More than a fractal, it is better to imagine it as a pile of recently fallen snow is a day with the correct climate (cold?), so the snow accumulates but it doesn't compact too much. So the density is much smaller than the density of ice that has been in a glaciar for years under a lot of pressure. Since the gravity is too low, it will no compact too much.
The main difference is that it's not a pile of real snowflakes, ut a pile of dust "snowflakes". Otherwise, the ice in the real snowflakes would have been partially evaporated by the sun and it will be classified as a comet.
Anyway, it would be interesting to read more technical details about the plausibility of this. Can the dust pile survive the micrometeorites? Does the color profile match a dust pile object. I really don't like the starship hypothesis paper, but at least it contains a good analysis of many of the (secondary) objections.
*It is also worth noting that this experiment was entirely ad-hoc and came about from Don basically just playing around with stuff in microgravity
It is, or at least calling it self-similar is, as well as what the image implies: https://www.youtube.com/watch?v=gB9n2gHsHN4 That's a 3Blue1Brown video explaining why "fractal" and "self-similar" are not the same thing.
It is widely agreed that self-similarity is required for fractal, although often interpreted as quasi/statistical/multiple similarity
Put another way, some things are self-similar but lack detail (for example, a straight line), and some things have detail but not similar detail at all scales (for example, a meterstick with ticks at every millimeter) and some things have infinite detail but no similarity (for example, purely entropic noise that cannot be compressed or expressed as a structure)
But snow flakes are fractals.
Ok, it's on my list of things to do this year to actually learn how statistics work, but my naive reaction to this supposition, which I read is "the fact that we have encountered Oumuamua means that it's likely it didn't come from far away, because if it did, it's less likely we would have encountered it," is: We did encounter it. Just this one, ever. How can we draw any statistical information from that? Either we encountered it, or didn't, how does that have any bearing on the statistical probability of seeing it?
I believe what you're getting at is the Ludic Fallacy, which could probably apply here. That said, whether it's a fallacy in the science or in the reporting, it's hard to say. I have a degree in statistics, and I'd say I spent half the time learning stats, and half the time learning to use language precisely to avoid overgeneralizing stats.
There's a really great TED talk about how even very educated people get it wrong when talking about stats: https://www.ted.com/talks/peter_donnelly_shows_how_stats_foo...
Does this single observation tell you anything about reality? I would argue that it does - it should strongly suggest to you that you're in the "every car is ARW 357" reality. Similarly, if you draw a ball from an urn and it's red, and you know you've drawn either from the "urn of red balls", or the "urn of one million green balls and one red one" you should be pretty confident you've drawn from the "urn of red balls".
If one theory can explain your observations but the explanation is highly unlikely, and another theory explains your observations and the explanation is likely, the second theory is more likely to be correct all else equal.
I think this scenario is incoherent after thinking about it for a minute. You say "there is equal probability that either explanation is true" but you imply that you, the storyteller, know something about license plates. Probability is a description of incomplete knowledge, so whose knowledge are we talking about, yours or mine?
I see no reason (in my hypothetical ignorance) to exclude the possibility you know I will see "ARW 357" next even if all license plates are different.
Instead, consider the example with the urns. I think that's a lot more realistic and illustrates the problem.
In both cases you do not have enough information to make any conclusions.
That's why the field of statistics exists in the first place.
However, are we able to reduce down our understanding of "which universe we're in" in such simple terms? I think I'd understand better if I knew how long we've been capable of detecting oumuamuas.
There's no evidence it is aliens. Obviously it could be, and it's unlikely there are not such things in our universe.
It just seems more appropriate to say "there's no evidence it is related to alien tech." Everyone having to say "it's NOT aliens" seems like some sort of cultural phenomenon.
Most theories on physics are evaluated this way. "We theorize that light is a particle, which would explain these properties of light, and means we should expect to see these other properties of light if we test them." If further observation of light matches those properties you predicted then that's pretty good evidence that your theory is on the right track.
If your ancient aliens theory didn't actually predict "Stonehenge", but predicted that the aliens would have left "all sorts of cool weird stuff", and then you point at Stonehenge and say "see, that's the sort of cool stuff I mean", then I'm no longer impressed by the predictive power of your ancient aliens theory.
