That makes total sense, but I don't think it would work. The expansion doesn't really cancel out. Imagine heating 1 mile of hyperloop by 11C, but only 1 mile. The result is 0.25m more steel that has to go somewhere.

Can that expansion really be pushed 175 miles north and 175 miles south simultaneously?

I'm not going to say that's impossible, because I'd imagine someone having similar objections to, say, the invention of A/C current. "Can pushing electrons back and forth really propagate thousands of miles?"

But if you visualize the implications of that, it's intuitively difficult to believe the expansion can be transmitted to the endpoints across the entire length of a solid steel tube 175 miles away. That would move an incredible amount of mass. Surely at some point the weight of the tube overcomes the steel's desire to expand, so the result would be the tube either scrunching up like an accordion or going in the lateral direction.

(Jacques said sleeves could be the solution so that thermal expansion can't accumulate, but it seems like sleeves would introduce problems for the pod, possibly severe ones. When a pod travels over a sleeve, it would feel like a jolt, if I'm understanding his idea of "sleeves" correctly.)

I'm so happy someone is actually engaging with the comment and tossing ideas around with me though.