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Science and Astronomy Questions
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| Hornblower | Date: Thursday, 06.10.2016, 12:00 | Message # 796 |
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| Watsisname, thanks, that is really intriguing, but that is for a massive electron. I bet a neutrino could accelerate a lot faster!
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| Huesudo | Date: Thursday, 06.10.2016, 13:22 | Message # 797 |
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Observer
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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?
or g-force is something we only feel as big creatures or machines in free fall or turning fast in the road
I'm not sure if I can answer your question. G-force IS acceleration. Indeed your eyelids must experience quite a lot when you blink, but they are not very massive and their inertia is very small, so they can cope with high acceleration without any trouble.
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| Watsisname | Date: Thursday, 06.10.2016, 16:27 | Message # 798 |
 Galaxy Architect
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| Quote Hornblower ( ) atsisname, thanks, that is really intriguing, but that is for a massive electron. I bet a neutrino could accelerate a lot faster!
That's a good thought -- the neutrino has very low mass -- but there are two problematic things with them. The first is that their masses are very poorly constrained. We know they are not massless since they experience a passage of time (the neutrino oscillation), but it is very difficult to measure what their masses are. The second problem is that they have no electric charge, so they are not accelerated by an electric field. We would have to instead consider interaction through the weak nuclear force. This can be stronger than the electromagnetic interaction, but only over much shorter distances. The nuclear forces are essentially limited to the scale of atomic nuclei.
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| midtskogen | Date: Thursday, 06.10.2016, 20:58 | Message # 799 |
 Star Engineer
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| How does time dilation work for the accellerated particle in this case?
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Thursday, 06.10.2016, 21:55 | Message # 800 |
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| It definitely becomes significant at these kinds of speeds. Here's how we figure it all out. In this case, let's go really crazy and accelerate the electron through this huge electric field strength for a distance of one meter. Recall it only took a few proton widths to reach 10% the speed of light!
To find the time dilation, we need the electron's velocity. To find its velocity, we need its kinetic energy. Actually, that's how I had planned to work this out, but ended up doing it in a different sequence. At any rate:
The relativistic kinetic energy of a particle is not the familiar 1/2mv2 that we learn in Newtonian mechanics. It's a good approximation at low speeds, but fails for large speeds. It incorrectly predicts energy goes to infinity as velocity goes to infinity. The correct relativistic version is:
where gamma is a factor related to its velocity:
We can also define the ratio of v/c (that is, the fraction of the speed of light) as a new number "beta" to make things a bit simpler:
It turns out that gamma also happens to be the time dilation factor. If gamma equals 2, then the time interval in the moving frame is twice as long as in the rest frame. Time passes more slowly by a factor of 2.
In computing the electron velocity, we use the change in its kinetic energy through conversion of electric potential energy by moving through that potential difference. So let's suppose it accelerates (from rest) through the potential difference of 1018 Volts per meter, for a distance of one meter. Its loss in potential energy is its charge times the potential difference, which is 0.2 joules. Which is also how much kinetic energy it gained. 0.2 joules is huge for an electron! In nuclear physics we also commonly define particle energy by the electron volt, which works out simply in this case as 1018 eV. A billion billion electron volts is a lot. 
Now let's relate that to the time dilation factor. If KE=(γ-1)mc2, then γ=KE/(mc2) + 1. The plus one becomes irrelevant here -- mc2 is tiny and 0.2 divided by it is huge. We get 2.44x1012! So time for this electron is passing about two and a half trillion times more slowly than time for us! A single second in its existence is over 77,000 years in the life of the universe!
Now we can go from this dilation factor to its velocity, as a fraction of the speed of light:
Plugging in 2.44x1012 for gamma, we get:
β=0.999999999999999999999999916c
[Holy ****]
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| steeljaw354 | Date: Thursday, 06.10.2016, 22:10 | Message # 801 |
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| What if Earth had a moon the mass the same as the one I have showed and had a rotation period of 6 days and looked the same as the one shown?
Edited by steeljaw354 - Thursday, 06.10.2016, 22:28 |
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| Tac1017 | Date: Thursday, 06.10.2016, 22:38 | Message # 802 |
 Explorer
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| two things:
1: Tides would be gigantic, and catastrophic. This is because of how massive the new moon would be, roughly as massive as earth. The gravitational pull would be greater, and more disaster. It's why i only look around K1-K3 dwarfs for earth-like planets, since the pull is suffice without a moon.
2: it wouldn't really be a moon, but instead a binary planet, since the barycenter would most likely be outside the earth.
The Terra Hunter of the Milky Way!
(By the way, I was born in 2001, NOT 1972 XD)
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| steeljaw354 | Date: Thursday, 06.10.2016, 22:44 | Message # 803 |
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| Tac1017, I don't think 0.0199 Earths is roughly as massive as the Earth itself.
The Scenario:
The Mars sized object never hits the Earth, and instead that Moon settles into an orbit. It is likely to be eccentric and about the distance from earth to our moon. It keeps it's rotation period and never gets tidal locked
Questions:
What would the system look like in space engine, properly? How long would a day be on Earth? What would intelligent life think of that moon?
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| midtskogen | Date: Friday, 07.10.2016, 16:40 | Message # 804 |
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| Brilliant, Watsis. Accellerated particles experience a universe pretty different from ours.
