Barring some kind of technological miracle, humanity won’t last forever. And the future of the universe is incomprehensibly long, big, and violent. So what, exactly, will eventually be the last evidence that we ever existed?
TRANSCRIPT:
From the moment humans became sentient, we’ve strived to leave our mark for future people to see…
To build and create iconic images and monuments to tell future generations that we were here. We existed. And we mattered.
The most powerful humans that have ever existed put countless treasure and years into places designed to last forever. But much as the great Ozymandias, over time, those colossal works were devoured by the Earth and turned to dust.
Today we’ve built cities and structures that previous rulers couldn’t have even dreamed of. But what we’ve built is not impervious to time. And there’s gonna be a LOOOOOOOOOT of time.
So let’s ask the question, out of all that we’ve built… What’s going to last the longest?
What will be the last evidence that we ever existed?
Perhaps the best way to consider what will last into the future is to look back at what we’ve built in the past and see how that lasted.
I did a video once on Gobekli Tepe, considered one of the oldest cities in human history, that goes back 10-12 thousand years. Like most archeology, it was buried underground, so at a cursory glance it would appear to have disappeared completely.
The same is true for many other, even older sites like Dolni Vestonice, which was a settlement of mammoth hunters dates back to 25,000 years ago.
Then there’s the Jebel Irhoud site in Morocco, which had the earliest modern human remains, dated to 360,000 years ago.
And just a couple of years ago a simple wooden structure was found in a riverbed in Zambia that was dated to half a million years ago, meaning it was built by a pre-human ancestor.
But these are wild exceptions, most of what was created by humans past say 10,000 years have been lost to the ravages of a living planet
Time is the great compressor, and it has compressed thousands of years of history into a layer of rock.
So how long will humans last? Average length is 1-2 million years
It’s impossible to know how much more of an impact we’ll make on our planet and beyond in the future so maybe for the sake of keeping our sanity let’s just assume we don’t make it. The Great Filter got to us. For all the reasons.
If we manage to wipe ourselves out in the next few hundred years; if that great filter gets to us, what of us will remain?
Our cities will crumble and be taken over by nature. Almost all outward evidence would be erased by 10,000 years. Our biggest structures like nuclear silos and giant concrete dams will last longest. It’s thought that Mount Rushmore might be one of the very last things that goes away.
Evidence will be left behind for anybody curious enough to look. If, in 500 million years another intelligent species evolves, they might find an odd layer filled with polycarbons from all the plastic we created, a spike in cesium atoms from our atomic testing, and a giant amount of carbon, like multiple supervolcanoes.
That species itself might come and go, and be followed by another and followed by another. These species and their development would just be another eroding force on planet Earth, further altering what we left behind.
Eventually, the Earth’s surface will reshape itself through tectonic activity. Whole layers of crust, containing entire countries will get subsumed underneath another plate and melted into the enamel, then erupting out of volcanoes back onto the surface. In a few billion years, almost every trace of our existence will have been literally melted down.
But even the last surviving evidence wouldn’t survive what happens in 5 billion years, when the sun enters its red giant phase and expands 200 times – which just happens to be right at Earth’s orbit.
Tiny chance Earth survives for gravitational stuff – but extremely unlikely.
So everything on Earth is toast. But what about off-earth?
Obviously everything in Earth orbit would be toast, and by this point most of what we’ve put in orbit would have come down already. So most of what we’ve launched would not survive red giant phase. So what we’re left with is…
All the stuff on Mars. Mars will survive the red giant phase, but it will be hot enough to melt rock, so I think it’s fair to say that whatever does survive would turn into an odd accumulation of melted metals, which might be considered evidence
We can go out further to the asteroid belt, where there are several probes that have landed on and studied asteroids out there.
DAWN – on Ceres
Launch – 2007
Arrived at Ceres – 2014
Ran out of propellant in 2018 and it in an uncontrolled orbit; will probably crash in 20 years
Clementine worth mentioning – it was a lunar orbiter that also studied a near-Earth asteroid. It did get flung out of lunar orbit but hasn’t strayed far from Earth’s orbit.
