What does weak nuclear force do

The principle that one can always find an inertial frame at every point of space and time in which physics follows the laws in the absence of gravitation is called the Equivalence Principle.

The fact that the gravitational force can be thought of as coordinate systems that differ from point to point means that gravity is a geometric theory. The true coordinate system that covers the whole of space and time is hence a more complex one than the ordinary flat ones we are used to from ordinary geometry.

This type of geometry is called Non Euclidean Geometry. The force as we see it comes from properties of space and time.

We say that space-time is curved. Consider a ball lying on a flat surface. It will not move, or if there is no friction, it could be in a uniform movement when no force is acting on it.

If the surface is curved, the ball will accelerate and move down to the lowest point choosing the shortest path. Similarly, Einstein taught us that the four-dimensional space and time is curved and a body moving in this curved space moves along a geodesics which is the shortest path. Einstein showed that the gravity field is the geometric quantity that defines the so-called proper time, which is a concept that takes the same value in all coordinate systems similar to distance in ordinary space.

The equations also give the measured value of the deflection of light rays that pass the sun and there is no doubt that the equations give the correct results for macroscopic gravitation. It was James Clark Maxwell who, in , finally unified the concepts of electricity and magnetism into one theory of electromagnetism. The force is mediated by the electromagnetic field. The various derivatives of this field lead to the electric and the magnetic fields, respectively.

The theory is not totally symmetric in the electric and the magnetic fields though, since it only introduces direct sources to the electric field, the electric charges. A fully symmetric theory would also introduce magnetic charges, predicted to exist by modern quantum theory but with such huge magnitudes that free magnetic charges must be extremely rare in our universe. There is one difference though.

While the gravitational force always is attractive, the electromagnetic one can also be repulsive. The charges can either have negative signs such as for the electron or be positive as for the proton.

This leads to the fact that positive and negative charges tend to bind together such as in the atoms and hence, screen each other and reduce the electromagnetic field.

Most of the particles in the earth screen each other in this way and the total electromagnetic field is very much reduced. Even so we know of the magnetic field of the earth. Also in our bodies most charges are screened so there is a very minute electromagnetic force between a human being and the earth.

The situation is very different for the gravity field. Since it is always attractive, every particle in the earth interacts with every particle in a human body, setting up a force with is just our weight.

However, if we compare the electromagnetic and the gravitational forces between two electrons we will find that the electromagnetic one is bigger by a factor which is roughly 10 This is an unbelievably large number! It shows that when we come to microcosm and study the physics of elementary particles we do not need to consider gravity when we study quantum electrodynamics, at least not at ordinary energies.

It is a static law. One also finds that the electromagnetic field travels as a wave just in the same way as light does. Hence it was established that light is nothing but electromagnetic radiation. In Max Planck proposed that light is quantised in order to explain the black body radiation. However, it was Albert Einstein who was the first to really understand the revolutionary consequences of this idea when he formulated the photoelectric effect.

The electromagnetic field can be understood as a stream of corpuscular bodies to be called photons that make up the electromagnetic field. The revolutionary aspect of this idea was that a stream of particles also could behave as a wave and there was much opposition to the idea from many established scientists of the day.

It was not until when Arthur Compton experimentally showed that a light quanta could deflect an electron just like a corpuscular body would do it, that this debate was over. If we think about the electric force between two charges as the electromagnetic field mediating it over a distance, we can now get a more fundamental picture as a stream of photons sent out from one particle to hit the other.

This is a more intuitive picture than a force acting over a distance. Our macroscopic picture of a force is that something hits a body that then feels a force. In the microscopic world this is then again a way to understand a force. However, it is more complex. Suppose there are two charged particles that interact. Which particle is sending out a photon and which is receiving the photon if the two particles are identical as quantum mechanics tells us about fundamental particles?

The answer must be that the picture should include both possibilities. The discovery that the electromagnetic field is quantised started the development of quantum mechanics and led us to a microcosm that is just built up by point-like objects and where forces occur when two particles hit each other.

