After shutting the LHC down back in 2013, the team at CERN began a number of repairs to the supercollider and the CERN's accelerator complex generally. This included consolidating 10,000 superconducting magnet interconnections, which probably took more than an afternoon. CERN officials are hopeful that the repairs made over the last few years will allow it to run at 13 TeV (nearly twice the power it ran when it found the Higgs).
Just a quick primer: 13 TeV (teraelectronvolts) is a measure of energy. A teraelectronvolt, or a trillion electron volts, is ... actually not that much energy. One TeV is equivalent to the kinetic energy of a flying mosquito. So, now you can imagine the LHC smashing 13 mosquitoes into each other. The real trick comes in how to squeeze that amount of energy into a stream of particles that are much much much lighter than a mosquito. To do that they need to increase the speed of the object by a lot. Let me explain.
Remember that kinetic energy is directly proportional to the mass of an object multiplied by the square of its velocity (i.e., KE = (mass*velocity^2)/2. Compare the mosquito to a car moving at the same speed. Since the car is much more massive than the mosquito if they move at the same speed, the car will possess a much higher level of kinetic energy.* Now realize that a mosquito is much much closer to being the same size as your car than it is to being the same size as a proton. An ungodly amount closer.
So if a proton is so much lighter than a mosquito, how can it possess a level of kinetic energy 13 times higher than a flying mosquito. Answer ... it's going really really fast. In fact, it's reported that protons in the LHC are accelerated to 99.9999991% of the speed of light. Of course, they will never reach the speed of light because each small amount closer requires more energy to achieve. Using the car analogy again, accelerating your car from 20 mph to 30 mph requires less fuel than going from 150 mph to 160 mph. In fact, the only things that can achieve the speed of light are things without mass. So ... just light. For things with mass like protons it requires infinite energy to reach the speed of light.
In this context then, the energy figure is directly related to the speed with which the beams of particles are moving. The higher the energy level the closer it is to the speed of light. And this is important because the higher the energy level at the point of collision the smaller the pieces of the wreckage from that collision. Again, use a car to think through it. Two cars that crash into each other at 10 mph will not usually break into a lot of pieces. Two cars crashing at 100 mph will obliterate each other into a million little pieces. If they're going near the speed of light, even the quarks in the protons in the atoms of the car will breakdown. It takes a lot of relative energy to break something as small as quark.
CERN put out a 5 minute video explaining the massive engineering effort that they just completed. To simplify a little their efforts resulted in:
- newer, stronger, and safer magnets,
- higher energy and more narrowly focused beams
- smaller and closer proton delivery packets
- higher voltage capacity,
- superior cryogenics,
- radiation-resistant electronics, and
- a more secure vacuum.
It's been close to three years since the LHC helped scientist glimpse the "God Particle." But that wasn't the only thing the LHC was designed to answer and CERN has a nice rundown of the experiments scheduled to make use of the LHC over the coming three year tour of duty. Below are just some of the questions that LHC-related experiments will attempt to answer:
- Do extra dimensions explain the relative weakness of gravity compared to the other fundamental forces (i.e., the electro-magnetic, weak, and strong forces)?
- What types of particles could make up dark matter (i.e., matter that doesn't interact with the matter you know and love and feel and are made of)?
- What are the properties of the quark-gluon plasma?**
- Why did the universe create so much more matter than anti-matter?
- Does the hypothetical monopole exist?***
The LHC is expected to start colliding small stuff again on March 23rd, but the process to reach 13 TeV is a slow one. No one wants to set the project back by jumping the gun with high energy levels. Full 13 TeV collisions are tentatively scheduled for the end of May or early June of 2015.
So what questions are you most excited for the LHC team to answer? What questions do you wish it could tackle?
* In fact the car's kinetic energy is equal to the number of mosquitoes required to make up the mass of the car multiplied by 1 TeV. If a car weighs 2 metric tons that's 800,000,000 TeV.
** Quarks, which make up particles like protons and neutrons, do not seem to exist in isolation. They are only ever seen in pairs. Scientists have discovered that the force of attraction between quarks does not decrease with distance the way it does for other things. For instance, the further you are from Earth the easier it is to move you even further from Earth. Gravity diminishes over distance. Not so for quarks. Stranger still, the level of energy needed to separate two quarks seems to be the exact amount needed to create a quark from scratch. So that when you separate a pair, it instantaneously becomes two pairs again, never passing through a moment of isolation. By creating extreme temperatures the ALICE experiment at CERN is trying to study quarks in a plasma state similar to that in the first millionths of a second after the Big Bang. The hope is that this will explain some of the peculiarities of quark behavior.
*** A monopole is a magnet with only one pole (i.e., only North, not North-South). All known magnets are magnetically neutral; the force they exert North is equal and opposite to the force they exert South. A monopole would have a "magnetic charge" conceptually similar to things with an electric charge and its discovery is important to some unified theories like string theory.