5 ms·

The tunnels aren't perfect vacuums

• jimnotgym 10mo ago
  That doesn't help me, I'm afraid. It must be low enough pressure to allow lower air resistance on the train, so must be a significant vacuum. Even if not a perfect vacuum, the carriage can presumably not exchange air with it, since the carriage is at a higher pressure. If you used aircon in the train the lower pressure air in the tunnel would be very poor at convecting heat away?