6 ms·

Note what is required to do something like this: You need to solve a 5-dimensional (+ time) nonlinear integro-differential equation. Not only that, but you nee

Note what is required to do something like this: You need to solve a 5-dimensional (+ time) nonlinear integro-differential equation. Not only that, but you need to keep it going for a long enough time for turbulent fluctuations to average out, and cover both ion and electron scales (that last bit is the big new contribution here). And once you're done with that, you need to repeat it at even higher resolution as evidence that what you're seeing is physical. Bravo!

wnevets 11y ago
I know some of those words. Anyone have a ELI5?
- drjesusphd 11y ago
  Fusion is hard.
- schwarrrtz 11y ago
  Take a simple differential equation as an example, like dy/dx = x. To solve this we need to find a function y(x) whose derivative is equal to x. This particular differential equation is well-behaved, and the solution is simply 0.5*x^2, which you can verify using basic calculus. Not all differential equations are nicely behaved. Many do not have analytic solutions at all, meaning that we can't even write down a function that satisfies the equation. However, such equations can still be solved approximately using computational techniques. This can be incredibly difficult and computationally expensive (note the huge resources required to achieve this breakthrough) but can produce very useful results.
  - stanmancan 11y ago
    How many 5 year olds do you know that understand "well behaved differential equations" and derivatives?
    - deleted 11y ago
      [deleted]
    - andrepd 11y ago
      ELI5 is not for actual 5 year olds.
      - nkrisc 11y ago
        In this case it should be ELIHAHSPE. Explain like I have a high school physics education.
        sliverstorm 11y ago
        They teach diffy-q in high school now?
        nkrisc 11y ago
        I don't know. But I would imagine most high schoolers could at least understand what a differential equation is, if explained. Aside from if they could solve one.
        poopchute 11y ago
        I did derivatives and integrals in my highschool calc course, circa 2007
        chrstphrhrt 11y ago
        Which order were they taught in? I had the same curriculum but was utterly bewildered by derivatives being the first topic. For the simple reason that until that point I had habitually looked at "wholes" in the external world, only then to wonder "what kinds of things progressively make it up?" I feel like to derive something, you start with the assumption that you know what you're talking about fist. Yet the thing is actually the sum of its parts. Therefore integration seems more natural at first, and only then can things similar to it be derived with confidence. So the teaching order seemed backwards. I wonder if anyone has felt the same way.
- cygnus_a 11y ago
  As you might know, turbulence is when simple streams of laminar flow (in say, plasma) turn into chaotic filaments and vortices. As a filament or vortex separates/stretches from your laminar flow region, it steals away heat/energy. Scientists often assume that you can accurately approximate stuff by neglecting irrelevant parts of the physics (basketballs vs ping pong balls; protons vs electrons). Turns out that ping pong balls greatly affect the outcome and amount of heat/energy dissipation in the basketballs. This doesn't surprise me too much, since critical behavior often happens in regimes where two separate aggregate effects become relevant. But the details are all still just a big mystery :) P.S. someone posted a much better description than the OP. I'll reiterate: http://news.mit.edu/2016/heat-loss-fusion-reactors-0121 http://news.mit.edu/2016/heat-loss-fusion-reactors-0121
- jwiley 11y ago
  You know that opening a Poke Ball releases a tremendous amount of energy, because on television they show a big flash of light. Imagine if you could open a thousand poke balls every second. We call that fusion. What MIT did was make it easier to open all these poke balls in a sustained way. This is important because once fusion is sorted out, our political leaders like Ted Cruz could use all that energy to do really interesting things. One side effect is that a lot of poke monsters will be released as well, which could cause problems...and so we as a society need to think about the long term ramifications.
