How many forces do we know?

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In summary: In other words, it's something that we experience as a force.In summary, there are 4 fundamental forces in the universe: gravity, strong, weak, and electromagnetism. These can be reduced to the electromagnetic and weak forces, which are unified in the electroweak theory. There are 3 fundamental forces now, with the weak hypercharge, weak isospin, and strong force being unified under a single force.
  • #1
Dash-IQ
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Other than the 4 natural forces that are conservative, and friction(the none conservative one).
Are there anything else? In the whole universe that's all the forces we know?
Can there other forces to be discovered?
 
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  • #2
I believe every force can be explained in terms of fundamental forces or inertial reference frames. For instance, friction is a result of electromagnetic repulsion between matter (and also dissipation via entropy). In the general relativity framework, even gravity can be considered a reference frame force.

I'm fairly confident that classical forces we experience in every day life can be reduced to the electromagnetic force, repulsion (Newton's third through electromagnetic force) experienced during collisions... and gravity.
 
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  • #3
There are 4 fundamental forces: gravity, strong, weak, and electromagnetic. Electromagnetic and weak forces are unified in the electroweak theory, so maybe you can say there are 3 fundamental forces now. There is another force, the entropic force, which typically isn't considered a fundamental force, because it acts somewhat differently, through thermodynamics, and doesn't actually exist at a microscopic level. It is associated with the second law of thermodynamics, and it is as important as the other four.

All other forces can be derived from these 5. There's probably hundreds of non-fundamental forces, and their definitions are proliferated in various special topics, so there's no point in listing them. For example, the Van Der Waals force is just some manifestation electromagnetic force viewed at a molecular scale.
 
  • #4
Khashishi said:
There are 4 fundamental forces: gravity, strong, weak, and electromagnetic. Electromagnetic and weak forces are unified in the electroweak theory, so maybe you can say there are 3 fundamental forces now. There is another force, the entropic force, which typically isn't considered a fundamental force, because it acts somewhat differently, through thermodynamics, and doesn't actually exist at a microscopic level. It is associated with the second law of thermodynamics, and it is as important as the other four.

All other forces can be derived from these 5. There's probably hundreds of non-fundamental forces, and their definitions are proliferated in various special topics, so there's no point in listing them. For example, the Van Der Waals force is just some manifestation electromagnetic force viewed at a molecular scale.

The electroweak theory describes the electromagnetic force and the weak force in terms of two separate forces - the weak isospin and the weak hypercharge - so the count remains 4 fundamental forces. In GUT theories the weak hypercharge, the weak isospin and the strong force are truly unified under a single force so the count comes down to 2 - GUT interaction and gravity.

I don't see why entropy should be counted as a force.
 
  • #5
Entropy results in statistical behavior that can be conceived as a force balance. For example, the Nernst potential can be viewed as a force balance between electrodynamics and the "force " of diffusion.
 
  • #6
Pythagorean said:
Entropy results in statistical behavior that can be conceived as a force balance. For example, the Nernst potential can be viewed as a force balance between electrodynamics and the "force " of diffusion.

That is a force, but it's not a new fundamental force. In your example, the nature of the force is also aerodynamical.
 
  • #7
Whether it's a fundamental force, or a force at all, is a matter of metaphysics. Some people even argue that some of our fundamental forces are actually a result of the so-called entropic force. I don't really know (or care much) about the metaphysics.

What's unambiguous (and useful in modelling) is that it can be treated as a force phenomenologically.
 

1. How many forces are there in the universe?

The current understanding in physics is that there are four fundamental forces in the universe: gravity, electromagnetism, strong nuclear force, and weak nuclear force. These forces govern the interactions between particles and are responsible for all observable phenomena.

2. How do these forces differ from each other?

Each of these four forces have unique properties and strengths. Gravity is responsible for the attraction between objects with mass, while electromagnetism governs the interactions between electrically charged particles. The strong nuclear force holds atomic nuclei together, while the weak nuclear force is involved in radioactive decay.

3. Are there any other forces that we don't know about?

There are theories that suggest the existence of additional forces, such as the fifth force or the gravitomagnetic force. However, these have not been conclusively proven and are still being studied by scientists.

4. Can these forces be unified into one theory?

Scientists have been working towards a theory of everything that would unify all four fundamental forces into one framework. However, this has not been achieved yet and is still an area of active research in the field of physics.

5. How do we measure or quantify these forces?

Each force has its own unit of measurement. For example, gravity is measured in Newtons, electromagnetism in Coulombs, and nuclear forces in MeV (mega-electron volts). Scientists use mathematical equations and experimental methods to measure and quantify these forces in different scenarios.

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