Dark Matter: A Massive Mystery

The mini, personalised computers that are smartphones have revolutionised the modern world. We're now more connected than ever before and, increasingly, thanks to the huge variety of applications available for download, we can enhance the capabilities of these devices way beyond being just a phone. Technology investor Peter Cowley explained to Graihagh Jackson just how big an impact this could make on the healthcare sector...

Peter - If you take a modern smartphone which is really a computer with a phone attached to it, there are a huge number of sensors in it. There's over a dozen sensors in there already. Not all of them are relevant of course to health applications, but things like the microphone, if we want to listen to our voice, there are temperature sensors in some of them. More modern ones have got means of measuring heart rate etc. So, if you take the number of sensors in there already, there's already an amount of data that can be derived from the phone. The phone is then connected of course to the cloud and that data can then be analysed by and then passed on to other people.

Graihagh - And it's not just the apps that we can download in the sensors that are already within our phones. There's actually stuff that we can plug on to our phones and enhance that even further.

Peter - Yes. There's an amazing number of sensors one can plug in - a glucose meter for instance if you're diabetic to save carrying around another device because it's built into your phone. There's a blood pressure monitor cuff. There's even an ultrasound device which when plugged in, really just to possibly check one's unborn baby.

Graihagh - So, you could just plug this into your phone via say, the volume port or even the charge port and get the ultrasound up and look at the baby in real-time. That's incredible!

Peter - Exactly, using the charge port. Yes, there was a little start up that I saw based at Slovenia that's now based in California that won a prize in Vienna recently. The device I brought in with me today is actually ECG. So, this detects the heart rate and also the electrical impulse of the heart. This plugs onto the back of the phone. It generates, turns the electrical signal into sound and then goes through the microphone on the phone. As you can see that my heart rate is even higher than it was earlier.

Graihagh - I was going to say, it was 98 before. It's now 115. So, you're obviously feeling a little bit nervous.

Peter - Yes. It's stressful being in front of a live microphone. You radio professionals don't seem to have that problem. But the important thing is you can see the wave form of the heart. Now, I can't interpret that. I'm not a medic, but I can then take a snapshot of that and send it to my heart surgeon who can then say, "Fine. Peter, you're okay" or "Please come and see me."

Graihagh - So, that's now, and these things are all available now, but what can we be looking forward to in the future?

Peter - In the near term, the big that's going to be coming into our high end phones which will gradually work its way down is a type of gas sensor. So, it's monitoring a whole variety of gases from carbon monoxide, possibly for situations where there's gas leak from a fire, carbon dioxide, volatile organic compounds. Now, these are very complex set of things like aldehydes and ketones, and hydrocarbons. The important thing there is air quality. So imagine going for a run in the summer in a polluted city and your phone telling you where to run and where not to run based on the quality of the air there.

Graihagh - Wow! That's quite something. All these monitoring, we're doing a lot of it already. What's the benefit? Why do we actually want to do this other than just say, a bit of personal interest I guess?

Peter - Yes, this goes for tech and early adopters. Two things really - one is the so-called quantified self where we weighed ourselves for a while, we've checked our calorific spend, we're also getting to the point where we want to measure other things like blood pressure and heart rate, etc. Medical profession would benefit a lot from having that data. Once it can be clinically proven that a data is correct, having that data so we don't have to continually visit our GPs to have tests done. So that our mobile devices will then in the end potentially predict when we should go and even book the appointment with one's GP actually if we look forward 10 or 20 years.

Graihagh -  And you say, when they're clinically proven to be accurate, does that mean they're currently not accurate and there are ongoing trials to see whether they are accurate enough to be used as a diagnostic tool?

Peter - That's a very complex question. The point between taking some data and making it clinically usable it's going to be a while before the medical profession will believe the sensors will be good enough to use instead of the devices they've got inside the hospital. But it's a precursor to that which will then warn to the point where you can have test done internally in the hospital. But go forward 5 or 10 years, there's no reason why we shouldn't get that far.

Making the best cheese requires milk from which the cream has been skimmed off. But waiting for the cream to rise to the top naturally can take hours, and even then some larger globules of fat remain behind, which can make the cheese less tasty. Now, scientists in Australia have discovered that a blast of high-frequency sound waves can make the separation process happen much more rapidly, and result in a superior product. Swinburne University's Tom Leong told Graihagh Jackson how it works...

