How big shall we make it then?
Have you ever wondered what the future will look like? Flying cars, teleportation and intelligent AI seem like the obvious fantasies, but I find myself pondering the future of the infamous Large Hadron Collider.
For those of you with only a passing familiarity with the world’s most OP science project, here’s some background information to get you as excited as the rest of us…
The LHC is the biggest (27km circumference), meanest (produces energies of up to 14TeV) most debonair (total cost of £8.7 Billion) particle smasher in the jungle.
To put these numbers in some context, if you decided to race a proton around the collider tunnel, being generous with my assumptions of your fitness, it would take you about 5 hours to run a lap. On this nail-biting race between man and machine you would be lapped by the proton about 10 thousand times. Every second. And by the end of the race you’d have been overtaken around 200 million times.
Don’t be embarrassed though! Even the most feeble of you could deliver a slap with 2.5 million times the energy of that proton who left you in the dust so easily. Yes, that’s right; 14 TERRA ELEVTRON VOLTS might sound like a large number, but when you convert it into joules, it begins to look a little feeble. That’s not so terra-fying is it?
Don’t be fooled though, 14Tev might not be much to you and I but for a particle with the same mass ratio with us (proton : person) as the earth has to the universe (earth : universe), it’s a rather impressive statistic.
What’s the big deal? You may ask. Well, the big deal stems from a nice piece of mathematics called special relativity, which was published by Albert Einstein in 1905.
Most people have come across what is probably the most famous equation of all time: E=mc2.
This equation tells us that the phenomena of mass and energy are proportional and interchangeable.
The puny energy of a proton no longer seems so funny when it can be converted directly into mass.
This is the principle behind the large hadron collider (and also behind nuclear power). Energy is given to very small particles by accelerating them down a long tube, and this energy is then converted into mass when it collides with a similar beam of fast moving particles. The higher the energy, the larger the mass of the particles produced by the collision.
Because of the incredibly small mass of a proton, it can be accelerated up to 99.9999991% the speed of light.
Now that we have a basic idea of what a particle accelerator does, we can move on to why it kinda sucks at the moment…
Despite the billions invested in the project, the LHC is still light years from being perfect: literally. Light years of length would needed to be added to the track if we wanted to accelerate it up to the energies seen at the beginning of the big bang. This coveted time frame is known as Planck’s epoch, and is the time period in which all of our fundamental forces; gravity, electromagnetism, the weak force and the strong force were all united as one force.
If we could observe this sort of environment, it could give us vital clues about how to make a ‘theory of everything’, or more technically, a unified field theory.
At this point there are many interesting avenues one could explore, but for now we’re going to move on and focus on an interesting question and the point of this blog post: how big would a particle accelerator need to be for us to reach the energies seen at Planck’s epoch?
The first step is to work out the relationship between energy gained by a proton and the distance it travels. The energy we want to reach is at what is known as the Planck scale, which is the energy at which gravity is expected to be as strong as all of the other forces. If we could observe the particle interactions at this level then perhaps we would learn everything we need to know about our universe’s fundamental forces.
Hang on a second! Is gravity weaker than the other forces? Well lets take a look at a simple example. (You could even try this yourself!)
Take any two magnetic or electrically charged objects such as two magnets, e.g. a fridge and a fridge magnet. If you hold one very close to the other, you will feel that they either repel or attract strongly. This is the electromagnetic force. To prove to you that this is the electromagnetic force and not the gravity I have a simple demonstration that you can very easily try.
So, what do we know about gravity? We know that it is an attractive force that acts between two objects with mass. Therefore, just as there was a force between the magnet and your fridge, there should be a force between you and your fridge. Now I’m not talking about the kind of attraction stirred by cold pizza; that kind of force is stronger than any in the universe. I hope that you would agree that both you and your fridge are both objects of mass, and therefore are attracted to each other by the force of gravity. So let’s give it a go. Stand in front of your fridge as close as you can get without touching it… Is there a noticable force? Is there an attraction of any kind? Can you lift your feet off the floor and hang off your fridge like a magnet? No. No you cannot. This is because gravity is incredibly weak compared to the electromagnetic force.
How weak though?
Well, imagine two schools of students, each on a different end of one giant rope: the ultimate tug-of-war. What would the students from the school of gravity look like compared to those from their rival school: electromagnetic academy.
It turns out that the electromagnetic force is about 1036 times stronger than gravity. In other words. Electromagnetic academy only needs to field one tugger, while the school of gravity would need to loop the circumference of the universe 100 million times in order to make it a fair game.
So then, it’s no surprise that despite the price tag, the LHC hasn’t quite managed to bring the school of gravity up to speed. Our question is, what would it take?
It’s important for me to clarify at this point what exactly we are asking. High energy particle collision is full of practical challenges with different possible solutions. There are two main limiters on our ability to reach Mr Planck that we have to address.
First, we have the issue of magnets.
Particle beams might be cool, but they’re not the smartest cookies in the jar. Moving in anything other than a straight line is almost impossible because of the speed at which they are moving. That’s where the magnets come in. In order to make the particles move around the accelerator in a circle, really big magnets are employed from electromagnetic academy to tug the charged particles towards the centre of the circle. The faster the particle, the more energy required. That’s why the LHC is so big. With a circumference of almost 27km, the curve is slight enough that if you traced the line of its curve on a piece of paper, it would look completely straight. Less curve means less turning. Less turning means less magnet power. And right now, the power of our magnets is the main limiting factor on how fast we can accelerate.
Second, we have an issue called synchrotron radiation. When particles moving near to the speed of light are accelerated by an electromagnetic field, they release radiation that increases with the strength of the field and speed of the particles. At some point, the energy released by our particles is equal to the energy being supplied by the accelerator, introducing a limit to their speed. But don’t worry, there’s good news. The bigger the particle, the less energy lost to synchrotron radiation. Protons are much more efficient than electrons for this reason.
Zac Lambert 