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Have we already been visited by aliens?

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Re: Have we already been visited by aliens?

#341

Post by openasocket »

GoblinSlayer wrote: post #317
openasocket wrote: post #221

Earlier quoted context omitted.

What axiom do you have to add, are you talking about the axiom of infinity, defining the set of natural numbers? Because you do need that, but without that wouldn't even be able to define uncountability. After that, you can define the reals using Dedekind cuts or Cauchy sequences, which was known at the time (I believe Cantor actually worked on the Cauchy sequence construction). But there's an even simpler uncountabl…

To construct R you need to repeat Dedekind cut uncountable number of times, i.e. you need to iterate over all real numbers, which would make them countable.

You don't need any sort of "repetition" of Dedekind cuts to construct the real numbers, it's actually fairly straightforward. The set of all Dedekind cuts is a subset of the power set of rational numbers (i.e. each Dedekind cut is a set of rational numbers) satisfying the following properties: for each Dedekind cut A

1. A is not the empty set

2. A is not the set of all rational numbers

3. A is closed downwards, meaning if x is in A and y 4. A has no greatest element, meaning for all x in A, there is a y in A such that y > x.

And each Dedekind cut is in one-to-one correspondence with a real number. You can define the usual arithmetic operations on them, show that every rational number has a corresponding Dedekind cut (for any rational q, we have {x in Q | y But as you can see, you don't need any sort of repetition to do the construction, it's just a set of sets of rational numbers satisfying a few simple properties. For more information, check out https://en.wikipedia.org/wiki/Construction_of_the_real_numbe...

Re: Have we already been visited by aliens?

#342

Post by pdimitar »

pdonis wrote: post #260
AnIdiotOnTheNet wrote: post #35

> Loeb, though, explicitly rejects the Sagan standard—“It is not obvious to me why extraordinary claims require extraordinary evidence,” he observes—and flips its logic on its head: “Extraordinary conservatism keeps us extraordinarily ignorant.” So long as there’s a chance that 1I/2017 U1 is an alien probe, we’d be fools not to pursue the idea. “If we acknowledge that ‘Oumuamua is plausibly of extraterrestrial-techno…

> “It is not obvious to me why extraordinary claims require extraordinary evidence” This is either very obtuse or very disingenuous on Loeb's part. Extraordinary claims require extraordinary evidence to establish them as true . But that doesn't mean extraordinary claims require extraordinary evidence to investigate . You investigate the claims in order to see what kind of evidence there is for them . I would expect t…

> Extraordinary claims require extraordinary evidence to establish them as true. But that doesn't mean extraordinary claims require extraordinary evidence to investigate.

Even your former claim might not be necessarily true. What constitutes "an extraordinary evidence" exactly?

Example: imagine aliens are freely living among us but our eyes are blind to certain light frequencies (they are in fact blind to most wavelengths) and that's how aliens utilize camouflage.

Would revealing this fact be an extraordinary evidence for aliens? It's IMO extremely subjective. People might get very excited with such a discovery, sure, but the explanation does sound rather bland and super obvious (as all things in hindsight).

So this whole "extraordinary" stuff reads more like popular old men bickering in front of the media for the goals of PR coverage and, who knows, maybe that increases their odds for scientific funding. I'd always look for the financial incentive and potential conflict of interest first.

Re: Have we already been visited by aliens?

#343

Post by pdimitar »

AnIdiotOnTheNet wrote: post #35

> Loeb, though, explicitly rejects the Sagan standard—“It is not obvious to me why extraordinary claims require extraordinary evidence,” he observes—and flips its logic on its head: “Extraordinary conservatism keeps us extraordinarily ignorant.” So long as there’s a chance that 1I/2017 U1 is an alien probe, we’d be fools not to pursue the idea. “If we acknowledge that ‘Oumuamua is plausibly of extraterrestrial-techno…

> If we assume that Oumuamua is an alien construct, what "new vistas of exploration for evidence and discovery" open up that we are not already pursuing?

Chicken and egg problem. We won't know until people are with unconventional ideas are free to try pursuing them without being mocked as "tin-foil hats" or "conspiracy nutjobs" or whatever.

Let's take a moment to remember how many similarly not-at-all-related-to-space travel inventions have been made due to fighting the space race (who gets first to the moon) (like the CDs).

I believe the quote is not a specific evidence for anything. It's a call for us to adhere to a slightly different principle:

"Let's explore, for we are far from knowing everything and we shouldn't mock people who investigate things that to the majority look absurd. They might indeed be absurd but every now and then we make interesting discoveries".

Re: Have we already been visited by aliens?

#344

Post by LargoLasskhyfv »

yoz-y wrote: post #330
LargoLasskhyfv wrote: post #284

Earlier quoted context omitted.

