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Watsisname
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### Re: Science and Astronomy Questions

A long time ago I did a simple calculation related to that. If you took every object in the Oort Cloud and squeezed them together into a flat, face-on disk at the same distance, how large would it appear on the sky? (In other words, what fraction of the sky do all the Oort Cloud objects take up, together?)  The answer is approximately the same as the apparent size of the planet Saturn on the sky. If you launched something in a random direction out of the solar system, the probability of hitting one of those objects is about one in ten billion. Or very close to zero.

So does the Oort Cloud dim our view of distant stars and rest of the universe? Absolutely not. It would be a rare event to even detect a stellar occultation by any Oort Cloud object with current telescopes and surveys. (As far as I am aware no such detection has even been made yet.)

midtskogen
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### Re: Science and Astronomy Questions

I think an estimate of objects in the Oort cloud and their sizes must be very approximate, but that one in ten billion chance for hitting something sounds reasonable.  A real figure within a few orders of magnitude can still be rounded to zero for practical purposes.

The asteroid belt is similarly often (extremely) incorrectly visualised as a densely packed region of rocks at bumping distance of each other.  In reality the chance of hitting something in the asteroid belt is extremely low, but surely greater than hitting something in the Oort cloud.

As for interstellar travel, I think the opposite is the case.  It's portrayed as something viable, but it's really more like Russian roulette.  Interstellar space is very empty, to a large degree "Oort cloud" empty, but if you're travelling several hundred or thousand lightyears, the chances of hitting something becomes something to consider.  The chances of hitting a large rock or even an asteroid sized object is still very, very small, but at speeds near (>99%) the speed of light, hitting something as small as a millimeter can be potentially catastrophic and there's no way to detect and avoid it if you're on a bad course.  So whilst we, by some magic form of propulsion, could travel to pretty much anywhere in the Milky Way within a couple of decades ship time if accellerating and decellerating at constant 1 G, the prospect of surviving it is pretty unknown and the low end of such an estimate would likely not be very encouraging.

The solution to the Fermi paradox could simply be that the aliens have calculated the odds of survival.
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longname
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### Re: Science and Astronomy Questions

Unless the Oort cloud can actually obscure some stars.....
Don't you realise how incredibly spaced out the asteroids there would be?
[dah<500,26>dah<180,14>dah<180,21>dah<500,19>dah<180,26>dah<500,21>]

Salvo
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### Re: Science and Astronomy Questions

Imagine being on the surface of Teegarden's Star b, which distance to its star is just ten times the distance between Earth and the Moon. An year on that planet is just 4.9 days!

Even if the planet is so close to its host star, the temperature is supposed to be very similar to that of Earth. So I was wondering... how much bright would that star be? It's a late M star so it's relatively cold, so maybe you could look directly at the sun like at sunset. Or maybe, since temperature is connected to flux/luminosity, it would look exactly as bright as our Sun since it's much closer.
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A-L-E-X
Galaxy Architect
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### Re: Science and Astronomy Questions

Could there be any water on that planet?  I heard there was recently a habitable planet discovered with water (at least in vapor form)?
Last edited by A-L-E-X on 31 Jan 2023 08:37, edited 1 time in total.

A-L-E-X
Galaxy Architect
Posts: 3498
Joined: 06 Mar 2017 20:19

### Re: Science and Astronomy Questions

I think an estimate of objects in the Oort cloud and their sizes must be very approximate, but that one in ten billion chance for hitting something sounds reasonable.  A real figure within a few orders of magnitude can still be rounded to zero for practical purposes.

The asteroid belt is similarly often (extremely) incorrectly visualised as a densely packed region of rocks at bumping distance of each other.  In reality the chance of hitting something in the asteroid belt is extremely low, but surely greater than hitting something in the Oort cloud.

As for interstellar travel, I think the opposite is the case.  It's portrayed as something viable, but it's really more like Russian roulette.  Interstellar space is very empty, to a large degree "Oort cloud" empty, but if you're travelling several hundred or thousand lightyears, the chances of hitting something becomes something to consider.  The chances of hitting a large rock or even an asteroid sized object is still very, very small, but at speeds near (>99%) the speed of light, hitting something as small as a millimeter can be potentially catastrophic and there's no way to detect and avoid it if you're on a bad course.  So whilst we, by some magic form of propulsion, could travel to pretty much anywhere in the Milky Way within a couple of decades ship time if accellerating and decellerating at constant 1 G, the prospect of surviving it is pretty unknown and the low end of such an estimate would likely not be very encouraging.

