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Science and Astronomy Questions
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| PlutonianEmpire | Date: Wednesday, 05.10.2016, 06:24 | Message # 781 |
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| Watsisname, that's what I was figuring, thank you! 
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| midtskogen | Date: Wednesday, 05.10.2016, 09:01 | Message # 782 |
 Star Engineer
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| Quote Alek (  ) How big (or small, for that matter) would an asteroid have to be to make the air unbreathable a few hundred miles away
What do you mean by unbreathable? The first thing that would be lethal at that distance would be fires, either by direct thermal radiation (a few hundred miles away the fireball will be over the horizon) or through fires ignited by falling ejecta. If the object is more than a few km in diameter (it really depends a lot on its impact speed, though), you really want to be far enough away for the fireball to be below the horizon, or you want to be in a bomb shelter. But if you're closer than a hundred miles or so, the seismic effects will kill you anyway.
Quote Alek ( ) would anything of this size hitting earth cause a guaranteed extinction of the hunan race simply by the shockwave?
Absolutely not. To kill the entire human race you probably need something 1000 km across.
NIL DIFFICILE VOLENTI
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| Alek | Date: Wednesday, 05.10.2016, 17:36 | Message # 783 |
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| Quote midtskogen ( ) What do you mean by unbreathable?
I mean there being enough dust, soot, ect. caused by the impact and fires afterward to make a person need a gas mask to breathe, at least for the most part (gas mask being preferred but maybe not critical to breathing)
Okay, that definately makes sense, thank you.
Quote midtskogen ( ) Absolutely not. To kill the entire human race you probably need something 1000 km across.
Thought that might be the case but I wasn't sure. Again, thank you
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
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| apenpaap | Date: Wednesday, 05.10.2016, 20:09 | Message # 784 |
 World Builder
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| Quote midtskogen ( ) Absolutely not. To kill the entire human race you probably need something 1000 km across.
I think the increase in temperature would destroy the biosphere at much smaller sizes than that. Universe Sandbox 2 gives me boiling seas when the impactor is 300 km in diameter or so already.
I occasionally stream at http://www.twitch.tv/magistermystax. Sometimes SE, sometimes other games.
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| Tac1017 | Date: Wednesday, 05.10.2016, 20:53 | Message # 785 |
 Explorer
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| how much of carbon dioxide or sulfur dioxide is dangerous?
The Terra Hunter of the Milky Way!
(By the way, I was born in 2001, NOT 1972 XD)
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| Watsisname | Date: Wednesday, 05.10.2016, 22:04 | Message # 786 |
 Galaxy Architect
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| At one atm of pressure, a few percent of CO2 causes drowsiness and increased breathing rate, and anything above 5% becomes deadly.
Our tolerance for SO2 is a lot lower. We can smell it at just one ppm, 10ppm starts becoming very unpleasant, and anything over 100ppm will kill within an hour.
Quote midtskogen ( ) To kill the entire human race you probably need something 1000 km across.
To kill the entire human race just by the airblast, this sounds about right. It would be lethal even at the antipodal point. The energy of the impact would also literally blow off a significant chunk of the atmosphere (about 10% of it).
Much smaller impacts than this could still end up wiping out humanity completely, though. It just takes a bit longer. After the immediate effects of the fireball, airblast, and seismic shockwave are done, there will be a global firestorm due to the heating of re-entering material. This is then followed by "impact-winter", with the layer of soot and fine particulates in the atmosphere blocking out a large portion of the sun's energy and cooling the planet by tens of Kelvin. Even a 10km impactor striking ocean can do this, resulting in mass extinction.
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| Tac1017 | Date: Wednesday, 05.10.2016, 22:06 | Message # 787 |
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Explorer
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| how many psi is in ppm?
The Terra Hunter of the Milky Way!
(By the way, I was born in 2001, NOT 1972 XD)
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| Watsisname | Date: Wednesday, 05.10.2016, 22:11 | Message # 788 |
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Galaxy Architect
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| At Earth surface pressure, 1ppm is 1.5x10-5 psi.
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| Hornblower | Date: Thursday, 06.10.2016, 03:01 | Message # 789 |
 World Builder
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United States
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| So obviously, the universal limit for velocity is the speed of light, but is there a universal limit for acceleration?
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| Watsisname | Date: Thursday, 06.10.2016, 03:36 | Message # 790 |
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Galaxy Architect
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| Not as far as we know. The largest accelerations we can find are in nuclear physics, with radioactive decay. You might imagine a particle must experience a huge acceleration in order to reach a large fraction of the speed of light over the short distance of the atomic nucleus.
In fact, let's do an example for fun. Consider the fission of Uranium-235 by neutron capture. This nucleus has a neutron capture cross section of 3 barns for neutrons with an energy of about 104 eV. That's a neutron velocity of about 14km/s. The nucleus' diameter is about 15 femtometers. So for the neutron to be captured within that nucleus, it must undergo an acceleration of at least 1021 m/s2. Pretty impressive!
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| spacer | Date: Thursday, 06.10.2016, 03:56 | Message # 791 |
 Star Engineer
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Israel
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| does huge acceleration of the particles. so fast as blink of an eye (far far faster)
does it also means the g-force it feels is pretty big?
or g-force is something we only feel as big creatures or machines in free fall or turning fast in the road
"we began as wanderers, and we are wanderers still"
-carl sagan
-space engine photographer
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| DoctorOfSpace | Date: Thursday, 06.10.2016, 04:00 | Message # 792 |
 Galaxy Architect
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Pirate
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| You can calculate approximate g forces on particles, but I don't think it applies could be mistaken though.
Obviously there would be limitations on acceleration for macroscale objects, especially more complex things. Seems to me each object has a different material strength and eventually the forces of acceleration will exceed the objects capability to hold itself together.
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| Watsisname | Date: Thursday, 06.10.2016, 04:04 | Message # 793 |
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Galaxy Architect
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| Quote spacer ( ) does huge acceleration of the particles. so fast as blink of an eye (far far faster)
does it also means the g-force it feels is pretty big?
Definitely, but I don't think the particles really "feel" it... not that I have actually asked one. 
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| Hornblower | Date: Thursday, 06.10.2016, 04:08 | Message # 794 |
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World Builder
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| So is g-force the only limitation so far to acceleration. We would be able to calculate if there's a limit to g-force (perhaps to avoid creating a black hole) and by extension an actual limit to acceleration.
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| Watsisname | Date: Thursday, 06.10.2016, 06:03 | Message # 795 |
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Galaxy Architect
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| A productive avenue might be to consider limits on the ability to accelerate charges. Charges are accelerated by electric field, with acceleration equal to their charge times the field strength divided by their mass. Electrons have a large charge to mass ratio, so they are a good choice for a particle to accelerate. Then the question is how strong can an electric field be?
This is given by the Schwinger limit of ~1018 Volts per meter, above which the classical electric field breaks down and becomes nonlinear.
So, considering electrons subjected to this field strength, they would undergo an acceleration of about 1029 m/s2.
Added: This acceleration is so big that it is hard to contemplate. Here's a way to think about it:
To accelerate the electron to 10% of the speed of light, it would take only 10-22 seconds, and a distance of 2.5 femtometers. This is barely more than the width of a proton! If accelerated over the width of a hydrogen atom (~1 angstrom, or 10-10 meters), it would reach 99.999% of the speed of light!
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