Quantum mechanics as such led to many new revolutionary concepts. For a nucleus, one can either determine the position of an electron and know nothing of its momentum or know its momentum and nothing about its position. In the picture showing the force field between two charges, we should think of it as photons travelling from one charge to another. Hence the energy cannot be determined better than what the uncertainty relation tells us because of the uncertainty in the determination of the time.

If we put the energy and the tree-dimensional momentum together into the four-momentum we see that it is not constrained by the masslessness condition, we say that the photon is virtual and consequently has a virtual mass. We can thus interpret the process above as either a certain photon going from particle 1 to particle 2 with a certain four-momentum or as one from particle 2 to particle 1 with the opposite four-momentum.

If two charges are close there should be more terms to the force. Incidentally in order to measure the velocity of light the photons must interact. Hence there is a slight uncertainty in its mass and a slight uncertainty in its velocity.

However, we measure always the same velocity for light which means that at the macroscopic distances that we measure, the virtuality and hence the mass of the photon is essentially zero to a very good accuracy.

It is then consistent to say that the velocity of light is constant. It is very elegantly formulated by so-called Feynman diagrams, where the elementary particles exchange photons as was described above and where each diagram constitutes a certain mathematical expression that can be obtained from some basic rules for the propagation of virtual particles and from the interaction vertices. The simplest diagram for the interaction between two electrons is.

Feynman now instructs us that we can combine any line for a propagating electron or when it travels backwards, the positron and any line for a propagating photon tied together with the vertex where an electron line emits a photon to make up new diagrams. Every other diagram differing from the one above constitutes quantum corrections to the basic force. This is what triggers nuclear fusion and causes stars to burn, according to CERN. The burning creates heavier elements, which are eventually thrown into space in supernova explosions to become the building blocks for planets, along with plants, people and everything else on Earth.

The Z boson is neutrally charged and carries a weak neutral current. Its interaction with particles is hard to detect. Experiments to find W and Z bosons led to a theory combining the electromagnetic force and the weak force into a unified "electroweak" force in the s. However, the theory required the force-carrying particles to be massless, and scientists knew that the theoretical W boson had to be heavy to account for its short range. According to CERN, theorists accounted for the W's mass by introducing an unseen mechanism dubbed the Higgs mechanism, which calls for the existence of a Higgs boson.

In , CERN reported that scientists using the world's largest atom smasher observed a new particle "consistent with the appearance of a Higgs boson. The process in which a neutron changes into a proton and vice versa is called beta decay.

According to the Lawrence Berkeley National Laboratory LBL , "Beta decay occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other. Beta decay can go in one of two ways, according to the LBL. One element can change into another element when one of its neutrons spontaneously changes into a proton through beta minus decay or when one of its protons spontaneously changes into a neutron through beta plus decay.

Protons can also turn into neutrons through a process called electron capture, or K-capture. When there is an excess number of protons relative to the number of neutrons in a nucleus, an electron, usually from the innermost electron shell, will seem to fall into the nucleus. According to Jacquelyn Yanch, a professor in the nuclear engineering department at Massachusetts Institute of Technology, in a paper " Decay Mechanisms ," "In electron capture, an orbital electron is captured by the parent nucleus, and the products are the daughter nucleus and a neutrino.

The weak force plays an important role in nuclear fusion, the reaction that powers the sun and thermonuclear hydrogen bombs. The strong nuclear force also binds protons and neutrons in the nucleus of atoms. The weak nuclear force enabled complex atoms to form through nuclear fusion. If the strong and weak nuclear forces did not exist, then stars, galaxies, and planets would never have been formed. Strong Nuclear Force: Two positive charges repel each other because of the electromagnetic force, so the strong nuclear force lives up to its name by overcoming the intense repulsion between similarly charged particles that coexist in the nucleus of atoms.

When the strong nuclear force that binds protons and neutrons in an atom is broken, extreme high-energy photons are released in the process.