use. Prior to this, there have been no ways of reproducing the smallest veins in the human body, which are less than 10 micrometres in diameter.

The team of researchers responsible for desecrating Popeye’s favourite food is led by bioengineering professor Glenn Gaudette and PhD student Joshua Gershlak at the Worcester Polytechnic Institute (WPI). They were discussing the dearth of organ donors over lunch when they were inspired to use their lunch to help solve the problem.

In 2015 the NHS released figures showing that in the last decade over 6000 people, including 270 children, had died while waiting for an organ transplant. Hearts, in particular, are in short supply as it is so far impossible to perfectly recreate a human heart. After a heart attack, often there is a portion of tissue that no longer beats, and so cannot push blood around the body. A major obstacle to resolving this is the inability to engineer dense heart muscle, peppered with enough capillaries. There must be adequate flow of oxygenated blood to every cell in order to avoid tissue death.

However, the scientists had an ingenious thought – each thin, flat spinach leaf already came equipped with its own microscopic system of channels. If these leaves were stacked together, the resulting hunk of human muscle would be dense and veiny. Cautiously, the team lined the cellulose matrix with cardiac muscle cells and monitored their progress. After five days they were amazed to note that the cells had begun to contract – like a beating heart. Microbeads, roughly the same size as blood cells, were pumped through the veins successfully.

Although the leafy engineering was a success, scientists are currently unaware of how to proceed with grafting their artificial channels into a real vasculatory system, not least because of the potential for rejection. Additionally, there is the worry that the detergents used to strip the rigid protein matrix from the rest of the leaf (in order for human endothelial cells to be seeded onto this “cellulose scaffolding”) may ruin the viability of the cells. Luckily, cellulose is known to be “biocompatible”, meaning your body is unlikely to reject it if it is properly buried under your skin.

Elsa Sotiriadis, Programme Director at RebelBio & SOSventures, told me: “cellulose is a promising, widely abundant scaffolding material, as it is renewable, inexpensive and biodegradable”, adding that “once major hurdles - like heat-induced decomposition and undesirable consistency at high concentrations - are overcome, it could rapidly transform 3D-bioprinting”. 

This is only the most recent instance of “bio-hacking”, the attempt to fuse plant and human biology. Last year scientists at the Pelling Laboratory for Biophysical Manipulation at the University of Ottawa used the same “scrubbing” process to separate the cellulose from a slice of Macintosh red apple and repopulate it with “HeLa” cervix cells. The human ear made from a garden variety piece of fruit and some cervix was intended as a powerful artistic statement, playing on the 1997 story of the human ear successfully grafted onto the back of a live mouse. In contrast to the WPI researchers, whose focus is on advancing regenerative medicine – the idea that artificial body parts may replace malfunctioning organic ones – Andrew Pelling, head of the Pelling Laboratory, is more interested in possible cosmetic applications and the idea of biohacking as simply an extension of existing methods of modification such as tattooing.

Speaking to WIRED, Pelling said: “If you need an implant - an ear, a nose - why should that aesthetic be dictated by the company that's created it? Why shouldn't you control the appearance, by doing it yourself or commissioning someone to make an organ?

The public health agency in Canada, which is unusually open to Pelling’s “augmented biology”, has supported his company selling modified body parts. Most significantly, the resources needed for this kind of biohacking – primarily physical, rather than pharmacological or genetic – are abundant and cheap. There are countless different forms of plant life to bend to our body ideals – parsley, wormwood, and peanut hairy roots have already been trialled, and the WPI team are already considering the similarities between broccoli and human lungs. As Pelling demonstrated by obtaining his equipment via dumpster-diving and then open-sourcing the instructions on how to assemble everything correctly, the hardware and recipes are also freely available.

Biohacking is gaining popularity among bioengineers, especially because of the possibility for even wackier uses. In his interview with WIRED, Pelling was excited about the possibility of using plants to make us sexier, wondering whether we could “build an erogenous interaction using materials that have textures you find pleasing [to change how our skin feels]? We're looking at asparagus, fennel, mushroom...” If he has his way, one day soon the saying “you are what you eat” could have an entirely different meaning.

Anjuli R. K. Shere is a 2016/17 Wellcome Scholar and science intern at the New Statesman

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