There is a well known thought experiment called Einstein’s Elevator. Everybody who has finished high school has been taught a modified version that uses an accelerating space ship instead of an elevator. Einstein used this thought experiment to make his assertion that gravity would bend light. In the experiment, the space ship has the ability to continuously accelerate for the duration of the experiment.

     The space ship is increasing in speed at a constant rate of 32 feet per second per second. The space ship has a main deck that is perpendicular to it’s direction of travel. There is a spaceman standing on the main deck. He is not weightless because the ship is accelerating. Mass resists being accelerated through space because of inertia. In fact, the spaceman standing on the deck of the accelerating ship can’t tell if he is accelerating through space or parked on the Earth.

     If the spaceman holds a ball in his hand and releases it, it falls to the floor and bounces back up. When it bounces up, it does not go quite as high as it was when it was first released. Whether the space ship is accelerating through space or parked on the Earth, the ball acts exactly the same.

     There is a nearby star, and it’s direction is perpendicular to the direction of the space ship’s travel. The star’s light is shining through a window in the side of the space ship. Light travels at about 186,000 miles per second. In the time that it takes the light to pass through the window glass and strike the opposite wall of the space ship, the space ship will have increased in velocity because it is accelerating.

     If the spaceman measures the straightness of the light ray, it will appear to him that the light ray is bent. As the light ray travels from the window glass towards the opposite wall, the space ship is increasing in speed. This will cause the light ray to strike the opposite wall at a slightly lower point than it would have, had the space ship not increased in speed during the light ray’s travel across it’s breadth.

     This is how Einstein reasoned that gravity would bend light. If the ball acts exactly the same in both a parked or an accelerating space ship, and the spaceman can’t feel the difference, this means that a light ray would act exactly the same in both space ships.

     In the year 1919, a special British expedition conducted an experiment to see if gravity bends light. They took photographs of a star during a total eclipse of the Sun. If the gravity from the Sun were bending light that passed nearby, this bending could be measured by plotting the position of the star, and then taking a photograph of it during a total eclipse. If the star’s light was being bent by the Sun’s gravity, then the star would appear to be in a slightly different position than it really is. This physical experiment verified the prediction made by the thought experiment. This experiment has been repeated many times since with the same results. It is now a widely accepted scientific fact that gravity bends light.

     There is one major problem with this thought experiment and the physical experiments that verify it. Light does not bend. In the accelerating space ship, the spaceman measures the straightness of the light ray. The light appears to bend. The light is not really bending, it simply appears to bend from the spaceman’s point of view as an observer. The light is actually moving in a straight line. What makes it appear to bend is simply the observer’s point of view. The observer must take into account the fact that he himself is part of his observation.

     So why would gravity bend light? The answer is: it doesn’t. The light is still moving in a straight line. When the British expedition photographed starlight being bent, the star simply appeared to be in a different position because of the observer’s point of view. Gravity does not bend light, it just makes light appear to bend from a certain point of view.

     Here is another thought experiment. An observer is standing in a field near a railroad track. A train goes by at 60 miles per hour. There is a flatcar in the train, and on the flatcar is a rubber ball. The observer measures the speed of the ball and calculates it to be 60 miles per hour.

     Another observer is standing on the flatcar. He measures the speed of the ball and calculates it to be 0 miles per hour. Both observers are measuring the speed of the same ball at the same time. The only difference is the two different points of view for the two different observers.

     The fact is, light does not bend, it ‘refracts.’ Whenever light passes through a material substance such as water or glass, it changes direction of travel. This is not really ‘bending’ light, it is ‘refracting’ light. You can also change the direction of light by reflecting it. When light travels through the vacuum of space, it travels in a straight line. When the spaceman in the accelerating spaceship measures the bending of the light ray, he’s really just measuring his rate of acceleration relative to the speed of light.