We all use the internet and expect it to perform every time, like magic. There is a maximum latency time here on Earth that is determined by the circumference of the Earth (133ms at the speed of light). Of course, the time is much longer because of signal amplification along the way as well as routing through various computers and data centers as well as the fact that the signal may not take a direct physical path. If our signal must travel up to a communications satellite that is in geosynchronous orbit and back down, you’ll achieve a much larger latency (240 to 290ms for the satellite bounce).
Do you want to see how slow it takes a signal to reach one city from another? Here’s a link to a site that shows ping statistics: Global Ping Statistics. As you can see some of them can take over 200ms (like London to Tokyo). You can add any large city to the list to see more stats.
Now that I’ve droned on about how many milliseconds it takes for a signal to arrive at a location, you’re probably wondering “who cares?” So far, nobody cares. However, what happens when we put a colony on Mars? The distance from the Earth and Mars varies, and at its minimum distance, a radio signal takes a little over 4 minutes. That’s not so bad, I’ve experienced websites that are as slow as that. At the longest distance between Earth and Mars, a signal will take 21 minutes. That occurs when Mars is on one side of the sun and Earth is on the other.
21 minutes is too long for the worldwide web. It’ll work for SMTP (email) and any other batch send protocols, but HTTP will not happen. So, what are the alternatives? We could set up data centers on Mars with copies of data from Earth. Let’s assume that disk space by the time we have a large colony on Mars is obscenely cheap. Keeping the data synchronized is a big problem. This includes sending updates back to Earth as well. If I post a picture of my cat on its tower at 1/3 gravity on Mars, I want mom to be able to see it within an hour or two.
There is, however, another wrinkle in our Internet from Mars plan: Bandwidth. The signal strength of the radio transmitter and the distance will determine the bandwidth. Currently, one fo the fastest transmissions to Mars operates at 5.22Mb/s. Most people have a faster connection to their house than that. Not to mention the fact that an entire colony on Mars will create more than 5 million bits of information per second.
Prioritize
We could triage or prioritize what is sent. For instance, the news would probably be compressed to text-only and be the highest priority so everyone on Earth can keep up with Mars events in near-real-time (and vice-versa). Then information could be divided according to time-sensitive vs. non-time-sensitive. For updates to Wiki and such, bulk data could be transported when supplies and shuttles cross back and forth between Earth and Mars. I imagine that 100 Petabytes of data could be transferred on something like the Amazon Snowmobile (stop laughing, okay, I admit, it’s funny).
Attempting to synchronize two Internets would be a “challenge.” It would consist of individual organizations, paying to have their data synchronized and they would each be responsible for keeping track of what data needs to be sent to Mars and what data needs to be sent from Earth. Perhaps a tiny bit of metadata would be sent using the live link to indicate that there is a huge block of data on Earth that is in transit. If you live on Mars and you click on a Wiki page that was recently updated, but the data is in physical transit, then a note might indicate that the data would arrive (and be available) on a certain day.
Increase Bandwidth
Of course, we could always just keep pumping up the bandwidth, though it will still be limited. Could we ever achieve a high enough bandwidth to keep two Internets synchronized? Sadly, no. Here’s an interesting site that shows how much data is created daily (and that number will climb): How Much Data Is Generated Each Day? According to the information on that site, Facebook users create 4 Petabytes of data per day!
We could use laser beams to transmit data. This could be used to narrow the transmission beam. A laser beam transmission system would have its own set of challenges, starting with the fact that it will only work outside of the atmosphere of Earth and Mars. Data would need to be transmitted from Earth to an Earth orbit satellite. The Earth satellite would have a laser beam locked onto a satellite around Mars, which would transmit the data down to the surface of Mars. There will probably be issues when Mars is on the opposite side of the sun (since the sun will block the beam). It appears that NASA has already thought of this technology: NASA Counts Down to Laser Communications for Mars. This technology will be available in 2026.
Beyond Mars
Now that I’ve talked endlessly about an Internet on Mars, what about Jupiter’s colonies? Saturn? Let’s pretend there is a colony on Triton, the largest moon of Neptune. Light takes from 241 to 258 minutes to travel from Earth to Neptune. The bandwidth of a radio beam from Earth to Neptune would be even smaller. A laser beam would spread fairly wide, but I assume that the bandwidth could be maintained.
I suspect that any colony outside of the asteroid belt will probably be isolated from Earth if only by the lack of bandwidth and the physical time it would take to truck Petabytes of data up to the colony and back.
Outside the solar system, colonies on other star systems would be impossible to keep data in sync. Alpha Centauri is a four year trip by laser beam, one-way. Maybe they could trade a small amount of data, but most data would be obsolete before it arrived. If sub-light speed is used to transfer colonists, then transferring data will almost be pointless. I suspect humans will need to solve the larger problem of faster-than-lightspeed travel before we worry about communicating between worlds. Otherwise, families that are separated by interstellar distances will find it difficult to stay in touch.