Could someone here explain briefly (or point me somewhere) the basic process through which someone is able to look at the sky and reliably say "there is grease floating out there umpty billion miles away"? I understand things like spectral emissions showing particular atomic elements, but does that extend to complex molecules too?
So, according to the abstract, this is looking at the absorbtion of a particular infrared band (3.4um). This band is presumably associated with the carbon-hydrogen bond, but I'm rusty on my IR spectroscopy so don't take my word on it. It's already known that there is attenuation of this band correlated with distance to a star, so they created molecules in the lab that mimic the absorbtion. This tells them how many molecules are needed to produce a particular amount of attenuation. From this, they can estimate the mass of a column between the Earth and a star, and extrapolate that to the Galaxy.
At the risk of sounding like a total idiot, could this explain some of the redshift seen at greater distances from earth. A.K.A explain away some of the expansion theory?
Very unlikely. They probably account for things like absorption when calculating redshift and the corresponding numbers that they're getting from their measurements. For instance, each star/galaxy has a spectral composition that can indicate what it's made of. This can be correlated with brightness for other stars and can be determined how bright it should be. Redshift would shift the entire spectral composition towards the red, while absorption would remove certain bands. There's probably many other ways they've verified redshift too that I'm not thinking of.
Also don't forget that these scientists are deeply immersed in their fields. Every single one of them has been through a PhD program and is an expert in some ___domain, likely a narrow one. When you are that good at something, even your shower thoughts (and especially your shower thoughts) will be scientifically productive.
We joke at my company that our contractors must charge us for thinking about our problems in the shower, but I must admit that I sympathize and wouldn't blame them if they did.
Even in CS I'm always amazed that an "easy" algorithm problem we expect a new grad to solve was solved in the 70s by CS professors who published papers about the topic.
As a self taught developer with no formal education in CS, I'm amazed to know this. I'd love to read a paper outlining the solution of a rather simple algorithm (by today's standards). Sounds fascinating.
edmonds-karp, dijkstra search, kruskal mst, floyd-warshall, bellman-ford, tarjans least common ancestor, danzig's simplex method, etc. are all algos that were paper pubs throughout last century, covered in CLRS i.e. good undergrad algos class, and come up in interview style questions.
In my understanding, the relevant quantity determining attenuation is the integrated amount of material in the column between the source and the observer. So, the small density is compensated by the large volume of column (distance to source).
This is tangentially related, but one of my favourite little spectral analysis factoids is that because of it Helium was discovered on the Sun before any samples of it were found on Earth. There's an explanation of the process in this link:
Yes, there is a whole field of organic infrared spectroscopy. Before we had more powerful instruments like NMR, it was one of the key ways molecular structures were elucidated.
You can get a good sense as to what functional groups are on a molecule with IR alone.
I'd say that "grease" isn't an appropriate word. Grease is greasy. The substance is based on the close interaction of molecules. These molecules are to far away from each other for there to be anything we could point to as grease. It's like finding H2O and saying that there is water up their. It is really steam, very thin steam spread over billions of cubic kilometers. So this isn't really "grease".
"Grease" was chosen by the science writers, astronomers call this stuff PAHs just like a chemist would. It condenses into "dust grains", so no, it's not only a gas. These reason you can't see much in the plane of our galaxy is that these dust grains block visible light.
I was trying to figure out why this material might be toxic, and the article explains nicely:
"Until now there has been uncertainty over how much carbon is drifting between the stars. About half is expected to be found in its pure form. The rest is chemically bound with hydrogen in either a grease-like form, known as aliphatic carbon, or as a gaseous version of naphthalene, the main chemical component of mothballs."
No, it wasn't added - it's a property of the physucs of our universe.
Hydrogen fuses into helium. Helium (by the triple-alpha process) fuses into novel isotopes of lithium and beryllium, which decay in attoseconds back into helium, unless the beryllium is fused with a third helium nucleus/alpha particle to form stable carbon-12. That carbon is in the presence of hydrogen, and is then blown off of the star surface, so you get interstellar mothballs wherever you have stars.
Clearly, the someone was whoever not within but above and before our universe. They wanted to guard their physics simulation against interdimensional pests.
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there was a House episode where someone was diagnosed with naphthalene poisoning due to termites in the walls. so following occams beliefs, we could also have lots of termites in space too. ;-)
It was just a matter of time that somebody from outer space would find us and conclude that we must be fumigated ASAP. All we need to find now is an huge spaceship shaped as an aerosol can
The Songs of Distant Earth by Arthur C Clarke makes it a large plot point that any vessel traveling through the stars would need some kind of "windshield" as mentioned in the article. His idea for implementing it seems as good as any to my layman imagination!
This is also the function of the "deflector" on ships in Star Trek. The idea being that when you're traveling that fast, even the tiniest debris will ruin your day, so you need something to push it out of the way.
Interestingly, this would apparently be a problem with Alcubierre drives from what I've read. The bubbles of spacetime around a ship would wind up "collecting" stray particles as it travels, then releasing them in a massive energetic burst when the bubble popped, probably annihilating anything in its path.
