Hello, SFIA audio listeners, in this month's Nebula exclusive, Big Alien Theory,

we're asked at the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content, check

out go.nebola.t.v.tv slash Isaac Arthur, and use my code, Isaac Arthur.

We often fly through thin air to get to places faster, but slash Isaac Arthur, and use my code, Isaac Arthur.

We often fly through thin air to get to places faster, but in the future, we might travel through no air at all, even here under the sky.

So today we'll be looking at the concept of the vacuum train, which is a very large

category of vehicles for use on and off planets, including one designed for getting off

planets like a mass driver, and more recently a strangely controversial subject.

I'm assuming some of this is because of Elon Musk's hyperloop, and all sorts of videos

point you out real or perceived engineering or economic issues with the design, or its planned

implementation, along with rebuttals.

I'm going to preface this video by noting that the Hyperloop is one type of vacuum train,

indeed one running on very low pressure rather than a full vacuum,

and there are many designs for many purposes, both of hyperlopes and of the wider category

of vacuum trains, along with pneumatic options like scaled-up versions of the message tube systems

a lot of office buildings or banks have.

Some, like the gravity train, aimed to move objects around a large body with virtually

no energy expended.

Some are akin to the Hyperloop, while others are meant to run around planetary-scale megastructures

at near orbital speeds.

There are a lot of points of overlap in basic function with the Hyperloop, so we will address

...