Launched in 94, mission ended in 95
NEAR-Shoemaker
Studied and landed on the near Earth asteroid Eros in 2001.
Eros – perihelion of 1.13AU, so could possibly survive red giant sun, but not likely.
Deep Space 1 – Outside Earth’s orbit and might survive
Launched in 1998
First ion propulsion
Studied asteroid 9969 Braille and comet 19P/Borrelly
LUCY – in the Asteroid Belt
Launched in 2021, planned to visit two main belt asteroids and six Jupiter trojan asteroids over the next 12 years.
They included a golden plaque featuring quotes from notable figures and info about the mission.
Will remain in the outer solar system after the mission ends
PSYCHE – at 16 Psyche
Launched in 2023
Will arrive in 2029 and orbit until 2031
16 Psyche is a metallic asteroid – possibly the core of a destroyed protoplanet; also super valuable
First probe to use Hall Effect Thrusters – a kind of ion engine
Will remain in the asteroid belt after the mission
All of these could be contenders for they might survive, but over billions of years, lots of opportunity to be smashed up in the asteroid belt.
Comets (67P, Tempel-1) go through the missions. They might survive the red giant phase, but again, they cross paths with many planets and asteroids, over a long enough time span, they could get smashed.
Comet 9P/Tempel 1 – Deep Impact mission
The impactor smashed on the comet, which might survive the red giant phase. The probe itself is very close to Earth’s orbit.
Rosetta – on Comet 67P
Launched in 2004, ended 2016
Philae lander on comet
Rosetta eventually was landed on there.
67P’s orbit gets as close as 1.2 AU from the sun. Might just barely survive. Maybe.
Ulysses – Launched 1990
Studied the polar regions of the sun so it had to do a gravity assist at Jupiter to get into solar polar orbit
Decommissioned in 2009.
Perihelions at 1.35AU so could survive red giant phase, likely to continue on indefinitely, though could get close enough to Jupiter at some point to change its trajectory – maybe even out of the solar system
All of these will continue to circle the solar system for billions of years, far longer than our planet will survive, but my bet is that they won’t last forever.
Billions of years is a lot of opportunity for collisions, especially in the asteroid best and more especially considering the changing nature of the sun going red giant and eventually white dwarf (3 billion years later), the chance for increasing instability in the system is huge, again, given enough time.
Moving out from the asteroid belt, you’ve got the planetary probes to Jupiter and Saturn like Galileo, Juno, and Cassini. But those all ended their missions by plunging into the atmosphere, so they burned up.
Missions to the moons of Jupiter and Saturn though, that’s another story.
Now these get interesting, there’s the Huygens probe that landed on Saturn’s moon Titan and the Europa Clipper mission that’s on its way to Europa around Jupiter.
Interesting because they both have a great opportunity for life – and when the sun goes red giant, they’ll be right in the habitable zone.
Based on what I found, the sun’s red giant phase could last about 3 billion years, which might be enough time for life to form.
So could an advanced, intelligent species come along later on and discover these space probes and learn that we existed?
Unlikely. It wouldn’t survive on Europa for a billion years any easier than it could here. Titan’s atmosphere and Europa’s oceans would destroy the probes.
Another Jupiter mission called JUICE, for Jupiter Icy Moons Explorer, launched in 2023 and will explore the moons of Jupiter in 2031. The plan is to end the mission by crashing into Ganymede, so it’ll just be a big ol mess, but it would be a big ol’ mess for damn near eternity.
So there are some potential candidates for evidence that would outlive the Earth, but when it comes down to it, as long as there are asteroids and comets zipping around the solar system, and the sun losing mass and other stars that could fly by and disrupt the Oort Cloud, over a long enough timespan, there’s a good chance it’s gonna get smashed to bits.
If you really want to go long-term, you’ve got to leave the solar system. Which leaves us with 5 possibilities.
Only five probes have left the solar system, and that’s Pioneer 10 and 11, Voyager 1 & 2, and New Horizons.