I've sort of decided one of the possible solutions for gamma ray bursts is just starships exiting to realspace.
>What would happen to radio transmissions from an Alcubierre drive fitted space ship while in transit?
I'm not an expert on the physics involved, but I imagine they would probably just get reflected back as Hawking radiation or something.
The point of the bubble is to separate an object entirely from our own universe, because while there is a limit to information travelling at the speed of light, and relativity makes it impossible for an object with mass to approach lightspeed, there are no such limitations on spacetime moving through spacetime.
If anything can cross the threshold and get into or out of the bubble in transit, then there is some degree of quantum entanglement and information transfer and it still counts as a "thing" in our universe, so I would assume the trick only works if the bubble is essentially a black box.
speculatory edit: this also seems to suggest that a ship in an Alcubierre bubble would be blind and unable to actually steer. I don't know if the bubble itself would decay (possible due to collisions with interstellar matter or some inherent instability) or would have to be collapsed from the outside. If the latter, then you need an existing infrastructure of stargate-like things already in place (either moved by conventional means or constructed) and just have to hope they're working and where you're aiming when you set off. There might be models that overcome these issues, I don't know.
If it turns out that Alcubierre drives are the only viable means of FTL, then one possible solution to the Fermi Paradox might lie in the complications inherent to using them - the civilizations that survive tend to be the ones that don't progress beyond simple rockets and radio telescopes, and FTL civilizations are still limited to expansion at below relativistic speeds, and even then the inherent complexity and risk means FTL travel isn't likely to be common.
>this also seems to suggest that a ship in an Alcubierre bubble would be blind and unable to actually steer. I don't know if the bubble itself would decay (possible due to collisions with interstellar matter or some inherent instability) or would have to be collapsed from the outside. If the latter, then you need an existing infrastructure of stargate-like things already in place (either moved by conventional means or constructed) and just have to hope they're working and where you're aiming when you set off.
I'm not sure even having stargates/mass relays would be enough if the bit about collected stray particles turning into omni-directional death-rays upon exiting the bubble is true. You'd need to somehow actually carve a clear path in space-time between any two points.
Alternatively, you might be able to create some sort of limiter and only do "short" hops that limit how much energy gets ejected upon exiting. If you're building up energy inside the bubble though, wouldn't it be putting some kind of strain or pressure on whatever has to maintain the bubble? Seems like that alone would create an upper limit on how much you can "charge" it up.
If I were writing this for a fictional setting, I would probably say that the bubbles act a bit like black holes, and decay over time. So the field's durability (and relative speed) is a function of the power used to create the field and apply the initial impulse to it.
And since heat and radiation may be factors inside the field, available shielding might also be a limiting factor.
And then I would solve the particle problem by saying the field somehow converts real particles into virtual particles and then put bars on my windows to protect against the bricks thrown by physicists ;)
This is one of my favorite Arthur C Clark books. What makes his books so interesting is that the technology aspects are very much sidelined by the human aspects. I don't think it appeals as much to people who enjoy hard sci-fi with a lot of jargon but I've always loved how interesting technological ideas are almost used offhandedly as plot devices but the real story is always the people (even if his concepts for the technology are groundbreaking to the reader or to the field at large).
Alastair Reynolds had his Lighthuggers (close to C capable interstellar ships) sheathed in a big shell of diamond I think (and cancerous machine growths in one case), which would be a cool sight.
I'm thinking it has more to do with spread than concentration. Trace amounts distributed over the entire universe, vs trace amounts in a localized area.
I wonder if this is a factor limiting interstellar travel. Where spaceships are not able to approach light speed because they will quickly accumulate a ton of space grease.
It wouldn't. Grease is slippery relative to e.g. metal sliding on metal, but still has friction. A vacuum has no friction at all, and so the tiny amount of matter present in space, hydrogen, this grease, dust, etc. can only slow you down.
That's true for a minority of living humans[1]. In the US, it's certainly not true for LGBTQ people, women, or racial minorities, all of whom have more rights now than we did in the 70s.
>That's true for a minority of living humans[1]. In the US, it's certainly not true for LGBTQ people, women, or racial minorities, all of whom have more rights now than we did in the 70s.
It could just as well be true for all of them as well (assuming it is for the rest of course).
The "but now X group has rights" argument doesn't mean much. Such rights are a small, and rather insignificant part of life. Women, gays, lesbians, and racial minorities had huge great movements and tons of fan in the 70s in their everyday life as well. It's not like their whole existence was diminished by how others conceived them or whether they had this or that law.
A black who had a steady Detroit job in the 70s in a nice home, family and so on, felt much better off than an unemployed same-aged man in Detroit today, even if the second has more nominal rights and articles about him now (not to mention that there are probably more police shootings of blacks today than in the 70s, and let's not even compare Trump to Carter or even Nixon on that regard).
