Post 1, intro/general

Post 2, flight enabled by plasma thrusters

Post 3, Immortality via brain-backups

We love trains on Hexbear. Trains are fast and efficient.

The reason is because friction is low: steel wheels on steel tracks.

What's got even less friction than steel-on-steel? Maglev trains. Steel-on-air.

What would have less friction than that? Steel-on-nothing. Therefore: put the maglev train in a tube and suck out the air.

Linear electric motors in the track create a moving magnetic field which pulls the levitated vehicle along.

Maintaining a vacuum thousands of km long is the number one engineering challenge, but is by no means impossible with sufficiently advanced tech. Advanced materials like nanotubes will help.

No vacuum is perfect. These have a pressure of 1 Pa (0.00001 atmospheres)

Various concepts have said 2,000 to 8,000 km/h. In this worldbuilding, they achieve 6,000 km/h, which is ambitious but not maxing out ambition.

Travel time

Two very distant cities like Shanghai and Mexico City: 2h10m

Two maximally-distant places like Galicia and New Zealand: 3h30m

Then you have to get from the train-station to the party, but that takes you less than 30 minutes (likely 10) with the urbanism discussed in post #1.

Submerged floating tunnels

The sea is crossed by submerged floating tunnels.

These are an entirely feasible concept that has never been built for investment-risk and regulatory reasons. The tunnel is neither on the surface of the sea nor on the seabed, but tethered either to floating things at the top or anchors on the bed, so the tunnel is suspended mid-water.

Deeper than 150m, there are no waves at all, but 20-50m is fine. The pressure difference between 0 on the inside of the tunnel and a few atmospheres on the outside underwater: well submarines handle that pressure difference every day.