Tom - Traditionally, we use the process called natural separation to remove the cream from milk and essentially what this is is we leave milk in a bucket and naturally, the cream will rise to the surface and we just collect it off. However, this is a very slow process requiring several hours. This is not feasible for large cow production. So today in the dairy industry, what we use is a machine called the centrifuge. What this does is that we spin milk at a very, very fast rate, several thousand times faster than the speed of gravity. This pulls out all the fat from your milk in a very, very fast timescale in the order of seconds to minutes.

Graihagh - That sounds like a pretty efficient method. What was wrong with this method that you then decided to go away and devise another?

Tom - One potential issue is that when we use a centrifuge, we rip out all the fat. So, what we will have remaining is very, very skim. And so, in order to make 3% fat milk you have to take a portion of this cream and put it back in.

Graihagh - Okay, I see. So, all milk is skinny milk if you like, no fat and then to make the semi-skim milk, you just have to go and put a load of fat back in it. So, it's a bit inefficient essentially.

Tom - Yes. So, one of our motivations was to have a technique where we could pretty much dial in a composition that you wanted. Let's say, 2% fat milk, you put it in and your process would spit that out without having to restandardise. And so, the technique that we're interested in using is applying soundwaves to speed up the rate of which natural separation occurs.

Graihagh - You say you're using soundwaves to do this. So, if we were to put our voices and channel it through the milk, would my voice produce a low fat milk or is it not quite as simple as that?

Tom - It's not quite as simple as that so the soundwaves that I'm talking about are actually, ultrasound waves. These oscillate at say, millions of times per second. The voice is tens to hundreds of oscillations per second. So, we're actually several orders of magnitude higher in terms of frequency.

Graihagh - There was me thinking that we could create a Naked Scientists cheese but...

Tom - Compared to say, natural separation itself, 5 minutes as opposed to say, 6 hours.

Graihagh - Wow! So, it's a huge improvement on the natural process then.

Tom - Obviously, we can't compare with a centrifuge in this respect because a centrifuge takes several seconds though. But one of the reasons as to why we're interested in accelerating natural separation as opposed to trying to improve centrifugation is that natural separation is a method still used today in traditional manufacturers of specialty cheese. For example in northern Italy, they use natural separation as the method to make the skim milk which they use to make parmesan cheese. The motivation for doing this is when you use natural separation, we're not pulling out all the fat globules we're specifically, pulling out the larger fat globules. So, what is retained in the semi-skim milk specifically has more of the smaller fat globules. So, if you have small fat globules and you eat the cheese it tastes creamier. And also, there's benefits in terms of when the cheese develops its flavour, the small fat globules contribute to this as well.

Graihagh - So, multiple benefits - not only is it faster, it's actually tastier and a little bit better for you. What's not to like? Is it going to be cheaper cheese for all?

Tom - It depends on how large the scale we can scale this technology to. At the moment, we're currently developing one that can go to say, 100 to 200 litres per hour.

Graihagh - As a non-dairy farmer I suppose, 100 litres an hour, what sort of scale is that? I'm finding it hard to imagine 100 litres of milk.

Tom - A hundred litres per hour is actually a very, very small scale. So, if we're talking about a large diary producer where they're making 10,000 litres per hour. 100 litres per hour is more along the lines of say, of a farmhouse style producer. Obviously, the larger the device that we can build, the higher the throughput and therefore, the more benefit in terms of profit that a potential dairy producer could obtain from it. Obviously, the scale is in terms of being cheaper to make if it's bigger relative to a smaller version.

Graihagh - A sound idea. Swinburne University's Tom Leong. 

The work was a collaboration between Swinburne University of Technology and the CSIRO, and was jointly funded by the Australian Research Council and the Geoffrey Gardiner Dairy Foundation.

Science has been grappling with a problem that's been around for nearly 100 years - what is our universe made of? When physicists look out into space, they're confronted with a mystery: the material or matter we can see makes up only about 5% of the mass that we know must be out there. The other 95% is totally invisible to us, and so scientists refer to it as dark. At least 20% of the mass out there is what we call Dark Matter. But if it's invisible, how do we know it's out there? University College London cosmologist Andrew Pontzen explained to Chris Smith... 

Andrew - Well, we can kind of take a census of what's out there in the universe and we do that by making indirect measurements. So for instance, you might measure how fast things are  moving around and one of the famous measurements of this was made by Fritz Zwicky. He was looking in clusters of galaxies and measuring how fast the galaxies within that were moving around relative to each other.

