Sure, I'll reduce it to "Unless people make an advancement in structural materials similar to the invention of steel itself, which is to say 'fundamentally world-changing,' hyperloop is nothing more than an inspirational pipe dream, similar to world peace." (EDIT: This comment may actually get called out in the future once Hyperloop is fully deployed, as an example of some idiot's words. So it's probably more than a little dumb of me to have said this. In my defense, it's based on Hyperloop Alpha, as it's presented in the whitepaper. Their design could change radically before deployment.)

If you're planning on building a closed loop out of steel, and there's nowhere for the steel to go when it expands in summer, the plan may need some rethinking.

The best I can think of is some kind of inner lining, so that it has a segmented hull, like a caterpillar: https://www.google.com/search?q=caterpillar&tbm=isch

But it would need to be very strong lining in order to prevent any leaks between the segments. And any kind of a leak would need to be detectable and would shut down the hyperloop until it's resolved.

Between the wildly optimistic cost projections and the fundamental engineering difficulties, I'm much more inclined to call it a pipe dream than a perhaps-future-possibility.

See my comment above - the expansion is specifically addressed. If you're going to criticize it, at least read the full whitepaper first.

> But it would need to be very strong lining in order to prevent any leaks between the segments.

The entire point of not requiring vacuum is to avoid having nearly as strict tolerances for leaks.

It's a "reduced-pressure tube." A leak is still a big deal, isn't it?

Regardless, the core structural engineering is the focus of the criticism, not whether it might leak. Also, since Space X's whole point is to compete on cost savings, it was a little strange to hear cost projections that were so optimistic.

The entire purpose of the design is explicitly to keep the tolerance for leaks at a level where, to quote the whitepaper "standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density"

Section 4.5.4 otherwise covers this, and does point out that for large leaks, braking would be required, but smaller leaks are intended to be dealt with as part of regular maintenance, with no indication that it'd need to affect operations.

> Regardless, the core structural engineering is the focus of the criticism, not whether it might leak.

That may be so, but most of the criticism I've seen of it appears to just ignore large sections of the whitepaper.

EDIT: For example, with respect to handling expansion/contraction, consider that the world has gas and oil pipelines that has to deal with far worse conditions without leaks.

Gas and oil pipelines typically use expansion loops to handle thermal expansion/contraction by flexing the pipe: http://demonstrations.wolfram.com/PipelineExpansionLoop/

Because the hyperloop cars are discrete (as opposed to the continuous flow in a pipeline), I'd expect them to cause a lot of stress on the pipeline walls if they had to run around the bends in an expansion loop.

That's why Elon's plan is to let the endpoints move instead.