Ask Anything Wednesday - Engineering, Mathematics, Computer Science

Submitted by AutoModerator t3_ywvph3 in askscience

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Engineering, Mathematics, Computer Science

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

Answering Questions:

Please only answer a posted question if you are an expert in the field. The full guidelines for posting responses in AskScience can be found here. In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for /r/AskScience.

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Past AskAnythingWednesday posts can be found here. Ask away!

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EchoReflection t1_iwm2kcx wrote

How exactly do the detectors in the LHC at CERN detect? How are all the different sizes, speed, and masses of particles detected? What is the science behind it?

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physicswizard t1_iwmas17 wrote

There are several different types of detectors in use, with each one specialized to detect specific particles or measure specific quantities, so the answer varies. Look up "silicon trackers", "hadronic/electromagnetic calorimeters", and "muon detectors" for some examples.

In general, the particles radiated by the collisions register "hits" with multiple detectors, and based on the trajectory of these hits and the energy deposited at each one, you can figure out the properties of the particle that made them (e.g. charge, momentum).

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Pharisaeus t1_iwmiris wrote

That's a complex question:

  • Charged particles passing through certain materials can induce electrical charge, so if you create a grate (lots of crossed strips, once a particle hit one you can see the voltage change) you can figure out where particle hit it. Now you can place multiple of those one after another, and this allows you to see how the particle trajectory was changing (eg. that it was curved)
  • Now you can create electrical field between those grates, you can figure out how much this electrical field is bending the particle trajectory (which is proportional to the particle momentum) and in which direction (which is related to the charge)
  • Finally you can make impenetrable shield at the very end which will completely stop the particle, and by measuring the impact you can figure out how much energy was this particle carrying.
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mfb- t1_iwnt52b wrote

> Now you can create electrical field between those grates, you can figure out how much this electrical field is bending the particle trajectory (which is proportional to the particle momentum) and in which direction (which is related to the charge)

A magnetic field.

> Finally you can make impenetrable shield at the very end which will completely stop the particle, and by measuring the impact you can figure out how much energy was this particle carrying.

Calorimeters are most important for uncharged particles (especially photons and neutral kaons) as we can't measure their energy in other ways. For charged particles the tracking system is typically more precise.

They are not the outermost detectors as muons still pass through and get detected in specialized muon chambers outside.

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pM-me_your_Triggers t1_iwmsbd1 wrote

Depends. One of the common sorts of detectors is called a scintillation detector, basically it’s a big hunk of special plastic/glass with a camera attached to it. When particles decay inside the material, they release photons of specific energies. These photons are then detected by the “camera” and the intensities of the photons can be used to figure out what particles decayed and what the energy/mass of the particle was.

Another kind of detector relies on a semi conductive tube with a thin wire passing through it and an inert gas filling the space (proportional tube particle detector). The exterior tube is grounded relative to the wire, which is held at a high voltage to induce a steep electric gradient inside the tube. Decays and electrically charged particles passing through the tube will create a pulse along the wire, which can be measured.

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Luxuriousmoth1 t1_iwn5vgf wrote

In Back to the Future part 3, the gang is forced to hijack a train to push the DeLorean up to 88mph after it's gasoline fuel tanks are accidentally punctured and emptied.

However, the train is only needed to get the DeLorean up to speed. The time circuits are powered by electricity, which the Mr. Fusion reactor is still able to provide.

Instead of a train, could they have used electric motors of the era (1885) to push the 2700lb DeLorean up to 88mph?

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ukezi t1_iwo0flu wrote

The first diesel engines were build in the 1890s so that is out. Also they were great cast iron motors, probably heavier then the car, with quite low power.

I think his best bet would have been to patch up the tank and use ethanol as fuel.

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atomfullerene t1_iwql5qc wrote

I don't think so. Electric motors were still quite primitive at the time. Also it would probably be very difficult to actually get one out in the west. Trains were much more accessible.

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Edgar-Allan-Pho t1_iwowkcs wrote

High acv alcohol (whiskey,vodka,moonshine, etc) strung up in a can or bottle with the fuel hose connected would of been just fine for a temporary fuel source.

Electric motors were extremely inefficient then and having the means to connect them to the power train or wheels would of been a ton of work that would require a forge, precise engineering and hundreds of hours of work.

Then there's the batteries, they would of needed a ton of amperage go get up to 88mph so a couple hundred pounds of batteries, they could of stolen them but that's a lot of batteries

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Nwadamor t1_iwmafzn wrote

What is space "expanding" into?

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theCumCatcher t1_iwmbql7 wrote

Itself. It's not expanding into anything there's just more of it all the time.

There's nothing outside of the universe.

If there was we would need to change our definition of universe.

The Big bang wasn't an explosion in space it was an explosion of space.

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Nwadamor t1_iwmc3t6 wrote

What do you mean expanding into itself. You are saying more space is being "created"?