He found that they were zooming around really fast. So fast, that that galaxy cluster would simply fall apart unless there was something sticking it together. And so, his explanation for that was, there must be some extra stuff in there with an extra pull of gravity, serving that purpose of gluing the galaxy clusters together. And since then we've seen this phenomenon all over the place

Chris - Because we know how things should move when gravity acts on them. When we make observations of things in the universe, we're seeing them moving at the wrong speed for they're not to be more mass there, more gravitational acting material than we can actually see and that's what we're calling dark matter.

Andrew - That's right. So, it builds on how we know gravity works and thanks to Newton and then later Einstein, we think we kind of have that pinned down. We think we know how gravity works and then this idea that there has to be extra stuff follows.

Chris - And when you take the estimates that people have made it, looks like it sums to about a fifth of the mass.

Andrew - Yeah. It's got to be something like that.

Chris - So, it's pretty prolific. Where is it distribute in the universe? Is there dark matter in this room with us?

Andrew - Yup! If we're right, there certainly is dark matter in this room, zipping through really fast., it has to be said. It doesn't clump together in the same concentrated waya normal matter does. So, the Solar System and everything within it - the Earth and the sun, and everything in this room is stuck together by forces that dark matter doesn't seem to feel. So, as a result, it's much more spread-out through the universe and it's zipping through the room at the moment maybe at hundreds of kilometres every second.

Chris - So, what physically might it be?

Andrew - Well, we think it's got to be some kind of extra fundamental particle. Particles are the things that make up normal matter. In fact, we talk about particles when we're talking about say, protons and neutrons, and electrons, the things that we know make up atoms and then make up the familiar world. So, we think there's an extra type of particle that as yet, hasn't been directly discovered but is out there in the universe.

Chris - Are these the WIMPs that physicists are fond of talking about?

Andrew - That's right. So, that's one particular type of WIMP or weakly interacting massive particle.

Chris - And how might we be able to detect the stuff that we can't see?

Andrew - Well, there are a number of different ways. One way is to try and make it: if you take something like the Large Hadron Collider for example, you can smash particles of normal matter together. We think if you could get to high enough energies in those collisions, occasionally, you'd actually manufacture one of these mysterious new particles. And then actually, you think, how would you find out? How would you know that you manufactured it if it's invisible? And the answer is, you would look for things going missing. You would put in a certain amount of energy and you would sum up everything that you saw come out and realise, something has gone missing. So, you'd know you made something extra. That's one way you could do it.

Another way is to actually go all out and just say, "Well surely, we must be able to detect these things. We must be able to see directly that they're there one way or another." That's what we call direct detection and people are certainly trying to do that as well. It's just really, really challenging because you need to be incredibly sensitive. If we're right about these particles, they so rarely and so weakly interact with normal matter that we're made out of and any detector that we could build would be made out of, that it's a real challenge just to build something that can do that.

Chris - And that's the reason they're invisible because they just don't interact with stuff.

Andrew - Exactly. In fact, when we say dark matter, it's almost a bit of a bad name because the stuff isn't actually dark. It's just transparent because exactly like you say, simply not interacting with stuff, except through its pull of gravity.

Chris - Does that mean that they're interacting with the other thing that's been big news in recent years, the Higgs Boson, which CERN made a great climax about announcing? They think they have discovered this particle that appears to add mass to things. Does that mean that these dark matter particles are in some way bound up with Higgs Bosons?

Andrew - Certainly what's true is that the Higgs Boson would feel the gravitational pull of a dark matter particle and vice versa. That's got to be true, but what we don't know is just how bound up are these two things. Could it be the case, for instance, that the Higgs Boson - when they start to probe its properties in more detail - the Large Hadron Collider - could it be that it points the way to understanding of where dark matter is coming from? Well, it could be but we just don't know at the moment.

Chris - Because I was going to say, the standard model, which is this jigsaw puzzle of how we think matter is constructed and what the particles are that give rise to matter, when the Higgs Boson came along, people said, "right. Look, that's the missing piece." Well now, we've got this extra piece in the puzzle, the dark matter particle, where does that go in a puzzle that's full then?

Andrew - . Within the standard model, there are certainly conundrums...

Chris - Then it's conundra.

Andrew - I'm sorry. I forgot that that's in Cambridge. Yes, there are certainly conundra within the puzzle and those conundra, as we try to start to answer them, for instance, how does - what we know about particle physics on very small scales, fit together with how we know the universe works on very large scales - this just doesn't fit together at the moment. It's as people try to work out how all that fits together, that they realise, "Okay, looks like we've got to have these extra particles."

