[dbingham]

Please correct me if I'm wrong, but my understand of the alien craft theory specifically for Oumuamua wasn't just because the object itself was new, but that it changed acceleration [1] without apparent off gassing in a way that isn't explained by our current understanding of orbital physics for a natural object.

It's not just "New object, must be aliens!" It's "This thing doesn't fit our understanding of orbital motion for natural objects, aliens is actually a rational, if still unlikely, possible explanation."

[1] https://en.wikipedia.org/wiki/1I/%CA%BBOumuamua#Non-gravitat...

[ryanblakeley]

There were a number of anomalous characteristics including its shape, acceleration, rotation, origin, and reflectivity.

[ceejayoz]

How do we know they're anomalous characteristics if it's literally the first one we've ever spotted? What is the normal shape of an interstellar comet core?

[cubefox]

For example, being flat like a pancake is obviously highly unusual and very different from anything we have seen from stellar comets.

[ceejayoz]

Stellar comets haven't been ejected from another solar system. We have vanishingly few examples of those, and we've not directly observed any up close.

"Flat as a pancake" is one of several theoretical possibilities from its light curve, not a known fact about the object.

"Highly unusual" in space tends to mean "there are a bunch, but we haven't seen them until now". In 1992, exoplanets were "highly unusual". Now they're everywhere.

[Sharlin]

Yes, and the exoplanets we found first were highly unusual and not at all what we expected to find, which triggered tons of new research to amend our models of planetary system formation and dynamics. I’m not even sure what you’re trying to argue here – we found an object that did not fit our model of what things should look like, which is very curious and calls for an explanation. That’s how science works. Doesn’t mean it’s aliens. But “oh well maybe it’s just how things are back where it’s from” does not satisfy anyone.

[ceejayoz]

I think we are actually in agreement.

I’m very onboard with “it was an interesting object and we should learn more”.

I object to UFO cranks jumping to “it was a starship” conclusions like Avi Loeb wants to. Just as I would have when those weird first exoplanets showed up.

[cubefox]

The highly unusual properties are such that they are genuinely hard to explain for astronomers. See my neighbouring comment.

[TheBlight]

The same as the ones from this system. Borisov had the same characteristics.

[ceejayoz]

> The same as the ones from this system.

Why would we assume non-interstellar comets are always the same as interstellar comets? Conditions obviously are a little different when something is ejected from a system and then spends millions of years in interstellar space.

> Borisov had the same characteristics.

We have a sample size of three thus far. Making conclusions right now is like saying all extrasolar planets are large gas giants because the first three were.

[TheBlight]

We'd assume most interstellar objects are comets because that's which objects you find on the outskirts of a solar system and are the easiest to get kicked out. We'd assume they're mostly like our comets due to the Copernican principle. We shouldn't assume we're special.

[ceejayoz]

> We'd assume they're mostly like our comets due to the Copernican principle.

We're still figuring out what our comets are like, let alone unusual ones spending a few million years in interstellar space. New types of comets(ish) bodies discovered in the 2000s:

https://en.wikipedia.org/wiki/Active_asteroid

https://en.wikipedia.org/wiki/Manx_comet

We've spotted ~5k out of an estimated trillion. Each one we've sent a probe to has brought surprises. The Oort cloud remains theoretical at this time, and the first Kuiper belt object other than Pluto/Charon was found in 1992. It would be deeply silly to think we know everything about our local comets, let alone unusual ones from elsewhere.

[jerf]

The history of science is that every freaking time we look somewhere new, we find something new. It happens over, and over, and over, and over again. We have a really bad track record of predicting things in advance in new domains. The exceptions are leaping to your mind precisely because you've heard about them because they're the exceptions.

Also, to date, zero of those things have been "aliens".

So rushing to declare the first instance of what was completely obviously a new class of objects as "aliens" because it didn't behave like what we expected is not rational, because we should expect that new things don't behave like we expect. The odds that the first one of these we detect is also the one from aliens is just not a good bet.

I'd bet a tidy sum of money that in 25 years it'll simply be common knowledge that these class of objects sometimes have those characteristics because of some characteristic special to them. Probably something to do with having a lot of things that turn to gasses and exert accelerations on the object because they were never blown off by the solar wind or something because of them being in deep space for millions of years. Might be most of them, might be a small-but-respectable fraction, but I bet in hindsight this is recorded in the history books right next to "pulsars are alien beacons!" and with the exact same tone of lightly sneering contempt we hold for that now. To which I can only say to the future, let the record show we did not all think it was aliens.

[dbingham]

It is every bit as irrational to dismissively rule out "aliens" as it is to rush to declare it the definitive answer.

It is a valid possible answer that should be included in the possibilities as we try to figure out what caused the acceleration. Right now, lots of things are being proposed. And many of them are seemingly being ruled out. It remains to be seen what the answer will be.

The physics and history of science books I read when I got my degree did not seem to include sneering contempt for those who thought pulsars could be alien in origin. I rather recall a tone of disappointment as they described how we figured out that they weren't alien. The Fermi paradox remains one of the great mysteries of astronomy and cosmology and a lot of people, both professional and amateur are still fascinated by it.

Extraordinary claims do require extraordinary evidence, but academics who sneeringly dismiss extraordinary claims as even a possibility are every bit as toxic to the rational advancement of science as those who advance those claims without enough evidence.

[mellosouls]

Yes (a change in acceleration was reported), but even in the link you yourself provide the hypotheses are framed within standard physics, not alien technology.

The latter got more than its fair share of press because Harvard's Avi Loeb proposed it as potential evidence of ET.

He later claimed more evidence from potential spaceship bits he reckons he found from an ancient meteor, and seems to specialize in these sorts of claims. [1]

Like you say, not irrational but perhaps over-hyped by people who ought to know better...

[1]https://www.independent.co.uk/news/world/americas/avi-loeb-i...