Tube trains could navigate the Underground using the rules of Quantum Physics • Hacker News Board

Re: Tube trains could navigate the Underground using the rules of Quantum Physics

#81

Post by foltik » Tue, Jan 06, 2026, 10:06 PM UTC

ACV001 wrote: post #56

Quite a dumb application of quantum physics. Cooling something to near zero, which takes energy, and is complex, and big, in order to obtain precisions which are magnitudes higher than what is necessary. As if one would use CPUs to prop up an uneven table and would boast that they use microelectronics. "Instead of relying on conventional sensors, these devices use clouds of atoms cooled to near absolute zero. At thos…

Quite an ignorant comment. It’s literally nothing like using a CPU to prop up an uneven table.

It’s precisely the application of quantum physics that enables current prototypes of these IMUs to achieve 1-2 orders of magnitude less position error accumulation vs. state-of-the-art gyroscopes. Think 0.1m/min vs. 10m/min.

Obviously the tube isn’t the holy grail of applications, it’s just a test bed to improve the technology. Think about why GPS is useful. Imagine that, but entirely self contained.

Re: Tube trains could navigate the Underground using the rules of Quantum Physics

#82

Post by thaumasiotes » Wed, Jan 07, 2026, 8:15 AM UTC

bluGill wrote: post #67

thaumasiotes wrote: post #37

Earlier quoted context omitted.

> their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it. Considering the tracks are linear, I would estimate the additional time needed to locate a fault within two meters as compared to two centimeters at "negligible". On the alternative assumption that the faults are too small f…

Do they repair track cracks? I'd expect they replace the entire track section - both rails - as long as they are there. Get within however much they can do in a work shift and good enough.

So.... how would it be faster to do that if you knew the location of the fault to within 2cm instead of knowing it to within 2m?

Re: Tube trains could navigate the Underground using the rules of Quantum Physics

#83

Post by bluGill » Wed, Jan 07, 2026, 2:53 PM UTC

thaumasiotes wrote: post #82

bluGill wrote: post #67

Earlier quoted context omitted.

Do they repair track cracks? I'd expect they replace the entire track section - both rails - as long as they are there. Get within however much they can do in a work shift and good enough.

So.... how would it be faster to do that if you knew the location of the fault to within 2cm instead of knowing it to within 2m?

I don't know, that is why I'm asking.

My general thought as someone who doesn't know how rail maintenance is done is that rails should not crack in normal operation. If there is a crack that implies either the rail is end of life anyway and you replace it, or there is likely a manufacturing problem and you want to replace all the rail from that branch. Either way rail is manufactures in long sections (20 meters is my guess, but that is slightly educated guess that I won't stand by), so you would only need within a few meters to find the track section in question.

However I don't know how track maintenance is done. It is entirely possible that they grind/cut out the crack and then fill in (either cast in place, fill with weld, or just replace a a few cm) and in that case you would need to know within a few mm (though maybe inspection could find it if you are within a few cm).

Again, I am not a rail expert here. This is a place where I want to know and thus would like an expert to say. (though likely no experts are reading this...)