You are walking down a sidewalk, but you are distracted, and you don’t notice a step, so you trip over. But instead of floating in the air, you get pushed down almost like you were pulled by the ground. Why does this actually happen?
We attribute this phenomenon to a force in accordance with the Newtonian model called gravity. This is how we have been taught and how we approach several problems, but it is not always the case.
In this moment you would not fell falling, instead you would perceive like everything is moving upwards, even the building itself, and you could not carry out any experiment that could prove you wrong in your reference frame. First of all, let’s define what ac reference frame actually is, and it is simpler to explain via an example. As you well know and studied, our perception over our surroundings are relative to our prospective. The most common paragon is the train traveler, who, sitting in the car, would think everything comes towards him while standing still, while the stationmaster, who sees the train arrive, knows for sure that the car is in motion while he remains seated. In this situation both of them is right because motion is relative (according to special relativity) and they are referring to their own point of view.
Now, clearly the building going upwards is just an illusion, a prospective effect, right? Well, think about it. In the general relativity Space-Time is a four-dimensional continuum, where gravity is its curvature due to the mass distribution, and it applies in the universe as on the Earth, so where is that force that Newton described? Can we say that it simply does not exists?
According to general relativity, yes, we can. Then what keeps us stick to the ground? The ground itself! We are basically accelerating upwards with it, and all the object and structures with it, but since we are not an inertial observer you cannot notice it. Fascinating, isn’t it?
Now, having said that, are we falling?
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