Split from another thread. Originally posted here. There are radiation pressure studies which generally use a laser or a collimated bean that show that radiation is repulsive. I use a hot plate heating element which nominally puts out 1000 W of "spreading" infrared radiation. I place this hot plate underneath a hollow copper sphere. The sphere does not touch the hot plate. It is suspended by wooden dowel to a thermally isolated force sensor ~80 cm above. I also place three copper containers filled with ice above the hollow sphere so that a good part of the heat generated from the heat-element will flow upwards in the vertical direction. When the hot plate reaches a temperature of ~400 C, the .21 Kg hollow sphere has increased its weight by ~2.0%. This experimental set up is varied in three other experiments. They all show a comparable weight increase. In one of the experiments, when just the heat element was suspended by a wooden dowel to the force sensor, and its temperature reached ~400 C, its weight had increased by 22%. My results conflict with the results from the radiation pressure studies. Your argument that "Of course radiation is gravitationally attractive, it carries energy so it must bend spacetime" is one I have never heard before except maybe when theorist throw in a radiation term in the Friedman equation and say since radiation varies as the fourth power of temperature, its effect on the scale factor can be ignored. In talking about his equation E = mc^2, Einstein mentions (I think in his Autobiography Notes) theoretically one should be able to heat a test mass and experimentally observe the equivalency of mass and energy. But because of the c^2 term in the expression m =E/c^2, one could never easily get the temperature high enough to observe a mass change. With not much effort I can get a relatively large gravitational mass increase with a relatively small temperature increase ( ~370 C). I do not deny the equivalency of mass and energy. But there is a need for a clarification between what Einstein said and my experiments.
