According to Donald Fagen, at the last I.G.Y. they thought it would be 90 minutes.
Nah…not if the tunnels were rigid. Hmmm…then again I suppose the rigid tunnel would weigh more with air in it so perhaps it would want to sink. I’m sure it could be compensated for though by filling bladder on the outside with air too that would compensate for the extra weight of the tunnel.
No, Mach number is based on the speed of sound in the local fluid, not sea level conditions. If you base it on sea level conditions, it is meaningless and you might as well use velocity. The point of using the Mach number in the first place is that the speed of sound changes but many flow conditions such as shock wave angles and pressure ratios vary with Mach number, not velocity. You know that a vehicle flying at Mach 2 will have a specific set of flow conditions regardless of its actual velocity.
To confirm this for yourself, grab any basic compressible flow text and look up the shock tables. These chart deflection angle and shock angle based on Mach number. Velocity is irrelevant. If one aircraft is flying Mach 2 at sea level and another is at Mach 2 at 50K feet, they’re at very different velocities but their shock configuration is identical.
This is why I made the comment. It was sarcastic and meant to imply that anyone who used Mach number in this way (as a replacement for velocity when it was clearly not relevant) had a fundamental misunderstanding of what is going on. Even if they mean very low pressure rather than vacuum (which they obviously would in a situation like this), citing a Mach number is misleading because it has so little to do with velocity unless you know the rest of the flow conditions.
A freely falling object takes approximately 45 minutes to go through an evacuated tunnel directly through the center of the earth. And it also takes 45 minutes to go through such a tunnel from New York to London or anywhere to anywhere.
Makes trip scheduling really simple and easy to remember. 
would it be possible to only make one side of the tunnel a vacuum, and have the other end pressurized, with a barrier in between. When the barrier was lifted, wouldn’t the air (and the train) be sucked to the other end of the tunnel?
Disclaimer: I am dumb, and don’t know much about physics (yet), so go easy on me on why this wouldn’t work…
In reply to Joe Mahma above.
From “How Things Work”:
“The X-33 offers a hint of the next generation of space flight being developed by NASA and private industry, mostly in cash-starved Russia, which aims for commercial space flight. So-called space planes, or hypersonic orbital planes, are the future of flight, says McCurdy; they fly to the edge of space, skirt over the Earth’s atmosphere and then re-enter to land at any major international airport. Space planes could take a passenger from New York to Tokyo in less than an hour. But billions of dollars are needed to research the engines, materials and design.
“Our ability to fly in space will depend on two things: money and risk,” says McCurdy, who expects space planes to be running in the next 20 to 50 years.”
Damn, Exapno, you beat me to it. This is one of the few things I remember from my physics major
A tunnel free-floating in the north Atlantic? Are you kidding me?
It may depend on more than that. When I was doing a post-doc at NASA, there was work on an “orient express”, a Mach 5-7 commercial carrier that would travel LA-Tokyo in something like two hours. It died on the vine as most projects do. While it was probably a funding problem, conventional wisdom held that the project was primarily killed by the marketing departments who determined that the two main problems with the project were that no one wanted to fly to Tokyo and not get served a real meal (and this vehicle’s flight plan barely permitted time to serve cocktails) and there was no way you could convince the general public that the wings were supposed to glow red in flight. This may be urban legend, but it led to a lot of resigned head-nodding among the really smart people who design these things.
Note: I can’t verify anything more than the anecdote and I don’t know if these marketing problems would really kill a viable high-speed carrier. I don’t intend to defend them here. I bring them up only to point out that there are a lot of non-technical issues that might affect any project like the one the OP mentions.
Wouldn’t plate tectonics become a factor in an intercontinental bridge?
Eventually. I think the other posts in the thread suggest more immediate obstacles though.
Ok, so more immediate means more important or something?
…
Fark that, where can I sign up?
Not free-floating, it would be anchored to the bottom by cables (really, really long cables; does anyone here know how deep the Atlantic is along that route?) that would keep it 100 feet below the surface.
I read somewhere that highway engineers had looked at something like this for a new crossing of Lake Washington east of Seattle. I suppose it’s somewhat similar to the floating bridges they already have. The idea was passed over as being too risky and expensive, and that’s only a two-mile crossing.
I can imagine the train and the vacuum tunnel. I want to know how the train gets into the tunnel without letting the air in with it.
I’m not so sure. The US is moving away from Europe at something like 0.5" per year. Not much maybe but your tube around the mid-Atlantic ridge will be stretched 0.5"…it’ll be torn apart unless it is somehow stretchable (I imagine engineers could do something to compensate perhaps).
What I’m saying about plate tectonics is that “it won’t work at all” is a more immediate problem than “what happens when it gets stretched to breaking point”. After all, there have been cables laid on the bed of the Atlantic.
Actually I didn’t read the linked article until now. The most damning condenmation must be that it’s the Daily Mail quoting Readers’ Digest. Personally I find it hard to believe a word in either publication. Even more strange is that Frank Davidson is quoted there as saying the main problems with tunnelling under the bed of the Atlantic are that it would be too expensive and time-consuming. No problem with it needing to average 12,000+ feet below sea level then?
On second thoughts the article suggested the tunnel might link Boston to Liverpool – excellent idea. Sign me up :).
Why not go from Canada to Greenland to Iceland to Scotland or Ireland with a series of shorter tunnels?
Yes, but that was for New York to Paris.
Our great great grandchildren in the 22nd century will see this, but not us.
What I want to see is a bridge or tunnel connecting the Bering Strait. Who wants to go to England??
Gimme a shovel, lets dig!
D’oh! That’s right. Ah well, Paris isn’t terribly far, just add a few minutes…