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Questions about Nasa's space drive answered

wired.co.uk

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Re: Questions about Nasa's space drive answered

#91

Post by SamReidHughes »

tobinfricke wrote: post #84
madaxe_again wrote: post #16

Earlier quoted context omitted.

Indeed. As to the whole "we don't actually understand how it works" - we still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. I suspect this will be similar for a long while - although puts physics hat on I think this is likely a relativistic temporal quantisation eff…

" We still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. " Time to trot out my favorite quote about how airplanes fly, from Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944: »The main fact of all heavier-than-air flight is this: the wing keeps the ai…

Okay but there's a difference in the nature of the "pushing down" of a rocket, a plane, and a hovering helicopter, and in how much of an impulse is actually inflicted on an external mass.

Re: Questions about Nasa's space drive answered

#92

Post by danbruc »

FiatLuxDave wrote: post #83

I've read the abstract, but apparently Wired has access to more information. Any idea where the primary source for that information is? I'm interested to see what magnetic shielding was used and how well they characterized the magnetic field in the experimental volume. There was a mention of shielding against electromagnetic effects, but that could just mean a Faraday cage or Helmholtz coils, neither of which will re…

http://www.libertariannews.org/wp-content/uploads/2014/07/An...

Re: Questions about Nasa's space drive answered

#93

Post by lukev »

gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

> Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something.

I presume you're referring to the third law of motion, but if so, you've mischaracterized it. Nothing in the laws of motion state that engines must "emit" something. My car drives along quite efficiently without relying on any emission of mass. So does a sailboat.

Of course, these are still third-law compliant. My car exerts force against the earth (slowing it slightly), the sailboat takes energy from the wind.

To be third-law compliant, this alleged "reactionless" drive would need to apply force against something. But ejecting matter or energy to gain moment in the opposite direction is only one way to do that.

The biggest red flag about this is that there's no physical explanation. It's true that an explanation would imply some new physics. But it wouldn't be breaking the existing physical laws of motion, it would just be discovering some new thing to apply force against (virtual particles, or dark matter/energy, or whatever).

Re: Questions about Nasa's space drive answered

#94

Post by happyscrappy »

Luc wrote: post #71
happyscrappy wrote: post #65

Earlier quoted context omitted.

Does Feynman's "if you can't explain it to a laymen in a few paragraphs then you don't truly understand it" no longer hold?

I'd really like the source for that quote, because it's dumb for obvious reasons, and I don't know Feynman to be dumb. In fact he said pretty much the opposite to the interviewer asking about magnets in this well known video: https://www.youtube.com/watch?v=MO0r930Sn_8

Hmm. The closest I can find is this:

"Once I asked him to explain to me, so that I can understand it, why spin-1/2 particles obey Fermi-Dirac statistics. Gauging his audience perfectly, he said, "I'll prepare a freshman lecture on it." But a few days later he came to me and said: "You know, I couldn't do it. I couldn't reduce it to the freshman level. That means we really don't understand it." David L. Goodstein, "Richard P. Feynman, Teacher," Physics Today, volume 42, number 2, February 1989, p. 70-75, at p. 75

Re: Questions about Nasa's space drive answered

#95

Post by colanderman »

gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

Just to be clear, because I think it's easy to forget this:

> If you are using a nuclear reactor, a small par of the mass of the atoms is transformed into energy and you put that energy in the photons

This applies equally to nuclear reactors and to AA batteries (like you mention earlier). All forms of energy have mass.

Re: Questions about Nasa's space drive answered

#96

Post by belovedeagle »

tobinfricke wrote: post #84
madaxe_again wrote: post #16

Earlier quoted context omitted.

Indeed. As to the whole "we don't actually understand how it works" - we still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. I suspect this will be similar for a long while - although puts physics hat on I think this is likely a relativistic temporal quantisation eff…

" We still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. " Time to trot out my favorite quote about how airplanes fly, from Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944: »The main fact of all heavier-than-air flight is this: the wing keeps the ai…

I'm truly baffled at how people keep claiming that we don't understand how wings work when this obvious explanation is out there, one that any 8-year-old could give you, and it's absolutely right. "We don't understand how planes could fly upside down"---nonsense; it's the same way they flight right-side-up: by pushing the air down (or pulling, if you like).

Re: Questions about Nasa's space drive answered

#97

Post by mikeash »

belovedeagle wrote: post #96
tobinfricke wrote: post #84

Earlier quoted context omitted.

" We still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. " Time to trot out my favorite quote about how airplanes fly, from Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944: »The main fact of all heavier-than-air flight is this: the wing keeps the ai…

I'm truly baffled at how people keep claiming that we don't understand how wings work when this obvious explanation is out there, one that any 8-year-old could give you, and it's absolutely right. "We don't understand how planes could fly upside down"---nonsense; it's the same way they flight right-side-up: by pushing the air down (or pulling, if you like).

The problem is that people see the various different explanations for how a wing works (pushing the air down, pressure differential, speed differential, circulation, what have you) and they think they're competing theories, not just different perspectives on the same phenomenon.

Edit: and of course it doesn't help at all that the silly and trivially disproven equal transit time theory continues to be the go-to explanation for how wings work for so many attempts to teach it.

Re: Questions about Nasa's space drive answered

#98

Post by gilgoomesh »

gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

NASA suspects the thrust comes from "quantum vacuum virtual particles". These literally come from nowhere and would be the balance in the conservation of momentum. See Casimir Effect or Hawking radiation for examples where quantum vacuum virtual particles have an effect.

Re: Questions about Nasa's space drive answered

#99

Post by mikeash »

jahnu wrote: post #15
noselasd wrote: post #11

Besides the frequency of the electromagnetic waves , is this the same concept as the "Pioneer Anomaly" - where they eventually figured out it was thermal radiation emitted from its satellite dish which slowed down the spacecraft ?

As far as I can tell it wouldn't matter what the cause of the apparent effect is. Not requiring reaction mass is what makes it interesting.

It would matter a great deal. If it was just radiated photons a la the Pioneer Anomaly, that's pretty boring. Yes, you can make a drive that runs on pure energy by shooting photons out the back. This is well known, and not very interesting. A flashlight is a really, really, really low-powered rocket. But the thrust you get out for the energy you get in is extremely small, and there's no way to improve on it with the same principle beyond increasing the efficiency of the system. Energy->light systems can already be built with 80% efficiency or better, so there's not much headroom.

What would make this phenomenon interesting if it actually works is not merely that it requires no reaction mass, but that it's much more powerful than a photon drive. If it turns out to just be a photon drive, then the magnitude of the effect has been greatly overstated, and this is a really complicated way to achieve the same effect as pointing a laser out the back of your spaceship.

Re: Questions about Nasa's space drive answered

#100

Post by mikeash »

tobinfricke wrote: post #34
mrfusion wrote: post #30

Would this be how impulse drives are supposed to work in Star Trek work? Just curious.

As you may be aware, Star Trek is a work of fiction.

And beyond that, a work of fiction that focuses on storytelling first, and science... well, not second, but maybe twenty-ninth or so.

Which is not a criticism. Not all science fiction has to be hard. But none of the technology is a product of scientists sitting down and thinking about how the technology of the future might work. It's a product of writers thinking about what technology would make for good stories, and any explanation you come up with (e.g. impulse drives are reaction drives with warp fields that let them have an exhaust velocity higher than the speed of light) is a retrofit made up to appease fans and sell more books.

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