Predictions have to be precise for a theory to be supported by them: they can't be vague generalities. cf. astrologers, who "predict" the future by predicting nothing.
My theory is wrong, but it assigns higher likelihood to Stonehenge than yours. That’s why I don’t like the license plate example.
A theory that is wrong will sometimes predict correct things by accident. That's unavoidable, but we a) have statistical methods for modelling how often things go right by chance, and b) have a philosophy of science in which theories are forever tentatively held: your aliens theory might beat any theory which says Stonehenge is impossible, but will soon be replaced by a theory which explains Stonehenge more economically.
We can suggest that there are N classes of objects in space, we picked one at random, and it happens to be Oumuamua belonging to the class of Oumuamua-like. To one of N classes. The more some class is common, the more probability for us to see element from this class. Here we can use Bayes' theorem and conclude that the fact of observation of Oumuamua is a weak evidence that the class of Oumuamua-like is more common in the interstellar space than any other class.
It is a weak evidence, and I dont know how much is it. But the point is this evidence points to an ordinariness of objects like Oumuamua not to a rareness.
You start monitoring it. Year 1, the thing happens. Which is more likely:
1. You've encountered a 1/1,000,000 event
2. Your prior is incorrect and the thing happens more often than once every million years?
Without more information we can't actually answer this question with certainty, but "re-evaluate your priors" would absolutely be a thing one might suggest in response to this event.
You press the button. The light bulb turns green. There's no windows to check for rain or internet to check for winning numbers. You have no further information beyond the fact that the light bulb turned green.
Which is more likely to be the case: That you're now a millionaire, or that you should grab an umbrella as you leave?
We know we saw 'Oumuamua (the green light). We now can construct many models for why we might see such results. The probability that we would see the results given the model (lotteries or rain) can be used to infer what the true model most likely is.
1) Somebody starts flipping a coin they claim is fair. You're not sure whether or not that's true. It comes up with 10 heads in a row.
2) Somebody tells you there's a 1 in 10,000 chance of something happening each day. You're not sure whether or not this is true. It happens tomorrow.
Which, if either, do you think has reasonable evidence to begin to doubt the claimed odds are the real odds? Which do you think is better evidence of the proposed claim being false?
With the logic you expressed in your post you might suggest the first is better evidence of a false claim, but it's not. The odds a fair coin going 10 heads in a row is 1 in 2^10, or 1 in 1024. Even though it's 10 'events', it's ultimately just a 1 in 1024 happening if we assume a fair coin. By contrast the second event is about an order of magnitude less likely to have happened by chance. So even though the second event is only one happening, it's more likely that that event is not a 1 in 10,000 event than it is that the coin is not fair.
But to answer your question more generally: you start with some model, with one or more parameters for which you don't know the value. e.g. "the galaxy contains N uniformly spread out interstellar objects that are big enough to see if they happen to come within 1 AU of Earth."
Then we start watching the sky, and after 10 years we see 1 such object.
Then for each possible value of N, you could calculate the probability of observing exactly 1 such object during a decade. One particular value of N is going to give us the highest likelihood of getting that result. We call that value the "maximum likelihood estimate" for N.
Certainly, any new information is going to radically adjust the posterior probabilities, but you can still make some tentative inferences.
This was worked out in WW II for estimating tank production.
In fact, an argument that it's more likely to have come from somewhere nearby holds even if it was sent by design. Conscious beings are more likely to want to explore the stuff they can reach sooner, and they are more likely to succeed at reaching nearby things. But without knowing their engineering constraints and their preferences, we can't quantify that like we can the random ejection scenario.
It seems far more likely that objects like 'Oumuamua are relatively rare, and that means it likely came from someplace close by (if it came from farther away, the odds are even lower we'd ever see one).
I'd rather look at the density of Oumuamua-like objects in space. First, it seems like these objects rarer than some things but dense enough for us to have seen them.
Their "terminal density" comes when their rate of production managers to equal their rate of consumption. Who knows how they're produced but I'd assume they are consumed when they are gravitationally captured by a solar system - actually flying into a sun is much less likely I'd assume. Such gravitational capture is more likely if these objects are moving at a similar speed to the solar system they encounter.