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warblingContinues t1_iwmgqh8 wrote

It means that the overall volume of space is increasing over time. There isn’t anything that the inverse sits in or expands into. We make measurements of how far things are from us in the universe and these objects get farther away in a manner not due to, say, moving through space. We deduce that the volume of space itself is increasing.

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Nwadamor t1_iwmh07n wrote

Cool. But where is the extra volume coming from?

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ashara_zavros t1_iwmmagr wrote

There’s no Conservation of Volume law in physics, mate: the volume doesn’t come from anywhere.

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theCumCatcher t1_iwnb4ep wrote

why does it have to come from anywhere?

okay...maybe it'd be simpler to explain it mathematically.

it's like the coordinate system is changing so there are more points, all the time.

there are more grid squares every time we look.

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Clearlybeerly t1_iwnm15n wrote

>We deduce that the volume of space itself is increasing.

so if there's no "outside" of the universe, what exactly is expanding "space", and what is this "non-space" it is expanding into and the universe?

Is it a balloon within a balloon, where the inner balloon is space, the outer ballon is the universe, except the other ballon is infinitely big, but the inner balloon called "space" is not infinitely big? If so, what is outside of space, as opposed to the universe, because the universe is not the same as space.

Or is space expanding into space, and you just have infinite balloons all the way down?

Just made me think - if space is expanding, are the molecules within by body expanding? If I lived for 20 million years, would I be a 7'10" man instead of my 4'11" height and so then in 20 million years I can finally get into the NBA?

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Ape_Togetha_Strong t1_iwnnet8 wrote

Why do you feel that space has to expand "into" something? "Into" requires some sort of spacial relationship. If there was something for space to "expand into" then that would just be space.

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Clearlybeerly t1_iwnnt0x wrote

So what does it mean when it is said that "space is expanding"? Is that misnomer?

How can space expand if it isn't expanding?

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Ape_Togetha_Strong t1_iwno8l3 wrote

I didn't say that it doesn't expand. I asked why you feel that there has to be something for it to expand into for it to expand.

Expand is just the best word we have for what space does, it doesn't mean it has to be exactly like other sorts of expansion you can think of.

Space is expanding. Space is not expanding into anything. The distances between things are just getting bigger.

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nivlark t1_iwnsmrq wrote

"Expand" is simply the closest English word to describe a particular behaviour we observe in distant objects.

For a more precise description, you need to turn to mathematics: an expanding space is one where the "metric tensor" - the mathematical object in general relativity that tells you how to calculate the distance between two points in curved spacetime - is time-dependant.

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Clearlybeerly t1_iwoaqmb wrote

OK, thanks. I looked up metric tensor on wiki and looked up other hyperlinks in the metric tensor entry, and I have a very, very vague understanding, but it sure does help me understand, because while I have a vague understanding, what it mainly does is allow me to cut away the extraneous. So very cool, thank you.

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ShortysTRM t1_iwo7t7j wrote

From what I can tell, these people keep referring to any type of known matter existing anywhere in any amount as "space," ignoring the infinite void that you and I and everyone else seem to be wondering about. I think they're saying that all matter in the void is expanding outwardly from one singular point, not that there isn't an endless expanse of nothingness for it to expand into. I don't know this for sure, but the ones who do seem to be ignoring the entire concept of "yes, the paint is expanding onto the blank canvas, but how big is the canvas, and does it ever end?"

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clintontg t1_iwob1w7 wrote

Space isn't matter, it is what matter exists inside of. And the space is expanding in all directions simultaneously, irrespective of a single point. An analogy would be like zooming in on the cartesian coordinate system and seeing more points appearing between the grid lines. So the distance between "1" and "2" increase despite our ruler staying the same length.

As for what space is expanding into, it's a bit of semantics and a bit of scientific definitions/limitations. There is no proof of there being more than 3 spacial dimensions and the universe is defined as the thing containing all of the space, matter, and energy in existence. So as far as we can see there is no "outside" of the universe. It's an all encompassing, self contained thing.

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boraras t1_iwo36wz wrote

Is it like the "CSI enhance" feature but in reverse? Like you can keep zooming out indefinitely and see more of what was already there?

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Vietoris t1_iwpdr99 wrote

When we say that space "expands" you probably imagine in your head watching something that grows in front of you. For example, you inflate a balloon and watch it expand, and you imagine that what is inside this balloon represents the universe that is expanding into the ambiant space where you are.

This is the wrong way to look at things, because it relies on that notion of "ambiant space"

Instead, imagine that you are Pac-Man, living in the Pacman world. For the sake of the example, let's say that the Pac-Man screen is 10m wide. For you the the world is finite and is exactly 100m^2. But more importantly, if you walk straight in the horizontal direction, you will get back to where you started after 10m. Same thing if you walk straight in the vertical direction (that's the main feature of the PacMan world). For Pac Man, there is absolutely nothing outside this 100m^2 of land. There is no "ambiant space" where this 100m^2 land sits in. There are no "exterior wall" walls in the Pac-Man universe.