The solution to the Fermi paradox could simply be that the aliens have calculated the odds of survival.
Yes, and to be able to do with with some semblance of safety we would have to create some version of the alcubierre drive and keep it active until we're in a "safe" zone where local space is free of these objects.
I have always thought that the solution to the Fermi paradox is technological species are self destructive and any species that becomes technological only exists at that stage for a few hundred years at most.

But even the asteroid belt is more densely packed than the so called Oort "cloud" I wish they would retire the word "cloud" and change it to the Oort belt.
Last edited by A-L-E-X on 31 Jan 2023 08:18, edited 1 time in total.

A-L-E-X
Galaxy Architect
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### Re: Science and Astronomy Questions

Unless the Oort cloud can actually obscure some stars.....
The Oort cloud is very, very empty.  The planets of the inner solar systems are more packed than objects of any size to speak of in the Oort cloud.  You can zip through it with a spacecraft at any angle and the probability that you hit something is zero.  "Cloud" not really a good description.  But the Oort cloud is extremely big, so it can contain extremely many objects.
Yes if it was more densely packed we could actually see it as a "cloud"-- but we can't  It's just a term used to differentiate it from interplanetary space.  I never thought of it as something that could actually be seen but apparently that term has stuck, just as "electron cloud" has stuck in describing the area of the atom outside the nucleus (for different reasons of course.)
Unless the Oort cloud can actually obscure some stars.....

Don't you realise how incredibly spaced out the asteroids there would be?
I do, which is why I worded it in an incredulous way (beginning with my post with "this part makes no sense" to refute what was said earlier)....the term cloud is a misnomer.  The objects in the asteroid belt are much closer together.  I believe that the Oort cloud terminology should be changed to Oort belt.

A-L-E-X
Galaxy Architect
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### Re: Science and Astronomy Questions

A long time ago I did a simple calculation related to that. If you took every object in the Oort Cloud and squeezed them together into a flat, face-on disk at the same distance, how large would it appear on the sky? (In other words, what fraction of the sky do all the Oort Cloud objects take up, together?)  The answer is approximately the same as the apparent size of the planet Saturn on the sky. If you launched something in a random direction out of the solar system, the probability of hitting one of those objects is about one in ten billion. Or very close to zero.

So does the Oort Cloud dim our view of distant stars and rest of the universe? Absolutely not. It would be a rare event to even detect a stellar occultation by any Oort Cloud object with current telescopes and surveys. (As far as I am aware no such detection has even been made yet.)
Thanks Wat-- how large would all the objects of the asteroid belt be if put together?  Of course the density calculation would need to be different since the volume of the asteroid belt (including space) is much smaller than that of the Oort cloud region.  It would be interesting to compare the density of one to the other-- of course the asteroid belt should have a much higher density since its total volume including space is much smaller.  Another reason to retire the term cloud and call it the Oort belt.

By the way did you hear about the asteroid that passed within 2200 miles of the earth's surface, right over the southern tip of South America the other night? It passed within the orbits of many satellites and I heard parts of it might have broken off and become fireballs and landed as small meteorites?  Did you see any news on that or the visibility of the objects from the ground?

Mr. Abner
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### Re: Science and Astronomy Questions

Personally, I think cloud is the right descriptor — after all is it not spherical in shape? Whereas a belt is more or less a ring. And where in the definition of "cloud" is there mention of a specific density?

midtskogen
Star Engineer
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### Re: Science and Astronomy Questions

Yes, and to be able to do with with some semblance of safety we would have to create some version of the alcubierre drive and keep it active until we're in a "safe" zone where local space is free of these objects.
I have always thought that the solution to the Fermi paradox is technological species are self destructive and any species that becomes technological only exists at that stage for a few hundred years at most.
I don't buy that.  Interstellar travel (beyond the stellar neighbourhood within a few generations) is likely impossible.  I see two reasons for that:

1. It requires too much energy, and an energy source needs to be carried with the craft.  Lasers from Earth or other means of wireless energy transfer are short range, and fuel scooping wont work either: Not enough mass in interstellar space, and if it were, drag would prevent it from to work anyway.  Obviously, anything chemical wont work as we just barely get things into orbit.  Even if we find a way to fuse hydrogen to iron for maximum energy density and can convert 100% of that to kinetic energy, I think the maths will fail, since the practical way to travel is by 1 g accelleration to near-lightspeed and that will still require enormous amounts of hydrogen fuel.  As for anti-matter fuel, still impossible.  The mass needed to contain anti-matter likely outweighs the pure energy-mass itself by magnitudes of order.  Warp drive is likely impossible for more than one reason, and its energy needs prohibitive by magnitudes of order.