The one thing we know about Oumuamua is it seemed to speed up as it left the solar system. This factor might imply that the chances of capture wind-up very low. Now, the rate of production could be low and thus life-span could be high. A high lifespan implies this came from far away. I could be wrong on the consumption chances. But still, I think arguments about how far these travel would do better with such life span analysis than with the quote argument, whose implications are foggy imo.
As to whether the thing is a product of alien intelligence? If the very low density analysis is correct, if such a thing could behave as Oumuamua did, then that too might be a good spacecraft design. Which is to say, the amount of information we have is low that making absolute answer seems pretty hard here.
- observe this thing at all
- accurately measure it's velocity and acceleration
- understand that it's velocity and acceleration were unusual?
A number that I saw quoted earlier was that it is expected that around 3 of these things go through the solar system every day. This one just happened to be the one caught by the survey, which itself required a bunch of coincidences since it means catching multiple pictures of the same object in different locations so as to establish a trajectory, so an ability to detect is not just resolution, but also timing and orbital trajectory.
We've been observing space 'forever'. Pre-telescope observers had quite accurate star maps (of the naked-eye stars, obviously) and were fully aware of the complex movements of the planets. Their models of the movements were good enough for predictions even if the underlying explanatory causal models were sometimes wrong.
What it really is, IMHO, is a call to action for better instrumentation so that the next time one of these things pays us "a visit", we're in a position to find out more about it.
I think what you are proposing is having a bunch of large space telescopes around planets. But this might not help very much. All the planets are in the plane of the ecliptic. Interstellar objects are not going to be aligned with the plane of the ecliptic.
The difficulty of putting Hubble or JWST sized telescopes in orbit of other plants is immense. They need constant maintenance as well and will take years to reach their intended targets.
B612/Sentinel has been "in the works" for at least 8 years, but still doesn't have consistent funding. This would be in a Venutian orbit to looks for near Earth objects.
IMHO, a more useful location for a space telescope rather than in orbit around another planet would be phased 6 months off of Earth at 1 AU. This would let us continuously observe the "sun side" of space.
It's frustrating because we already have the technology to be able to achieve basic intercepts here, even if they were at high velocity. The only thing in the way is a dilapidated space program.
NASA provides regular updates from Curiosity here.  What you might find there is that problems are never ending and that progress is very very slow. As an example one of the primary missions of the Curiosity rover was to try to drill into the surface of objects on the planet to start getting some basic idea of what was going on. The problem is that after superficially activating the drill 15 times, it broke. The drill feed mechanism became disabled. The most likely culprit is some dust or other particle caused a critical brake to get stuck. This is a 10 minutes fix for a human on site. For the rover? Countless minds at NASA spent years working out a solution and came up with a solution that is not really sustainable and still leaves major issues with sample collection. That solution, limited though it may be, is as much a testament to the capability of NASA's engineers as it is to the major limitations of probes and rovers. The Planetary Society had a really nice write up on this here .
Opportunity recently died after more than 15 years on Mars. An absolutely remarkable achievement for a rover with a planned mission length of 90 days! However, even then it's death may be premature. One of the most likely culprits for its demise is that after a substantial dust storm, which it went into hibernate during, its solar panels were left covered with dust. A Martian janitor with a broom could fix in about 10 seconds, but for a rover - it's time to enter the long sleep. Another side of the story is that during its long life, Opportunity was only able to travel 28 miles, a bit less than 2 miles a year. You end up getting a very limited view of what's going on. Curiosity, for comparison, has managed 12.5 miles of travel in its 6.5 years since landing.
Finally there is one last major point to be made. We don't know the cost of manned missions. We can speculate on the cost of sending the first man, but I mean once we actually get into the 'normal' phase of putting men on other planets much as we do to e.g. the ISS today. We currently spend about $70 million per person to send them up, and that's a greatly inflated price as we rely on foreign suppliers. But even at that price, sending a man into orbit on a station intercept for $70 million is something that at one time would have been unthinkable.
