13 ms·

This is pretty good news if only that we will get more research into this phenomenon. In 1933 von Neumann basically published a proof against the idea of any h

by jtchang 10y ago

This is pretty good news if only that we will get more research into this phenomenon. In 1933 von Neumann basically published a proof against the idea of any hidden-variable theory. It took 30 years but Bell then discredited it. My guess is that a lot of this will get revisited. The outcome of this in the next 10-20 years might be really cheap probes (via reusable launch vehicles like SpaceX is making) that need no propellent to continue onto their merry way for a long time. The current way of doing this would be using solar sails or something along those lines which is not exactly compact. Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed.

perlgeek 10y ago
> This is pretty good news if only that we will get more research into this phenomenon. Agreed. > Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed. I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.
- ajuc 10y ago
  > As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration. In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity. Or at least it's possible in Kerbal Space Program :)
  - cperciva 10y ago
    Yes, you move in ellipses; but you spend a lot of time far away and very little time close to the sun. I'm not sure that the average power is any higher than you would have for a circular orbit at the same energy... EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b). Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)
    - novaleaf 10y ago
      my attempt at a thought experiment that seems to suggest elliptical orbits are better in this regard: if you have an efficient insulator, you could absorb an arbitrarily large amount of heat at the perigee, and retain it for the remainder of the orbit. if you were in a circular orbit, you'd only be able to absorb up to the ambient temp.
      - cperciva 10y ago
        Ambient temperature is a red herring; the sun is hotter than the ambient temperature so you can always win by absorbing energy from the sun and then emitting it to the rest of space.
    - ajuc 10y ago
      > you'll absorb the most power at exactly the time you don't want to be changing your momentum Thanks for doing the math. But I'm still confused, I thought you do want to accelerate when near the sun, as that makes the far end of the orbit go further? Again, no math behind, just how it worked in KSP :)
- GenerocUsername 10y ago
  Nuclear/Batteries
lomnakkus 10y ago
> This is pretty good news if only that we will get more research into this phenomenon. Or maybe it's just a waste of time/money? (I'm not being facetious for the sake of it. See cjensen's comment[1]) [1] https://news.ycombinator.com/item?id=12995341 https://news.ycombinator.com/item?id=12995341
- lJ9Ni044GH3z 10y ago
  What similar research is the time and money better spent on?
- sonium 10y ago
  Speaking as a experimental physicist: The research shown is relatively inexpensive, and can be pulled off with what many labs probably have lying around anyways. I'm sure it's more a work of love anyways and the guys doing this are probably facing serious headwind for trying 'crazy stuff'.
  - lifeisstillgood 10y ago
    Shouldn't crazy stuff be exactly why we fund tenured positions? I would like to think tenure still produces crazy scientists
    - lutusp 10y ago
      > Shouldn't crazy stuff be exactly why we fund tenured positions? Crazy stuff becomes an option after one is granted tenure, it doesn't necessarily make one more likely to achieve tenure. On the other hand, theoretical physicists aren't very expensive -- they only need a blackboard and an eraser. Compare that to a philosopher -- much the same but without the eraser.
      - lifeisstillgood 10y ago
        Badah dum tish!
michwill 10y ago
Actually it's not as much useful as an engine as it may seem, at least at current parameters. Ion thrusters are pretty good as low-power engines. And it's not clear that emdrive is better than that even if it works. Maybe with powerful space-based nuclear reactors
- deleted 10y ago
  [deleted]
- jack9 10y ago
  > Actually it's not as much useful as an engine as it may seem, It's worth more than any existing or previous theoretical engine. Put this rotating around a center point. Now put 1000s of them. Now we have power generation for outposts in space. The implications of a working EM drive are staggering.
  - pugworthy 10y ago
    What makes the power to power them?
    - binarycoffee 10y ago
      easy: 1000000's of them rotating around a fixed point!
  - krylon 10y ago
    Naive questions from someone who does not understand a lot about physics (to put it mildly): Did you just invent the perpetuum mobile, or did I misunderstand what you said? Or do I just not understand how this thing is supposed to work?
    - Filligree 10y ago
      He did, yeah. If it works as described, then you'd expect it to break conservation of energy along with conservation of momentum. That's another good reason to think it doesn't work.
deepnotderp 10y ago
Wait, what? I thought Bell's Theorem made local hidden variables a no-go? Care to elaborate?
pjs_ 10y ago
Bell proved that there is no local hidden variable model that is consistent with quantum theory. He said the same thing as Von Neumann (quantum mechanics can't be understood merely in terms of hidden variables), only more robustly. No new physics was discovered.
- effie 10y ago
  No, that's not the whole story. Bell pointed out that Bohm's theory, already known but ignored, is a counterexample to von Neumann's and others' claims on impossibility of hidden variables. He analyzed how that is possible and found out: 1) von Neumann made some unreasonable assumptions in his analysis; 2) the fixation on hidden variables is missing the point; the real surprise is that locality, not theory with hidden variables, is inconsistent with quantum theory. That's quite a discovery. http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-Bell-paper.pdf http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-... https://arxiv.org/pdf/1408.1826.pdf https://arxiv.org/pdf/1408.1826.pdf
  - loup-vaillant 10y ago
    Wait a minute, my understanding of QM rejects both non-locality and hidden variables. Put it that way however, you kinda have to believe in macroscopic decoherence, that is, Everet's multiverse: there are 2 universes, one in which the cat is dead, and one in which the cat is alive, and observing one universe doesn't rule out the existence of the other. (Similarly, sending a photon (or settlers!) outside of the observable universe doesn't end its existence.) Non-locality sounds way, way weirder to me than macroscopic decoherence. Stuff like quantum collapse is really an additional, un-falsifiable claim: why the universe would zero-out precisely the stuff that the math says we can't observe?
    - ajkjk 10y ago
      Er, are you familiar with the Bohmian mechanics [1] that was mentioned above? It has, basically, 'non-local hidden variables', and that works fine. [1] (https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)

