>>16699590 (OP)Serious answer: it’s the old explanation for “Why doesn’t the water fall out when I lift the straw with my finger on it”. The water doesn’t fall out because that would leave a vacuum, and nature tries to fill vacuums—in this case, the water would go right back in.
More modernly, some italian guys theorized that the atmosphere had weight, and that the phenomenon could be explained by atmospheric pressure pushing from the botton, just like liquids do. This was confirmed experimentally by Fermat