Now, imagine that by some mechanism, the ground of the universe is getting bigger. The mechanism itself is not important, but you can imagine that the ground of the Pac-Man world is made of metal, and that you are applying heat to that metal (and metal expands when it's getting hotter). The metal will expand a little bit, by 10% in each direction for example. Now the world, is no longer 100m^2 but is 121m^2 . Now you have to walk 11m in the horizontal direction to get back where you started.

And yet, the Pac-Man universe didn't expand into an already existing piece of land. As there are no "borders" to th Pac Man universe, you cannot consider that the borders have moved further. It's just the ground that you are walking on that gets bigger.

This is the picture that you should keep in mind when imagining the universe expanding. Not as an outside observer, but as someone inside. "Expanding" just means that there is more space to cover to get from point A to point B.

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oh-propagandhi t1_iwmdhc6 wrote

What's our current situation with rocket propulsion? My latest update (which is quite dated) is based on an "XKCD what if" that essentially spelled out that we don't have nearly enough rocket fuel a lot of stuff off the planet "to get everyone off the earth comfortably" like a Wall-e type scenario. I know we have looked at railgun type situations as well as a space elevator. Have there been any new discoveries that are leading us to getting off the planet with fewer or different resources needed?

Edited for clarity.

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Pharisaeus t1_iwmh05m wrote

> we don't have nearly enough rocket fuel

This is completely wrong. Consider that many rockets fly using hydrolox engines -> they burn hydrogen and oxygen (in fact this is the most energetic bi-propellant mixture!). And you can get those by... splitting water :) So no, we're definitely not missing rocket fuel.

The issue is more about how inefficient this is, because fuel is heavy. It's sometimes called "tyranny of rocket equation". Adding more and more fuel to your rocket very quickly no longer provides any gains, because most of the fuel is wasted on lifting the fuel itself. Some sci-fi idea (but founded in science!) how this could be fixed would be to use matter-antimatter as fuel, because the amount of energy you can get from tiny amount of mass is huge.

> Have there been any new discoveries that are leading us to getting off the planet with fewer or different resources needed?

There are some crazy ideas like SpinLaunch, and some new rockets are working with methane instead of kerosene or hydrogen, but this is not really any special "revolution".

There is some new interest in nuclear-thermal rockets, but those are more interesting for travelling around the solar system and not lifting from the ground.

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oh-propagandhi t1_iwminsg wrote

I was slightly mistaken, it was "Enough to get everyone off the earth comfortably" like a Wall-e type scenario.

Thanks for the insight!

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noiamholmstar t1_iwq9yje wrote

In addition to the other poster, you have to think about how much other stuff you need to lift into space per person. If each person needs about a metric ton of stuff in order to survive once they're in space, then we would need to launch 8 billion tons of stuff into space. And that's not counting the mass of the vehicle to get them into space. Even if we figured out how produce enough antimatter and how to reliably contain it and use it as a fuel, thats still an epically large amount of mass to lift into orbit. Just building the ships and infrastructure to fuel and launch them would be a monumental task. It's as much an economic/labor/political challenge as an engineering one.

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oh-propagandhi t1_iwqcsxg wrote

Thanks for the insight. That's more what I was talking about. It's the thing that made me realize that space exploration is neat and important, but it's currently statistically meaningless to my life and the life of even my kids as far as a sci-fi type scenario where we all just kick around in space with our space dogs or whatever.

That's before you get into all the "not supporting life" problems of every other body in our solar system, and the "can't get out of the solar system with current tech" problem.

It's a hard splash of reality and I'm mostly curious about any new news on breaking that barrier where jet setting around space becomes a reality.

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swiing t1_iwn0aul wrote

Do people in Northern Latitudes still produce Vitamin D in the winter? Is it proportional to the amount of UV * exposed skin or is there a minimal level of UV required to generate any Vitamin D?

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Indemnity4 t1_iwnqikv wrote

Anyone living north of the 37th parallel gets effectively zero vitamin D from sunlight during the winter months (e.g. north of Los Angeles in the USA).

The UV index needs to be > 3 to generate any vitamin D. During those northern months no amount of sun exposure will cross that threshold. Basically, if you need to wear sunscreen, the UV index is high enough to make vitamin D.

The time exposure between min UV and max UV is minor. 5 minutes at the sunniest day and 15 minutes at the dimmest day. After that it falls off a cliff and no amount of sun will help.

Instead, you are rely on stores your body built during the summer months.

There are some limited dietary sources. Fatty fish such as salmon or tuna, eggs, mushrooms or fortified foods.

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swiing t1_iwo1hzq wrote

Thanks Indemnity4. Sounds like I need to head south for the winter.

