What are the four forces of nature?

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I am talking about gravity, electromagnetism, weak nuclear force and strong force.

In: Physics

3 Answers

Anonymous 0 Comments

Gravity – all matter attracts other matter

Electromagnetism – interaction between electrically charged particles

Strong nuclear force – the force that confines quarks together to form protons and neutrons

Weak nuclear force – force that governs the bosons that keep atom nucleus together

Anonymous 0 Comments

Are you talking about earth, wind, water, and fire?

Anonymous 0 Comments

So depending on who you ask, they might even say that there are three or five fundamental forces, but I’ll get to that later. Starting with the three that are definitely always considered fundamental forces: electromagnetism, strong, and weak interactions.

The one that most people already know is electromagnetism. This is a long-range force that has a single charge associated with it, the electromagnetic charge. There is a single particle associated with carrying the information about this force, which is the photon, and the photon is electrically neutral.

The weak interaction is a short-range force that tells us how particles change “flavor.” The particles that make up matter, called fermions, come in groups of three. For example, there is the electron, muon, and tau particle, each of which have identical properties except for a different masses. These are the three generations of charged leptons. Each of these are paired with a neutrino (i.e. the electron neutrino, mu neutrino, and tau neutrino, respectively) into “flavor pairs” where one flavor is the charged lepton and the other is the neutrino. The weak force tells us how to take a particle and turn it into a different flavor. This interaction also talks to quarks and is capable of changing e.g. up quarks to down quarks, which in a nucleus changes a proton to a neutron. So you typically hear about the weak interaction having to do with radioactive decay. The particles that carry this information are the W^+/- and the Z^0 bosons.

Now, the strong force kind of has two parts to it. There is the strong force at high energies and the strong nuclear force at low energies. The high energy force behaves very similar to electromagnetism, except that there are 3 different charges, called color charges, and the force-carrying particles known as gluons also have a charge. This means that gluons can directly interact with other gluons, making the theory more complicated. At low energies, this force gets, well, strong. So strong that the individual particles that are charged under this force (quarks and gluons) bind up together and can’t be separated. So the result is things like protons, neutrons, pions, glueballs, etc. and the strong *nuclear* force describes how these composite objects interact. At this level, the pions carry the force.

Okay, so those are the big three. If you notice, they all have a particle associated with them that “carries” the force. This is where the ambiguity comes in on the number of forces.

So, the fourth force that you are asking about is gravity. Our best theory of gravity right now says that it comes from spacetime being curved by energy densities. Things want to follow what would be straight lines, but when the underlying space is curved, straight lines no longer look very straight and it looks like the energy densities are bending the paths of these particles. To people looking at it, the effects are comparable to, say, electromagnetism, but we haven’t ever observed a force-carrying particle for gravity (a graviton) and the leading theories such as string theory which predict this particle have mostly been ruled out. However, that doesn’t mean there isn’t a graviton, it’s just that it’s hard to see and we aren’t sure where to look, so for now, we keep using Einstein’s picture of gravity (which we have good reason to think isn’t quite complete) which looks very different from the other three forces.

The final one is the Higgs interaction. This is the interaction that is responsible for giving particles their mass. It is carried by the Higgs boson. This one looks very similar to the big three, in that you have some interaction which is mediated by a specific particle, but its origin is very different. The main three forces come originally from a type of symmetry known as a gauge symmetry, while the Higgs boson is simply a fundamental particle that you can just write down in your theory. Now, there’s good reasons to include such a particle in your theory, but it isn’t the result of a special symmetry the same way that the other force carriers are.

Edit: accidentally mixed up flavors and generations in the original. Should be fixed.