4 ms·

I think there are two separate questions: 1) is there other life in the universe? 2) is other life visiting Earth? Considering the number of stars in the uni

by prirun 4y ago

I think there are two separate questions: 1) is there other life in the universe? 2) is other life visiting Earth? Considering the number of stars in the universe and the potential number of planets around those stars, IMO it is extremely unlikely that our particular star & planet are so special that we are the only life that exists and has ever existed. If you believe that yes, we are that unique, then of course you cannot believe in anyone visiting Earth. If you do believe there is other life in the universe, it's reasonable to believe they travel around, just like we have traveled around. But also, because of the vastness of the universe, if there is other life, IMO it's likely to be so far away that we will never cross paths. It's like 2 grains of sand on a beach getting next to each other.

laverya 4y ago
> It's like 2 grains of sand on a beach getting next to each other. Unless the grains of sand are "Grabby". An aggressively expansionist species (as in, one new colony per colony every 10,000 years) fills up a galaxy really remarkably quickly.
- roncesvalles 4y ago
  There's also the dimension of time. Two such civilizations need to be both spatially and temporally proximal. One of the "explanations" for the Fermi Paradox is that humans are too far out from the temporal peak, i.e. too late or too early to the scene.
Balgair 4y ago
I want to point out the currently known composition of the universe, because I think that the whole aliens thing wraps up with it: ~5% matter. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star's gravity well. Like, 99.99999% of it. The stuff you and I are made of (C, N, P, Fe, etc), that we would wish aliens would be made of too, is really rare. ~25% dark matter. We know a little about it. We know that it falls down and doesn't like to touch just about anything. But that's really kinda it. ~70% dark energy. It falls ... up (?!). We know pretty much nothing about it. And it's the large majority of 'stuff' in the universe. If there are buddies out there, then we may want to look at stuff that is a bit more common.
- remram 4y ago
  5% of what?
  - Balgair 4y ago
    5% of literally everything.
    - remram 4y ago
      5% of mass? Volume? Energy? The visible sky? If I said "this dessert is 30% milk, 40% sugar, and 30% good timing" you would be similarly confused.
      - rstuart4133 4y ago
        Your question contains its answer. Volume would be an odd measure to use given it changes with speed (due to special relativity) and gravity (general relativity). The visible sky is over 99% empty, so it can't be that. Which leaves us having to choose between mass and energy. But as e=mc2, they are effectively the same thing, which means we don't have to choose.
- laverya 4y ago
  There's about 1500 billion billion billion billion billion billion billion (1.5x10^48) tons of Carbon, Oxygen and Nitrogen in the universe. It might only be ~15 parts per thousand (and most of that is Oxygen), but there's a LOT of stuff out there.

by prirun 4y ago

laverya 4y ago

> It's like 2 grains of sand on a beach getting next to each other. Unless the grains of sand are "Grabby". An aggressively expansionist species (as in, one new colony per colony every 10,000 years) fills up a galaxy really remarkably quickly.

roncesvalles 4y ago
There's also the dimension of time. Two such civilizations need to be both spatially and temporally proximal. One of the "explanations" for the Fermi Paradox is that humans are too far out from the temporal peak, i.e. too late or too early to the scene.

Balgair 4y ago

I want to point out the currently known composition of the universe, because I think that the whole aliens thing wraps up with it: ~5% matter. Most of this is H and He though, bit of Li in there too. And it's all mostly burning in a star's gravity well. Like, 99.99999% of it. The stuff you and I are made of (C, N, P, Fe, etc), that we would wish aliens would be made of too, is really rare. ~25% dark matter. We know a little about it. We know that it falls down and doesn't like to touch just about anything. But that's really kinda it. ~70% dark energy. It falls ... up (?!). We know pretty much nothing about it. And it's the large majority of 'stuff' in the universe. If there are buddies out there, then we may want to look at stuff that is a bit more common.

remram 4y ago
5% of what?
- Balgair 4y ago
  5% of literally everything.
  - remram 4y ago
    5% of mass? Volume? Energy? The visible sky? If I said "this dessert is 30% milk, 40% sugar, and 30% good timing" you would be similarly confused.
    - rstuart4133 4y ago
      Your question contains its answer. Volume would be an odd measure to use given it changes with speed (due to special relativity) and gravity (general relativity). The visible sky is over 99% empty, so it can't be that. Which leaves us having to choose between mass and energy. But as e=mc2, they are effectively the same thing, which means we don't have to choose.
laverya 4y ago
There's about 1500 billion billion billion billion billion billion billion (1.5x10^48) tons of Carbon, Oxygen and Nitrogen in the universe. It might only be ~15 parts per thousand (and most of that is Oxygen), but there's a LOT of stuff out there.