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Comment by happyopossum | Hacker News Reader

> They are 50% faster

No, pretty sure light still travels through them at C. What they can do is carry more data, largely by having lower error rates.

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'c' is dependent on the medium. The value of c as it is commonly known, 300 million meters per second, is in vacuum. Light traveling through other media is affected by its index of refraction, in the case of silica fiber, that is approximately 1.5 so radiation propagates much slower through silica than it does a vacuum. Since gases have low refractive indicies already, within a hundred ppm or so of a vacuum, you could essentially round air to 1.

I've heard that high frequency traders are interested in Starlink's planned laser links because they could open up routes that are faster than traditional terrestrial fiber.

I think that if you are a HFT, you probably have a server set up next door.

The suggestion is about trading across multiple exchanges, for example between London and NY. Going via Starlink is potentially quicker than a fiber under the Atlantic.

They will have servers “next door” to the exchanges, but need the servers to have incredible low latency connections to each other.

Yeah, that would make sense. There are links that have been built by various HFT firms and banks [0] [1] that use microwaves instead of fiber buried in the ground simply because of this speed-of-light-in-media limitation. They can shave a few hundred nanoseconds (or something, I don't want to do the math right now) because of a higher signal propagation speed and get a trade in faster than their competitors. Same thing with a laser link like this.

Edit: cf.

[0] https://arstechnica.com/information-technology/2016/11/priva... [1] https://www.reuters.com/article/us-highfrequency-microwave/l...

I know the main people behind much of the hollow core work being done. Much of their financing is coming from HFT related firms.

"c" is the speed of light in a vacuum. Traditional fiber optic cables are very much not a vacuum, with an index of refraction of ~1.5, so light travels through them at ~2/3c. In contrast, light actually travels at nearly c through hollow core cables.

It's so nice when someone other than myself is confidently incorrect.

Light only travels at C in a vacuum (so it doesn't actually travel at C in a standard fiber optic cable, it's actually much slower).

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