Why does light bend due to gravity? I thought hard, read a lot and I found 3 reasons I can give as the answer. But first let me tell you what Newton said. According to Newton light (Photons) is massless so light cant bend due to gravity because only things with mass can be affected by gravity. But as per General Relativity Einstein says light bends due to gravity. Below are the reasons as per my understanding as to why light bends. Reasoning 1 In this scenario we assume Newton was right. So we say that massless particles aren't affected by gravity. But light has mass which is called "Effective Mass". In solid state physics, a particle's effective mass is the mass that it seems to have when responding to forces. This effective mass can be acted upon by gravity which only cares how much mass a particle has; alternately, gravity only cares about how much mass or EQUIVALENT ENERGY a particle has given by E = m c^2. Also, if you prefer the particle description of physics over the wave description, you can approximate all photons as 'bullets' each carrying a mass of m = hf/c^2 and traveling at the speed of light. EFFECTIVE MASS, is the same as the KINETIC ENERGY of photons divided by c2 (C is the speed of light). Thus, even though light has no REST MASS (because it can never be at rest!), it does have an effective mass which (it turns out) has all the properties one expects from MASS - in particular, it has weight in a gravitational field [photons can "fall", which happens in a black hole] and exerts a gravitational attraction of its own on other masses. Reasoning 2 Here we say that even though photons (Light Particles) have no mass they still have momentum. Photons cannot have mass because they travel at the speed of light, but they must have momentum for events like photoionization to occur. Photoionization means the removal of one or more electrons from an atom or molecule by absorption of a photon of visible or ultraviolet light. Also known as atomic photoelectric effect. (Remember Einstein's photoelectric equation). It is generally agreed that mass is not a requirement for having momentum. Particles made up entirely of energy can also have momentum according to modern physics. So as you know gravity affects anything that has energy and Light has energy as well as momentum. So you will say that momentum= mass x velocity. But remember Momentum is also p=E/c where p is the momentum and E is the energy also C is the speed of light. Photons have energy, and c is a constant. Reasoning 3 Light gets bent because it travels in space time that is warped around massive objects. Light sometimes passes through space (or space-time) that is warped or bent because of a nearby object having very strong gravity. The light passes through this space in what (from the light's point of view) is a straight line. To other observers the light may appear to have followed a bent path. So gravity warps space-time, and light appears to bend as it travels through this warped space-time. The light isn't doing anything except following what is a completely natural path through space. What general relativity says is that any massive object warps the spacetime around it. You can think of this with a simple analogy. Imagine a stretched rubber sheet that is completely flat. This represents the spacetime when there is no mass. Now, if you put a heavy ball in the rubber sheet, it will cause a distortion in the sheet. This is exactly what happens in space, except that it is in 3 dimensions instead of two. Further, a photon always travels by the shortest distance between two points. As spacetime is warped, the light appears to bend around a massive object. In reality, it is not that the object is attracting light, but it is just that the photons are traveling by the shortest distance in a curved spacetime. Photons of light are not technically affected by large gravitational fields; instead space and time become distorted around incredibly massive objects and the light simply follows this distorted curvature of space. Please tell me which of the above reasons is correct.