NIL DIFFICILE VOLENTI
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| Watsisname | Date: Friday, 07.10.2016, 23:28 | Message # 805 |
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| Totally. Another fun fact:
If we imagine that particle slamming into Earth, from its frame of reference the Earth's atmosphere (which I'll take to be 100km thick by the convention of where space begins) is only 41 nanometers thick. This is below the limit of what you can see with an optical microscope (~200nm). The whole Earth would be about the thickness of a particle of baker's yeast.
To calculate, the relativistically contracted length equals the length in the rest frame, divided by the dilation factor (gamma).
When two relativistic particles collide, it is not like two spheres hitting each other. It is more like two flat disks hitting each other. We can (indirectly) observe the effects of this in particle accelerators.
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| steeljaw354 | Date: Saturday, 08.10.2016, 01:10 | Message # 806 |
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| Watsisname, How would Earth be different with a moon like the one I suggested on page 54?
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| PlutonianEmpire | Date: Saturday, 08.10.2016, 01:27 | Message # 807 |
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| Psychologically speaking, why do a lot of people find disappointment in answers from scientists? Like for example, the answer that we can never ever achieve true FTL like in Star Trek/Star Wars, or the answer that Alf Cen cant have Gas giants like Avatar, or that Astrology is bogus?
Specs: Dell Inspiron 5547 (Laptop); 8 gigabytes of RAM; Processor: Intel® Core™ i5-4210U CPU @ 1.70GHz (4 CPUs), ~2.4GHz; Operating System: Windows 7 Home Premium 64-bit; Graphics: Intel® HD Graphics 4400 (That's all there is :( )
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| steeljaw354 | Date: Saturday, 08.10.2016, 01:29 | Message # 808 |
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| PlutonianEmpire, Science has many things unanswered, some believe that what they say is fake since they can't see it for themselves, the roundness of the Earth for example. They want to see what they want to see, not 'boring' answers from scientists.
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| Watsisname | Date: Saturday, 08.10.2016, 06:21 | Message # 809 |
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| Quote PlutonianEmpire ( ) Psychologically speaking, why do a lot of people find disappointment in answers from scientists?
A few reasons, I think. The obvious one is that sometimes people like believing things even if they're not supported or even contradicted by evidence, so it can be like science is ruining it for them.
Another is a problem of communication by scientists -- they spend many years working and communicating with one another with a technical jargon, which is hard for most people to access. And it's difficult for scientists to explain complex ideas in common language. The physics program at my college emphasized this difficulty by trying to get students to explain usual physics terms and concepts in common language. It's surprising how difficult it is for students to describe something as simple as 'acceleration' without using words like 'velocity' and 'per'. When you get to more advanced topics, explanations can be so filled with jargon or rely on previous knowledge that it becomes indistinguishable from 'techno-babble', and the people you explain it to might wonder what the heck it all means or how did you figure it out or how do you have any confidence in it or why should it be important to understand? I think this is a very hard problem in popular science reporting, and I have huge respect for people who are skilled at it. I try but think I am not very much good at it.
Lastly there are people who think the scientific process takes a lot of the mystery and wonder from nature, and turn it into some cold, mechanical explanation. Which I personally disagree with, and love Feynman's quote on it. I think studying nature and understanding how things work brings me an even stronger sense of wonder than I had before. It makes me more curious and raises new and fascinating questions.
Quote steeljaw354 ( ) Watsisname, How would Earth be different with a moon like the one I suggested on page 54?
To be sure I understood correctly, are you saying if the moon has an orbital period about the Earth of 6 days (so a smaller orbit), in addition to the larger mass?
0.0199 Earth masses is about 62% more massive than the Moon, so this would not in itself be a huge change. It would make tides 62% larger. But if its orbital period is just 6 days, then its distance must be reduced to about 140,000km, or 36% of its current orbital distance. This will have a very big effect.
The strength of the tidal force is proportional to the mass of the satellite and inversely proportional to the cube of its distance. Meaning if the moon is brought in to a third of its previous orbital distance, then the tidal force becomes 3^3=27 times stronger. A 62% more massive Moon with 36% less distance would make the lunar tidal force 35 times stronger! The current max tidal change is in the Bay of Fundy, Canada, at 16.3 meters. However, we can't just multiply that by 35 to get the new max tidal change, because part of the tidal change is due to the Sun, not just the Moon. Solar tidal force is about half as strong as the Moon's. This means about two-thirds of the current tidal change is caused by the Moon.
So the new, bigger, closer Moon would raise a maximum tide difference of 16.3*2/3*35 = 380 meters! And more average tidal changes around the world would be about 60 meters.
We can get a rough idea for how much of the world would be subjected to the new tidal change zones by matching maps of global tidal variation to maps of areas affected by sea level rise. Note that coastal tide variation is generally bigger than the variation over open ocean, due to how the tidal surge sloshes around local terrain.
I currently live about 30 meters above sea level on a bay, which experiences tide changes up to about 3 meters. The bay goes down to about 30 meters of depth. In this new Moon scenario, high tides would reach just above my house, and low tides would drain the bay out completely. Wow!
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| PlutonianEmpire | Date: Saturday, 08.10.2016, 06:46 | Message # 810 |
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| Actually I can quite relate to the difficulty of explaining the technical jargon I know to the average layman. My roommate, for example, has a hard time understanding the mechanics of just how our season changes even work, and I have had to it at least twice a year.
Quote steeljaw354 ( ) They want to see what they want to see, not 'boring' answers from scientists.
Yeah I think this explains a lot of it. I know Ive felt this way a few times myself, unfortunately. 
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