Lots of exciting news about gravitational waves going round since last week, but whenever some discovery is made in physics, such as the long awaited finding of the Higg's boson from a couple of years back, a lot of people see the news reports and ask "who cares?". They raise a fair point. Why should we care about such abstract discoveries?
First off the bat, what even is a gravitational wave? This may get complicated, so consider yourself warned. In possibly his greatest achievement, Einstein, so many decades ago, showed that there are two things that can bend space and time (or spacetime as he cleverly coined the combination); speed and mass. The first effect we know as special relativity, and it states that the speed of light is fixed at roughly 300 million metres per second. This may not seem like a big deal, Wikipedia tells us that sound travels at roughly 340 metres per second without needing its own theory. Well ... it's just not the same thing at all.
Let's imagine you've got a super precise ruler and clock, with which you can measure the speed of anything. You're stood on the side of the road and a car whizzes past you at 100 mph, and your magic ruler-clock combo tells you exactly how fast it was going. Now you get in a car that travels at 99 mph, and the same car whizzes past you ... except this time, because you're driving alongside it, the ruler and clock measure it at just 1 mph. It's the trees on the side of the road that it tells you are going really fast in the opposite direction! This is the concept of relativity - things only have a speed relative to an observer.
Next, apply this logic to sound waves. If you travel at 339 metres per second then sound waves travelling alongside you will look really slow. All's well so far. Now, let's say you've got a rocket in your pocket, and it lets you travel at 99.9999997% the speed of light (299999999 metres per second). Then, a beam of light travels past you. Quick, get out your ruler and clock. Like the car and sound, light should look slow because you're going alongside it, right? Actually, no. This is weird bit. Light speed is constant relative to any observer! The Universe conspires that no matter how fast you go, light will always travel past you at light speed as if you're completely still. This is special relativity, because, it's a special kind of relativity! The old rules of a speed changing relative to who's observing it do not apply for light (physicists, please excuse my skewed coordinate systems).
The Universe does this trick by doing two things: it shrinks rulers (well, it shrinks space itself actually) and slows clocks (well, it slows time itself actually). Unlike breaking the sound barrier, which makes a loud noise, breaking the light barrier would stop time and increase your mass to infinity, creating a black hole that would swallow the entire universe! It's impossible though, so don't panic. If this time-slowing-down thing doesn't make sense to you, that just means you're human. It's one of the toughest concepts for a physics undergrad to grasp, I remember my confusion very well!
Then there's gravity. Unlike the picture of gravity that Newton drew after the apple landed on his head (which almost certainly never happened), Einstein suggested in 1915 that gravity isn't a simple attraction between objects with mass, gravity, as we feel it, is just a consequence of the fact that masses warp spacetime.
In the Universe, things tend to follow straight lines in space. The animation on the right is a crude representation of what mass does to these straight lines in space. Here, as a ball moves through, the lines become warped by the ball, so if you were following one of these straight line paths, try as you might to stay straight, you'll end up being pulled toward the ball by the curving of space. This is what the Earth does to the space around it, and it's what keeps the moon from flying away. This is gravity. The bending of time by gravity is slightly more complicated, but if you remember that space and time are intertwined then you should expect both to be affected. This is the crux of the movie Interstellar, which I thoroughly recommend - Matthew McConaughey's voice more than makes up for the iffy science.
General relativity isn't just trapped in the realms of sci-fi though, our first good confirmation that gravity is Einsteinian and not Newtonian was the orbit of Mercury around the Sun. It was long a mystery why Mercury orbits in the way it does ... Einstein's idea solved the problem entirely by introducing the idea that the Sun's mass was warping spacetime. Hey presto, mystery solved.
It can be tough to convince yourself that space and time can be warped by mass, and that gravity is just the result, but it's been tested experimentally numerous times, and Einstein's explanation for gravity seems to hold up. In fact, GPS wouldn't work if you didn't account for time slowing down due to the Earth's gravity, and GPS is really useful! Thanks Albert!
There are caveats though. So far there is no explanation for how gravity works on the really small scales. There is no quantum description of gravity, and given that there's a quantum description of everything else, that's a problem for physics. There's also the matter of gravity not working on really large scales either. Look at the velocities of entire galaxies around each other, and you'll find that you need to invoke loads of invisible mass (or dark matter) to make the equations work ... This is another problem. Either dark matter is real, or Einstein was wrong. And finally, Einstein predicted that when objects interact, they should send little ripples off in the "fabric" of spacetime. Of course, simulations show that these ripples would be laughably tiny, but finding them would be an important confirmation of his important theory. These ripples are known as gravitational waves.
Today, there has been a highly anticipated announcement that gravitational waves have, finally, been directly detected. In the past their existence has only been inferred from indirect observations. For example, if gravitational waves exist, it turns out that two neutron stars rapidly spinning around each other should lose energy at a very specific rate, and eventually merge. This exact thing was observed, and the rate at which they decayed towards each other matched predictions perfectly. But this is only inference, in the same way that dark matter hasn't been detected, it has only be inferred from the motions of other things. This announcement is of the very first direct detection of gravitational waves.