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PieMastaSam t1_iwlldwd wrote

Why couldn't someone simply run an encryption algorithm in reverse to crack a hash (I'm not sure if I am asking this correctly lol)? I'm thinking of something like AES. Also, if it is possible can someone explain AES in a eli5 manner.

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physicswizard t1_iwlyj3k wrote

Hash functions are designed to be easy to perform, but difficult to undo, and multiple inputs could map to the same output. As an analogy, think about adding two numbers. It is simple to say 2+3=5, but if I gave you the number 5 and asked which two numbers I added together to get that, there are multiple answers. Now imagine the operation is even more complicated than addition, involving bit shifts, elliptic curves, etc.

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calcopiritus t1_iwnxzeb wrote

While you have received many answers on the AES thing, I've only seen one on the hash question.

Hashes are not difficult to reverse, they are impossible. That is because you lose information when performing a hash.

It's easy to see if we use the modulus operator (%). It's just the remainder you get after a division. So 1%3 = 1, 2%3 = 2, 3%3 = 0, then 4%3 = 1 again.

So if I tell you to solve x%3=1, you can't know what X is. It might be 1 or 4 or 7...

If I hash my password "1234" and it becomes "hfiek", you have no way to obtain "1234" back, because there is an infinite amount of passwords whose hash is "hfiek".

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Treacherous_Peach t1_iwp3pwy wrote

Wouldn't any solution be sufficient? Don't most places use the same hashing algorithms? So who cares if you got a different password from the real one, it will probably still work on other sites too?

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calcopiritus t1_iwp4k5e wrote

To "break" a hash yes, any solution is sufficient. However, getting 1 of those solutions is still really hard. In this case the total amount of "hashes" is 3: either 0, 1 or 2. Real hashing algorithms have many more possible hashes.

It won't necessarily work in other sites for 2 reasons.

  1. "1234" and "7463" might generate the same hash using algorithm X, but it probably won't using algorithm Y. If 2 sites use different algorithms, you have to know the actual password. EDIT: I just saw you mentioned this, but it's still interesting to point out.

  2. Just hashing a password is bad practice for exactly this reason, so the recommended technique is doing hash+salt. That means every site generates a random "salt" for every user, and adds it to the password before hashing. So the password for site X is actually "1234jdyendi" while in site Y is "1234udnfki". Although you type the same password in both sites, it's actually a different one from an attacker POV, you need to know "1234", any other solution won't work for both sites.

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Stevetrov t1_iwmsua6 wrote

I will describe streaming encryption with AES because that's easiest. To be clear AES is not a secure hash function, it's a symmetrical encryption algorithm.

Just think of aes as a black box that does the following

  • takes a key (128, 192, 256 bits long) basically a huge massive number. There are so many possible keys that all the computers in the world wouldn't be enough to try them all ... not even close.
  • from this key the box outputs a key stream of one's and zeros that is different for each key.
  • the key stream that comes out of the box appears completely random, has no structure and doesn't repeat.
  • two key streams of two related keys are not related.

To encrypt your data, XOR* each bit of the data with each bit of the key steam. The the result is your encrypted data.

To decrypt the data you do exactly the same you did to encrypt, use the same key and your original data is recovered.

*XOR (exclusive OR) takes two binary inputs and returns 1 if the two inputs are different, it returns 0 if they are the same.

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JiN88reddit t1_iwlsozs wrote

This may be more of a political question than a math question:

Is it even possible to "copyright" a mathematical theorem, or any proofs, for that matter? Considering something like a^2 +b^2 = c^2 can be proven by anyone in any number of ways through flow of logic, would it even be a futile attempt?

And to take it a step further: what will happen IF something like the Pythagorean theorem is being copyrighted?

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atomfullerene t1_iwm3z3r wrote

No, math like this explicitly cannot be copyrighted, at least in most countries (I don't know about every single one).

>what will happen IF something like the Pythagorean theorem is being copyrighted?

It would just be a huge mess and not really be enforcable, and if it was enforced would cause all sorts of problems, which is why math isn't copyrightable in the first place

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csamsh t1_iwnl8d9 wrote

No. Quantifying the natural world is tough to copyright. Example- human genome. I'm sure there are exceptions though

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humanspeech t1_iwprju3 wrote

Haha you should tell that to the CRISPR patent case. It’s complicated but biology esp bioinformatics is becoming insane with the patents and copyrights. There was a lawsuit to patent the BRCA gene that was shot down a few years back.

Here’s the latest on the CRISPR case if anyone wants to check it out: https://www.nature.com/articles/d41586-022-00721-3

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Indemnity4 t1_iwnp09j wrote

The IP laws for this are going to get very niche and confusing.

  • Patents cannot be an equation or a fact. Once you publish it you cannot lock it away and prevent people using it.