by jtchang 10y ago

perlgeek 10y ago

> This is pretty good news if only that we will get more research into this phenomenon. Agreed. > Having a way to push your little probe along (even at a little bit of acceleration) without having to carry a lot of heavy propellant is a big deal. Maybe just some solar panels to generate the energy needed. I'm not sure that actually works. Most use cases are for exploring the outer solar system, or even outside of our solar system. As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration.

ajuc 10y ago
> As the probe gets away from the sun, the solar energy it gets decreases with the square of the distance, and so it probably will stop providing even the little bit of acceleration. In space you move in elipses. It's possible to choose an elongated orbit that moves the probe closer and then further from the sun repeatedly and each time it is close to the sun it accelerates forward, moving the "far" side of orbit further away, until it gains enough speed to escape sun gravity. Or at least it's possible in Kerbal Space Program :)
- cperciva 10y ago
  Yes, you move in ellipses; but you spend a lot of time far away and very little time close to the sun. I'm not sure that the average power is any higher than you would have for a circular orbit at the same energy... EDIT: Ok, let's think through the calculus here. Kepler's 2nd law says that the area swept by the line between a planet and the Sun is constant, i.e., r^2 dθ/dt = 2 π a b / P where a and b are the semi-major and semi-minor axes and P is the orbital period. Thus dt / r^2 = P dθ / (2 π a b); and the former is the instantaneous power absorbed. Integrating over an orbit, we get E = P / (a b); or the average power absorbed is proportional to 1 / (a b). Since the energy of an orbit is determined solely by the semi-major axis a, this means the power absorbed for any given orbital energy is maximized for b ≪ a; so you're right, that highly eccentric orbits are a better way to acquire energy for the purpose of orbital escape. (Subject of course to practical considerations of energy storage -- you'll absorb the most power at exactly the time you don't want to be changing your momentum.)
  - novaleaf 10y ago
    my attempt at a thought experiment that seems to suggest elliptical orbits are better in this regard: if you have an efficient insulator, you could absorb an arbitrarily large amount of heat at the perigee, and retain it for the remainder of the orbit. if you were in a circular orbit, you'd only be able to absorb up to the ambient temp.
    - cperciva 10y ago
      Ambient temperature is a red herring; the sun is hotter than the ambient temperature so you can always win by absorbing energy from the sun and then emitting it to the rest of space.
  - ajuc 10y ago
    > you'll absorb the most power at exactly the time you don't want to be changing your momentum Thanks for doing the math. But I'm still confused, I thought you do want to accelerate when near the sun, as that makes the far end of the orbit go further? Again, no math behind, just how it worked in KSP :)
GenerocUsername 10y ago
Nuclear/Batteries