We will likely see that price drop the single digit millions of dollars, at least in real cost, before the end of this decade. And getting to orbit in space is 90% of the battle. There's an old quote that once you get into orbit you're halfway to anywhere. And that's pretty much true. There will be a serious up front cost for setting up habitation systems but once these are established, I think there's a very strong argument to be made that humans will quickly become cheaper than rovers.
And finally this all completely ignores the human aspect. Putting a man on the moon shaped an entire generation of people with hope, optimism, and a sharp increase in the drive towards scientific pursuits. In a world of needless division, petty diversion, and increasing pessimism towards pretty much everything - you can not overstate how monumental an effect there will be to once again start putting people on other planets.
 - https://mars.nasa.gov/msl/mission/mars-rover-curiosity-missi...
 - http://www.planetary.org/blogs/emily-lakdawalla/2017/0906-cu...
I think the recent discovery/confirmation that our moon has substantial reserves of water ice emphasizes the difficulties with technology outside of manned exploration. There's a lot of information you can obtain from probes and other forms of remote observation, but it tends to be extremely specialized and very limited. This is not something we should be discovering 40 years after landing on it -- water was confirmed in 2009.
 - https://en.wikipedia.org/wiki/Venera
 - https://www.youtube.com/watch?v=8jZDW53U8qQ
I wonder if it will find a resting place in some dark corner of the universe, maybe behind a black hole somewhere just out of our sight clinging tenuously to the outstretched arm of some far-off spiral galaxy and resisting every effort to slurp it back into the vacuum.
However, the idea of a porous surface like a snowflake or sponge or something doesn't add up because of exact speed it travels. Even if this is just ice/dust composite, with that kind of speed, it would be disintegrated by having its surface polished with cosmic energy long before it could reach 25km/s.
I hope we won't see another one. This one was so close to Earth it wasn't funny. And traveled so quick we wouldn't have time to call all family members to tell them we love them. Its nothing like meteor; even big one would just drop flat on earth, raise all dust for next 30,000 years, throw us back into stone age or close to extinction and some form of human life looking nothing like we do today would argue 250,000 years from now what caused the first human near-extinction. No. You're talking about razor-sharp thin and lightweight object traveling with insane speed. Upon impact, it would either penetrate Earth surface exploding inside the core, like any hollow bullet does, or it would cut Earth in half like a high power laser and deform itself on way out. Either way this wouldn't be your near extinction experience. This would be like all of sudden Earth spliced in half and both parts going away, while you are either being drown with oceans hundreds feet of water tall due to lack of gravity, or crushed by weight of same ocean who happened to froze in the upper atmosphere, caught some gravity and smashed on the top of you. I don't want to even think about super hot lava thrown everywhere without gravity it would be like spraying venom from a giant snake.
I have no idea how something like that would look like when Earth split in two, and no movies of that kind of extinction has ever been done. But something tells me it would be far from an easy death and I would rather carry on suicide pill in my tooth like they did during WW2, rather than witness such literal Hell on Earth.
…it was (and still will be) in the solar system for quite a while. The Solar System is big.
> it would be disintegrated by having its surface polished with cosmic energy long before it could reach 25km/s
…no? Relative to cosmic energy, it might as well be at rest.
> Upon impact, it would either penetrate Earth surface exploding inside the core, like any hollow bullet does, or it would cut Earth in half like a high power laser and deform itself on way out.
I suggest you read up on high velocity impacts: https://en.wikipedia.org/wiki/Impact_depth
Contains some tables with actual numbers (based on a 17km/s impact), including how big of a airburst a non-impacting object makes and how much of a crater an impacting object makes.
You aren't splitting the Earth with something the size we are talking about with any of the estimates of it's size, even at 25km/s, which basically a little over doubles impact energy, the same as a 29% increase in diameter does.
> and some form of human life looking nothing like we do today would argue 250,000 years from now what caused the first human near-extinction.
Well, they might, but they would probably be talking about the Toba supervolcano 320,000 years in their past.
> You're talking about razor-sharp thin and lightweight object traveling with insane speed.
Shape is not all that important (though I think that a long tumbling object is more likely to break up break up at altitude), the speed is high, sure, but not so far out of line with typical meteors as to make that big of a difference, and the low density offsets the effects of speed (also makes it more likely to break up at altitude). And the later estimates of it's size are not enormous. It would perhaps be a bag meteor impact, but quite possibly not the worst to hit during the existence of humans.