  • Copyright does not protect a fact, which would be the equation itself. For instance, you cannot copyright a cooking recipe of 1 cup flour, 2 cups sugar, etc. However, you can copyright a page of a book. That includes the font, typesetting, arrangement. So you can copyright a recipe book, copyright a page of a recipe, copyright the text instructions, but not copyright the weights and measure in the recipe.

  • Copyright can protect a logo or an image. For instance, you could create a company with the Pythagorean theorem as the name, then have a graphic designer create a logo for you. Anyone can still use the formula, but they can't use to name another company or product, and they have restrictions on how they write it on things.

  • Trade secret or national security restriction on an equation. You write it down on internal company documents, then everyone who reads it must sign a NDA. If any of those people reveal the equation to the outside world, you can sue that person for damages. If it's a government secret you can even put someone in prison, in some cases, pre-preemptively before they release the secret.

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Pharisaeus t1_iwmj7r9 wrote

It can't be copyrighted or patented because math is discovered and not invented. Those theorems were true and "existed in nature" always.

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TwoUglyFeet t1_iwm365l wrote

Did various countries around the world have the same understanding of various scientific discoveries? For example, the Soviet Union and the US seemed to keep pace with each other on atomic, nuclear and space. Did countries like China, Japan or other counties did their own concurrent advancements in understanding scientific principles or just waited around till other counties figured it out?

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physicswizard t1_iwmcubu wrote

The advancement of science is very much an international effort nowadays. People from all over the world collaborate on scientific projects together if they have the knowledge and desire to do so. However, some countries can't contribute as much resources to certain efforts due to many reasons including funding (small, poor countries don't have the budget), lack of expertise (one country monopolizes a single field because all the experts congregate there, or there is a brain drain from less developed countries), politics (some USSR/USA scientists/engineers were forbidden to collaborate during the cold war for national security reasons).

So everyone contributes what they can typically, just some are limited in what they can do alone.

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TwoUglyFeet t1_iwmecq2 wrote

It is now, but I was wondering if other countries had their own scientific research that say, made the discovery of the atom or dna or formulated predictions of things that were discovered by European, American or Russian science agencies?

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mfb- t1_iwnzk3x wrote

There are cases where things were discovered in multiple places, but that's usually the result of multiple groups having success at around the same time - and the groups know about each other. One group discovering X and then several years another group discovering X independently is very rare as that would mean they didn't talk to each other for years or the second group doesn't know what's happening in their field. That does occur for nuclear weapons and other sensitive technology, but it's very unusual otherwise.

https://en.wikipedia.org/wiki/List_of_multiple_discoveries

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chazwomaq t1_iwmromi wrote

Here's an interesting recent historical example of where a major superpower had a very different scientific (mis)understanding.

The Soviet Union's leadership rejected the scientific ideas of Darwin and Mendel, that genes were selected through evolution. Instead, they favoured the Lamarckian view that acquired characteristics could be inherited.

Geneticists were fired, imprisoned, and even executed, and Lysenko (the chief scientist) tried to increase crop yields using this technique, which of course failed. As a result crop yields fell and there were food shortages.

https://en.wikipedia.org/wiki/Lysenkoism

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noiamholmstar t1_iwqb1fb wrote

Technically, epigenetic inheritance is a thing, so they weren't entirely wrong.

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atomfullerene t1_iwqmid5 wrote

Epigenetics isn't really the inheritance of acquired characteristics, though. It's more the ability to alter what traits your offspring express in response to your environment. There's no requirement that those traits be the same as the ones you have. For example, you could imagine a situation where high food availability causes parents to lay down epigenetic markers that cause their offspring to also have a high tendency to gain weight. Or you could imagine a situation where high food availability causes parents to lay down epigenetic markers that cause their offspring to avoid gaining weight. Or a situation where high food availability cause parents to lay down epigenetic markers to suppress melanin production and produce lighter fur (although I have no idea why such a system would ever evolve). The point is, there's no necessary connection between the parent trait and the offspring trait. There can be a similarity, but there doesn't have to be. It just depends on what sort of adaptations the organism has.

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chazwomaq t1_iwqq18i wrote

Lysenkoism and Lamarckism are not the same as epigenetic inheritance and are entirely wrong.

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humanspeech t1_iwpr4nx wrote

Depends. More recently we tend to cooperate, but one of the reasons why Europe had such a rapid industrialization era is because they borrowed the basics from neighboring countries.

When countries are at war, they usually give their Ally their scientific discoveries to keep up the pace. Like you said the US & USSR are great examples of these.

But then you have stuff like library of Alexandria, or really a lot of the colleges/schools built in the old world which shows for the most part we probably were exchanging knowledge for a very long time.

Knowledge is highly prized in the Middle East so it makes sense that’s where a lot of the exchanges uses to happen.

Calculus is a good example of people discovering things on their own. Newton & Leibinz technically found out about it at the same time, Leibinz just popularized it.

Results might have different methods that lead up to their discovery due to different ethical guidelines and that’s when you can argue two people discovered things at different times. It’s truly one of the reasons we have to file patents and why patent law is soooo lucrative.

