The Distances Involved With Space

Humans Traveling Interstellar or Communicating with Aliens are Pipe Dreams

Nobody likes science fiction more than scientists, which is a bit of a paradox because it always tend to be more fiction than science. The distances in space are incredibly huge. Yet the distances in most science fiction stories are just blips, meant to progress a story that otherwise would be non-existent if you used, you know, actual science.¹

NASA came back into contact with the 1970’s era Voyager II spacecraft this last week, currently the second furthest man made object.² It had stopped receiving and transmitting due to an errant command to tilt its antennae a mere 2 degrees away from Earth. After using the International Deep Space Network, they sent a message to realign the antennae to Voyager, and the spacecraft picked up on the signal 12.3 billion miles away and sent a return message back to Earth, which was received 37 hours after the initial command.³

Which brings us into the discussion about distance. Voyager II was launched in 1977, and has traveled 12.3 billion miles. It’s slowed down some and has no propulsion of its own other than letting it’s continuing inertia guide it; the only movements of which it is capable is the occasional realignment as was just completed. So 46 years, 12.3 billion miles. Based on the synopsis I read, it’s averaged about 35,000 mph, so we’ll use that as a guideline going forward.

The talk of distance in space inevitably comes to light years. Basically, it’s the distance light (the fastest thing in the universe) travels in a year. To put it even into context, if the Voyager spacecraft were one light year away, it would take one whole year to send it an instruction, and another whole year to send it back to Earth confirming it. How far is that? Well, it’s ~6 trillion miles, with a T. So at the speed of Voyager, it would take roughly 19,557 years to travel one light year. That long ago in human history there were still neanderthals walking about.

You may say, “But we’ve made much better, faster technology since 1977, and should be able to shave off some time.” Fair enough. The New Horizons spacecraft was launched in 2006. It sped through the Solar System on it’s course with a rendezvous with Pluto in 2015. How fast is that traveling? Approximately 38,000 mph, but its slowly slowing down to Voyager’s speed. Nonetheless, we’ll give it the benefit of the doubt. How much time does that shave off? Congratulations, you got the total down to a little over 18,000 years, taking off 1500+ years.

But here’s the thing; we are not one light year away from the nearest star. The nearest star is Proxima Centauri, part of the Alpha Centuri star cluster, and that is 4.3 light years away. So traveling at the speed of New Horizons to Proxima Centauri, you would eventually make it there in just under 77,500 years. Needless to say, this could not be done in one lifetime. At an average lifespan of 77 years (we’ll 77.5 just to keep round numbers), it would take over 1000 GENERATIONS before you got there. I do genealogy as a hobby and getting over 10 is a huge achievement.

If you did make it there and sent a message back to Earth saying “Hi, we made it,” it would be 155,000 years after your launch before Earth got your message and the Morlocks would have definitely taken over by then, wondering who these strange star people are calling us through the skies. Even if you could travel at the speed of light, that would take you 8.6 years to accomplish that feat, which is still faster than it is taking George R.R. Martin to complete “The Winds of Winter” but still a lot of time. If it were possible to do that today and someone left tomorrow, my hunch is that he would still be working on it 9 years from now when you asked what was different than the HBO show.

The point I’m trying to make here is that the distances in space are incredibly vast. We love the idea of Star Trek and Star Wars of seeing alien creatures from other planets and interacting with intelligent beings from elsewhere. But these are just stories, and the idea of aliens are used as a useful convention, often to show us the error of our ways or as a fun “what if” scenario, such as “What if we could travel to distant galaxies light years away in the amount of time it takes to fly to Dallas?” It’s not real or even remotely plausible. These stories are just analogies for the way we as humans treat each other. This gimmick isn’t even original. Two thousand years ago it was myths and stories about strange places people traveled to across the seas. Tall tales and legends. During the Middle Ages through most of the 19th century, people would talk about cultural differences and strange customs of people seen on pilgrimages as exotic or adventurous. It was only 100 years ago people thought the moon was made of green cheese and that there were possibly people on Mars. The more we learned about the world and science, the more we put those stories to rest.

It wasn’t until the latter half of the 20th century we began exploring our own celestial neighborhood. It’s still relatively new and exotic to us. We’re still finding neat stuff out. However, the more we learn, the more we realize how special and unique Earth is in its own system. As such, it’s very easy to posit about how much we don’t know yet and wonder about foreign worlds and alien beings that we’ve never seen before; the same way those stories about exotic cultures were spread years ago.

However, time and space are still governed by the laws of physics, and distance is too. The science of today screams it’ll never happen, and it’s best not to spend too much time and effort thinking about it.