No, it would do neither of those things: it would either explode in the atmosphere or make a crater on the surface.
You seem to think it is a superstrong heat-resistant stabilized penetrator dart coming point first, rather than a tumbling body of (probably) rock and ice.
We can look at meteor impacts, too. The first source I found on the topic said meteors commonly impact with 11- 72 km/s.  This happens every day with small objects and we're fine. With bigger objects you'll get extinction events and features like the Chicxulub crater, but no way you'd see anything "penetrate Earth surface ... like any hollow bullet does, or ... cut Earth in half like a high power laser."
The speed of light is 300,000 km/s, more than 10,000 times faster than Oumuamua. An object at 0.1c or even 0.01c would be very threatening, but those are still orders of magnitude faster than Oumuamua.
In short - 25 km/s isn't that fast, don't worry about it. There are plenty of asteroids that could hit us faster than that that we also don't always see!
 - https://www.amsmeteors.org/meteor-showers/meteor-faq/
Quite a few spacecraft have reached this speed. Off the top of my head, I think Juno reached something like 70 km/s when approaching Jupiter.
The current record is Voyager 1, which got its speed from a flyby tour of the outer solar system. It is going 17 km/s.
The fact that it is tumbling and not coming on like a dart along it's long axis means it pretty much doesn't matter what it's made of, aside from it's total mass, it's not going to do some kind of radical penetration or anything else that unusual of it were to hit the Earth.
(Even if it was a stabilized penetrator dart of some kind, AFAIK, that doesn't really change much about surface impact unless you make radically implausible assumptions of composition, but I think it might effect the probability of it making a ground impact rather than an airburst.)
Huh? What's "cosmic energy? Do you mean cosmic rays? Those are actually atoms or electrons moving at an exceedingly high speed. Matter, albeit highly energized matter, but not energy itself.
If that is what you meant, the fact that this object was moving at 25 k/s is a fart in a whirlwind compared to the overall velocity of those atoms/electrons. It would have a virtually identical effect to something moving at 25 kph. Not to mention those particles are too small to really "disintegrate" anything. At best, they would knock a few particles off some of the atoms that comprise the object, perhaps changing a few into another element/isotope. There just isn't enough mass there to do any damage on a macro scale.
Here's a quote that works on imagination:
There are times when the human eye can behave like a camera lens, when a momentarily but brilliantly cast image can be not merely recalled but meticulously reconstructed as vividly as if viewed in the present. Minutes later, I could still visualize the surface of that colossus in the flare’s afterglow, its kilometers-long sides not smooth but pocked, almost lunar in texture; the way the light had spilled over its corrugated rills, bumps, and craterlike cavities—scars of its interminable wandering, dark and dead as it had entered the nebulae, from which it had emerged centuries later, dust-eaten and ravaged by the myriad bombardments of cosmic erosion. I can’t explain my certainty, but I was sure that it sheltered no living soul, that it was a billion-year-old carcass, no more alive than the civilization that gave birth to it.
This story (Pirx's Tale) is available on Google Books: https://books.google.com/books?id=n16z06cm1P0C&lpg=PT11&dq=%...
"... another aspect that needs to be studied is
whether its extremely low density could be maintained
while in the parent system, during its long interstellar
journey, and when entering the solar system."
Without analyzing the structural integrity of such a fluff ball it's tough to give any more or less merit to this concept than the others.
It never came all that close to the sun, so the gradient on different parts of it wouldn't be that extreme.
At Perihelion it was 38198320 km from the sun = an acceleration of 0.090962666582226 m/s^2
It's 1km long so on the other end the acceleration is 0.090962661819574 m/s^2
Subtract: .000000004762652 m/s^2 which is such a small amount I'm not sure how to put it into context.
Multiply by 1 metric ton = 1/5 weight-force of a single snowflake on earth.
Which means each metric ton of material needs to handle just that much force trying to separate it.
i.e. it won't be ripped apart in the slightest. Over centuries it might elongate a bit (and it's already elongated).
