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Comment by dr_dshiv | Hacker News Reader

>If we're going to eventually be able to send high-definition video messages to and from Mars without a significant delay, then this is a step towards the tech we need.

Won’t all Mars messages have a significant delay due to the speed of light more than bandwidth?

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You're mixing up two concepts here: Bandwidth and latency (ping). Latency will always be limited by the speed of light, but bandwidth is currently limited by radio transmission. The upload speed for rovers like Curiosity and Perseverance peaks at like 2000kb/s tops under ideal conditions and is also limited to a few minutes at a time when the relay orbiter is in the right position. With lasers, bandwidth is measured in hundreds of Gb/s. That's the difference between sending an image in less than a second vs. having to wait a day.

This will get us to Mars orbit, but don't we have to go to radio anyway to relay through the atmosphere to the surface?

Mars atmosphere can barely be called that. It's less than one percent of earth's pressure. People just have a wrong perception of it because of wildly inaccurate depictions in movies like The Martian. And even if you want to transmit using radio between the surface and low orbit, it's far less of a bandwidth issue than transmitting over millions of kilometers. Deep space transmissions of the future will use optical wavelengths instead of radio, there's no question about it.

It’s not just the atmosphere that’s an issue though, having a laser in earth’s orbit track something on mars’ surface and vice versa would require some incredible tracking, it would be easier to go from orbit to orbit

It's not that hard with modern electronics. Telescopes with adaptive optics have been doing that since the 90s. Also beware that a laser doesn't remain perfectly coherent over many kilometers (let alone millions). So it's not like you need to perfectly hit a satellite dish area of a few m^2 on the surface of mars from earth. It's not really any harder to do from the surface than from orbit. In fact it might actually be easier since you don't just have to account for the rotation and orbit of earth but also for the orbital velocity of the relay.

Aren't photos and radio waves basically the same thing?

I guess the only issue that could happen is the scattering due to atmosphere, but as others have noted it's barely existent.

The laser experiment in the OP terminated at a ground-based optical telescope in California.

If you wanted a solution robust against clouds, I don't know if it'd make more sense to have a optical->radio relay satellite in earth orbit, or to have a redundant network of ground-based optical receivers in multiple places.

(There's a quirk of physics that transmitting and receiving aren't symmetric in these setups. All of the atmospheric distortion happens in the few kilometers of atmosphere, out of tens of millions of km path lengths. Because the angular distortion happens at the start of their optical paths, laser signals going from Earth–outwards will have much larger absolute distortions, than signals being received on Earth from space).

Relevant quote: "Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway." -- Andrew S. Tanenbaum

How is he mixing up concepts there? Due to light speed bottleneck you would literally always have at least 3 minute delay unless you break the physics, in some way. So the ping would always be at least 6 minutes. 3 minutes is quite a significant delay for any sort of comms. Video or otherwise.

If anyone is mixing up concepts, it seems to be the article author to me, mixing up speed width bandwidth.

In the case of Perseverance, I think data has to be sent in batches to a relay satellite and the forwarded back to Earth. That time when the satellite has line-of-sight with the rover is short, before the signal is lost, and it has to wait before continuing.

It'll mean more data can be sent in these batches from what I understand.

This is why Star Trek uses "subspace" as a plot handwavium[1] to explain how a starship can hail Earth from hundreds of lightyears away with seemingly no latency.

[1] handwavium, my favourite new word: https://www.urbandictionary.com/define.php?term=handwavium

For some illogical reason I never had a problem with sending messages across such vast distances, but when the Enterprise detected another ship starting its engines from a light year away my suspension of disbelief collapsed.

Easy fix: subspace-based sensors. If the other ship is transmitting in any way, or its engine produces visible artifacts in the subspace field, it could be detected.

I think they meant "more significant than it need to be".

Recently I looked up how long it takes light to go to Mars from Earth : it's between 3 and 20 minutes depending on their relative positions.

That's my interpretation as well.

Traditionally deep space bandwidth is low so that sending huge amount of data takes a long time in addition to time of travel.

Yup, no realtime communications of any sort, even texting, with people living in the Mars cities. I think living in the moon will be much more attractive to people, given that you can still have video/voice calls with a slight lag (2600ms roundtrip) and text conversations with no perceptible latency increase (vs ones to people still on Earth).

Personally I don't think an up to 20-40 minute lag for communications will be that big of a deal, it'll take a bit of getting used to, plus mechanisms to synchronize internet data with Earth, but we're pretty used to asynchronous communications, and prior to the advent of electricity, not having realtime communication over large distances was normal and tolerable.

>plus mechanisms to synchronize internet data with Earth

Even in a future where there's a city on Mars, that seems unlikely.

I disagree, long term I think we'd have at least a significant portion of internet data synchronized between the two. Of course early on it'd probably just be in the form of certain popular entertainment sources and informational resources being periodically uploaded from Earth, more akin to a Plex or Invidious server and Wikipedia backup for Mars.

But as the size of a colony grows, it just makes more and more sense to sync up as much data as possible. Eg a YouTube Mars which downlinks ahead of time trending videos + videos from people subscribed to by Martians + videos the algorithm thinks Martians will like and uplinks the same stuff for Earth.

Some very small subset is perhaps plausible, but I think you're overestimating how much Google or Netflix would care about addressing a small and inconvenient market.

A major self-sustaining colony on Mars will probably take 50-100 years, at which point Google as well as its current jurisdiction of registration (Delaware) will likely both be history.

Self-sustaining? I think that's far enough out that is basically pointless to speculate a deadline. It would require too many breakthroughs.

Maybe you can get an AI agent for both of you who knows how to perfectly simulate you in a dialogue or predict to great accuracy what you would say on both sides.

Deleted due to incorrect understanding.

Faster-than-light communication of any sort breaks causality and is not permitted by physics.

Quantum entanglement does not allow you to communicate. It just means two particles have a linked but random state.

It will. It always will, no technology on Earth now or likely in the future allow this to change. The only thing that will change is bandwidth or how much data can be sent at once.

Yes, and that changes how long you have to wait for a fixed amount of data to arrive, especially when transmission windows are narrow and sufficiently low bandwidth would mean having to waste time waiting between several.

But the delay will always be significant either way.

No, the minimum delay is no more than a few minutes time of flight. But the transmission windows are only a few minutes long and they're hours apart. If you can't finish in one, you need to wait hours more to resume transmitting.

> the minimum delay is no more than a few minutes time of flight

And how is that not significant?

In time we might find ways to glitch the simulation.

Just a few minutes. Bandwidth could make that delay months.

Yeah, but the throughput will be incredible.

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