By Don Lincoln, Fermilab
The highest energy particle accelerator ever built collides protons together with an energy of 10 to the 13th eV, or 10 trillion. That particle accelerator is the Large Hadron Collider or LHC, used to find the Higgs boson. Is the Large Hadron Collider safe? Is the phenomena of the cosmic rays, recreated by it, more volatile? Read on to find out.
Understanding Cosmic Rays
There are high energy cosmic rays which tend to not be from the Sun. Coming from outside the solar system, some of them are from supernovae. Others occur in the proximity of massive black holes. Those make highly energetic cosmic rays. And there are other sources too, like when two neutron stars merge together. There are probably other sources of cosmic rays that we don’t yet fully understand.
Cosmic rays span a huge range of energy. The highest energy cosmic rays have an energy of as high as 10 to the 20th power electron volts. Ten to the 20th is 100 quintillion, which might seem miniscule, but it’s an unimaginably large number.
In terms of an electron volt, a unit of energy often written as eV, particles from nuclear reactions have an energy of about a million electron volts. That’s 10 to the 6th eV. The highest energy particle accelerator ever built collides protons together with an energy of about 10 million times higher than that. That’s 10 to the 13th eV, or 10 million, million, also called a trillion.
That accelerator is called the Large Hadron Collider, or LHC.
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The Large Hadron Collider
So, the highest energy cosmic rays are about 10 million times more energetic than the LHC beams. That’s the first important point. The Earth is hit by subatomic particles with way more energy than the LHC can generate.
However, those super high energy cosmic rays are actually quite rare. But there are a lot more cosmic rays closer to the energy of the Large Hadron Collider. In fact, cosmic rays with the energy of one of the LHC beams hit the Earth about a quadrillion times a second. And that’s every second.
Protons Smashing at LHC’s Energies
An accelerator like the Large Hadron Collider accelerates two beams of protons and smashes them together. Proton hitting proton. In cosmic rays, it is most likely that a proton from some collapsing star or something comes flying through space and smashes into an air molecule. Air molecules are made from protons and neutrons and, for the purposes of this discussion, there is no distinction between protons and neutrons.
Thus, we see that cosmic rays hitting the Earth result in high-energy protons hitting high-energy protons, which is exactly what is going on in a particle accelerator, and the collisions occur about a quadrillion times a second. And, this is the observation. We’re still here. In spite of the Earth being pummelled with cosmic rays for the entire 4.5 billion years that it has existed, we’re still here.
From this, we can conclude that smashing into other protons at LHC energies is entirely safe. If it weren’t, we wouldn’t exist.
And the situation is even more persuasive than that. After all, cosmic rays hit the other planets’ protons, including Jupiter, which is much bigger than the Earth. Cosmic rays hit stars, which are even bigger. They’re all still there and we don’t see any of them disappear due to a black hole eating them.
A Loophole in the Proton Collision Argument
However, there is a loophole in the above iron-clad argument. The loophole is that in a particle accelerator, the two beams are hitting head on, while in cosmic rays, one of the protons is stationary. And this is an important point.
In ordinary car collisions, if one car is stationary and another car of the same size hits it, after the collision, both cars end up moving in the direction in which the original car was moving. In a head-on collision, both cars stop right where they hit. In actuality, a head on collision is much more dangerous and damaging than when a moving car hits a stationary one.
The same is true for proton collisions. The Large Hadron Collider collisions end up being more violent even if the moving protons have the same energy. Luckily, even higher energy cosmic rays exist, and they are enough to compensate for this effect. So, that answers that criticism.
Common Questions about Cosmic Rays and the Large Hadron Collider
There are high energy cosmic rays which tend to not be from the Sun. Coming from outside the solar system, some of them are from supernovae. Others occur in the proximity of massive black holes. Those make highly energetic cosmic rays. And there are other sources too, like when two neutron stars merge together.
An accelerator like the Large Hadron Collider accelerates two beams of protons and smashes them together. Proton hitting proton.
The Large Hadron Collider collisions end up being more violent even if the moving protons have the same energy. Luckily, even higher energy cosmic rays exist, and they are enough to compensate for this effect.