Idk if this helps 😶‍🌫️

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LiamTheHuman t1_iwm68de wrote

Can someone explain the bell inequality to me in terms of odds of each possibility. I've seen many videos on YouTube that give 3 potential directional measurements(north, south east and south west). They then seem to claim that the odds of getting up down down, up up down and up down up are all the same. This doesn't seem right to me because it seems like you would have equal chance of getting one up as you do of getting two ups together.

I think this is probably an artifact of a simplification but could someone explain the more complex way to get the probabilities and what each one is?

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kukk007 t1_iwmyxnb wrote

After completing my renewable energy engeneering bachelor, I want to learn computer science as well but not through the university. Do you have any recommendations on which topics I should learn that would be useful, and do you have any links to good educational websites for this perpose? Learning Python is the one thing i have on my list, but I do not know if this is enough. I want to be able to make a website or an app by myself.

Apologies if it isn’t an acceptable question for this thread, but I would really appreciate any help!

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Weed_O_Whirler t1_iwn3ued wrote

I'm of the belief the best way to learn how to program is to choose a difficult, but "fun" (fun being fun for you, something you're interested in) project, and then just push through trying to figure out how to do it.

If you have literally no programming experience, you'll probably have to do some sort of classes (like an MIT Open Courseware class or something) just to learn the basics- but then just start on your difficult project, get stuck a bunch, ask questions (every programming language has a Reddit community), and push through.

I have found people get a lot more (and are much more willing to push through) working on something they actually care about, instead of pre-canned exercises.

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kukk007 t1_ix5l0nh wrote

Thank you for the reply and tips. I really appreciate it!

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bambataa199 t1_ix5bfhj wrote

Some time ago I wrote a blog post describing an introductory sequence of computer science topics: https://thecomputersciencebook.com/posts/how-to-learn-computer-science/

HOWEVER, I would argue that what you want to learn is first programming, and then if you're interested you can go further into computer science. Programming is getting computers to do things, computer science is at its core analysing computation itself. You might find it really interesting to study how a processor works and how a computer is structured, but this won't immediately help you to make websites or apps.

In computer science there is a hackneyed (any possibly apocryphal) quote by Edsger Dijkstra: "Computer Science is no more about computers than astronomy is about telescopes."

Python is a very good language to start with. It is easy to build simple command line programs that get you used to the fundamentals of programming. To build fancy websites you will need to know JavaScript, but the idiosyncrasies of JavaScript and the web environment add to the learning curve so starting with Python makes sense imo.

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kukk007 t1_ix5lfno wrote

Thank you for the explanation and tips. I appreciate that you took the time to elaborate om this and will take it into account!

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adamtheskill t1_iwphdy8 wrote

When we find solutions to a PDE through separation of variables are we guaranteed to get all possible solutions to the original PDE or could there be missing solutions where the variables are not separable?

For example: PDE P(x,y,z) assumed separable and we find a linear set of solutions in the form X(x)Y(y)Z(z). Could there be a solution in the form A(x,y)Z(z) where the variables x and y are not separable that we can not create through a linear combination of solutions in the form X(x)Y(y)Z(z)?

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PsychologyMiserable3 t1_iwlmjiw wrote

My niece is excellent at math amd I wamt her to nourish this talent so I have a two part question: 1. What activities or hobbies can I get her into to promote this talent 2. What are some high paying careers that will be in high demand in the upcoming years for engineers and computer scientists?

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Stevetrov t1_iwmu281 wrote

Cyber security has seen huge growth it the last 20 years. Machine learning is also huge. Data science is another field that has seen a lot of growth. Anyone these would be great or some combination of them.

Depending how old she is then i would focus on what she enjoys. If she is pushed into something that she doesn't enjoy or want to do that could put her off.

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xtreampb t1_iwoidny wrote

One hobby I recommend is F.I.R.S.T. It is an international robotics competition for high school aged students. It is heavily stem focused, but not exclusively. The kit of parts itself is ~$6k and encourages/requires students to raise money. This is a good way to incorporate the business focused students to generate marketing campaigns to raise funds. Also these robots require machining to assemble. This helps bring on shop students who like working with their hands welding, cutting, machining and the like. FIRST helps students learn how a business organization works where everyone has different skills and rely on each other. There’s also scholarships and career opportunities afterwards. Companies like Boeing, NASA, Raytheon, General Dynamics are just a few. Again this is an international competition. Try to find a team near you or start one at the high school. If the student isn’t in high school, FIRST has other competitions for elementary and middle schools that do similar things, on a smaller scale.

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PsychologyMiserable3 t1_iwpl38m wrote

Wow, that sounds really awesome. I do not know if her current school has those resources but I will do some research. Thank you

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NotoriousTD t1_iwma6fn wrote

Try TSD road rallies. Super fun and great mental challenge. Also great for quality time with the niece!