Or go talk to gay people, and see how they feel about the 70s and 80s, and various scenes that existed then compared to today. You'd be surprised Living in a looser and laxer decade can be more important than having some right in some law book (gays then partied far more widely and extravagantly than the meagre contemporary scene where they have rights, sure, but society is run by prudes and money spoilt most scenes).
Heck, in the same period we had a full blow military dictatorship in my country, and people can still wax poetically about the times and the fun they had. Even people persecuted then and even tortured by the police at this point or another.
Or that grease can be captured processed and burnt to reach the speed faster, (though I'm reading elsewhere the density is so thin there's no point almost)
I would suspect that accumulated space grease is an insignificant factor when compared to a ship's existing energy/mass ratio and the effects of relativity and time dilation, where energy requirements and an object's apparent mass tend towards infinity as it approaches lightspeed.
It's probably no more a factor than how thick the paint is on the hull.
A relative speed of 0.1c would make every fully ionised helium atom into an overly wordy description of 18.64 MeV alpha particle radiation.
Low density regions of interstellar medium can have as few as 10e-4 particles per cubic centimetre. At 0.1c, that density works out as 3e10 particles/m^2/s. At that density and energy per particle, 0.0895 W/m^2. Low enough you wouldn’t care.
Molecular clouds, on the other hand, can be up to 10e6 particles/cm^3. Most of those molecules are hydrogen, so they don’t hit as hard on average… but that’s a rounding error compared to the density, so let’s say about half a gigawatt per square meter.
TL;DR — go around the molecular clouds until you invent a Trek-like navigational deflector.
Like I said, half a gigawatt per square meter. The front of the ship would be glowing with about the same luminosity from the stuff it hits as the total power output of the space shuttle engines during launch.
To be totally fair, FTL implies time travel, and even sub-light (but hefty fractions of light) lead to staggering time dilation effects. None of this is ever touched in most sci-fi and certainly not Star Trek. Everyone is sipping around at high multiples of lightspeed, yet no one ever remarks that they constantly arrive before they leave. They use impulse drives to go at high fractions of c, yet they never return to an Earth many thousands of years in their subjective future.
It’s a great series, but it’s not hard sci-fi, just a great storytelling mechanic.
True, but no one ever claimed (or should claim) that Star Trek was "hard" sci-fi.
At best, it sometimes tried, depending on the writer, to make nods to actual science. The original series seemed to have input from actual engineers and scientists, which is why you have the nacelles separated (to protect from radiation) and Bussard collectors, but then as time went on, it sort of became magic particles and subspace and not even bothering with the pretense.
Not with a big graphite shield - single molecules should just ablate it. However should you hit be unfortunate enough to hit one of those dust specks which are out there... big kaboom.
The whole thing is also a case for building spacecraft with as small a cross section as possible, less chance of hitting something large.
Any matter starts to resemble a nuclear detonation as you impact it approaching c. As your relative velocity becomes Relativistic in relation to the matter you’re impacting, the energy liberated increases in a non-linear scale. Grease, individual hydrogen atoms, anything. You’d really need some kind of exotic material, a few kilometers of ablative shielding, or “energy shielding” to make near-c velocities work. You’d be slowed down, but you’d also be blown to bits... tricky thing relativistic velocities.
Though its job is mainly to capture deuterium, I presume for propulsion. (In a fusion process? This is where Star Trek veers off into literary freedoms with the dilithium crystals and what not.)
This is hardly surprising, given what we know of how violently the universe was created. When a massive explosion occurs it propels matter everywhere. Some debris is large but there is plenty of dust.
Yes, gravity is a factor. But stars, planets, and galaxies have already formed. Within the solar system is higher, within the arms of galaxies is higher than without. There are also web like structures between galaxies that have higher densities.
The Article talks about interstellar space, aside from some occasional planemos, there are no substantial gravity wells outside of solar systems. It would probably move along according to the local standard of rest (~flow of material) in the galaxy.
And this material would also probably not get trapped inside solar systems to a large degree, because as the article notes, the solar wind has a greater infuence on it than gravity.
It's incredibly thinly spread out, so I doubt it. Yes, there's a lot of it, but space is almost unimaginably big. Places where carbon is concentrated like some planets, comets, etc. would be much more economically viable, and we're sitting on a planet with far more of this type of stuff than we need already.
Yes, but we can't carry this stuff (or much of it) with us on orbits or space, but if we collect and process it it may open some doors to space exploration.
Why are people here always downvoting jokes? I mean especially jokes. You could say something racist or otherwise bigoted and it would still be slightly better than jokes.
And also it's almost impossible to get upvotes. Why are we so toxic on here?
Jokes don't contribute to the discussion. They're generally considered noise rather than signal here.
HN's official policy is that it isn't reddit and doesn't want to be reddit. In my opinion, intolerance of jokes is the entire distinction between the two.
There's also the issue that jokes are often misunderstood and end up causing even more wasted text.
We know so much more about the universe, discovered a huge number of exoplanets, and still hold on to these traditional ideas. Carbon is essential to life as we know it, that's it.
