How Cold Can a Supervoid Make the Microwave Sky? An Integrated Sachs-Wolfe Bound Against the Cold Spot's Central Depth

The Cold Spot, a cold region roughly ten degrees across centred near galactic coordinates (207.8 degrees, -56.3 degrees), has a published central depth near -150 microK, and the large underdensity reported in its direction has often been named as its cause through the integrated Sachs-Wolfe effect. This paper computes, from stated cosmological assumptions, the largest central decrement a compensated spherical void can produce and compares it directly with that depth. Across a grid spanning radii of 100 to 300 megaparsecs, density contrasts to -0.40, and redshifts from 0.5 to 1.0, the central decrement never exceeds 74.8 microK in magnitude; an Eridanus-like configuration gives -12.6 microK. Even the most favourable case supplies only 49.8 per cent of the Cold Spot's central depth. The plain conclusion is that a single supervoid of any plausible size and depth cannot be the main cause of the Cold Spot's core; the void explanation, taken at full strength, fails by arithmetic. The study is computed, not measured.