If the train moves sufficiently fast, is it possible, according to experimenters on the ground, for the entire train to be inside the tunnel at one instant of time?

Explanation:

One of the consecuences of Special Theory of Relativity is that when bodies move its length in the direction of the movement will decrease, and decrease will become bigger as speed goes up. At speed close to speed of light such decrease could be such as to make train become a point, of course tunnel is fixed it will not change, but close to light speed means somethyng like 300000 km/sec therefore could be just one instant of time inside tunnel no matter how long it is