PurpleAmerica’s Recommended Stories

The film “Powers of Ten” was made in 1977 (the same year Voyager II launched) and kind of puts things in perspective. The problem with it is that it shows things expanding exponentially (each box shows an increase in the power of 10) but space and time are experienced linearly. Still, it does help put the vastness of the universe in perspective.⁴

Carried aboard Voyager I and II are “Golden Records” which are time capsules of a sort on the off chance some aliens actually do come across the distant probes.⁵

As NASA puts it: “Pioneers 10 and 11, which preceded Voyager, both carried small metal plaques identifying their time and place of origin for the benefit of any other spacefarers that might find them in the distant future. With this example before them, NASA placed a more ambitious message aboard Voyager 1 and 2, a kind of time capsule, intended to communicate a story of our world to extraterrestrials. The Voyager message is carried by a phonograph⁶ record, a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth.”

You can read more about it here: https://voyager.jpl.nasa.gov/golden-record/

PurpleAmerica’s Obscure Fact of the Day

One of the more interesting aspects of maintaining connection with Voyager and other spacecraft is that in their calculations, NASA often has to include pi. That in itself is not interesting, but what is is how many digits they expand pi out to.

You see, pi is an irrational number relating to the ratio of a circle’s circumference to its radius, and when calculated it goes on practically forever. People, and mathematicians in particular, have mesmerized people by reciting the digits of pi from memory as far as they can go, often into the hundreds of digits. Using a high-performance computer, a team of Swiss researchers have calculated the new most accurate value of pi. The record-breaking value counts 62,831,853,071,796 digits, as confirmed by project leader Thomas Keller and his team on 19 August 2021, adding 12.8 billion new digits to pi.

So how many digits of pi does NASA use? For most calculations, NASA only uses 15 digits: 3.141592653589793. You see, if we take Voyager II again as an example, we can imagine this enormous distance as the radius of a huge circle centered on the sun, as if Voyager were in circular orbit around the sun. We can calculate the circumference of this circle by using 2πR. Using 15 digits of pi gives a circumference of something like 91 billion miles, which is indeed very long. If you use more digits of pi—like, say, 21 digits instead of 15—the circumference would actually be longer.

But here’s the important part: Even with the additional 6 digits, you only get a circumference that’s 5.95 inches longer. Could you imagine measuring 91 billion miles and only being off by less than half a foot? That’s super accurate. So there’s not much point in calculating beyond the fifteenth digit. The returns really diminish beyond that point. From a practical standpoint, it doesn’t make sense to go further than 15 digits of pi.

So the next time someone tries to impress you by spouting off digits of pi, stop at the 15th digit and then say “I’m good here, it’s good enough for NASA, it’s good enough for me.”

PurpleAmerica’s Final Word on the Subject

We’re going to give it to Carl Sagan. When Voyager I was 6 billion km from Earth in 1990, it turned around and took this picture, prompting Sagan to make this comment.

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Footnotes and Fun Stuff

1. Famous Astrophysicist Neil Degrasse Tyson has a habit of ruining otherwise good movies focusing on the minutiae of details, because the guy can’t suspend disbelief for a minor second. He once complained about Titanic because the stars in the April sky while Rose and Jack are floating for their lives wasn’t right to what they would see that time of year at that time of night, as if seeing Leo (the constellation, not the actor) was the most important thing in that scene. However, when it comes to most science fiction stuff, he can be a little picky but gives a lot of it a pass, which doesn’t quite seem right. One thing we can agree on, Disney’s “The Black Hole” is one of the worst science fiction movies ever.

2. Its twin, Voyager I, is now nearly 15 billion miles from Earth. An interesting note is that after being sent Jupiter, NASA programmed it to go “down” toward interstellar space. Voyager II, after investigating Jupiter, Saturn, Uranus and Neptune was programmed to go “up” into interstellar space. Thus, these two are not just the most distant objects from Earth, they’re the two most distant man-made objects from each other.

3. That’s how long it takes for a radio signal to reach Voyager and then send a message back to Earth saying “I got your message.” A day and a half. And teens erupt into fits if the person they like doesn’t text them back within 5 minutes.

4. Also of note is the quality of the video and the fashions viewed in it; it helps conceptualize that as far away as Voyager actually is now, it’s using this level of technology and quality. Imagine traveling out to interstellar space in a ‘70s Ford Pinto and that’s pretty close to what it is like.

5. Again, not going to happen.

6. I’d like to say that this just seems entirely antiquated using a phonograph but ever since hipsters brought back LPs I’m not sure what to think of it anymore. At least we didn’t put it on 8-track.