Eli5. Why is gravity classified as a weak force when it can bend and trap light?
In: Physics
Well, stating that gravity is a force on it’s own is a contentious thing. Especially if you are talking about bending and trapping light. It’s like saying that a circle is a weak force. From the standpoint of general relativity, gravity isn’t even a force, but rather a consequence of a curved spacetime.
From that standpoint, light doesn’t bend. Light propagates in accordance to the shape of spacetime, or I guess you can say it travels in a straight line.
It’s like saying that our spherical planet is somehow a force because the shortest distance between Alaska and New York by plane is a curved line on a map. It’s only curved if you look at one projection. Gravity is the same, but it gets harder to visualize because you need to think of a higher dimension projection.
But to answer the question, gravity is considered weak because the apparant force that gravity exerts is much much lower than strong forces do. It’s 10^38 times weaker than the strong interaction for example. This difference is obvious when you can use tiny magnets to hold papers on the fridge. You’ve got the mass of the entire earth pulling on the paper, and this little tiny magnet is able to hold the paper from falling down.
Think of forces like a wave that dissipates with each wavelength. Strong forces are like a very high intensity wave with a short wavelength, they’re really strong close up, but fall off quickly. Gravity is like a very low wavelength, it’s not strong at all, but because of that it retains more of its influence much further.
It’s important that gravity is weak, it is what stops us from collapsing into black holes ourselves. The other forces like electromagnetic force and strong interaction keep masses separate. If gravity were the strongest, all matter would just immediately fall together into a black hole because it would overpower the forces that kept it apart. But gravity being stronger doesn’t really make sense. Rather, if you consider gravity as a force, you know it’s weak because all matter doesn’t collapse together, and the other forces act more strongly to keep things separate in spacetime.
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