The main advantage to hydrogen would be overcoming the Kantrowitz choking effect caused by supersonic flow; this is one of the most significant design constraints of the Hyperloop. Increasing the speed of sound (by mixing the air with hydrogen) increases the speed at which the ambient gas can flow around the capsule, greatly reducing the pressure that builds up in front at a given speed. Hydrogen is cheap; liquid hydrogen can be had for less than $1/kg, so cost is a non-issue.

Another design constraint of the Hyperloop is cooling the compressed ski air. The Alpha design calls for a 300kg water tank and intercooler, flash-heating the water to steam and storing it in "steam tanks", the complications of which are swept under the rug. (300kg of water would become 500 m^3 of steam at 1atm, several times the volume of the capsule itself.) By injecting liquid H2 into the air stream to cool it, the need for the intercooler and steam tanks would go away. Hydrogen has an exceptionally high specific heat; liquid hydrogen is extremely effective at removing heat from a system. Some of the compressed air + H2 could be further compressed and stored onboard the capsule to maintain the tube at 100Pa, or perhaps the excess H2 could be handled by placing adsorbent material (e.g. activated charcoal) in the tube to soak it up, and replacing/recharging this material at intervals. Since hydrogen moves so fast, placing the adsorbent material only at the endpoints might be sufficient.

The stopping distance is just fine. At 30 second intervals at full speed, the distance between capsules is about 10km. A 1g deceleration (combined force = 1.4g, equivalent to pressing hard on car brakes) will stop the capsule in less than 6km. No internal organ squishing required.

Passenger aircraft commonly bank at up to 30, which is a vertical g-force of 1.15g. The Tesla Model S P85D accelerates off the line at 1G longitudinal, for a combined g-force of about 1.4g. The Gravitron (common at carnivals) pulls 3g's continuous. Roller coasters commonly pull 4-5g's for short times. (though admittedly, that can be barf-inducing.) The Hyperloop is designed for a maximum combined g-force of 1.4g, corresponding to a 45 banking angle. With reclining seats, this should feel similar to a Model S accelerating off the line, and should be easily tolerated. The key consideration will be to minimize "jerk"; abrupt changes in acceleration. So the curves will have to be designed so the banking radius changes gradually rather than abruptly. No doubt there will be people who are intolerant of the Hyperloop, just as there are people who are phobic/intolerant of air travel. Perhaps there could be a designated "slow hour" where the capsules are run at 3/4 speed to reduce the g-forces. But with appropriate warning and visual feedback provided, I think most passengers would quickly get used to it.

The Hyperloop will bank freely like a bobsled; the passengers will experience virtually no lateral acceleration. (The same is true of an airplane in a tight bank.) This will make the ride far less barf-inducing. The lack of turbulence will also help greatly.

The Hyperloop skis will be on a flexible suspension; the pylons can sway many centimeters (e.g. in earthquakes) before the ride quality would be affected. In other words, the skis can move quite a lot to maintain precise contact with the tube, while the passenger compartment remains stable. The raw materials and basic construction will be the expensive part; polishing the interior to the required smoothness is comparatively trivial. The vacuum part is also fairly simple; the vast majority of the tube is simple continuous inch-thick steel, which is trivial to make airtight. The complexity will be at the endpoint stations and airlocks, but given that it's only a soft vacuum being maintained (100Pa), even this is easily manageable.

You could do a mixture of air with other gases, and gain many of the advantages while still avoiding a hard air vacuum. For instance, 50Pa air + 50Pa water vapor, or even 50Pa air + 50Pa H2. A promising approach would be for the capsules to store on board some of the air they're compressing anyway, to help maintain the tube pressure. The alternate gases could even be added as part of the cooling system; if liquid nitrogen or liquid hydrogen were injected directly into the compressed air stream to cool it, it would greatly reduce the need for water intercoolers and onboard steam storage, increase the available pressure to the skis, and be balanced by onboard storage of some of the compressed air stream. And the pressures are low enough that combustion shouldn't be a problem, even with H2. Vacuum leaks are most likely to come from two sources: the end station airlocks, and the capsules themselves. Most of the tube is just Big Dumb Pipe (tm), which really shouldn't leak. And 100Pa is really not too difficult to maintain; the volume of the entire LA-SF Hyperloop tube is equivalent to a cube about 130 meters on a side.

Branching at full speed is probably not possible with the Hyperloop as designed; the skis are curved to match the diameter of the tube, with a ~1mm clearance with the tube surface, so there is no passive tube design that could accommodate a "switch". In order to continue from Section A to either Section B or Section C, you'd have to make an intermediate length of tube several hundred meters long that could be physically moved at one end from B to C, with sub-millimeter precision, with the entire thing enclosed in vacuum. By the time demand is great enough to warrant branches, it's probably more cost-effective to make a dedicated parallel tube than to re-purpose a single tube with a ridiculously complicated switch. Hydrogen (or water vapor) would be most helpful in reducing Kantrowitz effects near the sound barrier, but not necessarily in enabling higher absolute speeds. The reason is threefold: drag continues to increase at higher speeds regardless of the speed of sound, lateral acceleration increases with the square of velocity, and the vertical precision of the pipe also improves with the square of the velocity. If you consider that the steel Hyperloop pipe draped across 30m-spaced pylons will approximate a vertical sine wave, then at 700mph the allowable sag is only about 5cm between pylons before the capsule's vertical suspension is overwhelmed and it starts "bouncing". (Assuming the mass of the skis/suspension is 10% of the capsule mass, so it can accelerate vertically at 10g to keep contact with the track.) At 1500mph, the tube requires a vertical precision of 1cm between 30m-spaced pylons, and its trajectory would have to be ridiculously straight to avoid problematic lateral g-forces. Mechanical braking from 1500mph in the event of an emergency is also a non-starter; 700mph is right at the edge of what can be feasibly done without melting brakes or destroying the tube. And in the event of a rapid tube repressurization, a 700mph capsule will incur about 2g's of aerobraking deceleration; at 1500mph it would experience about 10g's, likely enough to destroy the capsule and/or kill the passengers.