Why is that? Let's say we've emitted since about 100 years. They are bound by lightspeed like we are. Our wavefront hasn't reached them so far, OR it has, and they are about 50 lightyears away, busy building a slow annihilation fleet, arriving here anytime about 100 years from now, depending on how high up to lightspeed they can go?

If your goal is annihilation you don't bother with a fleet, you hurl a relativistic kill vehicle (aka, a hunk of rock or metal) at them.

Nonono! Need to have the holy and heroic enforcers of the righteous path embedded and experience it with full sensorium, to conserve the glory of it for all eternity, and bring it back to be rememberd as it really happened(TM)!

Re: Have we already been visited by aliens?

#345

Post by pdimitar »

logicchains wrote: post #263
eloff wrote: post #106

Earlier quoted context omitted.

Yeah that's a good one. Another is recommending trans-fat based margarine over butter. That was counter-productive health advice that took decades to reverse - even although the evidence it was based on was extremely flimsy. Once the group-think machine gets going in a direction, it has a tremendous amount of inertia.

>That was counter-productive health advice that took decades to reverse - even although the evidence it was based on was extremely flimsy. I think this was more a case of lobbying by certain agricultural producers than ignorance. https://www.researchgate.net/publication/14823257_Food_Lobbi...

True, but the point still stands: a lot of people can be influenced by something no matter its origins. Once they can say "X thousand can't be wrong" then you and your pesky idea backed up by facts and evidence can go to hell.

Sadly history is full of such occurrences.

Re: Have we already been visited by aliens?

#346

Post by mrec »

SuoDuanDao wrote: post #339
mrec wrote: post #99

Earlier quoted context omitted.

> What are the odds of intelligent life arising ex nihilo? We'd assume infinitesimal. Why would we assume that? We've been seeing biologically interesting chemicals appear from much simpler ones for well over a century. https://en.wikipedia.org/wiki/Abiogenesis#Chemical_synthesis... Also, your "starseeder hypothesis" sounds a lot more deliberate than panspermia theories, but correct me if I'm misunderstanding you the…

Why wouldn't we assume that? Even with the ability to synthesize full DNA molecules, we haven't yet figured out how to make a living cell from scratch. If our best synthetic biologists still find it impossible to assemble a viable cell while having all the tools to do so in theory, I wouldn't expect it to be likely to happen by accident, barring some quantum weirdness that makes the starseeder hypothesis seem positiv…

> in the latter; life happened once in space

AIUI most panspermia theories don't posit either of those - definitely not that life originated in space, and not necessarily that it only originated once. The most common variants seem to be that life originates in gravity wells, is ejected by major impact events, drifts through space and eventually re-enters other gravity wells. Simulations suggest that bacteria can potentially survive all of these.

Re: Have we already been visited by aliens?

#347

Post by mrbonner »

alisonkisk wrote: post #214
mrbonner wrote: post #100

Earlier quoted context omitted.

I watch it on Netflix and the title shows 1993. I am confused as well but I realized that 1993 is the last season. The show itself was in the 80s.

Netflix dates series by their last episode, in a deceptive attempt to make their catalog look fresher.

Interesting, I have never thought of it this way.

Re: Have we already been visited by aliens?

#348

Post by deeeeplearning »

alisonkisk wrote: post #202
jwally wrote: post #195

Earlier quoted context omitted.

Bookmarking that. Thank you! I think I was starting to draw that conclusion. If a claim is in the Lancet, NEMJ, Nature, etc; its probably pretty credible. If a claim is in another journal; it shouldn't have much bearing on my decision (positive or negative) since I don't have the expertise to evaluate it.

But how do you know those are credible? It's fundamentally impossible to decide from first principles. You have to choose where to put your faith. Longstanding reputation is one popular way, but old things can sell out, or can be fairy tails (like at least all but one religions).

Right but at least Impact Factor gives you some kind of objective idea of the importance of a journal. Most researchers know Science and Nature are elite journals and impact factor at least backs that up by showing that their papers are highly cited by other "experts" in the field. But as I said it's still not perfect.

Re: Have we already been visited by aliens?

#349

Post by gfxgirl »

shrimp_emoji wrote: post #111
gfxgirl wrote: post #90

Earlier quoted context omitted.

I thought the idea that there are gazillions of advanced aliens has been pretty much disproven by the fermi paradox. If there are gazillion, at least one out of all the diversity out there should have already colonized the entire galaxy and evidence should be plentiful.

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…

> 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

This assumes that there are gazillons of alien civs yet somehow they all come to the same decision. That's much less likely than gazillions of alien civs all make different decisions and it only takes a single one to make the replicating probs or try to colonize.

Re: Have we already been visited by aliens?

#350

Post by naikrovek »

vladTheInhaler wrote: post #313
naikrovek wrote: post #303

Earlier quoted context omitted.

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 suf…

> I can't give details because they don't exist. Right. And if the argument depends on those details, then it's not a very convincing argument.

My argument is that pollution outlives a society that it kills by a non-zero amount of time.
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