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Comment by exDM69 | Hacker News Reader

It's the speed of light staying constant despite best efforts of physicists and engineers. The distance between California and the Netherlands hasn't changed either.

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Good time to dig out some lore:

http://www.ibiblio.org/harris/500milemail.html

Physicists and engineers actually are working on increasing the speed of light for fibers.

https://www.nature.com/articles/nphoton.2013.45?error=cookie...

Technically neutrino signalling could make it faster, but those extra milliseconds are not worth it, even for the HFT folks... but thanks to them we have shorter fiber routes across the atlantic at least.

> thanks to them we have shorter fiber routes across the atlantic at least.

Can you explain how HFT caused a shorter fiber route across the Atlantic? Is this route open to the non-HFT public?

I read Flash Boys and am aware of a custom fiber link between Weehauken, NJ and Chicago, IL, but I thought they are were moving to microwave. I thought there were some HFT links (fiber or microwave) within Europe.

I recall a new transatlantic cable constructed a few years ago being advertised as shaving off a few milliseconds. Trading and cloud providers were mentioned as target customers. I don't know whether they also route public internet traffic.

Microwave is great for latency, but the bandwidth sucks. When you need bandwidth & low latency, you need a more direct fiber link.

There are microwave links across Europe:

https://sniperinmahwah.wordpress.com/2016/01/26/hft-in-the-b...

There are apparently shortwave links across the Atlantic:

https://sniperinmahwah.wordpress.com/2018/05/07/shortwave-tr...

https://sniperinmahwah.wordpress.com/2018/07/16/shortwave-tr...

These should have a lower latency than fibre links although the shortwave link will probably have rather a low data rate.

> neutrino signalling could make it faster

you need a nuclear reactor for transmission and a deep array of detectors buried underground for reception...

And somehow distinguish between the signal and the flood of solar neutrinos.

It's actually about 60% the speed of light because there's no vacuum in buried fiber.

But yes the rest of your point is accurate.

Also, presumably light has to travel farther in fiber because it's constantly bouncing off of walls vs. straight line travel?

I was going to dismiss it as insignificant, but if I read this right:

https://en.m.wikipedia.org/wiki/Total_internal_reflection

an angle higer than ~42 degrees seems to indicate roughly a 50% longer path?

That said, I wonder what the average "fractal dimension" of a city to city fiber link is - I suspect wavering path around buildings and along roads dominate the increase in path VS theoretical straight (curved along the earth) path?

Don't forget fiber splices for accidental cuts. Engineers have to try their best to match the existing refraction when splicing in the new patch. Tools help, but there's a lot of skill and craftsmanship there.

But a splice should either work, or not work? It is literally welding two glass strands into one?

A splice may or may not work, or something in between. The splice might cause enough attenuation that you go over your optical budget (signal strength and receiver sensitivity) so no link comes up. But it might come up just barely and then you may have some bad frames as a result.

This is true for multimode, anywhere outside short distances in datacenters you use singlemode where light does not bounce at an angle. A singlemode fiber acts as a waveguide, the signal travels in a single mode, this is mainly why it's good for longer distances, no modal dispersion.

That is not true. Single mode fiber definitely comes in at an angle and bounces off the cladding. You still have a cone of acceptance at play. You're confusing multiple terms and concepts here.

The point seemed more along the lines of "the ping is a function of the speed of light" to me, so not necessarily inaccurate. Although that does leave room for improvement like introducing a vacuum or making the lines more direct.

I mean, it is 4844 nautical miles as the crow flies, but we could make that 4458 nmi (nautical miles) by taking a direct route through the crust.

I have to say I am disappointed/surprised by how limited those savings are.

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