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Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#751: Oct 30th 2024 at 11:10:23 AM

I would never personally consider breathing the air on an exoplanet without extensive chemical and biological analysis, but I apparently have more common sense than the average sci-fi character.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
amitakartok Since: Feb, 2010 Relationship Status: Don't hug me; I'm scared
#752: Oct 30th 2024 at 11:11:05 AM

[up][up][up][up][up] Yeah, I'm thinking that the Combine have simply invaded so many planets and assimilated so many species that at this point, they're Crazy-Prepared for almost every possible planetary environment. No matter where they go next, they already have minions that can survive there - and if they were to finish assimilating humanity, the transhuman soldiers would similarly be deployed in future invasions of other Earth-like worlds simply because that's their very purpose.

Or to put it differently, if you're going birdhunting, would you rather make your dog fly with a jetpack, or bring a trained falcon that can already do that without tech?

The right tool for the right job, as Scotty said.

Edited by amitakartok on Oct 30th 2024 at 7:12:15 PM

Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#753: Oct 30th 2024 at 11:16:00 AM

In the semi-canonical lore delivered via Word of God, the Combine are a Type 2 civilization that's colonized and/or conquered a large portion of the galaxy and considers Earth to be yet another addition to the empire. There's nothing particularly special about us other than our portal technology. It's our "successful" resistance to their rule that draws serious attention.

So yeah, such a civilization would be prepared to deal with just about any imaginable environment.

Edited by Fighteer on Oct 30th 2024 at 2:16:38 PM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
Kaiseror Since: Jul, 2016
#754: Oct 30th 2024 at 12:09:31 PM

And if a planet is somehow biochemically compatible, that would come with its own host of risks and complications. One of the most prominent to me would be alien diseases, since there's a chance that it can set up shop in a human body, but is still so different from what we have on earth that our immune system can't properly fight it off. Even the regular microbes in the air and water could be deadly pathogens to us.

EchoingSilence Since: Jun, 2013
#755: Oct 30th 2024 at 12:14:34 PM

Or our own microbes become the pathogen and kill off the planet.

Zendervai Since: Oct, 2009
#756: Oct 30th 2024 at 12:38:21 PM

[up][up] The issue there is that it'd go both ways. Like, a planet with opposite chirality (the amino acids have a flipped structure) would just result in everything, biochemically, looking at the stuff from the other biosphere and going "...what the heck is this? I don't know what to do with this", because everything's shaped wrong and the basic interactions can't happen.

And that's if the other biosphere has anything similar to our form of DNA in general, because if it's different, again, you'd get stuff like alien viruses getting in contact with a cell and going "...none of the things I interact with are here, I don't know what to do. Guess I'll die."

In real life, the sicknesses that don't hop species have this going on, where they're attempting to act on a feature that just straight isn't present. A bug can't get viral pneumonia, for example, because there's no actual lungs there.

MajorTom Since: Dec, 2009
#757: Oct 30th 2024 at 1:26:47 PM

more heavily fungi biosphere than Earth

Earth is biologically most akin to a mushroom planet than a forest one. We have more examples and species of fungi than entire swaths of the ecosystem.

If I remember correctly, there’s more varieties of fungi on Earth than there are animals and plants combined. Factoring in microbes such as fungal-like protists, there’s more varieties of that than there is multicellular life otherwise.

Edit:

I do realize with this statement that when you go by sheer numbers, Earth is a bacteria planet most of all.

Edited by MajorTom on Oct 30th 2024 at 1:28:17 AM

devak They call me.... Prophet Since: Jul, 2019 Relationship Status: [TOP SECRET]
They call me.... Prophet
#758: Oct 30th 2024 at 2:03:08 PM

I would argue the microbiology on alien worlds is going to be pretty much inert, but still, i think there could be a lot of harmful macrobiology going on. There's no particular reason alien life can't produce chemicals which are harmful to human life. Poisons, acids, bases, particular elements their biology relies on that ours can't handle, etc.

