Where Are All The Aliens? We Ranked Every Explanation

The Fermi Paradox has many solutions. Many explanations for the fact that we don't see any signs of intelligent life in the Universe. We ranked all the major ones and put them into tiers from S to D.

Why we might be alone by David Kipping:

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00:00:00 Intro
00:01:33 Fermi paradox
00:02:25 Zoo Hypothesis
00:06:19 Prime Directive
00:11:10 Simulation Hypothesis
00:16:54 Dark Forest
00:25:48 The Great Filter
00:33:54 Self-Destruction
00:40:16 We're The First
00:44:15 Rare Intelligence
00:49:00 We're Alone
00:56:00 Communication Barrier
01:04:35 Post-Biological Life
01:12:16 Hibernation Hypothesis
01:16:31 Our Tech Isn't Good Enough
01:20:49 We're Searching In Wrong Places
01:24:08 Aliens Are Among Us
01:27:01 Interstellar Travel is Impossible
01:36:19 Reapers
01:42:03 Expansion is Inefficient
01:47:48 There Is a Better Way

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Creative Commons Attribution 4.0 International (CC BY 4.0)

You are free to use my work for any purpose you like, just mention me as the source and link back to this video.

[neilzwaan]

So fun! Fraser this is the most enjoyable tier list I have ever watched. I found myself smiling through the entire 2 hour journey and was disappointed that it had to end. Excellent hosting, great colleague insights, a true YouTube gem! Thank you so much.

[woltersworld]

Nice. I had waited to listen to this until i had a nice drive and it was well worth it. Though, I was wondering about the 420 hypothesis where it is the scenario that they show in movies when someone gets "altered" mentally and wonders if our solar system isnt just an atom in a fingernail of a larger being 😅

[madscitechify]

my only disappointment is that you didn't include Isaac Arthur, President of the National Space Society, considering he has an entire youtube series covering fermi paradox solutions.

[mooferoo]

People try to pick "a solution" when i think it's lots of them combined, with each one lowering the chances of us seeing intelligent life near us.

[virtualjoedub]

I miss the weekly space hangout, but thank you for helping me find Moiya again! And thanks for promoting new and amazing talent. Found Dakotah a while back thanks to you as well. Amazing everyone! Thanks!

[Crushnaut]

I think the grabby alien's hypothesis is pretty compelling to us being among the first. I guess you could call this one Rare Intelligence too. I liked Dakotah's answer here about the hard steps from going from simple life to complex. It really is one of the single best pieces of data that we have towards the answer to the Fermi Paradox. That combined with the null results from all our searches, the other big piece of data we have, is basically the grabby aliens hypothesis. I think both of these should be S-tier. If you are reading this and haven't heard of the grabby alien's hypothesis, search for the video from PBS Spacetime. It is a good summary. You can also find the paper titled Grabby Aliens where they walk through their full argument and the math behind it. It is pretty easy to read in terms of science papers, and is very compelling.

[HorzaPanda]

I agree with Fraiser on one point for Dark Forest, any species powerful enough to be a threat already knows we’re here. Hiding is pointless

[RAFAELSANTOS-cnrm]

I think our tech is the most important bottle neck when we talk about detecting other intelligent life forms. Because light year travel time prohibits us from observing planets that are light years away in our current present time, due to the vast distance and the speed of light, any planet we observe would be a past version, not a current/present version of that planet. So complex life could have developed but all we can see is just the planet before any activity happens.

[christianartman]

Rare Earth is definitely my number 1 choice.... Now throw in the vast distances between Earth like planets + Drake equation and civilizations are just rare and too far apart (causally disconnected).

[EmilNicolaiePerhinschi]

a simulation would not have to simulate the whole universe, it would have to simulate only our perception of the universe

[catonthekbd]

We are one of many cilvizations, but due to the size of Universe, our Light Cones will never intersect :(

[jamescarroll]

With regard to Dakotah Tyler's comments on the simulation hypothesis, he had two criticisms:

1. to simulate every atom in the universe, would require a computer larger than the universe.
2. It makes no sense to simulate an entire universe, and then only put one planet of life in it.

