On one hand, on some scales, Newtonian mechanics is correct "enough" to give results that work, and so in that sense it is just incomplete in that its domain is restricted. On the other, relativity and QM change everything. These new theories may reduce to Newtonian mechanics given certain assumptions, but Newtonian physics assumes things about the structure of spacetime that are fundamentally incorrect (e.g. velocity is not additive). In this sense, one can fairly say that Newton's mechanics are not just incomplete or missing some fine details, but wrong.
I think there is more to the foundations than just the best numbers we can come up with for a given experiment. Our numbers for the gravitational constant, for example, are pretty similar (if more precise) to the numbers in 1891, but the setting in which that number is completely changed. There is no aether, no absolute space, velocities don't add (even though it's "mostly" right on most scales we experience and measure, it is false), space and time get mixed up, etc. Those were all pretty foundational ideas just over a hundred years ago.
>There is no aether, no absolute space, velocities don't add
There are two categories of things in that list: statements that had implications beyond what they had confirmed (the medium of light, the absoluteness of space) and an approximation (the addition of velocities.) Unsurprisingly the metaphysical interpretation of physics has not stood up to refinements in physics. The physics, however, remains true to within the bounds they knew. Likewise, the interpretation of physics is likely to change quite a bit over the next 1000 years, even 100. That's why you should never put too much stock in pop-sci articles that try to tell you that the universe is made of this-or-that. Fortunately on the philosophical side we now all realize that the interpretations are just humanizations of the knowledge itself, and are not knowledge themselves.
Realistically, if the government didn't tax and the benefits were available without payment, how many people would voluntarily pay? Many (most?) will accept a free ride when it is available.
The strength of that "unspoken contract" diminishes as you move from personal friend to distant organization.
I agree that this software has value and it would be nice for people to support it monetarily, but it seems unreasonable to get upset when people don't.
In the past, the GNU operating system tapes cost hefty money, for what is worth.
Also, I don't see anyone getting mad at people not paying. I only see one HN poster saying it's a shame that organization depending on GNU on their infrastructure don't support the work of the FSF, especially after what emerged in the wake of heartbleed (I know OpenSSL was not a GNU project, but the problem is similar).
"Pony up" must mean something different for me than it does for you. I don't know what it means to OP, in my comment I mistakenly assumed my understanding of the phrase was fairly universal.
Could you clarify what is nonlinear about that system? From your description, it sounds like a high (4+) order (mostly) linear system. The motor probably has nonlinear dynamics, but so does everything and treating it as linear should work ok.
I suspect the difficulties you've experienced stem not from nonlinearity, but from trying to control a system poorly approximated by a second order system with a second order controller. By cascading, both PID controllers effectively "see" a plant that looks more or less second order, so the controllers are much more effective.
Nonetheless, everybody calls the displays in Star Wars "holograms". Smalley notes this, and the title is using the word in this colloquial sense. There is an unfortunate disconnect between the technical and colloquial meanings of "hologram".
Cool stuff! I'm curious what limitations there are on how fast the particle can move. Is it theoretically possible to move a single particle fast enough to render complex shapes in real time, or will you need many particles for that?
Thanks for both your answers. Though I was also thinking perhaps you could just suspend the particles in mid-air, and use the movable prism in a laser projector to actually "render" the projection (thus not needing to move them at at a high frame rate or at all). However I guess, you probably do need to move the particles as well to be able to make it a 3D volumetric shape in space (seen from all angles etc).
I'm not very familiar with the plasma dots approach, but from a cursory look it appears that it is not capable of RGB. On the other hand, there is nothing that can fall out of confinement so the display is probably more stable.
That page says the femtosecond plasma display is pretty safe. This display was - and I believe still is, though I could be wrong - using a UV laser for confinement, which is sorta scary.
> Can you levitate multiple particles at the same time?
Yes, but their device currently is only capable of levitating a single particle. With the current approach, the device would need one laser for confining each particle. The lasers used for RGB could potentially be multiplexed between particles, but this is less likely to work for the confinement due to the instability of the trap.
> How fast are they moving?
Pretty slow. All the "big" images (Leia, grad student, etc) are long-exposure. You can see the particle moving in real-time at about 0:50. In the videos, you can see the device can almost do real-time persistence of vision for volumes substantially smaller than a fingertip.
> How sensitive is it to disturbances in the air?
As I mentioned above, the confinement is weak and the trap is pretty unstable. Its possible that they have improved the longevity of the trap in the last few months, but when doing long-exposure the device is surrounded by a heavy cloth barrier to block both external light and air movement.
The cellulose comes from the black liquor on a spoon (see 0:46 in the video). The put the spoon at the focus of the laser and with luck some particles get confined. After the trap is lost, the particle just sort of drifts away in the air, since they are only tens of microns.
good call. unsay those rocket words. on the up side his roof tile PV thing is a clean slate (hah) which has a huge market out there, irrespective of the supply chain dynamic questions behind EV. And his batteries are going gangbusters attached to solar and wind farms so there are sound, large business models behind tesla. But.. making them add up to the same net worth as GM which has factories and dealerships and side deals in ship engines, energy, military, worldwide... I am still adrift. Tesla is talking about gigafactory sites outside of the USA. GM owns factory sites worldwide.
Jobs had a $1 salary and no bonuses. That doesn't say anything about stock options, grants, etc. It sounds like Musk will get minimum wage and no stock anything if Tesla doesn't meet the thresholds.
On one hand, on some scales, Newtonian mechanics is correct "enough" to give results that work, and so in that sense it is just incomplete in that its domain is restricted. On the other, relativity and QM change everything. These new theories may reduce to Newtonian mechanics given certain assumptions, but Newtonian physics assumes things about the structure of spacetime that are fundamentally incorrect (e.g. velocity is not additive). In this sense, one can fairly say that Newton's mechanics are not just incomplete or missing some fine details, but wrong.
I think there is more to the foundations than just the best numbers we can come up with for a given experiment. Our numbers for the gravitational constant, for example, are pretty similar (if more precise) to the numbers in 1891, but the setting in which that number is completely changed. There is no aether, no absolute space, velocities don't add (even though it's "mostly" right on most scales we experience and measure, it is false), space and time get mixed up, etc. Those were all pretty foundational ideas just over a hundred years ago.