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I watched a program of his in which it was claimed that since mass bends space in accordance to General Relativity, then in the case of very large stars it becomes a strong force to the point of being able to crush a star to a single nucleus (Neutron Stars) or less (Black Holes).

His argument is that Gravity is a force that scales and that it is not simply a matter of adding individual components and hence to claim it's weak, but that since space is bent in those areas, then gravity as a fundamental force of nature becomes stronger.

Now, I wonder not only about the claim's accuracy, but also if it's only a matter of interpretation and nobody is really wrong or right, as long as the discussion is framed properly.

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2 Answers 2

We say that gravity is weak because its coupling to mass is far less than the couplings for the other forces: electroweak and strong. But we imagine it is 'strong' on earth because it holds everything down. It only does this however because the earth contains so much mass. Rubbing plastic to create a static charge can easily overcome the gravity of the entire earth when it holds up a piece of paper. So gravity is weak. But then when mass is so very concentrated that it forms (for instance) solar mass black holes, the amount of mass can make gravity seem 'strong'. And gravity in this case is 'strong' because the spacetime region develops high curvature.

But this is the low energy world only. In string theory all couplings are unified at a high energy scale. That is, they do change with scale, and gravity gets stronger.

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No, the comparison is not fair. If one of them can scale, you can just put as many of them together as possible to claim that it is strong. Considering the following analogue: After comparing a person with billion dollars and the total money in US citizen, you laugh at that the person and say that he is poor. It is just not fair at all.

One of the fair comparison is that the gravitation force is almost negligible when you measure the electric force between two protons, so we can say that gravitation is weaker than electric force. Similar, since the strong force can bind two protons together, so we can say that the electric force is weak than the strong force.

The electric charge is just hard to put together since they are repelling with each other. However, if you really want to compare in the macro scale, one example is that you can find a lab size equipment of magnet to let a frog floating in the air. So does that means the force of generated by this lab is as large as the whole Earth? You should know how to answer it.

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