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mineymonkey t1_iwlmxp6 wrote

Basically anything in industry. Though machine learning and data analytics can be lucrative. Similarly, chemical/nuclear engineering due to it being a bit more niche compared to electrical/mechanical/civil engineering.

Software engineering is another thing that they can look into.

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Mooide t1_iwmy0hi wrote

Hobbies wise you might try motorsport. Obviously actually racing is super expensive but she might like watching races or doing a bit of sim racing.

A sport like Formula 1 has a ton of engineering power behind it and therefore many of the people on these teams are strong at maths.

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nattersley t1_iwnuqf8 wrote

I’ll jump on this late and also say she may be interested in financial mathematics. The quant people where I worked were solving the same sorts of advanced differential equations that the best engineers are doing, and they get paid millions of dollars to do it.

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[deleted] t1_iwlnvko wrote

[removed]

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PeanutSalsa t1_iwlqxmn wrote

How much influence have ancient civilizations had on modern day engineering?

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physicswizard t1_iwm9nr5 wrote

The influence of ancient Rome on the modern-day space program is an interesting and widely-cited example: https://papersourceonline.com/roman-horses-butts-designed-space-shuttles/

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ashara_zavros t1_iwmn1p8 wrote

Could we shoot a metallic water container into orbit with a big enough cannon?

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Pharisaeus t1_iwn2u72 wrote

metallic water container is not a very strict definition so it's hard to tell what exactly you mean :)

In order to place something in orbit you need to accelerate it horizontally to about 7.5km/s. The issue of using a "cannon" is that such device applies force only for a very short time when object is moving through the barrel. This means the acceleration has to be extremely high and as a result the applied force has to be very high as well. So your "container" has to be able to withstand compressive stress.

There is another, more problematic issue - once you leave the barrel you hit the atmosphere, and hitting atmosphere when moving at such velocity will cause atmospheric compression and heating (just like when spacecraft come back from orbit) slowing you down. So the container has to be able to withstand the heating, and the cannon has to eject the payload much faster than orbital velocity.

If you can get material like that, then you could launch it in such a way :) However, a more "practical" version of this idea would be to build a very long vacuum tunnel somewhere in high mountains. Long tunnel means you accelerate over longer distance, and if you place the nozzle of the cannon very high (let's say 8km) you hit much thinner atmosphere.

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ashara_zavros t1_iwpt1sd wrote

Your last paragraph describes a different kind of cannon.

Thanks for the effort, but all you’ve done is describe the problems with orbital launch that affec any transportation method. I’m more interested in knowing if there’s a currently viable solution.

But, again, thanks anyway.

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Pharisaeus t1_iwq42zo wrote

> different kind of cannon

How so? It's a cannon, just with a very long barrel and without the impractical "instant acceleration" issue. It's pretty much the only semi-realistic design.

> that affec any transportation method

Only that it doesn't. Rockets accelerate pretty slowly, at 1.5-2G, so they have no significant issues with crossing through atmosphere or with high-G loads during acceleration.

> if there’s a currently viable solution

Does SpinLaunch count or is it also "different kind of cannon"?

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Sheldon121 t1_iwmohdn wrote

Okay, can someone please explain what causes fibromyalgia in people? In simple terms. I’ve read that people with it have brain inflammation. Is that true? Does the fibro cause the brain inflammation or is it the other way round? And what would be the symptoms and issues from brain inflammation?

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Stevetrov t1_iwmvrwq wrote

The short answer is we don't know.

Fibro is one of a number of disorders called functional disorders that are classified by their symptoms rather than their cause, because the cause isn't known or is disputed.

Other common function disorders you have probably heard of are chronic fatigue syndrome (aka ME) and irritable bowel syndrome. But there are loads others as well. Eg non epileptic seizures, tremors, blackouts, walking disorders, and some really weird stuff like not being able to move certain muscles.

Source I have a walking disorder, cfs and some fibro.

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Silent-Literature-41 t1_iwn0ii4 wrote

Can the sun create anti matter? If so, by what mechanism?

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mfb- t1_iworqvn wrote

Proton-proton fusion in the core produces positrons which are generally seen as part of antimatter, even though you would also need antiprotons (which are not produced) for neutral anti-atoms. The positrons quickly annihilate with electrons to photons, contributing to the power of the Sun.

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Pharisaeus t1_iwn1m31 wrote

One simple way is pretty much the same as we use to create anti-protons on Earth -> by accelerating protons and colliding them. With enough energy a proton-antiproton pair might be created. This means for example that solar wind (high-energy protons ejected from the sun) can collide with Earth's atmosphere and the collision can create anti-protons. There were even crazy ideas like: http://www.niac.usra.edu/files/studies/final_report/1107Jackson.pdf

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cookiemonsterwave t1_iwn51ru wrote

How long would spent fuel from a nuclear reactor that was stored in the spent fuel pool last if there was no human presence/interaction at the plant?

