Task is to prove gravity is not a fictitious force which makes it clear that it is a real force obeying newtons first law.

Observe light when light gets pulled in a black hole the formula for gravitational fictitious force F=ma cant work because light has no mass.

Now it obeys the first law of newton because the speed of light is not a constant when it falls in a black hole.

The speed of light is a constant, so it's a fair question to ask why it isn't constant near a black hole. The answer turns out to be quite subtle.

In special relativity the speed of light is a global constant in that all observers everywhere will measure the same value of c

. In general relativity this is still true only if spacetime is flat. If spacetime is curved then all observers everywhere will measure the same value of c

if the measurement is done locally.

This means that if I measure the speed of light at my location I will always get the value c

, and this is true whether I'm sitting still, riding around on a rocket, falling into a black hole or whatever. But if I measure the speed of light at some point that is distant from me I will generally get a value different from c. Specifically if I'm sitting well away from a black hole and I measure the speed of light near it's surface I will get a value less than c.

I will modify this a bit as i dont believe that a strong gravitational field causes spacetime curvature. My reasoning is that the reason as to why a strong gravitational field near a black hole causes the light to fall in is simply because Light is moving at a very high speed normally on the surface of the earth and gravity of the earth is not strong enough to pull it down towards the surface of the earth same logic here.

Even though the speed of light is very large it cant escape the pull of gravity in a black hole. Simple where is the scope of spacetime curvature?

Another simple theory proving light is a particle. Compare the results of throwing a ball into the black hole and light falling into the black hole both fall in a straight line but not at constant speed.

So similarity of behavior of the ball and light could prove light is a particle.