Today we say speed, in the world we live in, there is a speed limit, that is, the speed of light propagation in a vacuum, when human beings in the last century learned this basic principle, they have been trying to approach, even want to exceed this limit of speed.
We know that the speed of light in the vacuum is 209,977,292,458 meters per second, which is what we often call C, which is the speed that all massless particles in the universe are born with, in addition to photons, there are 8 gluons, which are particles that transmit strong forces, and of course, gravitons, which are born to move at the speed of light.
But unfortunately, the particles that make up everything in the world are not the bosons above, but the fermions with mass, as long as there is mass, special relativity limits it to the speed of light, let alone the speed of light, the reason is also very simple, because physics does not allow the destruction of the causality of reality, so we must adhere to the basic principle of the limit of the speed of light.
That being said, we still want to let mass fermions break the limit of the speed of light! I believe you have heard reports of neutrinos faster than the speed of light, the spin of neutrinos is 1/2, half an integer, so it is a fermion, and the electron is a member of the lepton family, the lowest mass elementary particle we know so far, even the second lightest electron in the universe is hundreds of thousands of times heavier than neutrinos.
So at that time, the report that neutrinos were faster than light came out, shocking the scientific community, because people thought that neutrinos were very small, and it might really be faster than light, but then it turned out that this was completely hilarious, and it was our experimental data that was poor.
Although we can't find faster-than-light particles in nature, we have a powerful tool in the laboratory, particle accelerators, which, as the name suggests, are devices that increase particle velocity or energy.
In fact, the purpose of particle accelerator construction is not to verify the speed limit of the universe, nor to break the speed limit, but to understand the structure of matter, to find new particles of large equipment, but this experimental process is also the place where we humans create the ultimate speed. So the question is, how do we accelerate particles through accelerators?
How do particle accelerators accelerate particles?
The accelerator is also called the collider, the earliest model of the collider can be traced back to the last century in Manchester worked rutherford, the time is about 1907, this year it hit the gold leaf with α particles, observed a large number of α particles scattered by the gold atom after the deflection angle, through this experiment, he knew that the mass of the atom is mostly concentrated in a small core, the electrons around this core, this is the most important human exploration of atomic structure.
So where did the α particles as probes come from? At that time, the α source used by Rutherford was radioactive radium element, which could naturally release α particles at a speed of about 2.5×10⁷ meters per second, about 1/10 of the speed of light, then Rutherford used α particles at this speed to understand the internal structure of atoms.
But with the development of science, people want to understand the particle structure inside atoms, and even want to know the structure of these particles themselves, so what to do?
Quite simply, there's a car now, and if you want to know the composition of the car inside, you just need to take it apart and look at it, but the subatomic particles are so small that we can't do such a fine job, so there's a simple and crude way to smash it. Like smashing a walnut, if you want to see what's inside, you have to knock it open.
But the particles released by radioactive atoms, its speed is not good, can not knock out the nucleus, it is impossible to crush the particles that make up the nucleus, so people wonder if there is any way to speed up the charged particles? So particle accelerators appeared.
So how do you speed up charged particles? It's simple, because it's charged, so we just need to provide him with an electric field, so where does the electric field come from? It is also very simple, now you connect two parallel metal plates to a positive and negative pole, that is, to apply a voltage, then a uniform electric field will be created between the metal plates.
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Now we put a charged particle into the electric field, the charged particle will be affected by the action of the electric field force to produce an acceleration, the size of the electric field force is equal to the charged particle charge multiplied by the electric field strength, the electric field strength can be divided by the voltage divided by the distance between the two metal plates, so we can very easily calculate the acceleration of a charged particle in the electric field.
We know that the force has a direction in addition to the size, because we specify the direction of the electric field, or the direction of the electric field line is from the positive charge outward and then to the negative charge, so the direction of the force of the positively charged particle in the electric field is the same as the direction of the electric field, and the negatively charged must be the opposite of the direction of the electric field.
Now that we know how to speed up charged particles, the next question is how to operate it? You see, in order for a particle to get the most energy in the accelerator, you need to speed him up through the electric field many times, so that it can accelerate for a longer time, so it will be faster.
So if we design the particle accelerator to be a straight line now, it is certain that the chances of particles getting acceleration will be very limited, and such a design will certainly not be reasonable.
Is it possible that we can limit the particle's trajectory to a ring-shaped runway so that it can pass through the electric field on the ring orbit multiple times and get more opportunities to accelerate?
This is actually the case, this design is called a cyclotron, and the current CERN Large Hadron Collider is such a circular runway.
But the problem is that if we want to bend the trajectory of the particle, we need to apply a force perpendicular to the direction of motion, and as the particle accelerates, this force also needs to be constantly adjusted to adapt to the speed of the particle, so as to ensure that although the speed of the particle is increasing, it always moves on a fixed circle without hitting the accelerator's pipe wall.
Is there a force that meets our requirements? Yes, that is, the magnetic field force, the stationary charged particle is not subject to force in the magnetic field, but as long as the charged particle moves, and its direction of motion is perpendicular to the direction of the magnetic field, it will be subject to the maximum magnetic field force perpendicular to the direction of motion.
In a given magnetic field, the magnitude of the magnetic field force is proportional to the charge of the charged particle and the speed of motion, so as long as a magnetic field is applied to the accelerator ring, the charged particle can be bent and let him do a ring motion.
The problem is that this magnetic field needs to change in time, so a fixed magnetic field is not enough, and an electromagnet must be used to provide magnetic constraints.
The magnetic field strength generated by the electromagnet is proportional to the current, so we can adjust the amount of the current to control the magnetic field strength to adapt to the change in the speed of the particles and ensure that the particles do not hit the tube wall of the accelerator. So in order for the magnetic field to be strong enough, so in accelerators we use superconducting magnets.
Okay, now we're combining electric field acceleration with magnetic confinement, and that's the particle accelerator, the basic principle of accelerating particles.
We went on to say that human speed is the limit
The proton and antiproton accelerator of Fermilab in the United States, with a circumference of 6.26 kilometers, accelerates particles in a vacuum tube in one direction and antiparticles in a vacuum tube in the opposite direction.
Then let the two collide in the detector to see what new subatomic particles will be produced? Of course, through the accelerators of FermiLab, we found the top quark, accurately measured the mass of the W boson, and discovered the ceramic neutrino, and at the same time created the speed limit of 99.999956% of the speed of light.
At present, CERN's Large Hadron Collider holds the record for the highest energy of particles, and its accelerated proton speed reaches a maximum of 299,792,455 meters per second, 99.9999991%C, which is only 3 meters per second slower than the speed of light.
But that speed isn't the fastest particle we've ever created!
LEP Large Positron collider, although its energy is only 1/33 of the energy of LHC, but the mass of a proton is about 2000 times that of an electron! So in LEP, the speed of electrons reaches a maximum speed of 209,979,224,577,000 meters per second, 99.99999988% C, 3.6 mm/s slower than the speed of light! Thus, all the protons and electrons that make up our world remain constrained by special relativity.