lomnakkus 10y ago

> This is pretty good news if only that we will get more research into this phenomenon. Or maybe it's just a waste of time/money? (I'm not being facetious for the sake of it. See cjensen's comment[1]) [1] https://news.ycombinator.com/item?id=12995341 https://news.ycombinator.com/item?id=12995341

lJ9Ni044GH3z 10y ago
What similar research is the time and money better spent on?
sonium 10y ago
Speaking as a experimental physicist: The research shown is relatively inexpensive, and can be pulled off with what many labs probably have lying around anyways. I'm sure it's more a work of love anyways and the guys doing this are probably facing serious headwind for trying 'crazy stuff'.
- lifeisstillgood 10y ago
  Shouldn't crazy stuff be exactly why we fund tenured positions? I would like to think tenure still produces crazy scientists
  - lutusp 10y ago
    > Shouldn't crazy stuff be exactly why we fund tenured positions? Crazy stuff becomes an option after one is granted tenure, it doesn't necessarily make one more likely to achieve tenure. On the other hand, theoretical physicists aren't very expensive -- they only need a blackboard and an eraser. Compare that to a philosopher -- much the same but without the eraser.
    - lifeisstillgood 10y ago
      Badah dum tish!

michwill 10y ago

Actually it's not as much useful as an engine as it may seem, at least at current parameters. Ion thrusters are pretty good as low-power engines. And it's not clear that emdrive is better than that even if it works. Maybe with powerful space-based nuclear reactors

deleted 10y ago
[deleted]
jack9 10y ago
> Actually it's not as much useful as an engine as it may seem, It's worth more than any existing or previous theoretical engine. Put this rotating around a center point. Now put 1000s of them. Now we have power generation for outposts in space. The implications of a working EM drive are staggering.
- pugworthy 10y ago
  What makes the power to power them?
  - binarycoffee 10y ago
    easy: 1000000's of them rotating around a fixed point!
- krylon 10y ago
  Naive questions from someone who does not understand a lot about physics (to put it mildly): Did you just invent the perpetuum mobile, or did I misunderstand what you said? Or do I just not understand how this thing is supposed to work?
  - Filligree 10y ago
    He did, yeah. If it works as described, then you'd expect it to break conservation of energy along with conservation of momentum. That's another good reason to think it doesn't work.

deepnotderp 10y ago

Wait, what? I thought Bell's Theorem made local hidden variables a no-go? Care to elaborate?

pjs_ 10y ago

Bell proved that there is no local hidden variable model that is consistent with quantum theory. He said the same thing as Von Neumann (quantum mechanics can't be understood merely in terms of hidden variables), only more robustly. No new physics was discovered.

effie 10y ago
No, that's not the whole story. Bell pointed out that Bohm's theory, already known but ignored, is a counterexample to von Neumann's and others' claims on impossibility of hidden variables. He analyzed how that is possible and found out: 1) von Neumann made some unreasonable assumptions in his analysis; 2) the fixation on hidden variables is missing the point; the real surprise is that locality, not theory with hidden variables, is inconsistent with quantum theory. That's quite a discovery. http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-Bell-paper.pdf http://www.ijqf.org/wps/wp-content/uploads/2014/11/Bricmont-... https://arxiv.org/pdf/1408.1826.pdf https://arxiv.org/pdf/1408.1826.pdf
- loup-vaillant 10y ago
  Wait a minute, my understanding of QM rejects both non-locality and hidden variables. Put it that way however, you kinda have to believe in macroscopic decoherence, that is, Everet's multiverse: there are 2 universes, one in which the cat is dead, and one in which the cat is alive, and observing one universe doesn't rule out the existence of the other. (Similarly, sending a photon (or settlers!) outside of the observable universe doesn't end its existence.) Non-locality sounds way, way weirder to me than macroscopic decoherence. Stuff like quantum collapse is really an additional, un-falsifiable claim: why the universe would zero-out precisely the stuff that the math says we can't observe?
  - ajkjk 10y ago
    Er, are you familiar with the Bohmian mechanics [1] that was mentioned above? It has, basically, 'non-local hidden variables', and that works fine. [1] (https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory)