Have we already been visited by aliens? • Hacker News Board

Re: Have we already been visited by aliens?

#301

Post by naikrovek » Thu, Jan 21, 2021, 5:54 AM UTC

matteocantiello wrote: post #276

naikrovek wrote: post #270

Earlier quoted context omitted.

Pollution capable of completely killing the dominant species of a planet would last a long time after the creation of that pollution ended. The pollution would vastly outlive the polluters, so it would be detectable for some time after their demise, especially if anything they automated also polluted. That stuff would continue to pollute after its creators all died, at least a bit. Also, it seems that the chance of d…

Why would the pollution vastly outlive the polluters? It's not obvious to me. Mixing and recycling timescale of an atmosphere seem very short compared to other relevant timescales of the problem. Impactors, volcanic eruptions... the memory of the atmospheric impact of those events is in the sediments, not the air we breathe (e.g. KT boundary). Finally, civilizations that do not destroy themselves in the short-lived p…

If the pollution is severe enough to KILL the species creating it, it is already being produced far faster than nature can absorb it or counteract it. It also seems feasible that other species are killed as well; species which may have helped clean the pollution from the planet, which would slow the cleaning process or, if enough species die off, stopping the cleansing process almost entirely.

Pollution doesn't vanish when it isn't being made anymore.

So, if there is so much pollution that it both kills life on the planet, it will take a good amount of time (millions of years? How big of a planet are we talking about?) to be cleansed back to undetectable levels.

Re: Have we already been visited by aliens?

#302

Post by ncmncm » Thu, Jan 21, 2021, 5:56 AM UTC

LargoLasskhyfv wrote: post #278

ncmncm wrote: post #112

Earlier quoted context omitted.

Their best future course is to stop sniping at one another. It is possible that it's aliens. It is possible that it's not. We don't have enough evidence even to estimate probabilities, so anything further is pure speculation. Speculation is a look that wears no better on conservatives than on radicals. There is hardly a field to be found where young radicals are not promoting evidence for what the tenured consider an…

https://en.wikipedia.org/wiki/Planck%27s_principle

From the article > A study of when different geologists accepted plate tectonics found that older scientists actually adopted it sooner than younger scientists.

But the paper cited refers, instead, to the relative safety of the tenured professors to speak out in favor of plate tectonics, vs. the younger researchers who knew that would be, as we say, career-limiting.

Re: Have we already been visited by aliens?

#303

Post by naikrovek » Thu, Jan 21, 2021, 5:59 AM UTC

vladTheInhaler wrote: post #271

naikrovek wrote: post #270

Earlier quoted context omitted.

Pollution capable of completely killing the dominant species of a planet would last a long time after the creation of that pollution ended. The pollution would vastly outlive the polluters, so it would be detectable for some time after their demise, especially if anything they automated also polluted. That stuff would continue to pollute after its creators all died, at least a bit. Also, it seems that the chance of d…

The phrases "a long time", "some time", and "at least a bit" are doing a lot of heavy lifting there. Oxygen has been in the Earth's atmosphere for over 2 billion years. How long, roughly, is "some time"?

How big, roughly is the planet in question? How thick, roughly, is the atmosphere? What, roughly, is the composition of the atmosphere? What is the median temperature of the planet? List all species capable of metabolizing pollution back into harmless compounds. What are their lifespans? How do they reproduce?

...hopefully my point is made, now. I can't give details because they don't exist.

If a species produces sufficient pollution that it kills that species, it is a reasonable assumption that it was also produced at a rate far higher than the planets natural ecosystem could absorb it. It is also reasonable that the pollution also kills one or more species which were consuming or absorbing the pollution, slowing the rate at which it can be removed, or maybe even stopping that process completely. Pollution does not disappear at the same time pollutants stop being introduced into the atmosphere.

There will be a time after which no pollutants are produced and before no pollutants are detectable. That is a non-zero amount of time. That is why I say that pollution could one day be detected on a planet that has not had a living civilization for "a long time." "A long time" being "more than five minutes" if you really want me to nail it down.

Re: Have we already been visited by aliens?

#304

Post by shvn » Thu, Jan 21, 2021, 6:01 AM UTC

eloff wrote: post #86

bostonsre wrote: post #54

Earlier quoted context omitted.

Ridiculing scientists for plausible hypothesis seems very unscientific.

This is very common in science. New theories are usually rejected and ridiculed until/if they develop enough evidence behind them to sway people. Some careers are destroyed. Some scientists are only vindicated posthumously. The process can take many decades. Scientists, like most humans, are not that open-minded and are subject to the same group-think blind spots. I think if we could get better at being open-minded a…

> I think if we could get better at being open-minded as a species, we'd make faster progress and better ideas would win out more often.

Given the current scenario we are certainly not sure if we are ever going to achieve it! Though that achievement can work wonders. Any thoughts how you see that change can be made possible?

Re: Have we already been visited by aliens?

#305

Post by tarsinge » Thu, Jan 21, 2021, 6:05 AM UTC

XorNot wrote: post #286

eloff wrote: post #45

Earlier quoted context omitted.