The team at LIGO (that's just one of those acronyms physicists use for their giant bases - don't worry about it) searched for the shrinking and stretching of space itself, right down to the atomic length scales, using two 4 km long arms and a series of lasers. After painstaking months of checking and rechecking data, one of these little stretches was detected, and confirmed as being caused by a gravitational wave (note: there were people employed to try and fool the scientists by creating fake signals, just to be sure they were looking for the right things!). The origin of this gravitational wave turned out to be an incredibly hostile-to-life event, a merger of two black holes. It's not at all surprising that it took colliding black holes to produce a ripple large enough we could detect, as these waves are usually pathetically small.
This is a major box ticked for not only Einstein's theory of gravity, but for our understanding of the Universe as a whole ... But as a Chemistry friend of mine was keen to ask me:
Why do we care?
Let's assume, like him, that you don't give much weight to the idea that having knowledge for knowledge's sake is all that much good. You're thinking that all of those millions spent on the gravitational wave detector could have gone to, say, cancer research, or impoverished nations, or solving climate change. Valid point.
First of all, he's right that this detection doesn't enable any new technology. It isn't a eureka moment. It isn't like when Prof. Hank Pym discovered the Pym particle and created the first Ant Man. This is just answers an old question - do gravitational waves exist? Now we've detected one though, you can be guaranteed that bigger and better detectors can be made, and pretty soon we'll be able to find them left right and centre. Let's imagine then that we plant a series of superdetectors in space and use it to make a gravity map of the Universe ... What will the use be then? Well for one thing we might be able to watch the Big Bang.
In the first 400 thousand years or so, the Universe was really dense and hot - it was a plasma. Plasmas are pretty opaque, and looking through one so hot would be like looking through the surface of the Sun. When we look up into space, because light takes time to get to us, the further we look, the further back in time we see. This opaque plasma however sets a boundary for how far back we can look. No matter how good the telescope, we'll never see past this plasma horizon. This horizon has been stretched out by the expansion of the Universe and now looks like a Microwave blanket around the Universe. Because of this limit, we'll never see any light from the first 400k years. Such a shame.
But we might see (or hear) gravity. Plasmas don't affect gravitational waves like they do light, so with this new technology we may be able to peer beyond the visible horizon of the Universe and see the very beginning of time! Maybe we'll see some giant footprint. Maybe we'll find out that this isn't even the first Universe (can gravitational waves travel through a Big Bang? I have no idea). Who knows what we'd find. It could solve all problems in physics, and finally tie up the mystery of gravity's place in quantum mechanics. We may also get some answers about this mysterious dark matter, which seems to only interact through gravity, and makes up 85% of the mass of the Universe. What is it? Why is it there? What does it know, does it know things, let's find out.
Still though, this is pretty blue sky thinking. What economic value are we getting now? Well, I'd argue that, if you look at the bigger picture of astronomy and physics, the value is everywhere. We've mentioned GPS already, but there are numerous inventions that have come out of NASA, simply because as they tried to get good at doing one thing (going to space) they got good at doing a load of other things along the way. Memory foam, cochlear implants, scratch resistant eyeglass lenses and insulin pumps can all be traced back to NASA. Further, Switzerland's CERN, a giant lab dedicated to discovering the fundamental building blocks of, well, everything, was largely responsible for why we have the world wide web. What they've been discovering with their actual subatomic particle work will hopefully pave the way for new quantum computing, or possibly a piece of information that will solve the energy crisis. It's hard to predict what will come of understanding physics better.
I feel I should also slightly cheekily point out that the money spent on these telescopes/supercolliders/secret bases is a drop in the pond compared to the money squandered on quangos and bank bail-outs. If you want to talk about having a cost effective economy, going after scientists really isn't the right place to start.
As for what gain we can get specifically out of gravitational waves ... Honestly, I have no idea. The discovery could lead to great inventions, or it could just be a great achievement on its own with no economic benefit at all. This is the way science works sometimes. Ideas are explored and sometimes they lead into dead ends. The problem with comparing science funding with business funding is that, to get the most out of scientists, you have to let great minds get carried away with the ideas they are passionate about, and not let these great minds fall to ruin if the ideas turn out to be wrong. Almost all new ideas will turn out to be wrong, but if we only chase the ones with the highest likelihood of turning a profit, we run the risk of setting ourselves back decades.
In the 19th century, Lord Kelvin had a "huh, that's funny" moment when looking at electric currents in magnetic fields. What he noticed was a small effect, and it went pretty much forgotten, until in the '80s when two groups went back and had another look with modern equipment, whose findings then led to the invention of the "spin valve", which is now part of every modern hard drive. This is a good example of how it's nearly impossible to know what value science done today could have on the future.
Sometimes science for science sake is just good. It's great to have a new iPhone that runs 52 times faster than the previous and has a million new gadgets to play with, but Apple will never bring me a hoverboard, and I really want a hoverboard!
In this blog I made the case that blue sky research has a lot of benefits, but there are certainly some examples of bad science that really should never have happened ... Bad science will be the topic of my next post.