- XaspR8d 11y ago
  A fusion reactor needs a lot of energy (heat & electricity) in order to make more. But a big problem is that the heat wants to escape. (Think of when you hold something warm -- the warmth you feel is the heat escaping into your hands! How would you stop it from doing that?) Different kind of reactors try to keep the heat in in different ways, but several of them do it with big magnets, which basically can keep the fuel floating so it doesn't touch anything. Now there are two main parts to the stuff inside the reactor, ions & electrons. Think of them as mac & cheese. When the reactor gets really hot, these bits start jostling around. (It's in the nature of hot things to want to move more, and really "hot" means that the little atomic components of everything are wiggling and moving faster and more excitedly.) Think of boiling the mac and cheese. For a long time scientists thought that the wiggles of the ions would diminish the wiggles of the electrons, because 1) the ions & electrons want to be near each other so they form a clump (like how the noodles absorb the cheese but waaaay stronger) and 2) because each ion/noodle is way bigger than each piece of cheese powder/electron, so its wiggles should be way stronger. Now to figure these things out, scientists have to use computers to predict how it all might work. But the formulas they use don't have a single answer they can just solve by hand. Instead the computer can take a guess and then spend a lot of time seeing how good the guess was, and trying to make it better. A computer can do things fast, but it's hard because when it does math, it's only figuring out how a single piece of cheese dust moves at a time! There are so many little pieces and knowing how a few cheese dusts move won't give us a good idea what a big pot of mac n' cheese is like. (Could you learn how sand feels by holding one grain?) So they have to keep the computer running until it can tell them what a lot of cheese moves like. Even harder is that they need to watch the cheese move for a long time to make sure it's "stable". (For example, if you put mac and cheese back on a hot stove it might be quiet for a bit before suddenly a big cheese bubble burst and splattered everywhere. We need to know if there are bursting bubbles or not, so just looking for a second won't be enough to tell us.) So the computer also has to do this guessing for many little tiny moments, until they add up to a longer amount of time. Then they can figure out how the sauce behaves when you leave it on the stove for a while. Ultimately these scientists found that the ions & electrons don't act exactly like we thought. The heat actually causes the electrons/cheese to stretch out into long strands that pull away from the main blob! Also when the cheese starts swirling around, instead of bumping into the noodles and stopping, they can bump strong enough that the noodles and cheese all start swirling together crazily. These two things give us big clues on why our reactors won't stay as hot as we want them to, because they explain why the mac and cheese gets so wiggly and wild, and with the discovery we can now try to find new ways to build better reactors that work better. All the guessing by the computers was so much work it would've taken a single computer 15 million hours (over 1700 years!), but they got 17000 computers to all work as a team and give them answers in about a month. Then the scientists could get a couple answers in a year, which made them feel more confident that they probably did things right. NOTE: Totally not a physicist or anything, and I probably started with a bad analogy, but wanted to try this as a writing challenge. Also I know you probably didn't want it this simpified, but I tried to take "ELI5" at face value for once.
- deleted 11y ago
  [deleted]
- samstave 11y ago
  [meta] - I love the crosspolination between HN and reddit wrt many things. The thought that some random off reddit invented the idea of ELI5 And now its a valid comment request is fucking awesome. The internet evolved a bit when they invented that.
  - colordrops 11y ago
    The "Explain it like I'm five" idiom was not invented by Reddit.
    - samstave 11y ago
      I didn't know this, thanks. Where was it invented?
      - colordrops 11y ago
        I don't know, I've just heard it before Reddit existed.

