The gravitational potential changes the length scale at each point in space (the closer to the gravitating mass, the smaller the scale). Light travels along the shortest trajectory, and in a space with a variable length scale, a straight line will no longer be a geodesic. Therefore, the path of light is curved.

That absolutely 100% is NOT the widely accepted explanation of gravitational lensing. If it were, they wouldn’t call it ”gravitational” lensing. Please look up “general relativity”

Hi Mike Albert, please take a look

Preprint Memoir on the Theory of Relativity and Unified Field Theory

Mike Albert I understand that the widely accepted explanation of gravitational lensing comes from general relativity, where light bends due to the curvature of spacetime around massive bodies. However, my research presents an alternative view. Since light is massless, this raises a fundamental question about how gravity alone can bend it inward. I propose that at least a portion of what we observe as gravitational lensing can be explained by the refraction of light through plasma, gas clouds, or changes in the medium around massive bodies. This is not just my idea; many published works also support the contribution of refraction to lensing (e.g., Gupta 2004; Bisnowaty-Kogan and Tsupko 2015; Cavalleri et al. 2016; Ye and Lin 2007). While general relativity remains the dominant explanation, I believe it is important to consider whether refraction-based models might provide additional insights or improvements. My aim is not to refute general relativity, but to explore whether lensing phenomena might also have an optical origin, which could complement gravitationally-only explanations, or in some cases challenge them.

Mike Albert Hi Sir, I can see your expertise in the field of light and lasers, so I would like to ask you directly: If light has no mass, what is the real reason for its bending near massive objects? Is it really due to gravity, or refraction from the surrounding medium (such as plasma or atomic cloud) can be the real reason? I would like to understand the real physical mechanism behind the bending of light.

According to general relativity gravity distorts time and space. I’m sure you’ve seen the rubber sheet model. As you get closer to a mass, time moves slower and space stretches larger. Picture a rod passing the earth in an orientation so that the length of the rod is parallel to a radial from the center of the earth, and the direction of motion is perpendicular to that radial (I.e. the motion is tangential). Time is moving slightly slower for the bottom of the rod and space is slightly larger. It falls behind the top of the rod. The rod curves, not because there is actually a force on it, but because space-time itself is curved.

This is not some obscure esoterica. It shows up in the real world. Yes there’s gravitational lensing, but the earth is a large enough to cause problems if you are measuring carefully enough. For example, the GPS system relies on nanosecond timing. It is literally a system of comparing clocks. If those calculations were not corrected for the time distortion caused by earth’s gravity via general relativity, GPS would not work. You can find YouTube videos where someone takes two synchronized atomic clocks, walks up and down a mountain with one of them, and shows they are no longer in sync. Going up a few thousand feet is enough to reduce gravity enough to make atomic clocks differ by nanoseconds after just a few hours apart.

>>>Mike Albert: According to general relativity gravity

First, we need to correct the error in STR -- return the scale (Doppler) factor to the Lorentz transformation formulas (see my `Memoir`). The consequences of this for the theory of gravity and cosmology will be truly grandiose.

The recession of galaxies (Hubble's law) is cancelled, because with an increase in the speed of the object's removal, the Doppler effect increases (the wavelength increases). This leads to an increase in the length scale. Accordingly, the distance to the object decreases. (It is possible that there will be a stationary Universe.)

Bittu Kumar

Your question, “If light has no mass, how does gravitational force bend light inwards?”, points directly toward the physics of electromagnetic–gravitational interaction.

Light is only a small part of the electromagnetic spectrum, carried by photons — the gauge bosons of the electromagnetic field. While relativity often states that photons are “massless,” this is misleading. In the ECM framework, photons possess an effective mass arising from two contributions:

These contributions manifest as a negative apparent mass, enabling photons to exhibit antigravitational characteristics. To understand light bending, one must therefore focus not on curved spacetime, but on how photons exchange energy and momentum with gravitational fields.

As a photon approaches or escapes a massive body, its momentum is altered through these interactions. The change in momentum results in the bending of its transit path, producing what we observe as gravitational lensing. Thus, light bending is not a geometric artifact of curved spacetime but a physical consequence of photon–gravity interaction within ECM.

For a deeper analysis, I invite you to consult the relevant papers on Extended Classical Mechanics (ECM), where these mechanisms are detailed.

Best regards, Soumendra Nath Thakur