2. Too dangerous.  Even if we could make a 1 g drive reaching near light-speed, interstellar matter would kill passengers at a random time.  A tiny grain would have enormous kinetic energy.  And even if that wasn't a problem, random atoms in interstellar space would make travel at near-lightspeed like being inside the universe's most powerful particle accellerator.  And passengers need to stay there for years.

People have known about the vastness of space and thought about interstellar travel for a century.  Still, it appears that no one has yet presented calculations proving it possible.
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Watsisname
Science Officer
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### Re: Science and Astronomy Questions

Personally, I think cloud is the right descriptor — after all is it not spherical in shape? Whereas a belt is more or less a ring. And where in the definition of "cloud" is there mention of a specific density?

Exactly.   We use belts to describe diffuse but disk-like distribution of objects, and clouds for diffuse but more spherical distribution of objects.

Watsisname
Science Officer
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Joined: 06 Sep 2016 02:33
Location: Bellingham, WA

### Re: Science and Astronomy Questions

Yes, and to be able to do with with some semblance of safety we would have to create some version of the alcubierre drive and keep it active until we're in a "safe" zone where local space is free of these objects.
I have always thought that the solution to the Fermi paradox is technological species are self destructive and any species that becomes technological only exists at that stage for a few hundred years at most.
I don't buy that.  Interstellar travel (beyond the stellar neighbourhood within a few generations) is likely impossible.  I see two reasons for that:
I agree. I think this is also likely to be part of the explanation for why we don't see obvious evidence a galaxy colonized with advanced life, because if even one civilization arose that could and decided to do this, it would achieve effectively complete galactic colonization on a much shorter timescale than the age of the galaxy. Otherwise, if fast (near light speed) interstellar travel were practical, the explanation must be that life advanced enough to do it must be outrageously unlikely to have developed over the entire history of the galaxy (and not simply that it must remain advanced for a very short time), which I don't think I buy. Or we are still unable to detect evidence of galactic colonization, or it deliberately avoids our detection, which I don't think I buy, either.

A-L-E-X
Galaxy Architect
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### Re: Science and Astronomy Questions

Personally, I think cloud is the right descriptor — after all is it not spherical in shape? Whereas a belt is more or less a ring. And where in the definition of "cloud" is there mention of a specific density?

Exactly.   We use belts to describe diffuse but disk-like distribution of objects, and clouds for diffuse but more spherical distribution of objects.
Is it really spherical though or more like a torus?  I always envisioned it like a torus because there is the "hole" in the middle (where the planets are.)
Last edited by A-L-E-X on 02 Feb 2023 08:03, edited 1 time in total.

A-L-E-X
Galaxy Architect
Posts: 3498
Joined: 06 Mar 2017 20:19

### Re: Science and Astronomy Questions

Yes, and to be able to do with with some semblance of safety we would have to create some version of the alcubierre drive and keep it active until we're in a "safe" zone where local space is free of these objects.
I have always thought that the solution to the Fermi paradox is technological species are self destructive and any species that becomes technological only exists at that stage for a few hundred years at most.
I don't buy that.  Interstellar travel (beyond the stellar neighbourhood within a few generations) is likely impossible.  I see two reasons for that:
I agree. I think this is also likely to be part of the explanation for why we don't see obvious evidence a galaxy colonized with advanced life, because if even one civilization arose that could and decided to do this, it would achieve effectively complete galactic colonization on a much shorter timescale than the age of the galaxy. Otherwise, if fast (near light speed) interstellar travel were practical, the explanation must be that life advanced enough to do it must be outrageously unlikely to have developed over the entire history of the galaxy (and not simply that it must remain advanced for a very short time), which I don't think I buy. Or we are still unable to detect evidence of galactic colonization, or it deliberately avoids our detection, which I don't think I buy, either.
I feel like the Fermi barrier lies ahead of us because of the great challenges we face as a species and multiple extinction level threats all going on together.  Aside from space travel, if continuous exploration and observation over the next 100 years provides no evidence of technological life anywhere even with better and better technology, I think this is the only conclusion that we can come to.  That technological civilizations exist for a relatively short period of time before falling back down or even going extinct.

While "galactic colonization" seems extremely unlikely to me too (and unnecessary-- I don't think there would be any urge to do that), relative stellar neighborhood colonization (that is within a radius of anywhere from 25 LY to 100 LY) should be possible across several generations even at sublight speeds (and I'm talking about 0.1c).
Last edited by A-L-E-X on 02 Feb 2023 08:02, edited 2 times in total.

A-L-E-X
Galaxy Architect
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### Re: Science and Astronomy Questions

https://studyfinds.org/ai-discovers-8-n ... o-signals/

How reliable could this be-- for example would it be able to tell the difference between a gamma ray burst and an "unnatural" signal (whatever that means.)

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