> I don't think very many people are saying it is impossible that Oumuamua was an alien construct and actively discouraging science based on the idea it could be. Actually yes. You'll be laughed out of the virtual room, not get funding, and potentially damage your career. As he points out in his interview with Lex (linked elsewhere in the comments here) is fine to propose a multi billion dollar experiment to detect o…

This is ignoring the obvious question: what are we not doing that we should be with researching Oumuamua on that basis? What concrete experiments would prove its an alien construct as opposed to being just interstellar rock? The scientific community isn't rejecting proposals to find more Oumuamua like objects, and has been actively trying to figure out how we could intercept another one when it turns up. So what exac…

It’s still possible to send a spacecraft in the coming years https://en.m.wikipedia.org/wiki/Interstellar_object#Hypothet...

Re: Have we already been visited by aliens?

#306

Post by giantrobot » Thu, Jan 21, 2021, 6:07 AM UTC

jrumbut wrote: post #174

shrimp_emoji wrote: post #111

Earlier quoted context omitted.

A possible chink is that civilizations just don't do that -- carpet colonize the whole galaxy, or fill it with their probes to the extent that we seem them all over the place. The Fermi paradox relies on material (probes, colonies) and light (signals). With the material explained away, the lack signals is much easier to explain in that we haven't listened long and we can only hear very loud signals. (Or maybe advance…

Do you know if about any simulations of what it would look like if there were alien radio operators? If there were 50 other Earths scattered around the galaxy (ones that have been broadcasting like us but for longer) should the first television have imnediately picked up interstellar "I Love Lucy" or would it be faint anomalies from SETI? Somewhere in between?

The inverse square law says no [0]. Even relatively high powered transmitters aren't detectable for an Arecibo-class antenna more than a few AU from Earth. If you want a signal detected light years away you need it to be highly directional. An isotropic radiator emitting enough power to be detected light years away is called a star.

So any SETI signals we might detect would almost certainly need to be intentional. That doesn't mean they would need to be responses to something we've broadcast just the sender was aiming their transmitter towards the solar system and sent a signal.

[0] https://web.archive.org/web/20140719094337/http://www.comput...

Re: Have we already been visited by aliens?

#307

Post by naikrovek » Thu, Jan 21, 2021, 6:16 AM UTC

stefanmichael wrote: post #274

naikrovek wrote: post #270

Earlier quoted context omitted.

Pollution capable of completely killing the dominant species of a planet would last a long time after the creation of that pollution ended. The pollution would vastly outlive the polluters, so it would be detectable for some time after their demise, especially if anything they automated also polluted. That stuff would continue to pollute after its creators all died, at least a bit. Also, it seems that the chance of d…

I thought this might be the case as well but at least for CFCs the lifespan without replenishment from human pollution is only about 140 years. so "a bit" for this particular circumstance is not very long at all in the eyes of the universe

CFCs are not the only pollutants.

An alien society may produce pollutants which last a million years. Plastics can last millions of years.

Sufficient pollution could cause climate change severe enough to keep all kinds of things airborne for who knows how long. We are constantly surprised by what we learn about other worlds. It is silly to me to presume that anything we know about Earth pollution will be a given on a planet from another star system.

Re: Have we already been visited by aliens?

#308

Post by godelski » Thu, Jan 21, 2021, 6:29 AM UTC

ChainOfFools wrote: post #296

godelski wrote: post #265

Earlier quoted context omitted.

I think this is strange thinking because it breaks our laws of physics. The clock ticks at the same rate in internal reference frames, it is only different when looking at two different frames. But if you're talking about them acting at slower speeds or faster, then that brings along other problems similar to the mechanics ones we discussed (assuming we're not counting that they are in a slower reference frame). It r…

https://archive.org/details/OnBeingTheRightSize-J.B.S.Haldan...

I'm sorry, you dropped a 130 page book with no other comment. Is there anything specific you want to say?

Re: Have we already been visited by aliens?

#309

Post by godelski » Thu, Jan 21, 2021, 6:31 AM UTC

LargoLasskhyfv wrote: post #281

godelski wrote: post #163

Earlier quoted context omitted.

The problem with this is that mechanics is not scale invariant. This puts bounds on creatures. Unless there's some crazy different way to compute I wouldn't expect a being to be able to have strong cognitive functions and be the size of a fly. They would also have a difficult time building advanced machinery to get to galactic travel scales. Similarly I wouldn't expect a creature the size of a Brontosaurus to become…

Have you heard of https://en.wikipedia.org/wiki/Portia_(spider) ? Or that birds brains are "wired" more dense, like our cerebellum?

I haven't, that's pretty cool. You can update my terrible range guesstimate accordingly. Though that doesn't change the main thesis of there being more likely sizes than others.

Re: Have we already been visited by aliens?

#310

Post by King-Aaron » Thu, Jan 21, 2021, 6:38 AM UTC

trestenhortz wrote: post #295

King-Aaron wrote: post #234

Earlier quoted context omitted.

Once upon a time, it was inconceivable that there could be any practical way to travel between continents. I feel that making this assertion based on our current understanding of the universe is fundamentally flawed.

This is a comparison that really doesn’t work. It takes month in a sailing ship to cross the ocean. It would take thousands of years at the very least to cross space.

So this wouldn't be an issue if you solved the ageing problem - a problem which we are presently working on solving ourselves.

I don't see why it's out of the question that a civilization that's hypothetically a hundred thousand years ahead of us wouldn't have worked out how to suspend themselves, preserve themselves or negate their ageing. Or for that matter, work out how to sidestep the distance argument though some other exotic method that we're yet to discover (i.e. wormholes or some such).

I'm not exactly a proponent for little green men visiting us, but I do think that arguing about distance or physical limits of speed/travel based on our current frame of reference is an incorrect position to take.