We accelerate upwards while sleeping

        Albert Einstein once said that the thing he found which made him the happiest is seeing a man falling from a roof. What made him so happy about this though? He actually made a law of equivalency between gravity and acceleration.

According to him, gravity is nothing but an illusion. Think you are in a rocket in space. The rocket is moving with uniform velocity. In accordance with your surrounding you are not moving, just floating still inside the rocket. You may have some things like a bottle, paper, helmet, screw etc. You will see them also at rest. If you hit them slightly they will start moving in that direction with uniform speed.

But, if one observes this system from outside the rocket he will find that all these things and you are going with a uniform speed along with the rocket. So motion is relative. 

Now, think, a person was painting a roof of a very very high building(say it was Burj khalifa). Suddenly, he slips and started falling down along with the bucket of colour and brush. Just imagine, you will get that the man will also experience as same as the man in the rocket.  He will experience no gravitational pull, his weight will be zero, he will see things falling with him are floating or rotating just like the things floats in a rocket.

Now the fact is that gravity is an illusion. The surface of the earth is constantly accelerating upwards. Therefore, when we are in contact with the ground we are also accelerating along with it. But, in the case of free fall, we feel like being motionless or having constant velocity because we are really in constant velocity. It seems like we are accelerating downwards, but, the truth is we are static or with constant velocity wrt inertial reference frame and the ground is accelerating upwards to us.

  Are you confused with all these? Let's understand everything step by step.

At first, forget everything you have read in school physics because that is classical physics. But, we are here discussing the more accurate description of our universe i.e. the relativistic physics.

I have told many times before that while free fall we are motionless or with constant velocity. Yes, being motionless and having constant velocity is the same because one static thing is constantly moving in a particular direction wrt another reference frame. But, both here are observed by inertial frame. 

An inertial frame is a frame (or you can think as an observer ) that is not accelerating i.e. net force on it is zero. 

There is also a non-inertial frame where the net force upon the frame is not zero therefore the frame is accelerating itself. That's why it will observe a static thing accelerating.

Think that your car is in constant velocity and you are the driver. Then you are the inertial reference frame. You will see a man who is 'actually' standing motionless by the road as he/she is moving backwards with a constant velocity.    But, if your car was accelerating you would see the same person accelerating backwards. Acceleration is caused by a force. Then wrt you, the person will also be under a force. We say it "Pseudo-force". Because there is no force felt by the person but wrt any non-inertial frame there should be a force upon him/her that makes him/her accelerating. So the person being static ( wrt road) or having constant velocity (wrt you ) is the same. You and the road were not accelerating and therefore both are inertial frames. So that for an inertial frame or IF, being motionless or having constant velocity is the same. But for NIF or non-inertial frame, it is not.

Now in the case of the earth, we feel while free falling that we are static and the earth comes towards us with a constant acceleration. In classical physics, it is said that you are actually accelerating, but according to einstein's relativistic theory, the earth's ground is accelerating towards you. 

Here's a confusion that if that is true then every side of the earth would accelerate upwards and the size would increase rapidly. I shall solve this later in this very post.

Now I will make you feel the topic by comparison. Think that you are floating in a constantly moving rocket. Suddenly, the rocket starts its thrust and gains an acceleration. You will stay in the same place for the observer outside the rocket who is observing you (he/she is an IF ) and will also see that the floor of the rocket is accelerating towards you. You being also an IF, will see the floor is coming towards you with an acceleration. But if the observer was connected with the floor of the rocket, being a NIF he or she would see that you are accelerating downwards to the floor. 

Is not this fact similar to the incident of free-falling? YES, you got it. The ground is nothing but the floor of the rocket and you are none but the astronaut of that rocket. According to you, you are not accelerating & the ground is accelerating instead. That means you are an IF. And whoever says being on the ground that you are accelerating downwards is a NIF and he/she is actually accelerating upwards. That means that the whole earth's surface is accelerating outwards.

But, why it is not expanding? Here's that confusion. I said I shall explain. Here it is ...

Not only the surface is expanding outwards but the spacetime fabric is going inwards the earth due to its mass. For every point in space-time the point is static wrt the space-time but as the spacetime itself is going inwards the earth the point in space-time will see that the earth is accelerating upwards. The expanding of earth outwards and the ingoing of spacetime inwards cancel each other.

Therefore from the outside, the earth seems static and neither expanding nor shrinking in on itself. But the effects are seen due to the disturbance in space-time what we see as gravity.

Conclusion:-

The earth accelerates upwards and we stay static. But non-inertial framed observers ( who are on the ground) see us accelerating downwards just the same as I described in the scene of the accelerating car.

Therefore the force of gravity is nothing but a pseudo-force.

NOW HERE'S A QUESTION FOR YOU:-

    The volume of the sun is 1.3 million times the volume of the earth. Do you think that 1.3 million earth will fit in sun?

Let me know in the comments.

If you have any problem do not hesitate to say that in the comment.

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