So, continuing this general line of thought: what's the largest tidal force it would have experienced? Differential solar pressure? Would it have encountered anything on its journey that should have dispersed it?
I have no idea of its past obviously, but near us this would be it, at closest approach to the sun the tidal force is greatest.
> Differential solar pressure?
Solar pressure is very low, it just applies that force for a very long time. It would act to compress it (flatten it), slightly.
But I don't know what orientation it had when approaching the sun. It could have been tumbling and randomized any force.
> Would it have encountered anything on its journey that should have dispersed it?
Vaporization from heating is the only thing energetic enough that I can think of.
But maybe other people can think of other things.
Does anyone know more about the initiatives by Yuri Milner with respect to this? I heard something like he is helping fund satellites that could specifically be better at looking at 'Oumuamua than our current means?
This should have been a big wake-up call to have pre-made probe craft ready to launch to investigate anything odd that entered the solar system. But expecting humanity to be that fore-sighted is pure folly.
Even if we had a probe ready today it's already too far and moving too fast to overtake. Even if we had a probe ready when we first detected the object it would have been difficult to intercept with today's technology. It would have to be something like a Falcon Heavy already in orbit and ready to burn at a moment's notice with a tiny probe at the top for gathering the data.
That's the other side of the problem: we didn't detect it until far too late. We should be able to detect objects of this size much, much sooner than we currently do. We're not looking very hard for them, so usually we end up seeing them after they've already whizzed by. There have been way too many times in the last decade or so when we're informed, "hey, we just barely got missed by some big asteroid, and we didn't even see it until it already went by the Earth!" That's just pathetic.
Edit: although, that would involve pointing a 100 gigawatt laser directly at Oumaouma, which might disturb it.
Maybe that would cause it to turn around and come back.
That means the system it originated from if a natural object would need to be coincidentally that close to our median local
More interesting would be if we could beam up energy to refuel, but for that we'd probably need yet-to-be-invented drives which use loads of energy per amount of matter to accelerate it further. Kind of like a particle collider but for propulsion.
Still, it'd mean reaching Uranus' orbit in about a year. That's a lot to ask for.
Big rocket or very small probe.
I mean I'd click on an "Another Oumauamua Theory" headline, but I guess that's not what kids are clicking on these days.
(see point 2 here: https://blogs.scientificamerican.com/observations/6-strange-... and the more detailed discussion of this it links to)
I never gave a moment's credence to the idea that it was an alien spaceship but I really enjoyed reading the thoughtful and well reasoned arguments for and against the idea. For me the space of thought that these arguments created was an interesting experience that gave me an interesting perspective.
So saying "hey no, it's not spaceship... it's weirder than that" (and then arguing that point) is fantastic.
I totally agree that there is a good chance that it wasn't alien, and we want to identify what it could be if it wasn't, but why dismiss it? Most scientist already believe we are not alone, even though it is unlikely we are close to any other intelligent life. The chance that it was alien should be explored as well, and I know their are scientist who believe it is alien.
Instead, the argument is surrounding the psychology of the hypothetical creators of said solar sail, or plausible ways we missed some data. Since we are just speculating at this point, who am I to say?
But to answer some specific criticisms:
- Perhaps the brightness/darkness cycles were the sail turning on and off as a mechanism to control velocity
- Perhaps the 25km/s speed being a crawl for interstellar travel was because it was meant to slow down while passing through our solar system. Either so we might notice it, or so it can collect data while here a bit better.
I am having a hard time understanding how rare an event this space-foam-fractal theory is predicting, but if it's extremely rare a solar sail seems a completely reasonable hypothesis still.
We know for a fact that the universe is filled with strange and interesting dynamics (not involving alien life forms) that we don't always understand at first. We don't yet know where else life may exist in the universe, if at all.
We make a differentiation between phenomenon wrought from cognition, but that cognition is - at least in part - a natural phenomenon too.
Is this distinction founded in dualist philosophies(mind-body and/or material-spirit)? Does it make sense to make for monistic materialists?
We might not ultimately recognise alien construction as coming from some intellect, plenty of creatures create structures on Earth (as do physical processes) with high complexity that are not considered to result from cognition.