But what if these two ideas are complimentary... what if to get around 1, they only simulate the parts of the universe at the detail and scale they need for the people on the single planet to have a compelling view of the rest of the universe, without simulating all the atoms of every star out there. In fact, that's how many modern computer games work, simulating finer grained details only as you get close enough for those details to become relevant to the view (Or whenever you zoom in on them with a telescope etc).

In that case, the simulation of only one world with conscious observers, might help them to solve the issue with the information theory and computational power issues involved.

I give it a C+. Only a little higher, but still.

[brick]

I remember reading a story about a hiker who got lost in Japan. This kind of baffled me, because surely if you walk in a straight line in Japan for a few kilometres you're bound to bump into a farm, city, railway, highway... I mean, it's pretty densely populated. But you can't see a city 25km away if you're in the woods. Space may well be the same, but we haven't really got the ability to see all that far. In 100+ years when we've surveyed the whole galaxy with future super telescopes and haven't found anything, then it gets interesting.

[maneatingduck]

Fascinating subject, I love the insight that the guests provide, and you all cooperate beautifully. Nice one, it's my favourite science video in a fairly long time.
Long time patreon supporter here, keep up the exceptional work :)

[richardgould-blueraven]

This was great, everyone seemed to have a good time

[kyststudio-epicartadventure]

If we live in a simulation, our ENTIRE experience of the entire universe is still INSIDE the simulation and we’d have zero idea of the real size and power abilities of entities outside this simulation.

[thomashelmka]

Time and distance is the biggest filter: Odds are against any peoples being at level of sophistication that they can find and begin communication with another peoples of the same mindset. There might be someone thinking almost the same as we do but they are three galaxies away and the odds of us finding each other are next to zero.

[marcodebruin]

My problem with many of these is that they have to account for ALL life. Any scenario where a species has to choose an option (go ethereal, stay home, don't spend extravagant energy, ...) may apply to SOME species, but not ALL. For me any solution has to be caused by nature/physics or there will be exceptions that we might detect. Anything else goes straight in the D-bucket for me.
The most plausable to me is a combination of rarity and not having looked wide enough - in other words, they exist, but are far and few between and we just need to keep looking (possibly for millennia to come).

[americanmanhood]

Fraser on the great filter: I don't want to think that we are doomed to self-destruction, so I give it A tier. Fraser on self-destruction: This is what Carl Sagan worried about. Preach. S tier. Huh?

[GiggaGMikeE]

Personally, I think a combination of the following factors makes the most sense:

1. Vast Distances(I feel like no matter how educated you are, it's really easy to handwaive the absolutely massive distances between planets, star systems, galaxies, and so forth)
2. Narrow scope of the places and methods we've looked for intelligent life(We really are just shining a laser pointer into the corner of a dark forest and assuming no life exists because the light didn't land squarely on Sasquatch's forehead)
3. Narrow definition of what we would consider "intelligence" (i.e. assuming intelligence = technological expansion across space at ever increasing power demands)
4. Timing (For instance, there could have been alien species relatively close to or greater than human intelligence, but say, lived 100 million years ago and went extinct after 100 thousand years)
5. Great Filters (I am more inclined to believe most of the filters are behind us, but some like the conditions needed to grow technologically are specific enough that there are probably tons of planets with life thats somewhere between single celled bacteria and the dinosaurs, but almost none that got to the "mining the planet for ancient stores of fossil fuels if they even have that equivalent to power their technology" stage)
6. We're the First/There are no advanced civilizations(tied in with 1 and 2 - It could just be that there hasn't been any other advanced intelligent life that developed in the relatively small amount of space we've looked at so far. Doesn't mean there isn't 100 star faring civilizations in Andromeda, but just that there aren't any Galactic Empires nearby)

In a nutshell, it's a lack of scope combined with just the vast distances/timescales and what we consider intelligence being heavily dependent on our own evolution that answers the Fermi Paradox. I don't think there are any invisible civilizations "hiding the truth" from us, but instead that life is possibly prolific, and space is just like, really, really big on timescales that don't mesh well with our current standards.