wnevets 11y ago

I know some of those words. Anyone have a ELI5?

drjesusphd 11y ago
Fusion is hard.
schwarrrtz 11y ago
Take a simple differential equation as an example, like dy/dx = x. To solve this we need to find a function y(x) whose derivative is equal to x. This particular differential equation is well-behaved, and the solution is simply 0.5*x^2, which you can verify using basic calculus. Not all differential equations are nicely behaved. Many do not have analytic solutions at all, meaning that we can't even write down a function that satisfies the equation. However, such equations can still be solved approximately using computational techniques. This can be incredibly difficult and computationally expensive (note the huge resources required to achieve this breakthrough) but can produce very useful results.
- stanmancan 11y ago
  How many 5 year olds do you know that understand "well behaved differential equations" and derivatives?
  - deleted 11y ago
    [deleted]
  - andrepd 11y ago
    ELI5 is not for actual 5 year olds.
    - nkrisc 11y ago
      In this case it should be ELIHAHSPE. Explain like I have a high school physics education.
      - sliverstorm 11y ago
        They teach diffy-q in high school now?
        nkrisc 11y ago
        I don't know. But I would imagine most high schoolers could at least understand what a differential equation is, if explained. Aside from if they could solve one.
        poopchute 11y ago
        I did derivatives and integrals in my highschool calc course, circa 2007
        chrstphrhrt 11y ago
        Which order were they taught in? I had the same curriculum but was utterly bewildered by derivatives being the first topic. For the simple reason that until that point I had habitually looked at "wholes" in the external world, only then to wonder "what kinds of things progressively make it up?" I feel like to derive something, you start with the assumption that you know what you're talking about fist. Yet the thing is actually the sum of its parts. Therefore integration seems more natural at first, and only then can things similar to it be derived with confidence. So the teaching order seemed backwards. I wonder if anyone has felt the same way.
cygnus_a 11y ago
As you might know, turbulence is when simple streams of laminar flow (in say, plasma) turn into chaotic filaments and vortices. As a filament or vortex separates/stretches from your laminar flow region, it steals away heat/energy. Scientists often assume that you can accurately approximate stuff by neglecting irrelevant parts of the physics (basketballs vs ping pong balls; protons vs electrons). Turns out that ping pong balls greatly affect the outcome and amount of heat/energy dissipation in the basketballs. This doesn't surprise me too much, since critical behavior often happens in regimes where two separate aggregate effects become relevant. But the details are all still just a big mystery :) P.S. someone posted a much better description than the OP. I'll reiterate: http://news.mit.edu/2016/heat-loss-fusion-reactors-0121 http://news.mit.edu/2016/heat-loss-fusion-reactors-0121
jwiley 11y ago
You know that opening a Poke Ball releases a tremendous amount of energy, because on television they show a big flash of light. Imagine if you could open a thousand poke balls every second. We call that fusion. What MIT did was make it easier to open all these poke balls in a sustained way. This is important because once fusion is sorted out, our political leaders like Ted Cruz could use all that energy to do really interesting things. One side effect is that a lot of poke monsters will be released as well, which could cause problems...and so we as a society need to think about the long term ramifications.
XaspR8d 11y ago
A fusion reactor needs a lot of energy (heat & electricity) in order to make more. But a big problem is that the heat wants to escape. (Think of when you hold something warm -- the warmth you feel is the heat escaping into your hands! How would you stop it from doing that?) Different kind of reactors try to keep the heat in in different ways, but several of them do it with big magnets, which basically can keep the fuel floating so it doesn't touch anything. Now there are two main parts to the stuff inside the reactor, ions & electrons. Think of them as mac & cheese. When the reactor gets really hot, these bits start jostling around. (It's in the nature of hot things to want to move more, and really "hot" means that the little atomic components of everything are wiggling and moving faster and more excitedly.) Think of boiling the mac and cheese. For a long time scientists thought that the wiggles of the ions would diminish the wiggles of the electrons, because 1) the ions & electrons want to be near each other so they form a clump (like how the noodles absorb the cheese but waaaay stronger) and 2) because each ion/noodle is way bigger than each piece of cheese powder/electron, so its wiggles should be way stronger. Now to figure these things out, scientists have to use computers to predict how it all might work. But the formulas they use don't have a single answer they can just solve by hand. Instead the computer can take a guess and then spend a lot of time seeing how good the guess was, and trying to make it better. A computer can do things fast, but it's hard because when it does math, it's only figuring out how a single piece of cheese dust moves at a time! There are so many little pieces and knowing how a few cheese dusts move won't give us a good idea what a big pot of mac n' cheese is like. (Could you learn how sand feels by holding one grain?) So they have to keep the computer running until it can tell them what a lot of cheese moves like. Even harder is that they need to watch the cheese move for a long time to make sure it's "stable". (For example, if you put mac and cheese back on a hot stove it might be quiet for a bit before suddenly a big cheese bubble burst and splattered everywhere. We need to know if there are bursting bubbles or not, so just looking for a second won't be enough to tell us.) So the computer also has to do this guessing for many little tiny moments, until they add up to a longer amount of time. Then they can figure out how the sauce behaves when you leave it on the stove for a while. Ultimately these scientists found that the ions & electrons don't act exactly like we thought. The heat actually causes the electrons/cheese to stretch out into long strands that pull away from the main blob! Also when the cheese starts swirling around, instead of bumping into the noodles and stopping, they can bump strong enough that the noodles and cheese all start swirling together crazily. These two things give us big clues on why our reactors won't stay as hot as we want them to, because they explain why the mac and cheese gets so wiggly and wild, and with the discovery we can now try to find new ways to build better reactors that work better. All the guessing by the computers was so much work it would've taken a single computer 15 million hours (over 1700 years!), but they got 17000 computers to all work as a team and give them answers in about a month. Then the scientists could get a couple answers in a year, which made them feel more confident that they probably did things right. NOTE: Totally not a physicist or anything, and I probably started with a bad analogy, but wanted to try this as a writing challenge. Also I know you probably didn't want it this simpified, but I tried to take "ELI5" at face value for once.
deleted 11y ago
[deleted]
samstave 11y ago
[meta] - I love the crosspolination between HN and reddit wrt many things. The thought that some random off reddit invented the idea of ELI5 And now its a valid comment request is fucking awesome. The internet evolved a bit when they invented that.
- colordrops 11y ago
  The "Explain it like I'm five" idiom was not invented by Reddit.
  - samstave 11y ago
    I didn't know this, thanks. Where was it invented?
    - colordrops 11y ago
      I don't know, I've just heard it before Reddit existed.