We know how strong the gravity is. Humans built powerful rockets to escape gravity. If gravity was weak we would not have to build such powerful rockets. Black holes are formed when massive stars collapse under their own weight. If gravity was weak black holes would not have been formed. Yet the particle physicists are telling us that among the 4 forces of nature gravity is the weakest one.
Physicists compare the strengths of the electromagnetic force, the strong nuclear force, the weak nuclear force and the gravity and find that gravity is indeed the weakest one.
According to some theories the strengths of all 4 forces become equal at high energies but in our natural environment the strength of the gravitational force is orders of magnitude smaller than the other forces. The repulsive electromagnetic force between two electrons is 1045 (1 followed by 45 zeros) times stronger than the gravitational attraction between them.
It cannot be shielded or concealed
It is interesting that all 3 forces other than gravity are confined to the atom. Outside of the atom there is only a fraction of the electromagnetic force, just enough to facilitate chemistry.
We know how to release the electromagnetic force from the atom. We learned how to separate electrons from atoms and move them in cables. We learned how to create electromagnetic waves. We learned how to build electronic devices.
Under normal circumstances the strong and the weak nuclear forces are confined to the nucleus of the atom and they are completely shielded. Yet, human beings learned how to release those powerful forces as well.
Gravitational force, on the other hand, cannot be concealed or shielded. It operates in the microscopic world. It operates in the macroscopic world. Nothing can stop it and nothing can shield it.
Source of gravity
Source of gravity is mass. What is mass? Bottled-up energy? Yes and No. According to the famous
formula the mass is bottled up energy. My intuition tells me that “mass” is actually the bottle itself. In my opinion “mass” comes from the “form”. I hope to write about the ontology of energy someday.
I am thinking along the lines of “form”, majority of physicists are thinking along the lines of Higgs field. It is ironic that the modern physics resurrected the aether of the 19’Th century and renamed it Higgs Field. According to this paradigm the “Higgs Field” pervades the entire universe. As elementary particles move through this universal field they gain an effective mass. The mechanism is similar to viscosity. The Higgs field resists the free motion of particles and this manifest as mass.
Physics cannot explain the differences in mass
Even though the Higgs field is the reigning paradigm in particle physics it is not good enough to explain the differences between the particle masses. For example
Electron mass = 0.510998910 MeV
Muon mass = 105.6583668 MeV
Tau mass = 1776.84 Mev
What causes the difference in mass? Current physics cannot explain this. Why do the particles have the precise masses they do? We don’t have an explanation yet. If you are curious about the other open questions in physics you can visit the FAQ prepared by DESY.
Action-at-a-distance, field, geometry, graviton exchange? Which one is it?
Newtonshowed us that the gravitational force between two objects is proportional to the masses of those objects and inversely proportional to the square of the distance between them. He could not explain why or how the force was mediated. The gravitational force was declared to be an action-at-a-distance without any further explanation.
Einstein showed us that the gravitational force can be described without invoking the action-at-a-distance. He showed that gravitation is not really a force but an effect caused by the distortion in space-time. He said that a massive object curves/distorts the space-time and the smaller object feels this curvature, the effect manifests as force. This is the geometrical explanation of gravity. Einstein’s theory describes the gravitational force with an incredible accuracy but it does not explain why the mass distorts space-time.
Another explanatory device in physics is the concept of field. Charged particles like electrons or protons emanate electric fields. Moving charged particles emanate magnetic fields. Other charged particles feel these electric and magnetic fields.
There is yet another explanatory device to describe forces. This is known as interaction by particle exchange. When you throw a ball the catcher feels a force. There is an interaction or force between the thrower and the catcher. The force is transmitted to the receiver by exchanging an object. According to this paradigm all forces work like this. Electromagnetic force is mediated by exchanging photons; the strong and weak nuclear forces are mediated by the exchange of various particles. In this paradigm gravitational force is mediated through a particle known as graviton. Why is the gravitational force attractive and not repulsive? There is no explanation.
The graviton-exchange paradigm is problematic. Interaction by particle exchange concept works very well for electromagnetism, and the nuclear forces but it is really problematic in the case of gravitation. Attempts to unify gravitation with quantum physics have not been successful because these theories use graviton exchange to explain gravitation.
In my opinion gravitation is special. The biggest evidence for this is the relative weakness of the gravitational force. Why is the gravitational force orders of magnitude weaker than the other forces? Gravitation is special and it is different from the other forces.
Can the gravitational force be neutralized? I am not talking about airplanes or rockets or electromagnetic levitation where we counter gravity with another force. I am talking about reversing it. Gravitational force is attractive. That’s why it holds the galaxies together. That’s why massive stars collapse under their own weight and turn into black holes. Can we have repulsive gravity? That’s the question. This subject fascinates many people. There is much speculation but no theories yet.
Gravity cannot be understood without an understanding of time
My hint to professional physicists is this: gravitation has something to do with time. Einstein was on the right track when he showed that the geometry of space-time can explain many properties of gravitation. We’ll know more about gravitation when we understand “time” better.
In a different essay I claimed that zero-chirality (spin-0) state effectively eliminates “time”. In my opinion this is the key to the understanding of non-locality as well as gravitation. Since the Higgs particle is a singlet (spin-0 or zero chirality) state of the Higgs field and since the Higgs field manifests the particle masses we can make a connection between the “time effect” and the gravitation because gravitation is a property of mass.
Higgs particles which pervade the entire universe make the whole universe connected in a “non-local” way. Think about the implications. I hope someday a young physicist sees the value in these notes and put it all together to come up with a better theory of gravitation. I wish I could do it myself but this requires tremendous focus, energy and motivation which I lack.
Gravity is weak but it is the dominant force
Despite the fact that galaxies are moving apart from each other as if the fabric of space-time is being stretched, within the galaxies gravity is still the dominant force. Gravity holds the galaxy together. Gravity holds the solar system together. Gravity binds us.