There is an inarguable qualitative difference between the types of objects and materials that can be produced from undirected mechanical and chemical processes and those that can be produced through the work of intelligent, living beings.
In picking this semantic nit, you've completely ignored the actual point made by the GP: we've seen countless examples of new and strange phenomena that end up being described by undirected physical and chemical processes. We have yet to find anything that requires intelligent life to explain, like an interstellar skyscraper would.
Particularly I like that it sent me in to thinking of an alien life form that could, maybe like ants, construct a large scale "artefact" - like a solar sail - that we would recognise as being wrought by intelligent life but would actually be the result of some sub-intelligent life form.
I like Fritjof Capra's rendition of Gaia hypothesis (as an idea), but had never really extended the idea of self-ordering, or complex-ordering, to how we might interact with alien constructions.
>In picking this semantic nit, you've completely ignored ...//
Just my reaction to it.
We know how much it’s acceleration as affected by solar pressure because we measured it, and it was very low, similar in scale to that caused by off-gassing of comments. Tiny both by interstellar travel standards, and in terms of its actual velocity.
The way you use ‘solar’ sails for interstellar travel is to propel them using a fixed laser at their point of origin, and possibly another laser to slow them down at their destination. Actual light pressure from a star is way too low to give them useful velocity for interstellar journeys.
What if someone sent out a bunch of these things to wander the galaxy until they encounter a civilization cable of detecting it and slowing it down? Perhaps it was even sent purposefully after signs of life were detected on earth. That seems like a feasible communication method with today's tech, the galactic equivalent of a station wagon full of hard drives.
Imagine a pre-industrial civilization that finds a ship's sail that was lost at sea washing up on its shore.
I don't believe the solar sail hypothesis, but I like the fantasy it provokes in my mind.
The reality is this is an extremely alien object, no matter if it was formed by intelligent beings or spun off from a star. Maybe this is a solar sail or maybe it is a giant snowflake.
And, contrary to the author's hand-waving, there is nothing that says an enormous, impossibly thin solar sail can't be formed by randomly bashing an infinity of rocks together over a near-infinity of time - after all, LIFE ITSELF comes from just such an action, so pretty much anything is in play if that is the standard!
Nobody is saying that it is impossible, the author is simply saying that it seems unlikely that is the origin. It's Occam's razor, whereby the simplest solution seems to not be alien intelligence or serendipitous solar sails, but rather something that we have seen appear naturally (fractals).
That's how an instance of life came about. A very simple, most likely extremely short-lived, not at all efficient form of life. The advancement to Eukaryotes took ~2 billion years from there, and multicellular life took about another billion years. These happened not by random bashing, but selection pressures.
While a solar sail could happen completely randomly, 'life itself' isn't really a good comparison, since that's not really how it happened. At least not any form of life that is really recognizable as life.
everything has selection pressures too: just like life forms exist and thrive in different environments, dust behaves differently at different temperatures and gravities.
life as an event, and specific things that happen thereafter are no less “random” than specific chunks of rock/dust in specific configurations
No. Incremental changes over millions of generations in response to environmental pressures are not "random".
This sliver of dusty ice may have formed in a one-in-a-million random chance, but there's no process that selects for this.
I don't know where you get this from...just because we have not observed it directly? Based on everything we have learned so far about life here on Earth, it seems entirely reasonable to think that life would be very common throughout the universe.
Yes, it is true that you have plenty of life here, but you have it only on a very (and I mean very) thin layer on this floating rock. It seems a lot on the surface (pun intended), but it actually isn't.
(And, if you are willing to invoke some form of the anthropic principle, maybe a universe that can support even one instance of intelligent life is itself incredibly rare in some landscape?)
There may be a large number of life-hposting planets in the Universe, while still fitting current data that they are extremely rare as a fraction of, for example, the region of space reachable by humans, by floating space rocks, or perhaps even the Earth's light-cone.
See also: Religion.
You won't get much acceleration from distant and/or dim stars. (Without a giant laser.)
Interestingly, Oumuamua is at the high end of in-system solar sail velocities, and extremely slow for powered inter-system travel.
The velocity profile matches a natural solar sail drifting rather randomly through space or - if you're going to go with "aliens", for the lulz - a probe deployed on the outskirts of the solar system with a low velocity.