So in the exceptionally unlikely event that we could eat alien meat for nutrition, it could still potentially kill us in other ways.

Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#759: Oct 30th 2024 at 2:11:22 PM

[up] That's right. It's extraordinarily unlikely that the alien viruses, bacteria, and/or fungi would find our biochemistry compatible with theirs, but there could still be simple chemical toxicity.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
MajorTom Since: Dec, 2009
#760: Oct 30th 2024 at 4:35:59 PM

A case of epic indigestion it is. [lol]

Zendervai Since: Oct, 2009
#761: Oct 30th 2024 at 7:11:06 PM

It would be kind of interesting if we encountered a biosphere where processing nutrients requires bases and not acids like we do. That has potential for a lot of really weird shit. Like, a digestive system built around a sort of super-ammonia or something like that.

Plus the potential for some wild biochemical interactions.

Edited by Zendervai on Oct 30th 2024 at 10:11:27 AM

Kaiseror Since: Jul, 2016
#762: Oct 30th 2024 at 8:07:28 PM

[up] We'd basically be mutually toxic to one another.

SeptimusHeap from Switzerland (Edited uphill both ways) Relationship Status: Mu
#763: Oct 31st 2024 at 1:18:49 AM

One thing to keep in mind is that while alternative geochemistries are hypothetical concepts, there are some theoretical limitations to biochemistry. It's quite plausible that your alternative lifeforms have a citric acid cycle, and share many if not most amino acids with Earthen life even conceding different chiralities, simply because alternatives are chemically costly/unlikely to evolve.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
devak They call me.... Prophet Since: Jul, 2019 Relationship Status: [TOP SECRET]
They call me.... Prophet
#764: Oct 31st 2024 at 9:28:42 AM

[up]The issue i have isn't that there won't be similarities. The issue i have is that there are lots and lots of processes involved to extract nutrition and there's no particular reason it *has* to be the way we do it.

Alien life could be completely identical to ours except the chirality is flipped, and it would be incompatible with our biomachinery.

Alien plants could be identical to ours except have a different cell wall structure, rendering us incapable of digesting those cells.

There are countless details like that in biological processes, and it simply isn't likely that alien life will make every single choice in an identical way.

SeptimusHeap from Switzerland (Edited uphill both ways) Relationship Status: Mu
#765: Oct 31st 2024 at 10:09:25 AM

The word "us" carries a lot of weight there - even if a human would only be able to consume a small fraction of nutrients in alien life, there will be some organisms that can or can develop the ability.

Completely different question: Do aliens on a planet with 2-3 times Earth's gravity have any hope of developing space travel. Converse question: If Earth's gravity decreased by 50%, how would this facilitate space travel to the Moon/Mars?

(Not LEO. Less gravity will cause the atmosphere to expand into low Earth orbit, rendering it unusable)

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#766: Oct 31st 2024 at 12:12:36 PM

[up]This has been discussed in the past in several different places. Using chemical propulsion (and not some hypothetical exotic system with much higher specific impulse and acceptable thrust-to-weight ratio), the maximum gravitational field that would allow any rocket to reach orbit is about 1.5g, and that would involve a Saturn V equivalent just to lift a few hundred kg of payload. Crewed spaceflight would be effectively impossible.

In 0.5g, we could easily build single-stage-to-orbit (SSTO) vehicles and interplanetary travel would be cake. In fact, you don't even need to go that low. With just ten percent less gravity, getting off Earth would be an order of magnitude easier than it is today.

Edit: LEO would still exist; it would just be at higher altitude. No real sweat, although I'd be interested in seeing the math on whether the extra energy needed to reach a stable orbit would offset some of the benefits of the lower gravity.