I covered the Pioneer and Voyager missions in a previous video, it’s kind-of a fan favorite so go check it out if you haven’t but those missions famously carried a message in case it was ever found by an alien species.
It was designed by Carl Sagan and Frank Drake, and it looks like this. Yes, in our first communication with aliens, we sent nudes and gave directions to where we live.
The plaque features a human couple standing next to a diagram of the probe, to give a clue to our size, and it shows our solar system across the bottom with Pioneer’s path out of it.
And this mess of lines over here shows the position of the sun relative to 15 galactic landmarks.
And this… thing is the key to it all. It represents the hyperfine transition of hydrogen atoms, this is when the electron’s spin direction changes.
This gets a little bit heady but basically light at this frequency has a wavelength of about 21 centimeters, so it’s often called the 21 centimeter line but equating 21 centimeters to this tic mark in this schematic is how they represent distances to whoever might find this.
NASA only gave them 3 weeks to come up with this by the way.
The Pioneer missions launched in 1972 and 73 respectively and we lost communication with them in the early 2000s.
The Pioneer 10 trajectory is expected to take it in the general direction of the star Aldebaran, currently located at a distance of about 68 light years. If Aldebaran had zero relative velocity, it would require more than two million years for the spacecraft to reach it.
Pioneer 11 is heading in the direction of the constellation Scutum and will pass near the star Lambda Aquilae in about four million years.
The Pioneer probes have since been overtaken by Voyager 1 and 2, which launched in 1977 and got flung out of the solar system at a higher speed. New Horizons followed in 2006 to study Pluto and the Kuiper belt, and will likely overtake them eventually, but it’ll take a while.
The Voyager missions kinda built on the Pioneer plaque and created a golden record, that has sounds and images encoded into it for a future alien species to find. I cover that in more detail in my Voyager video, but the first sound on the record is an introduction by the president at the time, Jimmy Carter. Rest in Peace
This is a present from a small, distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours.
— President Jimmy Carter
New Horizons didn’t have a plaque or a golden record, but they did include a CD with 430,000 names on it, they had a thing you could sign up to have your name on the CD. And apparently my name is on it twice!
I don’t remember signing up for that so it’s probably some other lucky fellows with my name but I’ll put a link to the site where you can search for names on the CD, you might find yours on there.
Aliens might find your name someday… If they have a CD player, which… Nobody on Earth has a CD player anymore.
They also included a couple of US flags, a postage stamp, a piece of Scaled Composite’s SpaceShipOne for some reason, and – this is the best one – 30 grams of Clyde Tombaugh’s ashes.
Clyde Tombaugh is the astronomer that found Pluto, so it’s appropriate but tens of billions of years in the future, the last human remains that exist in the universe might be Clyde Tombaugh.
Nick Oberg, a doctoral candidate at the Kapteyn Astronomical Institute in the Netherlands, calculated their trajectories in 2022.
- In 30,000 years (from now) it will fly past Ross 248 (which one?)
- In 500 million years they will complete an orbit of the Milky Way
- Voyager 1 will oscillate back and forth across the plane of the galaxy, bringing it into contact with dust clouds – dust will erode away the info on the golden record
- “Likely to survive partially intact for a span of 5 billion years”
- They say it’s likely it will pass near a solar system, but unlikely to get within 3 lengths of pluto to the sun (or 150 AU)
- Also about 5 billion years from now the Andromeda/Milky Way merger will occur – it’ll be difficult to predict their trajectories at that point
- 1 in 5 chance it gets flung out of the galaxy; unknown how much dust it will catch in the new Milkdromeda – might be more, might be less. They might be flung toward the galaxy core and get pummeled with high-energy cosmic rays
- If it survives all that, it will see the stars all die out and the universe become black holes punctuated by a random supernova every trillion years or so.
And that will be the final evidence we ever existed, a solitary probe floating in nothingness, occasionally flashing across unfathomable amounts of time, our singular and most consequential message to the universe.
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