Love is in the air... or is it dark matter?

It’s fair to say that science sometimes has a bit of an image problem. Hollywood loves to portray scientists as intellectual, hyper-rational people. Cold, perhaps even a little less human than normal people…. However, that’s complete poppycock – our hearts beat the same way as anyone else’s does, and every scientist has their passionate side. Since it’s Valentine’s Day, we thought we’d let you into a little secret - did you know that many of us spend our days contemplating the science of attraction?

Take the Universe, for example – it relies on gravity, one of the most irresistible of forces. Since the apple fell from the tree and inspired Sir Isaac Newton, we’ve had an answer for why the planets orbit the Sun, and how galaxies and even larger structures like galaxy clusters are formed. Except it’s not that simple, and – like a good first date – the Universe is preserving some of its mystery to keep us interested. There’s not enough visible matter (mass) in the Universe to account for all that attraction. We know that objects in galaxies, and galaxies in clusters, are moving too quickly – if it was only the gravitational attraction of the visible matter that was keeping them together, then they should have flown apart. Something is literally putting them all in a spin, and measurements indicate that perhaps as much as 85% of the matter in the Universe is “missing” – invisible due to a lack of interaction with light.

Dark matter science is very much like dating – some scientists preferred MACHOs and others are more attracted to WIMPs. MACHOs are Massive Astrophysical Compact Halo Objects, big things like black holes, neutron stars and white dwarfs that are very faint and hard to see. Their gravity deflects light from the distant stars behind them, an effect called ‘gravitational lensing’. We can infer the presence of MACHOs from the amount of gravitational lensing that we see, and we just don’t see enough of it to account for all that missing mass. Unfortunately it seems that there just aren’t enough MACHOs to go around.

Love might be in the air today, but are you sure you’re not just feeling the effects of dark matter? An alternative theory suggests that the entire Universe is swimming with WIMPs, Weakly Interacting Massive Particles (massive meaning they have mass, not that they’re huge!). Just like shy Valentines, WIMPs are exotic particles that don’t interact much with normal matter, and hence are hard to detect. Particle physicists all over the world are searching for these particles, or the traces they leave behind.

If you want to detect WIMPs here on Earth then you have to try and filter them out from the particles that arrive from space – cosmic rays. The best way to do that is to bury your detector under a mountain, or take it down a very deep mine. Several experiments to detect dark matter have taken place at Boulby Underground Laboratory in the north east of England, in Britain’s deepest mine. By day, it’s a common or garden salt and potash mine; at night in a secret lab scientists beaver away to uncover the secrets of dark matter (actually they work a normal day shift, the same as the miners, and the lab is not so much secret as unusual - but that doesn’t sound as romantic). These experiments, which are also occurring in other deep places on the planet, are looking for direct evidence of dark matter – the particles themselves.

Elsewhere, some astronomers are looking for dark matter indirectly by looking for those gravitational lensing effects, while others are looking for characteristic signals indicating the mutual annihilation when two WIMPs meet. Some relationships are destined to fail it seems.... But fear not - at CERN, particle physicists are trying to create brand new dark matter particles in the collisions of their normal matter counterparts. As they only interact weakly, even the amazing sophistication and grandeur of the big detectors such as ATLAS and CMS  have no hope of seeing these new particles directly, but the scientists should be able to infer their presence by looking for imbalances in the energy and momentum carried away from the collisions they see.

Even if we find dark matter and reveal the secrets of the Universe’s unexpected attraction, the Universe will still have some surprises up its sleeve. For example, despite gravity’s pull, we have discovered that the Universe as a whole is expanding – and that the rate of that expansion is increasing. Researchers are now investigating how a mysterious force known only as Dark Energy is overcoming gravity to make that happen.

The pioneering scientists of the 19th century couldn’t have foreseen the impact on society of their experiments, but their results have transformed the way we live our lives. Valentine’s Day wouldn’t be Valentine’s Day if there were no sparks flying, especially as we now can’t make it through a day without electricity and electronic devices. But all of that only became possible due to the work of scientists like JJ Thompson, whose experiments confirmed the existence of the electron and won him a Nobel prize. James Clerk Maxwell understood that electricity, magnetism and optics could all be explained by electromagnetism, and developed a set of equations that encompassed all three – a great unification of physics. And Michael Faraday worked in electromagnetism and electrochemistry and developed the laws of electrolysis.

It could be said that they were also simply looking at attraction and repulsion. Opposites attract, they say, and indeed like charges (and magnetic poles) repel each other, whilst differing charges and poles find each other strangely attractive. Such a simple concept now allows us to have tiny lithium-ion batteries powering our mobile phones and tablets, and scientists are working hard to make advanced materials for battery electrodes, so that the batteries have as long a life as possible (although hopefully they won’t outlast your current crush).

They’re using the ISIS neutron source as one way to investigate the structure of these new materials. ISIS is a spallation neutron source, powered by a particle accelerator. We have one or two of those hanging around the place, and a quick peek into a particle accelerator shows you that there are big magnets – really big magnets – all over the place. They do some very important jobs: dipole magnets (with one north and one south pole) use an irresistible force to bend the beams of particles around corners (which allows particle accelerators to fit into much smaller spaces than it the particles were accelerated in a straight line). Quadrupole magnets (with two north, and two south, poles) use the same force to focus the beam, in a similar way to that in which an optical lens focuses light.

Clearly particle accelerators rely on magnetism, but they’re no stranger to attraction either – it’s fundamental to the ways that particles are accelerated. These days it’s all done in RF cavities, where electromagnetic waves resonate at just the right frequency so that the particles are attracted by their positive amplitude, but hidden from their negative amplitude – giving particles a boost of energy at every cycle. As with any relationship, it’s crucial to get the timing right - this very clever process has to be properly synchronised, which is how synchrotron particle accelerators got their name.

This has been a light-hearted look at attraction in science for Valentine’s Day, but here at STFC we love science every day – and we’d love the chance to tell you why. Head over to Twitter and follow @STFC_Matters for more, or check out the #lovescience hashtag. We’re also on Facebook, so we’d love to see you there!

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