Edited by Fighteer on Oct 31st 2024 at 3:25:44 PM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
SeptimusHeap from Switzerland (Edited uphill both ways) Relationship Status: Mu
#767: Oct 31st 2024 at 1:12:41 PM

Hmm. Given same Earth radius, 50% gravity means that the atmospheric scale height is twice, so LEO lies at twice the elevation. That also means twice the way through atmospheric drag, but half as much "gravity drag"

The problem I have is that I can't find an obvious equation for converting orbital parameters into delta-v. Tried to backcalculate from orbital energy and got a nonsense result, so that's probably the wrong approach. If the approachnote  that yields 7.96km/s for 200km LEO is correct, it would give 5.66km/s for 0.5g 400km LEO. Given that for a Saturn V - only rocket where I have gravity and atmospheric drag data - gravity drag is much larger than atmospheric drag, 0.8km/s would be saved. So ... 3.1km/s less delta-v needs. About 30% less.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
Zendervai Since: Oct, 2009
#768: Oct 31st 2024 at 1:32:25 PM

I think in terms of biology, an important thing to remember is that our history is absolutely littered with examples of "this doesn't happen, it is not possible" and then it turns out it totally is possible, we just either didn't know about it or the scientists refused to believe the evidence.

The platypus is probably the most famous example, because it sounds weird as hell for a mammal (they even glow under UV light...in almost the exact colour as Perry the Platypus because I guess the universe fucking loves Dan Povenmire, that wasn't figured out until after Phineas and Ferb came out) and it took forever for European scientists to admit that oh, they do exist for real.

And that's before getting into the fights about whether or not a virus counts as "alive" because they're also really fucking weird by our understanding of biology. IMO, the correct answer there is "maybe our definition is too narrow", not "we need a special extra definition for this one type of entity that we don't call alive or inert". The latter solution is dumb as hell.

There are limits, (a fully gaseous alien is probably not going to be a thing), but it's pretty likely that said limits are way further out than we're assuming, because we only have one biosphere to compare to...and we make mistakes and we make bad assumptions about it on a regular basis. If our own biosphere is so varied and can get so strange, there's absolutely nothing stopping alien biospheres from being borderline incomprehensible, at least at first glance.

Edited by Zendervai on Oct 31st 2024 at 4:35:08 AM

Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#769: Oct 31st 2024 at 1:32:45 PM

[up][up]I'm sure there are some folks in the Twitter space community who could calculate it for you.

[up] The thing is, Zendervai, that planetary scientists well understand that life can come in a variety of forms, but we know that it must have certain characteristics: it must consume energy, it must alter its environment, and it must reproduce.

Our instruments for detecting xenobiological signatures are still extremely crude, mostly limited to transit spectroscopy of planetary atmospheres. As of yet we haven't found any evidence of chemicals that unambiguously hint at life, but we're super early into the investigation.

Scientists aren't limiting their studies to "Earthlike life", but we can still only work with what we know, or think we know. If there are lifeforms out there that are based on plutonium chemistry and communicate in gamma rays, we probably wouldn't be able to find them with our current instruments even if we knew what to look for.

Edited by Fighteer on Oct 31st 2024 at 4:37:56 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
Zendervai Since: Oct, 2009
#770: Oct 31st 2024 at 1:42:34 PM

My angle is more like, stuff like "well, chirality should be this way because it's more efficient" isn't really an argument. We've got a lot of really inefficient shit going on in our biologies because evolution doesn't really aim for efficiency, it aims for "good enough to not die before reproducing".

As long as it works good enough to not kill a creature before reproduction, it's a possibility to find it.

"Chemical alternatives are unlikely to evolve". Yeah, that doesn't mean anything. Everything alive on Earth that we're aware of came from a single source. It's not the simplest possible way for things to evolve, it's just the way it happened here.

Edited by Zendervai on Oct 31st 2024 at 4:44:47 AM

SeptimusHeap from Switzerland (Edited uphill both ways) Relationship Status: Mu
#771: Oct 31st 2024 at 1:46:31 PM

'fraid that I don't know these Twitterers.