Firing protons at each other to create dark matter may be one way of figuring out what this elusive substance is, but another is by detecting the dark matter particles that we believe must be bombarding us every second. But how do we do this? Last month, UK scientists were awarded a grant to build the biggest dark matter detector yet! It's called LZ - short for Lux Zeplin - and it will buried deep underground in the US. Scientists like UCL's Dr Cham Ghag, who's one of the researchers involved with the project, hope to start seeing results by 2021, as he explained to Chris Smith...

Cham - So, the LUX Zeplin or LZ experiment will be going about a kilometre and a half under the surface in the black hills of South Dakota.

Chris - When you say deep underground, what's actually there? Is it like a mine or something?

Cham - It is. It was a former gold mine. All the mining corporations have ended and now, it's a dedicated science laboratory with a couple of experiments, there ready.

Chris - Why go to the lengths of being 1.5 kilometres underground to do these experiments?

Cham - These sorts of experiments have to be made from low radioactivity materials. And that's because we're really looking for a needle in a haystack and we want to make their haystack as small as we can because all materials carry some trace amount of radioactivity.

There's a lot of that about on the surface of the Earth in particular. We're bombarded from space with cosmic rays and so, to get away from those, and the first line of defence, against all these radioactivity that's out there within which we're trying to find the faintest signals from dark matter, we go deep underground. And that really shields us from cosmic rays in particular.

Chris - What, in fact, is the detector your building? How will it work?

Cham - So, the detector is configured in a Russian doll set up where the first line of defence is the earth itself. It's 1.5 kilometres of rock above us. But then once we're down into the underground laboratory, we have a giant water tank that shields the detector within from radiation that's coming from the rock and the laboratory in the sort of ambient environment. And then within that, we have the primary LUX Zeplin instrument itself which is essentially a tank of liquid xenon.

Chris - Why do you need xenon?

Cham - So, xenon is a very efficient scintillator, which is to say that if you have something give a xenon atom a glancing blow, although it will only move sort of just a tiny fraction of a millimetre, this tiny energy that's been deposited in the xenon, it produces just a handful, just a few flashes of - well, one flash with a few photons of light. And so, we're detecting the light and the charges that's liberated from xenon when it's had anything interact with it.

Chris - How frequently do we expect that to happen, when your detector is running, how many particles, how many opportunities in a day let's say, are they going to be to see this happening?

Cham - Well, there are two things that we don't know and that's the mass of this WIMP particle and the interaction cross section which is to say, we don't know how likely it is to actually interact with an atom. This dark matter interacts so infrequently that we're only really expecting a few handfuls of events, after a couple of years of running.

Chris - Is there anything else that could look like a dark matter particle and fool you into thinking you're seeing one but you're not, you're seeing something else entirely.

Cham - Yes. Neutrons in particular are a troublesome background. They're sort of a blessing and a curse in that we use neutrons to calibrate our detectors to say, "Okay, if dark matter did hit, what would it look like?"

That's because neutrons produce signatures very similar to WIMPs. But neutrons can be separated from dark matter: The detectors are so large that any neutron that does get in, is likely to bounce around a few times. In contrast, the dark matter particle, we're lucky if we see it hit an atom in the first place. It's really not going to interact again within the detector.

So, single interactions mean dark matter. Multiple means neutrons.

Chris - If you do see some collisions, what will you be able to deduce?

Cham - The number of events that we detect will tell us about the cross section for a dark matter particle to actually interact with a regular atom. And so, that gives us a very nice handle on the interaction with standard model particles.

 On top of that, the energy distribution of the events that we do see, that tells us about the mass of the particle itself. So, if we have events that are really quite high energy, that corresponds to the dark matter particle itself being quite a massive particle. If they're all bunched towards very low energies, that tells us that the dark matter particle is a low mass or light WIMP.

Chris - You're the latest in a sequence of these sorts of detectors for dark matter particles. Why have your forebears failed and why do you think this experiment is going to be different?

Cham - All of these experiments have been pushing the envelopes, getting deeper and deeper into unexplored parameters based. So, they haven't seen dark matter but that's because nature hasn't been that kind. We've needed to get more sophisticated, larger, more sensitive essentially, in our searches and get deeper and deeper.

And so, far from previous experiments failing, we've been developing the technology to get to the size of detectors or a scale of many tons of target, and with the low energy thresholds so that we can see the rarest, tiniest of interactions.

And so, we're hoping that now, we have the technological readiness to really get down into where we hope the dark matter lives.