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csamsh t1_iwnlmvi wrote

It depends on the isotopic makeup of the fuel. If you know the composition, the decay is quite simple to model. If we're talking about the actual atomic material itself, some portion will last forever assuming it's not converted to energy- eventually the radioisotopes will decay to stable elements with no half life.

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Dragzel t1_iwnfl8f wrote

How to write complex formulas, like pre-calculus and onward, into computer code? What’s a good resources and concepts to start on?

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mfukar t1_iwygbk7 wrote

You're looking for 'computer algebra' or 'symbolic computation' systems. Here is a good list to get you started.

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Azures_Anvil t1_iwnmhfy wrote

I heard that quantum computers would render all of our current methods of encryption useless. Is this true and how is that possible?

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mfukar t1_iwyg4re wrote

No - not all. What most people refer to when they say something like this is public-key cryptography. That is because Peter Shor found an algorithm to factorise an integer efficiently and thus solve the problem some PKI relies on in time that classical computers cannot. What's more fascinating, is that we're approaching quantum computers with enough qubits to examine quantum Fourier transforms, which might allow us to see a realistic, albeit large, implementation of Shor pretty soon.

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Garfield-1-23-23 t1_iwnvui5 wrote

Why is spray foam insulation typically rated at R-6.5 per inch when XPS foam board is rated at only R-5 per inch? If it's basically the same stuff - polystyrene extruded with blower gases - why wouldn't the material produced in a factory setting (with presumably greater consistency) have at least the same R-value as the material produced and applied on-site?

Since R-6.5 is the rated R-value for polyisocyanate foam board, and because spray foam insulation is available in both polyiso and polystyrene form (with polystyrene being the most common), I wonder if manufacturers are just claiming the polyiso R-value for all of their spray foam products regardless of what their actual type is.

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redrabbitromp t1_iwoe477 wrote

Why does my rubbery stress ball stick to the ceiling tiles in my office (those compressed cardboard type of tiles, white with random holes) but not to surfaces such as metal that I would expect it to stick to.

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lesse1 t1_iwoga6l wrote

Wtf is fugacity?

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Luenkel t1_iwov6ys wrote

It's a trick that allows us to use the equations of ideal gasses for real gasses. Real gasses are a lot more complicated to work with but it turns out they "behave the same as" an ideal gas at a different pressure (meaning they have the same molar Gibbs energy and temperature). That's the fugacity: the pressure an ideal gas would have to be at to "behave the same as" your real gas.

For example: Let's say you have a real gas with a fugacity coefficient of 1.2 at a pressure of 1 bar. Then you could either use some complicated formulas for real gasses or you could use the same old equations for ideal gasses but instead of the actual pressure (1 bar) you use the fugacity (1.2×1 bar= 1.2 bar) and you will get the same result.

Side note: sometimes fugacity is defined to be unitless, sometimes people give it units of pressure.

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humanspeech t1_iwpporr wrote

I should probably know this because it’s my field but: How do you produce a drug with low toxicity but high effectiveness like anti-psychotics or benzodiazepines? Is it trial and error?

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ananon88114 t1_ix4phy1 wrote

Here's a fun one, about a month late. Assuming vampires were as fiction describes, could you carbonate blood as one does water for soda, or would the plasma aspect ruin it?

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DaniChicago t1_iwn502f wrote

What are your thoughts on the rise of Business Analytics/Data Analytics? Corporate America is sold on it. Minus the IT needed to deal with very large data sets is it a bastardization of applied statistics? Is it too watered down?

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csamsh t1_iwnm73v wrote

It's only as good as the people interpreting data to create useful information. I'm a chemist and mechanical engineer, and to me there are few things more dangerous than a business or finance guy holding a piece of paper that says "big data" on it.

But to answer your question, yes I think it's watered down. From my point of view the whole point of the analytics craze is to distill complicated concepts and statistics into buzzwords that one can sell to upper management and potential investors. That's just my experience- I'm sure there is proficiency in this area that makes real money.

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mfukar t1_iwygels wrote

Just a "marketable" term for applied statistics. Unfortunately there are already courses for it which teach entirely trivial and unrelated things along with very basic statistics and profit off people's ignorance.

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Clearlybeerly t1_iwnkreh wrote

In math, why do they name numbers after people, like Graham's number?

I mean, what if I say "Graham's number + 1"? Why wouldn't that be called Clearlybeerly's number, which, I must say, has a better ring to it. Or what about 6.9 x 10^69 ? That would be a good number to name after me as well. Who doesn't like a good 69? For sure this number needs a name.

But seriously, why name some rando number after someone?

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nivlark t1_iwnu5uz wrote

Because that person wrote a paper where they identified that number and showed some interesting result involving it. You could name a number yourself if you wanted, but unless you give the mathematical community a reason to adopt that name, it won't gain any notoriety.

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