(For funsies, I've done the same math for my setting abd it yields a delta-v to low-planet orbit of a mere 2143m/s compared to Earth's 9710m/s)

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
Fighteer Lost in Space from The Time Vortex (Time Abyss) Relationship Status: TV Tropes ruined my love life
Lost in Space
#772: Oct 31st 2024 at 1:58:13 PM

[up][up] There are other considerations, such as efficiency. Carbon is an excellent building block for life because of two main factors: it forms an immense variety of chemical bonds, and those bonds don't take a large amount of energy to break. Silicon has been proposed as a carbon replacement, but it forms much stronger bonds, meaning that lifeforms using it would have to expend a lot more energy to perform basic biochemical processes.

Water enjoys a similar place as a solvent due to its physical and chemical properties, ditto oxygen as a, well, oxidizer. Other oxidizers exist (chlorine, fluorine) but their reactions are much more energetic, meaning that it's much harder to govern the reactions and much harder to break the resulting chemical bonds.

Silicon-chlorine biochemistry might be possible, but carbon-oxygen biochemistry would outcompete it.

I'm not up on the latest science to know if amino acid chirality has similar competitive factors, but I don't consider it relevant to the broad likelihood of finding life elsewhere in the universe. We need a sample size greater than one to start drawing statistical conclusions.

Edited by Fighteer on Oct 31st 2024 at 5:17:49 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"
MajorTom Since: Dec, 2009
#773: Oct 31st 2024 at 3:41:05 PM

Alien plants could be identical to ours except have a different cell wall structure, rendering us incapable of digesting those cells.

Like the difference between eating corn and eating a pine tree? Cell wall structure of corn kernels is much different than eating the wood of a ponderosa pine.

SeptimusHeap from Switzerland (Edited uphill both ways) Relationship Status: Mu
#774: Oct 31st 2024 at 11:05:41 PM

Silicon-silicon bonds are much weaker than carbon-carbon bonds, making silicon-based compounds unstable and thus unsuitable for making things like genomes. Physics also put limitations on which elemental compositions planets can have, and the abundance of oxygen they lead to traps silicon in oxides.

Chlorine atmospheres could be possible in lieu of oxygen atmospheres, though. Ammonia oceans, too (not together, likely)

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
devak They call me.... Prophet Since: Jul, 2019 Relationship Status: [TOP SECRET]
They call me.... Prophet
#775: Nov 3rd 2024 at 1:24:42 AM

And that's before getting into the fights about whether or not a virus counts as "alive" because they're also really fucking weird by our understanding of biology. IMO, the correct answer there is "maybe our definition is too narrow", not "we need a special extra definition for this one type of entity that we don't call alive or inert". T
I would argue that a virus is a cellular automata, and so distinct from life. Depending on their construction, i would expect nanomachines to fit that category, but also proto-life. The other option is to consider it more as a list of features that have to be ticked and the more you tick the more life it is, but then i think you get into weird concepts like a cloud being more life-like than a rock.

Like the difference between eating corn and eating a pine tree? Cell wall structure of corn kernels is much different than eating the wood of a ponderosa pine.

Sure, although i was thinking more broadly about how those cell walls are made of cellulose and how we distinguish between life that can and cannot convert it. If it were made from some different sugar, or a different molecule alltogether, we would have immense trouble digesting it.

But even further, many biological processes involve long cycles to convert one molecule to another. If we have 99% of the capability present but we cannot break down the initial molecule, then no nutrients for you. If it produces side-chemicals that we cannot deal with, we poison ourselves. And perhaps it gets through the entire chain and ends with a misshaped molecule, so we process it but can't eat the end product. Or even more fun: the nanomachinery in foreign cells mess with the machinery in our cells, and so are toxic for other reasons.

My angle is more like, stuff like "well, chirality should be this way because it's more efficient" isn't really an argument.

I am not sure where this is coming from. Nobody has made this argument this entire page. We were discussing how alien life, even life that is nigh identical to us, would basically be inedible.

Besides, i've said this before but "this might happen but is astonishingly unlikely" and "this will never ever happen" are two very different arguments. With a big enough sample size basically any life could happen in basically every form you can imagine and countless ones we can't, but the majority of life is likely to be fairly boring carbon-chained oxygen-breahting because it's both common and efficient.


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