How to build an interplanetary internet

DW: How far off are we from real-time signals or communication from, say, Jupiter to Earth?

Vint Cerf: Your use of the term real-time is fanciful at best. The notion of simultaneity is nonsense in Einstein's universe. So the answer is: the speed of light is what it is and that means we're not going to have real-time interactive communication between Jupiter and Earth. It just isn't going to happen. And that's why the interplanetary design took so much effort. It was because we didn't have real-time communication at all.  

So where are we at with the interplanetary internet?

We already have an interplanetary network in operation between Earth, Mars and the International Space Station (ISS). We've standardized the protocols and we're encouraging people who make spacecraft for exploration to consider stockpiling the protocols as part of their off-the-shelf capability. So when NASA designs new missions, they can use constellations of spacecraft that can communicate with each other locally, as opposed to going all the way back to Earth, which is classically what has happened.

We have this Deep Space Network (DSN) that was built in 1964, consisting of three 70 meter dishes, and it's classic that you have point-to-point radio links, going from wherever the spacecraft is back to Earth. The original plan for Mars exploration had always been spacecraft landing on the surface of Mars, or possibly in orbit, transmitting data directly back to the DSN.

We tried to do that with the 2004 rovers [Spirit and Opportunity] that landed on Mars.  We discovered the radios were overheating, so we had to rethink how we'd get information back to Earth. And we reprogrammed the orbiters, which had been used to map the surface of Mars, so they would receive data from the rovers while they were in orbit and then hang onto the data until they get to a point in their orbit where they could transmit back to Earth. That's a store-and-forward network, which is what packet-switching [the way the terrestrial internet works] is all about.

So we've had a store-and-forward network to gather all the data coming back from Mars since 2004. And we've now expanded that to include the ISS.

By standardizing the protocols, we expect that as new missions get launched, like the Juno mission to Jupiter, once the spacecraft has completed its primary function it can become part of an interplanetary backbone. So as we launch more missions around our solar system, we will literally be able to accrete an interplanetary backbone, mission by mission, supporting future manned and robotic space exploration.     

So if the idea of real-time communication from Jupiter is "fanciful," are wormholes, which theoretically allow time travel, also fanciful? Isn't it possible that we could breakthrough these limitations - after all, scientists are still trying to disprove the theory of the speed of light. Think of the Gran Sasso neutrino experiment.

Well, the neutrino experiment was a mistake. There was a bug in the wiring, a faulty connector that led to improper time measurement… It's possible theoretically to build a wormhole. If you read any of Robert L. Forward's books you'll find in the appendix a description of how you do that. But he seems to say you need [magnetic] monopoles, among other things that are very exotic, and a huge amount of energy to construct such a thing. And then there's the question of what you can transmit through it.

Wormholes = real weirdness

So we shouldn't rely on wormholes to achieve real-time communication. Besides which, I think there's some real weirdness here, because when you use wormholes for communication, you also end up with a very odd time-effect. You're communicating backwards in time and it's not clear that that conversation makes any sense at all.

"Time Masters" by Robert L. Forward describes exactly that situation and the peculiar consequences of this communication, which is not simultaneous. That's the important thing: this is not simultaneous communication.

Still, if we expand deeper into the universe, through our solar system, as some probes have done…

That's the Voyager spacecraft, which have moved passed the essential envelope between the solar system and the rest of the galaxy.

Exactly. So if we do that and we expand our communication network that way, are we also opening ourselves up to the potential for communication from outside our solar system? If there's life out there, they could contact us...    

Even if we're trying to communicate with something inside our own galaxy, remember that the Milky Way galaxy is about 100,000 light years wide. That means it takes 100,000 years for a signal to travel from the edge of the galaxy to the other edge. And that is ten times longer than our civilization has existed. Assuming we don't destroy ourselves in less than 100,000 years, we might actually receive a signal from someone who picked up ours that started transmitting at the beginning of the last century. So I think the honest answer is that we may be able to do some communication, but as long as there is the speed of light limitation, the delays are going to be pretty dramatic.

Just to give you an example: the nearest star is Alpha Centauri. It's 4.3 light years away. Which means it takes 4.3 years for a signal to get from Earth to anything in the vicinity of Alpha Centauri, and another 4.3 years to get back, so it's 8.6 years round-trip time. This is not a highly interactive conversation.

Vinton (Vint) Cerf helped create the internet in the 1960s. Together with Bob Kahn, he developed the TCP/IP protocols, and worked on a data transfer method called packet switching, to create our global computer network. He has worked in various capacities, including at the US National Security Agency, and is currently Google's "chief internet evangelist."