It doesn't match the profile of a powered inter-system solar sail.
In a lightsail, if I understand this diagram correctly, the imparted momentum is proportional to the sum of the angle of incidence and the angle of reflection. (Which, come to think of it, is exactly how billiards works.) Therefore the sail travels perpendicular to its orientation, no matter where the incoming light came from (as long as it came from that side -- I'm guessing the other side is not reflective).
Is this truly the case, or is it just hard to monitor the paths of the multitude of objects passing by earth?
Rare enough to be a space ship?
Would have it been possible for thie Oumuamua to directly crash into the sun and just... end our solar system? Just like that?
> Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space.
An image which accurately shows both the Sun and other objects to size or at the correct distance doesn't give you an accurate measure of scale. Movies which show space sequences and ships flying from one planet to the other don't help, either.
An image of the Solar System which shows both the Earth and Sun in the same image is either distorting the size of the Earth, distorting the distance between the two, or both. Here's one tool that may help...get your scroll wheel warmed up, though:
Or maybe you could visit one of the many to-scale solar system models, and take a walk from a 1-meter-diameter sun 100 meters away to a 1-cm-diameter Earth and continue walking for 30 minutes to the outer planets.
At 1 meter scale for the Sun, Oumuamua is 0.1 microns, or 1/10th the size of a bacteria. If we multiply everything by 10,000 until the object is a 1mm grain of rice, now the Sun is 10 km in diameter, the size of a small city. Nothing the grain of rice could do, no matter how fast it moves or what it's made of, would harm the city-sized ball of fire. Granted, a 130 meter high-density (not Oumuamua) high-velocity asteroid impacting the Earth (100 meter diameter in our scaled-up rice-grain model) would cause significant distress for the very environmentally sensitive organisms clinging in a thin film to its surface (namely, humans), especially near the impact site.
Do we have example of naturally ocurring space object with such low density?
Depends what you mean by "object. Assuming the mass is mostly protons, that corresponds to a density of ~3e19 particles per cc. In comparison, molecular clouds in the galaxy have regions which are have densities as low as 1e2 particles per cc. And the hot X-ray emitting gas in clusters can be less than 1 particle per cc. There are things which span the gap, including disks around stars.
I would prefer to see a list of things it could be vs. the hubristic response of leading scientists.
It’s a great example of something unknown.
But isn't it through what leading scientists deem it could be that we get such a list that you want?
Otherwise, it could be:
- an icy fractal aggregate
- a rock
- a teapot
- a bunny rabbit
- a full-scale replica of the Titanic visible only to bees
- a fortnight's holiday in Benidorm
either these objects are way more frequent than we think and the reason it passed the sun so closely was simply that these would be the first to be observed, or it almost seems aimed to pass the sun closely?
"Astronomers estimate that several interstellar objects of extrasolar origin (like ‘Oumuamua) pass inside the orbit of Earth each year, and that 10,000 are passing inside the orbit of Neptune on any given day."
> [Oumuamua as a fractal] is a hypothesis worth investigating ...
> NO, 'OUMUAMUA IS NOT AN ALIEN SPACESHIP ...
I guess the use of 'Bad Astronomy' tag is apt.
Its not mutually exclusive
Its just clever and now we have hypothesis about how it was done
I dont understand the key component of the article about the radiation from the sun giving it a boost. These scientists were able to make all these deductions about its shape and why from this, but what? How does radiation propel in any circumstance? Are we saying molecules change composition? Electrons moving to another state? What
It depends on the type of radiation, but two mechanisms jump to mind for me:
The first is direct action of photons, as in a Crookes radiometer. The idea is that the black and white sides of the vanes respond to different types of EM radiation differently. How it actually works is somewhat beyond me (and apparently contentious), but it does work: https://en.wikipedia.org/wiki/Crookes_radiometer
The second is is through boiling. If the side of the object facing the sun were composed of a material that boiled when exposed to sunlight, the boiling off of that material would provide thrust against the object in the same way a rocket provides thrust (by expelling gas).
Note that I am not a physicist, and am not proposing that either of these are the reason for the object's anomalous trajectory - just throwing out two ideas through which radiation could propel an object.