We are (probably) not alone (in the universe)!

We've been proving that we're pretty boring for the past few thousand years... we'll probably keep doing that!
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~~ Citations ~~
1. Definition of the Principle of Mediocrity: www.britannica...
2. Geocentric (Ptolemaic) Model: www.britannica...
3. Heliocentric (Copernican) Model: archive.org/de...
4. Edmond Halley - Stellar Motion: royalsocietypu...
5. William Herschel - Moving Solar System: royalsocietypu...
6. Edwin Hubble - Other Galaxies: ui.adsabs.harv...
7. ALMA - Protoplanetary Disks: ui.adsabs.harv...
8. More than 5000 exoplanets discovered: exoplanetarchi...
9. Possibly 25% of Sun-like stars with Earth-like planets: arxiv.org/abs/...
Videos and Images from NASA and the European Space Agency either in public domain or available under a Creative Commons licence.
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Hi, I'm Thomas, a first year PhD student at Cardiff University. This is my channel where I share my experiences of academia and pieces of Physics and Astronomy I find interesting.
If you enjoy videos from Simon Clark, Dr Becky or Ruby Granger, I think you'll enjoy my videos!
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In this video, I discuss the Principle of Mediocrity - the idea that things that are most likely to happen, typically do and that things that appear exceptional to humans, rarely are. This is a foundation of the argument for the existence of extraterrestrial (i.e. alien) life - the idea that in a universe that is infinitely big, it is statistically unlikely that we are the only life in the universe.

[@victorianorth3610]

Brilliant! The best argument I have herad for life on other planets. Keep up the good work, and all the best for your PhD.

[@TheHogan883]

This is a very good way to look at it. I often tell people that it's more reasonable to assume there is life out there somewhere than it is to assume we're alone. If only for the fact that the universe is so big.

[@markstevens7147]

Excellent thought-provoking video. Good work.

[@thentil]

Completely agree. Completely rational take. However I fall down every time I ask "where are they". Given the age of the universe, aliens should be everywhere. They've had time to colonize or mine galaxies. Even if I concluded Intergalactic travel doesn't have a solution, we should see evidence of artificial structures, altered stars, etc. But we don't. The galaxy is eerily... Unaltered.

[@ThomasRintoul]

I used to fall down at that as well - I think there are some issues with this thinking though.
First off, it assumes that life is common nearby - that is not guaranteed at all. The reason that nearby would be important is because our technology is limited. Our best telescope is still limited in its ability to hunt for exoplanets, let alone alien mega structures.
There's then the assumption that "life" == "alien civilisation similar to us" (or from what you're suggesting, significantly more advanced. Life could be microbes, or plants, or animals - not necessarily intelligent life. There's also nothing to say that we're not part of the first generation of civilisations in our galaxy (I feel like I remember something about life having started on Earth pretty early after life would be able to start in our galaxy?). There could well be many civilisations much like ours in the galaxy - they just have similar technology - and we can't significantly alter anything yet (ignoring our own climate)

[@xBris]

0:00 - I actually thought that the idea of "Aliens" is less than 200 years old - just looked it up - even people in antiquity have thought about it - that's fascinating if you think about all that has happened in medieval times. We really did regress as a species ^^

[@susanne5803]

Nice breakdown of the concept! I would still be happy to find visible evidence of some sort of very primordial life like we had with cyanobacteria. It would just be so exciting!

[@ThomasRintoul]

Give it time and we're going to see more concrete biosignature detections on exoplanets with JWST but it's going to take time to be sure of anything

[@SlappyGomez]

Not alone does not equal not special.

[@whjk83921]

I think we are not alone but I also think there's a good chance they are ludicrously far away.

[@ThomasRintoul]

Very possibly - though on our scales, even the next star over is ludicrously far away to be practical

[@pauldietz1325]

The Copernican principle was used back in the 1700s to conclude we were not alone... in the Solar System! That's clearly false, so you should be careful about applying the principle too wildly. We can be pretty sure that most stellar systems do not have intelligent life (otherwise, the Fermi argument would bite impossibly hard), so we're already special in that respect as well.
More generally, we'll be special if intelligent life (or just life) is rare, so the assumption we cannot be special is really just assuming intelligent life cannot be rare. This is a strong conclusion to derive from no evidence, so this all smells like a circular argument. To turn this around: if life really were extremely rare, what would be see that would be different? If nothing would look different, how can we conclude it's not extremely rare?