How much does our shadow weigh?

 In the world of the ephemeral, there are few elements that accompany us wherever we go, every day of our life, in almost any circumstance.

Something we barely notice is our shadow. Shadow is nothing more than the absence of a light that was expected, but that does not reach its destination because it was blocked by an object. Explaining what light is is not so easy.

In a simplified way, we can say that it is made up of photons, elementary particles without mass but with energy and with "moment". This "moment" is the ability of physical objects to push each other. When the photons that make up a ray of light illuminate an object, they push it, exerting a slight pressure on it that we call "re Radiation Pressure". When we get in the sun, our body feels this pressure, while the area we overshadow, where the photons do not reach, does not feel it.

We can quantify this difference in pressure with weight, which is the force we exert on the ground, or on a scale. When we are illuminated we exert a greater force than when we are in the dark, since to the strength of our body we must add the moment transferred by the photons that collide against us.

Thus, we can affirm that an object weighs more when it is illuminated than when it is not.

In the same way, the region where our shadow extends feels a lower radiation pressure than I would feel if we were not there, blocking the light. In other words, the excess weight we feel when we are illuminated corresponds to a weight defect of our shadow. In the case of an adult person of medium height, located under the sun at the latitude of Madrid, and assuming that the dimensions of his shadow are the same as those of his body, that defect in weight in the shade will be equivalent to the one that would exert a mass of about 0.00000004 kilograms.