Air travel between LA and SF metro areas is the busiest air route in the US (and third-busiest in the world), with about 7.7 million passengers annually, or 21,000 per day. Assuming a 12-hour day, the Hyperloop could accommodate this with one 30-passenger capsule every two minutes each way, and the system is designed to quadruple this capacity at rush hour. (one capsule every 30 seconds.) Of course, if the Hyperloop is built, it will generate plenty of its own demand. And of course, it can be modified to carry cargo too (and possibly vehicles), not just passengers. The cost as outlined in the Hyperloop Alpha document is about 1/10th that of the proposed HSR.

"Existing elevated rail" is not a valid comparison. The Hyperloop infrastructure needs to support about 1/10th the weight per meter as traditional rail, therefore it can be done with 1/10th the materials. The proposed Keystone XL pipeline is 36 inches in diameter; the Hyperloop would be about 100 inches, but hollow and empty most of the time. Oil pipelines are full of oil, therefore quite heavy relative to diameter. In practice the total weight per linear meter of oil pipeline vs Hyperloop is about the same; 1 metric ton per meter. Traditional elevated rail is about 10 metric tons per meter.

Half the "old generation" didn't know half the time if they are redirected to a phony site by a phishing email. Anyway, that assumes you're going somewhere worth scamming. Email, online bank, ebay sure... but in the last 15+ years I haven't seen a single phishing attempt for my slashdot account info. And stuff that you just read, what's to phish? And that's why the important stuff is moving towards two-factor authentication so just stealing your password isn't enough.

It's the same generation

Zoom right in on the bits that you think are white, so that they fill your entire monitor. They're obviously blue. For a lot of us, that's the colour that we see when we look at it in context as well. I can see how you'd interpret it as being white by overcompensating for the colour in the bottom right, but that doesn't stop you from being wrong. The gold bits are gold when you zoom in (mostly, some are black), but a shiny black often looks yellow-gold in overexposed photos.

I wasn't talking about branching at (full) speed, just how effectively you can insert/extract trains from the loop though I suppose low speed exit/merge tubes could be built. Say you have stations 1-5 connecting two major cities with suburbs at 2-4, could you effectively have a schedule like:

1-5 express
1-5 express
1-5 express
1-5 express
1-4, same time 4-5
1-3, same time 3-5 (and maybe 3-4 local following)
1-2, same time 2-5 (and maybe 2-3 local following)
(pause long enough for train to get out of way at station #2
1-5 express
etc.

Then it would be a real boon to the people living at #2-4, because I think the "every 30 seconds" is to get volume up, I don't think it's very significant if you have to wait 5-10 minutes for your route to come into rotation.

What I'm interested in about the hyperloop is that unlike airplanes, high speed rail and traditional tube is that in the concept you'll have 6-8 passengers/capsule and 3 capsules/train = 18-24 passengers/train, which hopefully means you can have many more dedicated routes and/or a mix of long-hop/short-hop routes using the same infrastructure that'll serve the whole 3000 miles and not just the endpoints.

Around here the train is used for a lot of regional travel instead of bus, shorter than airplane and every time there's talk of building out high speed rail the problem is that it'll actually serve the regions worse since you don't have time to stop, so effectively you're just building a grounded airline. It's a lot easier to find 20 passengers going somewhere at the same time than 400-800 so that could be a major game changer if the technology works out.

As such it's not the brightness, it's the color temperature. The spectrum of light ranges in color temperature from 1850K at sunrise/sunset to 6500K on an overcast day to 15000K under a clear blue sky. The eyes adjust to this, if you look at someone using a cell phone at night it'll probably seem to have an eerie blue glow as it has daylight color temperature. So with "nightvision" the dress looks blue/black, with "dayvision" it looks white/gold.

The people trying to read the RGB values to determine the "truth" forget that the color space assumes you have a D65 white point. Basically your LCD screen is trying to show you correct colors for overcast daylight. If you stare at the red sunrise/sunset or the blue sky for a while and then look at the LCD screen, your color perception will be off. Apparently this picture is in just the right sweet spot to confuse a lot of people.

I live in a city in a "coastal region" and what's generally recognized as the city center is 10m above sea level with most areas trending upwards, 2 meters would affect <5% of the city. So there's coastal cities and there's "flat as a pancake cities that are 1 meter above sea level", you can take a look for yourself here. Note that the links in the top bar is showing you pretty much the worst case locations, zoom out and you can see the whole world. Take for example New York at 2m, the bulk of the city is intact. Even at +60m(!) you'll still have Manhatten and Staten Island peaking up above sea level.

I would worry about climate change and resource conflicts as a consequence, but the loss of land as such? Most people would do just fine relocating <1 km further inland. We're on all the beaches because we want beachfront property, maybe that's a bad idea in a 100 year perspective but feel free to buy the second row 50 meters back and 2 meters further up. Of course there's a few tropical islands where that's not an option, but they're <0,01% of the world population.